[Federal Register Volume 81, Number 201 (Tuesday, October 18, 2016)]
[Rules and Regulations]
[Pages 71906-71943]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2016-23153]
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Vol. 81
Tuesday,
No. 201
October 18, 2016
Part V
Environmental Protection Agency
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40 CFR Part 50
Review of the National Ambient Air Quality Standards for Lead; Final
Rule
Federal Register / Vol. 81 , No. 201 / Tuesday, October 18, 2016 /
Rules and Regulations
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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 50
[EPA-HQ-OAR-2010-0108; FRL-9952-87-OAR]
RIN 2060-AQ44
Review of the National Ambient Air Quality Standards for Lead
AGENCY: Environmental Protection Agency (EPA).
ACTION: Final rule.
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SUMMARY: Based on the Environmental Protection Agency's (EPA's) review
of the air quality criteria and the national ambient air quality
standards (NAAQS) for lead (Pb), the EPA is retaining the current
standards, without revision.
DATES: This final rule is effective on November 17, 2016.
ADDRESSES: The EPA has established a docket for this action under
Docket ID No. EPA-HQ-OAR-2010-0108. Incorporated into this docket is a
separate docket established for the Integrated Science Assessment for
this review (Docket ID No. EPA-HQ-ORD-2011-0051). All documents in
these dockets are listed on the www.regulations.gov Web site. Although
listed in the index, some information is not publicly available, e.g.,
CBI or other information whose disclosure is restricted by statute.
Certain other material, such as copyrighted material, is not placed on
the Internet and will be publicly available only in hard copy form. It
may be viewed, with prior arrangement, at the EPA Docket Center.
Publicly available docket materials are available either electronically
in www.regulations.gov or in hard copy at the Air and Radiation Docket
Information Center, EPA/DC, WJC West Building, Room 3334, 1301
Constitution Ave. NW., Washington, DC. The Public Reading Room is open
from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal
holidays. The telephone number for the Public Reading Room is (202)
566-1744 and the telephone number for the Air and Radiation Docket
Information Center is (202) 566-1742.
FOR FURTHER INFORMATION CONTACT: Dr. Deirdre L. Murphy, Health and
Environmental Impacts Division, Office of Air Quality Planning and
Standards, U.S. Environmental Protection Agency, Mail code C504-06,
Research Triangle Park, NC 27711; telephone: (919) 541-0729; fax: (919)
541-0237; email: [email protected].
Availability of Information Related to this Action
A number of the documents that are relevant to this action are
available through the EPA's Office of Air Quality Planning and
Standards (OAQPS) Technology Transfer Network (TTN) Web site at http://www.epa.gov/ttn/naaqs/standards/pb/s_pb_index.html. These documents
include the Integrated Review Plan for the National Ambient Air Quality
Standards for Lead (USEPA, 2011a), available at http://www.epa.gov/ttn/naaqs/standards/pb/s_pb_2010_pd.html, the Integrated Science Assessment
for Lead (USEPA, 2013a), available at http://www.epa.gov/ttn/naaqs/standards/pb/s_pb_2010_isa.html, the Review of the National Ambient Air
Quality Standards for Lead: Risk and Exposure Assessment Planning
Document (USEPA, 2011b), available at http://www.epa.gov/ttn/naaqs/standards/pb/s_pb_2010_pd.html, and the Policy Assessment for the
Review of the Lead National Ambient Air Quality Standards (USEPA,
2014), available at http://www.epa.gov/ttn/naaqs/standards/pb/s_pb_2010_pa.html. These and other related documents are also available
for inspection and copying in the EPA docket identified above.
SUPPLEMENTARY INFORMATION:
Table of Contents
Executive Summary
I. Background
A. Legislative Requirements
B. Related Lead Control Programs
C. Review of the Air Quality Criteria and Standards for Lead
D. Multimedia, Multipathway Aspects of Lead
E. Air Quality Monitoring
F. Summary of Proposed Decisions
G. Organization and Approach to Final Decisions
II. Rationale for Decision on the Primary Standard
A. Introduction
1. Background on the Current Standard
2. Overview of Health Effects Evidence
3. Overview of Information on Blood Lead Relationships With Air
Lead
4. Overview of Risk and Exposure Assessment Information
B. Conclusions on the Primary Standard
1. Basis for the Proposed Decision
2. CASAC Advice in This Review
3. Comments on the Proposed Decision
4. Administrator's Conclusions
C. Decision on the Primary Standard
III. Rationale for Decision on the Secondary Standard
A. Introduction
1. Overview of Welfare Effects Information
2. Overview of Risk Assessment Information
B. Conclusions on the Secondary Standard
1. Basis for the Proposed Decision
2. CASAC Advice in This Review
3. Comments on the Proposed Decision
4. Administrator's Conclusions
C. Decision on the Secondary Standard
IV. Statutory and Executive Order Reviews
A. Executive Order 12866: Regulatory Planning and Review and
Executive Order 13563: Improving Regulation and Regulatory Review
B. Paperwork Reduction Act (PRA)
C. Regulatory Flexibility Act (RFA)
D. Unfunded Mandates Reform Act (UMRA)
E. Executive Order 13132: Federalism
F. Executive Order 13175: Consultation and Coordination With
Indian Tribal Governments
G. Executive Order 13045: Protection of Children From
Environmental Health and Safety Risks
H. Executive Order 13211: Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution, or Use
I. National Technology Transfer and Advancement Act
J. Executive Order 12898: Federal Actions To Address
Environmental Justice in Minority Populations and Low-Income
Populations
K. Determination Under Section 307(d)
L. Congressional Review Act
References
Executive Summary
This document describes the completion of our current review of the
NAAQS for Pb. This review of the standards and the air quality criteria
(the scientific information upon which the standards are based) is
required by the Clean Air Act on a periodic basis. In conducting this
review, the EPA has carefully evaluated the currently available
scientific literature on the health and welfare effects of Pb, focusing
particularly on the information newly available since the conclusion of
the last review in 2008. Between 2008 and 2014, the EPA prepared draft
and final versions of the Integrated Science Assessment and the Policy
Assessment, multiple drafts of which were subject to public review and
comment and were reviewed by the Clean Air Scientific Advisory
Committee, an independent scientific advisory committee established
pursuant to the Clean Air Act and charged with providing advice to the
Administrator. The EPA issued a proposed decision on the standards on
January 5, 2015 (80 FR 278), and provided a 3-month period for
submission of comments from the public. After consideration of public
comments on the proposed decision and advice from the Clean Air
Scientific Advisory Committee, the EPA has developed this document,
which is the final step in the review process.
The prior review of the NAAQS for Pb was completed in 2008. As a
result of that review, we significantly revised
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both the primary and secondary standards, including a lowering of the
standard levels by an order of magnitude. The 2008 change to the
primary standard was focused on providing the requisite protection for
children and other at-risk populations against an array of adverse
health effects, most notably including neurological effects in
children, including neurocognitive effects (e.g., IQ loss) and
neurobehavioral effects. Although Pb has long been recognized to exert
an array of adverse health effects, over the three decades from the
time the standard was initially set in 1978 through its revision with
the NAAQS review completed in 2008, the evidence base expanded
considerably in a number of areas, including with regard to effects on
neurocognitive function in young children at increasingly lower blood
Pb levels. These effects formed the principal basis for the 2008
revisions to the primary standard.
The health effects evidence newly available in this review of the
2008 standard, as critically assessed in the ISA in conjunction with
the full body of evidence, reaffirms conclusions on the broad array of
effects recognized for Pb in the last review. Further, the currently
available evidence is generally consistent with the evidence available
in the last review, particularly with regard to key aspects of the
evidence on which the current standard (set in 2008) is based. These
key aspects include those regarding the relationships between air Pb
concentrations and the associated Pb in the blood of young children as
well as between total blood Pb levels and effects on children's IQ.
Based on consideration of the currently available health effects
evidence in the context of this framework, and with support from the
exposure/risk information, recognizing the uncertainties attendant in
both, as well as the increasing uncertainty of risk estimates for lower
air Pb concentrations, the Administrator concludes that the current
primary standard provides the requisite protection of public health
with an adequate margin of safety, including protection of at-risk
populations. With regard to the secondary standard, the EPA has
considered the currently available welfare effects evidence and
screening-level risk information, including the general consistency of
the current evidence with that available in the last review and the
substantial limitations in the current evidence that complicate
conclusions regarding the potential for Pb emissions under the current,
much lower standard to contribute to welfare effects. Based on these
considerations, the Administrator concludes that the current secondary
standard is requisite to protect public welfare from known or
anticipated adverse effects. Thus, based on the EPA's review of the air
quality criteria and the NAAQS for Pb, the EPA is retaining the current
standards, without revision.
I. Background
A. Legislative Requirements
Two sections of the Clean Air Act (CAA or the Act) govern the
establishment and revision of the NAAQS. Section 108 (42 U.S.C. 7408)
directs the Administrator to identify and list certain air pollutants
and then to issue air quality criteria for those pollutants. The
Administrator is to list those air pollutants that in her ``judgment,
cause or contribute to air pollution which may reasonably be
anticipated to endanger public health or welfare;'' ``the presence of
which in the ambient air results from numerous or diverse mobile or
stationary sources;'' and ``for which . . . [the Administrator] plans
to issue air quality criteria . . .'' Air quality criteria are intended
to ``accurately reflect the latest scientific knowledge useful in
indicating the kind and extent of all identifiable effects on public
health or welfare which may be expected from the presence of [a]
pollutant in the ambient air . . .'' 42 U.S.C. 7408(b). Section 109 (42
U.S.C. 7409) directs the Administrator to propose and promulgate
``primary'' and ``secondary'' NAAQS for pollutants for which air
quality criteria are issued. Section 109(b)(1) defines a primary
standard as one ``the attainment and maintenance of which in the
judgment of the Administrator, based on such criteria and allowing an
adequate margin of safety, are requisite to protect the public
health.'' \1\ A secondary standard, as defined in section 109(b)(2),
must ``specify a level of air quality the attainment and maintenance of
which, in the judgment of the Administrator, based on such criteria, is
requisite to protect the public welfare from any known or anticipated
adverse effects associated with the presence of [the] pollutant in the
ambient air.''
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\1\ The legislative history of section 109 indicates that a
primary standard is to be set at ``the maximum permissible ambient
air level . . . which will protect the health of any [sensitive]
group of the population,'' and that for this purpose ``reference
should be made to a representative sample of persons comprising the
sensitive group rather than to a single person in such a group.''
See S. Rep. No. 91-1196, 91st Cong., 2d Sess. 10 (1970).
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The requirement that primary standards provide an adequate margin
of safety was intended to address uncertainties associated with
inconclusive scientific and technical information available at the time
of standard setting. It was also intended to provide a reasonable
degree of protection against hazards that research has not yet
identified. See Lead Industries Association v. EPA, 647 F.2d 1130, 1154
(D.C. Cir. 1980), cert. denied, 449 U.S. 1042 (1980); American
Petroleum Institute v. Costle, 665 F.2d 1176, 1186 (D.C. Cir. 1981),
cert. denied, 455 U.S. 1034 (1982); American Farm Bureau Federation v.
EPA, 559 F. 3d 512, 533 (D.C. Cir. 2009); Association of Battery
Recyclers v. EPA, 604 F. 3d 613, 617-18 (D.C. Cir. 2010). Both kinds of
uncertainties are components of the risk associated with pollution at
levels below those at which human health effects can be said to occur
with reasonable scientific certainty. Thus, in selecting primary
standards that provide an adequate margin of safety, the Administrator
is seeking not only to prevent pollution levels that have been
demonstrated to be harmful but also to prevent lower pollutant levels
that may pose an unacceptable risk of harm, even if the risk is not
precisely identified as to nature or degree. The CAA does not require
the Administrator to establish a primary NAAQS at a zero-risk level or
at background concentration levels, see Lead Industries v. EPA, 647
F.2d at 1156 n.51, but rather at a level that reduces risk sufficiently
so as to protect public health with an adequate margin of safety.
In addressing the requirement for an adequate margin of safety, the
EPA considers such factors as the nature and severity of the health
effects involved, the size of sensitive population(s) at risk,\2\ and
the kind and degree of the uncertainties that must be addressed. The
selection of any particular approach to providing an adequate margin of
safety is a policy choice left specifically to the Administrator's
judgment. See Lead Industries Association v. EPA, 647 F.2d at 1161-62.
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\2\ As used here and similarly throughout this document, the
term population (or group) refers to persons having a quality or
characteristic in common, such as a specific pre-existing illness or
a specific age or life stage. As discussed more fully in section
II.A.2.d below, the identification of sensitive groups (called at-
risk groups or at-risk populations) involves consideration of
susceptibility and vulnerability.
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In setting primary and secondary standards that are ``requisite''
to protect public health and welfare, respectively, as provided in
section 109(b), the EPA's task is to establish standards that are
neither more nor less stringent than necessary for these purposes. In
so doing, the EPA may not consider the
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costs of implementing the standards. See generally, Whitman v. American
Trucking Associations, 531 U.S. 457, 465-472, 475-76 (2001). Likewise,
``[a]ttainability and technological feasibility are not relevant
considerations in the promulgation of national ambient air quality
standards.'' American Petroleum Institute v. Costle, 665 F. 2d at 1185.
Section 109(d)(1) requires that ``not later than December 31, 1980,
and at 5-year intervals thereafter, the Administrator shall complete a
thorough review of the criteria published under section 108 and the
national ambient air quality standards . . . and shall make such
revisions in such criteria and standards and promulgate such new
standards as may be appropriate. . . .'' Section 109(d)(2) requires
that an independent scientific review committee ``shall complete a
review of the criteria . . . and the national primary and secondary
ambient air quality standards . . . and shall recommend to the
Administrator any new . . . standards and revisions of existing
criteria and standards as may be appropriate . . .'' Since the early
1980s, this independent review function has been performed by the Clean
Air Scientific Advisory Committee (CASAC).\3\
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\3\ Lists of CASAC members and of members of the CASAC Lead
Review Panel are available at: http://yosemite.epa.gov/sab/sabproduct.nsf/WebCASAC/CommitteesandMembership?OpenDocument.
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B. Related Lead Control Programs
States are primarily responsible for ensuring attainment and
maintenance of the NAAQS. Under section 110 of the Act (42 U.S.C. 7410)
and related provisions, states are to submit, for EPA approval, state
implementation plans that provide for the attainment and maintenance of
such standards through control programs directed to sources of the
pollutants involved. The states, in conjunction with the EPA, also
administer the Prevention of Significant Deterioration program (42
U.S.C. 7470-7479) for these pollutants.
The NAAQS is only one component of the EPA's programs to address Pb
in the environment. Federal programs additionally provide for
nationwide reductions in air emissions of these and other air
pollutants through the Federal Motor Vehicle Control Program under
Title II of the Act (42 U.S.C. 7521-7574), which involves controls for
automobile, truck, bus, motorcycle, nonroad engine, and aircraft
emissions; the new source performance standards under section 111 of
the Act (42 U.S.C. 7411); emissions standards for solid waste
incineration units and the national emission standards for hazardous
air pollutants (NESHAP) under sections 129 (42 U.S.C. 7429) and 112 (42
U.S.C. 7412) of the Act, respectively.
The EPA has taken a number of actions associated with these air
pollution control programs since the last review of the Pb NAAQS
(completed in 2008), including completion of several regulations that
will result in reduced Pb emissions from stationary sources regulated
under the CAA sections 112 and 129. For example, in January 2012, the
EPA updated the NESHAP for the secondary lead smelting source category
(77 FR 555, January 5, 2012). These amendments to the original maximum
achievable control technology standards apply to facilities nationwide
that use furnaces to recover Pb from Pb-bearing scrap, mainly from
automobile batteries (13 existing facilities). This action was
estimated to result in a Pb emissions reduction of 13.6 tons per year
(tpy) across the category (a 68 percent reduction). Somewhat lesser Pb
emissions reductions are also expected from regulations completed in
2013 for commercial and industrial solid waste incineration units (78
FR 9112, February 7, 2013), as well as several other regulations since
2007 (72 FR 73179, December 26, 2007; 72 FR 74088, December 28, 2007;
73 FR 225, November 20, 2008; 78 FR 10006, February 12, 2013; 76 FR
15372, March 21, 2011; 78 FR 7138, January 31, 2013; 74 FR 51368,
October 6, 2009; Policy Assessment, Appendix 2A).
The presentation below briefly summarizes additional ongoing
activities that, although not directly pertinent to the review of the
NAAQS, are associated with controlling environmental Pb levels and
human Pb exposures more broadly. Among those identified are the EPA
programs intended to encourage exposure reduction programs in other
countries.
Reducing Pb exposures has long been recognized as a federal
priority as environmental and public health agencies continue to
grapple with soil and dust Pb levels from the historical use of Pb in
paint and gasoline and from other sources (Alliance to End Childhood
Lead Poisoning, 1991; 62 FR 19885, April 23, 1997; 66 FR 52013, October
11, 2001; 68 FR 19931, April 23, 2003). A broad range of federal
programs beyond those that focus on air pollution control provide for
nationwide reductions in environmental releases and human exposures.
Pursuant to section 1412 of the Safe Drinking Water Act (SDWA), EPA
sets public health goals and enforceable standards for drinking water
quality. The Lead and Copper Rule (LCR) is a treatment technique rule.
The LCR requires public water systems to treat the water to reduce
corrosion of Pb and copper from premise plumbing and drinking water
distribution system components. When corrosion control treatment isn't
enough, water systems must educate the public about Pb in drinking
water and replace lead service lines, which are the pipes that connect
buildings to the drinking water mains (40 CFR 141.80-141.91). The
importance of corrosion control treatment was illustrated by the recent
events in Flint, MI, when Pb levels in drinking water increased after
the water system did not maintain corrosion control treatment when the
system changed its water supply. Section 1417 of the SDWA additionally
prohibits the use of any pipe, any pipe or plumbing fitting or fixture,
any solder, or any flux in the installation or repair of any public
water system or any plumbing in a residential or non-residential
facility providing water for human consumption, that is not lead free
as defined by the Act.\4\
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\4\ Effective in January 2014, the amount of Pb permitted in
pipes, fittings, and fixtures was lowered (see ``Section 1417 of the
Safe Drinking Water Act: Prohibition on Use of Lead Pipes, Solder,
and Flux'' at http://www.epa.gov/dwstandardsregulations/section-1417-safe-drinking-water-act-prohibition-use-lead-pipes-solder-and).
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Additionally, federal Pb abatement programs provide for the
reduction in human exposures and environmental releases from in-place
materials containing Pb (e.g., Pb-based paint, urban soil and dust, and
contaminated waste sites). Federal regulations on disposal of Pb-based
paint waste help facilitate the removal of Pb-based paint from
residences (68 FR 36487, June 18, 2003).
Federal programs to reduce exposure to Pb in paint, dust, and soil
are specified under the comprehensive federal regulatory framework
developed under the Residential Lead-Based Paint Hazard Reduction Act
(Title X). Under Title X (codified as Title IV of the Toxic Substances
Control Act [TSCA]), the EPA has established regulations and associated
programs in six categories: (1) Training, certification and work
practice requirements for persons engaged in Pb-based paint activities
(abatement, inspection and risk assessment); accreditation of training
providers; and authorization of state and tribal Pb-based paint
programs; (2) training, certification, and work practice requirements
for persons engaged in home renovation, repair and painting (RRP)
activities; accreditation of RRP training providers; and authorization
of
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state and tribal RRP programs; (3) ensuring that, for most housing
constructed before 1978, information about Pb-based paint and Pb-based
paint hazards flows from sellers to purchasers, from landlords to
tenants, and from renovators to owners and occupants; (4) establishing
standards for identifying dangerous levels of Pb in paint, dust and
soil; (5) providing grant funding to establish and maintain state and
tribal Pb-based paint programs; and (6) providing information on Pb
hazards to the public, including steps that people can take to protect
themselves and their families from Pb-based paint hazards. The most
recent rule issued under Title IV of TSCA is for the Lead Renovation,
Repair and Painting Program (73 FR 21692, April 22, 2008), which became
fully effective in April 2010 and which applies to compensated
renovators and maintenance professionals who perform RRP activities in
housing and child-care facilities built prior to 1978. To foster
adoption of the rule's measures, the EPA has been conducting an
extensive education and outreach campaign to promote awareness of these
new requirements among both the regulated entities and the consumers
who hire them (http://www2.epa.gov/lead/renovation-repair-and-painting-program). In addition, the EPA is investigating whether Pb hazards are
also created by RRP activities in public and commercial buildings, in
which case the EPA plans to issue RRP requirements, where appropriate,
for this class of buildings (79 FR 31072, May 30, 2014).
Programs associated with the Comprehensive Environmental Response,
Compensation, and Liability Act (CERCLA or Superfund) and Resource
Conservation Recovery Act (RCRA) also implement abatement programs,
reducing exposures to Pb and other pollutants. For example, the EPA
determines and implements protective levels for Pb in soil at Superfund
sites and RCRA corrective action facilities. Federal programs,
including those implementing RCRA, provide for management of hazardous
substances in hazardous and municipal solid waste (e.g., 66 FR 58258,
November 20, 2001). Federal regulations concerning batteries in
municipal solid waste facilitate the collection and recycling or proper
disposal of batteries containing Pb.\5\ Similarly, federal programs
provide for the reduction in environmental releases of hazardous
substances such as Pb in the management of wastewater (http://www.epa.gov/owm/).
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\5\ See, e.g., ``Implementation of the Mercury-Containing and
Rechargeable Battery Management Act'' available from https://www.epa.gov/hw and facts and figures on recycling and disposal in
the U.S. at https://www.epa.gov/smm/advancing-sustainable-materials-management-facts-and-figures.
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A variety of federal nonregulatory programs also provide for
reduced environmental release of Pb-containing materials by encouraging
pollution prevention, promotion of reuse and recycling, reduction of
priority and toxic chemicals in products and waste, and conservation of
energy and materials. These include the ``National Waste Minimization
Program'' (https://archive.epa.gov/epawaste/hazard/wastemin/web/html/tools.html), ``Sustainable Management of Electronics'' (https://www.epa.gov/smm-electronics), and the ``Sustainable Materials
Management (SMM) Electronics Challenge'' (https://www.epa.gov/smm-electronics/sustainable-materials-management-smm-electronics-challenge).
The EPA's research program identifies, encourages and conducts
research needed to develop methods and tools to characterize and help
reduce risks related to Pb exposure. An example of one such effort is
the EPA's Integrated Exposure Uptake Biokinetic Model for Lead in
Children (IEUBK model), which is widely used and accepted as a tool
that informs the evaluation of site-specific data. More recently, in
recognition of the need for a single model that predicts Pb
concentrations in tissues for children and adults, the EPA has been
developing the All Ages Lead Model (AALM) to provide researchers and
risk assessors with a pharmacokinetic model capable of estimating
blood, tissue, and bone concentrations of Pb based on estimates of
exposure over the lifetime of the individual (USEPA, 2006a, sections
4.4.5 and 4.4.8; USEPA, 2013a, section 3.6). The EPA's research
activities on substances including Pb, such as those identified here,
focus on improving our characterization of health and environmental
effects, exposure, and control or management of environmental releases
(see http://www.epa.gov/research/).
Other federal agencies also participate in programs intended to
reduce Pb exposures. For example, programs of the Centers for Disease
Control and Prevention (CDC) provide for the tracking of children's
blood Pb levels in the U.S. and provide guidance on levels at which
medical and environmental case management activities should be
implemented (CDC, 2012; ACCLPP, 2012). As a result of coordinated,
intensive efforts at the national, state and local levels, including
those programs described above, blood Pb levels in all segments of the
population have continued to decline from levels observed in the past.
For example, blood Pb levels for the general population of children 1
to 5 years of age have dropped to a geometric mean level of 1.17 [mu]g/
dL in the 2009-2010 National Health and Nutrition Examination Survey
(NHANES) \6\ as compared to the geometric mean in 1999-2000 of 2.23
[micro]g/dL and in 1988-1991 of 3.6 [mu]g/dL (USEPA, 2013a, section
3.4.1; USEPA, 2006a, AX4-2). Similarly, statistics for the distribution
of blood Pb levels in non-Hispanic black and lower socioeconomic groups
of young children, which are generally higher than those for that
population as a whole, have also declined, as have the differences in
these statistics between non-Hispanic black and other groups, as well
as between lower and higher socioeconomic groups (USEPA, 2013a,
sections 3.4.1, 5.2.3 and 5.2.4; Jones et al., 2009).
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\6\ Since the completion of the ISA, more recent NHANES data
indicate the geometric mean blood Pb concentration for children in
the U.S. population, aged one to five, to have declined to 0.97
[mu]g/dL in the 2011-2012 survey (CDC, 2015).
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The EPA also participates in a broad range of international
programs focused on reducing environmental releases and human exposures
in other countries. For example, the Partnership for Clean Fuels and
Vehicles program engages governments and stakeholders in developing
countries to eliminate Pb in gasoline globally.\7\ From 2007 to 2011,
the number of countries known to still be using leaded gasoline was
reduced from just over 20 to six (USEPA, 2011c). As of January, leaded
gasoline for on-road use is known to be available (along with unleaded
gasoline) in three countries.\8\
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\7\ International programs in which the U.S. participates,
including those identified here, are described at: https://www.epa.gov/international-cooperation, http://www.unep.org/transport/pcfv/, http://www.unep.org/hazardoussubstances/Home/tabid/197/hazardoussubstances/LeadCadmium/PrioritiesforAction/GAELP/tabid/6176/Default.aspx.
\8\ UNEP. ``Leaded Petrol Phase-out: Global Status as at January
2016'' map downloaded from http://www.unep.org/transport/new/pcfv/.
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The EPA is a contributor to the Global Alliance to Eliminate Lead
Paint, a voluntary public-private partnership jointly led by the World
Health Organization and the United Nations Environment Programme (UNEP)
to prevent children's exposure to Pb from paints containing Pb and to
minimize occupational exposures to Pb paint. The objective of this
alliance is to promote a phase-out of the manufacture and sale of
paints containing Pb and eventually to eliminate the risks that such
paints
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pose. The UNEP is also engaged on the problem of managing wastes
containing Pb, including Pb-containing batteries. The Governing Council
of the UNEP, of which the U.S. is a member, has adopted decisions
focused on promoting the environmentally sound management of products,
wastes and contaminated sites containing Pb and reducing risks to human
health and the environment from Pb and cadmium throughout the life
cycles of those substances (UNEP Governing Council, 2011, 2013). The
EPA is also engaged in the issue of environmental impacts of spent Pb-
acid batteries internationally through the Commission for Environmental
Cooperation (CEC), where the EPA Administrator along with the cabinet-
level or equivalent representatives of Mexico and Canada comprise the
CEC's senior governing body (CEC Council).\9\
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\9\ The CEC was established to support cooperation among the
North American Free Trade Agreement partners to address
environmental issues of continental concern, including the
environmental challenges and opportunities presented by continent-
wide free trade.
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C. Review of the Air Quality Criteria and Standards for Lead
Unlike pollutants such as particulate matter and carbon monoxide,
air quality criteria had not been issued for Pb as of the enactment of
the CAA of 1970, which first set forth the requirement to set NAAQS
based on air quality criteria. In the years just after enactment of the
CAA, the EPA did not list Pb under section 108 of the Act, having
determined to control Pb air pollution through regulations to phase out
the use of Pb additives in gasoline (see 41 FR 14921, April 8, 1976).
However, the decision not to list Pb under section 108 was challenged
by environmental and public health groups, and the U.S. District Court
for the Southern District of New York concluded that the EPA was
required to list Pb under section 108. Natural Resources Defense
Council v. EPA, 411 F. Supp. 864 21 (S.D. N.Y. 1976), affirmed, 545
F.2d 320 (2d Cir. 1978). Accordingly, on April 8, 1976, the EPA
published a notice in the Federal Register that Pb had been listed
under section 108 as a criteria pollutant (41 FR 14921, April 8, 1976),
and on October 5, 1978, the EPA promulgated primary and secondary NAAQS
for Pb under section 109 of the Act (43 FR 46246, October 5, 1978).
Both primary and secondary standards were set at a level of 1.5
micrograms per cubic meter ([mu]g/m\3\), measured as Pb in total
suspended particles (Pb-TSP), not to be exceeded by the maximum
arithmetic mean concentration averaged over a calendar quarter. These
standards were based on the 1977 Air Quality Criteria for Lead (USEPA,
1977).
The first review of the Pb standards was initiated in the mid-
1980s. The scientific assessment for that review is described in the
1986 Air Quality Criteria for Lead (USEPA, 1986a; henceforth referred
to as the 1986 CD), the associated Addendum (USEPA, 1986b) and the 1990
Supplement (USEPA, 1990a). As part of the review, the agency designed
and performed human exposure and health risk analyses (USEPA, 1989),
the results of which were presented in a 1990 Staff Paper (USEPA,
1990b). Based on the scientific assessment and the human exposure and
health risk analyses, the 1990 Staff Paper presented recommendations
for consideration by the Administrator (USEPA, 1990b). After
consideration of the documents developed during the review and the
significantly changed circumstances since Pb was listed in 1976, the
agency did not propose any revisions to the 1978 Pb NAAQS. In a
parallel effort, the agency developed the broad, multi-program,
multimedia, integrated U.S. Strategy for Reducing Lead Exposure (USEPA,
1991). As part of implementing this strategy, the agency focused
efforts primarily on regulatory and remedial clean-up actions aimed at
reducing Pb exposures from a variety of nonair sources judged to pose
more extensive public health risks to U.S. populations, as well as on
actions to reduce Pb emissions to air, such as bringing more areas into
compliance with the existing Pb NAAQS (USEPA, 1991). The EPA continues
this broad, multi-program, multimedia approach to reducing Pb exposures
today, as described in section I.B above.
The last review of the air quality criteria and standards for Pb
was initiated in November 2004 (69 FR 64926, November 9, 2004); the
agency's plans for preparation of the Air Quality Criteria Document
(AQCD) and conduct of the NAAQS review were presented in documents
completed in 2005 and early 2006 (USEPA, 2005a; USEPA 2006b).\10\ The
schedule for completion of the review was governed by a judicial order
in Missouri Coalition for the Environment v. EPA (No. 4:04CV00660 ERW,
September 14, 2005; and amended on April 29, 2008 and July 1, 2008).
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\10\ In the current review, these two documents have been
combined in the Integrated Review Plan for the National Ambient Air
Quality Standards for Lead (USEPA, 2011a).
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The scientific assessment for the review is described in the 2006
Air Quality Criteria for Lead (USEPA, 2006a; henceforth referred to as
the 2006 CD), multiple drafts of which received review by CASAC and the
public. The EPA also conducted human exposure and health risk
assessments and a pilot ecological risk assessment for the review after
consultation with the CASAC and receiving public comment on a draft
analysis plan (USEPA, 2006c). Drafts of these quantitative assessments
were reviewed by CASAC and the public. The pilot ecological risk
assessment was released in December 2006 (ICF International, 2006), and
the final health risk assessment report was released in November 2007
(USEPA, 2007a). The policy assessment, based on both of these
assessments, air quality analyses and key evidence from the 2006 CD,
was presented in the Staff Paper (USEPA, 2007b), a draft of which also
received CASAC and public review. The final Staff Paper presented OAQPS
staff's evaluation of the public health and welfare policy implications
of the key studies and scientific information contained in the 2006 CD
and presented and interpreted results from the quantitative risk/
exposure analyses conducted for this review. Based on this evaluation,
the Staff Paper presented OAQPS staff recommendations that the
Administrator give consideration to substantially revising the primary
and secondary standards to a range of levels at or below 0.2 [micro]g/
m\3\.
Immediately subsequent to completion of the Staff Paper, the EPA
issued an advance notice of proposed rulemaking (ANPR) that was signed
by the Administrator on December 5, 2007 (72 FR 71488, December 17,
2007).\11\ The CASAC provided advice and recommendations to the
Administrator with regard to the Pb NAAQS based on its review of the
ANPR and the previously released final Staff Paper and risk assessment
reports. In 2008, the proposed decision on revisions to the Pb NAAQS
was signed on May 1, and published in the Federal Register on May 20
(73 FR 29184, May 20, 2008). Members of the public provided comments,
and the CASAC Pb Panel also provided advice and recommendations to the
Administrator based on its review of the proposal. The decision on
revisions to the Pb NAAQS was signed on October 15, 2008, and published
in the Federal Register on November 12, 2008 (73 FR 66964, November 12,
2008).
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\11\ The ANPR, one of the features of the revised NAAQS review
process that EPA instituted in 2006, was replaced by reinstatement
of the Policy Assessment prepared by OAQPS staff (previously termed
the OAQPS Staff Paper) in 2009 (Jackson, 2009).
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[[Page 71911]]
The November 2008 preamble to the final rule described the EPA's
decision to revise the primary and secondary standards for Pb, as
discussed more fully in sections II.A.1 and III.A below. In
consideration of the much-expanded health effects evidence on
neurocognitive effects of Pb in children, the EPA substantially revised
the primary standard level from 1.5 [micro]g/m\3\ to a level of 0.15
[micro]g/m\3\. The averaging time was revised to a rolling 3-month
period with a maximum (not-to-be-exceeded) form, evaluated over a 3-
year period. The indicator of Pb-TSP was retained, reflecting the
evidence that Pb particles of all sizes pose health risks. The
secondary standard was revised to be identical in all respects to the
revised primary standard (40 CFR 50.16). Revisions to the NAAQS were
accompanied by revisions to the data handling procedures, the treatment
of exceptional events and the ambient air monitoring and reporting
requirements, as well as emissions inventory reporting requirements.
One aspect of the revised data handling requirements is the allowance
for the use of monitoring for particulate matter with mean diameter
below 10 microns (Pb-PM10) for Pb NAAQS attainment purposes
in certain limited circumstances at non-source-oriented sites.
Subsequent to the 2008 rulemaking, additional revisions were made to
the monitoring network requirements (75 FR 81126, December 27, 2010).
Guidance on the approach for implementation of the new standards was
described in the preambles for the proposed and final rules (73 FR
29184, May 20, 2008; 73 FR 66964, November 12, 2008).
On February 26, 2010, the EPA formally initiated its current review
of the air quality criteria and standards for Pb, requesting the
submission of recent scientific information on specified topics (75 FR
8934, February 26, 2010). Soon after this, the EPA held a workshop to
discuss the policy-relevant science, which informed identification of
key policy issues and questions to frame the review (75 FR 20843, April
21, 2010). Drawing from the workshop discussions, the EPA developed the
draft Integrated Review Plan (draft IRP, USEPA, 2011d). The draft IRP
was made available in late March 2011 for consultation with the CASAC
Pb Review Panel and for public comment (76 FR 20347, April 12, 2011).
This document was discussed by the Panel via a publicly accessible
teleconference consultation on May 5, 2011 (76 FR 21346, April 15,
2011; Frey, 2011a). The final Integrated Review Plan for the National
Ambient Air Quality Standards for Lead (IRP), developed in
consideration of the CASAC consultation and public comment, was
released in November 2011 (USEPA, 2011a; 76 FR 76972, December 9,
2011).
In developing the Integrated Science Assessment (ISA) \12\ for this
review, the EPA held a workshop in December 2010 to discuss with
invited scientific experts preliminary draft materials and released the
first external review draft of the document for CASAC review and public
comment in May 2011 (USEPA, 2011e; 76 FR 26284, May 6, 2011; 76 FR
36120, June 21, 2011). The CASAC Pb Review Panel met at a public
meeting on July 20, 2011, to review the draft ISA (76 FR 36120, June
21, 2011). The CASAC provided comments in a December 9, 2011, letter to
the EPA Administrator (Frey and Samet, 2011). The second external
review draft ISA was released for CASAC review and public comment in
February 2012 (USEPA, 2012a; 77 FR 5247, February 2, 2012) and was the
subject of a public meeting on April 10-11, 2012 (77 FR 14783, March
13, 2012). The CASAC provided comments in a July 20, 2012, letter
(Samet and Frey, 2012). The third external review draft was released
for CASAC review and public comment in November 2012 (USEPA, 2012b; 77
FR 70776, November 27, 2012) and was the subject of a public meeting on
February 5-6, 2013 (78 FR 938, January 7, 2013). The CASAC provided
comments in a June 4, 2013, letter (Frey, 2013a). The final ISA was
released in late June 2013 (USEPA, 2013a, henceforth referred to as the
ISA; 78 FR 38318, June 26, 2013).
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\12\ As of this review, the document developed in NAAQS reviews
in which the air quality criteria are assessed, previously the AQCD,
is the ISA, and the document describing the OAQPS staff evaluation,
previously the Staff Paper, is the PA. These documents are described
in the IRP.
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In June 2011, the EPA developed and released the Risk and Exposure
Assessment Planning Document (REA Planning Document) for consultation
with the CASAC and public comment (USEPA, 2011b; 76 FR 58509). This
document presented a critical evaluation of the information related to
Pb human and ecological exposure and risk (e.g., data, modeling
approaches) newly available in this review, with a focus on
consideration of the extent to which new or substantially revised REAs
for health and ecological risk might be warranted by the newly
available evidence. Evaluation of the newly available information with
regard to designing and implementing health and ecological REAs for
this review led us to conclude that the currently available information
did not provide a basis for developing new quantitative risk and
exposure assessments that would have substantially improved utility for
informing the agency's consideration of health and welfare effects and
evaluation of the adequacy of the current primary and secondary
standards, respectively (REA Planning Document, sections 2.3 and 3.3,
respectively). The CASAC Pb Review Panel provided consultative advice
on that document and its conclusions at a public meeting on July 21,
2011 (76 FR 36120, June 21, 2011; Frey, 2011b). Based on its
consideration of the REA Planning Document analysis, the CASAC Pb
Review Panel generally concurred with the conclusion that a new REA was
not warranted in this review (Frey, 2011b; Frey, 2013b). In
consideration of the conclusions reached in the REA Planning Document
and CASAC's consultative advice, the EPA has not developed REAs for
health and ecological risk for this review. We have considered the
findings from the last review for human exposure and health risk
(USEPA, 2007a, henceforth referred to as the 2007 REA) and ecological
risk (ICF International, 2006; henceforth referred to as the 2006 REA)
with regard to any appropriate further interpretation in light of the
evidence newly available in this review, as described in the Policy
Assessment (PA) and proposal.
A draft of the PA was released for public comment and review by
CASAC in January 2013 (USEPA, 2013b; 77 FR 70776, November 27, 2012)
and was the subject of a public meeting on February 5-6, 2013 (78 FR
938, January 7, 2013). Comments provided by the CASAC in a June 4,
2013, letter (Frey, 2013b), as well as public comments received on the
draft PA were considered in preparing the final PA, which was released
in May 2014 (USEPA, 2014; 79 FR 26751, May 9, 2014). The proposed
decision (henceforth ``proposal'') on this review of the NAAQS for Pb
was signed on December 19, 2014, and published in the Federal Register
on January 5, 2015. Written comments were received from twelve
commenters during the public comment period on the proposal.
Significant issues raised in the public comments and the EPA's
responses to those comments are discussed in the preamble of this final
action.
As in prior NAAQS reviews, the EPA is basing its decision in this
review on studies and related information included in the ISA and
PA,\13\ which
[[Page 71912]]
have undergone CASAC and public review. The studies assessed in the ISA
\14\ and PA, and the integration of the scientific evidence presented
in them, have undergone extensive critical review by the EPA, the
CASAC, and the public. The rigor of that review makes these studies,
and their integrative assessment, the most reliable source of
scientific information on which to base decisions on the NAAQS,
decisions that all parties recognize as of great import. Decisions on
the NAAQS can have profound impacts on public health and welfare, and
NAAQS decisions should be based on studies that have been rigorously
assessed in an integrative manner not only by the EPA but also by the
statutorily mandated independent scientific advisory committee, as well
as the public review that accompanies this process. Some commenters
have referred to and discussed individual scientific studies on the
health effects of Pb that were not included in the ISA (`` `new'
studies''). In considering and responding to comments for which such
``new'' studies were cited in support, the EPA has provisionally
considered the cited studies in the context of the findings of the ISA.
The EPA's provisional consideration of these studies did not and could
not provide the kind of in-depth critical review described above.
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\13\ As a new REA was not warranted in this review, the exposure
and risk information from the last review (2007 REA; 2006 REA) is
summarized in the PA in the context of the currently available
health and welfare effects evidence.
\14\ Studies were identified for the Pb ISA based on the
review's opening ``call for information'' (75 FR 8934), as well as
literature searches conducted routinely ``to identify studies
published since the last review, focusing on studies published from
2006 (close of the previous scientific assessment) through September
2011'' (ISA, p. 1-2). In a subsequent step, ``[s]tudies that have
undergone scientific peer review and have been published or accepted
for publication and reports that have undergone review are
considered for inclusion in the ISA'' and ``[a]nalyses conducted by
EPA using publicly available data are also considered for inclusion
in the ISA'' (ISA, p. xlv). References ``that were considered for
inclusion or actually cited in this ISA can be found at http://hero.epa.gov/lead'' (ISA, p. 1-2).
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The decision to rely on studies and related information included in
the ISA, REAs and PA, which have undergone CASAC and public review, is
consistent with the EPA's practice in prior NAAQS reviews and its
interpretation of the requirements of the CAA. Since the 1970
amendments, the EPA has taken the view that NAAQS decisions are to be
based on scientific studies and related information that have been
assessed as a part of the pertinent air quality criteria, and the EPA
has consistently followed this approach. This longstanding
interpretation was strengthened by new legislative requirements enacted
in 1977, which added section 109(d)(2) of the Act concerning CASAC
review of air quality criteria. See 71 FR 61144, 61148 (October 17,
2006, final decision on review of NAAQS for particulate matter) for a
detailed discussion of this issue and the EPA's past practice.
As discussed in the EPA's 1993 decision not to revise the NAAQS for
ozone, ``new'' studies may sometimes be of such significance that it is
appropriate to delay a decision on revision of a NAAQS and to
supplement the pertinent air quality criteria so the studies can be
taken into account (58 FR at 13013-13014, March 9, 1993). In the
present case, the EPA's provisional consideration of ``new'' studies
concludes that, taken in context, the ``new'' information and findings
do not materially change any of the broad scientific conclusions
regarding the health and welfare effects and exposure pathways of Pb in
ambient air made in the air quality criteria. For this reason,
reopening the air quality criteria review would not be warranted.
Accordingly, the EPA is basing the final decisions in this review
on the studies and related information included in the Pb air quality
criteria that have undergone CASAC and public review. The EPA will
consider the ``new'' studies for purposes of decision making in the
next periodic review of the NAAQS for Pb, which the EPA expects to
begin soon after the conclusion of this review and which will provide
the opportunity to fully assess these studies through a more rigorous
review process involving the EPA, CASAC, and the public.
D. Multimedia, Multipathway Aspects of Lead
Since Pb is distributed from air to other media and is persistent,
our review of the NAAQS for Pb considers the protection provided
against effects associated both with exposures to Pb in ambient air and
with exposures to Pb that makes its way into other media from ambient
air. Additionally, in assessing the adequacy of protection afforded by
the current NAAQS, we are mindful of the long history of greater and
more widespread atmospheric emissions that occurred in previous years
(both before and after establishment of the 1978 NAAQS) and that
contributed to the Pb that is in human populations and ecosystems
today. Likewise, we also recognize the role of other, nonair sources of
Pb now and in the past that also contribute to the Pb that is in human
populations and ecosystems today.
Lead emitted to ambient air is transported through the air and is
also distributed from air to other media. This multimedia distribution
of Pb emitted into ambient air (air-related Pb) contributes to multiple
air-related pathways of human and ecosystem exposure (ISA, sections
3.1.1 and 3.7.1). Air-related pathways may also involve media other
than air, including indoor and outdoor dust, soil, surface water and
sediments, vegetation and biota. Air-related Pb exposure pathways for
humans include inhalation of ambient air or ingestion of food, water or
other materials, including dust and soil, that have been contaminated
through a pathway involving Pb deposition from ambient air (ISA,
section 3.1.1.1). Ambient air inhalation pathways include both
inhalation of air outdoors and inhalation of ambient air that has
infiltrated into indoor environments. The air-related ingestion
pathways occur as a result of Pb passing through the ambient air, being
distributed to other environmental media and contributing to human
exposures via contact with and ingestion of indoor and outdoor dusts,
outdoor soil, food and drinking water.
Lead currently occurring in nonair media may also derive from
sources other than ambient air (nonair Pb sources) (ISA, sections 2.3
and 3.7.1). For example, Pb in dust inside some houses or outdoors in
some urban areas may derive from the common past usage of leaded paint,
while Pb in drinking water may derive from the use of leaded pipe or
solder in drinking water distribution systems (ISA, section 3.1.3.3).
We also recognize the history of much greater air emissions of Pb in
the past, such as that associated with leaded gasoline usage and higher
industrial emissions which have left a legacy of Pb in other (nonair)
media.
The relative importance of different pathways of human exposure to
Pb, as well as the relative contributions from Pb resulting from recent
and historic air emissions and from nonair sources, vary across the
U.S. population as a result of both extrinsic factors, such as a home's
proximity to industrial Pb sources or its history of leaded paint
usage, and intrinsic factors, such as a person's age and nutritional
status (ISA, sections 5.1, 5.2, 5.2.1, 5.2.5 and 5.2.6). Thus, the
relative contributions from specific pathways are situation specific
(ISA, p. 1-11), although a predominant Pb exposure pathway for very
young children is the incidental ingestion of indoor dust by hand-to-
mouth activity (ISA, section 3.1.1.1). For adults, however, diet may be
the primary Pb exposure pathway (2006 CD, section 3.4). Similarly, the
relative importance of air-related and nonair-related Pb also varies
with the relative magnitudes of
[[Page 71913]]
exposure by those pathways, which may vary with different
circumstances.
The distribution of Pb from ambient air to other environmental
media also influences the exposure pathways for organisms in
terrestrial and aquatic ecosystems. Exposure of terrestrial animals and
vegetation to air-related Pb can occur by contact with ambient air or
by contact with soil, water or food items that have been contaminated
by Pb from ambient air (ISA, section 6.2). Transport of Pb into aquatic
systems similarly provides for exposure of biota in those systems, and
exposures may vary among systems as a result of differences in sources
and levels of contamination, as well as characteristics of the systems
themselves, such as salinity, pH and turbidity (ISA, section 2.3.2). In
addition to Pb contributed by current atmospheric deposition, Pb may
occur in aquatic systems as a result of nonair sources such as
industrial discharges or mine-related drainage, of historical air Pb
emissions (e.g., contributing to deposition to a water body or via
runoff from soils near historical air sources) or combinations of
different types of sources (e.g., resuspension of sediments
contaminated by urban runoff and surface water discharges).
The persistence of Pb contributes an important temporal aspect to
lead's environmental pathways, and the time (or lag) associated with
realization of the impact of air Pb concentrations on concentrations in
other media can vary with the media (e.g., ISA, section 6.2.2). For
example, exposure pathways most directly involving Pb in ambient air or
surface waters can respond more quickly to changes in ambient air Pb
concentrations, while pathways involving exposure to Pb in soil or
sediments generally respond more slowly.\15\ An additional influence on
the response time for nonair media is the environmental presence of Pb
associated with past, generally higher, air concentrations. For
example, after a reduction in air Pb concentrations, the time needed
for sediment or surface soil concentrations to indicate a response to
reduced air Pb concentrations might be expected to be longer in areas
of more substantial past contamination than in areas with lesser past
contamination. Thus, considering the Pb concentrations occurring in
nonair environmental media as a result of air quality conditions that
meet the current NAAQS is a complexity of this review, as it also was,
although to a lesser degree, with regard to the prior standard in the
last review.
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\15\ The time it takes for exposures to be reduced in response
to reductions in air Pb concentrations varies with the various
inhalation and ingestion exposure pathways. For example, exposures
resulting from human exposure pathways most directly involving Pb in
ambient air and exchanges of ambient air with indoor air (e.g.,
inhalation) can respond most quickly, while those for pathways
involving exposure to Pb deposited from ambient air into the
environment (e.g., diet) may be expected to respond more slowly. The
extent of this will be influenced by the magnitude of change, as
well as--for deposition-related pathways--the extent of prior
deposition and environment characteristics influencing availability
of prior deposited Pb.
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E. Air Quality Monitoring
Lead emitted to the air is predominantly in particulate form. Once
emitted, particle-bound Pb can be transported long or short distances
depending on particle size, which influences the amount of time spent
in the aerosol phase. In general, larger particles tend to deposit more
quickly, within shorter distances from emissions points, compared with
smaller particles that remain in the aerosol phase and travel longer
distances before depositing (ISA, section 1.2.1). Accordingly, airborne
concentrations of Pb near sources are much higher (and the
representation of larger particles generally greater) than at sites not
directly influenced by sources (PA, Figure 2-11; ISA sections 2.3.1 and
2.5.3).
Ambient air monitoring data for Pb, in terms of Pb-TSP, Pb-
PM10 or Pb in particulate matter with mean aerodynamic
diameter less than or equal to 2.5 microns (Pb-PM2.5), are
currently collected in several national networks. Monitoring conducted
for purposes of Pb NAAQS surveillance is regulated to ensure accurate
and comparable data for determining compliance with the NAAQS. In order
to be used in NAAQS attainment designations, ambient Pb concentration
data must be obtained using either the federal reference method (FRM)
or a federal equivalent method (FEM). The FRMs for sample collection
and analysis are specified in 40 CFR part 50. The procedures for
approval of FRMs and FEMs are specified in 40 CFR part 53. In 2013,
after consultation with the CASAC's Ambient Air Monitoring and Methods
Subcommittee, the EPA adopted a new FRM for Pb-TSP, based on
inductively coupled plasma-mass spectrometry (78 FR 40000, July 3,
2013). The previous FRM was retained as an FEM, and existing FEMs were
retained as well.
The Pb NAAQS surveillance network regulations (40 CFR part 58,
appendix D, paragraph 4.5) require source-oriented monitoring sites,
and also the collection of one year of Pb-TSP measurements at 15
specific airports. The indicator for the current Pb NAAQS is Pb-TSP,
although in some situations,\16\ Pb-PM10 concentrations may
be used in judging nonattainment. Currently, more than 200 Pb-TSP
monitors are in operation; these are a mixture of source- and non-
source-oriented monitors (PA, p. 2-14).
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\16\ The Pb-PM10 measurements may be used for NAAQS
monitoring as an alternative to Pb-TSP measurements in certain
conditions defined in 40 CFR part 58, appendix C, section 2.10.1.2.
These conditions include where Pb concentrations are not expected to
equal or exceed 0.10 [mu]g/m\3\ as an arithmetic 3-month mean and
where the source of Pb emissions is expected to emit a substantial
majority of its Pb in the size fraction captured by PM10
monitors.
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Since the phase-out of Pb in on-road gasoline, Pb is widely
recognized as a near-source air pollutant, the ambient air
concentrations of which generally fall off quickly with distance from
sources. Variability in ambient air Pb concentrations is highest in
areas including a Pb source, ``with high concentrations downwind of the
sources and low concentration at areas far from sources'' (ISA, p. 2-
92). The current requirements for source-oriented monitoring include
placement of monitor sites near sources of air Pb emissions that are
expected to or have been shown to contribute to ambient air Pb
concentrations in excess of the NAAQS. At a minimum, there must be one
source-oriented site located to measure the maximum Pb concentration in
ambient air resulting from each non-airport Pb source that emits 0.50
or more tons of Pb per year and from each airport that emits 1.0 or
more tons of Pb per year.\17\ The EPA Regional Administrators may
require additional monitoring beyond the minimum requirements where the
likelihood of Pb air quality violations is significant or where the
emissions density, topography, or population locations are complex and
varied. Such locations may include those near additional industrial Pb
sources, recently closed industrial sources and other sources of re-
entrained Pb dust, as well as airports where piston-engine aircraft
emit Pb associated with combustion of leaded aviation fuel (40 CFR part
58, appendix D, section 4.5(c)). A single year of monitoring was also
required near 15 specific airports\18\ in order to gather
[[Page 71914]]
additional information on ambient air Pb concentrations near airports,
including specifically on the likelihood of NAAQS exceedances due to
the combustion of leaded aviation gasoline (75 FR 81126, December 27,
2010; 40 CFR part 58, appendix D, 4.5(a)(iii)). These airport
monitoring data along with other data gathering and analyses will
inform the EPA's ongoing investigation under section 231(a)(2)(A) of
the CAA of whether Pb emissions from piston-engine aircraft cause or
contribute to air pollution which may reasonably be anticipated to
endanger public health or welfare (see for example, EPA's Advance
Notice of Proposed Rulemaking on Lead Emissions From Piston-Engine
Aircraft Using Leaded Aviation Gasoline, 75 FR 22439, April 28, 2010).
The EPA is conducting this investigation separate from the Pb NAAQS
review. As a whole, the various data gathering efforts and analyses are
expected to improve our understanding of Pb concentrations in ambient
air near airports and conditions influencing these concentrations.
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\17\ The Regional Administrator may waive this requirement for
monitoring near Pb sources if the state or, where appropriate, local
agency can demonstrate the Pb source will not contribute to a
maximum 3-month average Pb concentration in ambient air in excess of
50 percent of the NAAQS level based on historical monitoring data,
modeling, or other means (40 CFR part 58, appendix D, section
4.5(a)(ii)).
\18\ These airports were selected based on three criteria:
annual Pb inventory between 0.5 ton/year and 1.0 ton/year, ambient
air within 150 meters of the location of maximum emissions (e.g.,
the end of the runway or run-up location), and airport configuration
and meteorological scenario that leads to a greater frequency of
operations from one runway. These criteria or characteristics were
selected as they were expected, ``collectively, to identify airports
with the highest potential to have ambient air Pb concentrations
approaching or exceeding the Pb NAAQS'' (75 FR 81132, December 27,
2010).
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Monitoring agencies may also conduct non-source-oriented Pb
monitoring at the NCore monitoring sites.\19\ In 2015, all NCore sites
with a population of 500,000 or more (as defined by the U.S. Census
Bureau) \20\ were measuring Pb concentrations, with a 2014 analysis
indicating generally similar numbers of sites measuring Pb in TSP and
Pb in PM10 (Cavender, 2014). These numbers may change in the
future as the requirement for Pb monitoring at these sites was recently
eliminated in consideration of current information indicating
concentrations at these sites to be well below the Pb NAAQS and of the
existence of other monitoring networks that provide information on Pb
concentrations at similar types of sites (81 FR 17248, March 28, 2016).
The data available for the NCore sites indicate maximum 3-month average
concentrations (of Pb-PM10 or Pb-TSP) well below the level
of the Pb NAAQS, with the large majority of these sites indicating
maximum 3-month average concentrations at or below 0.01 [micro]g/m\3\
(Cavender, 2014). Other monitoring networks that provide data on Pb in
PM10 or PM2.5 at non-source-oriented urban, and
some rural, sites include the National Air Toxics Trends Stations for
PM10 and the Chemical Speciation Network for
PM2.5. Data on Pb in PM2.5 are also provided at
the rural sites of the Interagency Monitoring of Protected Visual
Environments network (also known as the IMPROVE network).
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\19\ The NCore network that formally began in January 2011, is a
subset of the state and local air monitoring stations network that
is intended to meet multiple monitoring objectives (e.g., long-term
trends analysis, model evaluation, health and ecosystem studies, as
well as NAAQS compliance). The complete NCore network consists of 63
urban and 15 rural stations, with each state containing at least one
NCore station; 46 of the states plus Washington, DC and Puerto Rico
have at least one urban station.
\20\ Metropolitan area population size information is available
at the Census Bureau Web site (http://www.census.gov/population/www/metroareas/metroarea.htm).
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The long-term record of Pb monitoring data documents the dramatic
decline in atmospheric Pb concentrations that has occurred since the
1970s in response to reduced emissions (PA, Figures 2-1 and 2-7).
Currently, the highest concentrations occur near some metals industries
where some individual locations have concentrations that exceed the
NAAQS (PA, Figure 2-10). Concentrations at non-source-oriented
monitoring sites are much lower than those at source-oriented sites and
well below the standard (PA, Figure 2-11).
F. Summary of Proposed Decisions
For reasons discussed in the proposal and summarized in sections
II.B.1 and III.B.1 below, the Administrator proposed to retain the
current primary and secondary standards for Pb, without revision.
G. Organization and Approach to Final Decisions
This action presents the Administrator's final decisions in the
current review of the primary and secondary Pb standards. The final
decisions addressing standards for Pb are based on a thorough review in
the ISA of scientific information on known and potential human health
and welfare effects associated with exposure to Pb associated with
levels typically found in the ambient air. These final decisions also
take into account the following: (1) Staff assessments in the PA of the
most policy-relevant information in the ISA as well as quantitative
health and welfare exposure and risk information; (2) CASAC advice and
recommendations, as reflected in its letters to the Administrator and
its discussions of drafts of the ISA and PA at public meetings; (3)
public comments received during the development of these documents,
both in connection with CASAC meetings and separately; and (4) public
comments received on the proposal.
The primary standard is addressed in section II and the secondary
standard is addressed in section III. Section IV addresses applicable
statutory and executive order reviews.
II. Rationale for Decision on the Primary Standard
This section presents the rationale for the Administrator's
decision to retain the existing primary Pb standard. This rationale is
based on a thorough review in the ISA of the latest scientific
information, generally published through September 2011, on human
health effects associated with Pb and pertaining to the presence of Pb
in the ambient air. This decision also takes into account: (1) The PA's
staff assessments of the most policy-relevant information in the ISA
and staff analyses of air quality, human exposure and health risks,
upon which staff conclusions regarding appropriate considerations in
this review are based; (2) CASAC advice and recommendations, as
reflected in discussions of drafts of the ISA and PA at public
meetings, in separate written comments, and in the CASAC's letters to
the Administrator; (3) public comments received during the development
of these documents, either in connection with CASAC meetings or
separately, and (4) public comments received on the proposal.
Section II.A provides background on the general approach for review
of the primary standard for Pb and brief summaries of key aspects of
the currently available health effects and exposure/risk information.
Section II.B presents the Administrator's conclusions on adequacy of
the current standard, drawing on consideration of this information,
advice from the CASAC, and comments from the public. Section II.C
summarizes the Administrator's decision on the primary standard.
A. Introduction
As in prior reviews, the general approach to reviewing the current
primary standard is based, most fundamentally, on using the EPA's
assessment of the current scientific evidence and associated
quantitative analyses to inform the Administrator's judgment regarding
a primary standard for Pb that protects public health with an adequate
margin of safety. In drawing conclusions with regard to the primary
standard, the final decision on the adequacy of the current standard is
largely a public health policy judgment to be made by the
Administrator. The
[[Page 71915]]
Administrator's final decision must draw upon scientific information
and analyses about health effects, population exposure and risks, as
well as judgments about how to consider the range and magnitude of
uncertainties that are inherent in the scientific evidence and
analyses. The approach to informing these judgments, discussed more
fully below, is based on the recognition that the available health
effects evidence generally reflects a continuum, consisting of levels
at which scientists generally agree that health effects are likely to
occur, through lower levels at which the likelihood and magnitude of
the response become increasingly uncertain. This approach is consistent
with the requirements of the NAAQS provisions of the Act and with how
the EPA and the courts have historically interpreted the Act. These
provisions require the Administrator to establish primary standards
that, in the judgment of the Administrator, are requisite to protect
public health with an adequate margin of safety. In so doing, the
Administrator seeks to establish standards that are neither more nor
less stringent than necessary for this purpose. The Act does not
require that primary standards be set at a zero-risk level, but rather
at a level that avoids unacceptable risks to public health including
the health of sensitive groups. The four basic elements of the NAAQS
(indicator, averaging time, level, and form) are considered
collectively in evaluating the health protection afforded by the
current standard.
To evaluate whether it is appropriate to consider retaining the
current primary Pb standard, or whether consideration of revision is
appropriate, the EPA has adopted an approach in this review that builds
upon the general approach used in the last review and reflects the
broader body of evidence and information now available. As summarized
in section II.A.1 below, the Administrator's decisions in the prior
review were based on an integration of information on health effects
associated with exposure to Pb with that on relationships between
ambient air Pb and blood Pb; expert judgments on the adversity and
public health significance of key health effects; and policy judgments
as to when the standard is requisite to protect public health with an
adequate margin of safety. These considerations were informed by air
quality and related analyses, quantitative exposure and risk
assessments, and qualitative assessment of impacts that could not be
quantified.
Similarly in this review, as described in the PA, we draw on the
current evidence and quantitative assessments of exposure pertaining to
the public health risk of Pb in ambient air. In considering the
scientific and technical information here as in the PA, we consider
both the information available at the time of the last review and
information newly available since the last review, including most
particularly that which has been critically analyzed and characterized
in the current ISA. We additionally consider the quantitative exposure/
risk assessments from the last review that estimated Pb-related IQ
decrements associated with different air quality conditions in
simulated at-risk populations in multiple case studies (PA, section
3.4; 2007 REA). The evidence-based discussions presented below draw
upon evidence from epidemiological studies and experimental animal
studies evaluating health effects related to exposures to Pb, as
discussed in the ISA. The exposure/risk-based discussions have drawn
from the quantitative health risk analyses for Pb performed in the last
Pb NAAQS review in light of the currently available evidence (PA,
section 3.4; 2007 REA; REA Planning Document). Sections II.A.2 through
II.A.4 below provide an overview of the current health effects and
quantitative exposure and risk information with a focus on the specific
policy-relevant questions identified for these categories of
information in the PA (PA, chapter 3).
1. Background on the Current Standard
The current primary standard was established in the last review,
which was completed in 2008 (73 FR 66964, November 12, 2008), and is
set at a level that is one-tenth the level of the prior standard. The
2008 decision to substantially revise the primary standard was based on
the extensive body of scientific evidence published over almost three
decades, from the time the standard was originally set in 1978 through
2005-2006. While recognizing that Pb has been demonstrated to exert ``a
broad array of deleterious effects on multiple organ systems,'' the
2008 review focused on the effects most pertinent to recent ambient air
exposures, which are those associated with relatively lower exposures
and associated blood Pb levels (73 FR 66975, November 12, 2008). Given
the general scientific consensus that the developing nervous system in
children is among the most sensitive health endpoints associated with
Pb exposure, if not the most sensitive one, primary attention was given
to consideration of nervous system effects, including neurocognitive
and neurobehavioral effects, in children (73 FR 66976, November 12,
2008). The body of evidence included associations of such effects in
study populations of variously aged children with mean blood Pb levels
below 10 [micro]g/dL, extending from 8 down to 2 [micro]g/dL (73 FR
66976, November 12, 2008). Particular focus was given to the public
health implications of effects of air-related Pb on cognitive function
(e.g., IQ).
The conclusions reached by the Administrator in the 2008 review
were based primarily on the scientific evidence, with the risk- and
exposure-based information providing support for various aspects of the
decision. In reaching his conclusion on the adequacy of the then-
current standard, which was set in 1978, the Administrator placed
primary consideration on the large body of scientific evidence
available in the review including significant new evidence concerning
effects at blood Pb concentrations substantially below those identified
when the standard was initially set (73 FR 66987, November 12, 2008; 43
FR 46246, October 5, 1978). He gave particular attention to the robust
evidence of neurotoxic effects of Pb exposure in children, recognizing:
(1) That while blood Pb levels in U.S. children had decreased notably
since the late 1970s, newer epidemiological studies had investigated
and reported associations of effects on the neurodevelopment of
children with those more recent lower blood Pb levels and (2) that the
toxicological evidence included extensive experimental laboratory
animal evidence substantiating well the plausibility of the
epidemiological findings observed in human children and expanding our
understanding of likely mechanisms underlying the neurotoxic effects
(73 FR 66987, November 12, 2008). Additionally, within the range of
blood Pb levels investigated in the available evidence base, a
threshold level for neurocognitive effects was not identified (73 FR
66984, November 12, 2008; 2006 CD, p. 8-67). Further, the evidence
indicated a steeper concentration-response (C-R) relationship for
effects on cognitive function at those lower blood Pb levels than at
higher blood Pb levels that were more common in the past, ``indicating
the potential for greater incremental impact associated with exposure
at these lower levels'' (73 FR 66987, November 12, 2008).
Based on consideration of the health effects evidence, supported by
the quantitative risk analyses, the Administrator concluded that, for
exposures projected for air Pb concentrations at the level of the 1978
[[Page 71916]]
standard, the quantitative estimates of IQ loss associated with air-
related Pb indicated risk of a magnitude that, in his judgment, was
significant from a public health perspective, and that the 1978
standard did not protect public health with an adequate margin of
safety (73 FR 66987, November 12, 2008). The Administrator further
concluded that the evidence indicated the need for a substantially
lower standard level to provide increased public health protection,
especially for sensitive or at-risk groups (most notably children),
against an array of effects, most importantly including effects on the
developing nervous system (73 FR 66987, November 12, 2008). In
identifying the appropriate revised standard, revisions to each of the
four basic elements of the NAAQS (indicator, averaging time, form and
level) were considered.
With regard to indicator, the Administrator decided to retain Pb-
TSP as the indicator. The EPA recognized that the difference in
particulate Pb captured by TSP and PM10 monitors may be on
the order of a factor of two in some areas, and that ultra-coarse Pb
particles may have a greater presence in areas near sources where Pb
concentrations are highest, contributing uncertainty with regard to
whether a Pb-PM10-based standard would also effectively
control ultra-coarse Pb particles (73 FR 66991, November 12, 2008).
Accordingly, Pb-TSP was retained as the indicator in order to provide
sufficient public health protection from the broad range of particle
sizes of ambient air Pb, including ultra-coarse particles, given the
recognition that Pb in all particle sizes contributes to Pb in blood
and associated health effects (73 FR 66991, November 12, 2008).\21\
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\21\ However, in order to take advantage of the increased
precision of Pb-PM10 measurements and decreased spatial
variation of Pb-PM10 concentrations without raising the
same concerns over a lack of protection against health risks from
all particulate Pb emitted to the ambient air that support retention
of Pb-TSP as the indicator (versus revision to Pb-PM10),
a role was provided for Pb-PM10 measurements in the
monitoring required for a Pb-TSP standard (73 FR 66991, November 12,
2008) at sites not influenced by sources of ultra-coarse Pb, and
where Pb concentrations are well below the standard (73 FR 66991,
November 12, 2008).
---------------------------------------------------------------------------
With regard to averaging time and form for the revised standard,
after giving consideration to a monthly averaging time, with a form of
second maximum, and to 3-month and calendar quarter averaging times,
with not-to-be exceeded forms, two changes were made. These were to a
rolling 3-month average, thus giving equal weight to all 3-month
periods, and to the method for deriving the 3-month average to provide
equal weighting to each month. Both of these changes afford greater
weight to each individual month than did the calendar quarter form of
the 1978 standard, thus tending to control both the likelihood that any
month will exceed the level of the standard and the magnitude of any
such exceedance. The Administrator decided on these changes in
recognition of the complexity inherent in this aspect of the standard
which is greater for Pb than in the case of other criteria pollutants
due to the multimedia nature of Pb and its multiple pathways of human
exposure. In this situation for Pb, the Administrator emphasized the
importance of considering in an integrated manner all of the relevant
factors, both those pertaining to the human physiological response to
changes in Pb exposures and those pertaining to the response of air-
related Pb exposure pathways to changes in airborne Pb, recognizing
that some factors might imply support for a period as short as a month
for averaging time, and others supporting use of a longer time, with
all having associated uncertainty. Based on such an integrated
consideration of the range of relevant factors, the averaging time was
revised to a rolling 3-month period with a maximum (not-to-be-exceeded)
form, evaluated over a 3-year period (73 FR 66996, November 12, 2008).
In reaching the decision on level for the revised standard, that,
in combination with the specified choice of indicator, averaging time,
and form, the Administrator judged requisite to protect public health,
including the health of sensitive groups, with an adequate margin of
safety, he considered the evidence using a very specifically defined
framework, referred to as an air-related IQ loss evidence-based
framework (73 FR 67004, November 12, 2008). This framework integrates
evidence for the relationship between Pb in air and Pb in young
children's blood with evidence for the relationship between Pb in young
children's blood and IQ loss (73 FR 66987, November 12, 2008). This
evidence-based approach considers air-related effects on neurocognitive
function (using the quantitative metric of IQ loss) associated with
exposure in those areas with elevated air concentrations equal to
potential alternative levels for the Pb standard. In simplest terms,
the framework focuses on children exposed to air-related Pb in those
areas with elevated air Pb concentrations equal to specific potential
standard levels, providing for estimation of a mean air-related IQ
decrement for young children with air-related exposures that are in the
high end of the national distribution of such exposures. Thus, the
conceptual context for the framework is that it provides estimates of
air-related IQ loss for the subset of U.S. children living in close
proximity to air Pb sources that contribute to such elevated air Pb
concentrations. Consideration of this framework additionally recognizes
that in such cases when a standard of a particular level is just met at
a monitor sited to record the highest source-oriented concentration in
an area, the large majority of children in the larger surrounding area
would likely experience exposures to concentrations well below that
level.
The two primary inputs to the air-related IQ loss evidence-based
framework are air-to-blood ratios \22\ and C-R functions for the
relationship between blood Pb concentration and IQ response in young
children (73 FR 67004, November 12, 2008). In applying and drawing
conclusions from the framework, the Administrator additionally took
into consideration the uncertainties inherent in these two inputs.
Application of the framework also entailed consideration of an
appropriate level of protection from air-related IQ loss to be used in
conjunction with the framework. The framework estimates of mean air-
related IQ loss are derived through multiplication of the following
factors: standard level ([micro]g/m\3\), air-to-blood ratio (albeit in
terms of [micro]g/dL blood Pb per [micro]g/m\3\ air concentration), and
slope for the C-R function in terms of points of IQ decrement per
[micro]g/dL blood Pb. In light of the uncertainties and limitations
associated with the evidence on these relationships, and other
considerations, application of the air-related IQ loss evidence-based
framework was recognized to provide ``no evidence- or risk-based bright
line that indicates a single appropriate level'' for the standard (73
FR 67005-67006, November 12, 2008). Rather, the framework was seen as a
useful guide, in the context of the specified averaging time and form,
for consideration of health risks from exposure to levels of Pb in the
ambient air to inform the Administrator's decision on a level for
[[Page 71917]]
a revised NAAQS that provides public health protection that is
sufficient but not more than necessary under the Act (73 FR 67004,
November 12, 2008).
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\22\ The term ``air-to-blood ratio'' describes the increase in
blood Pb (in [micro]g/dL) estimated to be associated with each unit
increase of air Pb (in [micro]g/m\3\). Ratios are presented in the
form of 1:x, with the 1 representing air Pb (in [micro]g/m\3\) and x
representing blood Pb (in [micro]g/dL). Description of ratios as
higher or lower refers to the values for x (i.e., the change in
blood Pb per unit of air Pb).
---------------------------------------------------------------------------
Use of the air-related IQ loss evidence-based framework to inform
selection of the standard level involved consideration of the evidence
for the two primary input parameters mentioned above. With regard to
air-to-blood ratio estimates, the evidence in the 2008 review indicated
a broad range of estimates, each with limitations and associated
uncertainties. Based on this evidence, the Administrator concluded that
1:5 to 1:10 represented a reasonable range to consider and focused on
1:7 as a generally central value (73 FR 67004, November 12, 2008). With
regard to C-R functions, in light of the evidence of nonlinearity and
of steeper slopes at lower blood Pb levels, the Administrator concluded
it was appropriate to focus on C-R analyses based on blood Pb levels
that most closely reflected the then-current population of young
children in the U.S.,\23\ recognizing the EPA's identification of four
such analyses and giving weight to the central estimate or median of
the resultant linear C-R functions (73 FR 67003, November 12, 2008,
Table 3; 73 FR 67004, November 12, 2008). The median estimate for the
four C-R slopes of -1.75 IQ points decrement per [micro]g/dL blood Pb
was selected for use with the framework. With the framework, potential
alternative standard levels ([micro]g/m\3\) are multiplied by estimates
of air-to-blood ratio ([micro]g/dL blood Pb per [micro]g/m\3\ air Pb)
and the median slope for the C-R function (points IQ decrement per
[micro]g/dL blood Pb), yielding estimates of a mean air-related IQ
decrement for a specific subset of young children (i.e., those children
exposed to air-related Pb in areas with elevated air Pb concentrations
equal to specified alternative levels). As such, the application of the
framework yields estimates for the mean air-related IQ decrements of
the subset of children expected to experience air-related Pb exposures
at the high end of the distribution of such exposures. The associated
mean IQ loss estimate is the average for this highly exposed subset and
is not the average air-related IQ loss projected for the entire U.S.
population of children. Uncertainties and limitations were recognized
in the use of the framework and in the resultant estimates (73 FR
67000, November 12, 2008).
---------------------------------------------------------------------------
\23\ The geometric mean blood Pb level for U.S. children aged 5
years and below, reported for NHANES in 2003-04 (the most recent
years for which such an estimate was available at the time of the
2008 decision) was 1.8 [micro]g/dL and the 5th and 95th percentiles
were 0.7 [micro]g/dL and 5.1 [micro]g/dL, respectively (73 FR
67002). Using the air-to-blood ratio 1:7, the estimated air-related
blood Pb level associated with the final standard level is
approximately 1 [micro]g/dL. In the 2008 decision, the EPA noted
that even if it assumed, as an extreme hypothetical example, that
the mean for the general population of U.S. children included zero
contribution from air-related sources and added that to the estimate
of air-related Pb, the result would still be below the lowest mean
blood Pb level among the set of C-R analyses (73 FR 67002).
---------------------------------------------------------------------------
In considering the use of the air-related IQ loss evidence-based
framework to inform his judgment as to the appropriate degree of public
health protection that should be afforded by the NAAQS to provide
requisite protection against risk of neurocognitive effects in
sensitive populations, such as IQ loss in children, the Administrator
recognized in the 2008 review that there were no commonly accepted
guidelines or criteria within the public health community that would
provide a clear basis for such a judgment. During the 2008 review,
CASAC commented regarding the significance from a public health
perspective of a 1-2 point IQ loss in the entire population of children
and, along with some commenters, emphasized that the NAAQS should
prevent air-related IQ loss of a significant magnitude, such as on the
order of 1-2 IQ points, in all but a small percentile of the
population. Similarly, the Administrator stated that ``ideally air-
related (as well as other) exposures to environmental Pb would be
reduced to the point that no IQ impact in children would occur'' (73 FR
66998, November 12, 2008). The Administrator further recognized that,
in the case of setting a national ambient air quality standard, he was
required to make a judgment as to what degree of protection is
requisite to protect public health with an adequate margin of safety
(73 FR 66998, November 12, 2008). The NAAQS must be sufficient but not
more stringent than necessary to achieve that result, and the Act does
not require a zero-risk standard (73 FR 66998, November 12, 2008). The
Administrator additionally recognized that the air-related IQ loss
evidence-based framework did not provide estimates pertaining to the
U.S. population of children as a whole. Rather, the framework provided
estimates (with associated uncertainties and limitations) for the mean
of a subset of that population, the subset of children assumed to be
exposed to the level of the standard. As described in the final
decision ``[t]he framework in effect focuses on the sensitive
subpopulation that is the group of children living near sources and
more likely to be exposed at the level of the standard'' (73 FR 67000,
November 12, 2008). Further description of the EPA's consideration of
this issue is provided in the preamble to the final decision rule (73
FR 67000, November 12, 2008):
EPA is unable to quantify the percentile of the U.S. population
of children that corresponds to the mean of this sensitive
subpopulation. Nor is EPA confident in its ability to develop
quantified estimates of air-related IQ loss for higher percentiles
than the mean of this subpopulation. EPA expects that the mean of
this subpopulation represents a high, but not quantifiable,
percentile of the U.S. population of children. As a result, EPA
expects that a standard based on consideration of this framework
would provide the same or greater protection from estimated air-
related IQ loss for a high, albeit unquantifiable, percentage of the
entire population of U.S. children.
In reaching a judgment as to the appropriate degree of protection,
the Administrator considered advice and recommendations from CASAC and
public comments and recognized the uncertainties in the health effects
evidence and related information as well as the role of, and context
for, a selected air-related IQ loss in the application of the
framework, as described above. Based on these considerations, the
Administrator identified an air-related IQ loss of 2 points for use
with the framework, as a tool for considering the evidence with regard
to the level for the standard (73 FR 67005, November 12, 2008). In so
doing, the Administrator was not determining that such an IQ decrement
value was appropriate in other contexts (73 FR 67005, November 12,
2008). Given the various uncertainties associated with the framework
and the scientific evidence base, and the focus of the framework on the
sensitive subpopulation of children that are more highly exposed to
air-related Pb, a standard level selected in this way, in combination
with the selected averaging time and form, was expected to
significantly reduce and limit for a high percentage of U.S. children
the risk of experiencing an air-related IQ loss of that magnitude (73
FR 67005, November 12, 2008). At the standard level of 0.15 [micro]g/
m\3\, with the combination of the generally central estimate of air-to-
blood ratio of 1:7 and the median of the four C-R functions (-1.75 IQ
point decrement per [micro]g/dL blood Pb), the framework estimates of
air-related IQ loss were below 2 IQ points (73 FR 67005, November 12,
2008, Table 4).
In reaching the decision in 2008 on a level for the revised
standard, the Administrator also considered the results of the
quantitative risk assessment to provide a useful
[[Page 71918]]
perspective on risk from air-related Pb. In light of important
uncertainties and limitations for purposes of evaluating potential
standard levels, however, the Administrator placed less weight on the
risk estimates than on the evidence-based assessment. Nevertheless, in
recognition of the general comparability of quantitative risk estimates
for the case studies considered most conceptually similar to the
scenario represented by the evidence-based framework, he judged the
quantitative risk estimates to be ``roughly consistent with and
generally supportive'' of the evidence-based framework estimates (73 FR
67006, November 12, 2008).
Based on consideration of the entire body of evidence and
information available in the review, as well as the recommendations of
CASAC and public comments, the Administrator decided that a level for
the primary Pb standard of 0.15 [micro]g/m\3\, in combination with the
specified choice of indicator, averaging time and form, was requisite
to protect public health, including the health of sensitive groups,
with an adequate margin of safety (73 FR 67006, November 12, 2008). In
reaching decisions on level as well as the other elements of the
revised standard, the Administrator took note of the complexity
associated with consideration of health effects caused by different
ambient air concentrations of Pb and with uncertainties with regard to
the relationships between air concentrations, exposures, and health
effects. For example, selection of a maximum, not to be exceeded, form
in conjunction with a rolling 3-month averaging time over a 3-year span
was expected to have the effect that the at-risk population of children
would be exposed below the standard most of the time (73 FR 67005,
November 12, 2008). The Administrator additionally considered the
provision of an adequate margin of safety in making decisions on each
of the elements of the standard, including, for example ``selection of
TSP as the indicator and the rejection of the use of PM10
scaling factors; selection of a maximum, not to be exceeded form, in
conjunction with a 3-month averaging time that employs a rolling
average, with the requirement that each month in the 3-month period be
weighted equally (rather than being averaged by individual data) and
that a 3-year span be used for comparison to the standard; and the use
of a range of inputs for the evidence-based framework, that includes a
focus on higher air-to-blood ratios than the lowest ratio considered to
be supportable, and steeper rather than shallower C-R functions, and
the consideration of these inputs in selection of 0.15 [mu]g/m\3\ as
the level of the standard'' (73 FR 67007, November 12, 2008).
The Administrator additionally noted that a standard with this
level would reduce the risk of a variety of health effects associated
with exposure to Pb, including effects indicated in the epidemiological
studies at lower blood Pb levels, particularly including neurological
effects in children, and the potential for cardiovascular and renal
effects in adults (73 FR 67006, November 12, 2008). The Administrator
additionally considered higher and lower levels for the standard,
concluding that a level of 0.15 [micro]g/m\3\ provided for a standard
that was neither more or less stringent than necessary for this
purpose, recognizing that the Act does not require that primary
standards be set at a zero-risk level, but rather at a level that
reduces risk sufficiently so as to protect public health with an
adequate margin of safety (73 FR 67007, November 12, 2008). For
example, the Administrator additionally considered potential public
health protection provided by standard levels above 0.15 [micro]g/m\3\,
which he concluded were insufficient to protect public health with an
adequate margin of safety. The Administrator also noted that in light
of all of the evidence, including the evidence-based framework, the
degree of public health protection likely afforded by standard levels
below 0.15 [micro]g/m\3\ would be greater than what is necessary to
protect public safety with an adequate margin of safety.
The Administrator concluded, based on review of all of the evidence
(including the evidence-based framework), that when taken as a whole
the selected standard, including the indicator, averaging time, form,
and level, would be ``sufficient but not more than necessary to protect
public health, including the health of sensitive subpopulations, with
an adequate margin of safety'' (73 FR 67007, November 12, 2008).
2. Overview of Health Effects Evidence
In this section, we provide an overview of the information
presented in section II.B of the proposal on policy-relevant aspects of
the health effects evidence available for consideration in this review.
Section II.B of the proposal provides a detailed summary of key
information contained in the ISA and in the PA on health and public
health effects of Pb, focusing particularly on the information most
relevant to consideration of effects associated with the presence of Pb
in ambient air (80 FR 290-297, January 5, 2015). The subsections below
briefly outline this information in the five topic areas addressed in
section II.B of the proposal.
a. Array of Effects
Lead has been demonstrated to exert a broad array of deleterious
effects on multiple organ systems as described in the assessment of the
evidence available in this review and consistent with conclusions of
past CDs (ISA, section 1.6; 2006 CD, section 8.4.1). A sizeable number
of studies on Pb health effects are newly available in this review and
are critically assessed in the ISA as part of the full body of
evidence. The newly available evidence reaffirms conclusions on the
broad array of effects recognized for Pb in the last review (see ISA,
section 1.10).\24\ Consistent with those conclusions, in the context of
pollutant exposures considered relevant to the Pb NAAQS review,\25\ the
ISA determines that causal relationships \26\ exist for Pb with effects
on the nervous system in children (cognitive function decrements and
the group of externalizing behaviors comprising attention, impulsivity
and hyperactivity), the hematological system (altered heme synthesis
and decreased red blood cell survival and function), and the
cardiovascular system (hypertension and coronary heart disease), and on
reproduction and development (postnatal development and male
reproductive function) (ISA, Table 1-2). Additionally, the ISA
[[Page 71919]]
describes relationships between Pb and certain types of effects on the
nervous system in adults, and on immune system function, as well as
with cancer,\27\ as likely to be causal \28\ (ISA, Table 1-2, sections
1.6.4 and 1.6.7).
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\24\ Since the last Pb NAAQS review, the ISAs, which have
replaced CDs in documenting each review of the scientific evidence
(or air quality criteria), employ a systematic framework for
weighing the evidence and describing associated conclusions with
regard to causality using established descriptors: ``causal''
relationship with relevant exposure, ``likely'' to be a causal
relationship, evidence is ``suggestive'' of a causal relationship,
``inadequate'' evidence to infer a causal relationship, and ``not
likely'' to be a causal relationship (ISA, Preamble).
\25\ In drawing judgments regarding causality for the criteria
air pollutants, the ISA places emphasis ``on evidence of effects at
doses (e.g., blood Pb concentration) or exposures (e.g., air
concentrations) that are relevant to, or somewhat above, those
currently experienced by the population. The extent to which studies
of higher concentrations are considered varies . . . but generally
includes those with doses or exposures in the range of one to two
orders of magnitude above current or ambient conditions. Studies
that use higher doses or exposures may also be considered . .
.[t]hus, a causality determination is based on weight of evidence
evaluation . . ., focusing on the evidence from exposures or doses
generally ranging from current levels to one or two orders of
magnitude above current levels'' (ISA, pp. lx-lxi).
\26\ In determining a causal relationship to exist for Pb with
specific health effects, the EPA concludes that ``[e]vidence is
sufficient to conclude that there is a causal relationship with
relevant pollutant exposures (i.e., doses or exposures generally
within one to two orders of magnitude of current levels)'' (ISA, p.
lxii).
\27\ The EPA concludes that a causal relationship is likely to
exist between Pb exposure and cancer, based primarily on consistent,
strong evidence from experimental animal studies, but inconsistent
epidemiological evidence (ISA, section 4.10.5). Lead has also been
classified as a probable human carcinogen by the International
Agency for Research on Cancer, based mainly on sufficient animal
evidence, and as reasonably anticipated to be a human carcinogen by
the U.S. National Toxicology Program (ISA, section 4.10).
\28\ In determining that there is likely to be a causal
relationship for Pb with specific health effects, the EPA has
concluded that ``[e]vidence is sufficient to conclude that a causal
relationship is likely to exist with relevant pollutant exposures,
but important uncertainties remain'' (ISA, p. lxii).
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Among the nervous system effects of Pb, the newly available
evidence is consistent with conclusions in the previous review which
recognized that ``[t]he neurotoxic effects of Pb exposure are among
those most studied and most extensively documented among human
population groups'' (2006 CD, p. 8-25) and took note of the diversity
of studies in which such effects of Pb exposure early in development
(from fetal to postnatal childhood periods) have been observed (2006
CD, p. E-9). While some studies are newly available of other effects in
children with somewhat lower blood Pb levels than previously available
for these effects, nervous system effects continue to receive
prominence in the current review, as in previous reviews, with
particular emphasis on those affecting cognitive function and behavior
in children (ISA, section 4.3), with conclusions that are consistent
with findings of the last review. For example, based on the extensive
assessment of the full body of evidence available in this review, the
major conclusions drawn by the ISA regarding health effects of Pb in
children include the following (ISA, p. lxxxvii).
Multiple epidemiologic studies conducted in diverse populations
of children consistently demonstrate the harmful effects of Pb
exposure on cognitive function (as measured by IQ decrements,
decreased academic performance and poorer performance on tests of
executive function). . . . Evidence suggests that some Pb-related
cognitive effects may be irreversible and that the
neurodevelopmental effects of Pb exposure may persist into adulthood
(Section 1.9.4). Epidemiologic studies also demonstrate that Pb
exposure is associated with decreased attention, and increased
impulsivity and hyperactivity in children (externalizing behaviors).
This is supported by findings in animal studies demonstrating both
analogous effects and biological plausibility at relevant exposure
levels. Pb exposure can also exert harmful effects on blood cells
and blood producing organs, and is likely to cause an increased risk
of symptoms of depression and anxiety and withdrawn behavior
(internalizing behaviors), decreases in auditory and motor function,
asthma and allergy, as well as conduct disorders in children and
young adults. There is some uncertainty about the Pb exposures
contributing to the effects and blood Pb levels observed in
epidemiologic studies; however, these uncertainties are greater in
studies of older children and adults than in studies of young
children (Section 1.9.5).
As in prior reviews of the Pb NAAQS, this review is focused on
those effects most pertinent to ambient air Pb exposures. Given the
reductions in ambient air Pb concentrations over the past decades,
these effects are generally those associated with the lowest levels of
Pb exposure that have been evaluated. Additionally, we recognize the
limitations on our ability to draw conclusions regarding the exposure
conditions contributing to the findings from epidemiological analyses
of blood Pb levels in populations of older children and adults,
particularly in light of their history of higher Pb exposures. For
example, the evidence newly available for Pb relationships with
cardiovascular effects in adults includes some studies with somewhat
lower blood Pb levels than in the last review. However, the long
exposure histories of these cohorts, as well as the generally higher Pb
exposures of the past, complicate conclusions regarding exposure levels
that may be eliciting observed effects (ISA, sections 4.4.2.4 and
4.4.7).\29\ Evidence available in future reviews may better inform this
issue. Recognizing this, the extensive assessment of the full body of
evidence available in this review contributed to the following major
conclusions drawn by the ISA regarding health effects of Pb in adults
(ISA, p. lxxxviii).
\29\ Studies from the late 1960s and 1970s suggest that adult
blood Pb levels during that period ranged from roughly 13 to 16
[mu]g/dL and from 15 to 30 [micro]g/dL in children aged 6 and
younger (ISA, section 4.4.1).
---------------------------------------------------------------------------
A large body of evidence from both epidemiologic studies of
adults and experimental studies in animals demonstrates the effect
of long-term Pb exposure on increased blood pressure (BP) and
hypertension (Section 1.6.2). In addition to its effect on BP, Pb
exposure can also lead to coronary heart disease and death from
cardiovascular causes and is associated with cognitive function
decrements, symptoms of depression and anxiety, and immune effects
in adult humans. The extent to which the effects of Pb on the
cardiovascular system are reversible is not well-characterized.
Additionally, the frequency, timing, level, and duration of Pb
exposure causing the effects observed in adults has not been
pinpointed, and higher past exposures may contribute to the
development of health effects measured later in life.
In the last review, while recognizing the range of health effects
in variously aged populations related to Pb exposure, we focused on the
health effects for which the evidence was strongest with regard to
relationships with the lowest exposure levels, neurocognitive effects
in young children. Similarly, given the strength of the evidence,
including the greater confidence in conclusions regarding the exposures
contributing to the observed effects, we focus in this review, as in
the last, on neurocognitive effects in young children.
b. Critical Periods of Exposure
As in the last review, we base our current understanding of health
effects associated with different Pb exposure circumstances at various
stages of life or in different populations on the full body of
available evidence and primarily on epidemiological studies of health
effects associated with population Pb biomarker levels (as discussed
further in section II.B.3 of the proposal). The epidemiological
evidence is overwhelmingly composed of studies that rely on blood Pb
for the exposure metric, with the remainder largely including a focus
on bone Pb. Because these metrics reflect Pb in the body (e.g., as
compared to Pb exposure concentrations) and, in the case of blood Pb,
reflect Pb available for distribution to target sites, they strengthen
the evidence base for purposes of drawing causal conclusions with
regard to Pb generally. The complexity of Pb exposure pathways and
internal dosimetry, however, tends to limit the extent to which these
types of studies inform our more specific understanding of the Pb
exposure circumstances (e.g., timing within lifetime, duration,
frequency and magnitude) eliciting the various effects.
A critical aspect of much of the epidemiological evidence,
particularly studies focused on adults (and older children) in the U.S.
today, is the backdrop of generally declining environmental Pb exposure
(from higher exposures during their younger years) that is common
across many study populations (ISA, p. 4-2).\30\ An additional factor
complicating the interpretation of health effect
[[Page 71920]]
associations with blood Pb measurements in older children and younger
adults is the common behaviors of younger children (e.g., hand-to-mouth
contact) that generally contribute to relatively greater exposures
earlier in life (ISA, sections 3.1.1, 5.2.1). Such exposure histories
for adults and older children complicate our ability to draw
conclusions regarding critical time periods and lifestages for Pb
exposures eliciting the effects for which associations with Pb
biomarkers have been observed in these populations (e.g., ISA, section
1.9.6).\31\ Thus, our confidence is greatest in the role of early
childhood exposure in contributing to Pb-related neurocognitive effects
that have been associated with blood Pb levels in young children. This
is due, in part, to the relatively short exposure histories of young
children (ISA, sections 1.9.4, 1.9.6 and 4.3.11).
---------------------------------------------------------------------------
\30\ The declines in Pb exposure concentrations occurring from
the 1970s through the early 1990s (and experienced by middle aged
and older adults of today), as indicated by NHANES blood Pb
information, were particularly dramatic (ISA, section 3.4.1).
\31\ The evidence from experimental animal studies can be
informative with regard to key aspects of exposure circumstances in
eliciting specific effects, thus informing our interpretation of
epidemiological evidence. For example, the animal evidence base with
regard to Pb effects on blood pressure demonstrates the
etiologically-relevant role of long-term exposure (ISA, section
4.4.1). This finding then informs consideration of epidemiological
studies of adult populations for whom historical exposures were
likely more substantial than concurrent ones, suggesting that the
observed effects may be related to the past exposure (ISA, section
4.4.1). For other health effects, the animal evidence base may or
may not be informative in this manner.
---------------------------------------------------------------------------
Epidemiological analyses evaluating risk of neurocognitive impacts
(e.g., reduced IQ) associated with different blood Pb metrics in
cohorts with differing exposure patterns (including those for which
blood Pb levels at different ages were not highly correlated) also
indicate associations with blood Pb measurements concurrent with full
scale IQ (FSIQ) tests at ages of approximately 6-7 years. The analyses
did not, however, conclusively demonstrate stronger findings for early
(e.g., at age 2 years) or concurrent blood Pb levels (ISA, section
4.3.11).\32\ The experimental animal evidence additionally indicates
early life susceptibility (ISA, section 4.3.15 and p. 5-21). Thus,
while uncertainties remain with regard to the role of Pb exposures
during a particular age of life in eliciting nervous system effects,
such as cognitive function decrements, the full evidence base continues
to indicate prenatal and early childhood lifestages as periods of
increased Pb-related risk (ISA, sections 4.3.11 and 4.3.15). We
recognize increasing uncertainty, however, in our understanding of the
relative impact on neurocognitive function of additional Pb exposure of
children by school age or later that is associated with limitations of
the currently available evidence, including epidemiological cohorts
with generally similar temporal patterns of exposure.
---------------------------------------------------------------------------
\32\ In the collective body of evidence of nervous system
effects in children, it is difficult to distinguish exposure in
later lifestages (e.g., school age) and its associated risk from
risks resulting from exposure in prenatal and early childhood (ISA,
section 4.3.11). While early childhood is recognized as a time of
increased susceptibility, a difficulty in identifying a discrete
period of susceptibility from epidemiological studies has been that
the period of peak exposure, reflected in peak blood Pb levels, is
around 18-27 months when hand-to-mouth activity is at its maximum
(ISA, section 3.4.1 and 5.2.1.1; 2006 CD, p. 6-60). The task is
additionally complicated by the role of maternal exposure history in
contributing Pb to the developing fetus (ISA, section 3.2.2.4.).
---------------------------------------------------------------------------
In summary, as in the last review, we continue to recognize a
number of uncertainties regarding the circumstances of Pb exposure,
including timing or lifestages, eliciting specific health effects.
Consideration of the evidence newly available in this review has not
appreciably changed our understanding on this topic. The relationship
of long-term exposure to Pb with hypertension and increased blood
pressure in adults is substantiated despite some uncertainty regarding
the exposure circumstances contributing to blood Pb levels measured in
epidemiological studies. For example, the evidence does not indicate
the exposure magnitude and timing that are eliciting such effects.
Across the full evidence base, the effects for which our understanding
of relevant exposure circumstances is greatest are neurocognitive
effects in young children. Moreover, available evidence does not
suggest a more sensitive endpoint. Thus, we continue to recognize and
give particular attention to the role of Pb exposures relatively early
in childhood in contributing to neurocognitive effects, some of which
may persist into adulthood.
c. Nervous System Effects in Children
The evidence currently available with regard to the magnitude of
blood Pb levels associated with neurocognitive effects in children is
generally consistent with that available in the review completed in
2008. Nervous system effects in children, specifically effects on
cognitive function, continue to be the effects that are best
substantiated as occurring at the lowest blood Pb concentrations (ISA,
pp. lxxxvii-lxxxviii). Associations of blood Pb with effects on
cognitive function measures in children have been reported in many
studies across a range of childhood blood Pb levels, including study
group (mean/median) levels ranging down to 2 [micro]g/dL (e.g., ISA, p.
lxxxvii and section 4.3.2).\33\
---------------------------------------------------------------------------
\33\ The value of 2 [mu]g/dL refers to the regression analysis
of blood Pb and end-of-grade test scores, in which blood Pb was
represented by categories for integer values of blood Pb from 1
[mu]g/dL to 9 and >10 [mu]g/dL from large statewide database. A
significant effect estimate was reported for test scores with all
blood Pb categories in comparison to the reference category (1
[mu]g/dL), which included results at and below the limit of
detection. Mean levels are not provided for any of the categories
(Miranda et al., 2009).
---------------------------------------------------------------------------
Among the analyses of lowest study group blood Pb levels at the
youngest ages are analyses available in the last review of Pb
associations with neurocognitive function decrement in study groups
with mean levels on the order of 3-4 [mu]g/dL in children aged 24
months or ranging from 5 to 7 years (73 FR 66978-66979, November 12,
2008; ISA, sections 4.3.2.1 and 4.3.2.2; Bellinger and Needleman, 2003;
Canfield et al., 2003; Lanphear et al., 2005; Tellez-Rojo et al., 2006;
Bellinger, 2008; Canfield, 2008; Tellez-Rojo, 2008; Kirrane and Patel,
2014).\34\ Newly available in this review are two studies reporting
association of blood Pb levels prior to 3 years of age with academic
performance on standardized tests in primary school; mean blood Pb
levels in these studies were 4.2 and 4.8 [mu]g/dL (ISA, section
4.3.2.5; Chandramouli et al., 2009; Miranda et al., 2009). One of these
two studies, which represented integer blood Pb levels as categorical
variables, indicated a small effect on end-of-grade reading score of
blood Pb levels as low as 2 [mu]g/dL, after adjustment for age of
measurement, race, sex, enrollment in free or reduced lunch program,
parental education, and school type (Miranda et al., 2009).
---------------------------------------------------------------------------
\34\ The tests for cognitive function in these studies include
age-appropriate Wechsler intelligence tests (Lanphear et al., 2005;
Bellinger and Needleman, 2003), the Stanford-Binet intelligence test
(Canfield et al., 2003), and the Bayley Scales of Infant Development
(Tellez-Rojo et al., 2006). The Wechsler and Stanford-Binet tests
are widely used to assess neurocognitive function in children and
adults. These tests, however, are not appropriate for children under
age 3. For such children, studies generally use the age-appropriate
Bayley Scales of Infant Development as a measure of cognitive
development.
---------------------------------------------------------------------------
Newly available in this review are also several studies in older
children on neurocognitive effects and other nervous system effects. As
described in section II.B.3 of the proposal, however, these studies are
focused on population groups of ages for which the available
information indicates exposure levels were higher earlier in childhood.
Thus, in light of this information, although the blood Pb levels in the
studies in older child population groups are lower (at the time of the
study) than the younger child study levels, the studies of older
[[Page 71921]]
children do not provide a basis for concluding a role for lower Pb
exposure levels than those experienced by the younger study groups.
Rather, this information makes these studies relatively uninformative
with regard to evidence of effects associated with lower exposure
levels than provided by evidence previously available.
Recognizing the complexity associated with interpretation of
studies involving older cohorts,\35\ as well as the potential role of
higher exposure levels in the past, we continue to focus our
consideration of this question on the evidence of effects in young
children for which our understanding of exposure history is less
uncertain.\36\ Within this evidence base, we recognize the lowest study
group blood Pb levels to be associated with effects on cognitive
function measures, indicating that to be the most sensitive endpoint.
As described above, the evidence available in this review is generally
consistent with that available in the last review with regard to blood
Pb levels at which such effects had been reported (ISA, section 4.3.2;
2006 CD, section 8.4.2.1; 73 FR 66976-66979, November 12, 2008). As
blood Pb levels are a reflection of exposure history, particularly in
early childhood (ISA, section 3.3.2), we conclude, by extension, that
the currently available evidence does not indicate Pb effects at
exposure levels appreciably lower than recognized in the last review.
---------------------------------------------------------------------------
\35\ Our conclusions regarding exposure levels at which Pb
health effects occur, particularly with regard to such levels that
might be common in the U.S. today, are complicated now, as in the
last review, by several factors. These factors include the scarcity
of information in epidemiological studies on cohort exposure
histories, as well as by the backdrop of higher past exposure levels
which frame the history of most, if not all, older study cohorts.
\36\ In focusing on effects associated with blood Pb levels in
early childhood, however, we additionally recognize the evidence
across categories of effects that relate to blood Pb levels in older
child study groups (for which early childhood exposure may have had
an influence) which provides additional support to an emphasis on
nervous system effects (ISA, sections 4.3, 4.4, 4.5, 4.6, 4.7, 4.8).
---------------------------------------------------------------------------
We additionally note that, as in the last review, a threshold blood
Pb level with which nervous system effects, and specifically cognitive
effects, occur in young children cannot be discerned from the currently
available studies (ISA, sections 1.9.3 and 4.3.12). Epidemiological
analyses have reported blood Pb associations with cognitive effects
(FSIQ or BSID MDI \37\) for young child population subgroups (age 5
years or younger) with individual blood Pb measurements as low as
approximately 1 [mu]g/dL and mean concentrations as low as 2.9 to 3.8
[mu]g/dL (ISA, section 4.3.12; Bellinger and Needleman, 2003;
Bellinger, 2008; Canfield el al., 2003; Canfield, 2008; Tellez-Rojo et
al., 2006; Tellez-Rojo, 2008). As concluded in the ISA, however, ``the
current evidence does not preclude the possibility of a threshold for
neurodevelopmental effects in children existing with lower blood levels
than those currently examined'' (ISA, p. 4-274).
---------------------------------------------------------------------------
\37\ The Bayley Scales of Infant Development, Mental Development
Index (BSID MDI) is a well-standardized and widely used assessment
measure of infant cognitive development. Scores earlier than 24
months are not necessarily strongly correlated with later FSIQ
scores in children with normal development (ISA, section 4.3.15.1).
---------------------------------------------------------------------------
Important uncertainties associated with the evidence of effects at
low exposure levels are similar to those recognized in the last review,
including the shape of the concentration-response relationship for
effects on neurocognitive function at low blood Pb levels in today's
young children. Also of note is our interpretation of associations
between blood Pb levels and effects in epidemiological studies, with
which we recognize uncertainty with regard to the specific exposure
circumstances (timing, duration, magnitude and frequency) that have
elicited the observed effects, as well as uncertainties in relating
ambient air concentrations (and associated air-related exposures) to
blood Pb levels in early childhood, as recognized in section II.A.2.b
above. We additionally recognize uncertainties associated with
conclusions drawn with regard to the nature of the epidemiological
associations with blood Pb (e.g., ISA, section 4.3.13) but note that,
based on consideration of the full body of evidence for neurocognitive
effects, the EPA has determined a causal relationship to exist between
relevant blood Pb levels and neurocognitive impacts in children (ISA,
section 4.3.15.1).
Based primarily on studies of FSIQ, the assessment of the currently
available studies, as was the case in the last review, continues to
recognize a nonlinear relationship between blood Pb levels and effects
on cognitive function, with a greater incremental effect (greater
slope) at lower relative to higher blood Pb levels within the range
thus far studied, extending from well above 10 [mu]g/dL to below 5
[mu]g/dL (ISA, section 4.3.12). This was supported by the evidence
available in the last review, including the analysis of the large
pooled international dataset comprised of blood Pb measurements and IQ
test results from seven prospective cohorts (Lanphear et al., 2005;
Rothenberg and Rothenberg, 2005; ISA, section 4.3.12). The blood Pb
measurements in this pooled dataset that were concurrent with the IQ
tests ranged from 2.5 [mu]g/dL to 33.2 [mu]g/dL.
The study by Lanphear et al. (2005) additionally presented analyses
that stratified the dataset based on peak blood Pb levels (e.g., with
cutpoints of 7.5 [mu]g/dL and 10 [mu]g/dL peak blood Pb) and found that
the coefficients from linear models of the association for IQ with
concurrent blood Pb levels were higher in the lower peak blood Pb level
subsets than the higher groups (ISA, section 4.3.12; Lanphear et al.,
2005).\38\ In other publications, stratified analyses of several
individual cohorts also observed higher coefficients for blood Pb
relationships with measures of neurocognitive function in lower as
compared to higher blood Pb subgroups (ISA, section 4.3.12; Canfield et
al., 2003; Bellinger and Needleman, 2003; Kordas et al., 2006; Tellez-
Rojo et al., 2006). Of these subgroup analyses, those involving the
lowest mean blood Pb levels and closest to the current mean for U.S.
preschool children are listed in Table 1 of the proposal (drawn from
Table 3 of the 2008 preamble to the final rule [73 FR 67003, November
12, 2008], and Kirrane and Patel, 2014).\39\ These analyses were
important inputs for the air-related IQ loss evidence-based framework
which informed decisions on a revised standard in the last review (73
FR 67005, November 12, 2008), discussed in section II.A.1 above.
Specifically, the framework focused on the median of the four average
linear slope estimates from the studies recognized in Table 3 of the
2008 decision (73 FR 67003, November 12, 2008). As shown in Table 1 of
the proposal, the median is unchanged by
[[Page 71922]]
consideration of the information newly available in this review.\40\
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\38\ As described in the PA and noted in the proposal, since the
completion of the ISA, two errors have been identified with the
pooled dataset analyzed by Lanphear et al. (2005) (Kirrane and
Patel, 2014). A recent publication and the EPA have separately
recalculated the statistics and mathematical model parameters of
Lanphear et al. (2005) using the corrected pooled dataset (see
Kirrane and Patel, 2014). While the magnitude of the loglinear and
linear regression coefficients are modified slightly based on the
corrections, the conclusions drawn from these coefficients,
including the finding of a steeper slope at lower (as compared to
higher) blood Pb concentrations, are not affected (Kirrane and
Patel, 2014).
\39\ One of these four subgroup analyses is the analysis of the
lowest blood Pb subset of the pooled international study by Lanphear
et al. (2005). The nonlinear model developed from the full pooled
dataset is the basis of the C-R functions used in the 2007 REA, in
which risk was estimated over a large range of blood Pb levels (PA,
section 3.4.3.3). Given the narrower focus of the evidence-based
framework on IQ response at the end of studied blood Pb levels
(closer to U.S. mean level), the C-R functions in Table 1 are from
linear analyses (each from separate publications) for the study
group subsets with blood Pb levels closest to mean for children in
the U.S. today.
\40\ As the framework focused on the median of the four slopes
in Table 1, the change to the one from Lanphear et al. (2005) based
on the recalculation described above has no impact on conclusions
drawn from the framework.
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Several studies newly available in the current review have, in all
but one instance, also found a nonlinear blood Pb-cognitive function
relationship in nonparametric regression analyses of the cohort blood
Pb levels analyzed (ISA, section 4.3.12). These studies, however, used
statistical approaches that did not produce quantitative results for
each blood Pb group (ISA, section 4.3.12). Thus, newly available
studies have not extended the range of observation for quantitative
estimates of this relationship to lower blood Pb levels than those of
the previous review. The ISA further notes that the potential for
nonlinearity has not been examined in detail within a lower, narrower
range of blood Pb levels than those of the full cohorts thus far
studied in the currently available evidence base (ISA, section 4.3.12).
Such an observation in the last review supported the consideration of
linear slopes with regard to blood Pb levels at and below those
represented in Table 1 of the proposal. In summary, the newly available
evidence does not substantively alter our understanding of the C-R
relationship (including quantitative aspects) for neurocognitive
impact, such as IQ, with blood Pb in young children.
d. At-Risk Populations
In this section, as elsewhere, we use the term ``at-risk
populations'' \41\ to recognize populations that have a greater
likelihood of experiencing Pb-related health effects, i.e., groups with
characteristics that contribute to an increased risk of Pb-related
health effects. These populations are also referred to as sensitive
groups (as in section I.A above). In identifying factors that increase
risk of Pb-related health effects, we have considered evidence
regarding factors contributing to increased susceptibility, generally
including physiological or intrinsic factors contributing to a greater
response for the same exposure and those contributing to increased
exposure, including that resulting from behavior leading to increased
contact with contaminated media (ISA, Chapter 5). Physiological risk
factors include both conditions contributing to a group's increased
risk of effects at a given blood Pb level and those that contribute to
blood Pb levels higher than those otherwise associated with a given Pb
exposure (e.g., ISA, sections 5.3 and 5.1, respectively).
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\41\ In the context of ``at-risk populations,'' the term
``population'' refers to persons having one or more qualities or
characteristics including, for example, a specific pre-existing
illness or a specific age or lifestage, with lifestage referring to
a distinguishable time frame in an individual's life characterized
by unique and relatively stable behavioral and/or physiological
characteristics that are associated with development and growth.
---------------------------------------------------------------------------
In considering factors that increase risk by contributing to
increased exposure or to increased blood Pb levels over those otherwise
associated with a given Pb exposure, we note that the currently
available evidence continues to support a nonlinear relationship
between neurocognitive effects and blood Pb that indicates
incrementally greater impacts at lower as compared to higher blood Pb
levels (ISA, section 4.3.12), as described in section II.B.3 of the
proposal and briefly noted in section II.A.2.c above. An important
implication of this finding is that while children with higher blood Pb
levels are at greater risk of Pb-related effects than children with
lower blood Pb levels, on an incremental basis (e.g., per [mu]g/dL) the
risk is greater for children at lower blood Pb levels. This was given
particular attention in the last review of the Pb NAAQS, in which the
standard was revised with consideration of the incremental impact of
air-related Pb on young children in the U.S. and the recognition of
greater incremental impact for those children with lower absolute blood
Pb levels (73 FR 67002, November 12, 2008). Such consideration included
a focus on those C-R studies involving the lowest blood Pb levels, as
described in section II.A.1 above.
The information newly available in this review has not appreciably
altered our previous understanding of at-risk populations for Pb in
ambient air. As in the last review, the factor most prominently
recognized to contribute to increased risk of Pb effects is childhood
(ISA, section 1.9.6). As discussed in section II.B.2 of the proposal
and briefly noted in section II.A.2.b above, while uncertainties remain
with regard to the role of Pb exposures during a particular age of life
in eliciting nervous system effects, such as cognitive function
decrements, the full evidence base continues to indicate prenatal and
early childhood lifestages as periods of increased Pb-related risk
(ISA, sections 4.3.11 and 4.3.15). Thus, in the current review, as at
the time of the last review of the Pb NAAQS, we recognize young
children as an important at-risk population, with sensitivity extending
to prenatal exposures and into childhood development.
An additional physiological risk factor that contributes to
increased blood Pb levels is nutritional status, which can play a role
in Pb absorption from the gastrointestinal tract, with iron-, calcium-
and zinc-deficient diets contributing to increased Pb absorption and
associated blood Pb levels (ISA, sections 3.2.1.2, 5.1, 5.3.10 and
5.4). Risk factors based on increased exposure include spending time in
proximity to sources of Pb to ambient air or other environmental media,
such as large active metals industries or locations of historical Pb
contamination (ISA, sections 1.9.6, 3.7.1, 5.2.5 and 5.4). Residential
factors associated with other sources of Pb exposure (e.g., leaded
paint or plumbing with Pb pipes or solder) are another exposure-related
risk factor (ISA, sections 3.7.1, 5.2.6 and 5.4). Additionally, some
races or ethnicities have been associated with higher blood Pb levels,
with differential exposure indicated in some cases as the cause (ISA,
sections 5.2.3 and 5.4).
Lower socioeconomic status (SES) has been associated with higher Pb
exposure and higher blood Pb concentration in some study groups,
leading the ISA to conclude the evidence is suggestive for low SES as a
risk factor (ISA, sections 5.3.16, 5.2.4 and 5.4).\42\ Although the
differences in blood Pb levels, nationally, between children of lower
and higher income levels (as well as among some races or ethnicities)
have lessened, blood Pb levels continue to be higher among lower-income
children indicating higher exposure and/or greater influence of factors
independent of exposure, such as nutritional factors (ISA, sections
1.9.6, 5.2.1.1 and 5.4).\43\ The evidence is also suggestive of
increased risk associated with several other factors: older
adulthood,\44\ pre-
[[Page 71923]]
existing disease (e.g., hypertension), variants for certain genes and
increased stress (ISA, section 5.3.4).
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\42\ The approach used by the EPA in evaluating the evidence
regarding factors that may influence the risk of Pb-related health
effects is described in chapter 5 of the ISA.
\43\ Although the evidence for SES continues to indicate
increased blood Pb levels in lower income children, its role with
regard to an increased health risk for the same blood Pb level is
unclear and its role generally with regard to Pb-related risk is
somewhat complicated. SES often serves as a marker term for one or a
combination of unspecified or unknown environmental or behavioral
variables. Further, it is independently associated with an adverse
impact on neurocognitive development, and a few studies have
examined SES as a potential modifier of the association of childhood
Pb exposure with cognitive function with inconsistent findings
regarding low SES as a potential risk factor.
\44\ The ISA identifies older adulthood as a lifestage of
potentially greater risk of Pb-related health effects based
primarily on the evidence of increases in blood Pb levels during
this lifestage (ISA, sections 5.2.1.2, 5.3.1.2, and 5.4), as well as
observed associations of some cardiovascular and nervous system
effects with bone and blood Pb in older populations, with biological
plausibility for the role of Pb provided by experimental animal
studies (ISA, sections 4.3.5, 4.3.7 and 4.4). Exposure histories of
older adult study populations, which included younger years during
the time of leaded gasoline usage and other sources of Pb exposures
which were more prevalent in the past than today, are likely
contributors to their blood Pb levels (ISA, pp. lx-lxi; Figure 2-1
and sections 2.5.2, 3.3.5 and 5.2.1.2).
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In summary, we recognize the sensitivity of the prenatal period and
several stages of childhood to an array of neurocognitive and
behavioral effects, and we particularly recognize young children as an
important at-risk population in light of current environmental exposure
levels. Age or lifestage was used to distinguish potential groups on
which to focus in the last review in recognition of its role in
exposure and susceptibility, and young children were the focus of the
REA in consideration of the health effects evidence regarding endpoints
of greatest public health concern and in recognition of effects on the
developing nervous system as a sentinel endpoint for public health
impacts of Pb. This identification continues to be supported by the
evidence available in the current review.
e. Potential Impacts on Public Health
There are several potential public health impacts associated with
Pb exposure in the current U.S. population. In recognition of effects
causally related to blood Pb levels somewhat near those most recently
reported for today's population and for which the weight of the
evidence is greatest, the potential public health impacts most
prominently recognized in the ISA are population IQ impacts associated
with childhood Pb exposure and prevalence of cardiovascular effects in
adults (ISA, section 1.9.1). With regard to the latter category, as
discussed above, the full body of evidence indicates a role of long-
term cumulative exposure, with uncertainty regarding the specific
exposure circumstances contributing to the effects in the
epidemiological studies of adult populations, for whom historical Pb
exposures were likely much higher than exposures that commonly occur
today (ISA, section 4.4). There is less uncertainty regarding the
exposure patterns contributing to the blood Pb levels reported in
studies of younger populations (ISA, sections 1.9.4 and 1.10).
Accordingly, the discussion of public health implications relevant to
this review is focused predominantly on nervous system effects,
including IQ decrements, in children.
The magnitude of a public health impact is dependent upon the type
or severity of the effect, as well as the size of populations affected.
Intelligence quotient is a well-established, widely recognized and
rigorously standardized measure of neurocognitive function, as well as
a global measure reflecting the integration of numerous processes (ISA,
section 4.3.2; 2006 CD, sections 6.2.2 and 8.4.2). In considering
population risk, the distribution of effects across members of the
population is important. For example, if Pb-related decrements are
manifested uniformly across the range of IQ scores in a population, ``a
small shift in the population mean IQ may be significant from a public
health perspective because such a shift could yield a larger proportion
of individuals functioning in the low range of the IQ distribution,
which is associated with increased risk of educational, vocational, and
social failure'' as well as a decrease in the proportion with high IQ
scores (ISA, section 1.9.1). Examples of other measures of cognitive
function negatively associated with Pb exposure include other measures
of intelligence and cognitive development and measures of other
cognitive abilities, such as learning, memory, and executive functions,
as well as academic performance and achievement (ISA, section 4.3.2).
Although some neurocognitive effects of Pb in children may be
transient, some may persist into adulthood (ISA, section 1.9.5).\45\ We
also note that deficits in neurodevelopment early in life may have
lifetime consequences as ``[n]eurodevelopmental deficits measured in
childhood may set affected children on trajectories more prone toward
lower educational attainment and financial well-being'' (ISA, section
4.3.14). Thus, population groups for which neurodevelopment is affected
by Pb exposure in early childhood are at risk of related impacts on
their success later in life.
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\45\ The ISA states that the ``persistence of effects appears to
depend on the duration and window of exposure as well as other
factors that may affect an individual's ability to recover from an
insult,'' with some evidence of greater recovery in children reared
in households with more optimal caregiving characteristics and low
concurrent blood Pb levels (ISA, p. 1-77; Bellinger et al., 1990).
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As indicated above, young children are the at-risk population that
may be most at risk of health effects associated with exposure to Pb,
and children at greatest risk from air-related Pb are those children
with highest air-related Pb exposure, which we consider to be those
living in areas of higher ambient air Pb concentrations (e.g.,
concentrations near or above the current standard). Analyses in the PA
indicate this group to be a very small subset of all young children in
the U.S. Together the analyses indicate that well below one-tenth of
one percent of the full population of children aged 5 years or younger
in the U.S. today live in areas with air Pb concentrations near or
above the current standard, with the current monitoring data indicating
the size of this population to be approximately one-hundredth of a
percent of the full population of children aged 5 or younger (PA, pp.
3-36 to 3-38, 4-25, 4-32). It is these children that were the
Administrator's focus in revising the primary standard in 2008.
3. Overview of Information on Blood Lead Relationships With Air Lead
This section provides a brief overview of the information
summarized in section II.C of the proposal on key aspects of the
information available in this review on blood Pb as a biomarker and on
relationships of blood Pb with air Pb (80 FR 298-300, January 5, 2015).
Blood Pb is well established as a biomarker of Pb exposure and of
internal dose, with relationships between air Pb concentrations and
blood Pb concentrations informing consideration of the NAAQS for Pb
since its initial establishment in 1978. The blood Pb concentration in
childhood (particularly early childhood) can more quickly (than in
adulthood) reflect changes in total body burden (associated with the
shorter exposure history) and can also reflect changes in recent
exposures (ISA, section 3.3.5). The relationship of children's blood Pb
to recent exposure may reflect their labile bone pool, with their rapid
bone turnover in response to rapid childhood growth rates (ISA, section
3.3.5). The relatively smaller skeletal compartment of Pb in children
(particularly very young children) compared to adults is subject to
more rapid turnover. Multiple studies have demonstrated young
children's blood Pb levels to reflect Pb exposures, including exposures
to Pb in surface dust (e.g., Lanphear and Roghmann, 1997; Lanphear et
al., 1998). These and studies of child populations near sources of air
Pb emissions, such as metal smelters, have further demonstrated the
effect of airborne Pb on interior dust and on blood Pb (ISA, sections
3.4.1, 3.5.1 and 3.5.3; Hilts, 2003; Gulson et al., 2004).
As blood Pb is an integrated marker of aggregate Pb exposure across
all pathways, the blood Pb C-R relationships described in
epidemiological studies of Pb-exposed populations do not distinguish
among different sources of Pb or pathways of
[[Page 71924]]
Pb exposure (e.g., inhalation, ingestion of indoor dust, ingestion of
dust containing leaded paint). Thus, our interpretation of the health
effects evidence for purposes of this review necessitates
characterization of the relationships between Pb from those sources and
pathways of interest in this review (i.e., those related to Pb emitted
into the air) and blood Pb.
The evidence for air-to-blood relationships derives from analyses
of datasets for populations residing in areas with differing air Pb
concentrations, including datasets for circumstances in which blood Pb
levels have changed in response to changes in air Pb. The control for
variables other than air Pb that can affect blood Pb varies across
these analyses. At the conclusion of the last review in 2008, the EPA
interpreted the evidence as providing support for use (in informing the
Administrator's decision on standard level) of a range of air-to-blood
ratios \46\ ``inclusive at the upper end of estimates on the order of
1:10 and at the lower end on the order of 1:5'' (73 FR 67002, November
12, 2008). This conclusion reflected consideration of the air-to-blood
ratios presented in the 1986 CD \47\ and associated observations
regarding factors contributing to variation in such ratios, ratios
reported subsequently and ratios estimated based on modeling performed
in the REA, as well as advice from CASAC (73 FR 66973-66975, 67001-
67002, November 12, 2008). The information available in this review,
which is assessed in the ISA and largely, although not completely,
comprises studies that were available in the last review, does not
alter the primary scientific conclusions drawn in the last review
regarding the relationships between Pb in ambient air and Pb in
children's blood. The ratios summarized in the ISA in this review span
a range generally consistent with the range concluded in 2008 (ISA,
section 3.5.1).
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\46\ The quantitative relationship between ambient air Pb and
blood Pb, often termed a slope or ratio, describes the increase in
blood Pb (in [mu]g/dL) estimated to be associated with each unit
increase of air Pb (in [mu]g/m\3\). Ratios are presented in the form
of 1:x, with the 1 representing air Pb (in [mu]g/m\3\) and x
representing blood Pb (in [mu]g/dL). Description of ratios as higher
or lower refers to the values for x (i.e., the change in blood Pb
per unit of air Pb). Slopes are presented as simply the value of x.
\47\ The 2006 CD did not include an assessment of then-current
evidence on air-to-blood ratios.
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The evidence on the quantitative relationship between air Pb and
air-related Pb in blood is now, as in the past, limited by the
circumstances (such as those related to Pb exposure) in which the data
were collected. Previous reviews have recognized the significant
variability in air-to-blood ratios for different populations exposed to
Pb through different air-related exposure pathways and at different air
and blood levels, with the 1986 CD noting that ratios derived from
studies involving the higher blood and air Pb levels pertaining to
occupationally exposed workers are generally smaller than ratios from
studies involving lower blood and air Pb levels (ISA, p. 3-132; 1986
CD, p. 11-99). Consistent with this observation, slopes in the range of
3 to 5 were estimated for child population datasets assessed in the
1986 CD (ISA, p. 3-132; 1986 CD p. 11-100; Brunekreef, 1984).
Additional studies considered in the last review and those assessed in
the ISA provide evidence of ratios above this older range (ISA, p. 3-
133). For example, a ratio of 1:6.5 to 1:7 is indicated by the study by
Hilts (2003), one of the few studies that evaluate the air Pb-blood Pb
relationship in conditions that are closer to the current state in the
U.S. (ISA, p. 3-132). We additionally note the variety of factors
identified in the ISA that may potentially affect estimates of various
ratios (including potentially coincident reductions in nonair Pb
sources during the course of the studies) and for which a lack of
complete information may preclude any adjustment of estimates to
account for their role (ISA, section 3.5).
In summary, as at the time of the last review of the NAAQS for Pb,
the currently available evidence includes estimates of air-to-blood
ratios, both empirical and model-derived, with associated limitations
and related uncertainties. These limitations and uncertainties, which
are summarized here and also noted in the ISA, usually include
uncertainty associated with reductions in other Pb sources during the
study period. The limited amount of new information available in this
review has not appreciably altered the scientific conclusions reached
in the last review regarding relationships between Pb in ambient air
and Pb in children's blood or with regard to the range of ratios. The
currently available evidence continues to indicate ratios relevant to
the population of young children in the U.S. today, reflecting multiple
air-related pathways in addition to inhalation, to be generally
consistent with the approximate range of 1:5 to 1:10 given particular
attention in the 2008 NAAQS decision, including the ``generally central
estimate'' of 1:7 (73 FR 67002, 67004, November 12, 2008; ISA, pp. 3-
132 to 3-133).
4. Overview of Risk and Exposure Assessment Information
This section provides a brief overview of key aspects of the risk
and exposure assessment information available in this review, which is
based primarily on the exposure and risk assessment developed in the
last review of the Pb NAAQS.\48\ This overview is drawn from the
summary presented in the proposal (80 FR 300-305, January 5, 2015). As
described in the REA Planning Document, careful consideration of the
information newly available in this review, with regard to designing
and implementing a full REA for this review, led to the conclusion that
performance of a new REA for this review was not warranted. We did not
find the information newly available in this review to provide the
means by which to develop an updated or enhanced risk model that would
substantially improve the utility of risk estimates in informing the
current Pb NAAQS review (REA Planning Document, section 2.3). Based on
its consideration of the REA Planning Document analysis, the CASAC Pb
Review Panel generally concurred with the conclusion that a new REA was
not warranted in this review (Frey, 2011b).\49\ Accordingly, the
exposure/risk information considered in this review is drawn primarily
from the 2007 REA, augmented by a limited new computation for one case
study focused on risk associated with the current standard, as
described in section II.D of the proposal and in section 3.4 and
Appendix 3A of the PA.
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\48\ The information in this review is based on the assessment
from the last review, described in the 2007 REA, the 2007 Staff
Paper and the 2008 notice of final decision (USEPA, 2007a; USEPA,
2007b; 73 FR 66964, November 12, 2008), as considered in the context
of the evidence newly available in this review (PA, section 3.4;
proposal, section II.D).
\49\ In its review of the draft PA, the CASAC Pb Review Panel
reinforced its concurrence with the EPA's decision not to develop a
new REA (Frey, 2013).
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The focus for the risk assessment and associated estimates is on Pb
derived from sources emitting Pb to ambient air. In order to
characterize exposure and risk from these pathways, however, the
assessment also recognized the role of Pb exposure pathways unrelated
to Pb in ambient air (2007 REA, section 2.1). Sources of human Pb
exposure include current and historical air emissions sources, as well
as miscellaneous nonair sources, which can contribute to multiple
exposure media and associated pathways, such as inhalation of ambient
air, ingestion of indoor dust, outdoor soil/dust and diet or drinking
water (as recognized in section I.D above). In addition to airborne
emissions (recent or
[[Page 71925]]
those in the past), sources of Pb to these pathways also include old
leaded paint, including Pb mobilized indoors during renovation/repair
activities, and contaminated soils. Lead in diet and drinking water may
have air pathway-related contributions as well as contributions from
nonair sources (e.g., Pb solder on older water distribution pipes and
Pb in materials used in food processing).
Limitations in our data and modeling tools handicapped our ability
to address the various complexities associated with exposure to ambient
air Pb and to fully separate the nonair contributions to Pb exposure
from estimates of air-related Pb exposure and risk. As a result, the
assessment included a number of simplifying assumptions in a number of
areas, and the estimates of air-related Pb risk produced are
approximate, characterized by bounds within which air-related Pb risk
is estimated to fall. The lower bound is based on a combination of
pathway-specific estimates that do not completely represent all air-
related pathways, while the upper bound is based on a combination of
pathway-specific estimates that includes pathways that are not air-
related but the separating out of which is precluded by modeling and
data limitations (PA, section 3.4).
Key aspects of the 2007 REA, such as the exposure populations,
exposure or dose metric, health effects endpoint and risk metric were
based on consideration of the then-currently available evidence as
assessed in detail in the 2006 CD. As discussed in the REA Planning
Document (USEPA, 2011b), these selections continue to be supported by
the evidence now available in this review as described in the ISA. The
REA focused on risk to the central nervous system in childhood as the
most sensitive effect that could be quantitatively assessed, with
decrement in IQ used as the risk metric. Exposure and biokinetic
modeling was used to estimate blood Pb concentrations in children
exposed to Pb up to age 7 years.\50\ This focus reflected the evidence
for young children with regard to air-related exposure pathways and
susceptibility to Pb health impacts (e.g., ISA, sections 3.1.1, 4.3,
5.2.1.1, 5.3.1.1, and 5.4). For example, the hand-to-mouth activity of
young children contributes to their Pb exposure (i.e., incidental soil
and indoor dust ingestion), and ambient air-related Pb has been shown
to contribute to Pb in outdoor soil and indoor house dust (ISA,
sections 3.1.1 and 3.4.1; 2006 CD, section 3.2.3).
---------------------------------------------------------------------------
\50\ The pathways represented in this modeling included
childhood inhalation and ingestion pathways, as well as maternal
contributions to newborn body burden (2007 REA, Appendix H, Exhibit
H-6).
---------------------------------------------------------------------------
The 2007 REA relied on a case study approach to provide estimates
that inform our understanding of air-related exposure and risk in
different types of air Pb exposure situations. Lead exposure and
associated risk were estimated for multiple case studies that generally
represent two types of residential population exposures to air-related
Pb: (1) Location-specific urban populations of children with a broad
range of air-related exposures, reflecting existence of urban
concentration gradients; and (2) children residing in localized areas
with air-related exposures representing air concentrations specifically
reflecting the standard level being evaluated (see PA, Table 3-6).
Thus, the two types of case studies differed with regard to the extent
to which they represented population variability in air-related Pb
exposure.
In drawing on the 2007 REA for our purposes in this review, we
focused on two case studies, one from each of these two categories: (1)
The location-specific urban case study for Chicago and (2) the
generalized (local) urban case study (PA, Table 3-6). The generalized
(local) urban case study (also referred to as general urban case study)
was not based on a specific geographic location and reflected several
simplifying assumptions in representing exposure including uniform
ambient air Pb levels associated with the standard of interest across
the hypothetical study area and a uniform study population. Based on
the nature of the population exposures represented by the two
categories of case study, the generalized (local) urban case study
includes populations that are relatively more highly exposed by way of
air pathways to air Pb concentrations near the standard level
evaluated, compared with the populations in the location-specific urban
case. The location-specific urban case studies provided representations
of urban populations with a broad range of air-related exposures due to
spatial gradients in both ambient air Pb levels and population density.
For example, the highest air concentrations in these case studies
(i.e., those closest to the standard being assessed) were found in very
small parts of the study areas, while a large majority of the case
study populations resided in areas with much lower air concentrations.
Air-related risk estimates for the two case studies are accompanied
by a number of uncertainties (summarized in section II.D.3 of the
proposal and described in detail in section 3.4 of the PA). Exposure
and risk modeling conducted for this analysis was complex and subject
to significant uncertainties due to limitations in the data and models,
among other aspects, as recognized at the time of the last review.\51\
The multimedia and persistent nature of Pb, the role of multiple
exposure pathways, and the contributions of nonair sources of Pb to
human exposure media all present challenges and contribute significant
additional complexity to the health risk assessment that goes far
beyond the situation for similar assessments typically performed for
other NAAQS pollutants (e.g., that focus only on the inhalation
pathway). Of particular note among the assessment limitations are
limitations in the assessment design, data and modeling tools that
handicapped us from sharply separating Pb linked to ambient air from Pb
that is not air related. The resultant, approximate, air-related risk
bounds, however, encompass estimates drawn from the air-related IQ loss
evidence-based framework, providing a rough consistency and general
support, as was the case in the last review (73 FR 67004, November 12,
2008).
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\51\ As summarized in section II.D.3 of the proposal, a range of
limitations and areas of uncertainty were associated with the
information available in the last review (PA, sections 3.4.4, 3.4.6
and 3.4.7), and the newly available information in this review did
not substantially reduce any of the primary sources of uncertainty
identified to have the greatest impact on risk estimates (USEPA,
2011b). Thus, the key observations regarding air-related Pb risk
modeled for the set of standard levels assessed in the 2007 REA, as
well as the risk estimates interpolated for the current standard,
are not significantly affected by the new information. Nor is our
overall characterization of uncertainty and variability associated
with those estimates (as summarized above and in sections 3.4.6 and
3.4.7 of the PA).
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B. Conclusions on the Primary Standard
In drawing conclusions on the adequacy of the current primary Pb
standard, in view of the advances in scientific knowledge and
additional information now available, the Administrator considers the
evidence base, information and policy judgments that were the
foundation of the last review and reflects upon the body of evidence
and information newly available in this review. The Administrator has
taken into account both evidence-based and exposure- and risk-based
considerations, advice from CASAC and public comment. Evidence-based
considerations draw upon the EPA's assessment and integrated synthesis
of the scientific evidence from epidemiological studies and
experimental animal studies evaluating health effects related to
exposures to Pb,
[[Page 71926]]
with a focus on policy-relevant considerations as discussed in the PA.
The exposure- and risk-based considerations draw from the results of
the quantitative analyses presented in the 2007 REA (augmented as
described in the PA and summarized in section II.D of the proposal) and
consideration of those results in the PA.
As described in section II.A.2 of the proposal, consideration of
the evidence and exposure/risk information in the PA and by the
Administrator is framed by consideration of a series of key policy-
relevant questions. Section II.B.1 below summarizes the rationale for
the Administrator's proposed decision, drawing from section II.E.4 of
the proposal. A fuller presentation of PA considerations and
conclusions, and advice from the CASAC, which were taken into account
by the Administrator, is provided in sections II.E.1 through II.E.3 of
the proposal. Advice received from CASAC in this review is briefly
summarized in section II.B.2 below, and public comments on the proposed
decision are addressed in section II.B.3. The Administrator's
conclusions in this review regarding the adequacy of the current
primary standard are described in section II.B.4.
1. Basis for the Proposed Decision
At the time of the proposal, the Administrator carefully considered
the assessment of the current evidence and conclusions reached in the
ISA; the currently available exposure/risk information, including
associated limitations and uncertainties; considerations and staff
conclusions and associated rationales presented in the PA; the advice
and recommendations from CASAC; and public comments that had been
offered up to that point. In reaching her proposed conclusion on the
primary standard, the Administrator first took note of the PA
discussion with regard to the complexity and associated uncertainties
involved in considering the adequacy of protection in the case of the
primary Pb standard, which differs substantially from that involved in
consideration of the primary standard in other NAAQS reviews. For the
pollutants in the other reviews, the focus is on inhalation as the
single route of exposures, which provides a relatively simpler context
than the multiple exposure pathways that are relevant to Pb.
Additionally, an important component of the evidence base for most
other NAAQS pollutants is the availability of studies that have
investigated an association between concentrations of the pollutant in
ambient air and the occurrence of health effects plausibly related to
ambient air exposure to that pollutant. Such studies of associations
with air concentrations do not figure prominently in the review of the
NAAQS for Pb. Rather, the evidence base in this review includes most
prominently epidemiological studies focused on associations of blood Pb
levels in U.S. populations with health effects plausibly related to Pb
exposures occurring by multiple pathways. Support for conclusions
regarding the plausibility for ambient air Pb to play a role in such
findings derives, in part, from studies linking Pb in ambient air with
the occurrence of health effects. However, such studies (dating from
the past or from other countries) involve ambient air Pb concentrations
many times greater than those that would meet the current standard.
Thus, in considering the adequacy of the current Pb standard, rather
than considering studies that have directly investigated current
concentrations of Pb in ambient air (including in locations where the
current standard is met) and the occurrence of health effects, we
primarily consider the evidence for, and risk estimated from, models
based upon key relationships, such as those among ambient air Pb, Pb
exposure, blood Pb and health effects. This evidence, with its
associated limitations and uncertainties, contributes to the EPA's
conclusions regarding a relationship between ambient air Pb conditions
under the current standard and health effects.
In considering the nature and magnitude of the array of
uncertainties that are inherent in the scientific evidence and
analyses, the Administrator recognized that the current understanding
of the relationships between the presence of a pollutant in ambient air
and associated health effects is based on a broad body of information
encompassing not only more established aspects of the evidence, but
also aspects in which there may be substantial uncertainty. In her
considerations for the proposal, she took into account both the well-
established body of evidence on the health effects of Pb, which
continues to support identification of neurocognitive effects in young
children as the most sensitive endpoint associated with Pb exposure,
and of the recognition in the PA, with which the CASAC concurred, of
increased uncertainty in characterizing the relationship of effects on
IQ with blood Pb levels below those represented in the evidence base
and also in projecting the magnitude of blood Pb response to ambient
air Pb concentrations at and below the level of the current standard.
In this light, she based her proposed decision on her consideration of
the current evidence within the conceptual and quantitative context of
the air-related IQ evidence-based loss framework; the available
information and advice from CASAC regarding the public health
significance of neurocognitive effects; and the limitations and
uncertainties inherent in the evidence and its consideration within
this framework. The Administrator additionally recognized support from
the exposure/risk information, with its attendant uncertainties.
In her consideration of the air-related IQ loss evidence-based
framework, the Administrator took note of the PA finding, with which
the CASAC concurred, that application of the air-related IQ loss
evidence-based framework, developed in the last review, continues to
provide a useful approach for considering and integrating the evidence
on relationships between Pb in ambient air and Pb in children's blood
and risks of neurocognitive effects (for which IQ loss is used as an
indicator). She additionally took note of the PA finding (described in
section II.E.1 of the proposal, and with which the CASAC concurred)
that the currently available evidence base, while somewhat expanded
since the last review, is not supportive of appreciably different
conclusions with regard to air-to-blood ratios or C-R functions for
neurocognitive decrements in young children.
In the Administrator's consideration of the level of public health
protection provided by the current standard, she gave weight to CASAC
advice in the last review (and similar views expressed in the last
review by public health experts, such as the American Academy of
Pediatrics), which recognized a population mean IQ loss of 1 to 2
points to be of public health significance and recommended that a very
high percentage of the population be protected from such a magnitude of
IQ loss (73 FR 67000, November 12, 2008). In so doing, she additionally
noted that the EPA is aware of no new information or new commonly
accepted guidelines or criteria within the public health community for
interpreting public health significance of neurocognitive effects in
the context of a decision on adequacy of the current Pb standard, and
CASAC provided no alternate advice in this area in the current review
(PA, pp. 4-33 to 4-34). Accordingly, with the objective identified in
the CASAC advice from the 2008 review in
[[Page 71927]]
mind, the Administrator considered the role of the air-related IQ loss
evidence-based framework in reviewing the level of protection provided
by the current standard. In so doing, the Administrator recognized
distinctions between estimates produced by the framework, for which the
conceptual context is a subset of U.S. children, and specific
quantitative public health policy goals for air-related IQ loss for the
entire U.S. population of children. She additionally took note of the
PA conclusion on the size of the population subset that might pertain
to the situation represented by the framework (areas with elevated air
Pb concentrations equal to the standard level), as well as
uncertainties associated with the framework estimates, particularly at
successively lower standard levels. In summary, the Administrator
concluded in the proposal that the current evidence, as considered
within the conceptual and quantitative context of the evidence-based
framework, and current air monitoring information indicate that the
current standard provides protection for young children from
neurocognitive impacts, including IQ loss, consistent with advice from
CASAC regarding IQ loss of public health significance.
The Administrator based her proposed conclusions on consideration
of the health effects evidence, including consideration of this
evidence in the context of the air-related IQ loss evidence-based
framework, and with support from the exposure/risk information,
recognizing the uncertainties attendant with both. In so doing, she
took note of the PA description of the complexities and limitations in
the evidence base associated with reaching conclusions regarding the
magnitude of risk associated with the current standard, as well as the
increasing uncertainty of risk estimates for lower air Pb
concentrations. Inherent in the Administrator's proposed conclusions
are public health policy judgments on the public health implications of
the blood Pb levels and risk estimated for air-related Pb under the
current standard, including the public health significance of the Pb
effects being considered, as well as aspects of the use of the
evidence-based framework that may be considered to contribute to the
margin of safety. These public health policy judgments include
judgments related to the appropriate degree of public health protection
that should be afforded to protect against risk of neurocognitive
effects in at-risk populations, such as IQ loss in young children, as
well as with regard to the appropriate weight to be given to differing
aspects of the evidence and the exposure/risk information, and how to
consider their associated uncertainties. Based on these considerations
and the judgments summarized here, the Administrator proposed to
conclude that the current standard provides the requisite protection of
public health with an adequate margin of safety, including protection
of at-risk populations, such as young children living near Pb emissions
sources where ambient concentrations just meet the standard.
The Administrator's proposed conclusion that the current standard
provides the requisite protection and that a more restrictive standard
would not be requisite additionally recognized that the uncertainties
and limitations associated with many aspects of the estimated
relationship between air Pb concentrations and blood Pb levels and
associated health effects are amplified with consideration of
increasingly lower air concentrations. In reaching her proposed
conclusion, she took note of the PA conclusion, with which CASAC has
agreed, that based on the current evidence, there is appreciable
uncertainty associated with drawing conclusions regarding whether there
would be reductions in blood Pb levels and risk to public health from
alternative lower levels of the standard as compared to the level of
the current standard (PA, pp. 4-35 to 4-36; Frey, 2013b, p. 6). The
Administrator judged this uncertainty to be too great for the current
evidence and exposure/risk information to provide a basis for revising
the current standard. Thus, based on the public health policy judgments
described above, including the weight given to uncertainties in the
evidence, the Administrator proposed to conclude that the current
standard should be retained, without revision.
2. CASAC Advice in This Review
In comments on the draft PA, the CASAC concurred with staff's
overall preliminary conclusions that it is appropriate to consider
retaining the current primary standard without revision, stating that
``the current scientific literature does not support a revision to the
Primary Lead (Pb) National Ambient Air Quality Standard (NAAQS)''
(Frey, 2013b, p. 1). The CASAC further noted that ``[a]lthough the
current review incorporates a substantial body of new scientific
literature, the new literature does not justify a revision to the
standards'' (Frey, 2013b, p. 1).
The CASAC comments additionally indicated agreement with key
aspects of staff's consideration of the exposure/risk information and
currently available evidence in this review (Frey, 2013b, Consensus
Response to Charge Questions, p. 7).
The use of exposure/risk information from the previous Pb NAAQS
review appears appropriate given the absence of significant new
information that could fundamentally change the interpretation of
the exposure/risk information. This interpretation is reasonable
given that information supporting the current standard is largely
unchanged since the current standard was issued.
The CASAC agrees that the adverse impact of low levels of Pb
exposure on neurocognitive function and development in children
remains the most sensitive health endpoint, and that a primary Pb
NAAQS designed to protect against that effect will offer
satisfactory protection against the many other health impacts
associated with Pb exposure.
The CASAC concurs with the draft PA that the scientific findings
pertaining to air-to-blood Pb ratios and the C-R relationships
between blood Pb and childhood IQ decrements that formed the basis
of the current Pb NAAQS remain valid and are consistent with current
data.
The CASAC concurred with the appropriateness of the application of
the evidence-based framework from the last Pb NAAQS review. With regard
to the key inputs to that framework, the CASAC concluded that ``[t]he
new literature published since the previous review provides further
support for the health effect conclusions presented in that review''
and that the studies newly available in this review ``do not
fundamentally alter the uncertainties for air-to-blood ratios or C-R
functions for IQ decrements in young children'' (Frey, 2013b, Consensus
Response to Charge Questions, p. 6). The comments from the CASAC also
took note of the uncertainties that remain in this review which
contribute to the uncertainties associated with drawing conclusions
regarding air-related exposures and associated health risk at or below
the level of the current standard, stating agreement with ``the EPA
conclusion that `there is appreciable uncertainty associated with
drawing conclusions regarding whether there would be reductions in
blood Pb levels from alternative lower levels as compared to the level
of the current standard''' (Frey, 2013b, Consensus Response to Charge
Questions, p. 6).
3. Comments on the Proposed Decision
The majority of public comments on the proposal supported the
Administrator's proposed decision to retain the current primary
standard, without revision. This group includes the National
Association of Clean Air
[[Page 71928]]
Agencies (NACAA), both of the state agencies that submitted comments
and nearly all of the industry organizations that submitted comments.
All of these commenters generally noted their agreement with the
rationale provided in the proposal and noted the CASAC's concurrence
with the EPA conclusion that the current evidence does not support
revision to the standard. Most also cited the EPA and CASAC statements
that information newly available in this review has not substantially
altered our previous understanding of at-risk populations, C-R
relationships or effects from exposures lower than what was previously
examined and does not call into question the adequacy of the current
standard. Some commenters stated that multimedia or multipathway
aspects of Pb make the review of the primary standard for Pb subject to
greater uncertainty than reviews of primary NAAQS for other pollutants
and/or noted greater uncertainty with consideration of lower blood Pb
and standard levels. Some also noted that EPA's task in setting NAAQS
is not to reduce risk to zero but to identify a standard that is
neither more nor less stringent than necessary. The EPA generally
agrees with these commenters and with the CASAC regarding the adequacy
of the current primary standard and the lack of support for revision of
the standard.
Four submissions recommending revision of the standard were
received; all four advocated a tightening of the standard. These
commenters include two individuals, a secondary Pb smelting company,
and the Children's Health Protection Advisory Committee to the EPA
(CHPAC).\52\ In support of their view that the standard should be
revised, all four commenters generally stated that there is no safe
level of Pb exposure.\53\ The CHPAC submission, to which the smelting
company submission repeatedly cited, asserted that a lower standard is
needed to protect children from impacts related to neurodevelopmental
and low birthweight effects, stating that studies it cited that have
been published since the cut-off for the ISA indicate effects on
children's IQ at ``appreciably lower'' Pb exposures than those
recognized in the last review and raise concerns regarding cumulative
effects of multiple chemical exposures. These commenters additionally
cited the PA's presentation of the 2007 REA results that included lower
risk estimates for alternative more stringent standards, stating that
minority and low-income groups are more greatly impacted by Pb, and
that for these reasons the standard should be lowered. The CHPAC
submission also suggests consideration of some transient sources to
provide support for a more stringent standard. Among the reasons given
for their recommendations to substantially lower the standard level,
the individual commenters variously stated that not revising or
lowering the standard will allow increases in air Pb in locations near
some sources of Pb emissions, such as airports, and that the
persistence of Pb indicated the need for a more stringent standard.
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\52\ As described in its charter, the CHPAC is a policy-oriented
committee providing policy advice to EPA related to the development
of regulations, guidance and policies to address children's
environmental health, consistent with provisions of the Federal
Advisory Committee Act (http://www.epa.gov/faca/childrens-health-protection-advisory-committee-charter-september-11-2015). The role
and scope of activities for the CHPAC differs from those of the
CASAC, which is the independent scientific review committee
fulfilling the function described in the CAA of reviewing the air
quality criteria and the NAAQS for protection of public health and
welfare and making recommendations to the Administrator concerning
revisions as may be appropriate (as described in section 109(d)(2)
of the Act and summarized in section I.A above).
\53\ In expressing this view, some commenters cited statements
by various government agencies regarding their interpretation of
children's blood Pb levels with regard to risk management decisions
based on consideration of the available information in those risk
management contexts (e.g., CDC, 2005; Cal EPA, 2007; NYDHMH, 2010).
The scientific information on health effects of Pb considered by
these agencies was also available and, to the extent relevant to
consideration of the adequacy of the NAAQS, was assessed in the
current and, in some cases, also the prior review. As discussed
below, the conclusion that a threshold level for neurocognitive
effects has not been identified was a consideration of the EPA in
the last review, and the current one.
---------------------------------------------------------------------------
The four commenters that supported revision of the standard
suggested a wide array of alternatives. The CHPAC repeated the view it
expressed in the 2008 review that the standard should be revised to the
most stringent alternative analyzed in the 2007 REA (a potential
standard with an averaging time of one month and a level of 0.02
[micro]g/m\3\). One individual commenter expressed a preference for a
standard level of 0.0005 [micro]g/m\3\. Another individual commenter
urged revision to the lowest feasible standard, and the smelting
company recommended that EPA adopt an approach similar to a local air
quality management district's emissions standards regulation \54\ that
requires air monitoring at large Pb acid battery recycling metal
melting facilities to meet, by a future date, a 30-day average Pb
concentration of 0.1 [micro]g/m\3\, which the company indicated its
technology can address.
---------------------------------------------------------------------------
\54\ This commenter referred to a March 2015 amendment of a
California South Coast Air Quality Management District rule on
emission standards for lead and other toxic air contaminants from
large lead-acid battery recycling facilities in that state air
quality district.
---------------------------------------------------------------------------
We agree with commenters that a threshold level for neurocognitive
effects has not been identified in the current evidence, as stated in
section II.A.2.c above, and described in more detail in the ISA. We
additionally note that the lack of an established threshold of effects
is not uncommon among the criteria pollutant evidence bases. For
example, in past reviews of the primary standards for ozone and
particulate matter, the EPA has recognized that the available
epidemiological evidence neither supports nor refutes the existence of
thresholds at the population level, while noting uncertainties and
limitations in studies that make discerning thresholds in populations
difficult (e.g., 73 FR 16444, March 27, 2008; 71 FR 61158, October 17,
2006). The lack of a discernible threshold of exposure associated with
health effects does not of itself provide support for revision of an
existing standard or for revision to the most stringent standard one
might identify. As recognized in section I.A above, the CAA does not
require the Administrator to establish a primary national ambient air
quality standard at a zero-risk level or at background concentrations
(Lead Industries v. EPA, 647 F.2d at 1156 n.51; Mississippi v. EPA, 744
F. 3d at 1351), but rather at a level that reduces risk sufficiently so
as to protect public health with an adequate margin of safety, and the
selection of any particular approach for providing an adequate margin
of safety is a policy choice left specifically to the Administrator's
judgment (Lead Industries Association v. EPA, 647 F.2d at 1161-62;
Mississippi, 744 F. 3d at 1353). The CAA requirement in establishing a
standard is that it be set at a level of air quality that is requisite,
meaning ``sufficient, but not more than necessary'' (Whitman v.
American Trucking Ass'ns, 531 U.S. 457, 473 [2001]).
In the setting of the current standard in 2008, a key consideration
of the Administrator was the recognition of the lack of a discernible
threshold level in the evidence with respect to neurocognitive effects
associated with Pb exposure. This recognition, which differed from the
scientific consensus at the time the previous standard was set in 1978,
led the Administrator in 2008 to depart from the threshold-based
approach used in setting the 1978 standard and to focus on
consideration of air-related Pb in the context of the air-related IQ
loss evidence-based framework (described in section II.A.1
[[Page 71929]]
above). In the current review of the 2008 standard, while recognizing
the continued lack of a discernible threshold of exposure associated
with neurocognitive effects, the CASAC commented regarding effects at
very low Pb levels when expressing its view that the scientific
evidence does not support revision to the Pb NAAQS. It stated that
``[a]lthough there is evidence that even very low Pb levels are related
to measurable reductions in IQ in children, the extent to which the
blood Pb levels observed in children are linked to ambient air Pb
levels below the current standard (as opposed to other sources of Pb in
the environment) has not been established'' (Frey, 2013b, Consensus
Response to Charge Questions, pp. 7-8).\55\
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\55\ The CASAC recognized the multimedia and legacy aspects of
Pb that, unlike the case for other criteria air pollutants,
complicate consideration of the risks of Pb concentrations in
ambient air (Frey, 2013b, p. 1).
---------------------------------------------------------------------------
The four submissions recommending a revised standard variously cite
a number of studies as providing support for their view. Some of these
studies have been reviewed in the ISA, some were published too late to
be included in the ISA, and a few others were of a type that are not
generally included in the ISA (e.g., review articles).\56\ As discussed
in section I.C above, we have provisionally considered studies that
were not in the ISA or in previous AQCDs (``new'' studies) \57\ which
some of these commenters cite in statements about evidence of effects
at low exposures and in the presence of other pollutants. We conclude
that these studies are consistent with the scientific conclusions
reached in the ISA, including those related to blood Pb levels in
studies from which effects on IQ have been reported and related to co-
exposure with other metals. Taken in context, the information from
these studies and these findings do not materially change any of the
broad scientific conclusions of the ISA regarding the health effects
and exposure pathways of Pb in ambient air on which the Administrator
based her proposed conclusions as well as her final conclusions in this
review, as described in section II.B.4 below. We additionally note that
with regard to the inputs for the air-related IQ loss evidence-based
framework, a key aspect of the Administrator's rationale for her
proposed decision to retain the current primary standard (as described
in section II.E.4 of the proposal), none of the cited studies indicate
a steeper blood Pb-IQ slope or greater air-to-blood ratio than those
assessed in the ISA and considered in the PA and the proposal.
---------------------------------------------------------------------------
\56\ Some studies cited by commenters are review articles or
government reviews (e.g., Henn et al., 2014; Grandjean and
Landrigan, 2014; Jakubowski, 2011; NTP, 2011), which are not
generally cited in the ISA because the ISA considers the original
studies underlying a review article, rather than a review's
interpretation of the studies. Further, in the case of government
reviews, such reports generally review the literature for specific
purposes of those government agencies (which differ from the focus
for the ISA). Many of the scientific studies reviewed in these
reports (as well as the other reviews), however, were considered
relevant to review of the lead air quality criteria (based on the
description of study selection for inclusion in the preamble to the
ISA), and thus were assessed in this review.
\57\ These studies are listed in a memorandum to the rulemaking
docket (Kirrane, 2016).
---------------------------------------------------------------------------
We respectfully disagree with the comment from CHPAC that studies
available since the cut-off date for the ISA contradict the PA
conclusions regarding blood Pb levels in children and effects on
cognitive function measures, such as IQ.\58\ Of the studies cited in
the comment that were published subsequent to the date for publication
in the ISA, one is an analysis that relies on data from studies that
were published prior to 2008 and assessed in the last review (Budtz-
Jorgensen et al., 2013). These data were the subject of the pooled
analysis by Lanphear et al (2005) which we assessed in both the last
and the current review. As such, this commenter-cited publication does
not present a new study of children with lower blood Pb levels; rather,
it reanalyzes existing data using a different approach for a different
purpose.\59\ The other two of the commenter-cited publications are
review articles that do not present information on specific blood Pb
levels associated with IQ effects. Thus, we do not find these
publications to be contrary to the discussion and associated
conclusions in the PA or to indicate the current standard to be
inadequate.
---------------------------------------------------------------------------
\58\ The PA recognized the complexity associated with
considering the evidence regarding exposure levels associated with
health effects, and in particular effects on cognitive function
measures, including IQ, which the evidence base indicates to be the
most sensitive endpoint. The PA observed that the evidence available
in this review is generally consistent with that available in the
last review with regard to blood Pb levels in young children at
which such effects have been reported. Noting that blood Pb levels
are a reflection of exposure history, particularly in early
childhood, the PA concludes by extension that the currently
available evidence does not indicate Pb effects at exposure levels
appreciably lower than recognized in the last review. In so doing,
the PA continued to focus in this review (as in the last review) on
the evidence of effects in young children for which our
understanding of exposure history is less uncertain (PA, pp. 3-21 to
3-26).
\59\ This analysis uses the data from the same studies analyzed
by Lanphear et al (2005) to extrapolate below the blood Pb
concentrations measured in the studies and estimate a 95 percent
lower confidence bound on the estimated blood Pb concentration
associated with a 1 point decrement in IQ (Budtz-Jorgensen et al.,
2013). Unlike the prior study by Lanphear et al (2005) and similar
epidemiological analyses of IQ and blood Pb, which are intended to
produce a quantitative description of the change in IQ associated
with blood Pb concentrations in the studied children, this analysis
is focused on estimating a lower bound confidence limit on the
incremental concentration in blood Pb, as compared to zero,
associated with a single point IQ decrement. Even if we were to
interpret the results of the Budtz-Jorgensen et al (2013) analysis
as providing another estimate of C-R function for IQ decrement based
on the pooled dataset from Lanphear et al (2005), we note that that
dataset is already represented among the four low blood Pb analyses
on which we focused in identifying a slope estimate for use with the
air-related IQ loss evidence-based framework, and as noted in
section II.B.3 of the proposal, revision or replacement of the
estimate for the pooled dataset has no impact on conclusions drawn
from the framework (80 FR 29295, January 5, 2015).
---------------------------------------------------------------------------
We further disagree with the suggestion in the CHPAC submission
that the evidence related to co-exposures to other pollutants, such as
metals, provides a basis for concluding that the current standard is
not requisite. The ISA assessment of the strength of the evidence for
co-exposures to other pollutants, such as other metals, to contribute
to increased risk of a Pb-related health effects concluded the evidence
to be suggestive, ``but overall the evidence was limited'' (ISA,
sections 1.9.6 and 5.4). With regard to the articles cited by the CHPAC
that have been published subsequent to the ISA, the general conclusions
of these review articles (Henn et al., 2014; Grandjean and Landrigan,
2014) are consistent with conclusions of the ISA. As stated in the ISA,
``interactions between Pb and co-exposure with other metals were
evaluated in recent epidemiologic and toxicological studies of health
effects'' and ``[h]igh levels of other metals, such as Cd and Mn, were
observed to result in greater effects for the associations between Pb
and various health endpoints but evidence was limited due to the small
number of studies'' (ISA, p. 5-43). We note that even in raising co-
exposure as a concern, the comments recognize that the potential for
such impacts is not well understood. Further, the comments do not
explain how the limited information regarding this factor supports
their conclusion that the current standard does not provide the
requisite protection or leads to the specific revisions the comments
suggest, and we find no such support in the current evidence.
We additionally disagree with the comment that the currently
available evidence indicates that the current standard is not
protective of effects such as low birth weight. For example, the
[[Page 71930]]
CHPAC cites epidemiological studies reporting associations of maternal
or cord blood Pb concentrations with reduced fetal growth (Xie et al.,
2013; Nishioka et al., 2014), stating that these studies strengthen the
association of decreased birth weight and maternal blood Pb levels.
Although we would agree that these studies present an addition to the
evidence base overall, they do not provide a basis for change in the
conclusion of the ISA, which states, ``Some well-conducted
epidemiologic studies report associations of maternal Pb biomarkers or
cord blood Pb with preterm birth and low birth weight/fetal growth;
however, the epidemiologic evidence is inconsistent overall and
findings from experimental animal studies are mixed'' (ISA, p. 1-18).
In citing these studies, in fact, the CHPAC also stated its view that
the findings of these studies are consistent with a larger study that
was assessed in the ISA; it did not explain how these studies support
its view that the current standard provides inadequate protection from
such effects, and we find no such support.
With regard to information related to Pb impacts in minority and
low-income populations, which some comments suggested provided a basis
for a more stringent standard, we note that we have considered the
available information on such impacts, as recognized in section
II.A.2.d above and summarized more fully in section II.B.4 of the
proposal and in section 3.3 of the PA. As all of these documents have
recognized, the ISA identifies non-white populations as at-risk
populations, with this conclusion based primarily on findings of higher
blood Pb levels in black compared to white populations (ISA, section
5.4).\60\ Blood Pb levels have also been found to be higher in low SES
groups as compared to higher SES \61\ (ISA, sections 5.3.6, 5.2.4 and
5.4). However, as noted in the ISA, the number of studies examining the
relationship of SES with Pb-related health effects is limited, and the
results have differed with regard to finding increased risk with higher
or lower SES (ISA, Table 5-1, p. 5-42). The comments generally identify
impacts in minority and low income groups as a reason EPA should revise
the standard, although they provide no explanation for how the
currently available information leads to that conclusion or provides a
basis for the alternative standards the comments suggest. \62\ While
our assessment of the health effects evidence in this review concluded
there was adequate evidence for race or ethnicity (and suggestive
evidence for SES) to contribute to increased risk of Pb-related health
effects, we do not find this information to call into question the
adequacy of protection provided by the current primary standard. Nor
did the CASAC find this to be the case, based on its review of the
scientific materials in this review, including three drafts of the ISA
in which the evidence for these factors was presented. Further, to the
extent such differences may be related to exposure contributions from
air Pb and proximity to air sources,\63\ we note that children that are
exposed to air-related Pb in areas with elevated air Pb concentrations
near or equal to the level of the standard are among those that were
the focus of the 2008 decision, as recognized in sections II.A.1 and
II.A.2.e above, and are the focus of the decision described in section
II.B.4 below to retain the standard set in 2008.\64\
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\60\ Recent data suggest that differences in blood Pb levels
between young black and white children is decreasing over time (ISA,
section 5.2.3, 5.4). Although more recent data are not available by
age group, the CDC data through 2011-2012 indicate little or no
difference between non-Hispanic blacks, Mexican Americans or all
Hispanics and non-Hispanic whites at the central tendencies of the
populations and reduced differences at the 95th percentile (CDC,
2015). Findings of some studies indicate that non-white populations
may be at greater risk of Pb-related health effects although, as
described in the ISA, this could be related to confounding by other
factors (ISA, sections 5.3.7 and 5.4).
\61\ As with differences among groups of different races and
ethnicities, ``[t]he gap between SES groups with respect to Pb body
burden appears to be diminishing,'' although blood Pb levels
continue to be higher among lower-income children (ISA, p. 1-80,
sections 1.9.6, 5.1, 5.2.1.1, 5.2.4 and 5.4), leading the ISA to
conclude that the evidence is suggestive of SES as a risk factor for
Pb-related health effects (as summarized in section II.A.2.d above).
\62\ In making this statement, these commenters cite a 1988
study on blood Pb and early childhood scores on the BSID MDI infant
cognitive development test (Bellinger et al., 1988). The study found
that 18 and 24 month BSID MDI scores of the ``lower'' SES children
were adversely affected at lower cord blood Pb levels than were
scores of the ``higher'' SES children, finding significantly lower
scores of the lower SES children with cord blood Pb levels of 6-7
[micro]g/dL as compared to children of this SES group with cord
blood Pb levels less than 3 [micro]g/dL (Bellinger et al., 1988;
USEPA, 1990a; USEPA, 2006). As the study cohort was mostly middle to
upper-middle class, the ``lower'' SES group ``refers to [families of
SES] less than the highest SES levels and is probably in fact [of
SES levels] much closer to the median of the U.S. population than
the term suggests'' (USEPA, 1990a, p. 53). The ISA considered these
study findings in the context of considering available evidence on
this issue in the current review (ISA, section 5.3.6; Bellinger et
al., 1990). The ISA found that the available study results are
limited, have differed with regard to finding increased risk with
higher or lower SES and that ``they do not clearly indicate whether
groups with different socioeconomic status differ in Pb-related
changes for cognitive function'' (ISA, p. 5-34, Table 5-1, p. 5-42).
\63\ As noted in section I.D above and described in more detail
in the PA and ISA, sources of Pb to which children are exposed also
include consumer goods, dust or chips of peeling Pb-containing paint
and ingestion of Pb in drinking water conveyed through Pb pipes, as
well as historically deposited Pb in urban soils (ISA, pp. pp. lxxix
to lxxx).
\64\ Additionally, the focus of the air-related IQ loss
evidence-based framework on C-R functions observed for children with
low blood Pb levels closer to those observed in U.S. children today
reflects evidence-based conclusions from the last review, affirmed
in this review, of a steeper slope for the C-R relationship at lower
as compared to higher blood Pb levels. As noted in section II.A.2.d
above, while children with higher blood Pb levels are at greater
risk of Pb-related effects than children with lower blood Pb levels,
on an incremental basis (e.g., per [micro]g/dL) the risk is greater
for children at lower blood Pb levels. The 2008 revision of the
primary Pb standard focused on the incremental impact of air-related
Pb on young children and in so doing, recognized the greater
incremental impact for those children with lower absolute blood Pb
levels. Accordingly, the decision focused on those C-R studies
involving the lowest blood Pb levels (as summarized in II.A.1
above). Although the comment did not indicate how information that
some groups may be generally more highly exposed to Pb should be
used, we note that for the Administrator to rely on C-R functions
from analyses for higher blood Pb study groups (with a less steep
slope) would lead to consideration of a higher standard level, and
would not provide the desired protection for the sensitive group of
children with lower blood Pb levels that are exposed to air-related
Pb in areas with air Pb concentrations at the level of the standard
(73 FR 67002-07, November 12, 2008; 80 FR 311-313, January 5, 2015).
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With regard to consideration of the potential for risk reduction
from lower air concentrations, the PA stated that ``the uncertainties
and limitations associated with many aspects of the estimated
relationships between air Pb concentrations and blood Pb levels and
associated health effects are amplified with consideration of
increasingly lower air concentrations'' (PA, p. 4-35). Contrary to the
suggestion by the CHPAC and the smelter company, the PA did not
conclude that there would be public health benefits from a lower
standard and that such benefits were not large enough to warrant
revising the standard. Rather, the PA notes that ``[a]s recognized at
the time of the last review, exposure and risk modeling conducted for
[the REA] was complex and subject to significant uncertainties'' (PA,
p. 3-67) and recognizes ``increasing uncertainty of risk estimates''
for air Pb concentrations below those associated with the current
standard (PA, p. 4-35). The PA further stated that that ``there is
appreciable uncertainty associated with drawing conclusions regarding
whether there would be reductions in blood Pb levels and risk to public
health from alternative lower levels of the standard as compared to the
level of the current standard'' (PA, pp. 4-35 to 4-36). The CASAC
stated that it agreed with this conclusion regarding ``[t]he obvious
uncertainty'' articulated in the PA, additionally stating, as noted
above, that ``[a]lthough there is evidence that even
[[Page 71931]]
very low Pb levels are related to measurable reductions in IQ in
children, the extent to which the blood Pb levels observed in children
are linked to ambient air Pb levels below the current standard (as
opposed to other sources of Pb in the environment) has not been
established'' and, accordingly (as noted below), that the current
information does not provide support for lowering the primary standard
(Frey, 2013b, Consensus Response to Charge Questions, pp. 6-8). These
conclusions from the CASAC and the PA findings were among the
considerations that led to the Administrator's proposed decision
(summarized in section II.B.1 above) and her final decision in this
review, as described in section II.B.4 below, that, based on the
current scientific information, including information regarding at-risk
populations, as well as uncertainties and limitations associated with
the current information, the current primary standard provides the
requisite protection of public health with an adequate margin of
safety, including the health of at-risk populations.
The comment regarding a potential for increases in air Pb near
sources of Pb emissions if the standard is not revised does not explain
how such a potential provides support for revising the standard. The
comment also suggests that EPA consider two alternative standard levels
well below the current standard level while providing no explanation of
why a revised standard with either of the suggested levels would be
requisite. With regard to the potential for increases in air Pb near
sources of Pb emissions if the standard is not revised, we note that
such a concern, to the extent it applies to the current standard, would
also pertain to any more stringent Pb standard except in the extreme
case in which the standard is set such that there is no location with
air quality conditions better than those that just meet the standard.
As discussed in sections II.B.1 above and II.B.4 below, the
Administrator has considered the current evidence and exposure/risk
information with regard to the potential for a revised standard to
offer additional protection, found there to be substantial uncertainty
associated with such a potential, and concluded that the current
standard is requisite. Regarding the possibility that air Pb
concentrations could increase in some locations, we additionally note
that the Clean Air Act and associated EPA permitting regulations
restrict increases in air Pb concentrations (and in other pollutants
for which there are NAAQS) in various circumstances, both in areas
already meeting the NAAQS as well as those in nonattainment (e.g., New
Source Review regulations at 40 CFR part 51, subpart I, applicable in
attainment and nonattainment areas; General Conformity regulations at
40 CFR 93.150-165, applicable in nonattainment and maintenance areas;
and, the general anti-backsliding requirements under Section 110(l) of
the Clean Air Act).
Regarding the view expressed by some commenters that the most
restrictive standard assessed in the 2007 REA should be adopted, \65\
or that the standard level should be revised to a concentration
described in one comment as the average air Pb concentration in
pristine locations, we note the greater uncertainty in risk estimates
associated with air quality scenarios for air Pb concentrations
increasingly below those of current conditions. Additionally, the PA
described the ``increasing uncertainty recognized for air quality
scenarios involving air Pb concentrations increasingly below the
current conditions for each case study, recognizing that such
uncertainty is due in part to modeling limitations deriving from
uncertainty regarding relationships between ambient air Pb and outdoor
soil/dust Pb and indoor dust Pb'' (PA, 4-34). Further, the PA
concluded, and the CASAC agreed, that ``there is appreciable
uncertainty associated with drawing conclusions regarding whether there
would be reductions in blood Pb levels from alternative lower levels as
compared to the level of the current standard' (Frey, 2013b, Consensus
Response to Charge Questions, p. 6; PA, p.4-35 to 4-36). The CASAC
further stated that ``there is not justification for modifying the
current standard based on these data at this time'' (Frey, 2013b,
Consensus Response to Charge Questions, p. 8). In reaching her proposed
decision to retain the current standard, the Administrator took note of
the PA conclusion and associated CASAC agreement and additionally
recognized that ``the uncertainties and limitations associated with the
many aspects of the estimated relationships between air Pb
concentrations and blood Pb levels and associated health effects are
amplified with consideration of increasingly lower air concentrations''
(80 FR 313). Finally, in the proposal, as in the final decision
described in section II.B.3 below, the Administrator judges this
uncertainty to be too great for the current evidence and exposure/risk
information to provide a basis for revising the current standard. With
regard to comments recommending consideration of technological
feasibility in judging the requisiteness of the primary standard, we
note, as we have described in section I.A above, the EPA may not
consider technological feasibility or attainability in determining what
standard is requisite to protect public health with an adequate margin
of safety.
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\65\ The alternative more stringent primary standard suggested
by the CHPAC was the most stringent assessed in the 2007 REA and
included both a lower level and a shorter averaging time than those
for the current standard. In establishing the current standard in
2008, the EPA considered these suggestions regarding level and
averaging time, which were also made by the CHPAC at that time. The
EPA's considerations with regard to averaging time in establishing
the current standard in 2008 are summarized in section II.E.1 of the
proposal and section 4.1.1.2 of the PA. The comments from the CHPAC
repeat its recommendation from the last review and do not provide
any additional information or explanation in support of its view on
a revised averaging time. The EPA response to substantive comments
on averaging time in the last review from the CASAC and the public,
including the CHPAC, is described in the notice of final decision
(73 FR 66991-996, November 12, 2008).
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Comments on topics less directly related to consideration of the
primary standard included recommendations for addressing data gaps and
uncertainties to inform future reviews. Additionally, one comment
focused on pathways by which Pb may be further distributed in the
environment, recommending use of a ``more robust [monitoring] network
to adequately estimate children's lead exposures from transient and
other sources,'' emphasizing building demolition and Pb wheel weights.
This comment also states that the PA overlooks the contribution from
these and other sources and therefore may underestimate the number of
children exposed to Pb from transient sources. Another comment
described leaded aviation gasoline and airports as a source of Pb
emissions but did not explain how such information was relevant to the
Administrator's proposed decision that the current standard provided
the requisite protection and should be retained without revision.
With regard to the need for research, the PA highlighted key
uncertainties associated with reviewing and establishing NAAQS for Pb
and areas for future health-related research, model development, and
data gathering. The topic areas of key uncertainties, research
questions and data gaps that were highlighted in the PA with regard to
review of the health-based primary standard overlap with many raised by
commenters. We encourage research in these areas, although we note that
research planning and priority setting are beyond the scope of this
action.
With regard to the monitoring network in place for Pb NAAQS
[[Page 71932]]
surveillance, the current regulations require air monitors in areas
that are expected to or have been shown to experience or contribute to
exceedance of the standards. As described in section I.E above, this
includes requirements for monitors in areas with non-airport sources
emitting 0.5 tpy or where an airport emits 1.0 or more tpy, based on
either the most recent National Emissions Inventory or other
scientifically justifiable methods and data (40 CFR part 58, appendix
D, section 4.5). The establishment of the source-oriented monitoring
requirement reflects our conclusion that monitoring should be
presumptively required at sites near sources that have estimated Pb
emissions in exceedance of a Pb ``emissions threshold'' (73 FR 67025).
This monitoring requirement applies not only to existing industrial
sources of Pb, but also to fugitive sources of Pb (e.g., mine tailing
piles, closed industrial facilities) and airports where leaded aviation
gasoline is used. Additionally, as noted in section I.E above, to
account for other sources that may contribute to a maximum Pb
concentration in ambient air in excess of the Pb NAAQS, the monitoring
regulations also grant the EPA Regional Administrator the authority to
require additional monitoring ``where the likelihood of Pb air quality
violations is significant or where the emissions density, topography,
or population locations are complex and varied'' (40 CFR part 58,
appendix D, section 4.5(c)).
In addition to this monitoring required for Pb NAAQS surveillance,
state or local agencies may site additional monitors and there are also
particulate matter monitoring networks that collect Pb data in specific
particle size fractions in many urban areas (40 CFR part 58, appendix
D, section 4.5). Further, as described in section I.E above,\66\
monitoring data collected at NCore sites in large population areas, in
combination with the data for all other non-source-oriented sites,
including those in urban areas, indicate air Pb concentrations well
below the Pb NAAQS (as summarized in section I.E above). Accordingly,
we believe that the current Pb monitoring requirements are consistent
with the currently available information regarding sources of Pb to the
ambient air and areas with the potential for exceedance of the Pb
standards. Further, as described below, the information available
regarding the transient sources mentioned by the commenters does not
indicate the potential for such transient sources to result in
exceedances of the NAAQS.
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\66\ The various air Pb monitoring networks are summarized in
section I.E above and described in more detail in section 2.2.1 of
the PA.
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As to the comment on the significance of building demolition or Pb
wheel weights in contributing to environmental Pb exposure pathways,
the ISA and PA considered the very limited available data pertaining to
these issues. With regard to building demolition, for which the data
are in terms of loading of dust containing Pb on alleys and sidewalks
immediately following an event, the ISA concludes that the limited data
``suggest that building demolition may be a short-term source of Pb in
the environment,'' and that ``it is unclear if demolition is related to
long-term Pb persistence in the environment'' (ISA, p. 2-21).\67\
Accordingly, we do not interpret the limited available information,
which does not include measurements of air Pb concentrations, to
indicate a potential for such occasional activities as demolition of
buildings containing leaded paint to result in air Pb concentrations
near or in exceedance of the NAAQS. \68\ With regard to the comment on
lead wheel weights, we note that the commenter states they are unaware
of studies that have assessed the impact of Pb wheel weights on
childhood blood Pb levels, as are we. The ISA examined the very limited
data on potential contribution of Pb wheel weights to Pb near roadways;
these data yield widely varying and uncertain estimates of associated
Pb releases (ISA, section 2.2.2.6). Contrary to the commenter's
assertion that the PA overlooks these potential Pb exposure pathways,
the assessment and consideration of policy-relevant information in the
PA \69\ reflects these ISA findings based on consideration of the
current information for these potential transient pathways.
Specifically, the current information does not provide support for
specific estimates of exposures associated with these pathways.
Further, data for monitoring sites near roads find Pb concentrations
well below the NAAQS (e.g., ISA, Figure 2-20). Thus, we conclude that
the current information does not provide support for changes to the
current Pb monitoring regulations with regard to roadways or occasional
activities such as building demolition.
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\67\ Characterization of this activity by the study published
subsequent to the ISA that was cited by the CHPAC (Jacobs et al.,
2013) is consistent with findings from the limited number of studies
included in the ISA (ISA, p. 2-21).
\68\ We note that airborne dust release from demolition of large
buildings in some areas may be regulated under various state and/or
local programs (e.g., demolition activities in some particulate
matter non-attainment or maintenance areas may be subject to
specific state implementation plan requirements on airborne dust
releases).
\69\ Consistent with the strength and specificity of information
described in the ISA, the PA recognizes the loss of Pb wheel weights
as an additional source of Pb emissions and notes the potential for
previously deposited Pb to be resuspended into the air, without
providing detailed consideration (PA, sections 2.1.2.2 and 2.1.2.4).
Further, the input for air-to-blood ratio in the air-related IQ loss
evidence-based framework, which the Administrator has used as a
guide in her consideration of the adequacy of the current standard,
does not restrict sources of Pb from consideration. Thus, such
ratios, which are drawn from empirical studies, would be expected to
reflect all sources contributing to children's blood Pb, including
the transient sources identified by commenters to the extent they
provide contributions (ISA, section 3.5; PA, section 3.1; 80 FR 298-
300, January 5, 2015; 73 FR 66973-66975,67004, November 12, 2008).
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4. Administrator's Conclusions
Having carefully considered the public comments, as discussed
above, the Administrator believes that the fundamental scientific
conclusions on the effects of Pb in ambient air reached in the ISA and
PA, and summarized in sections II.B and II.C of the proposal, remain
valid. Additionally, the Administrator believes the judgments she
reached in the proposal (section II.E.4) with regard to consideration
of the evidence and quantitative exposure/risk information remain
appropriate. Thus, as described below, the Administrator concludes that
the current primary standard provides the requisite protection of
public health with an adequate margin of safety and should be retained.
In considering the adequacy of the current primary Pb standard, the
Administrator has carefully considered the current policy-relevant
evidence and conclusions contained in the ISA; the evaluation of this
evidence and the exposure/risk information, rationale and conclusions
presented in the PA; the advice and recommendations from the CASAC; and
public comments. In the discussion below, the Administrator gives
weight to the PA conclusions, with which the CASAC has concurred, as
summarized in section II of the proposal, and takes note of key aspects
of the rationale for those conclusions that contribute to her decision
in this review.
As an initial matter, the Administrator recognizes the complexity
involved in considering the adequacy of protection in the case of the
primary Pb standard, which differs substantially from that involved in
consideration of the health protection provided by the primary
standards in other NAAQS reviews. For the pollutants in the other
reviews, the more limited focus solely on the inhalation pathways of
exposure is a relatively simpler context. Further, as
[[Page 71933]]
described in the PA and noted in section II.B.1 above, the influence of
multimedia and historical exposure on the internal biomarkers in Pb
epidemiological studies contrasts with the epidemiological studies
considered for other NAAQS pollutants which focus on generally current
concentrations of those pollutants in ambient air. While the use of an
internal biomarker strengthens conclusions regarding Pb as the causal
agent in associations observed in epidemiological studies, the
persistence of Pb and the role of multimedia and historical exposures
limit the conclusions that can be drawn regarding the particular
exposure circumstances eliciting the reported effects. Thus, as we lack
studies that can directly assess current concentrations of Pb in
ambient air (including in locations where the current standard is met)
and the occurrence of health effects, we primarily consider the
evidence for, and risk estimated from, models, based upon key
relationships, such as those among ambient air Pb, Pb exposure, blood
Pb and health effects. This information base, both with its strong,
long-established evidence of the health effects of Pb in young
children, and the associated limitations and uncertainties mentioned
here, contributes to our conclusions regarding relationships between
ambient air Pb conditions under the current standard and health
effects.
The Administrator recognizes that in primary NAAQS reviews, our
understanding of the relationships between the presence of a pollutant
in ambient air and associated health effects is based on a broad body
of information encompassing not only more established aspects of the
evidence, but also aspects in which there may be substantial
uncertainty. In the case of this review of the primary standard for Pb,
she takes note of the increased uncertainty in characterizing the
relationship of effects on IQ with blood Pb levels below those
represented in the evidence base and in projecting the magnitude of
blood Pb response to ambient air Pb concentrations at and below the
level of the current standard. The PA recognizes this increased
uncertainty, particularly in light of the multiple factors that play a
role in such a projection (e.g., meteorology, atmospheric dispersion
and deposition, human physiology and behavior), each of which carry
attendant uncertainties. These aspects of the scientific evidence and
analyses, and the associated uncertainties, collectively contribute to
the Administrator's recognition that for Pb, as for other pollutants,
the available health effects evidence and associated information
generally reflect a continuum, consisting of levels at which scientists
generally agree that health effects are likely to occur, through lower
levels at which the likelihood and magnitude of the response become
increasingly uncertain.
With regard to the current evidence, as summarized in the PA and
discussed in detail in the ISA, the Administrator takes note of the
well-established body of evidence on the health effects of Pb, which
has been augmented in some aspects since the last review and continues
to support identification of neurocognitive effects in young children
as the most sensitive endpoint associated with Pb exposure. For
example, while the ISA continues to recognize cardiovascular effects in
adults, in addition to neurodevelopmental effects in children, as being
associated with the lowest blood Pb levels compared to other health
effects (ISA, pp. xciii), the ISA also notes uncertainties regarding
the timing, frequency, duration and level of Pb exposures contributing
to the effects observed in adult epidemiologic studies and indicates
that higher exposures in the past (rather than lower current exposures)
may contribute to the development of health effects measured later in
life (ISA, p. lxxxviii). Given the evidence-based identification of
neurocognitive effects in young children as the most sensitive endpoint
associated with Pb exposure, the Administrator has accordingly focused
on nervous system effects in young children and particularly
neurocognitive effects. In so doing, she finds that the evidence, while
describing a broad array of health effects associated with Pb,
continues to indicate that a standard that provides protection from
neurocognitive effects in young children additionally provides
protection from other health effects of Pb, such as those reported in
adult populations.
The Administrator takes note of the PA finding that application of
the air-related IQ loss evidence-based framework, developed in the last
review, continues to provide a useful approach for considering and
integrating the evidence on relationships between Pb in ambient air and
Pb in young children's blood and risks of neurocognitive effects (for
which IQ loss is used as an indicator). In so doing, as in the 2008
review, she notes that the framework, and the IQ loss estimates yielded
by it for specific combinations of standard level, air-to-blood ratio
and C-R function, does not provide an evidence- or risk-based bright
line that indicates a single appropriate level for the standard.
Further, the Administrator recognizes uncertainties associated with IQ
estimates produced by the framework, noting the PA conclusion that the
uncertainties increase with estimates associated with successively
lower standard levels. She additionally takes note of the PA finding
(described in section II.E.1 of the proposal) that the currently
available evidence base, while somewhat expanded since the last review,
is not appreciably expanded or supportive of appreciably different
conclusions with regard to air-to-blood ratios or C-R functions for
neurocognitive decrements in young children. The Administrator further
notes the concurrence from the CASAC on both of these points and the
lack of recommendations in public comments for a change to either of
these inputs to the evidence-based framework. Thus, she judges the
evidence base and related air-related IQ loss framework to be an
appropriate tool for informing her decision on the adequacy of the
current standard.
In light of the continuum referenced above, the Administrator
additionally recognizes in this review, as in the 2008 review, the role
of judgment in reaching conclusions regarding Pb health effects that
are important from a public health perspective. Most specifically, the
Administrator has considered the public health significance of a
decrement of a very small number of IQ points in the at-risk population
of young children, in light of associated uncertainties. With regard to
making a public health policy judgment as to the appropriate protection
against risk of air-related IQ loss and related effects, the
Administrator believes, as did the Administrator at the time of the
last review, that ideally air-related (as well as other) exposures to
environmental Pb would be reduced to the point that no IQ impact in
children would occur. She recognizes, however, that in the case of
setting NAAQS, she is required to make a judgment as to what degree of
protection is requisite (neither more nor less than necessary) to
protect public health with an adequate margin of safety. As described
in the proposal with regard to considering the public health
significance of IQ loss estimates in young children, the Administrator
gives weight to the comments of the CASAC and some public commenters in
the last review which recognized a population mean IQ loss of 1 to 2
points to be of public health significance and recommended that a very
high
[[Page 71934]]
percentage of the U.S. population be protected from such a magnitude of
IQ loss (73 FR 67000, November 12, 2008). She additionally notes that
the CASAC did not provide a different goal in the present review. The
Administrator additionally notes that the EPA is aware of no new
information or new commonly accepted guidelines or criteria within the
public health community for interpreting public health significance of
neurocognitive effects in the context of a decision on adequacy of the
current Pb standard (PA, pp. 4-33 to 4-34), and no new information has
been identified by public commenters.
With the objective identified by the CASAC in the 2008 review in
mind, the Administrator recognizes, as was recognized at the time of
the last review, that her judgment on the degree of protection against
IQ impacts that should be afforded by the primary standard is
particularly focused on consideration of impacts in the at-risk
population and is not addressing a specific quantitative public health
policy goal for air-related decrements in IQ that would be acceptable
or unacceptable for the entire population of children in the U.S. As in
the last review, the at-risk population to which she gives particular
attention is the small subset of U.S. children living in close
proximity to air Pb sources that contribute to elevated air Pb
concentrations that equal the level of the standard). Accordingly, she
is considering IQ impacts in this small subset of U.S. children that is
expected to experience air-related Pb exposures at the high end of the
national distribution of such exposures (as described in section II.E.4
of the proposal and summarized in section II.B.1 above), and not a
projection of the average air-related IQ loss for the entire U.S.
population of children. The evidence-based framework estimates, with
which there are associated uncertainties and limitations (as described
in section II.A.1 above), relate to this small subset of children
exposed at the level of the standard. Based on these considerations,
the Administrator judges the conceptual evidence-based framework to
continue to be appropriate for her consideration of the public health
protection afforded by the current standard. Further, she concurs with
the PA findings (summarized in section II.E.1 of the proposal and
briefly outlined in II.B.1 above) that the current evidence, as
considered within the conceptual and quantitative context of the
evidence-based framework, and current air monitoring information
indicate that the current standard would be expected to satisfy the
public health policy goal recommended by the CASAC in the last Pb NAAQS
review, from which it did not indicate a departure in the present
review.
In the context of the Administrator's use of the framework as a
tool to inform her decision on the adequacy of the current standard,
the EPA additionally notes that the maximum, not to be exceeded, form
of the standard, in conjunction with the rolling 3-month averaging
time, is expected to result in the at-risk population of children being
exposed below the level of the standard most of the time (73 FR 67005,
November 12, 2008). In light of this and the uncertainty in the
relationship between time period of ambient level, exposure, and
occurrence of a health effect, the air-related IQ loss considered for
the current standard in applying the framework should not be
interpreted to mean that a specific level of air-related IQ loss will
occur in fact in areas where the standard is just met or that such a
loss has been determined as acceptable if it were to occur. Instead,
judgment regarding such an air-related IQ loss is one of the judgments
that need to be made in using the evidence-based framework to provide
useful guidance in the context of public health policy judgment on the
degree of protection from risk to public health that is sufficient but
not more than necessary, taking into consideration the patterns of air
quality that would likely occur upon just meeting the standard and
uncertainties in relating those patterns to exposures and effects.
In drawing conclusions regarding adequacy of the current standard
based on considering application of the evidence-based framework, the
Administrator further recognizes the degree to which IQ loss estimates
drawn from the air-related IQ loss evidence-based framework reflect
mean blood Pb levels that are below those represented in the currently
available evidence for young children, as described in section II.B.4
of the proposal. The Administrator views such an extension below the
lowest studied levels to be reasonable given the lack of identified
blood Pb level threshold in the current evidence base for
neurocognitive effects and the need for the NAAQS to provide a margin
of safety. She additionally takes note, however, of the PA finding that
the framework IQ loss estimates for standard levels lower than the
current standard level represent still greater extrapolations from the
current evidence base with corresponding increased uncertainty (PA,
section 3.2, pp. 4-32 to 4-33). The Administrator also gives weight to
the PA conclusion of greater uncertainty with regard to relationships
between concentrations of Pb in ambient air and air-related Pb in
children's blood, and with regard to estimates of the slope of the C-R
function of neurocognitive impacts (IQ loss) for application of the
framework to levels below the current standard, given the weaker
linkage with existing evidence as discussed in the PA (PA, sections
3.1, 3.2 and 4.2.1). Thus, consistent with the conceptual continuum
referenced above, the Administrator recognizes the increasing
uncertainty with regard to likelihood of response and magnitude of the
estimates at levels extending below the current standard.
With respect to exposure/risk-based considerations, as in the last
review, the Administrator notes the complexity of the REA modeling
analyses and the associated limitations and uncertainties. Based on
consideration of the risk-related information for conditions just
meeting the current standard, the Administrator takes note of the
attendant uncertainties, discussed in detail in the PA (PA, sections
3.4 and 4.2.2), while finding that the quantitative risk estimates,
with a focus on those for the generalized (local) urban case study, are
roughly consistent with and generally supportive of estimates from the
air-related IQ loss evidence-based framework. She further takes note of
the PA finding of increasing uncertainty for air quality scenarios
involving air Pb concentrations increasingly below the current
conditions for each case study, due in part to modeling limitations
that derive from uncertainty regarding relationships between ambient
air Pb and outdoor soil/dust Pb and indoor dust Pb (PA, sections
3.4.3.1 and 3.4.7).
Based on the above evidence- and exposure/risk-based considerations
and with consideration of advice from CASAC and public comment, the
Administrator concludes that the current standard provides protection
for young children from neurocognitive impacts, including IQ loss, that
is consistent with advice from CASAC regarding IQ loss of public health
significance. Based on consideration of the evidence and exposure/risk
information available in this review with its attendant uncertainties
and limitations, and information that might inform public health policy
judgments, as well as advice from CASAC, including its concurrence with
the PA conclusions that revision of the primary Pb standard is not
warranted at this time, the Administrator further concludes that it is
appropriate to retain
[[Page 71935]]
the current standard without revision. The Administrator bases these
conclusions on consideration of the health effects evidence, including
consideration of this evidence in the context of the air-related IQ
loss evidence-based framework, and with support from the exposure/risk
information, recognizing the uncertainties attendant with both. In so
doing, she takes note of the PA description of the complexities and
limitations in the evidence base associated with reaching conclusions
regarding the magnitude of risk associated with the current standard,
as well as the increasing uncertainty of risk estimates for lower air
Pb concentrations. Inherent in the Administrator's conclusions are
public health policy judgments on the public health implications of the
blood Pb levels and risk estimated for air-related Pb under the current
standard, including the public health significance of the Pb effects
being considered, as well as aspects of the use of the evidence-based
framework that may be considered to contribute to the margin of safety
(as noted in section II.A.1 above and the 2008 decision preamble to the
final rule, 73 FR 67007, November 12, 2008). These public health policy
judgments include judgments related to the appropriate degree of public
health protection that should be afforded to protect against risk of
neurocognitive effects in at-risk populations, such as IQ loss in young
children, as well as the appropriate weight to be given to differing
aspects of the evidence and exposure/risk information, and how to
consider their associated uncertainties. Based on these considerations
and the judgments identified here, the Administrator concludes that the
current standard provides the requisite protection of public health
with an adequate margin of safety, including protection of at-risk
populations, such as, in particular, young children living near Pb
emissions sources where ambient concentrations just meet the standard.
In reaching this conclusion with regard to the adequacy of public
health protection afforded by the existing primary standard, the
Administrator recognizes that in establishing primary standards under
the Act that are requisite to protect public health with an adequate
margin of safety, she is seeking to establish standards that are
neither more nor less stringent than necessary for this purpose. The
Act does not require that primary standards be set at a zero-risk
level, but rather at a level that avoids unacceptable risks to public
health, even if the risk is not precisely identified as to nature or
degree. The CAA requirement that primary standards provide an adequate
margin of safety was intended to address uncertainties associated with
inconclusive scientific and technical information available at the time
of standard setting, as described in section I.A above. This
requirement was also intended to provide a reasonable degree of
protection from hazards that research has not yet identified.
In this context, the Administrator has considered conclusions drawn
in the ISA and PA with regard to interpretation of the information
concerning the broader array of health effects of Pb beyond those on
the nervous system of young children. Based on the body of evidence in
support of identification of neurocognitive effects in young children
as the most sensitive endpoint associated with Pb exposure, as noted
previously in this section and briefly summarized in section II.A.2
above, she judges that a standard providing protection from such
effects additionally provides adequate protection against the risk of
other health effects and she further concludes that consideration of
the more limited and less certain information concerning Pb exposures
associated with such other effects does not lead her to identify a need
for any greater protection.
Further, the Administrator's conclusion that the current standard
provides the requisite protection and that a more restrictive standard
would not be requisite additionally recognizes that the uncertainties
and limitations associated with the many aspects of the estimated
relationships between air Pb concentrations and blood Pb levels and
associated health effects are amplified with consideration of
increasingly lower air concentrations. In reaching this conclusion, she
additionally takes note of the PA conclusion, with which the CASAC has
agreed, that based on the current evidence, there is appreciable
uncertainty associated with drawing conclusions regarding whether there
would be reductions in blood Pb levels and risk to public health from
alternative lower levels of the standard as compared to the level of
the current standard (PA, pp. 4-35 to 4-36; Frey, 2013b, Consensus
Response to Charge Questions, p. 6). The Administrator judges this
uncertainty to be too great for the current evidence and exposure/risk
information to provide a basis for revising the current standard. Thus,
based on the public health policy judgments described above, including
the weight given to uncertainties in the evidence, the Administrator
concludes that the current standard should be retained, without
revision.
C. Decision on the Primary Standard
For the reasons discussed above, and taking into account
information and assessments presented in the ISA and PA, the advice
from CASAC, and consideration of public comments, the Administrator
concludes that the current primary standard for Pb is requisite to
protect public health with an adequate margin of safety, including the
health of at-risk populations, and is retaining the standard without
revision.
III. Rationale for Decision on the Secondary Standard
This section presents the rationale for the Administrator's
decision to retain the existing secondary Pb standard, which, as
discussed more fully below, is based on a thorough review in the ISA of
the latest scientific information, generally published through
September 2011, on welfare effects associated with Pb and pertaining to
the presence of Pb in the ambient air. This decision also takes into
account (1) the PA's staff assessments of the most policy-relevant
information in the ISA and staff analyses of potential ecological
exposures and risk, upon which staff conclusions regarding appropriate
considerations in this review are based; (2) the CASAC advice and
recommendations, as reflected in discussions of drafts of the ISA and
PA at public meetings, in separate written comments, and in the CASAC's
letters to the Administrator; (3) public comments received during the
development of these documents, either in connection with CASAC
meetings or separately; and (4) public comments on the proposal.
Section III.A provides background on the general approach for the
review of the secondary NAAQS for Pb and brief summaries of key aspects
of the current body of evidence on welfare effects associated with Pb
exposures and the exposure/risk information considered in this review.
Section III.B summarizes the basis for the proposed decision and advice
from the CASAC, addresses public comments and presents the conclusions
the Administrator has drawn from a full consideration of the
information. Section III.C summarizes the Administrator's decision on
the secondary standard.
A. Introduction
As provided in the Act, the secondary standard is to ``specify a
level of air quality the attainment and maintenance of which in the
judgment of the
[[Page 71936]]
Administrator . . . is requisite to protect the public welfare from any
known or anticipated adverse effects associated with the presence of
the pollutant in the ambient air'' (CAA, section 109(b)(2)). The
secondary standard is not meant to protect against all known or
anticipated Pb-related effects, but rather those that are judged to be
adverse to the public welfare, and a bright-line determination of
adversity is not required in judging what is requisite (78 FR 3212,
January 15, 2013; 80 FR 65376, October 26, 2015). Thus, the level of
protection from known or anticipated adverse effects to public welfare
that is requisite for the secondary standard is a public welfare policy
judgment to be made by the Administrator. In exercising that judgment,
the Administrator seeks to establish standards that are neither more
nor less stringent than necessary for this purpose. This section
presents the rationale for the Administrator's decision to retain the
existing secondary NAAQS for Pb, without revision. The Administrator's
decision draws upon scientific information and analyses about welfare
effects, exposure and risks, as well as judgments about the range of
uncertainties that are inherent in the scientific evidence and
analyses. This approach is consistent with the requirements of the
NAAQS provisions of the Act.
In the last review, completed in 2008, the current secondary
standard for Pb was revised substantially, consistent with the revision
to the primary standard (73 FR 66964, November 12, 2008). The 2008
decision considered the body of evidence as assessed in the 2006 CD
(USEPA, 2006a) as well as the 2007 Staff Paper assessment of the
policy-relevant information contained in the 2006 CD and the screening-
level ecological risk assessment (2006 REA; USEPA, 2007b), the advice
and recommendations of CASAC (Henderson 2007a, 2007b, 2008a, 2008b),
and public comment. At that time, the Staff Paper concluded, based on
laboratory studies and current media concentrations in a wide range of
locations, that it seemed likely that adverse effects were occurring
from ambient air-related Pb, particularly near point sources, under the
then-current standard (73 FR 67010, November 12, 2008). Given the
limited data on Pb effects in ecosystems, and associated uncertainties,
such as those with regard to factors such as the presence of multiple
metals and historic environmental burdens, the EPA also considered the
evidence of Pb effects on organisms with regard to implications for
ecosystem effects. Taking into account the available evidence and
information on media concentrations in a wide range of locations, the
Administrator concluded that there was potential for adverse effects
occurring under the then-current standard; however there were
insufficient data to provide a quantitative basis for setting a
secondary standard different from the primary (73 FR 67011, November
12, 2008). Therefore, citing a general lack of data that would indicate
the appropriate level of Pb in environmental media that may be
associated with adverse effects, as well as the comments of the CASAC
Pb panel that a significant change to current air concentrations (e.g.,
via a significant change to the standard) was likely to have
significant beneficial effects on the magnitude of Pb exposures in the
environment, the EPA revised the secondary standard substantially,
consistent with revisions made to the primary standard (73 FR 67011,
November 12, 2008).
Building on the approach and findings in the last review, this
current review of the secondary standard considers the currently
available scientific and technical information in the context of key
policy-relevant questions. This review focuses on the consideration of
the extent to which the body of scientific evidence now available calls
into question the adequacy of the current standard. In considering the
scientific and technical information, we draw on the ecological effects
evidence presented in detail in the ISA and aspects summarized in the
PA, along with the information associated with the screening-level risk
assessment also in the PA. Thus, we have taken into account both
evidence-based and risk-based considerations pertaining to the series
of policy-relevant questions presented in the PA. These questions
generally address the extent to which we are able to characterize
effects and the likelihood of adverse effects in the environment under
the current standard. Our approach to considering this information
recognizes that the available welfare effects evidence generally
reflects laboratory-based evidence of toxicological effects on specific
organisms exposed to concentrations of Pb (ISA, section 6.5).
Additionally, it is widely recognized that environmental exposures from
atmospherically derived Pb are likely to be lower than those commonly
assessed in laboratory studies and that studies of exposures similar to
those in the environment are often accompanied by significant
confounding and modifying factors (e.g., other metals, acidification),
increasing our uncertainty about the likelihood and magnitude of
organism and ecosystem responses (ISA, Section 6.5).
1. Overview of Welfare Effects Information
Welfare effects include, but are not limited to, ``effects on
soils, water, crops, vegetation, man-made materials, animals, wildlife,
weather, visibility and climate, damage to and deterioration of
property, and hazards to transportation, as well as effects on economic
values and on personal comfort and wellbeing'' (CAA, section 302(h)).
In this section, we provide an overview of the key aspects of the
current evidence of Pb-related welfare effects that is assessed in the
ISA and the 2006 CD, drawing from the summary of policy-relevant
aspects in the PA (PA, section 5.1) and section III.B of the proposed
rulemaking (80 FR 314-317, January 5, 2015).
Lead has been demonstrated to have harmful effects on reproduction
and development, growth, and survival in many species as described in
the assessment of the evidence available in this review and consistent
with the conclusions drawn in the last review (ISA, section 1.7; 2006
CD, sections 7.1.5 and 7.2.5). A number of studies on ecological
effects of Pb are newly available in this review and are critically
assessed in the ISA as part of the full body of evidence. The full body
of currently available evidence reaffirms conclusions on the array of
effects recognized for Pb in the last review (ISA, section 1.7). In so
doing, in the context of pollutant exposures considered relevant the
ISA determines \70\ that causal \71\ or likely causal \72\
relationships exist at the individual and population level in both
[[Page 71937]]
freshwater and terrestrial ecosystems for Pb with effects on
reproduction and development in vertebrates and invertebrates; growth
in plants and invertebrates; and survival in vertebrates and
invertebrates (ISA, Table 1-3). With regard to saltwater ecosystems,
the ISA concludes that the current evidence is inadequate to make
causality determinations for most effects, while finding the evidence
to be suggestive of a linkage between Pb and effects on reproduction
and development in marine invertebrates (ISA, Table 1-3, sections
6.3.12 and 6.4.21). In drawing judgments regarding causality for the
criteria air pollutants, the ISA places emphasis on ``evidence of
effects at doses (e.g., blood Pb concentration) or exposures (e.g., air
concentrations) that are relevant to, or somewhat above, those
currently experienced by the population.'' The ISA notes that the
``extent to which studies of higher concentrations are considered
varies . . . but generally includes those with doses or exposures in
the range of one to two orders of magnitude above current or ambient
conditions.'' Studies ``that use higher doses or exposures may also be
considered . . . [t]hus, a causality determination is based on weight
of evidence evaluation for health, ecological or welfare effects,
focusing on the evidence from exposures or doses generally ranging from
current levels to one or two orders of magnitude above current levels''
(ISA, pp. lx to lxi). Although considerable uncertainties are
recognized in generalizing effects observed under particular, small-
scale conditions, up to the ecosystem level of biological organization,
the ISA also determines that a causal relationship is also likely at
higher levels of biological organization between Pb exposures and
community and ecosystem-level effects in freshwater and terrestrial
systems (ISA, section 1.7.3.7).
---------------------------------------------------------------------------
\70\ Since the last Pb NAAQS review, the ISAs, which have
replaced CDs in documenting each review of the scientific evidence
(or air quality criteria), employ a systematic framework for
weighing the evidence and describing associated conclusions with
regard to causality, using established descriptors: ``causal''
relationship with relevant exposure, ``likely'' to be a causal
relationship, evidence is ``suggestive'' of a causal relationship,
``inadequate'' evidence to infer a causal relationship, and ``not
likely'' to be a causal relationship (ISA, Preamble).
\71\ In determining that a causal relationship exists for Pb
with specific ecological or welfare effects, the EPA has concluded
that ``[e]vidence is sufficient to conclude that there is a causal
relationship with relevant pollutant exposures (i.e., doses or
exposures generally within one to two orders of magnitude of current
levels)'' (ISA, p. lxii).
\72\ In determining a likely causal relationship exists for Pb
with specific ecological or welfare effects, the EPA has concluded
that ``[e]vidence is sufficient to conclude that there is a likely
causal association with relevant pollutant exposures . . . but
uncertainties remain'' (ISA, p. lxii).
---------------------------------------------------------------------------
As in prior reviews of the Pb NAAQS, this review is focused on
those effects most pertinent to ambient air Pb exposures. Given the
reductions in ambient air Pb concentrations over the past decades,
these effects are generally those associated with the lowest levels of
Pb exposure that have been evaluated. Additionally, we recognize the
limitations on our ability to draw conclusions about environmental
exposures from ecological studies of organism-level effects, as most
studies were conducted in laboratory settings which may not accurately
represent field conditions or the multiple variables that govern
exposure.
The relationship between ambient air Pb and ecosystem response is
important in making the connection between current emissions of Pb and
the potential for adverse ecological effects. The limitations in the
data available on this subject for the last review were significant.
There is no new evidence since the last review that substantially
improves our understanding of the relationship between ambient air Pb
and measurable ecological effects. As stated in the last review, the
role of ambient air Pb in contributing to ecosystem Pb has been
declining over the past several decades. It remains difficult to
apportion exposure between air and other sources to inform our
understanding of the potential for ecosystem effects that might be
associated with air emissions (ISA, section 6.4). Further, considerable
uncertainties also remain in drawing conclusions from effects evidence
observed under laboratory conditions with regard to effects expected at
the ecosystem level in the environment (ISA, section 6.5). In summary,
the ISA concludes that ``[r]ecent information available since the 2006
Pb AQCD, includes additional field studies in both terrestrial and
aquatic ecosystems, but the connection between air concentration and
ecosystem exposure continues to be poorly characterized for Pb and the
contribution of atmospheric Pb to specific sites is not clear'' (ISA,
section 6.5).
The bioavailability of Pb is also an important component of
understanding the effects Pb is likely to have on organisms and
ecosystems (ISA, section 6.3.3, 6.4.4 and 6.4.14). It is the amount of
Pb that can interact within the organism that can lead to toxicity, and
there are many factors which govern this interaction (ISA, sections
6.2.1 and 6.3.3). The bioavailability of metals varies widely depending
on the physical, chemical, and biological conditions under which an
organism is exposed (ISA, section 6.3.3). Studies newly available since
the last Pb NAAQS review provide additional insight into factors that
influence the bioavailability of Pb to specific organisms (ISA, section
6.3.3). On the whole, the current evidence, including that newly
available in this review, supports previous conclusions regarding
environmental conditions affecting bioavailability and the associated
potential for adverse effects of Pb on organisms and ecosystems (ISA,
section 6.3.3). Looking beyond organism-level evidence, the evidence of
adversity in natural systems remains sparse due to the difficulty in
determining the effects of confounding factors such as co-occurring
metals or system characteristics that influence bioavailability of Pb
in field studies. As summarized in the ISA, ``in natural environments,
modifying factors affect Pb bioavailability and toxicity and there are
considerable uncertainties associated with generalizing effects
observed in controlled studies to effects at higher levels of
biological organization'' and ``[f]urthermore, available studies on
community and ecosystem-level effects are usually from contaminated
areas where Pb concentrations are much higher than typically
encountered in the environment'' (ISA, p. xcvi).
There is no new evidence since the last review that substantially
improves our understanding of the relationship between ambient air Pb
and measurable ecological effects beyond what was understood in the
last review. As stated in the last review, the role of ambient air Pb
in contributing to ecosystem Pb has been declining over the past
several decades. It remains difficult to apportion exposure between air
and other sources to better inform our understanding of the potential
for ecosystem effects that might be associated with air emissions. As
noted in the ISA, ``[t]he amount of Pb in ecosystems is a result of a
number of inputs and it is not currently possible to determine the
contribution of atmospherically-derived Pb from total Pb in
terrestrial, freshwater or saltwater systems'' (ISA, section 6.5).
Further, considerable uncertainties also remain in drawing conclusions
from evidence of effects observed under laboratory conditions with
regard to effects expected at the ecosystem level in the environment.
In many cases it is difficult to characterize the nature and magnitude
of effects and to quantify relationships between ambient concentrations
of Pb and ecosystem response due to the existence of multiple
stressors, variability in field conditions, and differences in Pb
bioavailability at that level of organization (ISA, section 6.5). In
summary, the ISA concludes that ``[r]ecent information available since
the 2006 Pb AQCD, includes additional field studies in both terrestrial
and aquatic ecosystems, but the connection between air concentration
and ecosystem exposure continues to be poorly characterized for Pb and
the contribution of atmospheric Pb to specific sites is not clear''
(ISA, section 6.5).
2. Overview of Risk Assessment Information
The risk assessment information available in this review and
summarized
[[Page 71938]]
here is based on the screening-level risk assessment performed for the
last review, described in the 2006 REA, 2007 Staff Paper and 2008
notice of final decision (73 FR 66964, November 12, 2008), as
considered in the context of the evidence newly available in this
review (PA, section 5.2). Careful consideration of the information
newly available in this review, with regard to designing and
implementing a full REA for this review, led us to conclude that
performance of a new REA for this review was not warranted (REA
Planning Document, section 3.3). The CASAC Pb Review Panel generally
concurred with the conclusion that a new REA was not warranted for the
secondary standard in this review (Frey, 2011b). Accordingly, the
exposure/risk information considered in this review is drawn primarily
from the 2006 REA as summarized in the PA, section 5.2 and Appendix 5A;
REA Planning Document, section 3.1.
The 2006 screening-level assessment focused on estimating the
potential for ecological risks associated with ecosystem exposures to
Pb emitted into ambient air (PA, section 5.2; 2006 REA, section 7).
Both a national-scale screen and a case study approach were used to
evaluate the potential for ecological impacts that might be associated
with atmospheric deposition of Pb (2006 REA, section 7.1.2). Detailed
descriptions of the location-specific case studies and the national
screening assessment, key findings of the risk assessment for each, and
an interpretation of the results with regard to past air quality
conditions are presented in the 2006 REA. This information, which is
outlined below, is summarized more fully in section 5.2 of the PA and
section III.C of the proposal for this review (80 FR 317-319, January
5, 2015).
In interpreting the results from the 2006 REA, the PA considers the
availability of new evidence that may inform interpretation of risk
under the now-current standard (PA, section 5.2). Factors that could
alter our interpretation of risk would include new evidence of harm at
lower concentrations of Pb, new linkages that enable us to draw more
explicit conclusions as to the air contribution of environmental
exposures, and new methods of interpreting confounding factors that
were largely uncontrolled in the previous risk assessment. In general,
however, such new evidence is limited, and the key uncertainties
identified in the last review remain today. For example, with regard to
new evidence of Pb effects at lower concentrations, it is necessary to
consider that the evidence of adversity in natural systems due
specifically to Pb is limited, in no small part because of the
difficulty in determining the effects of confounding factors such as
multiple metals and modifying factors influencing bioavailability in
field studies, as noted in section III.A.1 above. Modeling of Pb-
related exposure and risk to ecological receptors is subject to a wide
array of sources of both variability and uncertainty resulting in
differences in Pb bioavailability as well as exposure (USEPA, 2005b).
Additionally, there are also significant difficulties in quantifying
the role of air emissions under the current standard, which is
significantly lower than the previous standard. As recognized in the
PA, Pb deposited before the standard was enacted remains in soils and
sediments, complicating interpretations regarding the impact of the
current standard (PA, section 1.3.2). For example, media in ecosystems
across the U.S. are still recovering from the past period of greater
atmospheric emissions and deposition, as well as from Pb derived from
nonair sources (PA, section 1.3.2).
As summarized in the PA and proposal, we have considered what the
risk information from the 2006 REA analyses indicates regarding the
potential for adverse welfare effects to result from levels of air-
related Pb that would meet the now-current standard. The circumstances
assessed in all but one of the case study locations, however, likely
include a history of ambient air Pb concentrations that exceeded the
NAAQS. Consequently, these analyses are not considered informative for
predicting effects at the far lower concentrations associated with the
current NAAQS. The nationwide surface water screen was likewise not
particularly informative because potential confounding by both nonair
inputs and resuspension of Pb related to historic sources was not
easily accounted for. The remaining case study was a site remote from
Pb sources for which atmospheric deposition was expected to be the
primary contributor to media Pb concentrations without obvious
confounding inputs. This case study, based on a summary review of
published findings for the study site, concluded that atmospheric Pb
inputs do not directly affect stream Pb levels because deposited Pb is
almost entirely retained in the soil profile, with the soil serving as
a Pb sink, appreciably reducing pore water Pb concentrations as it
moves through the soil layers to streams. As a result, this case study
(and the publications on which it was based) concluded that the
contribution of dissolved Pb from soils to streams was insignificant
(2006 REA, Appendix E). Additionally, we note that the 2006 CD, in
considering the findings for this site and other terrestrial sites with
Pb burdens derived primarily from long-range atmospheric transport,
found that ``[d]espite years of elevated atmospheric Pb inputs and
elevated concentrations in soils, there is little evidence that sites
affected primarily by long-range Pb transport have experienced
significant effects on ecosystem structure or function'' (2006 CD, p.
AX7-98). The PA and proposal concluded that this information suggests
that the now-lower ambient air concentrations associated with meeting
the current standard would not be expected to directly impact stream Pb
levels (PA, p. 6-10; 80 FR 319, January 5, 2015).
C. Conclusions on the Secondary Standard
1. Basis for the Proposed Decision
The basis for the proposed decision, which is described in section
III.D of the proposal, is very briefly summarized here. In considering
the welfare effects evidence and risk-based information with respect to
the adequacy of the current secondary standard, the Administrator
considered the array of evidence newly assessed in the ISA with regard
to the degree to which this evidence supports conclusions about the
effects of Pb in the environment that were drawn in the last review and
the extent to which it reduces previously recognized areas of
uncertainty. Further, she considered the current evidence and
associated conclusions about the potential for effects to occur as a
result of the much lower ambient Pb concentrations allowed by the
current secondary standard (set in 2008) than those allowed by the
prior standard, which was the focus of the last review. These
considerations informed the Administrator's proposed decision to retain
the current standard.
With regard to the evidence, the proposal noted there is very
limited evidence to relate specific ecosystem effects with current
ambient air concentrations of Pb through deposition to terrestrial and
aquatic ecosystems and subsequent movement of deposited Pb through the
environment (e.g., soil, sediment, water, organisms). The potential for
ecosystem effects of Pb from atmospheric sources under conditions
meeting the current standard is difficult to assess due to limitations
on the availability of information to fully characterize the
distribution of Pb from the atmosphere into ecosystems over the long
term, as well as limitations
[[Page 71939]]
on information on the bioavailability of atmospherically deposited Pb
(as affected by the specific characteristics of the receiving
ecosystem). Therefore, while there are newly available field studies in
this review, ``the connection between air concentration and ecosystem
exposure and associated potential for welfare effects continues to be
poorly characterized for Pb'' (ISA, section 6.4). Such a connection is
even harder to characterize with respect to the current standard than
it was in the last review with respect to the previous, much higher
standard.
With regard to the currently available risk and exposure
information, which continues to be sufficient to conclude that the 1978
standard was not providing adequate protection to ecosystems, the
proposal concluded that, when considered with regard to air-related
ecosystem exposures likely to occur with air Pb levels that just meet
the now-current standard, this current information also does not
provide evidence of adverse effects under the current standard.
Accordingly, in consideration of the risk information in combination
with the current evidence and the associated data gaps and
uncertainties, the Administrator proposed that the current standards be
retained, without revision.
2. CASAC Advice in This Review
In its review of the draft PA, the CASAC agreed with staff's
preliminary conclusions that the available information since the last
review is not sufficient to warrant revision to the secondary standard
(Frey, 2013b). On this subject, the CASAC letter said that ``[o]verall,
the CASAC concurs with the EPA that the current scientific literature
does not support a revision to the . . . Secondary Pb NAAQS'' (Frey,
2013b, p. 1). It additionally stated that ``[g]iven the existing
scientific data, the CASAC concurs with retaining the current secondary
standard without revision'' (Frey, 2013b, p. 2). The CASAC additionally
noted areas for additional research to address data gaps and
uncertainties (Frey, 2013b, p. 2).
3. Comments on the Proposed Decision
All of the public comments on the proposed decision to retain the
current secondary standard, without revision, indicated support. These
commenters include the NACAA, as well as both of the state agencies and
nearly all of the industry organizations that submitted comments. Only
a small subset of this group provided rationales for their concurrence
with EPA's proposed decision. These commenters emphasized limitations
and uncertainties in the welfare effects evidence, including
particularly those with regard to relationships between ambient air Pb
concentrations, levels of deposition, ecosystem exposures, and adverse
public welfare effects. One commenter also noted the CASAC's
concurrence with the EPA conclusion that the current evidence does not
support revision to the standard, and that information newly available
in this review does not substantially improve our understanding in the
identified areas of uncertainty or that would indicate that the current
standard is inadequate. The EPA generally agrees with these commenters
and with the CASAC regarding the adequacy of the current secondary
standard and the lack of support for revision of the standard.
4. Administrator's Conclusions
Based on the evidence and risk assessment information that is
available in this review concerning the ecological effects and
potential public welfare impacts of Pb emitted into ambient air, the
Administrator concludes that the current secondary standard provides
the requisite protection of public welfare from adverse effects and
should be retained. In considering the adequacy of the current
standard, the Administrator has considered the assessment of the
available evidence and conclusions contained in the ISA; the staff
assessment of and conclusions regarding the policy-relevant technical
information, including screening-level risk information, presented in
the PA; the advice and recommendations from CASAC; and public comments.
In reaching her decision, the Administrator gives weight to the PA
conclusions, with which CASAC has concurred, and takes note of key
aspects of the rationale presented for those conclusions which
contribute to her decision.
As she did in reaching her proposed decision, the Administrator
notes that the body of evidence on the ecological effects of Pb,
expanded in some aspects since the last review, continues to support
identification of ecological effects in organisms relating to growth,
reproduction, and survival as the most relevant endpoints associated
with Pb exposure. In consideration of the appreciable influence of
site-specific environmental characteristics on the bioavailability and
toxicity of environmental Pb in our assessment, there is a lack of
studies conducted under conditions closely reflecting the natural
environment. The currently available evidence, while somewhat expanded
since the last review, does not include evidence of significant effects
at lower concentrations or evidence of higher-level ecosystem effects
beyond those reported in the last review. There continue to be
significant difficulties in relating effects evidence from laboratory
studies to the natural environment and linking those effects to ambient
air Pb concentrations. Further, as the proposal and the PA note, the
EPA is aware of no new critical loads information that would inform our
interpretation of the public welfare significance of the effects of Pb
in various U.S. ecosystems (PA, section 5.1). In summary, while new
research has added to the understanding of Pb biogeochemistry and
expanded the list of organisms for which Pb effects have been
described, there remains a significant lack of knowledge about the
potential for adverse effects on public welfare from ambient air Pb in
the environment and the exposures that occur from such air-derived Pb,
particularly under conditions meeting the current standard (PA, section
6.2.1). Thus, the scientific evidence presented in detail and assessed
in the ISA, inclusive of that newly available in this review, is not
substantively changed, most particularly with regard to the adequacy of
the now-current standard, from the information that was previously
available and supported the decision for revision in the last review
(PA, section 6.2.1).
With respect to exposure/risk-based considerations identified in
the PA, the Administrator notes the complexity of interpreting the
previous risk assessment with regard to the ecological risk of ambient
air Pb associated with conditions meeting the current standard and the
associated limitations and uncertainties of such assessments. The
Administrator additionally takes note that the previous assessment is
consistent with and generally supportive of the evidence-based
conclusions about Pb in the environment, yet the limitations on our
ability to apportion Pb between past and present air contributions and
between air and nonair sources remain significant.
In summary, based on the considerations summarized above, the
Administrator judges that the information available in this review of
the Pb secondary standard, including the currently available welfare
effects evidence and exposure/risk information, does not call into
question the adequacy of the current standard to provide the requisite
protection for public welfare (PA, section 6.3). In so doing, she also
notes the advice from CASAC in this review, including that ``[g]iven
the existing scientific data, the CASAC concurs with retaining the
current secondary standard without revision.''
[[Page 71940]]
Thus, the Administrator concludes that the current standard is
requisite and should be retained.
C. Decision on the Secondary Standard
For the reasons discussed above, and taking into account
information and assessments presented in the ISA and PA, the advice
from CASAC, and consideration of public comments, the Administrator
concludes that the current secondary standard for Pb is requisite to
protect public welfare from known or anticipated adverse effects and is
retaining the standard without revision.
IV. Statutory and Executive Order Reviews
Additional information about these statutes and Executive Orders
can be found at http://www2.epa.gov/laws-regulations/laws-and-executive-orders.
A. Executive Order 12866: Regulatory Planning and Review and Executive
Order 13563: Improving Regulation and Regulatory Review
This action is not a significant regulatory action and was,
therefore, not submitted to the Office of Management and Budget for
review.
B. Paperwork Reduction Act (PRA)
This action does not impose an information collection burden under
the PRA. There are no information collection requirements directly
associated with revisions to a NAAQS under section 109 of the CAA and
this action does not make any revisions to the NAAQS.
C. Regulatory Flexibility Act (RFA)
I certify that this action will not have a significant economic
impact on a substantial number of small entities under the RFA. This
action will not impose any requirements on small entities. Rather, this
action retains, without revision, existing national standards for
allowable concentrations of Pb in ambient air as required by section
109 of the CAA. See also American Trucking Associations v. EPA. 175
F.3d at 1044-45 (NAAQS do not have significant impacts upon small
entities because NAAQS themselves impose no regulations upon small
entities).
D. Unfunded Mandates Reform Act (UMRA)
This action does not contain any unfunded mandate as described in
the UMRA, 2 U.S.C. 1531-1538 and does not significantly or uniquely
affect small governments. This action imposes no enforceable duty on
any state, local or tribal governments or the private sector.
E. Executive Order 13132: Federalism
This action does not have federalism implications. It will not have
substantial direct effects on the states, on the relationship between
the national government and the states, or on the distribution of power
and responsibilities among the various levels of government.
F. Executive Order 13175: Consultation and Coordination With Indian
Tribal Governments
This action does not have tribal implications as specified in
Executive Order 13175. It does not have a substantial direct effect on
one or more Indian tribes. This action does not change existing
regulations; it retains the current NAAQS for Pb, without revision. The
NAAQS protect public health, including the health of at-risk or
sensitive groups, with an adequate margin of safety and protect public
welfare from known or anticipated adverse effects. Executive Order
13175 does not apply to this action.
G. Executive Order 13045: Protection of Children From Environmental
Health and Safety Risks
This action is not subject to Executive Order 13045 because it is
not economically significant as defined in Executive Order 12866. We
note, however, that the primary standard retained with this action
provides protection for children and other at-risk populations against
an array of adverse health effects, most notably including nervous
system effects in children. The health effects evidence and risk
assessment information for this action, which focuses on children, is
summarized in sections II.A.2, II.A.3 and II.A.4, and described in the
ISA and PA, copies of which are in the public docket for this action.
H. Executive Order 13211: Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution, or Use
This action is not subject to Executive Order 13211, because it is
not a significant regulatory action under Executive Order 12866.
I. National Technology Transfer and Advancement Act
This action does not involve technical standards.
J. Executive Order 12898: Federal Actions To Address Environmental
Justice in Minority Populations and Low-Income Populations
The EPA believes that this action does not have disproportionately
high and adverse human health or environmental effects on minority
populations, low-income populations and/or indigenous peoples as
specified in Executive Order 12898 (59 FR 7629, February 16, 1994). The
action described in this document is to retain, without revision, the
existing NAAQS for Pb.
The NAAQS decisions are based on an explicit and comprehensive
assessment of the current scientific evidence and associated exposure/
risk analyses. More specifically, the EPA expressly considers the
available information regarding health effects among at-risk
populations, including that available for low-income populations and
minority populations, in decisions on the primary (health-based) NAAQS.
Where low-income populations or minority populations are among the at-
risk populations, the decision on the standard is based on providing
protection for these and other at-risk populations and lifestages.
Where such populations are not identified as at-risk populations, NAAQS
that are established to provide protection to the at-risk populations
would also be expected to provide protection to all other populations,
including low-income populations and minority populations.
As discussed in sections II.A.2.d and II.B above, and in sections
II.A and II.B of the proposal, the EPA expressly considered the
available information regarding health effects among at-risk
populations in reaching the decision that the existing primary (health-
based) standard for Pb is requisite. The ISA and PA for this review,
which include identification of populations at risk from Pb health
effects, are available in the docket, EPA-HQ-OAR-2010-0108. Based on
consideration of this information and the full evidence base,
quantitative exposure/risk analyses, advice from the CASAC and
consideration of public comments, the Administrator concludes that the
existing NAAQS for Pb protect public health, including the health of
at-risk or sensitive groups, with an adequate margin of safety and
protect public welfare from known or anticipated adverse effects (as
discussed in sections II.B.4 and III.B.4 above).
K. Determination Under Section 307(d)
Section 307(d)(1)(V) of the CAA provides that the provisions of
section
[[Page 71941]]
307(d) apply to ``such other actions as the Administrator may
determine.'' Pursuant to section 307(d)(1)(V), the Administrator
determines that this action is subject to the provisions of section
307(d).
L. Congressional Review Act
The EPA will submit a rule report to each House of the Congress and
to the Comptroller General of the U.S. This action is not a ``major
rule'' as defined by 5 U.S.C. 804(2).
References
Advisory Committee on Childhood Lead Poisoning Prevention (ACCLPP).
(2012). Low Level Lead Exposure Harms Children: A Renewed Call for
Primary Prevention. Report of the Advisory Committee on Childhood
Lead Poisoning Prevention of the Centers for Disease Control and
Prevention. January 4, 2012. Available at: http://www.cdc.gov/nceh/lead/ACCLPP/blood_lead_levels.htm.
Alliance to End Childhood Lead Poisoning. (1991). The First
Comprehensive National Conference: Final Report. October 6,7,8,
1991.
Bellinger, D. (2008). Email message to Jee-Young Kim, U.S. EPA.
February 13, 2008. Docket document number EPA-HQ-OAR-2010-0108-0031.
Bellinger, D.; Leviton, A.; Sloman, J. (1990). Antecedents and
correlates of improved cognitive performance in children exposed in
utero to low levels of lead. Environ Persp 89: 5-11.
Bellinger, D.; Leviton, A.; Waternaux, C.; Needleman, H.;
Rabinowitz, M. (1988). Low-level lead exposure, social class, and
infant development. Neurotoxicol. Teratol. 10: 497-503. {This
journal issue is dated November-December 1988, while the date in the
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List of Subjects in 40 CFR Part 50
Environmental protection, Air pollution control, Carbon monoxide,
Lead, Nitrogen dioxide, Ozone, Particulate matter, Sulfur oxides.
Dated: September 16, 2016.
Gina McCarthy,
Administrator.
[FR Doc. 2016-23153 Filed 10-17-16; 8:45 am]
BILLING CODE 6560-50-P