[Federal Register Volume 59, Number 158 (Wednesday, August 17, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-18941]
[[Page Unknown]]
[Federal Register: August 17, 1994]
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ENVIRONMENTAL PROTECTION AGENCY
[FRL-5027-1]
Fuels and Fuel Additives; Waiver Decision/Circuit Court Remand
AGENCY: Environmental Protection Agency (EPA).
ACTION: Notice
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SUMMARY: On July 12, 1991, under section 211(f)(4) of the Clean Air Act
(Act), the Ethyl Corporation (Ethyl) requested a waiver to permit the
sale of its gasoline additive, methylcyclopentadienyl manganese
tricarbonyl (MMT), an octane enhancer commercially labeled by Ethyl as
HiTEC 3000, for use in unleaded gasoline. The Administrator of EPA
denied Ethyl's application for a waiver on January 8, 1992, based
primarily on concerns regarding the potential for increases in
hydrocarbon emissions resulting from MMT use. Ethyl subsequently sought
judicial review of that decision in the U.S. Court of Appeals for the
District of Columbia Circuit. Based on new emissions data developed and
submitted to EPA by Ethyl, EPA requested that the Court of Appeals
remand Ethyl's application to the Agency for further action.
On November 30, 1993, the Administrator of EPA found that Ethyl had
met its burden to demonstrate under section 211(f)(4) that approval of
its remanded application would not cause or contribute to a failure to
meet emission standards. Ethyl agreed to resubmit its application at
that time, thereby affording further time for the Agency to consider
the issue of potential health effects associated with use of MMT in
unleaded gasoline. Ethyl and EPA later agreed to further extend the
deadline for final action on Ethyl's application to July 13, 1994. The
Agency is today denying Ethyl's request for a waiver for HiTEC 3000
based on unresolved concerns regarding the potential impact of
manganese emissions resulting from MMT use on public health.
ADDRESSES: Copies of the information relative to this application are
available for inspection in public docket A-93-26, A-91-46 and A-90-16
at the Air Docket (LE-131) of the EPA, Room M-1500, 401 M Street, S.W.,
Washington, D.C. 20460, (202) 260-7548, between the hours of 8:30 a.m.
to noon and 1:30 p.m. to 3:30 p.m. weekdays. As provided in 40 CFR Part
2, a reasonable fee may be charged for copying services.
FOR FURTHER INFORMATION CONTACT: Joseph R. Sopata, Chemist, or James W.
Caldwell, Chief, Fuels Section, Field Operations Support Division
(6406J), U.S. Environmental Protection Agency, 401 M Street, S.W.,
Washington, D.C. 20460, (202) 260-2635.
SUPPLEMENTARY INFORMATION:
Index
I. Background
II. Statutory Framework
A. History of Statute
B. Two Stage Process
C. Consideration of Potential Health Effects
III. Method of Review
A. ``Causes or Contributes'' to Emission Standard Failure
B. Discretionary Review
IV. Analysis of Emissions Data
A. Description of Previous Test Programs
B. Comments on Vehicle Emissions Issues
C. Available Data Meet Previously Utilized Criteria
D. Data on Newer-Technology Vehicles Meet More Stringent
Criteria
E. Finding
V. The Onboard Diagnostics Issue
VI. Manganese Health Assessment
A. Introduction
B. Health Effects Assessment
1. Background
2. Earlier Assessments
3. 1993 Revised RfC
4. Alternative Approaches to Deriving RfCs
a. Conventional NOAEL- or LOAEL-Based Approach
b. NOSTASOT Approach
c. Benchmark Analyses
d. Bayesian Analyses
e. Summary of RfC Estimates
C. Exposure Assessment
1. Background
2. Additional Canadian Studies
3. The PTEAM Study
4. Estimated Mn Exposure Levels Associated with MMT
D. Risk Characterization
E. References
F. Comments on Health Assessment and EPA Response
VII. Fuel and Fuel Additive Registration and Research Needs
VIII. Other Issues
IX. Decision
I. Background
Section 211(f)(1)(A) of the Act makes it unlawful, effective March
31, 1977, for any manufacturer of a fuel or fuel additive to first
introduce into commerce, or to increase the concentration in use of,
any fuel or fuel additive for use in light-duty motor vehicles
manufactured after model year 1974 which is not substantially similar
to any fuel or fuel additive utilized in the certification of any model
year 1975, or subsequent model year, vehicle or engine under section
206 of the Act. An interpretive rule defining the term ``substantially
similar'' under section 211(f)(1)(A) was promulgated for unleaded
gasoline at 46 FR 38582 (July 28, 1981), and revised at 56 FR 5352
(February 11, 1991). Section 211(f)(1)(B) of the Act makes it unlawful,
effective November 15, 1990, for any manufacturer of a fuel or fuel
additive to first introduce into commerce, or to increase the
concentration in use of, any fuel or fuel additive for use by any
person in motor vehicles manufactured after model-year 1974 which is
not substantially similar to any fuel or fuel additive utilized in the
certification of any model year 1975, or subsequent model year, vehicle
or engine under section 206 of the Act. Thus, section 211(f)(1)(B)
expands the prohibitions of 211(f)(1)(A), which apply only to light-
duty vehicles.
Section 211(f)(4) of the Act provides that upon application by any
fuel or fuel additive manufacturer, the Administrator of EPA may waive
the prohibitions of section 211(f)(1) if the Administrator determines
that the applicant has established that such fuel or fuel additive will
not cause or contribute to a failure of any emission control device or
system (over the useful life of any vehicle in which such device or
system is used) to achieve compliance by the vehicle with the emissions
standards to which it has been certified pursuant to section 206 of the
Act. If the Administrator does not act to grant or deny a waiver within
180 days of receipt of the application, the statute provides that the
waiver shall be treated as granted. The subject of this notice is an
application by Ethyl under section 211(f)(4) of the Act for a waiver
for the fuel additive methylcyclopentadienyl manganese tricarbonyl
(MMT), commercially labeled by Ethyl as HiTEC 3000, to be blended in
unleaded gasoline resulting in a level of 0.03125 (1/32) gram per
gallon manganese (gpg Mn).
This Agency action is a reconsideration of Ethyl's fourth
application for a waiver for MMT. Ethyl's first application was
submitted on March 17, 1978 for concentrations of MMT resulting in 1/16
and 1/32 gpg Mn in unleaded gasoline. Ethyl's second application was
submitted on May 26, 1981 for concentrations of MMT resulting in 1/64
gpg Mn in unleaded gasoline. The Administrator denied these requests
for waivers due to concerns regarding increases in exhaust hydrocarbon
emissions resulting from MMT use. The decisions and justifications
thereof may be found in the September 18, 1978 Federal Register, 43 FR
41424, and the December 1, 1981 Federal Register, 46 FR 58630. Ethyl's
third application was submitted on May 9, 1990, for concentrations of
MMT resulting in a level of 0.3125 (1/32) gpg Mn in unleaded gasoline
(the same levels which are requested in the application which is the
subject of today's notice). Ethyl withdrew its third application on
November 1, 1990, before the deadline for the Administrator to make a
determination on the application. Because no determination had been
made at the time Ethyl withdrew that application, EPA accepted the
withdrawal and immediately terminated the proceeding without action on
the application.
Ethyl's fourth application was submitted on July 12, 1991. This
application was, from a practical standpoint, an extension of the third
application, the entire record of which was incorporated by Ethyl into
the current proceeding. On January 8, 1992, the Administrator of EPA
denied Ethyl's fourth application for a waiver (57 FR 2535, January 22,
1992). The application was denied based in part upon data submitted by
Ford Motor Company (Ford) which indicated that, for the model groups
tested by Ford and, for the conditions under which Ford tested its
vehicles, the increases in hydrocarbon exhaust emissions as a result of
the use of MMT were substantially greater than those observed in the
Ethyl test program. The Agency stated in its decision that a likely
factor which might account for the differences observed between the
Ethyl and Ford test programs was the severity of the driving cycle.
However, the Agency also concluded that other factors might be
responsible for the observed differences. In the denial decision, the
Agency stated that it had always accepted data from test programs which
``model'' the fleet in support of waiver applications, but that if an
interested party were to present data indicating that a potentially
significant subset of the fleet, not tested by the applicant, was
especially susceptible to the negative effects of the additive, the
Agency could reasonably require specific testing on representative
models of that sub-fleet.
In its decision, the Agency also stated that it believes it is
reasonable to consider the effect of a fuel on vehicles' ability to
meet future emissions standards. (The ``Tier I'' tailpipe standards
prescribed by section 202(g) of the Act began to take effect in model
year 1994, which began approximately in September 1993.\1\) Therefore,
regarding the Ford data mentioned above, the Agency stated in its
decision that the concerns raised by that data related to both current
and future standards.
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\1\56 FR 25724-25790 (June 5, 1991).
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Although not the basis of the 1992 denial, another important issue
arose during the consideration of Ethyl's third and fourth
applications. The Agency, as well as several commentors, expressed
concerns regarding the possible adverse health effects of an increase
in airborne manganese resulting from MMT use. These concerns were
centered around: (1) The known severe neurotoxic effects of high-level
exposure to manganese through inhalation, (2) the lack of data
regarding the chronic effects of low-level inhalation exposure to
manganese in humans, and (3) the lack of knowledge regarding potential
exposures due to MMT use. It was repeatedly pointed out by commenters
that neurotoxic damage could occur prior to the onset of overt
symptoms.
In those proceedings, Ethyl also submitted comments regarding
manganese emissions. Ethyl indicated that the manganese emissions
resulting from the use of MMT in unleaded gasoline would be so small as
to not materially affect human exposure to airborne manganese. In
support of its view, Ethyl submitted analyses and data on exposure
modeling and monitoring in both its 1990 and 1991 applications (and in
subsequent submissions associated with the remand discussed below).
(The issue of manganese emissions and public health is discussed in
more detail in Section VI of this document.)
During EPA's consideration of the 1990 Ethyl submission, EPA's
Office of Research and Development (ORD) conducted a manganese
inhalation risk assessment based on the available data which found that
because of ``the considerable uncertainties and data gaps in the
available information * * * it is not possible * * * to conclude
definitively that the increased use of MMT as a fuel additive will (or
will not) increase public health risk.''\2\ (EPA also investigated
potential hazards associated with water contamination resulting from
accidental spills or leakages of pure MMT and concluded that spills or
leaks, if they occurred, are likely to be contained and therefore would
not pose a human health risk due to groundwater contamination. However,
data available to EPA are insufficient to determine whether spills and
leaks could affect exposure to benthic organisms.)
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\2\See ``Comments on the Use of Methylcyclopentadienyl Manganese
Tricarbonyl in Unleaded Gasoline'', Docket A-90-16.
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Additionally, in order to obtain assistance in describing
information needed to improve its manganese health risk assessment (and
also to improve its environmental hazard identification of issues
associated with MMT itself), EPA, in conjunction with the National
Institute of Environmental Health Sciences, conducted a Manganese/MMT
Symposium and Workshop on March 12-15, 1991. The conference allowed the
Agency to solicit scientific information from invited extramural
scientists reflecting a wide range of scientific disciplines. Invited
participants included representatives of Ethyl Corporation, the
Environmental Defense Fund, the Centers for Disease Control, the U.S.
Food and Drug Administration and Environment Canada. A summary of the
workshop discussions was provided to each participant and the
information obtained from this meeting was also used by EPA to prepare
a report on prioritized research needed for improving its manganese
inhalation risk assessment.\3\
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\3\Preuss, P.W. (1991) ORD Document on Information Needed to
Improve the Risk Characterization of Manganese Tetraoxide
(Mn3O4) and Methylcyclopentadienyl Manganese Tricarbonyl,
December 12, 1991 (memorandum to Richard Wilson). Washington, DC:
U.S. Environmental Protection Agency, Office of Research and
Development; December 16, 1991. For further information the reader
is referred to Air Docket A-93-26, II-A-16.
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EPA raised the issue of potential health effects associated with
manganese exposure as a concern in its January 1992 denial, but did not
base its decision on this concern because the Agency concluded that the
uncertainties regarding hydrocarbon emissions increases prevented EPA
from making the requisite ``cause or contribute'' determination
concerning effects on regulated emissions.
On February 13, 1992, Ethyl filed a petition for review of the
January 8, 1992 waiver denial decision in the United States Court of
Appeals for the District of Columbia Circuit. EPA and Ethyl
subsequently entered discussions concerning a possible settlement of
the court case. In the context of those discussions, Ethyl submitted to
the Agency new emissions test data developed by Ethyl since the denial
decision.
Based on its inspection and analysis of the new Ethyl data, EPA
tentatively concluded that the data indicated that driving cycle did
not contribute significantly to MMT-induced increases in HC emissions.
(EPA's preliminary analysis was placed in docket A-92-41.) However, in
addition to addressing the issue of driving cycle, the Ethyl data
appeared to confirm the finding by Ford that 1991 Escorts experienced a
much higher MMT-induced HC increase than that observed in other models
tested (either in Ethyl's new program or in the original Ethyl test
program). The Agency remained concerned that these data might indicate
that certain engine and emissions control system configurations are
more vulnerable to a MMT-induced emissions increase irrespective of
driving cycle.
To facilitate further settlement discussions with Ethyl, EPA
decided to attempt to formulate an emission testing program intended to
address in a timely manner specific unresolved issues concerning the
effect of MMT on emissions: (1) whether other vehicles utilizing fuels
containing MMT are likely to experience increases in hydrocarbon
emissions similar to those observed in 1991 Ford Escorts; and (2)
whether fuels containing MMT have significant adverse effects on
emissions from vehicles utilizing the technologies most likely to be
employed to meet future standards. On October 28, 1992, EPA held a
public workshop to assist the Agency in its attempt to formulate such
an emission testing program (57 FR 44740, September 29, 1992). In
particular, EPA hoped to obtain information and assistance from
technical experts outside of the Agency concerning the test program
and, in view of the significance of any future waiver decision
concerning MMT for the auto industry and the general public, EPA was
interested in obtaining comments concerning a decisional framework
designed to address and resolve these issues. A proposed emission test
program developed by the Agency and presented at the public workshop,
was effectively adopted by Ethyl as its most recent vehicle emissions
test program involving the 1993 model fleet.
Although further settlement discussions between Ethyl and EPA were
held subsequent to the public workshop, the parties were not successful
in reaching a settlement. However, despite the failure of the parties
to reach agreement, EPA concluded that the Administrator's denial
decision should be reconsidered in light of the new emissions data
generated by Ethyl subsequent to the decision. Accordingly, EPA
requested that the United States Court of Appeals for the District of
Columbia remand the denial decision to EPA for reconsideration.
On April 6, 1993, the Court of Appeals issued a decision granting
the Agency's motion and remanding the case to the Agency to redetermine
within 180 days whether to grant or deny Ethyl's application. The
mandate implementing this judgement was transmitted to the Agency on
June 3, 1993. Pursuant to the court's remand decision, the Agency
published a notice indicating the commencement of a comment period (58
FR 35950, July 2, 1993). The Administrator's final decision on remand
was due within 180 days after the transmittal of the court's mandate,
or by November 30, 1993.
After the Court of Appeals granted the Agency's motion to remand
the denial decision concerning Ethyl's July 12, 1991 application, Ethyl
submitted to EPA a substantial amount of additional data on emission
testing with fuels containing MMT. (Specific aspects of these data are
discussed below in Section IV of this document).
During the course of the remand of Ethyl's waiver application, the
EPA Office of Research and Development (ORD) reviewed the available
data concerning the health effects associated with inhalation of
manganese as part of a process to revise the reference concentration
(RfC) for inhaled manganese.\4\ An inhalation reference concentration
is defined as an estimate (with uncertainty spanning perhaps an order
of magnitude) of a continuous inhalation exposure to the human
population (including sensitive subgroups) that is likely to be without
appreciable risk of deleterious non-cancer health effects during a
lifetime. The methodology for establishing an RfC accounts for
uncertainties and gaps in the health data base through the assignment
of uncertainty factors. In November, 1993, ORD completed preparation
and review of, and EPA released to Ethyl, a document identifying and
describing the rationale for a new inhalation RfC of 0.05 ug/m\3\ for
manganese and manganese compounds.
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\4\In 1990, an inhalation reference concentration (RfC) for
manganese of 0.4 ug/m\3\ was verified and placed on IRIS. The
original RfC for manganese figured into a 1990 risk assessment of
MMT prepared by the EPA Office of Research and Development (ORD).
Subsequently, in light of new information submitted by Ethyl and new
results from more recently published studies concerning manganese
inhalation health effects in workers, EPA reexamined the RfC for
manganese and revised it to a value of 0.05 ug/m\3\ in 1993. This
revised RfC for manganese was made available to Ethyl and placed on
IRIS in November 1993.
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Ethyl subsequently provided to EPA a detailed critique of the
approach utilized to derive the revised manganese RfC. Among other
things, Ethyl argued that EPA used an inappropriate procedure to derive
the RfC from a study of occupational manganese exposures by Roels, et
al. (1992). Ethyl also argued that use of MMT would not result in
significant changes in background manganese exposures, and that the
favorable effects on public health resulting from changes in the
composition of gasoline when MMT is utilized would outweigh any
potential for adverse health effects. (Copies of documents describing
the revised RfC and of the Ethyl comments are available in the public
docket.)
As the deadline of November 30, 1993, for final action by EPA on
Ethyl's waiver application approached, EPA concluded that the extensive
data base on the emission effects of MMT assembled by Ethyl and others
during the consideration of the application was sufficient to permit a
decision concerning whether Ethyl had satisfied the statutory
requirement to show that use of MMT will not cause or contribute to
exceedence of emission standards. However, there had been insufficient
opportunity for public comment concerning the use of a revised
manganese inhalation RfC in assessing any risks that might be posed by
granting Ethyl's application. Ethyl argued that it had not been
afforded an adequate opportunity to study the derivation of the RfC and
to comment on its implications for Ethyl's application. While EPA
scientists did not necessarily agree with the specific technical
arguments concerning the revised RfC and other issues pertaining to
health effects made by Ethyl, EPA concluded that it might be useful to
review the revised RfC in light of further analyses of the available
data as well as the underlying data from occupational studies of
inhaled manganese if such data could be readily obtained. EPA also
concluded that it would be desirable in any case to have further
dialogue with Ethyl and other interested parties on issues related to
the health effects of manganese before EPA was to make a final decision
concerning Ethyl's waiver application.
As a result of these factors, Ethyl and EPA entered into
discussions concerning a possible extension of the deadline for a
decision. Ultimately, an agreement between Ethyl and EPA concerning
such an extension was implemented on November 30, 1993, and notice of
the agreement was published in the Federal Register on December 9, 1993
(58 FR 64761). The agreement provided for an extension of 180 days in
the deadline for final action by EPA on Ethyl's waiver application for
HiTEC 3000.\5\ EPA was thus required to take final action either
granting or denying Ethyl's resubmitted application by May 29, 1994.
For purposes of the resubmitted application, the EPA Administrator
determined that Ethyl had demonstrated, as required by section
211(f)(4), that use of HiTEC 3000 at the specified concentration will
not cause or contribute to a failure of any emission control device or
system (over the useful life of any vehicle in which such device or
system is used) to achieve compliance by the vehicle with the emission
standards with respect to which it has been certified.\6\ The Agency
stated clearly in the December 9, 1993 Federal Register notice that
this determination would not preclude any subsequent regulatory action
based on emission effects under Clean Air Act section 211(c) or any
other provision of the Clean Air Act in the event that the resubmitted
Ethyl waiver application were to be granted in the future. The Agency
also made it clear that this determination would not apply in the
context of any other new waiver application concerning HiTEC 3000 or
MMT which might be submitted in the future if EPA were to deny Ethyl's
resubmitted waiver application on other grounds. Further review of
Ethyl's application during this 180 day period focused in particular on
the issues relating to the potential health effects on public health if
EPA were to permit use of MMT as a fuel additive.
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\5\To implement this agreement, Ethyl withdrew its July 12, 1991
waiver application, as remanded by the Court of Appeals, and
immediately resubmitted the application.
\6\As is explained in section IV of this document, this decision
was based primarily upon application of the previously used
statistical tests to the submitted emissions data. As is also
explained in section IV, the Agency believes that these tests may be
outdated and is considering a formal change in its method of
analysis of such data.
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Ethyl and EPA both desired and intended to assure continuity
between the proceedings concerning the July 12, 1991 waiver
application, as remanded to EPA by the Court of Appeals, and Ethyl's
resubmitted waiver application. The entire administrative record
compiled by EPA in support of the original denial decision, as well as
all submissions to the public docket concerning the remanded
application, was incorporated in the record this final decision on the
resubmitted application. The docket number for the resubmitted waiver
application also remained the same.
The additional 180 days that were provided by Ethyl's agreement to
resubmit the waiver application were utilized by EPA to evaluate
remaining issues that may have been relevant to today's decision. In
particular, EPA continued to examine the effects on public health that
might be associated with approval of Ethyl's application. EPA
considered any additional underlying data concerning studies of
occupational manganese exposure that were obtained by or submitted to
EPA, as well as any additional data or information pertaining to the
health effects of manganese submitted by Ethyl or other interested
persons during the comment period. Any additional information that was
submitted was also considered in exploring alternative candidate RfC
estimates and their relationship to the verified revised RfC. EPA also
used the additional time provided by the extension to make a decision
on how the RfC should be utilized in assessing health effects that may
be associated with MMT use, evaluate potential exposure to manganese
compounds associated with MMT use, complete a risk assessment
concerning Ethyl's application, and decide what additional data, if
any, should be provided by Ethyl either before or after MMT is
introduced into the market.
On April 28, 1994, EPA provided Ethyl Corporation with a draft of
the revised risk assessment, which updated the 1991 ORD assessment and
incorporated further analyses performed during the 180-day extension
period. Subsequent to providing Ethyl with this draft, Ethyl provided
EPA with comments on the draft and some additional new data on ambient
manganese concentrations in several Canadian cities. In order to allow
the Agency time to consider this new data, Ethyl requested, and the
Agency agreed to, an extension of the decision deadline until July 13,
1994. An agreement implementing this extension was executed by EPA and
Ethyl counsel on May 24, 1994.
II. Statutory Framework
A. History of Statute
Congress first added section 211(f) to the Clean Air Act in 1977
based primarily on concerns that fuels or additives might damage
vehicle emission control devices. Thus, the original statute focused on
vehicles designed to use unleaded gasoline, prohibiting the general use
in fuels of materials not ``substantially similar'' to fuels used to
certify vehicles to emissions standards. Section 211(f) also provided
that the Administrator of EPA ``may waive the prohibitions * * * if he
determines that the applicant has established that such fuel or fuel
additive * * * will not cause or contribute to a failure of any
emission control device or system * * * to achieve compliance by the
vehicle with the emission standards with respect to which it has been
certified pursuant to section 206.''\7\ Additionally, the statute
provides that if the Administrator does not act to grant or deny the
waiver request within 180 days of receipt of the application, the
waiver request shall be treated as granted.
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\7\Section 206 of the Act sets forth the certification
requirements with which vehicle manufacturers must comply in order
to introduce into commerce new model year motor vehicles. Under
Sec. 202 of the Act, standards for hydrocarbon (HC), carbon monoxide
(CO), and oxides of nitrogen (NOx) emissions for gasoline, gaseous
fuel, diesel and methanol-powered motor vehicles have been
established. For gasoline, gaseous fuel and diesel-powered motor
vehicles, standards have also been established for particulate
emissions.
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Section 211(f) was initially interpreted by the Agency as applying
only to unleaded gasoline. In the 1990 Amendments, section 211(f)(1)
was broadly expanded to cover all other fuels and fuel additives,
including leaded gasoline, diesel fuel, and consumer additives.\8\ The
1990 Amendments also apply the provisions of this subsection to
vehicles other than lightduty vehicles. Section 211(f)(1)(B) of the Act
makes it unlawful, effective November 15, 1990, for any manufacturer of
a fuel or fuel additive to first introduce into commerce, or to
increase the concentration in use of, any fuel or fuel additive for use
by any person in motor vehicles manufactured after model year 1974
which is not substantially similar to any fuel or fuel additive
utilized in the certification of any model year 1975, or subsequent
model year, vehicle or engine under section 206 of the Act. Thus,
section 211(f)(1)(B) expands to all motor vehicles the fuel
prohibitions of the original section 211(f)(1) (now redesignated as
section 211(f)(1)(A)), which apply only to light-duty vehicles.\9\
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\8\H.R. Rep. No. 490, Part 1, 101st Cong., 2d Sess. 313 (1990).
\9\An interpretive rule defining the term ``substantially
similar'' under section 211(f)(1)(A) was promulgated for unleaded
gasoline at 46 FR 38582 (July 28, 1981), and revised at 56 FR 5352
(February 11, 1991). An advance notice of proposed rulemaking
(ANPRM) has been published to begin the proces of promulgating an
interpretive rule to define the term ``substantially similar'' under
Sec. 211(f)(1)(B) for diesel fuel and diesel fuel additives. See 56
FR 24362 (May 30, 1991).
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In adding section 211, the first focus of Congress was to prevent
the introduction of new additives which may prove harmful to emission
control devices but to allow for the introduction of such additives if
it could be demonstrated that they would not harm emission control
devices. Furthermore, in framing the statute such that the
Administrator was not required to grant a waiver, Congress provided
authority to the Administrator to take into account other
considerations associated with introduction of the new material into
commerce.
B. Two Stage Process
Section 211(f)(4) of the Act provides the legal authority for this
waiver decision.\10\ The Agency interprets section 211(f)(4) of the Act
as establishing a two stage process for the decision to grant or deny a
waiver application. The first stage of the process focuses solely on
whether a waiver applicant has met its burden to demonstrate that a
fuel does not cause or contribute to a failure to meet emission
standards. The second stage of the process reflects the discretionary
authority provided to the Agency by the statute.
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\10\Section 211(f)(4) states that ``The Administrator, upon
application of any manufacturer of any fuel or fuel additive, may
waive the prohibitions established under paragraph (1) or (3) of
this subsection, or the limitation specified in paragraph (2) of
this subsection, if he determines that the applicant has established
that such fuel or fuel additive or a specified concentration
thereof, and the emission products of such fuel or additive or
specified concentration thereof, will not cause or contribute to a
failure of any emission control device or system (over the useful
life of any vehicle in which such device or system is used) to
achieve compliance by the vehicle with the emission standards with
respect to which it has been certified pursuant to section 206. If
the Administrator has not acted to grant or deny an application
under this paragraph within one hundred and eighty days of receipt
of such application, the waiver authorized by this paragraph shall
be treated as granted.''
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In the first stage of the waiver process, the sole issue is whether
a fuel ``causes or contributes'' to an emission standard failure. The
waiver applicant bears the burden of demonstrating that a fuel will
neither cause nor contribute to an emission standard failure for any
regulated pollutant. Balancing of the emission effects of a fuel for
one pollutant against those for other pollutant(s) is not permissible
under the statutory language. For example, an applicant would not meet
its burden of proof if its testing of a fuel shows that it causes or
contributes to an emission standard failure for CO, even though testing
shows decreases in emissions of HC and NOx. If an applicant does not
meet its burden of demonstrating that the ``cause or contribute'' test
is met, the Agency cannot grant a waiver. If an applicant does meet its
burden, the Agency may then exercise its discretion to grant or to deny
a waiver in the second stage of the process.\11\
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\11\Under the statute, if the Agency does not take action to
grant or deny a waiver application within 180 days of submittal, the
waiver is deemed granted.
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The statute provides that the Agency ``may'' grant a waiver
application if the ``cause or contribute'' test is met, but does not
require such an action. The Agency may therefore choose not to grant a
waiver based on other issues (e.g., public health effects) that
indicate that it would not be in the public interest to do so. In this
second stage of the process, the Agency has a great deal of discretion
to determine which issues should be examined and to balance the
potential positive and negative impacts of a waiver. Such discretionary
authority is grounded not only in Congress' use of the term ``may''
rather than the term ``shall'' in section 211(f)(4), but also in the
goals and purposes of section 211 when read as a whole. The Agency does
not believe that Congress intended to require EPA to grant a waiver
under section 211(f)(4) when available information indicates that the
fuel would be potentially subject to regulatory control under section
211(c)(1) immediately upon issuance of the waiver. Similarly, EPA
believes that Congress did not intend to preclude a determination of
whether issuance of a waiver is consistent with other important goals
of the Act once it has been demonstrated that the mandatory ``cause or
contribute'' test has been met.
This does not mean that the Administrator has unfettered discretion
to deny a waiver application for any reason. The grounds for any denial
must not be arbitrary or capricious or constitute an abuse of
discretion. Thus, in using discretion to deny an application, the
Administrator must identify and explain the factors on which a
discretionary denial decision is based and must assure that the policy
adopted is consistent for all similarly situated waiver applicants.
C. Consideration of Potential Health Effects
Although the basis for a discretionary denial must be rational and
non-arbitrary, nothing in the statute limits the type of factors which
the Administrator may consider in deciding whether to deny an
application. Section 101(b)(1) states that one of the purposes of the
Act is to ``protect and enhance the quality of the Nation's air
resources so as to promote the public health and welfare and the
productive capacity of its population.'' Given this general goal of the
Act, certainly the potential effects on public health of vehicle
emissions would be a factor which the Administrator may reasonably
consider when utilizing the discretion which section 211(f)(4)
authorizes.
Furthermore, under sections 211(b)(2) and 211(e), the Administrator
must require the manufacturer of a fuel or additive to produce data
concerning potential health effects as a condition of, or a
prerequisite to, registration of the fuel or additive.\12\ Under
section 211(c)(1), the Administrator may, based on data collected under
sections 211(b) and 211(e) or otherwise available, issue regulations
controlling manufacture or sale of any fuel or fuel additive which the
Administrator finds ``may reasonably be anticipated to endanger the
public health or welfare.'' These provisions indicate that Congress
intended that the Administrator be concerned about the potential health
effects of fuels and fuel additives.
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\12\Sections 211(a) and 211(b)(1) require the registration of
fuels and additives designated by the Administrator as a
precondition to introduction into commerce.
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The fact that the Administrator may control fuels or fuel additives
which pose potential health effects under section 211(c)(1) does not
mean that the Administrator may not consider health effects as a factor
in deciding whether to grant a waiver under section 211(f)(4). Such a
construction of the statute would lead to absurd results, precluding
the Administrator from denying a waiver application and leading to
potential introduction of a fuel or additive into commerce, even in the
specific circumstances where the Administrator has concluded that there
are grounds for issuance of a proposed regulation prohibiting the fuel
or additive under section 211(c). However, although this reasoning
indicates that Congress could not have reasonably intended to
completely preclude the consideration of health effects under section
211(f)(4), this does not mean that section 211(c) limits the
circumstances in which the Administrator may consider potential health
effects as part of a waiver decision. Clearly, it was the intention of
Congress to treat fuels and fuel additives already registered and being
sold for a particular purpose differently than those which have not
already been introduced into commerce.
III. Method of Review
A. ``Causes or Contributes'' to Emission Standard Failure
Under section 211(f)(4) of the Act, twenty-three applications for
waivers of the section 211(f)(1) prohibitions have been received. Of
these, twenty-two applications have sought a waiver for additives for
unleaded gasoline. One, the most recent, sought a waiver of the section
211(f)(1)(B) prohibitions for an additive to diesel fuel.\13\ Of these
twenty-three applications, ten applications have been granted (some
with conditions attached), ten have been denied, and three were
withdrawn by the applicant prior to the Agency's decision.
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\13\57 FR 45790 (October 5, 1992).
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Section 211(f)(4) clearly places upon the waiver applicant the
burden of establishing that its fuel will not cause or contribute to
the failure of any vehicle to meet emission standards. Absent a
sufficient showing, the Administrator cannot make the required
determination and cannot grant the waiver. If interpreted literally,
however, this burden of proof imposed by the Act would be virtually
impossible for an applicant to meet, as it requires the proof of a
negative proposition: that no vehicle will fail to meet emission
standards to which it has been certified. Such a literal interpretation
could be construed as requiring the testing of every vehicle.
Recognizing that Congress contemplated a workable waiver provision, EPA
has previously indicated that reliable statistical sampling and fleet
testing protocols may be used to demonstrate that a fuel under
consideration would not cause or contribute to a significant failure to
meet emission standards by vehicles in the national fleet.\14\
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\14\See Waiver Decision on Tertiary Butyl Alcohol (``TBA''), 44
FR 10530 (February 2, 1979).
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To determine whether a waiver applicant has established that the
proposed fuel will not cause or contribute to vehicles failing emission
standards, EPA reviews all the material in the public docket, including
the data submitted with the application and public comments on the
application, and analyzes the data to ascertain the fuel's emission
effects. The analysis concentrates on four major areas of concern--
exhaust emissions, evaporative emissions, materials' compatibility, and
driveability--and evaluates the data under statistical methods
appropriate to the various types of emission effects. Emission data are
analyzed according to the effects that a fuel is predicted to have on
emissions over time. If the fuel is predicted to have only an
instantaneous effect on emissions (that is, the emission effects of the
fuel are immediate and remain constant throughout the life of the
vehicle when operating on the waiver fuel), then ``back-to-back''
emissions testing will suffice.\15\
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\15\Back-to-back emission testing involves testing a vehicle on
a base fuel (i.e., a gasoline which meets specifications for
certification fuel or is representative of a typically available
commercial gasoline), then testing that same vehicle on the fuel for
which the waiver is requested. The difference in emission levels is
attributed to the waiver fuel.
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Unlike materials traditionally allowed in unleaded gasoline,
metallics, such as MMT, produce non-gaseous combustion products, some
of which may be deposited in the parts of the vehicle that come in
contact with the combustion products of the burned fuel. These areas of
the vehicle include the combustion chamber, the catalyst, the oxygen
sensor, and all parts of the exhaust system.\16\ Since these materials
build up over time,\17\ it has been traditionally accepted that the
emissions effects of such additives occur over time as miles are
accumulated, and that the method of deposition suggests that the
effects are permanent. If the fuel is predicted to have such a long-
term deteriorative effect, durability testing over the useful life of
the vehicle,\18\ in addition to back-to-back testing, is
appropriate.\19\
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\16\Automakers and catalyst manufacturers point out that, since
catalysts are designed with a honeycomb structure in order to
maximize contact between engine combustion gases and catalyst
materials, if channels within the honeycomb become blocked, the
catalyst is less able to break down the exhaust gases. Furthermore,
although the mechanisms associated with manganese deposits have not
been completely described, catalyst manufacturers suggest that the
mere disposition of manganese (without blockage of channels) would
hinder the catalytic activity of the catalyst. Ethyl, however,
believes that the manganese deposition on the catalyst does not
hinder its activity.
\17\Reply Comments of Ethyl Corporation in Support of the HiTEC
3000 Waiver Application, August 10, 1990, 28.
\18\The ``useful life'' of a 1993 or earlier model year light-
duty vehicle (LDV) (i.e., the amount of time or mileage accumulation
through which the LDV must meet the standards to which it has been
certified) is 50,000 miles or five years, whichever occurs first
(Sec. 202(d)). The 1990 Amendments extended the useful life of LDVs
to 100,000 miles or ten years, beginning with 1994 model year
vehicles. The amendments also tightened emissions standards for 40
percent of a vehicle manufacturer's LDV and light-duty truck (LDT)
sales in model year 1994, 80 percent in model year 1995 and for all
vehicles after model year 1995 (Sec. 202(g)). The useful life for
heavy-duty vehicles and engines is generally 120,000 miles or eleven
years.
\19\Durability testing over the useful life of the vehicle has
involved testing two identical sets of vehicles for 50,000 miles (in
the case of pre-1994 standards for LDVs), one set using the base
fuel and the other using the waiver fuel. Each vehicle is tested for
emissions at 5,000 mile intervals. This is essentially the same
testing pattern which has been required for certification of a new
motor vehicle under Sec. 206 of the Act. As noted above, under the
1990 Amendments, the useful life of LDVs has been extended to
100,000 miles beginning with the 1994 model year when more stringent
emissions standards took effect (see Sec. 202 (d) and (g)).
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In addition to emissions data, EPA also reviews data on fuel
composition and specifications, both to fully characterize a proposed
fuel, and to determine whether that fuel would cause or contribute to a
failure of vehicles to comply with their emission standards. Such a
failure often can be predicted from characterization data. For example,
volatility specifications of the fuel could demonstrate a tendency for
high evaporative emissions. Similarly, data on materials compatibility
could show potential failure of fuel systems, emission related parts,
and/or emission control parts from use of the fuel. Such failures could
result in greater emissions. Likewise, fuel characteristics that could
cause significant driveability problems could result in tampering with
emission controls and, thus, increased emissions.
One issue raised previously in the context of Ethyl's present
application was whether Ethyl was required to show that MMT will not
cause or contribute to noncompliance with emission standards by
vehicles certified to ``future'' emission standards (i.e., 1994 model
year standards, which were not in effect at the time of the waiver
application), as well as vehicles certified to ``current'' standards
(i.e., standards in effect at the time of the waiver application).
Ethyl believes that the statute only requires it to establish that MMT
will not cause or contribute to the failure of vehicles to meet current
emission standards. For the reasons outlined in the Agency's January
1992 waiver decision, EPA disagrees with this reading of the statute
and continues to believe that it is appropriate to consider the effects
of an additive on vehicles' ability to meet more stringent future
standards under circumstances similar to these.\20\ (See 57 FR 2537-8
January 22, 1992.)
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\20\EPA also considered effects on compliance with future
standards in a previous MMT decision. See 43 FR 41424 (September 18,
1978), In Re Application for MMT Waiver.
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In the past, EPA has analyzed both instantaneous emission effects
and durability effects using statistical tests to determine if the fuel
additive will cause a ``significant'' number of vehicles to fail
emissions tests.\21\ Generally speaking, these tests have focused on
the portion of the fleet that will actually fail emission standards as
a result of using the fuel or additive.\22\ Thus, the tests used to
date by the Agency primarily consider only the ``cause'' language in
the statute and do not consider the portion of the statute which
requires that the applicant must also show that the fuel or additive
will not ``contribute'' to the non-compliance of vehicles with emission
standards.
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\21\For a detailed description of the statistical tests which
have been used in the past for instantaneous effects see ``Decision
Document'', Texas Methanol Waiver Decision, U.S. EPA Air Docket
Number EN-87-06, and for those used for durability effects, see 43
FR 41426.
\22\In fact the primary criteria allows for the failure of some
portion of the fleet as a result of use of the fuel or additive.
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The Agency believes that its present statistical tests and criteria
do not give adequate weight to the requirement in Section 211(f)(4)
that an applicant demonstrate that a fuel will not ``contribute'' to an
emission standard failure.\23\ This is of particular significance in
light of the Clean Air Amendments of 1990, which evidence a strong
Congressional concern that more needs to be done to ensure that people
are not exposed to unhealthy levels of airborne pollution. EPA is
presently reviewing alternative criteria and statistical methodologies
for determining whether use of a fuel or fuel additive will ``cause or
contribute'' to emission exceedances. The Agency expects to initiate a
rulemaking in the near future which will propose more appropriate
criteria and statistical methodologies for reviewing waiver
applications and will afford formal notice to future applicants of the
Agency's intention to adopt revised criteria and methodologies.
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\23\In fact, the Agency raised questions about the
appropriateness of these previously used approaches in its original
decision on Ethyl's 1991 MMT waiver application. See 57 FR 2535,
2537 and 2538 (January 22, 1992).
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As explained below, the Agency has concluded that it would not be
appropriate to utilize new criteria and statistical tests concerning
which Ethyl received no prior notice in evaluating Ethyl's application.
However, in the event that Ethyl reapplies in the future for a section
211(f)(4) waiver to allow the use of MMT or any other additive, that
application will be evaluated in accordance with any new fuel waiver
criteria in effect at that time.
B. Discretionary Review
As discussed in part II of this decision, above, the Agency
believes that the use of the term ``may'' in Section 211(f)(4) of the
Act affords the Administrator broad discretion to consider other
factors in deciding whether to grant a waiver, once a waiver applicant
has demonstrated that a fuel or fuel additive will not cause or
contribute to an emission standard failure. This construction of
section 211(f)(4) is also consistent with the other provisions of and
the general purposes underlying the Clean Air Act. Although the
Administrator has not relied on this discretionary authority to deny a
waiver in the past, certain general principles should guide the
Administrator's exercise of such authority.
Although the discretion of the Administrator to consider other
factors in making a waiver decision is broad, it is not unfettered. To
assure that any decision based on factors other than emission standard
failures is not arbitrary and is based on a proper record, the
applicant and other interested persons should be afforded proper notice
of any additional factors to be considered by the Administrator and an
opportunity to comment or submit information concerning those factors.
Any decision based on the discretionary authority of the Administrator
to consider other factors should include an explanation of the factors
which were considered and the relation of those factors to the
decision. Moreover, any policy adopted as part of a decision to deny a
waiver on a discretionary basis should be applied consistently to all
similarly situated applicants.
Protection of the public health is a major goal of both the Clean
Air Act in general and the section 211 fuels provisions in particular.
Accordingly, the Agency believes that when a waiver is sought for a
fuel or fuel additive and there are unresolved concerns regarding the
potential impact of that fuel or fuel additive on public health,
potential health effects can and should be examined as part of the
waiver process. As part of this examination of the potential health
effects of a fuel or additive, the Agency should review any relevant
studies or analyses of which it is aware or which are brought to its
attention by the waiver applicant or by commenters on the waiver
application.
In addition to potential health effects, the Agency may consider
other factors as appropriate in deciding whether it would be in the
public interest to grant a waiver. In particular, the Agency may
consider whether a waiver would be consistent with the objectives of
the Clean Air Act. In each instance, the factors considered and relied
upon should be clearly identified.
IV. Analysis of Emissions Data
A. Description of Previous Test Programs
In support of its request, Ethyl conducted an extensive test
program to determine the effect of MMT on the ability of vehicles to
comply with current and future emission standards. It also considered
the impact of MMT on nonregulated vehicle emissions, urban smog or
ozone, refinery emissions, and crude oil use. Ethyl claimed that its
test results established that MMT would not cause or contribute to
exceedences of current or future emission standards. It also claimed
that MMT use would result in other benefits consistent with Clean Air
Act goals.
In 1988, Ethyl assembled a test fleet of 48 light-duty vehicles,
composed of eight different model types (six Buick Centurys (2.5
liter), six Buick Centurys (2.8 liter), six Buick Centurys (3.8 liter),
six Chevrolet Cavaliers (2.0 liter), six Ford Escorts (1.9 liter), six
Ford Tauruses (3.0 liter), six Ford Crown Victorias (5.0 liter) and six
Dodge Dynastys (3.0 liter)) that together represented a broad spectrum
of then current (1988) technology vehicles. To accumulate mileage,
Ethyl utilized the ``Alternative Mileage Accumulation Cycle'' (AMA)
which is a standard procedure utilized to accumulate mileage for
certification purposes.\24\ It utilized two laboratories to measure
each vehicle's exhaust emissions of the regulated pollutants (HC,
oxides of nitrogen (NOx) and carbon monoxide (CO)) at 5,000-mile
intervals up to 75,000 miles in the case of most vehicles and up to
100,000 miles in the case of several.\25\ It also tested a number of
these vehicles for evaporative HC, particulate and manganese emissions,
materials compatibility, driveability and catalyst durability.
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\24\A driving cycle is a description of how to drive a vehicle
to accumulate mileage, including such things as a what percentage of
driving should be done at what speed and what the overall average
speed should be. The AMA cycle is described in EPA Mobile Source
Advisory Circular 37-A, (See Docket A-91-46) and is essentially
prescribed for use by manufacturers to accumulate mileage for
certification of vehicles (See 40 CFR 86.092-26). A driving cycle is
used so that test vehicles accumulate mileage in a manner that is
supposedly representative of in-use vehicles. The emissions of a
test vehicle that has accumulated mileage according to a driving
cycle representative of in-use vehicles are more likely to be
representative of in-use vehicles' emissions. There are actually
three alternative cycles associated with the AMA; however, the
average speeds of the three alternatives are very similar, ranging
from 29.9 mph to 30.72 mph.
\25\The ``useful life'' of model year 1993 and earlier light-
duty vehicles (LDV's) is 50,000 miles or five years, whichever
occurs first (section 202(d)). However, the Clean Air Act Amendments
of 1990 extended the useful life of LDV's to 100,000 miles or ten
years, beginning with 1994 model year vehicles. For the standards
that begin to take effect in model year 1994, section 207(c)
provides for intermediate in-use standards for several years.
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Ethyl analyzed the data collected using EPA's previously used
statistical tests (43 FR 41424, September 18, 1978) and additional
tests developed by its consultants to further characterize the data.
Its analysis indicated that, on average, MMT at the requested
concentration would result in a 0.018 gpm increase in HC emissions and
decreases in NOx and CO emissions. The analyses further indicated
that, when EPA's previously used tests are applied, the increase in HC
emissions would not cause or contribute to vehicles' failure to meet
the current HC emission standard. The results of Ethyl's testing for
materials compatibility, driveability and catalyst durability also
indicated that MMT would have no significant adverse effects on
vehicles' ability to meet current emission standards under average
driving conditions. On that basis, Ethyl claimed that it had made its
statutorily required showing.
Ethyl also submitted data on the catalyst efficiency of the
vehicles which it tested. Ethyl performed back-pressure tests\26\ on
all its vehicle fleet except one model group after accumulation of
75,000 miles. Back-pressure tests were also performed on a pair of Ford
Crown Victorias, one operated on MMT-fuel and one on clear fuel, at
speeds higher than those used in Ethyl's 48-vehicle test program.\27\
The results of these tests indicated that back-pressure was not
significantly different in the MMT vehicles when compared to the clear
fuel vehicles. Ethyl also operated two 5.7 liter Corvettes at extremely
high speeds (100 mph) for 25,000 miles, one using MMT fuel and one
using clear fuel. Although similar in magnitude, the back pressure for
the MMT vehicle was slightly higher than that for the clear vehicle.
Ethyl also presented catalyst efficiency\28\ data based on engine-out
emissions of its fleet and based on ``slave engine'' testing\29\ for
half of its fleet. Results of the slave engine testing indicated no
statistically significant difference between the catalyst efficiencies
for the MMT vehicle components when compared with the clear vehicle
components. Finally, four Chevrolet Corsicas were operated to 100,000
miles, two utilizing MMT fuel and two with clear fuel. The purpose of
this testing was to investigate MMT's effect on the catalyst for a
longer mileage interval than the 75,000 miles over which most of
Ethyl's fleet had been driven. Catalyst efficiencies of the MMT
vehicles were not significantly different when compared to the clear
fuel vehicles.
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\26\Back pressure tests are used to determine if significant
plugging has occurred in a vehicle's catalyst. The total pressure
ahead of the catalyst is back pressure. This pressure is a measure
of constriction in flow through the exhaust system caused by flow of
the exhaust through the emissions control system and the noise-
reducing components of the vehicle. If plugging has occurred in a
vehicle, the total pressure ahead of its catalyst, the back
pressure, should be greater than expected (e.g., greater than a
matching control vehicle).
\27\In this program the maximum speed was 65 mph for the first
25,000 miles and 80 mph for an additional 10,000 miles.
\28\Catalyst efficiency is a measure of what fraction of the
emissions entering the catalyst are actually removed (or catalyzed)
by the catalyst.
\29\``Slave engine'' testing is the testing of vehicle
components on a single engine which is not in a vehicle. In this
case, catalyst efficiencies between control and MMT vehicles were
investigated using exhaust gases from this single engine which were
routed through the removed catalysts. This would likely result in a
more accurate analysis of catalyst efficiency, since one possible
confounding factor, vehicle to vehicle variability, would be
eliminated.
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Ford presented original test data which Ford said supported its
contention that actual in-use MMT-induced HC emissions increases are
potentially far greater than those reported by Ethyl.\30\ Ford
conducted testing on a more limited scale utilizing eight vehicles,
representing two model groups, run for 105,000 miles. Ford chose two
model groups which were representative of its newest technology
vehicles at the time. One (the Explorer) represented a technology that
Ford believed may be especially prone to exhibit a buildup of
manganese, due to significantly higher operating temperatures and loads
than those of passenger cars. The other model group, the Escorts, had
close-coupled catalysts, a design which is being incorporated into many
new vehicles in order to meet tighter emissions standards. Like Ethyl,
Ford operated part of its test fleet on clear fuel and part on fuel
containing 1/32 gpg MMT. However, Ford's test program differed from
Ethyl's program in several ways. When accumulating mileage, Ford
utilized a commercial gasoline which contained all of the additives
(detergents, etc.) typically found in such fuels. Ethyl utilized a very
high quality test fuel with tight specifications and no additives.
(Although used for actual emissions testing purposes, Ethyl's fuel
would not be allowed for mileage accumulation when certifying vehicles
since it is not representative of in-use fuel.) When accumulating
mileage, Ford utilized what it called its ``durability cycle'' which it
had previously developed. Compared to the AMA cycle used by Ethyl,
Ford's driving cycle had a higher average speed (54 miles per hour
(mph) versus 30 mph), and a higher percentage of high speed
driving.\31\ (As previously mentioned, Ethyl utilized the AMA cycle
used for certification purposes.) Additionally, in the Ford program,
vehicles were tested for emissions at five mileage intervals (5,000,
20,000, 55,000, 85,000\32\ and 105,000 miles) and six emissions tests
were done at each testing interval. Ethyl, by comparison, conducted
testing every 5,000 miles to 75,000 miles (15 intervals) and utilized
two emissions tests at each interval.\33\ Ford's test vehicles showed
an elevation of HC emissions with MMT that was substantially greater
than the 0.018 gpm reported by Ethyl from its test program.
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\30\EPA's emissions testing lab and Ford's lab routinely undergo
correlation testing and the data indicate that correlation is good
between the labs. (See memorandum, with attached data, from Martin
E. Reineman, EPA Manager of Correlation and Engineering Services,
Office of Mobile Sources, January 3, 1992, Docket A-91-46.)
\31\Ford indicated that drivers who accumulated mileage in its
test program were asked to follow posted speed limits. Ford
indicated that the cycle consisted of 5% city driving (25 to 45
mph), 5% gravel or off road driving (25 to 45 mph), 20% rural
driving (45 to 55 mph), and 70% highway driving (65 mph). Posted
speed limits are shown in parentheses. By way of comparison, the AMA
cycle consists of 16.1% of driving at 30 mph, 22.6 at 35 mph, 20.9
at 40 mph, 6.4 at 45 mph, 17% at variable speed and one of the three
following options: 16.7% at 50 mph or 16.5% at 55 mph or 8.6% and
7.9% at 55 mph and 70 mph, respectively.
\32\In fact, only two of the four Escorts were tested at 85,000
miles.
\33\Although Ethyl conducted additional emissions tests at some
mileage intervals when the initial two tests showed high variation,
these additional tests were not used in Ethyl's analysis of its
data.
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Toyota also submitted data on a single vehicle which was operated
for 30,000 miles on MMT-containing fuel after which the oxygen sensor
and catalyst were replaced with new components and then driven on fuel
not containing MMT for 30,000 miles. Toyota also used a driving cycle
with an average speed (41.7 mph) higher than that used by Ethyl for
mileage accumulation and used fuel with what Toyota believed was a
relatively high trace level of lead than that usually found in unleaded
gasoline (0.0045 gpg lead) and oil with a relatively high phosphorus
level (0.13 weight percent). Toyota referred to this test procedure as
the ``Toyota 9-Laps'' and presented evidence which it said suggested
that the catalyst degradation seen by vehicles using the Toyota 9-Lap
test was very similar to in-use catalysts tested by Toyota. Hence,
Toyota suggested, these ``adjustments'' made in creating the Toyota 9-
Lap make the testing of a vehicle more consistent with what would
happen in actual in-use driving. Toyota's data indicated an HC level
after the first 30,000 miles of vehicle use (on MMT fuel) about 0.1 gpm
higher than the same vehicle after the vehicle was driven for a second
30,000 mile interval with a new catalyst and oxygen sensor. Toyota also
submitted data indicating that the efficiency at which the catalyst was
operating for the MMT-exposed components was less than that for the
non-MMT exposed components.
Some time after EPA's January 8, 1992 denial decision, EPA and
Ethyl entered into discussions concerning a possible settlement of the
court case which Ethyl had filed. In the context of these discussions,
Ethyl submitted to the Agency new data it had developed since the
denial decision. Ethyl tested six 1991 Escorts, using both the
relatively high-speed driving pattern similar to that utilized by Ford
in its testing of 1991 Escorts (the Ford cycle) and, also, after
changing emissions system components (catalyst and oxygen sensor), the
driving cycle used by Ethyl in the original test program (EPA's
durability certification cycle also known as the AMA). Half of the
vehicles utilized MMT-containing fuel and half were run on clear fuel
(fuel not containing MMT). Ethyl also performed some catalyst
efficiency tests on these vehicles utilizing a ``slave engine.''
Ethyl also tested six 1988 Escorts which were used in its original
test program driven on the AMA cycle. In the new program, after
replacing the catalyst and oxygen sensor, Ethyl continued mileage
accumulation, from 75,000 to 100,000 miles, utilizing the Ford cycle.
Likewise, Ethyl tested six 1988 Buicks from its original fleet
accumulating mileage (100,000 to 115,000 miles) using the Ford cycle
but without replacing any components. Ethyl also accumulated mileage on
seven pairs of 1992 vehicles (four Crown Victorias, Six Buick Regals
and four Ford Mustangs) in test programs covering from 45,000 to
100,000 miles beyond break-in with and without MMT, using the Ford
cycle.
Based on its inspection and analysis of the new Ethyl data, the
Agency ultimately concluded that Ethyl's program had demonstrated
driving cycle does not contribute significantly to MMT-induced
increases in hydrocarbon emissions. However, in addition to addressing
the issue of driving cycle, the Ethyl data appeared to confirm the
finding by Ford that 1991 Escorts experienced a much higher MMT-induced
HC increase than that observed in other models tested (either in
Ethyl's 1992 fleet or in the original 1988 Ethyl fleet). The Agency was
concerned that these data could indicate that certain engine and
emissions control system configurations were more vulnerable to an MMT-
induced emissions increase irrespective of driving cycle.
To further assist the Agency in developing a test program, EPA held
a workshop in October of 1992 and presented a proposed test program
which could address in a timely manner specific unresolved issues
concerning the effect of MMT on emissions: (1) Whether other vehicles
utilizing fuels containing MMT are likely to experience increases in
hydrocarbon emissions similar to those observed in 1991 Ford Escorts;
and (2) whether fuels containing MMT have significant adverse effects
on emissions from vehicles utilizing the technologies most likely to be
employed to meet future standards.
Ultimately the court case was not settled; however, the test
program presented by the Agency at the workshop was largely adopted by
Ethyl and is the basis of its most recent test program involving the
1993 fleet. These vehicles (with the previously mentioned 1992
vehicles) comprise Ethyl's most recent dataset.\34\
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\34\On May 25, 1993, and on subsequent dates, Ethyl provided
summaries of the 1992/93 test data to EPA staff and these have been
placed in public docket A-93-26.
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Ethyl accumulated mileage on three 1992 model year vehicles (four
Crown Victorias to 100,000 test miles,\35\ six Buick Regals to 65,000
test miles and four Ford Mustangs to 45,000 test miles) and six 1993
model year vehicles (six Toyota Camrys to 85,000 test miles, six
Oldsmobile Achievas to 65,000 test miles, six Dodge Shadows to 55,000
test miles, six TLEV Ford Escorts to 85,000 test miles, six Honda
Civics to 80,000 test miles and four 49-state Ford Escorts to 30,000
test miles) with and without MMT. The driving cycles used for these
vehicles were an intermediate driving cycle of 45 mph on average for
the 1993 model year vehicles, an average 55 mph driving cycle (i.e.,
the Ford Cycle) for all mileage accumulation on the 1992 Ford Mustangs
and for the initial 45,000 miles of operation on the 1992 Crown
Victorias and Buick Regals and an average driving cycle of 45 mph was
utilized for these two models thereafter.
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\35\As referred to here, ``test miles'' indicates mileage
accumulated after break-in (break-in mileages vary among these
models) and during which some vehicles were run on fuel containing
MMT while control vehicles were run on clear fuel.
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B. Comments on Vehicle Emissions Issues
EPA provided an opportunity for the public to submit written
comments.\36\ Many comments were received from a wide variety of
interests, including refiners, automakers, emission control
manufacturers, states committees, environmental and public interest
groups and private citizens. Taken together, the comments touched on
every aspect of Ethyl's application. The following is a summary of the
comments.
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\36\As mentioned previously, the comments received concerning
Ethyl's remanded waiver application are available in public docket
A-93-26.
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Four automakers (Ford Motor Company (Ford), General Motors
Corporation (GM), Toyota Technical Center, U.S.A., Inc. (Toyota), and
Chrysler Motors Corporation (Chrysler)), the American Automobile
Manufacturers Association (AAMA), and the Manufacturers of Emission
Controls Association (MECA) all recommended denial of Ethyl's request
and expressed several concerns with regard to the addition of MMT to
unleaded gasoline. First, they noted that the use of MMT will cause an
increase in HC emissions. Most indicated that the more stringent
emissions standards that began taking effect in model year 1994 will
make any increase in HC emissions particularly troublesome. Further,
they stated that newer technology vehicles will likely be equipped with
catalysts which are nearer the engine (more ``closely coupled'') and
that such close coupling, they stated, results in higher catalyst
temperatures that may make the catalyst more prone to the deposition of
manganese. These commenters indicated that deposition of manganese
compounds on the surface of the catalyst would impair the catalytic
breakdown of emissions from the engine, thereby decreasing catalyst
effectiveness. Additionally, they were concerned that MMT, even at the
1/32 gpg Mn concentration requested, would plug catalysts and thus
reduce the surface area of the catalyst available to break down
emissions from the engine, especially in the case of vehicles operated
under driving conditions which result in higher temperatures such as
heavy load or high speed. Under such conditions, it was pointed out,
the vehicle may be more prone to deposition of manganese.
Ethyl indicated that the assertions that it must ``conclusively''
demonstrate the absence of negative effects is not required by the
section 211(f)(4) standard. Ethyl believes that it need only
demonstrate, by a preponderance of evidence, that the additive will not
cause or contribute to the failure of emission control devices to
comply with applicable emission standards, and, further, it believes
that it has made this showing. Ethyl also stated that the EPA test
program proposed at its October 1992 workshop involving the
accumulation of 65,000 test miles, would be sufficient for purposes of
gauging the effect of MMT on emissions. Ethyl commented that it
followed this proposal in the 1992/93 test fleet, although mileage
accumulation has continued beyond 65,000 miles for three of the eight
model year vehicles tested without new emission results different from
the trends established through 65,000 miles.
With respect to the automakers' concerns about effect of MMT on
newer emission technology such as close-coupled catalysts, Ethyl
indicated that the use of the 1993 Transitional Low Emission Vehicle
(TLEV) Honda Civic in its most recent test program was intended so as
to introduce a vehicle which has the most physically possible close-
coupled emission technology (i.e., one connected directly to the
exhaust manifold). Despite such close-coupling, Ethyl indicated that
the differences in hydrocarbon emissions between clear and MMT-fueled
1993 TLEV Honda Civics was minimal. Ethyl also indicated that this
concern about close-coupled catalysts completely ignores that Ethyl
tested two 1988 models and three 1993 models equipped with close-
coupled catalysts without showing any significant adverse effects on
emissions.
Toyota submitted data on catalysts and oxygen sensors from in-use
customer vehicles from Canada where MMT is used as a fuel additive.
Toyota believes that these catalysts and oxygen sensors indicate that
exhaust emissions of hydrocarbons and carbon monoxide are higher from
catalysts/oxygen systems collected in Canada than comparable catalyst/
oxygen systems from U.S. vehicles. Also Toyota submitted photographs of
a catalyst taken from a high mileage Canadian Hilux pickup truck which
showed plugging of the catalyst passages.
Ethyl's response to Toyota's catalyst/oxygen system data is that it
is not clear from the description of the Toyota test results precisely
what can be concluded from the test program. Ethyl stated that, without
a detailed vehicle history, there is no basis to conclude that MMT had
an effect on the catalyst/oxygen system data.
Chrysler submitted data on the analysis of four catalysts, which
was completed by Johnson Matthey Incorporated (JMI) at Chrysler's
request, that had various degrees of manganese deposition from Canadian
vehicles exposed to MMT in the fuel. It indicated that the results of
the analysis demonstrate that the washcoat of both the partially
plugged catalysts and unaffected catalysts exhibit a clear layer of
``densified'' washcoat containing large quantities of manganese oxides.
Chrysler believes that the JMI report supports its concern that
manganese oxides can fill the catalyst pores, thereby covering precious
metal sites or decreasing wash coat surface area, consequently
eventually decreasing catalyst activity. Regarding the automakers'
concerns about the Additive's effect on emissions system components,
such as exhaust oxygen sensors, exhaust gas recirculation valves,
catalysts and oxygen sensors, Ethyl stated that it has already provided
extensive data showing that the Additive does not adversely effect any
of these emission system components.\37\ (Ethyl's test programs are
discussed in the previous section.)
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\37\Public Docket A-92-41, No. IV-D-3 (summarizing Ethyl's
emission control component testing.)
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Nineteen small refiners including the National Petroleum Refiners
Association all recommended approval. They concurred in Ethyl's
assessment of the economic benefits and reduced refinery and vehicle
emissions that would accrue from the replacement of octane obtained
through higher-severity refining with octane obtained from MMT. Several
emphasized that MMT would be especially helpful to small refiners since
octane enhancement from MMT requires less capital investment than other
means of increasing octane. Many refiners also pointed out that
refinery operations at lower severity would result in decreased
aromatic and benzene emissions from vehicles and increased yield for
each barrel of crude oil refined.
C. Available Data Meet Previously Used Criteria
The criteria and statistical tests previously used by EPA to
examine durability waiver applications were used only once by the
Agency prior to Ethyl's 1990 application for the use of MMT.\38\ These
tests include a variety of approaches to durability data designed to
determine whether the additive causes increases in regulated pollutants
and, if so, whether those increases bring about failure of vehicles in
the fleet to meet the standards to which they were certified. While EPA
has some concerns regarding the appropriateness of these criteria and
tests for current conditions, the Agency does not intend in this action
to hold Ethyl to any new criteria and/or tests that are not currently
in place. Accordingly, the following discussion is addressed primarily
to the results of applying the most critical of the previously used EPA
tests.\39\
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\38\The test were used in EPA's examination of Ethyl's 1978
application. For a description of these tests, see EPA's decision on
the application at 43 FR 41424, September 18, 1978.
\39\EPA has carefully reviewed Ethyl's application of the test
to these data in various combinations and has concluded that the
tests were conscientiously and accurately applied. This review
focused particularly upon the application of the ``integrated
emissions test'', the ``cause or contribute'' test, and the overall
sign test.
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The earliest set of test results under consideration here (tests of
1988 vehicles submitted with Ethyl's 1990 application) exhibit the most
pronounced MMT-caused emissions increases of the data generated by the
applicant (about 0.02 gm/mi\40\, but these increases fall substantially
short of failure on the determinative ``cause or contribute'' test\41\
(3 of 8 vehicle models tested fail for HC and 4 of 8 models fail for
CO, while 7 of the 8 models tested are required to fail before the
additive fails this overall test on either pollutant).
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\40\Determined by integration of emissions test results gathered
over the full range of mileage supplied by the applicant.
\41\Ethyl's consultant, Systems Applications, Inc., describes
this test on page 19 of a report that was included as Appendix 2A in
Ethyl's May 9, 1990 application for waiver. This co-called ``cause
or contribute'' test, really addresses the question of whether the
additive ``causes'' a failure to meet the certified standard for a
regulated pollutant for each model group and then looks to see if
enough model groups failed the test to warrant the conclusion with
high confidence that more than half of the models are caused to fail
by operation on the additive.
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When the larger body of all available and appropriate\42\ long-term
emissions data on High-Tech 3000 is evaluated using these previously
used EPA tests, the conclusion is that these increases (averaging 0.02
gm/mi for HC) bring about failure of the ``cause or contribute'' test
in only 4 (for HC) or 5 (for CO) of the 19 model groups tested by the
applicant and others. Failure of that test\43\ must occur in at least
13 of the 19 model groups examined before the additive is deemed to
have failed the overall test with 90% confidence. Fourteen of 19 must
fail before the test is failed at the 95% confidence level.\44\
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\42\Appropriate data are considered to be those collected with
Federal Test Procedure (FTP) testing using an experimental design
with a control group and no obvious sources of bias. The data
referred to here include the eight 1988 models tested by Ethyl, the
two 1991 models tested by Ford, and the eight 1992 and 1993 models
tested by Ethyl.
\43\In order for a model to fail the test, emissions from the
additive-fueled vehicles must be sufficiently high that then percent
of the represented fleet of that model group using the additive is
predicted to exceed the standard beofre the end of its useful life.
The control vehicles must reach this failure rate at a higher
mileage than the additive-fueled vehicles.
\44\These ``confidence levels'' correspond, respectively, to the
0.10 and 0.05 significance levels. The significance level is the
probability that a decision to reject the null hypothesis (and find
an increase) will be a result of sampling error and thus be
incorrect.
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If the newer technology 1992 and 1993 vehicles tested by the
applicant are examined in isolation from the earlier test programs, the
data (with an average HC effect of 0.002 gm/mi) pass the historical
tests even more easily than is the case for the data combinations
examined above. None of the nine models failed the ``cause or
contribute'' test for hydrocarbons and only one failed for carbon
monoxide. Seven of nine models would have to fail for the additive to
fail the overall sign test at the 90 percent confidence level and eight
would have to fail for 95 percent confidence.
The overall conclusion from the above analysis, then, is that
Ethyl's additive passes the most critical of the historical tests with
a comfortable margin.
D. Data on Newer-Technology Vehicles Meet More Stringent Criteria
Notwithstanding the Agency's conclusion that it would not be
appropriate to require Ethyl to satisfy new statistical tests
concerning which it has not been given prior notice and the Agency's
decision to evaluate Ethyl's application primarily according to the
previously utilized statistical tests, the Agency nevertheless
considers its existing tests and the criteria that they implement to be
obsolete under current conditions.\45\
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\45\The tests are extremely conservative in that they place most
of the burden of proof on the Agency rather than on the applicant.
The ``cause or contribute'' test is failed by an engine family only
under circumstances where emissions from the family are so high that
an additive--caused increase in some pollutant pushes more than ten
percent of the vehicle fleet into violation of the standard.
Moreover, the final sign test that is applied to the model-specific
results is failed by the additive only when it may be concluded with
high confidence that more than half of the models in the represented
population would fail the model-specific test. In practical
situations with relatively small samples, this sign test permits a
high percentage of the models in the sample to fail before the
additive is declared to have failed the test. These tests, then, may
permit the granting of waivers in the face of substantively
significant emissions increments attributable to an additive--
increments that would tend to offset the benefits from an
increasingly stringent regulatory program aimed at bringing the
nation's most serious air quality problems under control. Agency
concerns with these tests were addressed previously in its decision
on Ethyl's 1990 application (57 FR 2535, January 22, 1992) and in
(58 FR 64761, December 9, 1993).
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Therefore, EPA has gone beyond the historical tests to examine
Ethyl's data on the use of the additive with newer technology vehicles
under more stringent criteria of the sort that seem to be warranted by
current conditions. For this analysis, EPA chose to examine the
additive's performance against the most stringent of the possible
criteria--a requirement that the additive cause no statistically
significant increase in emissions.
If one uses a one-sided null hypothesis that the additive causes no
increase in HC emissions, one may employ various statistical tests to
examine the credibility of that hypothesis in light of the test
results. One such test is the computer-intensive ``permutation test''
in a form called an ``approximate randomization'' test.\46\ Application
of this test to the full mileage range of HC emissions data from
Ethyl's tests of 1992 and 1993 vehicles results in a failure to discern
any ``real'' emissions increase at all--that is, no increase that we
may not reasonably attribute to sampling error rather than to an
additive effect on HC in the sampled vehicle population.\47\
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\46\The permutation test is built around the idea that, if the
null hypothesis is correct, the increase due to the additive in the
sample is only one member of a distribution of all possible such
increases computed from assignments of vehicle emissions to fuel
groups within models. Only if the fuel-related increase from the
sample is an extremely unusual result in theis distribution of
possible increases is it reasonable to reject the null hypothesis
and conclude that the additive actually brought about an increase in
emissions. The way that this method works in practice is that, on
each iteration of the computer program, the computer randomly
rearranges the fuel group assignments among the emission results
within each model group separately. The emission values assigned
(for that iteration) to the additive fuel group are then summed over
the entire sample to form the test statistic. This process is
repeated a very large number of times (one million in this case) and
the resulting test statistics are tabulated. Only if the same test
statistic, as computed from the empirical sample, exceeds a pre-
determined percentage of the simulated test statistics may we reject
the ``no-difference'' hypothesis and conclude with the necessary
degree of certainty that an increase has occurred.
\47\This conclusion holds even when the test is performed at the
0.10 significance level used in conducting the statistical testing
on the data from Ethyl's 1978 application. It is important to note
that the original Ethyl test fleet of 1988 model year vehicles that
are now older than those representing the newest Ethyl data set did
not fare as well and, as mentioned previously, do demonstrate
statistically significant increases in HC emissions.
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E. Finding
Based on all of the information then available concerning the
potential effect of use of MMT in unleaded gasoline on regulated
emissions, as submitted by Ethyl and others, the Administrator of EPA
determined on November 30, 1994 that, ``Ethyl has satisfied its burden
under Clean Air Act 211(f)(4) to establish that use of HiTEC 3000 at
the specified concentration will not cause or contribute to a failure
of any emission control device or system (over the useful life of any
vehicle in which such device or system is used) to achieve compliance
by the vehicle with the emission standards with respect to which it has
been certified.'' The basis for this determination was described
briefly in the Administrator's November 30, 1994 notice, and has been
reviewed in detail above.
The November 30, 1994 determination was specific to Ethyl's present
waiver application. As the Administrator made clear in the notice
announcing the determination, it does not apply to any new application
concerning either HiTEC 3000 or MMT in the event that this decision to
deny Ethyl's application on the basis of concerns regarding potential
health effects is upheld in any subsequent judicial review. Although
Ethyl may be able to sustain its burden under Section 211(f)(4) in the
context of any future waiver application, any such application must
include satisfactory data addressing the effect on vehicles in
production at that time and will be evaluated according to the
statistical methods and criteria for evaluation of waiver applications
in effect at that time.
V. The Onboard Diagnostics Issue
Prior to the Administrator's November 30, 1994 finding concerning
emission effects, three auto manufacturers, Ford, General Motors (GM),
and Chrysler, and the American Automobile Manufacturers Association
(AAMA), all commented on concerns about the impact of the oxidative
products of MMT on onboard diagnostic (OBD II) systems employing
before-catalyst and after-catalyst oxygen sensors.\48\
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\48\An Onboard Diagnostic System, with the present generation
commonly known as OBD-II, monitors the activity of an automobile's
emission control system, primarily the catalytic converter, and
alerts the driver via a dashboard light in the event of a
malfunction. Put simply, this aspect of the OBD system functions by
utilizing devices before and after the catalyst which ``sense'' the
presence of oxygen. If the catalyst is functioning properly, it will
absorb a certain amount of oxygen and a specified decrease in oxygen
content in the exhaust gases can be determined by comparing the
oxygen ``sensed'' before and after the catalyst. If the catalyst is
functioning improperly, oxygen storage by the catalyst is impaired
and a drop in exhaust gas oxygen after the catalyst beyond the
proper range is ``sensed'' by the OBD system.
---------------------------------------------------------------------------
GM concerns regarding the OBD II system were two-fold. Its first
concern was that since it is known that manganese oxide has the ability
to store oxygen, a potential problem could occur with dual oxygen
sensor systems. GM stated that, with manganese oxide covering the
catalyst and the oxygen sensors, a false oxygen storage capacity of the
catalyst could be indicated by the OBD II system, which could then
indicate that the catalyst was still working properly while the
opposite could be true. GM's second concern was that the catalyst would
act as a ``filter'' and manganese oxide from MMT combustion passing
through the exhaust system would coat the before-catalyst oxygen sensor
and after-catalyst oxygen sensors unevenly, thus causing the OBD II
system to malfunction. GM also stated that in the 1994 model year GM
planned to market two engine families equipped with OBD II systems
employing before- and after-catalyst oxygen sensors.
With respect to the automakers' concern that use of MMT would
adversely affect operation of the OBD II system, on July 15, 1993,
Ethyl submitted data which it believed demonstrated that this concern
has no basis.\49\ Ethyl stated that no production vehicles were then
equipped with OBD-II systems and that the primary hardware approach
being considered by the automobile manufacturers involves the use of
exhaust gas oxygen (EGO) sensors before and after the catalytic
converter to monitor converter efficiency. Ethyl further commented that
test data generated by Ethyl showed that use of the additive would have
no adverse effect on either the hardware component of these planned
ODB-II systems (i.e., the oxygen sensors), or on the catalytic
converter itself. Ethyl noted that, ``[s]ince these future systems are
currently under development, it is impossible to consider the long term
effects of MMT on these systems.''
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\49\See Public Docket A-93-26, Number II-D-8, Appendix 5.
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On November 4, 1994, only 26 days prior to the mandatory date for a
decision on Ethyl's waiver application, Ford Motor Company submitted a
report describing bench testing\50\ of catalysts, in which Ford
measured the oxygen storage capacity of catalysts which had been
deliberately degraded and then exposed to the emissions from MMT-
containing fuel. Ford's conclusion based on these tests was that the
exhaust gas oxygen (EGO) sensors would be affected by the deposition of
manganese oxides associated with MMT use, thus sending incorrect
signals to the diagnostic control system in the vehicle.
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\50\Bench testing means the testing of components during which
time the components are not actually in the vehicle. The details of
this testing can be found in Document II-D-56 in Docket A-93-26. (An
incomplete preliminary report of this information was submitted to
the Agency in Document II-D-38, Docket A-93-26.)
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Although the Agency regarded the concerns expressed by Ford in its
November 4, 1994 submission regarding the effect of MMT use on OBD
systems as potentially very important, based on the very limited
analysis which could be undertaken prior to the November 30, 1994
deadline for a decision concerning Ethyl's application, the Agency
concluded that the limited bench testing submitted by Ford did not
allow a conclusion concerning the likelihood that a significant impact
would actually occur during vehicle operation. In addition, the Agency
had several questions regarding the procedures involved in the Ford
testing which could not be resolved within the available time. The
November 30, 1994 notice announcing the Administrator's determination
concerning emission effects made it clear that EPA was concerned about
this issue and would retain the authority to take appropriate action in
the future pursuant to Clean Air Act Section 211(c).
EPA met with staff of Ford in February of 1994 in order to discuss
Ford's concerns raised in its November 4, 1993 submission. Ford
generally expressed the same concerns as had been expressed by GM (and
discussed above).\51\ According to Ford, its testing showed that
combustion of gasoline containing MMT deposits a layer of manganese
oxide on top of the catalyst washcoat and that this causes the EGO
Sensor to measure a lower oxygen level, thereby indicating a higher
oxygen storage capacity than that which would be indicated by the
catalyst without MMT. As a result, a malfunctioning catalyst might not
be detected. Ford expressed particular concern because it had just
introduced three 1994 model year vehicle families employing OBD-II,
whereas the other automakers will not have systems out until the 1996
model year.
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\51\Ford's concerns are discussed in more detail in a memo to
docket A-93-26, with an attachment submitted to the Agency entitled
``Section 211(c) Impacts of MMT''.
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Recently, on May 3, 1993, Ford submitted additional information
which the Agency is currently reviewing. This new information appears
to provide further evidence to substantiate the concerns expressed by
Ford regarding the impact of MMT use on OBD systems. Unlike the
previously submitted Ford data, the new data address an actual
production vehicle fitted with a failed catalyst and the effect use of
MMT had on the OBD system's ability to detect failure of the catalyst.
The Agency is continuing to investigate the question of the
potential impact of use of MMT in unleaded gasoline on OBD systems. If
after further investigation EPA concludes that the concerns expressed
by the vehicle manufacturers are warranted, EPA intends to initiate an
appropriate rulemaking under Section 211(c).
VI. Manganese Health Assessment\52\
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\52\The assessment presented here is taken from ``Reevaluation
of Inhalation Health Risks Associated with Methylcyclopentadienyl
Manganese Tricarbonyl (MMT) in Gasoline'' (United States
Environmental Protection Agency, 1994b) which can be found in the
docket in its entirety.
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A. Introduction
In 1990, the EPA Office of Research and Development (ORD) assessed
the potential health risks associated with the use of
methylcyclopentadienyl manganese tricarbonyl (MMT) as an additive in
unleaded gasoline (U.S. Environmental Protection Agency, 1990).\53\
Later, ORD (Preuss, 1991) reaffirmed its assessment after considering a
resubmitted waiver application for MMT from Ethyl Corporation. As
identified in earlier ORD evaluations (U.S. Environmental Protection
Agency, 1990; Preuss, 1991), a key issue is the potential health risk
associated with inhalation exposure to manganese tetroxide
(Mn3O4), which is the primary by-product resulting from the
combustion of MMT in gasoline. New information on manganese (Mn) health
effects and exposure is incorporated in this revised risk assessment.
(United States Environmental Protection Agency, 1994b)
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\53\The many references in this section of the decision dealing
with manganese health effects are referred to in parentheses and
listed at the end of this section in subsection E.
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This reevaluation has four components: (1) a health effects
assessment, (2) an exposure assessment, (3) a risk characterization
relating the first two, and (4) a summary and conclusions. This
evaluation summarizes earlier ORD assessments and incorporates
information from certain other major new reports and analyses.\54\
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\54\The reader is referred to the appendices of the full EPA/ORD
reevaluation for more detailed background information. This report,
``Reevaluation of Inhalation Health Risks Associated with
Methylcyclopentadienyl Manganese Tricarbonyl (MMT) in Gasoline'',
can be found in its entirety, including the appendices, in docket A-
91-46. Appendix A presents dose-response analyses, Appendix B
presents an exposure assessment, and Appendix C contains the current
verified Mn inhalation reference concentration (RfC) as it appears
in the U.S. EPA Integrated Risk Information System (IRIS, 1993).
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B. Health Effects Assessment
1. Background
The toxicity of Mn varies according to the route of exposure. By
ingestion, Mn has relatively low toxicity at typical exposure levels
due in part to a low rate of absorption from the gastrointestinal tract
and in part to efficient regulation by homeostatic mechanisms.
Manganese is considered a nutritionally essential trace element and is
required for certain enzymes important for normal functioning of the
central nervous system and other body organs. However, by inhalation,
Mn has been known since the early 1800s to be toxic to workers. It
should be noted that Mn occupational studies predominantly (and
sometimes exclusively) involve men. Neurobehavioral, respiratory, and
reproductive effects are the primary features of excessive occupational
exposure to Mn. Manganism is characterized by various psychiatric and
movement disorders, with some general resemblance to Parkinson's
disease in terms of difficulties in the fine control of some movements,
lack of facial expression, and involvement of underlying
neuroanatomical and neurochemical factors. Neurobehavioral effects of
Mn intoxication are generally more clinically prominent than
respiratory or reproductive effects. However, respiratory effects
(e.g., pneumonitis) and reproductive dysfunction (e.g., reduced libido)
are also frequently reported features of occupational Mn intoxication.
The available evidence is inadequate to determine whether or not Mn is
carcinogenic; some reports suggest that it may even be protective
against cancer. Based on this mixed but insufficient evidence, EPA has
placed Mn in a Group D weight-of-evidence category, which signifies
that it is not classifiable as to human carcinogenicity. Given these
features of Mn toxicity, the health assessment focuses on the potential
for chronic noncancer effects.
Various epidemiological studies of male workers exposed to Mn at
average levels below the current American Conference of Governmental
Industrial Hygienists Threshold Limit Value (TLV) (5 mg/m\3\)\55\ have
shown neurobehavioral, reproductive, and respiratory effects, both by
objective testing methods and by workers' self-reported symptoms on
questionnaires. Neurobehavioral effects generally have reflected
disturbances in the control of hand movements (e.g., tremor, reduced
hand steadiness) and/or the speed of movement (e.g., longer reaction
time, slower finger-tapping speed). Reproductive effects have included
a decrease in the number of children born to Mn-exposed workers
(compared to matched controls) and various self-reported symptoms of
sexual dysfunction. In recent studies at low to moderate occupational
exposure levels, respiratory effects have been reflected primarily in
self-reported symptoms of respiratory tract illnesses rather than in
differences between objective pulmonary function measurements in Mn-
exposed and control workers. However, the lack of studies using more
sensitive investigational methods and the existence of some limited
evidence from an epidemiological study of school children raise a
degree of concern about pulmonary function effects in relation to lower
level Mn exposure.
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\55\The American Conference of Governmental Industrial
Hygienists (1992) has given notice of intent to lower the TLV to 0.2
mg/m\3\.
---------------------------------------------------------------------------
The precise mechanisms of Mn neurotoxicity are not well understood,
but it appears that Mn can affect several different aspects of central
nervous system (CNS) function and structure. Some experimental evidence
suggests that the mechanisms of Mn toxicity may depend on the oxidation
state of Mn. However, both the trivalent form (Mn3+) and the
divalent form (Mn2+) have been demonstrated to be neurotoxic.\56\
Also, both forms of Mn can cross the blood-brain barrier, although
research suggests that Mn3+ is predominantly transported bound to
the protein transferrin (Aschner and Gannon, 1994), whereas Mn2+
may enter the brain independently of such a transport mechanism (Murphy
et al., 1991). Unlike ingested Mn, inhaled Mn is transported directly
from the respiratory system to the vicinity of the brain before its
first pass by the liver. Depending on the form of Mn inhaled, its
conversion to other oxidation states (e.g., oxidation of Mn2+ to
Mn3+ or reduction of Mn4+ to Mn3+), and its ability to
enter the brain (through a protein transport mechanism or otherwise),
it is quite possible that a significant fraction of even small amounts
of inhaled Mn would be able to reach target sites in the CNS. Thus, the
apparently greater toxicity of inhaled versus ingested Mn may reflect
important pharmacodynamic and pharmacokinetic differences of Mn that
enters the body by different routes. A more definitive understanding of
these issues will require more empirical information.
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\56\Various elements can exist in more than one form of charged
atom, depending on the number of negatively charged and positively
charged particles contained in the atom. Manganese is one such
element where, depending on the number of charged particles
associated with the atom, the atom may have a net charge of two or
three ``plus'' charges resulting in a ``divalent'' or ``trivalent''
form, respectively.
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2. Earlier Assessments
Earlier ORD health assessments have been based on the RfC, which is
defined as an estimate (with uncertainty spanning about an order of
magnitude) of a continuous inhalation exposure level for the human
population (including sensitive subpopulations) that is likely to be
without appreciable risk of deleterious noncancer effects during a
lifetime. The basic procedure for derivation of an RfC entails
identifying a no-observed-adverse- effect level (NOAEL) and a lowest-
observed-adverse-effect level (LOAEL) from a ``principal'' study,
generally defined as the available study that best defines the highest
NOAEL or lowest LOAEL for the most sensitive endpoint affected by a
chemical. When an investigation of occupationally exposed humans is the
principal study (as in the case of the Mn RfC), the NOAEL or LOAEL is
adjusted for differences in ventilation rates and exposure durations
between the occupational exposure scenario (10 m\3\ air breathed per 8-
h workday, 5 days/week) and the ``general public'' scenario (20 m\3\
air breathed per 24-h day, 7 days/week). The adjusted NOAEL or LOAEL is
then divided by uncertainty factors and a modifying factor. In the case
of the original (1990) RfC for Mn, uncertainty factors of 10 each were
used for extrapolating from a healthy worker population to the general
population (including sensitive subpopulations) and for extrapolating
from a LOAEL to a NOAEL. Also, an uncertainty factor of 3
(approximately one-half of 10 on a log scale) was used for
extrapolating from subchronic to chronic exposure. A modifying factor
of 3 was used because of statements by the authors of the principal
study (Roels et al., 1987) that past exposure levels of workers in the
subject study were probably lower than those measured at the time the
study was conducted. The resulting RfC of 0.4 g Mn/m\3\ was
used for the earlier ORD risk assessment (U.S. Environmental Protection
Agency, 1990) and was entered on EPA's IRIS computer database of human
health risk and regulatory information in December 1990.
3. 1993 Revised RfC
The original RfC for Mn was revised, in part, because newer
information supplied in conjunction with the resubmittal of the MMT
waiver application by Ethyl indicated that the workers' exposure levels
in the principal study had probably not increased over time, and thus
the modifying factor could be ``eliminated'' (i.e., set equal to 1).
Another reason for revising the original RfC was that more recent
studies (Roels et al., 1992; Mergler et al., 1994) provided additional
evidence of health effects in workers at relatively low airborne
concentrations of Mn.
Independently of their earlier study of Mn-exposed workers (Roels
et al., 1987), Roels et al. (1992) conducted a cross-sectional study of
neurobehavioral and other endpoints in another group of workers from a
different factory-namely, 92 male alkaline-battery plant workers
exposed to manganese dioxide (MnO2) dust--who were compared to a
matched control group of 101 male workers without industrial Mn
exposure. The geometric mean occupational-lifetime integrated
respirable dust concentration was 793 g Mn/m\3\ x years
(range: 40 to 4,433). The equivalent value for total dust was 3,505
g Mn/m\3\ x years (range: 191 to 27,465). The authors noted
that the monitored concentrations were representative of the usual
exposures of the workers because work practices had not changed during
the last 15 years of the plant's operation. No data on particle size or
chemical purity were provided in the report by Roels et al. (1992), but
based on information provided by Roels et al. (1992) and Roels (1993),
the median cut point for the respirable dust fraction was 5 m
aerodynamic diameter. The respirable fraction is more representative of
the toxicologically significant particles (i.e., the smaller particles
that are inhaled and deposit predominantly in the lower respiratory
tract). Total dust measurements comprised the respirable dust as well
as larger particles that deposit predominantly in the nose and throat
region (via nasal breathing) and would be cleared more rapidly from the
respiratory tract than the smaller particles retained in the lower
regions. Therefore, the respirable dust measurements were considered to
be a more accurate indicator of exposure in relation to the observed
health effects.
Manganese-exposed workers in the 1992 study by Roels et al.
performed significantly worse than matched controls on several measures
of neurobehavioral function, particularly visual reaction time, eye-
hand coordination, and hand steadiness. Similar neurobehavioral
impairments were also found in the earlier study by Roels et al. (1987)
of a different occupational population exposed to mixed Mn oxides and
salts at approximately the same levels of total dust (respirable dust
was not measured). In addition, a recent study in Canada by Mergler et
al. (1994) indicated that, among other effects, performance on tests of
the ability to make rapid alternating hand movements, to maintain hand
steadiness, and to perform other aspects of fine motor control was
significantly worse, compared to matched controls, in workers who were
exposed to even lower concentrations of respirable dust (35 g
Mn/m\3\ at the time of the study). If Mergler et al. had included
information on integrated past exposure levels (which they have since
provided to ORD in a preliminary form not yet submitted for
publication), their study would have provided a fivefold lower LOAEL
for the derivation of the RfC. In addition, reports of a Swedish study
of Mn-exposed steel workers (Iregren, 1990; Wennberg et al., 1991,
1992) provided compelling evidence of comparable neurobehavioral
impairments, including slower reaction time and finger-tapping speed.
The median total dust concentration in the Swedish study was 140
g Mn/m\3\, with respirable dust reported as constituting 20 to
80% of individual workers' total dust exposures. Thus, the LOAEL from
this study would be somewhat lower than that from Roels et al. (1992),
but the less fully characterized exposure histories in the Swedish
study made it more appropriate as a supporting (rather than principal)
study for deriving the Mn RfC.
Taken together, the above epidemiological studies provide a
consistent pattern of evidence indicating that neurotoxicity is
associated with low-level occupational Mn exposure. The fact that speed
and coordination of motor function are especially impaired is
particularly noteworthy, given its consistency with other
epidemiological, clinical, and experimental animal evidence of higher
concentration Mn intoxication.
Differences among these studies in the duration of workers'
exposure to Mn raise another issue of relevance to this discussion. In
the Roels et al. (1992) study, the mean period of exposure was 5.3
years (range: 0.2 to 17.7 years). In the other studies, the mean
durations of exposure were longer: 7.1 years in Roels et al. (1987),
9.9 years in Iregren (1990), and 16.7 years in Mergler et al. (1994).
The indications of lower LOAELs in the Canadian and Swedish studies
suggest that neurobehavioral effects might occur at lower
concentrations of Mn if the exposure periods were longer. In addition,
the age of the workers may be an important factor in interpreting these
findings. The oldest worker in the Roels et al. (1992) study was less
than 50 years old; also, the average age in that study was only 31.3
years, versus 34.3 years in Roels et al. (1987), 43.4 years in Mergler
et al. (1994), and 46.4 years in Iregren (1990). These points suggest
that longer exposure and/or testing later in life might result in the
detection of effects at lower concentrations than is possible after
shorter periods of exposure and/or in younger workers. On the other
hand, it is also evident from these studies that a much shorter period
than a full lifetime of occupational Mn exposure may be sufficient to
induce Mn neurotoxicity.
As Roels et al. (1992) and other investigators have noted, a
threshold for the neurotoxic effects of Mn has not been reported in the
epidemiological literature. Therefore, instead of a NOAEL, a LOAEL was
obtained from the study by Roels et al. (1992) by dividing the
geometric mean integrated respirable dust concentration (793 g
Mn/m3 x years) by the average period of worker exposure (5.3
years) to eliminate time (in years) from the time-weighted average,
thereby yielding a LOAEL of 150 g Mn/m3. (The geometric
mean concentration was used to represent the average exposure because
the workers' exposure measurements were log-normally distributed, and
the arithmetic mean exposure period was used because it was the only
value reported by Roels et al. (1992).) The workplace-based LOAEL of
150 g Mn/m3 was then adjusted for nonoccupational
lifetime exposure by multiplying it by (1) the quotient of 10 m3/
day divided by 20 m3/day (for worker versus nonworker ventilation
rates) and (2) the quotient of 5 days divided by 7 days (for work week
versus full week). The resulting adjusted LOAEL, labeled the human
equivalent concentration (HEC), was 50 g Mn/m3, which was
then divided by a total uncertainty factor of 1,000 to yield an RfC of
0.05 g/m3. The total uncertainty factor of 1,000
incorporated the following factors: 10 to protect sensitive
individuals; 10 for using a LOAEL in lieu of a NOAEL; and a composite
factor of 10 for database limitations reflecting the less-than-chronic
periods of exposure and the lack of reproductive and developmental
toxicity data, as well as potential but unquantified differences in the
toxicity of different forms of Mn. A modifying factor was not used
(i.e., it was set equal to 1).
Each RfC is assigned an overall rating of low, medium, or high
confidence level, based on two subsidiary confidence ratings reflecting
the quality of the evidence from the principal studies and the quality
of the overall database for the chemical in question, respectively. The
revised Mn RfC was assigned a medium level of confidence. The evidence
for the neurobehavioral effects of low-level Mn exposure by inhalation
was compelling and consistent across several well-conducted studies.
However, the limited duration of exposure and the lack of a NOAEL for
neurotoxicity in any of the principal or supporting studies prevented
assigning a confidence level greater than medium. Also, the lack of
definitive data on the concentration-response relationship and on the
potential reproductive and developmental toxicity of inhaled Mn limited
the degree of confidence in the database to a medium rating. Virtually
all of the human health evidence is based on healthy, adult male
workers. No known studies have investigated human female reproductive
function, and even though male worker reproductive function is known to
be affected by Mn exposure, it has not received adequate investigation.
The limited available information concerning the developmental toxicity
of inhaled Mn suggests the possibility that prenatal exposure of
laboratory rodents to MnO2 (via the air supplied to the pregnant
mother) may depress neurobehavioral activity in neonatal rats and that
continued postnatal exposure of the pups may intensify this depression.
In addition, several studies have demonstrated alterations in
neurochemical (dopamine) levels in young mice and rats exposed during
early postnatal development to Mn via other routes. Thus, the potential
for developmental toxicity due to Mn exposure exists. The
concentrations and durations of exposure sufficient to induce such
effects are not known. Although adequate epidemiological studies of
children and the elderly have not been conducted, it is known that
certain populations, such as children, pregnant women, elderly persons,
iron- or calcium-deficient individuals, and individuals with liver
impairment, may have an increased potential for excessive Mn body
burdens due to increased absorption or altered clearance mechanisms.
Another concern raised by the lack of studies involving longer
periods of exposure and/or older subjects is that the compensatory or
reserve capacity of certain neurological mechanisms may be stressed by
Mn exposure earlier in life, with manifestations of impairments only
becoming evident much later, perhaps at a geriatric stage. One reason
for the latter concern is that Parkinson's disease is typically a
geriatric disease in which symptoms are only seen when the loss of
brain cells that produce dopamine (which is also apparently involved in
Mn toxicity) reaches 80% or more. Indeed, some neurologists think that
a long latency period of perhaps several decades may precede various
parkinsonian syndromes. These points lead to a concern that if Mn
reduces the compensatory or reserve capacity of the nervous system,
parkinsonian-type effects might occur earlier in life than they would
otherwise. Thus, several questions remain to be answered before higher
confidence in the accuracy of the RfC can be achieved.
The two studies of Roels et al. (1992, 1987) were considered
coprincipal studies for the derivation of the revised RfC, with
supporting evidence in the reports of Mergler et al. (1994), Iregren
(1990), and Wennberg et al. (1991, 1992). Given the fact that these
studies involved exposure to various oxides and salts of Mn, the RfC is
designated as applying to Mn and Mn compounds (including
Mn3O4). The previous RfC of 0.4 g Mn/m3 applied
to Mn only, due to undifferentiated forms of Mn in the principal study.
Given that different forms of metals may have different toxic
properties (due to different oxidation states, different solubilities,
and possibly other factors), it is likely that different compounds of
Mn vary in toxicity. However, sufficient data on the comparative
toxicity of various compounds of Mn are not available to judge the
relative toxicity of Mn3O4 specifically.
As noted above, Mn affects multiple organ systems, including the
respiratory and reproductive systems as well as the CNS. However,
because the only available evidence suggests that the CNS is the most
sensitive target for Mn toxicity, neurobehavioral endpoints were the
focus of the RfC derivation. Although other types of effects remain a
concern, it is presumed, based on the limited data now available, that
protecting against neurotoxicity provides protection against these
other, apparently less sensitive endpoints.
In revising the RfC for Mn, a draft version was subjected to peer
review by external experts (from academic and non-EPA governmental
institutions) as well as internal experts. Following this peer review,
a further-revised version was submitted to and verified by an EPA-wide
RfD/RfC work group in September 1993. The current RfC for Mn was made
available through IRIS in early November 1993 through two mechanisms. A
special notice beginning November 1 in the news section of EPA's
internal IRIS2 database announced the availability of a hard copy of
the text to EPA requesters who contacted the Risk Information Hotline;
also, the text was obtainable through the National Library of
Medicine's publicly accessible on-line computer database, TOXNET,
beginning November 10, 1993. It also became available on line via the
EPA IRIS database beginning December 1, 1993.\57\
---------------------------------------------------------------------------
\57\The complete text of the revised RfC as it exists on IRIS2
may be found in Appendix C in the docket.
---------------------------------------------------------------------------
4. Alternative Approaches to Deriving RfCs
After the revised RfC for Mn became available to the public, Ethyl
Corporation and other interested parties submitted comments on the RfC
and issues related to it. One of the primary comments concerned the
availability of various statistical techniques for deriving a NOAEL
from the study by Roels et al. (1992) and/or from supplementary data
for that study provided to ORD by Roels (1993). In response to Ethyl
Corporation's request that EPA consider alternative approaches to
analyzing these data and deriving an RfC for Mn, further analyses of
the subject data were undertaken using a variety of statistical
methods. These approaches may be identified as (1) conventional NOAEL-
or LOAEL- based analyses, (2) ``no statistical significance of trend''
(NOSTASOT) analyses of the type described by Tukey et al. (1985), (3)
benchmark dose analyses of the type described by Crump (1984), and (4)
Bayesian analyses of the type described by Jarabek and Hasselblad
(1991). These analyses and their results\58\ yield several possible RfC
estimates, so designated because the current and only verified RfC for
Mn is that which has been verified by the EPA-wide RfD/RfC work group
and entered on IRIS. It must be emphasized that the RfC estimates
developed for the purpose of this risk assessment do not represent a
revision of the current verified RfC for Mn. Reexamination of the
current Mn RfC, and any decision to revise or reaffirm the current RfC,
will be under the purview of the EPA-wide RfD/RfC work group at some
future date.
---------------------------------------------------------------------------
\58\See ``Reevaluation of Inhalation Health Risks Associated
with Methycycloentadienyl Manganese Tricarbonyl (NMT) in Gasoline'',
Appendix A, Docket A-91-46.
---------------------------------------------------------------------------
A fundamental issue pertaining to all of the approaches presented
here is the selection of a measure of exposure. Roels et al. (1992)
described two measures of respirable dust, the occupational lifetime
respirable dust concentration (LIRD), expressed as g/m3 x
years, and the current concentration of respirable dust (CRD),
expressed as g/m3. The CRD concentration was measured at
the time the study was conducted by Roels et al. and refers to a
representative concentration measured for the type of job performed by
a worker (e.g., electrician, maintenance worker). The LIRD value for
each worker was a cumulative exposure measure derived by adding the CRD
values over the worker's entire period of employment. If a worker
changed jobs within the plant during his period of employment, the CRD
for each job held was multiplied by the number of years the worker
performed that job. Thus, if more than one job classification was
worked, the worker's LIRD was the sum of the products of CRD multiplied
by years of performance of the respective jobs. However, if a worker
held only one job classification, his LIRD was simply equal to his CRD
multiplied by the number of years employed. Another measure of exposure
may be derived from LIRD by dividing an individual worker's LIRD value
by his total number of years of employment. The latter measure,
designated as the average concentration of respirable dust (ACRD),
reflects a worker's time-weighted cumulative exposure level but removes
years from the unit of measurement of LIRD and is expressed as
g/m3. Although Roels et al. (1992) did not refer to ACRD,
this value could be calculated for each individual and for the entire
cohort by using the unpublished data provided to ORD by Roels (1993).
For reasons to be discussed later, ACRD offers advantages for certain
analyses and, unless otherwise noted, is the exposure measure used in
the alternative RfC estimates discussed here.
a. Conventional NOAEL- or LOAEL-Based Approach. The conventional
method, and only method used thus far by EPA, to derive an RfC has been
to identify a NOAEL or LOAEL from a study and divide that concentration
by uncertainty factors, as described above for the Mn RfC. In the case
of the study by Roels et al. (1992), the geometric mean LIRD
concentration of the Mn-exposed workers was used as a LOAEL. Roels et
al. (1992) also performed an exposure-response analysis of their data
by grouping the exposed workers into three exposure categories and
comparing the prevalence of abnormal neurobehavioral scores for each of
the three groups to those of controls. As indicated in the summary
sheet for the Mn RfC (see Appendix C), the results of this exposure-
response analysis were not used in deriving the revised Mn RfC because
the reported analysis did not correct for multiple comparisons.
However, ORD's analyses of additional data provided by Roels (1993)
suggest a possible RfC estimate of 0.03 g/m3 (versus the
current RfC of 0.05 g/m3), if a one-tailed test of
statistical significance is accepted (see Appendix A, ``Reevaluation of
Inhalation Health Risks Associated with Methyl- cyclopentadienyl
Manganese Tricarbonyl (MMT) in Gasoline'' as referenced in the
reference section below, hereafter referred to as Appendix A.). Because
it was based on an exposure-response analysis, this RfC estimate is
labeled as such in Figure 1, which could not be reproduced in the
Federal Register. It is available by calling the person listed in the
FOR FURTHER INFORMATION CONTACT section of this notice. It is also
available in docket A-93-26, item number II-A-17, page 12 (see ADDRESS
section of this notice for docket location).
b. NOSTASOT Approach. Another approach to analyzing dose-response
data makes use of a procedure known as NOSTASOT, described by Tukey et
al. (1985). In essence, the procedure applies a trend test sequentially
to determine the highest noneffective dose of a series of doses by
eliminating one dose at a time. In this manner, the dose level at which
the response is not significantly different from controls is determined
to be the NOSTASOT dose, which could therefore be considered a NOAEL.
Applied to Roels' (1993) epidemiologic data by beginning with the
highest individual ACRD exposure and moving downward (i.e., a ``top-
down'' approach), the procedure yielded a NOSTASOT of 285 g/
m3 for eye-hand coordination (see Table A-4, Appendix A). This
approach implies that once nonsignificance is reached, further
application of trend tests to lower dose groups would also yield
nonsignificance. However, this was not the case with Roels' (1993)
epidemiologic data, and thus it was important to determine not simply
the highest NOAEL but the highest NOAEL below the lowest LOAEL. By this
``bottom-up'' approach, the highest nonsignificant exposure below the
lowest statistically significant exposure was 21 g/m3,
for visual reaction time. Using the latter value as a NOAEL and a total
uncertainty factor of 100 (the same as that used for the current Mn
RfC, except omitting a factor of 10 for extrapolating from a LOAEL to a
NOAEL), one would obtain a value of 0.07 g/m3 for an RfC
estimate (Figure 1). Disparities in the NOSTASOTs obtained for various
endpoints by the top-down and bottom-up approaches raise questions
about the suitability of this technique for deriving a NOAEL from the
data of Roels (1993).
c. Benchmark Analyses. Another approach to deriving an RfC estimate
is the benchmark dose (BMD) approach, which has been described by Crump
(1984) and others (e.g., Kimmel and Gaylor, 1988; Faustman et al.,
1994; Allen et al., 1994). A BMD is an estimate of the dose (the term
dose is used interchangeably here with concentration, although the
latter is more appropriate for inhalation exposure) that will produce a
specified effect (e.g., a 10% increase in the prevalence of abnormal
scores on a neurobehavioral test in the case of the study by Roels et
al. (1992)). The BMD is calculated by fitting a mathematical model to
the available data and obtaining a maximum likelihood estimate of the
dose associated with a specified increase in response (typically 10, 5,
or 1%). A lower confidence limit is then calculated for the BMD
(usually the 95th percentile), and the result is denoted as a benchmark
dose level (BMDL), which has been proposed as a substitute for a NOAEL
in deriving RfDs or RfCs (Crump, 1984; Barnes et al., 1994). Subscripts
designate the effect level (10, 5, or 1%) for which the BMDL has been
calculated, as in BMDL10, BMDL5, or BMDL1.
A large number of mathematical models could be used for deriving
BMDLs, but six frequently used models have been selected for the
present exercise (as discussed in Appendix A). In applying these models
to the dataset provided by Roels (1993), it appears that the models fit
the CRD and ACRD data better than the LIRD data. (As explained in
Appendix A, it made little difference whether the LIRD values were
obtained from the group data provided in the report by Roels et al.
(1992) or from the individual exposure data supplied by Roels (1993),
so the latter LIRD data were used here.) In principle, LIRD is superior
to CRD as a measure of long-term or cumulative exposure. One reason for
the difference in goodness of fit between LIRD and either CRD or ACRD
is that two workers with low LIRD values had abnormal eye-hand
coordination responses (exceeding the 95th percentile of control
scores). These two subjects appear to have had rather short exposure
durations (0.3 and 0.4 years) and moderately high CRD values (201
g/m\3\ each). Thus, these two data points suggest an LIRD
exposure-response relationship that is better fit by a supralinear
curve with a power term <1 (see Figures A-3 and A-5 in Appendix A) than
by the more nearly linear curve such as that produced by the quantal
linear or restricted Weibull model (see Figures A-1 and A-4 in Appendix
A). If CRD or ACRD exposure data are used, however, the two individuals
tend to fall in line better with a linear model (see Figures A-7 to A-
10 in Appendix A). Another factor contributing to difficulty in fitting
the Roels (1993) data with linear models is a tendency for the
prevalence of abnormal eye-hand coordination responses to decline
slightly at the highest LIRD, CRD, and ACRD concentrations (evident in
Figures A-1 to A-6).
The supralinear exposure-response curve for abnormal eye-hand
coordination scores suggests a possible corollary to the healthy worker
phenomenon; namely, the existence of newly employed, relatively
sensitive workers vis-a-vis long-term, relatively nonsensitive workers.
It may be that the two above-noted workers happened to be rather
susceptible to Mn toxicity but had not been employed long enough for
their greater sensitivity to become otherwise evident. There could be a
tendency for such workers to move to other types of employment, leaving
a greater proportion of relatively less sensitive individuals among the
older workers. Although irregularities of the type posed by the data
for these two workers create complexities for model fitting, it is
important to recognize that statistical curve fitting is secondary to
the objective of selecting the most biologically appropriate exposure
variable. However, given that the final results obtained with LIRD,
CRD, and ACRD are roughly equivalent, ACRD has been selected for
discussion here because it estimates an average exposure over time and
yet provides as good or better goodness of fit as CRD or LIRD for most
of the models considered.
Of the six models considered, the quantal linear model fits the
data reasonably well and is the least complex (see Appendix A). It also
gives equivalent results to the restricted Weibull model for BMDL
calculations (although the two models differ slightly when used in the
Bayesian analyses, to be described below). Although much more
conservative results would be obtained if the unrestricted Weibull or
unrestricted log-logistic model were used, the NOAEL/LOAEL surrogates
obtained with the latter models are so small as to be practicably
incalculable and extend far below the range of actual measurements.
Therefore, the following discussion is focused on the results obtained
with the quantal linear model.
In addition to choosing a model, a specified rate of increase in
the effect of concern must be selected in using the BMD approach. This
percentage increment is expressed in terms of the effective
concentration that would yield the stated increase. Increases of 10, 5,
and 1% in the incidence of abnormal eye-hand coordination scores (as
dichotomized by Roels et al., 1992) have been considered, with the
concentrations associated with these levels called ``effective
concentrations'' and designated as EC1, EC5, and EC10,
respectively. One guide to the choice of an effect level is that the
resulting BMD (before calculating the lower confidence limit) is
preferably near or within the range of observed exposure concentrations
(cf. Barnes et al., 1994). Because the BMD for EC1 falls outside
this range of observed concentrations, the primary focus in this
discussion is devoted to the BMDL5 and the BMDL10.
It should be kept in mind that the BMDL represents the lower 95th
percent confidence interval for the effective concentration in
question, and therefore the BMDL probably inherently reflects some
degree of conservatism. However, the degree of conservatism obviously
varies with the effective concentration for different percentage effect
levels and with the nature of the effect (e.g., severe versus moderate
impairment). For the purposes of this assessment, if one treats the
BMDL10 derived from the dichotomized (quantal) data of Roels as if
it were a minimal (less severe) LOAEL and the BMDL5 as if it were
a NOAEL, uncertainty factors of 3 and 1, respectively, would be
warranted. On this basis, as shown in Figure 1 and in Table A-39 of
Appendix A for the quantal linear model using ACRD, an RfC estimate of
0.09 g/m\3\ would be obtained by using the quantal BMDL10
as if it were a LOAEL and a total uncertainty factor of 300 (10 for
intraspecies sensitivity, 10 for database limitations, and 3 for a
minimal severity LOAEL). Similarly, the quantal BMDL5 would yield
an RfC estimate of 0.1 g/m\3\, based on a total uncertainty
factor of 100 (10 for intraspecies sensitivity, 10 for database
limitations, and 1 for a NOAEL). As applied here, the benchmark
approach yields candidate RfC estimates of 0.09 to 0.1 g/m3.
d. Bayesian Analyses. Another approach to deriving a substitute for
a conventional LOAEL or NOAEL, which bears some resemblance to the BMD
approach just described, is known as the Bayesian approach (see
Appendix A). In essence, the Bayesian approach yields a distribution of
concentrations (rather than a point estimate) associated with a
specified effect. Some features of the BMD approach are common to the
Bayesian approach: a mathematical model must be fit to the data, an
effect level must be selected, and a confidence bound on the estimated
concentration associated with a given effect level must be calculated
(although the calculation procedures are different). If these choices
are consistent with those for the BMD approach, the results are quite
similar. By the Bayesian analysis, for a 10% increase in abnormal eye-
hand coordination scores, the lower 90% credible set limit (roughly
equivalent to the quantal BMDL 95% confidence limit\59\ based on the
estimated median concentration obtained with the quantal linear model
is 73 g/m\3\. Adjusting this value to a human equivalent
concentration (HEC) and treating the result (26 g/m\3\) as if
it were a LOAEL(HEC), one may divide by a total uncertainty factor of
300 (10 for intraspecies sensitivity, 10 for database limitations, and
3 for a minimal severity LOAEL) and obtain an RfC estimate of 0.09
g/m\3\. Similarly, the 5% effect level yields an RfC estimate
of 0.1 g/m\3\, based on a total uncertainty factor of 100.
Thus, as applied here, the Bayesian approach yields candidate RfC
estimates of 0.09 to 0.1 g/m\3\, essentially identical to the
results of the benchmark analysis (Figure 1).
---------------------------------------------------------------------------
\59\U.S. Environmental Protection Agency. (1994a) ``Reevaluation
of inhalation health risks associated with methylcyclopentadienyl
manganese tricarbonyl 9MMT) in gasoline.'' Washington, DC: Office of
Research and Development; EPA report no. 600/R-94/062. For further
information see Air Docket A-93-26, II-A-12.
---------------------------------------------------------------------------
One advantage of the Bayesian approach is that it lends itself well
to using continuous as well as dichotomous data. Although Roels et al.
(1992) did not provide individual continuous data (i.e., actual raw
scores instead of designations of normal/abnormal) on the performance
of the workers in their study, they did report mean differences and
standard deviations. With this information, it is possible to estimate
the concentration at which certain effect levels would occur based on
the Bayesian posterior distribution. For example, a 10% increase in the
proportion of subjects with abnormal scores would be associated with a
median concentration of 112 g/m\3\, which has a lower 90%
credible set limit of 90 g/m\3\. Adjusting the latter value as
if it were a LOAEL(HEC) yields a concentration of 32 g/m\3\
and an RfC estimate value of 0.1 g/m\3\, based on a total
uncertainty factor of 300 (10 for intraspecies sensitivity, 10 for
database limitations, and 3 for a minimal severity LOAEL). Note that
these calculations based on continuous data essentially approximate the
quantal BMD and Bayesian calculations for a 10% effect level based on
dichotomous data (see Figure 1). Similar calculations for the actually
observed difference (i.e., 13%) between the Mn-exposed and control
workers in the Roels et al. (1992) study yield an RfC estimate of 0.2
g/m\3\, based on a total uncertainty factor of 300 (including
a factor of 3 for a minimal severity LOAEL). Calculating the
concentration associated with the difference between the exposed and
control mean values that just achieves statistical significance (a 4%
difference in this case) also results in a candidate RfC value of 0.2
g/m\3\, based on a total uncertainty factor of 100
(eliminating the minimal LOAEL factor of 3). Thus, as applied here, the
Bayesian analyses of continuous data yield candidate RfC estimates of
0.1 to 0.2 g/m\3\.
e. Summary of RfC Estimates. Figure 1 displays the current,
verified RfC along with over 100 possible Mn RfC estimates based on
various exposure measures, models, effects measures, and uncertainty
factors. Not all of these RfC estimates are equally plausible or worthy
of consideration in assessing the potential health risks associated
with Mn inhalation exposure due to MMT usage. As discussed above, some
combinations of the three exposure measures and six mathematical models
fit one another better than other combinations. Based primarily on
considerations of cumulative dose toxicity, statistical goodness-of-
fit, and parsimony, ACRD and the quantal linear model appear to achieve
the best results in this respect. Given the similarities of the
benchmark and Bayesian analytic results using ACRD and the quantal
linear model, little distinction can be made between the two analytic
approaches in the present application. As for the results obtained for
different effect levels, using a severity uncertainty factor of 3 with
a 10% effect level (for either benchmark or Bayesian analyses) is
essentially equivalent to using a severity UF of 1 with a 5% effect
level. Note that the terms LOAEL and NOAEL do not actually correspond
to the results for 10% and 5% effect levels, and therefore neither is
preferable to the other in the sense that a NOAEL is preferable to a
LOAEL in deriving an RfC. Therefore, benchmark and Bayesian results for
10% and 5% effect levels (using ACRD with the quantal linear model) are
regarded as equally worthy of consideration here. These particular
analyses yield Mn RfC estimates of 0.09 to 0.1 g/m\3\.
In general, continuous response data are preferred to dichotomized
data, primarily because they provide more information and avoid the
basically arbitrary division of effect measurements into categories
(e.g., normal versus abnormal). The Bayesian analysis based on mean
differences between exposed and control groups offers some of the
advantages of using continuous data, in that the reported means and
standard deviations (from Roels et al., 1992) provide a basis for
estimating the distribution of continuous response measures. However,
this use of continuous data is not immune to certain common problems,
such as the issue of statistical power associated with studies of
limited size, for the approaches calculating observed or just-
statistically significant differences. Also, whereas the dichotomous
data analyses yield more precision in estimating the effective
concentration associated with a somewhat imprecise response variable,
the continuous data analyses offer the opposite trade off (i.e., more
precision in the response variable but less in the exposure estimate).
Nevertheless, the continuous data analyses appear to merit
consideration as well as the analyses based on dichotomous data. By the
Bayesian analyses of continuous data, Mn RfC estimates of approximately
0.1 to 0.2 g/m\3\ are obtained.
Based on the available data and on decisions and assumptions
involved in analyses of these data, the leading candidate estimates for
an alternative Mn RfC appear to fall in a range of approximately 0.09
to 0.2 g/m\3\. (Ethyl Corporation (1994) has proposed an
alternative RfC estimate based on a BMDL10 value of 87 g/
m\3\. Treating this value as essentially a NOAEL (thereby eliminating
an uncertainty factor for use of a LOAEL), Ethyl Corporation divided
the adjusted NOAEL(HEC) by a single uncertainty factor of 10 for
sensitive subpopulations to derive a Mn RfC estimate of 3 g/
m\3\.)\60\
---------------------------------------------------------------------------
\60\The RfC listed here is not simply the BMDL10 of 87
g/m\3\ reduced by the uncertainty factor of 10 because the
BMDL10 must first be adjusted to produce an adjusted NOAEL(HEC)
(i.e., to go from an occupational exposure scenario to a scenario
for the general public) prior to reduction by the uncertainty
factor.
---------------------------------------------------------------------------
C. Exposure Assessment
1. Background
Very limited data have been available by which to estimate
potential Mn personal exposure levels likely to be associated with the
use of MMT as an additive in unleaded gasoline. For example, after the
completion of ORD's 1990 exposure assessment for Mn (U.S. Environmental
Protection Agency, 1990), Ethyl Corporation provided EPA a brief report
of a personal monitoring study as part of Ethyl Corporation's
resubmittal of a waiver application for MMT. The study focused on 6
taxi drivers and 17 office workers in Toronto, ON, where the allowable
MMT concentration in gasoline is \1/16\ (0.062) g Mn/gal. (In the
Toronto study, the actual concentration was reported as \1/26\ (0.039)
g Mn/gal, which is only slightly greater than the \1/32\ (0.031) g Mn/
gal concentration proposed for the United States. As confirmed by
Kirshenblatt (1993), MMT concentrations in Canadian gasoline average
well below the allowable limit there.) In comments on Ethyl's
resubmittal, ORD considered the Toronto data in conjunction with
results from independent field studies of personal exposures to carbon
monoxide to develop a revised Mn exposure assessment (Preuss, 1991). A
key element of the 1991 ORD assessment was the assumption that taxi
drivers (six of whom were monitored in Toronto within a 2-week period)
were members of a high-exposure cluster reflecting the upper 4% of the
population in a model based on the carbon monoxide field studies. The
result of the 1991 assessment was an estimate that 4% of the general
public might be exposed to Mn at approximately 0.09 g/m\3\,
although this estimate had an undetermined amount of uncertainty due to
the inadequacies of the available data.
2. Additional Canadian Studies
Since the 1991 ORD assessment, additional personal exposure studies
have been completed in Montreal and Toronto (described in Appendix B,
``Reevaluation of Inhalation Health Risks Associated with Methyl
cyclopentadienyl Manganese Tricarbonyl (MMT) in Gasoline'' as
referenced in the reference section below, hereafter referred to as
Appendix B.) As shown in Figure B-10 of Appendix B, the average
concentrations reported in the Canadian studies vary by as much as an
order of magnitude for small groups (5 to 19 persons each) of garage
mechanics, taxi drivers, and office workers. The highest average Mn
personal exposure level was 0.25 g/m\3\ for Montreal garage
mechanics while at work; the other averages ranged from 0.002 to 0.035
g/m\3\ for various particle size fractions. Although it is
impossible to extrapolate the results of these studies to the
distribution of Mn exposure levels for the general population, it does
appear that there is a general relationship between personal exposure
levels of Mn and proximity to vehicular emissions of combusted MMT.
Thus, populations living near high traffic-volume areas such as inner
cities and expressways would probably tend to experience higher Mn
exposure levels in relation to MMT usage.
Some of the limitations of the Canadian studies with respect to
development of a quantitative exposure assessment are reviewed in
detail in Appendix B and may be summarized briefly as follows.
The studies did not have adequate sample sizes and did
not sample according to a probabilistic statistical design that
would help ensure the representativeness of the sampled individuals.
The sampling periods were relatively short, 1 to 2
weeks at most. Meteorological and other factors that would be
expected to influence ambient measurements over relatively short
periods of time were not characterized.
Because the studies did not use ambient monitors
collocated with reference monitors (such as the dichotomous samplers
used by Canadian agencies), it is difficult to relate data from the
studies to larger databases from the government monitoring networks.
Because the studies did not use identical monitors to
measure personal exposure levels and outdoor ambient levels, it is
difficult to distinguish between personal exposures and ambient
levels or to relate one to the other.
Quality assurance and certain other important
methodological details are not fully provided in the available
reports.
Because of the substantial limitations of the above exposure
studies, no quantitative assessment of personal exposures to Mn in a
Canadian population is possible at present.
3. The PTEAM Study
The only published study that has used a probability-based
representative sampling design for evaluating exposure levels of Mn in
a general population is the Particle Total Exposure Assessment
Methodology (PTEAM) study, which was conducted in Riverside, CA, over a
7-week period in the fall of 1990 (Pellizzari et al., 1992). This study
used personal and stationary monitors to measure Mn concentrations
indoors and outdoors. The personal samplers collected PM10, and
the stationary samplers collected PM2.5 as well as PM10 (see
glossary of terms in Attachment B-6 to Appendix B). Of the 139,000
nonsmoking residents age 10 years and older in Riverside, 178
individuals were selected through a stratified sampling plan to
represent the general population and were monitored over two 12-hour
periods (daytime and nighttime). More than 2,750 particle samples were
collected. Quality assurance and other procedures are summarized in
Appendix B and are described extensively elsewhere (e.g., Pellizzari et
al., 1992; Clayton et al., 1993; Thomas et al., 1993). The PTEAM study
has been presented in various peer-reviewed publications and discussed
in several scientific forums (see Attachment B-5 to Appendix B). It
represents the best available information on an actual distribution of
general population exposures to Mn. It also provides valuable
information on potential Mn exposure associated with MMT use, because
MMT was used in leaded gasoline in California prior to and during the
period of the PTEAM study.
4. Estimated Mn Exposure Levels Associated with MMT Usage
As noted above, the substantial limitations of the available
Canadian exposure studies make them unsuitable for estimating
population exposure levels of Mn in relation to MMT usage. In addition,
ambient monitoring data typically underestimate and may be uncorrelated
with personal exposure levels of automotive-source pollutants.
Therefore, of the currently existing published evidence pertaining to
Mn exposure levels in relation to MMT usage, only the PTEAM Riverside
study (Pellizzari et al., 1992) provides a reasonable basis for
estimating potential future exposure levels in relation to a scenario
where 100% of unleaded gasoline contains \1/32\ g Mn/gal as proposed by
Ethyl Corporation.
In the PTEAM study, measurements of personal exposure levels of
PM10 Mn indicated that approximately half of the population in
Riverside in the 1990 study period had 24-hour personal exposures to
PM10 Mn above 0.035 g/m\3\, with the highest 1% of the
population having exposures above 0.223 g/m\3\ PM10 Mn.
However, given the use of PM5 Mn exposure measurements in the
study of Roels et al. (1992), it would be preferable to consider a
population distribution of personal exposure levels of PM5 Mn. Due
to limitations in the available data, the exposure assessment in
Appendix B focuses on estimated personal exposure levels for PM4
Mn, not PM5. Although the difference is probably small, PM4
levels are an underestimate of PM5 levels. The derivation of the
projected exposure estimates involved several steps, which may be
summarized as follows.
The automotive and nonautomotive contributions to particulate Mn
exposures in the PTEAM study were estimated using data from Lyons et
al. (1993), who reported particle size distributions up to PM4 of
selected trace metals, including Mn, at two locations near Riverside in
the winter and summer of 1989. They attributed most of the PM4 Mn
to automotive sources. Based on their findings and data from other
sources, it is possible to estimate that 69% of the PM2.5 fraction
of PM4 Mn they measured was derived from automotive sources
(namely the combustion of MMT in motor vehicle fuel, as then allowed in
leaded gasoline in California) and that 31% was derived from paved road
dust (mostly earth crustal material). Next, the PTEAM Mn measurements
from stationary indoor monitors (SIMs) were used to estimate personal
exposure levels by adjusting the SIM PM2.5 Mn data to reflect the
typically higher levels of all elements measured by personal exposure
monitors (PEMs). This adjustment was made in two ways, either by the
PEM:SIM ratio obtained for Mn or by the ratio obtained for lead (Pb),
another element related to automotive fuel usage. These two methods of
adjusting the SIM data to PEM values resulted in two projected
distributions, as will be described below. The next step in the
derivation procedure involved adjusting the PM2.5 personal
exposure estimates to reflect PM in the size range from 2.5 to 4
m (based again on data from Lyons et al., 1993).
With these estimates of PM4 Mn personal exposure levels due to
automotive sources, it was then possible to project from the situation
in Riverside around the time of the PTEAM study (when leaded-MMT
gasoline constituted about 14% of the gasoline sold and contained an
average of 0.048 g Mn/gal) to a future scenario that assumes 100% of
the unleaded gasoline contains MMT at \1/32\ (0.031) g Mn/gal. This
aspect of the derivation is described in detail in Attachment B-4 to
Appendix B. In essence, a factor was calculated to reflect the
estimated increase in MMT usage between 1990 and 1995 (i.e., the first
full year in the near future). This projection factor assumed an
increase of 1% per year in gasoline usage and no difference in the Mn
emission rate (grams Mn emitted per gram Mn in fuel combusted) for
noncatalyst vehicles using leaded-MMT gasoline in 1990 versus catalyst
vehicles using unleaded-MMT gasoline in 1995.
Next, the nonautomotive contribution to PM4 Mn was estimated
and added to the estimated automotive contribution to obtain the
projected personal exposure levels of total PM4 Mn. Assuming the
estimated PM4 Mn distribution has the same form as the PM10
Mn distribution from PTEAM (approximately lognormal with equal
geometric standard deviations), the ratio of the PM4:PM10
arithmetic mean personal exposure levels yields a scaling factor that
can be applied to the PM10 distribution to obtain the PM4
distributions. Because of the alternative bases for adjusting the SIM
PM2.5 data for personal exposures (as noted above), two different
scaling factors were multiplied by the PM10 distribution, thereby
producing a higher and a lower estimate of the distribution of 24-hour
average PM4 Mn personal exposure levels.
In addition, because long-term exposures are likely to have less
variance than 24-hour exposures, it is appropriate to adjust the
distributions of 24-hour average exposure levels to better reflect
longer periods of exposure. Of various methods that may be used for
this purpose (Wallace et al., 1994), two approaches were applied to
adjust the geometric standard deviations of the two projected exposure
distributions, based on data from either the PTEAM study or the smaller
pilot study that preceded the PTEAM Riverside study. These alternative
methods were applied to the two estimated distributions of 24-hour
average exposures to yield the distributions of long-term average
PM4 Mn personal exposure levels depicted as lines 1 and 2 in
Figure 2 (only the highest and lowest of the four resulting estimates
are shown). It must be emphasized that these two distributions do not
represent upper and lower bounds, because even higher or lower
estimates could be produced by alternative assumptions and adjustments
of the data. Moreover, if data were available for another time of the
year (e.g., spring in addition to fall), the estimates would not be
season-specific and could possibly be much higher or much lower.
Nevertheless, given the limited available data, lines 1 and 2 in Figure
2 represent two reasonable estimates of the projected long-term
(autumnal) personal exposure levels of PM4 Mn in relation to MMT
usage at \1/32\ g Mn/gal in 100% of unleaded gasoline.
By examination of the logarithmic-probability plot of long-term
personal exposure levels of Mn, it is estimated that half of the
population would be exposed to PM4 Mn levels of more than
approximately 0.045 to 0.050 g/m\3\. Also, based on the two
projection estimates, approximately 5 to 10% of the population would
have personal exposure levels around 0.1 g/m\3\ PM4 Mn or
higher. The highest 1% would be predicted to have PM4 Mn exposure
levels above 0.15 g/m\3\. It should be noted that these
projections refer specifically to Riverside, CA, with a population of
more than 139,000 persons. However, in many significant respects (e.g.,
meteorology and traffic volume), Riverside is reasonably representative
of the greater metropolitan area of Los Angeles, which has a total
population of over 14.5 million persons. The exposure projection
estimates for Riverside imply the possibility that hundreds of
thousands of persons in the Los Angeles area alone could be exposed to
PM4 Mn levels exceeding 0.1 g/m\3\. To the extent that
any other U.S. cities (e.g., in the Southwest) share some degree of
resemblance in meteorology, vehicle miles traveled (VMT), and possibly
other characteristics of relevance to automotive Mn levels, the
estimated exposure levels for Riverside could be pertinent, at least
qualitatively, to other locales or portions of locales as well.
Similarities and differences in point-source contributions to Mn
exposure would also figure into comparisons with other communities. The
presence of a major point source or sources of Mn in a community (which
was not a factor in Riverside) would add some increment to the level of
Mn exposure experienced by the persons in that community. Although
these Riverside estimates cannot be applied quantitatively to any other
U.S. metropolitan areas, the total population of the U.S. counties with
VMT levels greater than that of Riverside (apart from the four counties
Los Angeles comprises) is approximately 15 million persons. Possibly,
then, several hundreds of thousands of persons could be exposed to
PM4 Mn levels of approximately 0.1 g/m\3\ or higher if
MMT were used in 100% of the unleaded gasoline in all of these areas.
However, it must be emphasized that because of the limited available
data, a great deal of uncertainty surrounds such estimates. The actual
exposure levels could be much higher or lower.
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D. Risk Characterization
To assess the public health risk associated with the use of MMT in
gasoline in the United States, the available qualitative and
quantitative health effects information on Mn must be related to the
available exposure information. From the standpoint of a qualitative
hazard identification, the available evidence amply demonstrates that
inhaled Mn is toxic to the nervous system, the respiratory system, and
the male reproductive system. The toxicity of Mn by different routes of
exposure has been demonstrated by numerous medical reports and
epidemiological and experimental studies. However, available data do
not allow quantitative estimation of the relative toxicological potency
of different Mn compounds or permit quantitative route-to-route
extrapolations for predicting the effects of Mn3O4.
The focus of the above health assessment discussion has been on the
RfC and the types of risks associated with chronic Mn exposures
because, for the most part, acute effect levels appear to be
considerably higher than the highest projected exposure levels.
However, the issue of less-than-chronic exposures does arise with
respect to the potential for developmental toxicity. It is widely
recognized that the human CNS develops over a period of several years,
prenatally and postnatally, and can be vulnerable to long-term or
irreversible effects if damage occurs during certain ``critical
stages'' of development. Recent evidence from ongoing longitudinal
studies of children indicates that lead (Pb) exposure (measured as
blood Pb level) around 2 years of age in particular is associated with
reduced cognitive performance at 4 to 10 years of age. Such evidence
raises the concern that exposure to another neurotoxic metal such as Mn
during part of early development might also be capable of inducing
permanent or irreversible damage to the developing CNS. Moreover, the
ramifications of such damage might extend to other important functions,
such as reproduction.
Children may also be at higher risk in terms of exposure because of
biomedical and metabolic differences at a young age (greater uptake and
retention) and/or because of the longer duration of their exposure over
a lifetime. Over time, small impairments in neurobehavioral function
may accumulate. For this reason, the elderly, whose neurobehavioral
function may already be compromised by normal aging processes and
possibly by other disease states (e.g., parkinsonism or preclinical
parkinsonism), also represent a special population of concern. The
ability of the elderly or other subpopulations to compensate for such
declines in neurobehavioral function may be overwhelmed eventually by
additional, albeit possibly quite small, insults due to Mn. If so, the
effect could be manifested as a more severe or earlier onset of
declining function in senescence, with consequent implications for
increased societal health-care costs.
Special subpopulations at increased risk may be defined not only in
terms of their biological susceptibility, as exemplified above by the
young and the elderly, but also by their increased risk of exposure. In
this respect, inner city residents and others who live near high
traffic areas such as expressways (e.g., low-income and minority
communities) would possibly have a disproportionate likelihood of
higher Mn exposure levels due to their closer proximity to vehicular
emissions.
The nature of the neurobehavioral effects observed in occupational
studies such as Roels et al. (1992) should be understood as effects
that probably would not be treated by, or even be readily evident to, a
clinical physician. Nonetheless, they are significant from a public
health standpoint when considered in terms of population effects. This
concept is illustrated by the well documented findings on low-level Pb
neurotoxicity in children, where changes of as little as 1 or 2 points
in IQ have been repeatedly demonstrated in several independent,
prospective, epidemiological studies in recent years. Such changes
could not be reliably demonstrated either in a clinical setting or in
earlier cross-sectional epidemiological studies; yet they are now well
established to be ``real'' and significant from a public health
standpoint. With regard to the reductions in neurobehavioral function
observed in various epidemiological studies of Mn-exposed workers,
these studies independently converge on findings of impaired motor
function (e.g., reductions in eye-hand coordination, slower hand or
finger movements, and less control of fine movement). As recently
expressed in a document prepared by the Subcommittee for Risk
Assessment of the Federal Coordinating Council for Science, Engineering
and Technology (Federal Register, 1993), an adverse effect can include
``both unwanted effects and any alteration from baseline that
diminishes the ability to survive, reproduce or adapt to the
environment.'' Thus, it can be argued that these effects in themselves
warrant consideration as adverse health effects. They may also have
ramifications for health and safety of an even more serious nature, if
a person's ability to react quickly and accurately to a situation
(e.g., traffic conditions) was impaired.
Another aspect of the findings from available occupational studies
concerns the temporal relationship between exposure and effect. As
noted above, the geometric mean average period of Mn exposure of the
workers in the Roels et al. (1992) study was only 4 years, with the
longest period of Mn exposure for any one individual being less than 18
years. Also, the oldest worker in the Roels et al. (1992) study was
less than 50 years old. This relatively limited period of exposure
along with the absence of older subjects in the Roels study raises the
question of whether sufficient time had elapsed for the full expression
of the toxic effects of Mn. Some reports in the literature indicate
that Mn toxicity may not be clinically evident until some years after
exposure occurred or terminated (e.g., Cotzias et al., 1968; Rodier,
1955), and other reports point to a greater sensitivity of elderly
persons, compared to middle-aged or young adults, for acute as well as
chronic Mn toxicity (e.g., Kawamura et al., 1941). An uncertainty
factor for extrapolation from a subchronic exposure to chronic exposure
was included in deriving the RfC estimates shown in Figure 1. However,
a ``half-factor'' of 3 was used for this area of uncertainty. If the
average period of Mn exposure (geometric mean: 4 years) in the Roels et
al. (1992) study is compared to an assumed lifetime of 70 years, one
could argue that a factor of 70/4=17.5, or at least 10, would be a more
appropriate adjustment for subchronic to chronic exposures. Given the
limited available data, this area of uncertainty is difficult to
express in a quantitative manner, but in general practice, EPA has used
an uncertainty factor of 3 for other chemicals with comparable
databases. Nevertheless, this area of concern suggests that the Mn RfC
estimates derived here with an uncertainty factor of 3 for subchronic
to chronic exposure probably do not tend to err in the direction of
being too conservative.
Another qualitative concern that should be recognized in
considering the potential health effects of Mn is the possibility of
certain types of effects that are suggested by clinical and other
evidence but are difficult to measure quantitatively or demonstrate
with currently available methods. Specifically, much of the clinical
literature on manganism refers to a psychiatric component of the
illness, which often involves striking emotional or mood changes that
tend to appear before changes in motor function are evident. Such
effects are inherently difficult to measure in a quantitative manner.
However, the possibility of such effects at lower levels of exposure
than those at which motor control is affected should not be discounted
out of hand. Some reports in the literature (e.g., Gottschalk et al.,
1991) suggest that aggressive behavior may be associated with Mn
exposure (as reflected in the concentration of Mn in hair of prison
inmates). Such reports require substantiation by further studies, and
the validity and relevance of hair Mn levels to environmental Mn
exposure remains to be established, but the suggestion that an
association might exist between hair Mn and behavior cannot be totally
dismissed.
Quantitative analyses of neurobehavioral data obtained from an
occupational cohort provide a range of possible RfC estimates in
addition to the current, verified Mn RfC value of 0.05 g/m\3\.
In ORD's judgment, the leading candidates for a possible alternative
RfC estimate are approximately 0.09 to 0.2 g/m\3\, based on
currently available information. By definition, RfC analyses do not
yield a precise concentration that defines a demarcation between safety
and hazard. Rather, interpretation of a Mn RfC estimate is best made in
relation to an assessment of population exposures to Mn, with the
understanding that the RfC is a protective level, not a predictive
value.
The exposure assessment, based largely on data from the PTEAM
study, provides some reasonable but necessarily uncertain estimates of
personal exposure levels of Mn that might result from the use of MMT in
gasoline. These estimates indicate that if MMT (at \1/32\ g Mn/gal)
were used in all unleaded gasoline in Riverside, CA (or the greater Los
Angeles metropolitan area), approximately 40 to 50% of the population
could experience PM4 Mn exposures exceeding the current RfC of
0.05 g/m\3\ (derived from PM5 Mn health effects data),
and approximately 5 to 10% could experience PM4 Mn exposure levels
around 0.1 g/m\3\ or higher (see Figure 2). In terms of the
Los Angeles area population of 14.5 million persons, even an estimate
of 5% of the population implies over 700,000 persons.
Uncertainties are inherent in any risk assessment. In this case, on
the health assessment side, the numerical uncertainty factors used in
the RfC analyses presented here have been explicitly described and
explained in and summarized above. These factors are intended to
provide a reasonable degree of public health conservatism reflecting
areas of biological knowledge as well as areas of information deficit.
In addition, an RfC estimate by definition reflects uncertainty
spanning perhaps an order of magnitude, and thus there is no
significant difference between the verified RfC of 0.05 g/m\3\
and alternative estimates of 0.09 to 0.2 g/m\3\. Other
qualitative uncertainties are also discussed above. On the exposure
assessment side, the primary uncertainties are related to projections
from the PTEAM data, rather than the PTEAM data per se. Inferences
about the relative contributions of crustal and automotive sources to
PM4 Mn were drawn from studies conducted in geographical and
temporal proximity to the PTEAM study, but both the data from these
studies and the inferences based on them introduce uncertainties.
Attempts to adjust the PTEAM data in various ways, including any
extrapolation from the 24-hour average distribution obtained in the
fall of 1990 to a long-term average for other seasons, introduce
progressively greater uncertainties at each step. Some adjustments have
not even been attempted. For example, a weighting of the daytime and
nighttime PTEAM exposure data to reflect a higher average ventilation
rate during daytime activities and a lower ventilation rate during
nighttime activities (e.g., sleeping) would have resulted in higher
personal exposure estimates. Thus, given other approaches or
assumptions, different projection estimates are possible. It must
therefore be emphasized that the two projections of Mn exposure levels
in Figure 2 should not be interpreted as upper and lower bound
estimates, for even the higher projection could possibly underestimate,
or the lower projection overestimate, the PM4 Mn exposure levels
associated with MMT.
As for the relevance of the PTEAM Riverside personal exposure
estimates to other communities, the PTEAM study was, strictly speaking,
only designed to statistically represent Riverside, CA. In that
respect, the design and conduct of the PTEAM study provide a high
degree of confidence that it does accurately represent 24-hour average
Mn exposure concentrations for the Riverside population in the fall of
1990. In ORD's judgment, the PTEAM study provides a reasonable
representation of the Los Angeles Basin as well, given the
commonalities in geography, vehicle usage, and meteorology. However,
the relevance of the Riverside data to other U.S. communities depends
upon their similarities or differences in the most relevant
characteristics or dimensions. For example, to the extent that several
other major U.S. metropolitan areas (or subcommunities in these areas)
also have a high level of vehicle usage, the Riverside projections may
have greater relevance. To the extent that these same areas do not
share the meteorological conditions that contribute to the Mn exposure
levels measured in Riverside, the Riverside projections have lesser
relevance. It is also important to consider other sources of Mn
exposure apart from automotive and crustal sources. Although Riverside
had no major point sources of Mn contributing to the personal exposure
levels measured in the PTEAM study, other communities may have such
sources, and thus the personal exposure levels of Mn from all sources
might be higher in other communities than in Riverside.
The exposure estimates shown in Figure 3 are in the range of or
exceed some candidate RfC estimates as well as the current RfC.
Exceeding the RfC does not necessarily indicate that a public health
risk will occur. At present, it is impossible to state whether
projected exposures above the RfC would result in an adverse health
effect for either an individual or the general population. At a
sufficiently high level of exposure, adverse effects would be expected
to occur, first in any sensitive subpopulations, then with greater
prevalence in the general population and extending to other types of
effects (e.g., reproductive and/or respiratory as well as
neurobehavioral effects in the case of Mn). However, the relationship
between such ``sufficiently high'' levels and the population exposure
levels estimated by the projection methods employed here is unknown.
Expressed differently, given the gap between observed or modeled effect
levels and the RfC values obtained by applying uncertainty factors of
orders of magnitude, it is impossible to state whether projected
population exposures would lie above or below a presumed threshold
level on the actual concentration-response curve for Mn neurotoxicity.
This gap between projected exposure levels and the lowest
concentrations obtained by modeling the concentration-response
relationship (at least, by the quantal linear model) makes it
impossible to make any assertion regarding the likelihood of a health
risk at projected exposure levels. However, this conclusion should not
be interpreted to imply that, therefore, no health risk is expected to
exist at exposure levels exceeding the RfC.
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E. References
Allen, B. C.; Kavlock, R. J.; Kimmel, C. A.; Faustman, E. M. (1994)
Dose-response assessments for developmental toxicity: II. Comparison
of generic benchmark dose estimates with NOAELS. Fundam. Appl.
Toxicol.: in press.
American Conference of Governmental Industrial Hygienists. (1992)
1992-1993 threshold limit values for chemical substances and
physical agents and biological exposure indices. Cincinnati, OH:
American Conference of Governmental Industrial Hygienists, Technical
Information Office; pp. 40-45.
Aschner, M.; Gannon, M. (1994) Manganese (Mn) transport across the
rat blood-brain barrier: saturable and transferrin-dependent
transport mechanisms. Brain Res. Bull. 33: 345-349.
Barnes, D. G.; Daston, G. P.; Evans, J. S.; Jarabek, A. M.; Kavlock,
R. J.; Kimmel, C. A.; Park, C.; Spitzer, H. L. (1994) Benchmark dose
workshop: criteria for use of a benchmark dose to estimate a
reference dose. Regul. Toxicol. Pharmacol.: submitted.
Clayton, C. A.; Perritt, R. L.; Pellizzari, E. D.; Thomas, K. W.;
Whitmore, R. W.; Ozkaynak, H.; Spengler, J. D.; Wallace, L. A.
(1993) Particle total exposure assessment methodology (PTEAM) study:
distributions of aerosol and elemental concentrations in personal,
indoor, and outdoor air samples in a southern California community.
J. Exposure Anal. Environ. Epidemiol. 3: 227-250.
Cotzias, G. C.; Horiuchi, K.; Fuenzalida, S.; Mena, I. (1968)
Chronic manganese poisoning: clearance of tissue manganese
concentrations with persistence of the neurological picture.
Neurology 18: 376-382.
Crump, K. S. (1984) A new method for determining allowable daily
intakes. Fundam. Appl. Toxicol. 4: 854-871.
Ethyl Corporation. (1994) Comments of Ethyl Corporation in response
to EPA's December 9, 1993 Federal Register notice 58 Fed. Reg. 64761
(1993). Washington, DC: Ethyl Corporation, Office of the Vice
President for Government Relations. Available for inspection at:
U.S. Environmental Protection Agency, Central Docket Section,
Washington, DC: docket no. A-93-26.
Faustman, E. M.; Allen, B.C.; Kavlock, R.J.; Kimmel, C.A. (1994)
Dose-response assessment for developmental toxicity: I.
characterization of data base and determination of NOAELs. Fundam.
Appl. Toxicol.: in press.
Federal Register. (1993) Draft report: principles of neurotoxicology
risk assessment. F. R. (August 4) 58: 41556-41599.
Gottschalk, L. A.; Rebello, T.; Buchsbaum, M. S.; Tucker, H. G.;
Hodges, E. L. (1991) Abnormalities in hair trace elements as
indicators of aberrant behavior. Compr. Psychiatry 32: 229-237.
Iregren, A. (1990) Psychological test performance in foundry workers
exposed to low levels of manganese. Neurotoxicol. Teratol. 12: 673-
675.
IRIS, Integrated Risk Information System (data base). (1993)
(Printout of reference concentration (RfC) for chronic manganese
exposure as revised November, 1993). Cincinnati, OH: U.S.
Environmental Protection Agency, Office of Health and Environmental
Assessment, Environmental Criteria and Assessment Office. Available
online from: TOXNET, National Library of Medicine, Rockville, MD.
Jarabek, A. M.; Hasselblad, V. (1991) Inhalation reference
concentration methodology: impact of dosimetric adjustments and
future directions using the confidence profile method. Presented at:
84th annual meeting and exhibition; June; Vancouver, British
Columbia, Canada. Pittsburgh, PA: Air and Waste Management
Association; paper no. 91-173.3.
Kawamura, R.; Ikuta, H.; Fukuzami, S.; Yamada, R.; Tsubaki, S.;
Kodama, T. (1941) Intoxication by manganese in well water. Kitasato
Arch. Exp. Med. 18: 145-169.
Kimmel, C. A.; Gaylor, D. W. (1988) Issues in qualitative and
quantitative risk analysis for developmental toxicology. Risk Anal.
8: 15-20.
Kirshenblatt, M. (1993) (Letter to Ms. M. T. Smith, U.S. EPA,
regarding the August 30, 1993, rebuttal comments from Ethyl
Corporation in support of their waiver request for HITEC 3000 fuel
additive.) Ottawa, Ontario, Canada: Environment Canada,
Transportation Systems Division, Industrial Programs Branch;
September 23.
Lyons, J. M.; Venkataraman, C.; Main, H. H.; Friedlander, S. K.
(1993) Size distributions of trace metals in the Los Angeles
atmosphere. Atmos. Environ. Part B 27B: 237-249.
Mergler, D.; Huel, G.; Bowler, R.; Iregren, A.; Belanger, S.;
Baldwin, M.; Tardif, R.; Smargiassi, A.; Martin, L. (1994) Nervous
system dysfunction among workers with long-term exposure to
manganese. Environ. Res. 64: 151-180.
Murphy, V. A.; Wadhwani, K. C.; Smith, Q. R.; Rapoport, S. I. (1991)
Saturable transport of manganese (II) across the rat blood-brain
barrier. J. Neurochem. 57: 948-954.
Pellizzari, E. D.; Thomas, K. W.; Clayton, C. A.; Whitmore, R. W.;
Shores, R. C.; Zelon, H. S.; Perritt, R. L. (1992) Particle total
exposure assessment methodology (PTEAM): Riverside, California pilot
study, volume I (final report). Research Triangle Park, NC: U.S.
Environmental Protection Agency, Atmospheric Research and Exposure
Assessment Laboratory; EPA report no. EPA/600/R-93/050. Available
from: NTIS, Springfield, VA; PB93-166957/XAB.
Preuss, P. W. (1991) ORD's comments on Ethyl Corporation's July 12,
1991 resubmittal of a waiver application for the use of
methylcyclopentadienyl manganese tricarbonyl (MMT) in unleaded
gasoline (memorandum to Richard Wilson). Washington, DC: U.S.
Environmental Protection Agency, Office of Research and Development;
December 12.
Rodier, J. (1955) Manganese poisoning in Moroccan miners. Br. J.
Ind. Med. 12: 21-35.
Roels, H. (1993) (Letter to Dr. M. Davis, U.S. EPA, on definitions
of ``respirable,'' ``total,'' and ``inhalable'' dusts). Bruxelles,
Belgium: Universite Catholique de Louvain, Unite de Toxicologie
Industrielle et Medecine du Travail; October 19.
Roels, H.; Lauwerys, R.; Genet, P.; Sarhan, M. J.; de Fays, M.;
Hanotiau, I.; Buchet, J.-P. (1987) Relationship between external and
internal parameters of exposure to manganese in workers from a
manganese oxide and salt producing plant. Am. J. Ind. Med. 11: 297-
305.
Roels, H. A.; Ghyselen, P.; Buchet, J. P.; Ceulemans, E.; Lauwerys,
R. R. (1992) Assessment of the permissible exposure level to
manganese in workers exposed to manganese dioxide dust. Br. J. Ind.
Med. 49: 25-34.
Thomas, K. W.; Pellizzari, E. D.; Clayton, C. A.; Whitaker, D. A.;
Shores, R. C.; Spengler, J. D.; Ozkaynak, H.; Wallace, L. A. (1993)
Particle total exposure assessment methodology (PTEAM) study: method
performance and data quality for personal, indoor, and outdoor
aerosol monitoring at 178 homes in southern California. J. Exposure
Anal. Environ. Epidemiol. 3: 203-226.
Tukey, J. W.; Ciminera, J. L.; Heyse, J. F. (1985) Testing the
statistical certainty of a response to increasing doses of a drug.
Biometrics 14: 295-301.
U.S. Environmental Protection Agency. (1990) Comments on the use of
methylcyclopentadienyl manganese tricarbonyl in unleaded gasoline.
Washington, DC: Office of Research and Development.
U.S. Environmental Protection Agency. (1991) Information needed to
improve the risk characterization of manganese tetraoxide
(Mn3O4) and methylcyclopentadienyl manganese tricarbonyl
(MMT). Washington, DC: Office of Research and Development; December
12.
Wallace, L. A.; Duan, N.; Ziegenfus, R. (1994) Can long-term
exposure distributions be predicted from short-term measurements?
Risk Anal. 14: 75-85.
Wennberg, A.; Iregren, A.; Struwe, G.; Cizinsky, G.; Hagman, M.;
Johansson, L. (1991) Manganese exposure in steel smelters a health
hazard to the nervous system. Scand. J. Work Environ. Health 17:
255-262.
Wennberg, A.; Hagman, M.; Johansson, L. (1992) Preclinical
neurophysiological signs of parkinsonism in occupational manganese
exposure. Neurotoxicology 13: 271-274.
F. Comments on Health Assessment and EPA Response
The focus of most of Ethyl's comments regarding the effects on
public health and welfare resulting from the use of MMT in unleaded
gasoline deal with issues related to EPA's risk assessment and
specifically to the calculation of an RfC for manganese by the
utilization of various analytical methods, to the uncertainty factors
used by the Agency in determining the RfC for manganese, and to the
exposure assessment for manganese. A summary discussion of the
significant issues related to these comments follows.\61\
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\61\For a complete description of the EPA response to Ethyl's
comments, the reader is referred to Air Docket A-93-26, (Docket A-
93-26, II-A-15) ``ORD's Response to Public Comments on the Reference
Concentration for Manganese and on the Draft ORD Risk Assessment of
MMT.''
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Generally, Ethyl states that ``ORD openly concedes that after four
years of efforts it is unable to conclude that a public health risk
would exist for even the most highly exposed segment of the
population.'' The Agency indicated to Ethyl in 1991 the research it
could conduct to provide for a more quantitative assessment of the MMT
issue. Thus, assessment of the risks or benefits of MMT could be, or
perhaps could already have been, improved if more empirical information
were provided by Ethyl to the Agency.
Ethyl commented on ORD's April 28, 1994 draft MMT Risk Assessment
that, depending on the methodology used for the derivation of the RfC
for manganese, the level of manganese concentrations ``without
appreciable risk'' lies somewhere within the range of 0.1 to 3.0
g/m3 and that all of ORD's RfC calculations fall within
this range. Contrary to Ethyl's statement, the inclusion of Ethyl's
proposed RfC estimate of 3.0 g/m3 in tables and figures
summarizing the RfC estimates obtained by different methods was merely
an attempt by the Agency to illustrate all of the RfC estimates. The
Agency did not imply or state a conclusion that ``The majority of ORD's
RfC calculations fall in the 0.1-3.0 g/m3 range.'' ORD
focused on a leading candidate RfC estimate of approximately 0.1
g/m3, while explicitly noting that the current official
RfC of 0.05 g/m3 is not meaningfully different from a
possible alternative RfC estimate of 0.1 g/m3.
To more effectively avoid possible ambiguity that is reflected in
Ethyl's comment, Figure 1 of the final MMT Risk Assessment (U.S.
Environmental Protection Agency, 1994b) shows all of the RfC estimates
contained in Table A-39 of Appendix A. Ethyl's preferred RfC estimate
of 3 g/m3 is now omitted from Figure 1 because it is not
a value obtained by any of ORD's analyses. Moreover, it is ORD's view
that the best estimate of an alternative RfC estimate for Mn, based on
the analyses and data considered to date, probably lies in the range of
0.09 to 0.2 g/m3. This judgment is based on the strengths
and weaknesses of the various analytic approaches considered by ORD in
the April 28 draft assessment.\62\
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\62\The reader is referred to Air Docket A-93-26, II-A-15,
``ORD's Response to Public Comments on the Reference Concentration
for Manganese and on the Draft ORD Risk Assessment of MMT, for
further evaluation of the various analytical approaches that were
investigated by the Agency. ORD views the 10 and 5% benchmark and
Bayesian analyses of dichotomous data and the Bayesian analyses of
continuous data using the quantal linear model as having greater
scientific strengths than the other analyses considered by ORD or by
Ethyl.
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Ethyl has stated that EPA has failed to address issues regarding
both the statistical treatment of the data underlying the RfC and EPA's
decision to employ a 1000-fold factor of uncertainty in calculating the
RfC. EPA disagrees. Appendix A of the ORD Risk Assessment addresses
each of these issues. The extensive analyses the Agency has conducted
represent a concerted effort to respond to the statistical issues
raised by Ethyl. The fact that EPA does not adopt Ethyl's advocated
position is not a failure to address the issues. In fact, no scientific
consensus or policy exists on many of these issues, such as the
selection of a specific mathematical dose-response model, the selection
of an effect level, how to address continuous data, and the appropriate
magnitude of severity regarding production of uncertainty factors for
the various effect levels. As is specifically described in the
``Response to Comments'' document, ORD utilized scientific judgment in
determining the appropriateness of certain models and the inclusion of
specific uncertainty factors.
Ethyl also expressed concerns that EPA had not adequately addressed
alternative analyses for estimating an RfC by utilizing different
groupings of subjects in the Roels analysis. ICF Kaiser, a consultant
for Ethyl, commented that ``ORD ignores alternative analyses which most
closely resemble the conventional method for calculating RfCs.'' The
alternative approach Ethyl employed to group the data from the study by
Roels et al. (1992) has no evident rationale other than providing a
statistically nonsignificant effect level. The groupings employed by
Roels et al. (1992) and used by ORD appear to have been selected
because they provided approximately equal numbers of subjects per
group. The groupings selected by Ethyl result in both smaller and more
disparate numbers of subjects per group, with a consequent reduction in
statistical power to detect a significant difference between a Mn-
exposed group and controls. Further, as explained in the Response to
Comments Document previously cited, ORD does not view the use of the
upper boundary of the concentration associated with a group as a
scientifically appropriate or representative metric to describe the
exposure of the entire group.
Ethyl also took issue with the Agency for focusing on analyses
using the average concentration of respirable dust (ACRD). The decision
to focus on ACRD was not arbitrary or designed to yield lower RfC
estimates but, as explained in Appendix A of the ORD Risk Assessment,
was based on both an explicit consideration of the advantages ACRD
offered for fitting dose-response models and its ability to reflect
average past exposure, thereby obviating some of the apparent
disadvantages of the two exposure measures reported by Roels et al.
(1992), LIRD and CRD. Although the Agency views ACRD as the best choice
of these three available exposure measures for the analytical
approaches employed in the ORD risk assessment, Figure 1 (See Section
VI-B, above.) illustrates all of the RfC estimates presented for all
three exposure measures and all analytical approaches.
Ethyl recommends that certain analyses should be omitted from
consideration on the ORD risk assessment. To some extent, the Agency
believes the difference between Ethyl's and EPA's positions is related
to differing interpretations of what is reasonable versus unreasonable,
biologically plausible versus implausible, or valid versus invalid. As
addressed before, the Agency's basic approach in the ORD risk
assessment was to present all of the results of its analyses and then
identify a subset of the total that have a scientifically stronger
basis for being considered preferentially.\63\
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\63\For specific discussion related to these issues the reader
is referred to Air Docket A-93-26, II-A-12.
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Ethyl offers several arguments directed at reducing the overall
uncertainty and specifically the composite uncertainty factor (UF) of
10 for database limitations applied in deriving estimates of an RfC for
manganese. Ethyl's first argument concerns the basic ``biological
plausibility'' of the RfC, suggesting that inhaled manganese cannot be
as toxic (compared to ingested manganese) as the roughly 100-fold
difference in RfC and RfD estimates would indicate.\64\ The Agency
believes that a fundamental problem with Ethyl's comparison is that it
is limited to what Ethyl estimates is the ``systemic dose.'' The key
issue is not systemic dose but delivered dose, i.e., the amount of
manganese that actually reaches and enters a critical target organ such
as the brain. Furthermore, the Agency believes that, depending on the
form of manganese inhaled, and its ability to enter the brain, it is
quite possible that a significant fraction of even small amounts of
inhaled manganese would be able to reach target sites in the central
nervous system. Thus, the apparently greater toxicity of inhaled versus
ingested manganese may reflect important pharmacodynamic and
pharmacokinetic differences of manganese that enters the body by
different routes of exposure. Ethyl's analysis of systemic dose does
not adequately address this issue.\65\
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\64\See Air Docket A-93-26. The Reference Dose or RfD is
analogous to the RfC but for ingestion as opposed to inhalation.
Document II-A-13 (in the docket), Table 1, compares the ``systemic
dose'' of manganese for the Recommended Daily Intake (now termed
``Recommended Daily Allowance'' by FDA) of ingested manganese, the
RfC for inhaled manganese, and the RfD for manganese in drinking
water. This tabular comparison does not address several issues that
the Agency has identified as factors in its assessment on inhaled
manganese toxicity.
\65\In fact, as is indicated in ``ORD's Response to Comments on
MMT'' document, many studies indicate that inhalation exposure does
result in a greater delivered dose. This evidence includes, for
example, a report by Coulston and Griffin (1977), who exposed
monkeys to the whole combustion products of MMT (Mn3O4)
for 23 hr/day for up to 66 weeks. According to the authors, monkeys
breathed 0.86 L/min, or 119 L in a 23-hr exposure day. AT 100
g/m3, approximately 120 g Mn would be inhaled
daily, which would equate to a systemic dose of about 24 g/
day (assuming 20% deposition and 100% absorption). In addition, both
control and inhalation-exposed monkeys ingested about 4-5 mg Mn/day
in their diet, which would equate to a systemic dose of
approximately 135 g/day (assuming 3% absorption). Even
though these calculations indicate that the diet accounted for about
six times more Mn entering the body of the exposed animals, the
relatively small inhalation fraction doubled the delivered dose of
Mn in the brains of the inhalation-exposed monkeys. Furthermore, the
authors found blood levels of Mn to be equivalent in the exposed and
control monkeys, despite the higher brain levels in the inhalation-
exposed animals. Thus, extrapolations based on estimated systemtic
dose by ingestion underpredict doses delivered to the brain by
inhalation.
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The more specific critique Ethyl offers regarding the composite UF
of 10 for database limitations deals with three areas of inadequate
information represented by the composite factor: chronic exposure
effects, reproductive/developmental effects, and differences in
toxicity of different forms of manganese. In deriving RfCs for other
chemicals, any one of these three areas of uncertainty has, in one case
or another, warranted a full UF of 10.\66\
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\66\The decision whether to utilize the full uncertainty factor
of 10 is based on a judgement by the RfC workgroup on a case-by-case
basis.
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The Agency believes that given the possible accumulation of
manganese, the effects of chronic exposure to inhaled manganese are of
concern. The maximum average exposure duration of the available
occupational studies cited by both ORD and Ethyl is 16.7 years (Mergler
et al. 1994),\67\ which does not constitute chronic exposure. Ethyl's
comments ignore the point that the RfC is in fact aimed at
extrapolation to 70 exposure years. Reproductive and developmental
toxicity are widely recognized as significant public health concerns
and therefore warrant specific consideration as uncertainties in RfC
derivation. The available animal studies on reproductive and
developmental effects almost exclusively involved oral dosing of
manganese and are inadequate for inhalation RfC purposes. Studies of
such effects in humans are limited for males and nonexistent for
females.
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\67\Mergler D.; Huel, G.; Bowler, R.; Iregren, A.; Belanger, S.;
Baldwin, M.; Tardif, R.; Smargiassi, A.; Martin, L.; (1994) Nervous
system dysfunction among workers with long-term exposure to
manganese. Environ. Res. 64: 151-180.
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The potential difference in toxicity potency of Mn3O4 in comparison
to MnO2 or other compounds of manganese is a significant uncertainty
because no existing study has directly compared the toxicities of these
compounds by inhalation exposure. Ethyl's comparison of studies
involving not only different routes of exposure but significant
differences in methods, subjects/subject populations, and other key
features does not constitute an adequate quantitative assessment.
In summary, the three areas of uncertainty reflected in the
composite UF of 10 used in deriving the manganese RfC estimates are
appropriate because they are not adequately addressed by available
studies.
Ethyl stated that ORD has overlooked evidence from the Canadian
exposure studies that indicate personal exposure levels of manganese
are likely to be lower than indicated by the PTEAM Riverside Study. The
Agency considers Ethyl's exposure assessment based on Canadian data to
be deficient in several respects. Given the fundamental differences in
the sampling procedures for the Canadian and Riverside studies, as well
as other differences in the design and conduct of the studies in
question, the Agency continues to judge the PTEAM Riverside data to be
far more useful to exposure assessment purposes that the Canadian data.
The ``consistency'' in the Canadian data that Ethyl emphasizes is a
subjective matter that can be considered from more than one
perspective.\68\
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\68\For specific discussion related to these issues the reader
is referred to Air Docket A-93-26, II-A-15.
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Ethyl also disagrees with certain assumptions and features of ORD's
draft exposure assessment. In particular, Ethyl claims that ORD's draft
``PTEAM Riverside exposure model'' overestimates manganese exposure
levels for selected Canadian cities by a factor of approximately three
when used with a factor for projected increases in MMT usage. Ethyl's
application of the ``Riverside model'' is incorrect for several
reasons, including Ethyl's use of ambient monitoring data to estimate
personal exposure levels (ORD used stationary indoor monitoring data
collected as part of a personal exposure study). The Agency notes that
qualitative differences in meteorology and the degree of automobile
usage provide a more likely basis for the differences between Riverside
and the Canadian cities cited by Ethyl.
Ethyl also states that the manganese emission rate from catalyst
vehicles should be a factor of three lower than that for noncatalyzed
vehicles, which would lower ORD's projected exposure estimates by
almost the same factor. After reevaluating the limited data on
manganese emissions from noncatalyst and catalyst vehicles, ORD has
concluded that no specific emission rate can be justified by the
available data and that, consequently, an assumption of equivalent
emission rates for both types of vehicles is reasonable and
appropriate.
Ethyl cited data pertaining to the amount of iron and manganese in
soil and paved road dust (PRD) in Riverside that indicate the
percentage of automotive contribution to personal exposure levels of
PM4 manganese should be lower than the value ORD used. ORD agrees
that the iron:manganese data for Riverside PRD provide a more
geographically specific basis for estimating automotive contributions,
and therefore the projection estimates of personal exposure levels of
manganese would be slightly lower because of this adjustment.\69\ This
adjustment in the exposure assessment was incorporated into the final
assessment as described above in section VI-C.
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\69\This and other adjustments in the exposure assessment are
incorporate in to the final ORD assessment. For further information
regarding this matter, see Air Docket A-93-26, II-A-12.
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Ethyl states that Riverside is not representative of other U.S.
cities, and ORD does not disagree. Nevertheless, ORD believes Riverside
is reasonably representative of the greater Los Angeles metropolitan
area. Consequently, the PTEAM Riverside exposure assessment can be
considered representative for at least 14.5 million people (the
population of the greater Los Angeles area). To the extent that other
U.S. cities share some degree of resemblance in meteorology, vehicles
miles traveled, and possibly other characteristics of relevance to
automotive manganese levels, the estimated exposure levels for
Riverside may be pertinent to other locales and portions of locales as
well. However, ORD can only point to qualitative similarities and is
unable to make any quantitative statement on the degree of relevance of
the Riverside data to other U.S. cities.
In its May 27 submission,\70\ Ethyl has noted that a distribution
of 24-hour average exposure levels is likely to have higher exposures
at the upper portion of the distribution than would a longer term
average for the same population. ORD agrees that this is likely, but
the lack of adequate exposure data make it impossible to determine what
the actual distribution would be. Although Ethyl attempts to correct
the distribution of 24-hour average data to represent a longer term
average, ORD notes unstated assumptions and possible errors in Ethyl's
calculations and prefers alternative approaches to estimating such a
correction to the distribution.\71\
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\70\See Air Docket A-93-26, Category II-D-98.
\71\For further information regarding this matter, see Air
Docket A-93-26, Category II-A-15, page 40.
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Ethyl commented that ORD's newly released PTEAM exposure modeling
shows that no (emphasis in original) portion of the population would
experience manganese exposures above the 0.1-0.3 g/m3
range. The Agency believes that Ethyl is mistaken in making this
conclusion. Statements and graphical information in ORD's risk
assessment indicate that an estimated 5-10% of the Riverside/Los
Angeles population would be projected to experience personal exposure
levels of PM4 manganese at or above 0.1 g/m3.
Ethyl's statement regarding EPA's exposure assessment would be correct
only if it were to replace ``0.1-0.3 g/m3 range'' with
``0.3 g/m3 range''.
Ethyl commented that the ``ORD risk assessment projects that the
99th percentile manganese exposure would be about 0.2 g/
m3 or lower, while the 90th to 95th percentiles would experience
manganese exposures below even 0.1 g/m3.'' On the
contrary, as shown in the ORD risk assessment, by one estimate, the
98th percentile exposure level would be approximately 0.2 g/
m3, and both estimates are above 0.1 g/m3 at the
95th percentile. (See Figure 2, Section VI-C of this Decision.)
Finally, Ethyl raises issues from comparing ORD's assessment of MMT
with ORD's assessment of methyl tertiary butyl ether (MTBE). Ethyl
reduces the official EPA RfC for MTBE by inappropriate uncertainty
factors, compares the result to both appropriate and inappropriate
exposure values for MTBE, finds an overlap of these health and exposure
assessments for MTBE, and concludes that, by comparison, MMT was
treated too conservatively or erroneously. Basically, because of
substantial differences between the databases and characteristics of
MTBE (a volatile organic compound that remains in the body for a matter
of hours to days) and Mn (a metal that accumulates in the body),
Ethyl's direct comparisons are not valid.\72\
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\72\For further discussion regarding this matter, the reader is
referred to Air Docket A-93-26, II-A-15, Section IV.
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Comments from other interested parties regarding potential health
concerns related to manganese exposure are addressed in ``ORD's
Response to Public Comments'' found in Docket A-93-26.
VII. Fuels and Fuel Additives Registration and Research Needs
To more accurately define an RfC for manganese and to more
accurately predict the distribution of expected manganese exposures
associated with MMT use, additional research will have to be completed.
Such research would ultimately lead to a risk assessment which could
better define the risk associated with MMT use. Furthermore,
regulations under sections 211(a), (b), and (e) of the Act, set forth a
procedure under which required health and exposure data must be
submitted prior to any new use of a fuel or additive. Given the basis
for today's decision and the purpose of the testing requirements
imposed by these regulations, the Agency expects that the testing
required to resolve the concerns upon which today's decision is based
will also be required under these regulations. The following section
explains these newly promulgated requirements and how they would apply
to the use of MMT in unleaded gasoline.
Under section 211 of the Clean Air Act, certain fuels and additives
must be registered with EPA as a precondition to introduction into
commerce. Section 211(a) of the Act authorizes EPA to designate any
fuel or fuel additive for registration. Upon designation, fuels or
additives may not be introduced into commerce unless they have been
registered by EPA in accordance with section 211(b). In 1975, EPA
issued regulations (40 CFR Part 79) implementing basic registration
requirements, as stipulated by section 211(b)(1), that required
applicants to submit certain information, such as commercial
identifying information, range of concentration, purpose-in-use, and
chemical composition, in order to register a fuel or fuel additive.
The 1970 Clean Air Act also gave EPA discretionary authority to
establish additional registration requirements under section 211(b)(2).
This section authorized EPA to require fuel and fuel additive
manufacturers ``to conduct tests to determine potential public health
effects of such fuel(s) or additive(s) (including but not limited to,
carcinogenic, teratogenic, or mutagenic effects),'' and to further
furnish other ``reasonable and necessary'' information to identify fuel
and fuel additive emissions and determine their effects on vehicular
emission control performance and on public health and welfare.
EPA did not exercise its discretionary authority to require testing
of fuels and fuel additives under section 211(b)(2) when general
registration regulations were first adopted in 1975. However, in the
Clean Air Act Amendments of 1977 (Public Law 95-95, August 7, 1977),
Congress added section 211(e), which required EPA to take certain
actions to implement section 211(b)(2). A final rule was signed by the
Administrator of EPA on May 27, 1994 and was published in the Federal
Register on June 27, 1994 (59 FR 33042). The final rule, ``Fuels and
Fuels Additives Registration Regulations'', implemented additional
registration requirements under sections 211(b)(2) and 211(e) of the
Clean Air Act. The rule requires manufacturers to provide EPA with
information to assist EPA in identifying and evaluating potential
adverse health effects of motor vehicle fuel and fuel additive
emissions, and to support and guide related regulatory actions in the
future.
The recently promulgated health effects testing requirements
incorporate a three-tiered health effects evaluation structure. Under
Tier 1, fuel and fuel additive manufacturers are required to perform a
literature search on the health and welfare effects of fuel and fuel
additive emissions, characterize the emissions, and provide exposure
information. Tier 2 includes short-term biological testing to screen
for specific health effects endpoints, involving the exposure of
laboratory animals to the whole emissions of fuels or fuel/additive
mixtures.
Where appropriate, EPA has retained authority to modify or augment
the standard Tier 2 test requirements. Under ``alternative Tier 2''
procedures set forth in Sec. 79.58(c), EPA may substitute alternative
tests for standard Tier 2 tests or impose additional testing
requirements. Alternative Tier 2 procedures may be utilized to modify
standard Tier 2 requirements, but may not be utilized to entirely
delete testing for any of the standard endpoints. The alternative Tier
2 provision affords the Agency flexibility when available information
indicates that another testing regimen is preferable to the standard
set of Tier 2 tests. Instances where Alternative Tier 2 requirements
may be appropriate include scenarios where previously available
information may cause EPA to be concerned about potential health
effects related to an endpoint not specifically addressed in Tier 2, or
when otherwise available information identifies a potentially
significant public health risk related to a Tier 2 endpoint such that
more definitive testing will be required for this endpoint than is
ordinarily required. In both of these scenarios, alternative Tier 2
testing can facilitate earlier and potentially more efficient
acquisition of the required data.
After receipt and review of a manufacturer's Tier 1 and Tier 2
submittals, EPA determines, on a case-by-case basis, if additional
testing is needed under Tier 3 to evaluate the risk of a particular
fuel or fuel additive (or group of fuels or fuel additives) on human
health or welfare. Tier 3 testing could include any emission analysis,
health effects, welfare effects, and/or exposure testing or analysis
deemed necessary by EPA for this purpose.
The Agency has considerable discretion to formulate and impose
appropriate testing requirements under either alternative Tier 2 or
Tier 3 procedures. In practice, EPA will be more likely to utilize
alternative Tier 2 procedures in instances where additional data needs
are apparent even prior to completion and submission of the standard
Tier 2 tests, and prompt formulation of appropriate alternative testing
requirements will result in a more efficient use of industry and
governmental resources. Tier 3 procedures will be preferred in those
instances where standard Tier 2 tests are necessary to assist EPA in
identification of potential hazards and/or in design or selection of
appropriate follow-up studies.
For fuels and fuel additives registered as of the date of
promulgation of the final rule, registrants must submit Tier 1 and Tier
2 test data within six years of that date. On the other hand,
manufacturers seeking to register new fuel and fuel additive products
after the date of promulgation must satisfy all testing requirements
before registration will be granted.
In this regard, the new rule clarifies what constitutes a ``new''
fuel or fuel additive, distinguishing between two types of unregistered
products which a manufacturer might seek to register after the
promulgation of the final rule: (1) fuel and fuel additive products
similar in composition and usage to those already allowed wide
commercial distribution (e.g., registered for general use by other
manufacturers), and (2) fuel and fuel additive products which differ
significantly in composition and/or usage from such current products.
To effectuate this distinction, EPA's final rule, promulgated under
sections 211(b) and (e), makes use of grouping system concepts and
definitions. Specifically, a fuel additive product not registered by
its manufacturer\73\ for a specific type of fuel as of the date of
promulgation of this rule is designated as ``registrable'' if the fuel/
additive mixture resulting from use of the additive in the specific
fuel is in the same fuel/additive group as one or more currently
registered fuels or bulk additives.\74\ The grouping system establishes
various fuel/additive groups within each fuel family.\75\ Conversely, a
fuel additive product not registered by its manufacturer for a specific
type of fuel as of the date of promulgation is designated as ``new'' if
the fuel/additive mixture resulting from use of the additive in the
specific fuel cannot be grouped with one or more currently registered
fuels or bulk additives. In these definitions, the term ``currently
registered'' refers to the date on which the prospective applicant
seeks registration for the fuel or fuel additive in question.
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\73\For purposes of these definitions, registration is product-
specific. Thus, if a particular fuel or fuel additive product has
not been registered by its manufacturer, then that manufacturer does
not have the right to introduce, market, and/or sell this product,
even if a compositionally similar or identical product has been
registered by another manufacturer.
\74\A ``bulk additive,'' sometimes called a ``general use''
additive was defined as a product added to fuel at the refinery as
part of the original blending stream or after the fuel is
transported from the refinery, but before the fuel is purchased for
introduction into the fuel tank of a motor vehicle. In contrast, an
``aftermarket additive,'' sometimes called a consumer additive, is
an additive product marketed for introduction directly into the fuel
system of a motor vehicle.
\75\``Fuel Family'' refers to the primary categorization of
fuels and fuel additives within the proposed grouping system. A fuel
family was defined as a set of F/FAs which share basic chemical and
physical formulation characteristics and can be used in the same
engine or vehicle. Six such fuel families were proposed (unleaded
gasoline, leaded gasoline, diesel, methanol, ethanol, methane, and
propane). EPA did not include a leaded gasoline family in the final
rule because Clean Air Act section 211(n) prohibits on-road use of
leaded fuel after December 31, 1995. In the definition of
``registrable,'' the restriction ``in the same fuel family'' means
that the similarity of an applicant F/FA to a bulk additive
currently registered for use in another fuel family would not
suffice to make the applicant F/FA registrable. This restriction is
consistent with the general principles of the grouping system, which
permits grouping of F/FAs only within defined fuel families.
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According to these definitions, an unregistered fuel additive which
meets the criteria for grouping only with a currently registered
aftermarket additive (and not also with a currently registered fuel
and/or bulk additive) is not registrable. This does not preclude an
unregistered aftermarket additive from being registrable (since
aftermarket additives can group with fuels and bulk additives), nor
does it affect the registration status of currently registered
aftermarket additives.
For example, an unregistered detergent additive (either bulk or
aftermarket) intended for use in unleaded gasoline and conforming to
the ``substantially similar'' criteria for unleaded gasoline (56 FR
5352) would be registrable, since it would be able to group with
currently registered baseline unleaded gasoline fuels and bulk
additives.\76\ On the other hand, MMT is considered ``new'' rather than
``registrable'' for unleaded gasoline, because there are no currently
registered manganese-containing fuels or bulk additives in the unleaded
gasoline family with which a mixture of MMT and unleaded gasoline could
be grouped. This is true even though products containing MMT are
currently registered for bulk use in leaded gasoline and as aftermarket
additives grandfathered prior to the ban on such aftermarket
additives.\77\
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\76\The ability to join the unleaded gasoline baseline group
assumes that the detergent additive does not exceed oxygen and
sulfur limits applicable to the baseline unleaded gasoline category.
\77\Until the 1990 CAA Amendments went into effect, the
statutory language of section 211(f) was interpreted as applying
only to unleaded gasoline fuels and related bulk additives. Thus,
prior to November 15, 1990 (the effective date of the CAA
Amendments), aftermarket additives intended for use in unleaded
gasoline and containing elements other than carbon, hydrogen,
oxygen, nitrogen, and sulfur were allowed to be registered. Under
the 1990 CAA Amendments, all types of motor vehicle fuels and fuel
additives were placed under 211(f) jurisdiction. All aftermarket
additives that were not ``substantially similar'' and were
introduced on or after November 15, 1990, were banned. However, this
ban does not apply to products first introduced into commerce prior
to November 15, 1990 (CAA section 211(f)(1)(B)). Thus, ``non-sub-
sim'' gasoline aftermarket additives which had been registered prior
to that date were allowed to retain their registrations. These are
so-called ``grandfathered'' aftermarket additives.
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The recently finalized rule requires that manufacturers of new fuel
and fuel additive products (i.e., fuel and fuel additive products not
registered by their specific manufacturers as of the date of
promulgation and not fitting the registrable criteria) submit all
testing requirements prior to registration, including any alternative
Tier 2 tests or Tier 3 tests prescribed by the Agency. As discussed
above, under the fuel and fuel additive testing rule, MMT is designated
as ``new'' for purposes of registration for use in unleaded gasoline.
Accordingly, any data required to register MMT for use in unleaded
gasoline must be submitted prior to registration.
As noted above, Tier 1 requires manufacturers of designated fuels
or fuel additives (or groups of manufacturers pursuant to Sec. 79.56)
to supply to the Administrator: (1) the identity and concentration of
certain emission products of such fuel and fuel additives, (2) an
analysis of potential emissions exposures, and (3) any available
information regarding the health and welfare effects of the whole and
specified emissions.
Under the General Provision of the emission characterization
requirements of Tier 1, it is stated in Sec. 79.52(b)(1)(ii) that the
emissions shall be generated three times (on three different days)
without a functional aftertreatment device and, if applicable, three
times (on three different days) with a functional aftertreatment
device, and each such time shall be analyzed according to the remaining
provisions in this section (b). Measurement of background emissions,
under Sec. 79.52(b)(1)(iii), states that it is required that ambient/
dilution air be analyzed for levels of background chemical species
present at the time of emission sampling (for both combustion and
evaporative emissions) and that background chemical species profiles be
reported with emissions speciation data. Ethyl has yet to provide the
Agency with data on the characterization of emissions resulting from
the use of MMT in unleaded gasoline which meets the requirements of
Tier 1 under these subsections. Thus, to EPA's knowledge, data has not
yet been collected which would fully satisfy Tier 1 requirements under
Sec. 79.52(b)(1) (ii) and (iii).
Standard Tier 2 testing includes certain specific types of short-
term biological testing to screen for specific health effects
endpoints, involving the exposure of laboratory animals to the whole
emissions of the fuel additive (when added to a base fuel). Where
appropriate, the Agency may impose an alternative Tier 2 test in lieu
of a standard Tier 2 test or prescribe additional Tier 2 testing in
addition to the standard Tier 2 tests.
EPA's Office of Research and Development has prepared a report that
specifically identifies research which would allow a more accurate
evaluation of the risk involved in utilizing MMT in unleaded
gasoline.\78\ Some of the research described in the ORD report is
intended to address toxicologic endpoints which are also addressed by
standard Tier 2 tests,\79\ while other research described in the report
is intended to address other endpoints. EPA presently has an adequate
basis to conclude that there are public health concerns associated with
the potential use of MMT in unleaded gasoline, and anticipates that
research addressing each of the areas identified in the ORD report will
be necessary to support registration of MMT for use in unleaded
gasoline. It is not necessary, and would be inefficient, to wait for
the completion and submission of all of the standard Tier 2 tests in
order to identify the requisite test data, and use of alternative Tier
2 procedures is therefore appropriate.
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\78\ORD originally reviewed the information needed to improve
the risk characterization in: Preuss, P.W. (1991) ORD Document on
Information Needed to Improve the Risk Characterization of Manganese
Tetraoxide (Mn3O4) and Methylcyclopentadienyl Manganese
Tricarbonyl, December 12, 1991 [memorandum to Richard Wilson].
Washington, DC: U.S. Environmental Protection Agency, Office of
Research and Development; December 16, 1991. For further information
the reader is referred to Air Docket A-93-26, II-A-16. ORD has
reevaluated these information needs in light of new information. See
Memo from Peter W. Preuss to Richard Wilson dated July 13, 1994,
Docket A-93-26, II-A-18.
\79\For example, it is clear that the standard Tier 2
neurotoxicity will not address adequately the potential
neurotoxicity of inhaled manganese to humans. Although the precise
mechanisms of such neurotoxicity are not fully understood, it has
been shown that manganese toxicity may be associated with
degeneration of certain tissues in the brain. These brain tissues
include the substantia nigra which is found only in primates and not
in lower mammals. Laboratory rodents typically employed in the
standard Tier 2 neurotoxcity test do not physically possess this
target for manganese toxicity in the brain.
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If Ethyl or any other party seeks to register MMT for use in
unleaded gasoline, it will need to submit the required test data in
addition to obtaining the required waiver. In that case, EPA expects to
identify specific alternative Tier 2 tests which must be performed
prior to registration.\80\ In the case of endpoints addressed by the
ORD report, that report will serve as the starting point for EPA in
identifying appropriate alternative Tier 2 tests. In each instance
where EPA does not adopt any alternative Tier 2 requirement for an
endpoint which is addressed by standard Tier 2 tests, standard
information or testing requirements will continue to apply. The process
for establishment of alternative Tier 2 testing requirements for a
product includes specific procedures for notification of the
manufacturer and an opportunity for comment, and is set forth in 40
C.F.R. 79.58(c).
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\80\If there is any reason why Ethyl would prefer to complete
the standard set of Tier 2 tests and submit such tests prior to
imposition of further data requirements, EPA is willing in the
alternative to impose additional testing requirements under Tier 3
procedures.
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Submission of any data which is required by the registration
regulations prior to registration of MMT for use in unleaded gasoline
is not itself a specific legal prerequisite to the granting of a waiver
under section 211(f)(4). However, in these circumstances, since the
Agency is declining to grant the requested waiver based on potential
health effects, the Agency considers it reasonable to require that
Ethyl submit the same health effects and exposure test data which will
be required prior to registration of MMT for unleaded gasoline before
it will consider taking favorable action on another waiver application.
As the health effects testing rule indicates, EPA believes that it
should exercise particular caution in registering new fuel or fuel
additive products that are significantly different from, or have a
usage pattern which is significantly different in scope or character
from, currently registered fuel or fuel additive products. EPA also
believes that the same cautious approach is appropriate in evaluating
waiver applications under section 211(f)(4).
In the event that Ethyl wishes to undertake the testing required to
register MMT for unleaded gasoline, EPA will work with Ethyl to resolve
the details of all necessary test data. Further, once the data
requirements for registration have been duly established, EPA will not
require submission of any additional health effects and exposure data
as part of a new waiver application.
VIII. Other Issues
Ethyl has stated that certain other considerations and data
associated with MMT use should be taken into account by the
Administrator in utilizing the discretion authorized under section
211(f)(4). These issues include (1) decreased emissions of toxic air
pollutants due to decreases in aromatic use when MMT is substituted as
an octane enhancer; (2) decreased refinery emissions due to decreased
reformer severity; (3) decreased carbon monoxide (CO) and oxides of
nitrogen (NOX) vehicle emissions, (4) increased crude oil yield
and associated energy savings, and (5) decreased levels of tropospheric
ozone associated with lower levels of reactive hydrocarbon emissions
and NOX emission decreases.
Regarding CO emission decreases, EPA's analysis indicates that
examination of all of the available test data on the CO effects of MMT
shows a small (0.07 gpm or 2% of applicable standards\81\) decrease
attributable to the additive.\82\ With the exceptions of two vehicle
models, the CO effects in both directions were relatively small. The
most significant exception to this general pattern is the test data
from the 1988 Ford Crown Victoria 5L, which showed a decrease of 0.72
gpm (or 21% of the standard). The other unusual vehicle was also a Ford
Crown Victoria--a 1992 model with a 0.36 gpm decrease (11% of
standard). The small average size and somewhat erratic nature of the CO
decreases seen in the vehicle sample lead to questions about whether
this small potential benefit is likely to actually occur in the vehicle
fleet.
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\81\This effect was calculated by integrating emissions,
separately for clear and MMT fuels, over the full range of mileage
for which data were available, taking the difference between fuel
groups within models to get a model-by-model effect, and then
averaging these effects over model groups.
\82\For a complete description the reader is referred to Air
Docket A-93-26, II-A-14, ``Evidence of CO and NOX Emission
Decreases Attibutable to MMT in Durability Testing Data''.
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EPA also examined NOX emissions changes demonstrated by the
data which had been submitted by both Ethyl and Ford. The test data for
NOX show a more substantial and more consistent decrease for this
pollutant than was the case for CO. The average across models was 0.08
gpm or 8% of the standard. The largest decreases were seen in the 1992
Ford Mustang 5.0L model and the 1988 Ford Crown Victoria 5L (each
showing a 0.30 gpm decrease or 30% of the standard). Other models with
substantial decreases were the 1988 Ford Taurus (0.22 gpm or 22% of the
standard) and the 1992 Buick Regal 3.8L (0.19 gpm or 19% of the
standard).
It is difficult to clearly determine the effects which NOX
decreases of this magnitude might have on tropospheric ozone
concentrations, since such effects are influenced heavily by the mix of
ozone precursors and the atmospheric chemistry of particular non-
attainment areas. Modeling studies performed by EPA have shown that
NOX reductions in NOX limited areas can significantly reduce
regional ozone levels. However, although the regional ozone decreased,
some urban areas showed slight increases in ozone levels. It is not
possible to quantify the degree of reduction in ozone associated with
the introduction of MMT in general because many factors affect ambient
ozone. In order to achieve such a quantification, individual cities
would need to be analyzed to determine their VOC/NOX ratios and
the mobile source contribution to those ratios.
EPA has therefore concluded that it is likely that in certain
NOX-limited areas, ambient levels of ozone would decrease based on
the expected NOX reductions resulting from MMT use. It is
impossible to quantify the exact degree of these decreases or the
magnitude of the area which would be affected.\83\
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\83\For a complete description and response to Ethyl's comments,
the reader is referred to Air Docket A-93-26, II-A-15, ``ORD's
Response to Public Comments on the Reference Concentration for
Manganese and on the Draft ORD Risk Assessment of MMT''.
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Ethyl indicates that ``use of the Additive will result in as many
as 25 fewer cancer cases [emphasis in the original] attributable to
automotive exhaust over the 1995-2010 span.'' Although ORD has not
independently verified Ethyl's current analysis, it is nevertheless
possible to evaluate their analysis by taking it at face value.
Significant uncertainties are inherent in any prediction of a net
change in cancer risk. For example, there are various models and
assumptions underlying estimated changes in carcinogen exposures.
Assumptions must be made regarding the composition of gasoline at
different times in the future; projected fleet emissions must be
estimated based on measurements from a few vehicles; the impact of MMT
on such emissions must be estimated. In addition, the relationship of
changes in emissions is assumed to be related to population exposure
levels.
Cancer risk, whether characterized in terms of the number of cases
in the entire U.S. population or in terms of individual unit risk
estimates, also has inherent uncertainties. According to Ethyl, the
predicted reduction in estimated cancer cases is 0.6 to 2.0 cases per
year. These represent upper bound estimates, and thus the true impact
is very unlikely to be higher and may in fact be less. Ethyl also
predicts that the changes in the probability of an individual
contracting cancer is lowered with MMT use from about 12 cases per
100,000 to 6 cases per 100,000. Again these estimates represent upper
bounds, so the true risk to an individual would not be expected to be
higher and could well be lower. In any case, the individual risk level
remains in the 10-5 range. Relative to the uncertainties in the cancer
risk estimates as well as in the emission and exposure aspects of
Ethyl's analysis, the magnitude of the claimed change in risk is
comparatively quite small.
The accuracy of these estimates also depends very much on the
estimates of decreased aromatics use for individual refiners. Very
significant changes are taking place in the refining industry to comply
with various aspects of programs being implemented pursuant to the 1990
Clean Air Act amendments. Programs such as the introduction of
``reformulated gasoline'' will dramatically change the overall chemical
and physical properties of gasoline. Thus, estimates of aromatics usage
associated with refining are even more highly speculative over the next
several years as these programs are implemented.
In any case, it is not possible to weigh these predicted changes in
cancer incidence or in ozone formation against the concerns which have
been explained above in relation to increased manganese emissions.
Therefore, the Agency disagrees with Ethyl's claim that it can be shown
scientifically that a net public health benefit results from the use of
MMT in unleaded gasoline. While the Agency agrees that such risk-
benefit comparisons can be important, the present data are inadequate
for this purpose. With regard to the potential risks associated with
inhalation exposure to manganese, the Agency's Risk Assessment as
described above indicates that there are insufficient data to conclude
quantitatively whether the increased use of MMT will (or will not)
increase public health risk. With regard to the potential reductions in
cancer incidence and tropospheric ozone levels associated with MMT use
claimed by Ethyl, the above analysis indicates that, while reductions
are possible, the data are too sparse to provide reasonable
quantitative estimates of the magnitude of such reductions. The
estimated cancer reduction is not truly discernable as a quantifiable
benefit. This is because relative to the uncertainties in the cancer
risk estimates as well as in the emission and exposure aspects of
Ethyl's analysis, the estimated magnitude of change in risk is quite
small, even when based on the ``upper bound'' cancer estimates. For
ozone, it is not possible in general to quantify the degree of
reduction associated with the introduction of MMT because many factors,
including local volatile organic compound (VOC)/NOX ratios affect
ambient ozone levels. To achieve a quantification, all appropriate
individual cities would have to be analyzed.
IX. Decision
As previously discussed, the Agency interprets section 211(f)(4) of
the Act as establishing a two-stage process for evaluating waiver
applications. The first stage requires that EPA determine whether an
applicant has met its burden of demonstrating that a fuel does not
cause or contribute to a failure to meet regulated emission standards.
Unless EPA finds that the waiver applicant has met this burden, a
waiver may not be granted. The second stage of the process reflects the
discretionary nature of the waiver authority provided to the EPA
Administrator by the statute. In this second stage, the Administrator
may consider other factors in determining whether granting a waiver is
in the public interest and consistent with the objectives of the Clean
Air Act. In this stage, the Administrator has broad discretion in
selecting the issues to be examined and in balancing the potential
positive and negative impacts of a waiver.
For purposes of the pending waiver application, as remanded to EPA
by the D.C. Circuit Court of Appeals and resubmitted by Ethyl, I
determined on November 30, 1993 that use of Ethyl's product HiTEC 3000
in unleaded gasoline at the specified concentration will not cause or
contribute to a failure to achieve compliance with vehicle emission
standards. The data and analysis upon which this determination was
based are described in Section IV above. The data submitted by Ethyl in
connection with this waiver application satisfy all of the quantitative
criteria for determining whether an additive will ``cause or
contribute'' to a failure to meet emission standards previously
utilized by EPA. As noted above, EPA has serious reservations
concerning the present suitability of these criteria. In light of the
intractability of the nation's air pollution problems, EPA is
considering adoption of new criteria which would be utilized in
assessing future waiver applications. However, for purposes of Ethyl's
present application, EPA concluded that it would not be appropriate to
make the required determination concerning emission effects by
utilizing a new methodology or new criteria concerning which Ethyl was
not afforded any prior notice. My decision that Ethyl has met the
requisite statutory burden for purposes of the present waiver
application is also based on the Agency's assessment of the newest data
provided by Ethyl on newer-technology vehicles which do not, when
evaluated separately, indicate any statistically significant increase
in regulated vehicle emissions.
The Agency remains concerned about the possible effects of fuels
containing MMT on the functioning of onboard diagnostics (OBD)
equipment. At the time that EPA completed the assessment of emissions
issues underlying my finding concerning emissions on November 30, 1993,
the evidence to support the assertions by automakers that MMT would
prevent the oxygen sensors in OBD systems from operating properly was
quite limited and these assertions had not at that time been tested in
any actual vehicles utilizing OBD systems. I expressed concern about
the effect of MMT on OBD systems at that time, and indicated that if
EPA ultimately concluded that MMT could prevent proper functioning of
OBD systems, the Agency would consider appropriate action under Clean
Air Act section 211(c). Since that time, the Ford Motor Company has
submitted further research involving use of fuel containing MMT in an
actual vehicle equipped with an OBD system, which Ford contends
demonstrates that manganese oxides resulting from MMT use prevent the
oxygen sensors in its OBD systems from functioning properly. EPA
intends to fully investigate the significance of these findings. If
further investigation supports the concerns expressed by Ford and other
automakers, EPA intends to initiate an appropriate rulemaking under
section 211(c).
Since I determined that Ethyl had met its burden regarding the
``cause or contribute'' finding required by the statute, the Agency has
been reviewing other issues bearing on the exercise of my discretionary
authority to grant or deny Ethyl the requested waiver for use in
unleaded gasoline, focusing in particular on the potential effects of
manganese emissions resulting from use of MMT on public health and
welfare.
The Agency remains concerned regarding the issue of manganese
emissions from vehicles utilizing fuels containing MMT. From a hazard
identification perspective, manganese can clearly be toxic to the
central nervous system, the respiratory system, and the male
reproductive system. The level of manganese which may safely be
breathed over a lifetime is not known with precision. EPA has assessed
potential health risks associated with potential exposures utilizing a
Reference Concentration (RfC), which is defined as an estimate (with
uncertainty spanning perhaps an order of magnitude) of a continuous
inhalation exposure level for the human population (including sensitive
subpopulations) that is likely to be without appreciable risk of
deleterious noncancer effects during a lifetime of exposure.
Beginning with existing data on the effects of manganese exposures,
the Agency utilized its standard procedure to develop a verified
Reference Concentration (RfC) of 0.05 g/m\3\. In response to
comments and criticisms by Ethyl and others, the Agency then utilized a
variety of additional techniques to consider potential alternative
RfC's based on additional data from the occupational exposure study on
which the current RfC is based (discussed in detail in Section VI-B-4
above). The techniques judged by EPA scientists to be most appropriate
produced alternative candidate RfC's ranging from 0.09 to 0.2
g/m\3\. Since any formal revision of the present verified RfC
of 0.05 g/m\3\ based on the ORD reassessment will occur in the
future and could not be completed prior to the deadline for this
decision, I have evaluated the potential health effects associated with
use of MMT in unleaded gasoline based on all of the likely values,
focusing in particular on a potential alternative RfC of 0.1
g/m\3\ and the present RfC of 0.05 g/m\3\.
Utilizing the newest and most accurate data available on personal
exposures to particulate emissions of manganese from vehicular sources,
Agency scientists also prepared an exposure analysis in which they
attempted to predict the range of increases in personal exposure to
particulate manganese that would occur in Riverside, California urban
areas if MMT were to be used in all unleaded gasoline. If MMT were
utilized in unleaded gasoline at the specified concentration in urban
areas similar to Riverside, California, the Agency's exposure
assessment predicts that the exposures of forty to fifty percent of the
population in such areas to airborne manganese levels would exceed the
present verified RfC of 0.05 g/m\3\, and the exposures of five
to ten percent would exceed manganese levels exceeding a potential
alternative RfC of 0.1 g/m\3\. Although it is impossible to
state whether a health risk would definitely exist at the projected
exposure levels, neither can the possibility of such a risk be ruled
out.
It is reasonable to anticipate that persons living near major
thoroughfares and in inner cities, often among the most economically
disadvantaged Americans, will be disproportionately represented among
persons with higher manganese exposure. Moreover, there is reason to
believe certain subpopulations such as the young, the elderly, and
persons with certain preexisting conditions, such as Parkinson's
disease, might be more susceptible to any adverse effects of manganese
exposure.
Certain occupational groups who work in proximity to vehicular
emissions such as toll takers, parking garage attendants, traffic
policemen, taxi dispatchers, and service station attendants, are
represented in the Agency's exposure estimates only to the extent of
their prevalence in the general population. These occupational groups
would likely experience manganese exposures attributable to MMT use
near or even exceeding the highest predicted exposures\84\. I realize
that if Ethyl is granted the requested waiver, MMT would not be
utilized immediately in all congested urban areas. Some of the urban
areas with higher vehicular usage are areas which will be required to
begin using a cleaner gasoline referred to as ``reformulated gasoline''
beginning in 1995. If Ethyl were to obtain the waiver under section
211(f)(4) which is the subject of this decision, MMT could not be used
in reformulated gasoline unless and until Ethyl obtained an additional
waiver under Clean Air Act section 211(k)(2)(D). However, I am
nevertheless concerned about the effects of potential MMT use in areas
required to utilize reformulated gasoline, both because a waiver under
section 211(f)(4) of the Act is a necessary prerequisite to the use of
MMT in either conventional or reformulated gasoline and because Ethyl
has made it clear that it does not seek the present waiver solely to
permit use in conventional gasoline.
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\84\The Agency realizes that exposures to manganese deemed
acceptable in particular industrial or occupational contexts will
often significantly exceed the levels considered by EPA to pose
acceptable risks for the general population. The establishment of
appropriate limits for occupational exposures to manganese is an
entirely separate process from the establishment of an RfC for the
general population. Nevertheless, I do not believe it would be
appropriate to completely disregard the likelihood of substantial
incremental additions to manganese exposure for certain categories
of working Americans where such increased exposure would be
attributable solely to approval of MMT use.
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I have concluded based on the assessments prepared by EPA
scientists that, if I were to approve use of MMT in unleaded gasoline
at the specified concentration, a significant number of persons could
thereby be exposed to manganese concentrations in the ambient air which
approach or exceed the current RfC or the candidate RfCs described in
the risk assessment. Although all risk assessments have some degree of
uncertainty, in some cases it is reasonable to conclude that the risk
of adverse health effects is either very great or very small because
estimated exposure levels are either far above or far below a potential
health effect level. However, this is not the case with MMT.
Although it is not possible based on the present information to
conclude whether specific adverse health effects will be associated
with manganese exposures in the vicinity of or exceeding the RfC,
neither is it possible to conclude that adverse health effects will not
be associated with such exposures. Moreover, it is likely that, if
adverse effects do occur as a result of MMT usage, such effects will be
subtle and difficult to detect. In these circumstances, I am very
reluctant to conduct a massive experiment in which the citizens of
numerous American cities are subjected to the additional exposures to
particulate manganese associated with MMT use.
I am aware of the proposal by Ethyl that EPA conditionally grant
its waiver application for HiTEC 3000, with conditions which would
require Ethyl to develop in a specified period the additional health
effects and exposure data necessary to address present uncertainties in
the risk assessment, require Ethyl to conduct ambient monitoring of
particulate manganese levels in certain cities where unleaded gasoline
containing MMT would be sold, and provide for prompt withdrawal of
HiTEC 3000 from the market in the event that ambient monitoring were to
demonstrate airborne manganese levels exceeding a specified level of
concern (e.g. 0.1 g/m\3\). However, I believe that the
additional information on health effects and exposure necessary to
provide greater assurance that manganese emissions from MMT use will
not jeopardize public health should be provided before I decide whether
to expose Americans to such emissions on even a temporary basis.
Moreover, Ethyl's proposal to monitor ambient exposure levels would not
assure that personal exposures exceeding the specified threshold do not
occur. The EPA risk assessment makes it clear that a substantial
portion of the population exposed to airborne manganese as a result of
MMT use would be expected to experience personal exposures exceeding
measured ambient exposure levels.
I recognize that there are some benefits that will be likely to
accrue from approval of MMT use. In addition to the obvious economic
benefits associated with reductions in petroleum use and in fuel
prices, there might also be some favorable health and environmental
effects. It is probable that, if MMT use were to result in reduced
NOX emissions from motor vehicles, this would be accompanied by
some site-specific decreases in ozone formation. The small decreases in
cancer risks claimed by Ethyl are considerably more speculative and
cannot be quantified with existing information. In any case, it is not
possible for me to weigh any modest hypothetical decrease in cancer
risk or limited site-specific ozone benefit against a risk of effects
on the nervous system that could significantly decrease the quality of
life for a large number of individuals. In addition, EPA is or will be
taking a number of other actions under the Clean Air Act to reduce
emissions of carcinogenic air pollutants and to limit ozone
formation.\85\
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\85\For example, reductions in levels of carcinogenic
particulates will accrue due to controls placed on diesel sulfur (55
FR 34120, August 21, 1990). Reductions in carcinogenic toxic
emissions (and NOX emissions after the year 2000) will accrue
as a result of regulations requiring the introduction of
reformulated gasoline in 1995 promulgated under section 211(k) of
the Act as amended in 1990 (59 FR 7716, February 16, 1994) and as a
result of the Agency's vehicle-based refueling emissions regulations
(59 FR 16262, April 6, 1994). EPA has already issued tighter
tailpipe standard for NOX as required under the new amendments,
and future ozone state implementation plans will address other
NOX control strategies. In addition, the recently-promulgated
enhanced emission I/M program regulations for the first time
establish a performance standard to reduce in-use NOX emissions
in the more serious ozone nonattainment areas. Regarding stationary
source control strategies, other provisions of the Act call for a
two million ton NOX reduction from certain utilities.
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Based on the EPA analyses described in this decision and on the
administrative record compiled by EPA as part of this decision, I have
concluded that there is a reasonable basis for concern about the
effects on public health that could result if EPA were to approve use
of MMT in unleaded gasoline pursuant to Ethyl's application. I have
also concluded that the actual and hypothetical benefits which could
accrue from MMT use are insufficient to outweigh the concerns regarding
potential adverse health effects. In circumstances where there is
substantial uncertainty regarding the nature of potential health
effects which would result if a fuel additive waiver were approved, the
burden of resolving such uncertainties should fall on the waiver
applicant rather than on the public. This policy is consistent with the
general policy established by the recently promulgated health effects
testing rule, which requires that manufacturers of new fuels or fuel
additives complete all necessary testing prior to registration.
Therefore, for the reasons set forth above, utilizing the
discretion afforded me under section 211(f)(4) of the Act, I am today
denying Ethyl's request for a waiver of the section 211(f)(1)
prohibitions against the use of MMT in unleaded gasoline. As previously
stated in this decision, should Ethyl wish to undertake research
intended to alleviate the present uncertainties concerning the adverse
health effects which could be associated with the use of MMT in
unleaded gasoline, the Agency will work with Ethyl to resolve the
details of the needed research. If Ethyl decides to undertake the
research which is needed, and which would likely be required in any
case to register MMT for unleaded gasoline under the Agency's recently
promulgated fuel and fuel additive health effects testing regulations,
EPA will reconsider granting a waiver to Ethyl at that time.
EPA has determined that this action does not meet any of the
criteria for classification as a significant regulatory action under
Executive Order 12866. Therefore, no regulatory impact analysis is
required. This action is not a ``rule'' as defined in the Regulatory
Flexibility Act, 5 U.S.C. 601 et seq., because EPA has not published,
and is not required to publish, a Notice of Proposed Rulemaking under
the Administrative Procedure Act, 5 U.S.C. 553(b), or any other law.
Therefore, EPA has not prepared a supporting regulatory flexibility
analysis addressing the impact of this action on small entities.
This is a final Agency action of national applicability.
Jurisdiction to review this action lies exclusively in the U.S. Court
of Appeals for the District of Columbia Circuit. Under section
307(b)(1) of the Act, judicial review of this action is available only
by the filing of a petition for review in the U.S. Court of Appeals for
the District of Columbia Circuit within 60 days of August 17, 1994.
Under section 307(b)(2) of the Act, today's action may not be
challenged later in a separate judicial proceeding brought by the
Agency to enforce the statutory prohibitions.
Dated: July 13, 1994.
Carol M. Browner,
Administrator.
[FR Doc. 94-18941 Filed 8-16-94; 8:45 am]
BILLING CODE 6560-50-P