[Federal Register Volume 66, Number 5 (Monday, January 8, 2001)]
[Notices]
[Pages 1344-1359]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 01-217]


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ENVIRONMENTAL PROTECTION AGENCY

[FRL-6924-8]


Water Quality Criteria: Notice of Availability of Water Quality 
Criterion for the Protection of Human Health: Methylmercury

AGENCY: Environmental Protection Agency (EPA).

ACTION: Notice of availability of water quality criterion for the 
protection of human health: methylmercury.

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SUMMARY: Pursuant to the Clean Water Act (CWA) section 304(a), EPA is 
announcing the availability of its recommended water quality criterion 
for methylmercury. This water quality criterion describes the 
concentration of methylmercury in freshwater and estuarine fish and 
shellfish tissue that should not be exceeded to protect consumers of 
fish and shellfish among the general population. EPA expects the 
criterion recommendation to be used as guidance by States, authorized 
Tribes, and EPA in establishing or updating water quality standards for 
waters of the United States and in issuing fish and shellfish 
consumption advisories. This is the first time EPA has issued a water 
quality criterion expressed as a fish and shellfish tissue value rather 
than as a water column value. This approach is a direct consequence of 
the scientific consensus that consumption of contaminated fish and 
shellfish is the primary human route of exposure to methylmercury. EPA 
recognizes that this approach differs from traditional water column 
criteria, and will pose implementation challenges. In this notice, EPA 
is providing suggested approaches for relating the fish and shellfish 
tissue criterion to concentrations of methylmercury in the water 
column. EPA also plans to develop more detailed guidance to assist 
States and Tribes with implementation of the methylmercury criterion in 
water quality standards and related programs. EPA believes that 
flexibility will be needed when designing control programs to meet this 
water quality criterion because mercury is highly persistent in the 
environment and because air deposition is the primary source of mercury 
for many waterbodies.

ADDRESSES: Copies of the complete document, titled Water Quality 
Criterion for the Protection of Human Health: Methylmercury can be 
obtained from EPA's National Service Center for Environmental 
Publications (NSCEP), telephone number 1-800-490-9198. Alternatively, 
the document and related fact sheet can be obtained from EPA's web site 
at http://www.epa.gov/waterscience/standards/methylmercury/ on the 
Internet. Copies of the draft EPA internal report National 
Bioaccumulation Factors for Methylmercury, the peer review report on 
the draft bioaccumulation factors, responses to public comments on the 
notice of intent to develop a methylmercury water quality criterion, 
and responses to peer review comments on the methylmercury reference 
dose are in Water Docket W-00-20 methylmercury. These materials are 
available for inspection at the Water Docket Room EB 57, 401 M Street 
SW, Washington, DC 20460, open between 9 am and 3:30 pm EST. 
Appointments to review the material may be made by calling 202-260-
3027.

FOR FURTHER INFORMATION CONTACT: For general questions regarding the 
methylmercury water quality criterion guidance, contact Mary Manibusan, 
USEPA, Health and Ecological Criteria Division (4304), Office of 
Science and Technology, 1200 Pennsylvania Avenue, NW, Washington, DC 
20460; or call (202) 260-3688; fax (202) 260-1036; or e-mail 
[email protected]. For specific issues regarding mercury 
bioaccumulation, contact Erik Winchester, USEPA, Health and Ecological 
Criteria Division (4304), Office of Science and Technology, 1200 
Pennsylvania Avenue, NW, Washington, DC 20460; or call (202) 260-6107. 
For questions about implementation of the water quality criterion, 
contact William Morrow, USEPA, Standards and Health Protection 
Division, Office of Science and Technology, 1200 Pennsylvania Avenue, 
NW, Washington, DC 20460; or call (202) 260-3657.

SUPPLEMENTARY INFORMATION: This Supplementary Information Section is 
organized as follows:

I. Introduction
II. Background Information
    A. What are human health ambient water quality criteria?
    B. How is the 2000 Human Health Methodology used?
    C. How does EPA use its recommended section 304(a) water quality 
criteria?
    D. What water quality criteria must a State or authorized Tribe 
adopt into its water quality standards?
    E. May States and authorized Tribes adopt water quality criteria 
based on local conditions?
    F. How does 40 CFR 131.21 affect water quality standards adopted 
by States and authorized Tribes?
III. Mercury Sources, Environmental Fate, and Implications for Water 
Quality Criterion Derivation
    A. What are the mercury emissions and deposition sources in the 
United States?
    B. How does mercury cycle in the environment?
    C. Does methylmercury bioaccumulate?
    D. Why is the section 303(a) human health water quality 
criterion for methylmercury expressed as a fish tissue residue 
value?
IV. Current Activities to Address Mercury Pollution
    A. Fish consumption advisory activities
    B. Water quality standards
    C. Total maximum daily load
    D. Pollution minimization activities
    E. National air emissions regulations
V. Derivation of the Methylmercury Fish Tissue Residue Water Quality 
Criterion
    A. What is the health risk assessment for methylmercury?
    B. How are mercury exposure and relative source contribution 
assessed?
    C. How is the methylmercury water quality criterion calculated?
VI. How Can the Fish Tissue Residue Water Quality Criterion Be 
Related to a Mercury Concentration in Water?
VII. What is the Relationship Between Fish Advisories and the Fish 
Tissue Residue Water Quality Criterion?
VIII. How Does EPA Suggest Implementing the Methylmercury Water 
Quality Criterion?
IX. Literature Cited

I. Introduction

    Pursuant to section 304(a)(1) of the Clean Water Act (CWA), the 
Environmental Protection Agency is announcing the availability of EPA's 
recommended section 304(a) human health water quality criterion for 
methylmercury. Section 304(a) human health ambient water quality 
criteria are numeric guidance values considered to be protective of 
human health for pollutant concentrations in aquatic media, such as 
ambient waters and edible tissues of aquatic organisms. EPA's 
recommended section 304(a) water quality criteria provide guidance

[[Page 1345]]

for States and authorized Tribes to use in establishing water quality 
standards and, when adopted into water quality standards and approved 
for CWA purposes, may form a basis for controlling discharges or 
releases of pollutants. Section 304(a) water quality criteria also 
provide guidance to EPA when promulgating Federal regulations under CWA 
section 303(c) when such actions are necessary. Under the CWA and its 
implementing regulations, States and authorized Tribes are to adopt 
water quality criteria to protect designated uses. EPA's recommended 
human health water quality criteria do not substitute for the Act or 
regulations, nor are they regulations themselves. Thus, EPA's 
recommended section 304(a) water quality criteria do not impose legally 
binding requirements. States and authorized Tribes retain the 
discretion to adopt, where appropriate, other scientifically defensible 
water quality standards that differ from these recommendations. EPA may 
change the section 304(a) water quality criteria in the future.
    Mercury is a complex multi-media pollutant that requires a more 
unique approach to source management, pollution reduction and control, 
and development of a water quality criterion than is typically required 
for a less complex pollutant. In the United States, humans are exposed 
primarily to methylmercury rather than to inorganic mercury. The 
dominant exposure pathway is through consumption of contaminated fish 
and shellfish rather than from ambient water. The water quality 
criterion published in this notice is for methylmercury, and it is 
expressed as a fish tissue (including shellfish) residue criterion 
rather than a water column criterion. Henceforth, EPA will refer to 
today's methylmercury water quality criterion as a fish tissue residue 
criterion, which should be understood to include shellfish as well. The 
Agency's basis for expressing the methylmercury water quality criterion 
in this format is discussed later in this notice and in more detail in 
the water quality criterion document titled Water Quality Criterion for 
the Protection of Human Health: Methylmercury (USEPA, 2001), which is 
available today.
    EPA recognizes that a fish tissue residue water quality criterion 
is new to States and authorized Tribes and will pose implementation 
challenges for traditional water quality standards programs. Water 
quality standards, water quality-based effluent limits, total maximum 
daily loads, and other activities generally employ a water column 
value. In this notice, EPA suggests approaches for relating the fish 
tissue residue water quality criterion to concentrations of 
methylmercury in water. EPA also plans to develop guidance to assist 
States and Tribes to implement this methylmercury water quality 
criterion in their water quality programs. EPA believes that the range 
of implementation issues would be addressed best through broad national 
implementation guidance, and will work to develop such guidance with 
input from the public. Mercury is highly persistent in the environment 
and reductions in environmental concentrations are likely to occur over 
years or decades. For many waterbodies the primary source of mercury 
pollution is through air deposition and not pont source discharge, EPA 
believes that flexibility may be appropriate as water quality standards 
based on this methylmercury water quality criterion are implemented. 
Flexible approaches will enable environmental protection to be achieved 
efficiently given the resource constraints that exist for both 
regulators and the regulated community.
    This notice also discusses the unique aspects of mercury and 
methylmercury as an environmental pollutant; announces EPA's intention 
to publish methylmercury water quality criterion implementation 
guidance, which will support prevention and reduction of mercury 
contamination of surface water and fish; and invites the public to 
provide information and their views on approaches to prevent or reduce 
mercury pollution and to implement water quality standards for 
methylmercury.
    This document has been approved for publication by the Office of 
Water, United States Environmental Protection Agency. Mention of trade 
names or commercial products does not constitute endorsement or 
recommendation for use.

II. Background Information

A. What Are Human Health Ambient Water Quality Criteria?

    Human health ambient water quality criteria (AWQC) are numeric 
values considered to be protective of human health for pollutant 
concentrations in aquatic media, such as ambient waters and edible 
tissues of organisms. Under section 304(a) of the Clean Water Act 
(CWA), water quality criteria are based solely on data and scientific 
judgments about the relationship between pollutant concentrations and 
environmental and human health effects. Protective assumptions are made 
regarding potential human exposure intakes. Water quality criteria do 
not reflect consideration of economic impacts or the technological 
feasibility of meeting the pollutant concentrations in ambient water. 
Section 304(a)(1) of the CWA requires EPA to develop and publish, and 
from time to time revise, criteria for water quality accurately 
reflecting the latest scientific knowledge. EPA's recommended section 
304(a) water quality criteria may serve as guidance for States and 
authorized Tribes in establishing water quality standards. The 
resulting standards may ultimately may provide a basis for controlling 
discharges or releases of pollutants. Section 304(a) water quality 
criteria also provide guidance to EPA when promulgating Federal 
regulations under CWA Section 303(c) when such actions are necessary.

B. How Is the 2000 Human Health Methodology Used?

    In November 2000, EPA published the revised Methodology for 
Deriving Ambient Water Quality Criteria for the Protection of Human 
Health (2000) (hereafter the 2000 Human Health Methodology (USEPA, 
2000a). See 65 FR 66444 (November 3, 2000). Previous to this, 
recommended human health ambient water quality criteria were developed 
using the 1980 Ambient Water Quality Criteria National Guidelines 
(hereafter the 1980 Methodology; USEPA 1980). The 2000 Human Health 
Methodology incorporates significant scientific advances that have 
occurred over the last two decades, particularly in the areas of cancer 
and noncancer risk assessments (using new information, procedures, and 
published Agency Guidelines), exposure assessments (using new studies 
on human intake and exposure patterns, and new Agency Guidelines) and 
methodologies to estimate bioaccumulation in fish.
    EPA intends to use the 2000 Human Health Methodology to develop new 
section 304(a) water quality criteria for additional pollutants and to 
revise existing section 304(a) water quality criteria. The 2000 Human 
Health Methodology is an important component of EPA's efforts to 
improve the quality of the Nation's waters and enhance the overall 
scientific basis of water quality criteria. Furthermore, the 2000 Human 
Health Methodology should help States and authorized Tribes address 
their unique water quality issues and make risk management decisions to 
protect human health consistent with section 303(c). It will also 
afford them greater flexibility in developing their water quality 
programs. The 2000 Human Health provides the detailed means for 
developing water quality criteria,

[[Page 1346]]

including systematic procedures for evaluating cancer risk, noncancer 
health effects, human exposure, and bioaccumulation potential in fish.
    One particular area of new science is in developing the Reference 
Dose (RfD) value. An RfD is an estimate (with uncertainty spanning 
perhaps an order of magnitude) of daily exposure to the human 
population (including sensitive subgroups) that is likely to be 
protective without an appreciable risk of deleterious health effects 
during a lifetime. For noncarcinogenic pollutants, the process for 
deriving a level of exposure considered to be without appreciable risk 
of effect has evolved over time. EPA has developed guidance on 
assessing noncarcinogenic effects of chemicals and for the RfD 
derivation. The 2000 Human Health Methodology recommends consideration 
of other issues related to the RfD process including integrating 
reproductive and developmental, immunotoxicity, and neurotoxicity data 
into the calculation. In the 2000 Human Health Methodology, EPA 
recommends using quantitative dose-response modeling for the derivation 
of RfDs when the available data support its use. EPA has provided 
additional guidance (in its Risk Assessment Technical Support Document 
(USEPA, 2000b)) to States and authorized Tribes on conducting their own 
risk assessments.
    For exposure assessment, States and authorized Tribes are 
encouraged to use local studies on human fish and shellfish consumption 
that better reflect local intake patterns and choices. In the absence 
of local data, EPA recommends separate default fish consumption values 
for the general population, recreational fishers and subsistence 
fishers. A factor to account for other sources of exposure, such as 
other fish, non-fish food, and air, is included when deriving AWQC for 
noncarcinogens and for carcinogens based on a nonlinear low-dose 
extrapolation. In other words, consumption of contaminated water and 
fish (including shellfish) are not the only exposures considered.
    The 2000 Human Health Methodology places greater emphasis on the 
use of bioaccumulation factors (BAFs) for estimating potential human 
exposure to contaminants via the consumption of contaminated fish and 
shellfish than did the 1980 Methodology. BAFs reflect the accumulation 
of chemicals by aquatic organisms from all surrounding media (includes 
water, food, and sediment). Compared with bioconcentration factors, 
which reflect chemical accumulation by aquatic organisms from water 
only, BAFs are considered to be better predictors of chemical 
accumulation by fish and shellfish for chemicals where exposure from 
food and sediment is important (e.g., highly persistent, hydrophobic 
chemicals). EPA prefers to use high quality field data (e.g., water and 
fish data collected in the waterbody of interest) to derive BAFs over 
laboratory or model-derived estimates of BAFs. This preference is 
because field data best reflect site-specific factors that can affect 
the extent of bioaccumulation (e.g., chemical metabolism, food web 
structure).

C. How Does EPA Use Its Recommended Section 304(a) Water Quality 
Criteria?

    Water quality standards consist of designated uses, water quality 
criteria to protect those uses, a policy for antidegradation, and 
general policies for application and implementation. As part of the 
water quality standards triennial review process defined in section 
303(c)(1) of the CWA, States and authorized Tribes are responsible for 
maintaining and revising water quality standards. Section 303(c)(1) 
requires States and authorized Tribes to review, and modify if 
appropriate, their water quality standards at least once every three 
years.
    EPA's recommended section 304(a) water quality criteria form the 
basis for Agency decisions, both regulatory and nonregulatory, until 
superseded by EPA publication of new or revised section 304(a) water 
quality criteria. These recommended water quality criteria are used in 
the following ways: (1) As guidance to States and authorized Tribes in 
adopting water quality standards; (2) as guidance to EPA in 
promulgating Federal water quality standards; (3) to interpret a 
State's narrative water quality standard (in the absence of a State 
adopted numeric standard) in order to establish National Pollutant 
Discharge Elimination System (NPDES) water quality-based permit limits; 
and (4) for all other purposes of section 304(a) under the Act. It is 
important to emphasize the two distinct purposes that are served by the 
section 304(a) water quality criteria. The first is as guidance to the 
States and authorized Tribes in the development and adoption of water 
quality criteria that will protect designated uses (e.g., aquatic life, 
primary contact recreation). The second is as the basis for 
promulgation of Federal water quality criteria for States or authorized 
Tribes when such action is necessary.

D. What Water Quality Criteria Must a State or Authorized Tribe Adopt 
Into Its Water Quality Standards?

    States and authorized Tribes must adopt water quality criteria that 
protect designated uses. See CWA section 303(c)(2)(A). Water quality 
criteria must be based on a sound scientific rationale and must contain 
sufficient parameters or components to protect the designated uses, See 
40 CFR 131.11(a). Water quality criteria may be expressed in either 
narrative or numeric format. States and authorized Tribes may employ 
one of four approaches when adopting water quality criteria: (1) 
Establish numerical values based on section 304(a) recommended water 
quality criteria; (2) modify the section 304(a) recommended water 
quality criteria to reflect site-specific conditions; (3) use other 
scientifically defensible methods to derive protective water quality 
criteria; and (4) establish narrative water quality criteria where 
numeric criteria cannot be determined or to supplement numeric water 
quality criteria. See 40 CFR 131.11(b).
    EPA encourages States and authorized Tribes to use EPA's CWA 
section 304(a) water quality criteria as guidance in adopting water 
quality standards consistent with section 303(c) of the CWA and the 
implementing Federal regulations at 40 CFR Part 131. These water 
quality criteria are contained in EPA's last compilation of National 
Recommended Water Quality Criteria. See 63 FR 68354, December 10, 1998; 
correction in 64 FR 19781, April 22, 1999. In the future, EPA will be 
publishing new and revised section 304(a) water quality criteria 
guidance for pollutants of high priority and national importance based 
upon the 2000 Human Health Methodology. Because this process will take 
time, EPA encourages States and authorized Tribes, prior to publication 
of a revised section 304(a) water quality criterion, to make 
appropriate changes when necessary to their water quality standards to 
reflect the guidance in the 2000 Human Health Methodology. EPA expects 
that it would promptly consider for approval any new or revised water 
quality criterion submitted by a State or authorized Tribe that is 
based on the 2000 Human Health Methodology.
    Once EPA publishes new or revised section 304(a) water quality 
criteria guidance that reflects the 2000 Human Health Methodology, EPA 
expects States and authorized Tribes to reassess their water quality 
standards and, where necessary, establish new or revised water quality 
criteria consistent with one of the four approaches described above. 
With today's publication of this section 304(a) human health water 
quality criterion for methylmercury, EPA is withdrawing the previous 
ambient human health water quality criteria for mercury (see 63 FR 
68354,

[[Page 1347]]

December 10, 1998; correction in 64 FR 19781, April 22, 1999) as the 
recommended section 304(a) water quality criteria for States and 
authorized Tribes to use as guidance in adopting water quality 
standards. Implementation issues for this criterion are discussed in 
Section VIII of today's Notice.

E. May States and Authorized Tribes Adopt Water Quality Criteria Based 
on Local Conditions?

    EPA encourages States and authorized Tribes to develop and adopt 
water quality criteria to reflect local and regional conditions. In the 
2000 Human Health Methodology, EPA published default values for risk 
level, fish intake, drinking water intake, and body weight for use by 
EPA or States in deriving human health water quality criteria. EPA also 
intends to publish default bioaccumulation factors and relative source 
contribution (RSC) factors as chemical-specific water quality criteria 
are developed or revised. EPA believes these default values result in 
water quality criteria protective of the general population. States and 
authorized Tribes may also use these default values when deriving their 
own water quality criteria, or they may use other values more 
representative of local conditions if data have been collected 
supporting the alternative values. However, when establishing a numeric 
value based on a section 304(a) water quality criterion modified to 
reflect site-specific conditions, or water quality criteria based on 
other scientifically defensible methods, EPA strongly cautions States 
and authorized Tribes not to selectively apply data in order to ensure 
water quality criteria less stringent than EPA's section 304(a) water 
quality criteria. Such an approach would inaccurately characterize 
risk.

F. How Does 40 CFR 131.21 Affect Water Quality Criteria Adopted by 
States and Authorized Tribes?

    On April 27, 2000, EPA published new regulations addressing its 
review and approval of water quality standards adopted by States and 
authorized Tribes. See 65 FR 24642 April 27, 2000. Under the new 
regulations, which are codified at 40 CFR 131.21(c)-(f), State or 
authorized Tribal water quality standards that were adopted, in effect, 
and submitted to EPA prior to May 30, 2000, are in effect for CWA 
purposes unless superseded by replacement Federal water quality 
standards. See 40 CFR 131.21(c). However, under the new regulation, 
State or authorized Tribal water quality criteria adopted and in effect 
after May 30, 2000, are in effect for CWA purposes only after EPA 
approval of any new or revised water quality standards. Therefore, any 
new or revised water quality criterion for methylmercury adopted by 
States or authorized Tribes would not take effect for CWA purposes 
until after EPA approves such standards.

III. Mercury Sources, Environmental Fate, and Implications for 
Water Quality Criterion Derivation

    The 1997 Mercury Study Report to Congress (The Mercury Study) 
(USEPA, 1997a) describes mercury emission sources, fate and transport, 
exposure to humans and wildlife, human health and ecological impacts of 
mercury exposure, and control technologies for air emissions. The most 
recent data and reviews on human health impacts are described and 
updated in the Water Quality Criterion for the Protection of Human 
Health: Methylmercury (USEPA, 2001), that we are announcing the 
availability of today.

A. What Are the Mercury Emissions and Deposition Sources in the United 
States?

    Based on the EPA's National Toxics Inventory, the highest emitters 
of mercury to the air include coal-burning electric utilities, 
municipal waste combustors, medical waste incinerators, chlor-alkali 
plants, hazardous waste combustors, and cement manufacturers. The 
Mercury Study estimated that the annual anthropogenic United States 
emissions of mercury in 1994-1995 was 158 tons. Roughly 87 percent of 
these emissions were from combustion sources, including waste and 
fossil fuel combustion. Contemporary anthropogenic emissions are only 
one part of the mercury cycle. Releases from human activities today are 
adding to the mercury reservoirs that already exist in land, water, and 
air, both naturally and as a result of previous human activities. The 
deposition of mercury from the atmosphere to land or water at any 
location comes from: (1) The natural global cycle (including re-
emissions from the oceans); (2) regional sources; and (3) local 
sources. Local sources can include direct water discharges in addition 
to mercury from air emissions. Past uses of mercury, such as fungicide 
application to crops, are also a component of the present mercury 
burden in the environment. The Mercury Study estimated that, for 1995, 
the United States sources contributed approximately 3 percent (or 165 
tons) of the total global mercury emissions (5,500 tons). The Mercury 
Study further estimated that, of United States anthropogenic mercury 
emissions, approximately one-third (52 tons) are deposited through wet 
and dry deposition within the lower 48 States. The remaining two-thirds 
(approximately 107 tons) of anthropogenically emitted mercury is 
transported outside of the United States' borders where it enters the 
global reservoir. In addition to mercury deposited from United States 
sources, approximately another 35 tons of mercury from the global 
reservoir is deposited for a total deposition of roughly 87 tons within 
the lower 48 States. In the United States, the highest deposition rates 
from anthropogenic and global contributions for mercury are predicted 
to occur in the southern Great Lakes and Ohio River valley, the 
Northeast and scattered areas in the South, with the Miami and Tampa 
areas having the most elevated levels in the South. The location of 
sources, the chemical species of mercury emitted, and the climate and 
meterology are key factors in where and how rapidly mercury deposition 
occurs.

B. How Does Mercury Cycle in the Environment?

    Mercury cycles in the environment as a result of natural and human 
(anthropogenic) activities. The amount of mercury mobilized and 
released into the biosphere has increased since the beginning of the 
industrial age. Most of the mercury in the atmosphere is elemental 
mercury vapor, which can circulate in the atmosphere for up to a year 
(USEPA, 1997a). Mercury in the atmosphere can be widely dispersed and 
transported thousands of miles from likely sources of emission (USEPA, 
1997a). Inorganic mercury in the atmosphere, when either bound to 
airborne particles or in a gaseous form, is deposited to soils and 
waterbodies through wet and dry deposition events. Wet deposition as 
precipitation is the primary mechanism for transporting mercury from 
the atmosphere to surface waters and land. After it deposits, mercury 
can be emitted back to the atmosphere, either as a gas or associated 
with particles, to be re-deposited elsewhere. As it cycles among the 
atmosphere, land, and water, mercury undergoes a series of complex 
chemical and physical transformations, many of which are not completely 
understood. Most of the mercury that ends up in water, soil, sediments, 
and plants and animals is in the form of inorganic mercury salts and 
organic forms of mercury, such as methylmercury. Detailed discussions 
of mercury chemistry can be found in Nriagu (1979) and Mason et al. 
(1994).
    Mercury from air emissions can be deposited to watershed soils, 
where a

[[Page 1348]]

portion of it can be methylated through soil microbial activity. 
Mercury in soils can be washed from the watershed into wetlands, lakes, 
streams, and rivers where microbial activity in sediments converts 
inorganic mercury to methylmercury. In particular, wetlands appear to 
be key environments for microbially enhanced conversion of mercury into 
methylmercury. Once in aquatic systems, mercury can exist in dissolved 
or particulate forms and can undergo a number of chemical 
transformations. Contaminated sediments at the bottom of surface waters 
can serve as an important mercury reservoir, with sediment-bound 
mercury recycling back into the aquatic ecosystem for decades or 
longer. Mercury also has a long retention time in soils; as a result, 
mercury that has accumulated in soils may continue to be released to 
surface waters and other media for long periods of time, possibly 
hundreds of years.

C. Does Methylmercury Bioaccumulate?

    Methylmercury is highly bioaccumulative and is the form of mercury 
that bioaccumulates most efficiently in the aquatic food web. 
Methylation of mercury is a key step in the entrance of mercury into 
food chains. The biotransformation of inorganic mercury species to 
methylated organic species in water bodies can occur in the sediment 
and the water column. Inorganic mercury can be absorbed by aquatic 
organisms but is generally taken up at a slower rate and with lower 
efficiency than is methylmercury. Methylmercury continues to accumulate 
in fish as they age. Predatory organisms at the top of aquatic and 
terrestrial food webs generally have higher methylmercury 
concentrations because methylmercury is typically not completely 
eliminated by organisms and is transferred up the food chain when 
predators feed on prey; for example, when a largemouth bass feeds on a 
bluegill sunfish, which fed on aquatic insects and smaller fish, all of 
which could contain some amount of methylmercury that gets transferred 
to the predator. Nearly 100 percent of the mercury that bioaccumulates 
in upper trophic level fish (predator) tissue is methylmercury (Bloom, 
1992; Akagi, 1995; Kim, 1995; Becker and Bigham, 1995). Methylmercury 
BAFs for upper trophic level freshwater and estuarine fish and 
shellfish typically consumed by humans generally range between 500,000 
and 10,000,000 (Glass et al. 1999; Lores et al., 1998; Miles and Fink, 
1998; Monson and Brezonik, 1998; Watras et al., 1998; Mason and 
Sullivan, 1997).
    Numerous factors can influence the bioaccumulation of mercury in 
aquatic biota. These include, but are not limited to, the acidity (pH) 
of the water, length of the aquatic food chain, temperature, and 
dissolved organic material. Physical and chemical characteristics of a 
watershed, such as soil type and erosion or proportion of area that is 
wetlands, affect the amount of mercury that is transported from soils 
to water bodies. Interrelationships among these factors are poorly 
understood and are likely to be site-specific. No single factor 
(including pH) has been correlated with extent of mercury 
bioaccumulation in all cases examined. Two lakes that are similar 
biologically, physically, and chemically can have different 
methylmercury concentrations in water, fish, and other aquatic 
organisms (Cope et al., 1990; Grieb et al., 1990; Jackson, 1991; Lange 
et al., 1993). For more indepth discussions about the chemical, 
physical, and biological interactions affecting methylmercury 
bioaccumulation in aquatic organism see the compilation of papers in 
Mercury Pollution: Integration and Synthesis (Watras and Huckabee, 
1994).
    Because mercury methylation and entrance of methylmercury at the 
base of the food web is critical to the overall bioaccumulation process 
and magnitude of biomagnification, it is EPA's belief that reductions 
in the available pool of total mercury will ultimately lead to reduced 
concentrations in fish and shellfish typically consumed by humans. The 
extent to which concentrations of methylmercury will be reduced in fish 
and shellfish as a result of reduced pools of total mercury in the 
environment will be location specific and depend on the unique 
chemical, physical, and biological interactions that occur in a given 
system.

D. Why Is the 304(a) Human Health Water Quality Criterion for 
Methylmercury Expressed as a Fish Tissue Residue Value?

    To derive section 304(a) water quality criteria for the protection 
of human health, EPA needs to conduct a human health risk assessment on 
the pollutant in question and gather information on the target 
population's exposure to the pollutant. Traditionally, EPA has 
expressed its section 304(a) water quality criteria guidance to protect 
human health in the form of pollutant concentrations in ambient surface 
water. To account for human exposure through the aquatic food pathway 
when deriving a water column-based water quality criterion, EPA uses 
national BAFs (USEPA, 2000a). A BAF is a ratio (in L/kg) that relates 
the concentration of a chemical in water to its expected concentration 
in commonly consumed aquatic organisms in a specified trophic level 
(USEPA, 2000a). A national BAF is meant to be broadly applicable to all 
waters in the United States, whereas a site-specific BAF is based on 
local data and integrates local spacial and temporal factors that can 
influence bioaccumulation. Some pollutants not only bioaccumulate, but 
also biomagnify in aquatic food webs. Biomagnification is a process 
whereby chemical concentrations increase in aquatic organisms of each 
successively higher trophic level due to increasing dietary exposures 
(e.g., increasing concentrations from algae, to zooplankton, to forage 
fish, to predator fish). For pollutants that biomagnify, EPA's 
preferred approach for deriving national BAFs for use in deriving 
section 304(a) water quality criteria is to use empirical field data 
collected in the natural environment. With this preference in mind, EPA 
explored the feasibility of developing field-derived national 
methylmercury BAFs for each trophic level of the aquatic food chain 
consumed by humans (i.e., trophic levels 2-4). Using Agency guidance on 
BAFs contained in the 2000 Human Health Methodology and procedures 
outlined in Volume III, Appendix D of the peer reviewed Mercury Study, 
EPA empirically derived draft national methylmercury BAFs for each 
trophic level of the aquatic food chain. The draft national BAFs were 
single value trophic level-specific BAFs calculated as the geometric 
mean of field data collected across the United States and reported in 
the open literature as well as other publically available reports. 
These draft methylmercury BAFs were compiled in a draft internal report 
and submitted to a panel of external scientific experts for peer 
review. The methylmercury water quality criterion document presents a 
summary of the draft internal BAF report as well as a summary of the 
peer review comments. The entire internal draft methylmercury BAF 
report and peer review report can be obtained from the Water Docket. 
See the Addresses section of today's Notice to obtain a copy of the BAF 
peer report from the Water Docket.
    Within any given trophic level, the individual empirically derived 
draft methylmercury BAFs generally ranged up to two orders of 
magnitude. This range in BAFs reflects the various biotic factors (such 
as food chain interactions and fish age/size) and abiotic factors (such 
as pH and dissolved organic carbon). The large range in the

[[Page 1349]]

individual empirically derived draft methylmercury BAFs results in 
uncertainty as to the ability of single trophic level-specific national 
methylmercury BAFs to accurately predict bioaccumulation of 
methylmercury in general across the waters of the United States. 
Presently, it is EPA's understanding that the mechanisms that underlie 
many of the influencing factors are not well understood and cannot be 
accurately predicted. As the science of methylmercury improves, in the 
future it may be possible to predict or model these processes and use 
such information to more accurately predict bioaccumulation. Until such 
time, EPA is unable to improve the predictive power of the 
methylmercury BAFs by universally accounting for influencing factors. 
This is not the case for other highly bioaccumulative pollutants, for 
example polychlorinated biphenyls (PCBs). For such pollutants, EPA has 
methods that improve the predictive capability of empirically derived 
or model predicted BAFs (e.g., normalizing fish tissue concentrations 
to lipid and normalizing ambient water concentrations to dissolved and 
particulate organic carbon). EPA is actively involved in, and will 
continue to support, various types of research aimed at better 
understanding the fate of mercury in the environment and the processes 
that underlie methylmercury bioaccumulation. EPA hopes that results of 
new research will enable EPA to make better predictions about 
methylmercury bioaccumulation.
    The BAF peer reviewers recognized the need for methylmercury BAFs 
and were supportive of most aspects of the methodology used to derive 
the draft national methylmercury BAFs. The peer reviewers did have 
issues with certain data used to derive the methylmercury BAFs and 
certain assumptions about food chain relationships. Overall, most of 
the peer reviewers believed that derivation of single-value trophic 
level-specific national BAFs for methylmercury that would be generally 
applicable to all waters of the United States under all conditions is 
difficult at best. This opinion was based on consideration of the 
highly site-specific nature of methylmercury bioaccumulation in aquatic 
environments and the large range in the empirically derived draft 
methylmercury BAFs. These peer reviewers recommended developing 
methylmercury BAFs on a more local or regional scale, if not on a site-
specific basis. See the Addresses section of today's Notice to obtain a 
copy of the BAF peer report from the Water Docket.
    After considering the various issues about mercury fate in the 
environment, the recent report by the National Academy of Sciences' 
National Research Council (NRC, 2000) on the toxicological effects of 
mercury (see Section V.A. of this Notice), and the methylmercury BAF 
peer review comments, EPA concluded that it is more appropriate at this 
time to derive a fish tissue (including shellfish) residue water 
quality criterion for methylmercury rather than a water column-based 
water quality criterion. EPA believes a fish tissue residue water 
quality criterion for methylmercury is appropriate for many reasons. A 
fish tissue residue water quality criterion integrates spacial and 
temporal complexity that occurs in aquatic systems and that affect 
methylmercury bioaccumulation. A fish tissue residue water quality 
criterion in this instance is more closely tied to the CWA goal of 
protecting the public health because it is based directly on the 
dominant human exposure route for methylmercury. The concentration of 
methylmercury is also generally easier to quantify in fish tissue than 
in water and is less variable in fish and shellfish tissue over the 
time periods in which water quality standards are typically implemented 
in water quality-based controls, such as NPDES permits. Thus, the data 
used in permitting activities can be based on a more consistent and 
measurable endpoint. Finally, this approach is consistent with how fish 
advisories are issued. Fish advisories for mercury are also based on 
the amount of methylmercury in fish tissue that is considered 
acceptable, although such advisories are usually issued for a certain 
fish or shellfish species in terms of a meal size. A fish tissue 
residue water quality criterion should enhance harmonization between 
these two approaches for protecting the public health.
    Because EPA did not use national, empirically derived methylmercury 
BAFs to establish today's section 304(a) recommended methylmercury 
water quality criterion, EPA has deferred further efforts to derive 
national BAFs for methylmercury at this time. EPA notes, however, that 
there may be adequate field data for some waterbodies or geographical 
regions to derive, accurate predictive, site-specific methylmercury 
BAFs. EPA may reconsider developing national methylmercury BAFs in the 
future once more field data is available for a broader range of species 
and aquatic ecosystems, or once more information is available 
describing the mechanisms that affect bioaccumulation. Such information 
could enable EPA to more accurately predict methylmercury 
bioaccumulation on a broader scale given a certain total mercury 
concentration in water.

IV. Current Activities To Address Mercury Pollution

    EPA is very aware of the multimedia character of mercury as an 
environmental contaminant. As has been discussed, releases of mercury 
are largely into the air, but releases directly into water and onto the 
land can also be significant. Moreover, statutory authority over 
mercury releases into various media are under the purview of all of 
EPA's statutes. To coordinate its various activities dealing with 
mercury, EPA issued a draft Mercury Action Plan for public comment in 
1998 and expects to issue a revised Plan shortly. The Plan lays out a 
comprehensive program to address all aspects of the mercury problem 
from all sources and into all media, using all of the Agency's tools, 
and includes the issuance and implementation of this human health 
water-quality criterion. Some of the approaches currently employed to 
inform the public of the human health risks of mercury, and to manage, 
control, and reduce its release to the environment are briefly 
discussed below.

A. Fish Consumption Advisory Activities

    States and authorized Tribes have primary responsibility for 
protecting residents from the health risks of consuming contaminated 
noncommercially caught fish and wildlife. They do this by issuing fish 
consumption advisories for the general population, recreational and 
subsistence fishers, as well as for sensitive subpopulations (such as 
pregnant women, nursing mothers, and children). These advisories inform 
the public that unacceptable concentrations of chemical contaminants 
(e.g., methylmercury and dioxins) have been found in local fish and 
wildlife. The advisories include recommendations to limit or avoid 
consumption of certain fish and wildlife species from specific 
waterbodies or, in some cases, from specific waterbody types (e.g., all 
lakes). States typically issue five major types of advisories and bans 
to protect both the general population and specific subpopulations. 
When levels of chemical contamination pose a health risk to the general 
public, States may issue a no consumption advisory for the general 
population. When contaminant levels pose a health risk to sensitive

[[Page 1350]]

subpopulations, States may issue a no consumption advisory for the 
sensitive subpopulation. In waterbodies where chemical contamination is 
less severe, States may issue an advisory recommending that either the 
general population or a sensitive subpopulation restrict their 
consumption of the specific species for which the advisory is issued. A 
commercial fishing ban can be issued, that prohibits the commercial 
harvest and sale of fish, shellfish, and/or wildlife species from a 
designated waterbody and, by inference, the consumption of all species 
identified in the fishing ban from that waterbody.
    EPA has published guidance for States and Tribes to use in deriving 
their recommended fish consumption limits. See Guidance for Assessing 
Chemical Contaminant Data for Use in Fish Advisories, Volume 2 (USEPA, 
2000e). That guidance addresses chemical contaminants with carcinogenic 
and/or noncarcinogenic effects, calculating consumption limits for a 
single contaminant in a multiple species diet or for multiple 
contaminants causing the same chronic health effects endpoints. The 
guidance recommends expressing species-specific consumption limits as 
fish meals per month, calculated at various fish tissue concentrations 
for both noncancer and cancer endpoints. Developing fish consumption 
limits requires making assumptions about the edible portions of fish 
because most chemical contaminants are not evenly distributed 
throughout the fish. The fish advisory guidance also recommends that 
human exposure via sources of contaminants other than consumption of 
recreationally or subsistence caught fish should be quantified.

B. Mercury Water Quality Standards

    As discussed above, once EPA publishes new or revised section 
304(a) water quality criteria guidance that reflects the 2000 Human 
Health Methodology, EPA expects States and authorized Tribes to 
reassess their water quality standards and, where necessary, establish 
new or revised water quality criteria consistent with one of the four 
approaches described above.
    EPA has published numerous recommended water quality criteria for 
mercury throughout the years, reflecting changes in the best available 
scientific information. Consistent with CWA Section 303(c)(2)(B), 
States and authorized Tribes have adopted a numeric criterion, or an 
appropriate narrative translator, for mercury. Some States have adopted 
a previously recommended AWQC for aquatic life of 0.12 ng/L total 
mercury (USEPA, 1984). This value is based on a tissue residue value 
and bioconcentration factor and was derived using an aquatic life 
criteria methodology that was superceded by the 1985 aquatic life 
guidelines (Stephen et al., 1985). EPA's promulgation of the National 
Toxics Rule in 1992 (see 40 CFR 131.36) included this value with an 
additional footnote directing States to measure methylmercury in the 
edible portion of aquatic species of concern, and initiate a revision 
of its criterion in water quality standards to protect designated uses, 
if the ambient water concentration exceeds 12 ng/L more than once in a 
three year period.
    More recently, many States have adopted EPA's 1997 criteria 
recommendations of 50 ng/L total mercury for human health protection 
from the consumption water and organisms and 51 ng/L total mercury for 
human health protection from the consumption of organisms only. See 62 
FR 42160. These value was derived using toxicological and exposure 
input values current at the time of its publication, including a 
bioconcentration factor. The criterion published today reflects EPA's 
2000 Human Health Methodology, reflects the best available science, and 
supercedes all previous section 304(a) human health mercury criteria 
recommendations published by EPA, except for the waters of the Great 
Lakes System as discussed below. EPA encourages States and authorized 
Tribes to adopt the methylmercury criterion published today in their 
water quality standards to protect human health. States and authorized 
Tribes may alternatively develop data which indicates a site-specific 
water quality criteria for a particular pollutant is appropriate and 
take action to adopt such a criteria into their water quality 
standards. Site-specific criteria are allowed by regulation and are 
subject to EPA review and approval.
    In 1995, EPA promulgated the Final Water Quality Guidance for the 
Great Lakes System. See 60 FR 15366, 40 CFR 132). This rule established 
a numeric criterion, based in part on bioaccumulation factors (BAFs) 
and a factor to account for other exposure sources, of 3.1 ng/L for 
total mercury in ambient waters of the Great Lakes System for human 
health protection. EPA continues to view this criterion as 
appropriately protective for these waters. Great Lakes States and 
authorized Tribes are also encouraged to adopt today's criterion for 
methylmercury in fish tissue in addition to the ambient water criterion 
for mercury contained in 40 CFR 132.
    As discussed above, water quality standards consist of designated 
uses, water quality criteria to protect designated uses, an 
antidegradation policy, and general policies for application and 
implementation. States and authorized Tribes have considerable 
discretion in designating uses, and may find that changes in use 
designations are warranted. EPA reviews any new or revised use 
designation, including refinement of a designated use, adopted by 
States and authorized Tribes to determine if the standards meet the 
requirements of the CWA and implementing regulations. Under 40 CFR 
131.10(j), a use attainability analysis (UAA) must be conducted 
whenever a State or authorized Tribe designates or has designated uses 
that do not include the uses specified in Section 101(a)(2) of the CWA 
(i.e., suitable for fishing and swimming), or when the State wishes to 
remove a designated use that is specified in section 101(a)(2) of the 
Act, or adopt subcategories of uses that require less stringent 
criteria. Uses are considered by EPA to be attainable, at a minimum, if 
the uses can be achieved (1) when effluent limitations under Section 
301(b)(1)(A) and (B) and Section 306 are imposed on point source 
dischargers, and (2) when cost effective and reasonable best management 
practices are imposed on nonpoint source dischargers. 40 CFR 131.10 
lists grounds upon which to base a finding that attaining the 
designated use is not feasible, as long as the designated use is not an 
existing use.
    States and authorized Tribes may also adopt water quality standards 
variances. EPA believes variances are particularly suitable when the 
cause of nonattainment is discharger-specific and/or it appears that 
the designated use in question will eventually be attainable. EPA has 
approved the granting of water quality standards variances by States in 
circumstances which would otherwise justify changing a use designation 
on grounds of nonattainability (i.e., the six circumstances contained 
in 40 CFR 131.10(g)). In contrast to a change in standards which 
removes a use designation for a water body, a water quality standards 
variance can apply only to the discharger to whom it is granted and 
only to the pollutant parameter(s) upon which the finding of 
nonattainability was based; the underlying standard remains in effect 
for all other purposes.
    The essential elements of a variance are: a variance should be 
granted only where there is a demonstration that one of the use removal 
factors (see 40 CFR

[[Page 1351]]

131.10(g)) has been satisfied; a variance is granted to an individual 
discharger for a specific pollutant(s) and does not otherwise modify 
the standards; a variance identifies and justifies the numerical 
criteria that will apply during the existence of the variance; a 
variance is established as close to the underlying numerical criteria 
as is possible; a variance is reviewed every three years, at a minimum, 
and extended only where the conditions for granting the variance still 
apply; upon expiration of the variance, the underlying numerical 
criteria have full regulatory effect; a variance does not exempt the 
discharger from compliance with applicable technology or other water 
quality-based limits; and, a variance does not affect effluent 
limitations for other dischargers.
    In l995, EPA and the Great Lakes states agreed to a comprehensive 
plan to restore the health of the Great Lakes. Using the Final Water 
Quality Guidance for the Great Lakes System (see 40 CFR 132), Great 
Lakes States and authorized Tribes established water quality criteria, 
methodologies, policies and procedures to establish consistent, 
enforceable, long term protection for fish and shellfish in the Great 
Lakes and their tributaries, as well as the people and wildlife who 
consume them. Under 40 CFR 132, the State of Ohio adopted, and EPA 
approved, a statewide variance specifically for mercury.
    The basis for this mercury variance was the adverse social and 
economic impacts of end of pipe treatment to attain effluent limits for 
mercury of less than 12 ng/L total mercury. Ohio determined a cost of 
$10 million per pound for mercury removal from NPDES permitted 
discharges. Ohio also specified implementation procedures whereby the 
discharger requests coverage under the mercury variance; describes the 
mercury control measures taken to date; provides a plan of study 
intended to identify and control sources of mercury (including 
documenting current influent and effluent concentrations, identifying 
known sources, describing how known sources will be reduced or 
eliminated, identifying other potential sources, and providing a 
schedule for evaluating sources and control methods); and, provides an 
explanation of the permittee's basis for concluding that there are no 
readily available means of complying without resorting to end of pipe 
treatment. Where the discharger demonstration is inadequate (including 
an inadequate demonstration that end of pipe treatment is the only 
readily available option for complying), Ohio denies the applicability 
of the mercury variance to the individual discharge. In this case, each 
variance is also submitted to EPA for review and action.
    It is important to note that Ohio's mercury variance relieves 
individual dischargers of the responsibility to demonstrate social and 
economic impacts of complying with the mercury criteria. Individual 
dischargers must still demonstrate that end of pipe treatment is the 
only viable compliance option. In addition, in this case EPA retains 
review and approval authority over individual variance decisions, but 
EPA's review is limited to the technical merits of the alternatives 
analysis (e.g., are there options other than end of pipe treatment).

C. Total Maximum Daily Load

    Section 303(d) of the CWA requires States and authorized Tribes to 
identify and establish a priority ranking for waters for which existing 
pollution controls are not stringent enough to attain and maintain 
applicable water quality standards; to establish total maximum daily 
loads (TMDLs) for those waters; and to submit from time to time the 
list of waters and TMDLs to EPA. Section 303(d) of the CWA requires EPA 
to review and approve or disapprove lists and TMDLs within 30 days of 
the date they are submitted. If EPA disapproves a State's or Tribe's 
identification of waters or a TMDL, EPA must establish the list or a 
TMDL for the State or authorized Tribe.
    TMDLs specify the amount of a particular pollutant that may be 
present in the water and still allow the waterbody to meet applicable 
water quality standards, including a margin of safety and after 
considering seasonal variability. TMDLs allocate the allowable 
pollutant loads among point and nonpoint sources of pollution. TMDLs 
also provide the basis for attaining or maintaining applicable water 
quality standards through implementation of pollutant reductions in the 
NPDES permit program and in nonpoint source controls programs.
    On the 1998 lists of impaired waterbodies, 33 States reported at 
least one waterbody as being impaired due to mercury contamination. 
Over 1,000 individual waterbody segments were identified by the States 
as specifically having mercury contamination. In addition, over 3,900 
waterbody segments were identified as impaired due to contamination by 
metals, which may include mercury.
    In many cases, as described earlier in this document, atmospheric 
deposition can be a significant source of mercury to waterbodies. On 
the 1998 lists of impaired waters, atmospheric deposition of mercury 
was identified as a source of impairment in over 600 waterbody 
segments. As States are not required to identify atmospheric deposition 
as a source of impairment, this is likely to be an underestimate.
    EPA is currently conducting pilot studies to assist States in 
developing TMDLs for waterbodies impaired by mercury from atmospheric 
deposition. One goal of the pilot studies is to evaluate modeling 
approaches, such as techniques for identifying the relative 
contribution of various types of mercury sources to a waterbody. 
Another goal of the studies is to examine how TMDLs can incorporate 
ongoing efforts to address sources of mercury, pollution including 
programs under the Clean Air Act and water-related pollution prevention 
activities.

D. Pollution Minimization Activities

    The CWA prohibits the discharge of any pollutant (other than 
dredged of fill material) from a point source into waters of the United 
States except in compliance with an NPDES permit. See section 301(a) 
and section 402 of the CWA. NPDES permits are issued by EPA or by 
States and Tribes that are authorized to administer the NPDES program. 
These permits commonly contain numerical limits on the amounts of 
specified pollutants that may be discharged. In place of or in addition 
to numerical limits, permits may contain best management practices 
(BMPs) (e.g., practices or procedures that a facility installs or 
follows that result in a reduction of pollutants to waters of the 
United States). These ``effluent limitations'' implement both 
technology-based and water quality-based requirements of the Act. 
Technology-based effluent limitations represent the degree of control 
that can be achieved by point sources using various levels of pollution 
control technology. See sections 301, 304, and 306 of the CWA For a 
publicly owned treatment works (POTW), section 301(b)(1)(B) of the CWA 
specifies the applicable technology-based control standard as 
``secondary treatment.'' See CWA sections 301(b)(1)(B).
    As discussed above, the CWA directs the States to establish water 
quality standards. See CWA section 303(c). If necessary to achieve 
applicable water quality standards, NPDES permits must contain water 
quality-based limitations (WQBELs) more stringent than the applicable 
technology-based requirements. See CWA section 301(b)(1)(C). The need 
for a WQBEL is based on a determination that pollutants in a 
discharger's effluent will cause, have the reasonable potential to 
cause,

[[Page 1352]]

or contribute to a violation of the applicable water quality standards. 
See 40 CFR 122.44(d)(1).
    Many point source dischargers of mercury have either technology-
based limits or water quality-based limits for mercury in their NPDES 
permits. Many point source dischargers install treatment technologies 
that will treat their effluent, resulting in lower quantities of 
mercury in their discharged effluent. In addition, point sources that 
discharge mercury to the Great Lakes System are required to develop a 
pollutant minimization program (PMP) for mercury whenever their WQBELs 
for mercury are calculated to be less than the quantification level of 
the applicable analytical method. See 40 CFR 132, Appendix F, Procedure 
8.D. Implementation of PMPs should be viewed as an iterative process as 
new and improved methods to reduce or eliminate mercury become 
available, including a control strategy which identifies control 
measures to be implemented that become enforceable requirements in 
their NPDES permit. These PMPs are subject to revision as the 
implementation of PMPs is viewed as an iterative process recognizing 
that there will be new and improved methods to reduce or eliminate 
mercury that are not currently available.
    Some pollution prevention strategies focus on changing existing 
processes or replacing uses of mercury in production activities with 
alternative substances as a way of achieving water quality-based 
effluent limitations. Also, some facilities with mercury do not 
discharge mercury to waters of the United States, but rather transport 
the waste to hazardous waste disposal facilities or incinerate it. EPA 
expects mercury dischargers to use one or a combination of these 
approaches to reduce or eliminate discharges of mercury to the 
environment. Pollution prevention, however, is the preferred approach 
because it reduces mercury releases to the environment in general.

E. National Air Emissions Regulations

    Most of the mercury currently entering the United States 
environment is the result of air emissions of mercury that are 
deposited on land or water. In addition to publishing mercury water 
quality criteria guidance under the Clean Water Act, under the Clean 
Air Act EPA has issued a number of regulations to reduce mercury 
pollution through air emissions. The following summarize the key 
regulations pertaining to air sources of mercury.
    --Municipal waste combustors emitted about 20 percent of total 
national mercury emissions into the air in 1990. EPA issued final 
regulations for municipal waste combustors in 1995. These regulations 
are predicted to reduce mercury emissions from these facilities by 
about 90 percent from 1990 emission levels.
    --Medical waste incinerators emitted about 24 percent of total 
national mercury emissions into the air in 1990. EPA issued emission 
standards for medical waste incinerators in 1997. When fully 
implemented, the final rule is expected to reduce mercury emissions 
from medical waste incinerators by about 94 percent from 1990 emission 
levels.
    --Hazardous waste combustors emitted about 2.5 percent of total 
national mercury emissions in 1990. In February 1999, EPA issued 
emission standards for these facilities, which include incinerators, 
cement kilns, and light weight aggregate kilns that burn hazardous 
waste. When fully implemented, these standards are predicted to reduce 
mercury emissions from hazardous waste combustors by more than 50 
percent from 1990 emission levels.
    In addition to the above regulations, EPA is developing a 
regulation that will limit mercury emissions from chlorine production 
plants. Proposed and final rules are scheduled for late 2000 and 2001, 
respectively. Under the Integrated Urban Air Toxics Strategy, which was 
published in 1999, EPA is developing emissions standards for categories 
of smaller sources of air toxics, including mercury, that pose the 
greatest risk to human health in urban areas. These standards are 
expected to be issued by 2004.
    Also, on December 14, 2000 EPA announced that it intends to develop 
a regulation to limit mercury emissions from coal-fired power plants. A 
proposal is expected in late 2003 and a final regulation at the end of 
2004. These plants are the largest source of mercury emissions in the 
United States of mercury emissions from coal-fired power plants will be 
a significant next step in this ongoing effort to address mercury 
emissions.

V. Derivation of the Methylmercury Fish Tissue Water Quality 
Criterion

A. What Is the Health Risk Assessment for Methylmercury?

    Methylmercury is highly toxic to mammalian species and causes a 
number of adverse effects. There are no data to indicate that it is 
carcinogenic in humans, and it induces tumors in animals only at highly 
toxic doses. The quantitative health risk assessment for a non-
carcinogen is a reference dose (RfD). This is an estimate (with 
uncertainty spanning perhaps an order of magnitude) of a daily exposure 
to the human population (including sensitive subgroups) that is likely 
to be without an appreciable risk of deleterious health effects during 
a lifetime. EPA has revised the current RfD for methylmercury. The 
value of the RfD has not changed from 0.1 g/kg/day, but the 
basis for the RfD has been updated using the most current data and 
analyses. This RfD is protective of all populations in the United 
States, including sensitive subpopulations. It is applied to lifetime 
daily exposure as are other RfDs. The basis for the RfD update is 
discussed below.
    EPA previously published two RfDs for methylmercury representing 
the Agency's views at the time. An RfD of 0.3 g/kg/day was 
established in 1985 and published on EPA's Integrated Risk Information 
System (IRIS) in 1986. The critical effects were multiple central 
nervous system (CNS) effects, including ataxia (problems with muscle 
co-ordination) and paresthesia (changes in the sense of touch) in Iraqi 
adults who had eaten methylmercury-contaminated grain (summarized by 
Clarkson et al., 1976; Nordberg and Strangert, 1976; and WHO, 1976).
    An RfD of 0.1 g/kg/day was established as the Agency 
consensus estimate in 1995. It was published in IRIS in 1996 and in 
extended form in 1997 in the Mercury Study (which included a state-of-
the-science evaluation of the health effects of methylmercury). Prior 
to the 1997 Mercury Study, many scientists and other concerned parties 
had questioned whether the 1985 RfD based on effects in exposed adults 
was protective against developmental effects. The 1995 RfD was thus set 
on clinical neurological signs and symptoms in 81 Iraqi children who 
had been exposed when their mothers ate methylmercury-contaminated 
grain while pregnant. Maternal hair mercury was the indication of 
exposure. EPA used a mathematical procedure, calculation of a benchmark 
dose (BMD), to estimate the functional equivalent of a no adverse 
effect level from the data. A one compartment pharmacokinetic model was 
used to determine an amount of daily methylmercury ingestion which 
would result in the BMD. An uncertainty factor of 10 was applied to 
deal with the following areas of uncertainty and variability: Wide 
variation in half-life of methylmercury in the body and the variation 
that occurs in the hair-to-blood ratio for mercury; lack of a two-
generation reproductive study; and lack of data on possible

[[Page 1353]]

chronic manifestations of the adult effects.
    Since 1997 there has been continuing discussion in the scientific 
community as to regarding the level of human exposure to methylmercury 
that is likely to present no appreciable risk of adverse health 
effects. Congress directed EPA through the House Appropriations Report 
for FY99 to contract with the National Research Council (NRC) to 
evaluate the data on the health effects of methylmercury, with emphasis 
on data available after the 1997 Mercury Study. NRC was to provide 
recommendations on issues relevant to the derivation of an appropriate 
RfD for methylmercury. EPA received the NRC report Toxicological 
Effects of Methylmercury in July, 2000 (NRC, 2000). EPA has thoroughly 
reviewed this document and generally concurs with the NRC findings and 
recommendations. Based on the NRC report, EPA has revised the RfD for 
methylmercury. A draft EPA RfD document was submitted for external 
scientific review in late October 2000; at the same time it was 
circulated for comment to other Federal Agencies through the Committee 
on Environment and Natural Resources (CENR) and Office of Science and 
Technology Policy (OSTP). See the ADDRESSES section of this Notice to 
obtain a copy of the RfD peer review report from the Water Docket. A 
public scientific review meeting was held November 15, 2000; the final 
peer review report was delivered to EPA on December 7, 2000. See the 
ADDRESSES section of today's Notice to inspect the peer review report 
in the Water Docket. The draft RfD document was revised to reflect the 
scientific critique received from the peer review, and it is now 
available as the risk assessment chapter in the water quality criterion 
document for methylmercury.
    The revised RfD was derived to be protective of the population 
(including sensitive subgroups) against the many adverse health effects 
associated with methylmercury exposure. Most data are on neurotoxicity, 
particularly in developing organisms; there is a substantial amount of 
data on effects of methylmercury on human development. The brain is 
considered to be the most sensitive target organ for which there are 
data suitable for derivation of an RfD.
    The NRC report and EPA's review considered human epidemiological, 
longitudinal developmental studies from the Seychelles Islands, the 
Faroe Islands, and New Zealand in assessing the quantitative risk from 
mercury exposure. These are all studies wherein effects were measured 
in children of mothers exposed to methylmercury through consumption of 
fish and seafood. The Seychelles study showed no evidence of impairment 
related to methylmercury exposure, while both the Faroe Islands and New 
Zealand studies found dose-related adverse effects on a number of 
neuropsychological endpoints. The Faroe Islands study is the larger of 
the latter two studies and has been extensively peer reviewed. EPA has 
used the Faroe Islands study for derivation of the RfD. A BMD was 
chosen as the most appropriate method of quantifying the dose-effect 
relationship. The BMD EPA used is the lower limit (BMDL) on a 5% effect 
level obtained by applying a K power model (K  1) to dose-
response data based on mercury measured in cord blood.
    There are several endpoints which are sensitive measures of 
methylmercury effects in the Faroese children. EPA considered the 
recommendations of the NRC and our external peer review panel in coming 
to a decision as to the appropriate endpoint. The NRC recommended the 
use of a BMDL of 58 ppb mercury in cord blood from the Boston Naming 
Test (BNT). This is a test in which the subject is shown drawings and 
is asked to name what they depict. The BNT score is related to language 
ability, assessing word formulation and word retrieval. NRC considered 
the score from the whole cohort to be the most sensitive, reliable 
endpoint. The NRC noted that the scores for the Continuous Performance 
Test (CPT) gave a lower BMDL, 46 ppb mercury in cord blood, but that 
these results were from a smaller number of children (there had been 
test administration problems in one year of the study).
    The external peer panel disagreed with the NRC choice. They felt 
that the BNT scores showed an effect of concomitant PCB exposure in 
some analyses. They preferred a PCB-adjusted BMDL of 71 ppb mercury in 
cord blood for the BNT. A difficulty with this choice is that this BMDL 
is based on scores from only about one-half of the total cohort.
    EPA prepared a comparison of the NRC and peer reviewer recommended 
approaches; this analysis also includes BMDLs from mercury-associated 
Faroese endpoint, results of the NRC integrated analysis and geometric 
means of four scores from the Faroes. The table of comparisons can be 
found in the methylmercury water quality criterion document. When one 
completes the dose conversion and applies an uncertainty factor (see 
paragraphs below), the calculated RfD values converge at the same 
point: 0.1 g/kg/day. Rather than choosing a single measure for 
the RfD critical endpoint, EPA considers that this RfD is based on 
several scores. These test scores are all indications of 
neuropsychological processes which are involved with the ability of a 
child to learn and process information. In the Water Quality Criterion 
for the Protection of Human Health: Methylmercury, EPA uses the NRC 
recommended BMDL of 58 ppb mercury in cord blood as an example in the 
dose conversion and RfD calculation.
    The BMDL of 58 ppb mercury in cord blood was converted to an 
ingested daily dose using a one-compartment pharmacokinetic model 
similar to that used in the Mercury Study. The ingested daily dose at 
the benchmark dose is 1 g/kg per day.
    In the water quality criterion guidance for methylmercury, EPA 
discusses several sources of variability and uncertainty in its 
estimate and chose an uncertainty factor of 10. This was based on a 
factor of 3 for pharmacokinetic inter-individual variability 
(particularly methylmercury half-life and uncertainty concerning the 
relationship between cord and maternal blood mercury concentrations). 
An additional factor of 3 was applied for pharmacodynamic variability 
and uncertainty. EPA also describes additional areas of concern 
including inability to quantify long-term sequelae; concern for effects 
that may be observed at exposures below the BMDL; and lack of a two-
generation reproductive effects assay. Given the over all robustness of 
the data base for methylmercury, EPA considered that a composite 
uncertainty factor of 10 was sufficient; this conclusion was affirmed 
by the external peer review panel.
    The resulting RfD for methylmercury is, thus, 0.1 g/kg per 
day. This RfD is applied to lifetime daily exposure for all populations 
in the United States, including sensitive subpopulations.

B. How Are Mercury Exposure and Relative Source Contribution Assessed?

    The exposure assessment and estimate of the relative source 
contribution (RSC) for methylmercury follows the recently published 
2000 Human Health Methodology. When an AWQC is based on noncarcinogenic 
effects, anticipated exposures from sources other than drinking water 
and freshwater/estuarine fish and shellfish ingestion are taken into 
account so that the entire RfD is not apportioned to drinking water and 
freshwater/estuarine fish and shellfish consumption alone. The amount 
of exposure attributed to each source compared to total exposure is 
referred to as the RSC. The RSC is

[[Page 1354]]

used to adjust the RfD to ensure that the water quality criterion is 
protective enough, given the other anticipated sources of exposure. 
Detailed discussion of the RSC method is described in the 2000 Human 
Health Methodology.
    The method of determining the RSC differs depending on several 
factors: (1) The magnitude of total exposure compared with the RfD; (2) 
the adequacy of data available; (3) whether more than one criterion is 
to be set for methylmercury; and (4) whether there is more than one 
significant exposure source for the chemical and population of concern. 
The population of concern, sources of methylmercury exposure, and 
estimates of exposure and the RSC for the identified population are 
discussed in detail in the 2001 methylmercury water quality criterion 
document.
    The population basis for the exposure estimate are adults in the 
general population. The health risk measure, the RfD, is intended to be 
protective of the whole population, including sensitive subpopulations. 
This is not a developmental RfD per se; even though the critical 
endpoint was neurotoxic effects observed in children, application of 
the RfD is not restricted to pregnancy only, or to developmental 
periods only.
    The exposure assessment section of the 2001 methylmercury water 
quality criterion document characterizes the sources of methylmercury 
exposure in environmental media, provides available information on 
levels of occurrence, and provides estimates of intake from the 
relevant sources. Specifically, the evaluation includes estimates of 
methylmercury in ambient surface water, drinking water, fish, non-fish 
foods, air, soil and sediment.
    As discussed in the 2000 Human Health Methodology, the Agency's RSC 
policy approach allows for use of a subtraction method to account for 
other exposures when one health-based water quality criterion is 
relevant for the chemical in question. In this circumstance, other 
sources of exposure can be considered ``background'' and can be 
subtracted from the RfD. Such is the case with methylmercury; that is, 
there are no health-based criteria, pesticide tolerances, or other 
regulatory activities to apportion with the alternate percentage 
approach (see discussion in the 2000 Human Health Methodology).
    The assessment of human exposure in the methylmercury water quality 
criterion document includes estimates from multiple media sources. 
Based on available data, human exposures to methylmercury from all 
media sources except freshwater/estuarine and marine fish are 
negligible, both in comparison to exposures from fish and compared to 
the RfD. Estimated exposure from ambient water, drinking water, non-
fish dietary foods, air, and soil are all, on average, at least several 
orders of magnitude less than those from freshwater/estuarine fish and 
shellfish intakes. In units of g/kg-day, non-fish sources of 
intake are in the range of 10-5 to 10-9 
g/kg-day for adults in the general population (USEPA, 2001). 
The combined methylmercury exposure intakes from water ingestion, non-
fish diet, air, and soil represent approximately 0.07 percent of total 
estimated exposure to methylmercury (less than \1/100\ of one percent 
of the RfD). Therefore, these exposures were not factored into the RSC.
    Ingestion of marine fish is a significant contributor to total 
methylmercury exposure. This intake has been accounted for in the 
derivation of the fish tissue water quality criterion value. The 
estimate of marine fish methylmercury exposure is based on data 
available primarily from the National Marine Fisheries Survey. See the 
exposure section of the 2001 methylmercury water quality criterion 
document. Species-specific mean concentrations of methylmercury in 
marine fish and shellfish were used to estimate daily exposure from 
methylmercury. A consumption-weighted mean concentration of 
methylmercury for all marine fish and shellfish was then calculated by 
EPA (USEPA 2001) based on the mean consumption rates from the United 
States Department of Agriculture's Continuing Survey of Food Intake by 
Individuals (CSFII) 1994-1996 (USDA 1998). The CSFII 1994-1996 
consumption rates are also the source of EPA's recommended intake rates 
for freshwater/estuarine fish. Detailed discussion of this procedure is 
included in the methylmercury water quality criterion document (USEPA, 
2001). Following the Mercury Study (USEPA, 1997a), 100 percent of the 
mercury in marine fish was assumed to be present as methylmercury. The 
estimated weighted-average methylmercury concentrations in marine fish 
is 0.157 mg methylmercury/kg fish tissue, and the estimated average 
exposure to methylmercury from marine fish is 2.7  x  10-5 
mg methylmercury/kg fish tissue-day. This exposure represents almost 30 
percent of the RfD.
    As indicated above, the RSC from marine fish has been calculated 
with an assumed average intake of 12.46 gm/day of marine fish based on 
the CSFII, for all respondents aged 18 and over. The Mercury Study 
(USEPA, 1997a) indicates that in the general population of fish 
consumers, those that consume freshwater/estuarine species of fish are 
also consumers of marine species of fish and shellfish. EPA has, 
therefore, made the same assumption in the derivation of the 
methylmercury fish tissue residue water quality criterion. EPA's 
recommended default fish intake rate to protect the general population 
of consumers of freshwater/estuarine fish is 17.5 grams/day. This value 
is the 90th percentile from the CSFII 94-96 survey (USEPA, 2000f). As 
described in the 2000 Human Health Methodology, the Agency selected 
this default intake rate as protective of a majority of the population. 
The recommended body weight for the general adult population used in 
this estimate is 70 kg (USEPA, 2000a). While EPA acknowledges that 
consumers of freshwater/estuarine fish are also typically consumers of 
marine fish, EPA does not believe that the high-end consumer of 
freshwater/estuarine fish is also a high-end consumer of marine fish. 
EPA believes that it is more appropriate, and a reasonably conservative 
assumption, to use a central tendency intake rate (approximately 12.5 
grams/day) for the marine fish component of the RSC estimate.
    For deriving the fish tissue water quality criterion for 
methylmercury, the mean daily exposure estimate from ingestion of 
marine fish for adult consumers in the general population (which is 
also protective of the developmental endpoint), 2.7  x  10-5 
mg/kg-day, is used for the RSC in the subtraction approach to calculate 
the methylmercury fish tissue water quality criterion.

C. How Is the Methylmercury Water Quality Criterion Calculated?

    The derivation of a methylmercury water quality criterion requires 
a human health risk assessment (e.g., an RfD), exposure data (e.g., the 
amount of pollutant ingested or inhaled per day), and data about the 
target population to be protected. The equation for calculating the 
methylmercury fish tissue residue water quality criterion for the 
protection of human health is:
[GRAPHIC] [TIFF OMITTED] TN08JA01.017

Where:
    TRC = Fish tissue residue criterion (mg methylmercury/kg fish 
tissue) for freshwater and estuarine fish and shellfish
    RfD = Reference Dose (based on noncancer human health effects). For 
methylmercury it is 0.0001 mg/kg BW-day (0.1 g/kg BW-day)

[[Page 1355]]

    RSC = Relative source contribution (subtracted from the RfD to 
account for marine fish consumption) estimated to be 2.7  x  
10-5 mg/kg BW-day
    BW = Human body weight default value of 70kg (for adults)
    FI = Fish intake at trophic level (TL) i (i = 2, 3, 4); total 
default intake is 0.0175 kg fish/day for general adult population. 
Trophic level breakouts for the general population are: TL2 = 0.0038 kg 
fish/day; TL3 = 0.0080 kg fish/day; and TL4 = 0.0057 kg fish/day.

This equation is the same equation used in the 2000 Human Health 
Methodology to calculate a water quality criterion for a 
noncarcinogenic pollutant, but is rearranged to solve for a protective 
concentration in fish tissue rather than in water. Thus, it does not 
include a BAF or drinking water intake value (as discussed above, 
exposure from drinking water is negligible). When all of the numeric 
values are put into the generalized equation, the Tissue Residue 
Criterion = 0.3 mg methylmercury/kg fish (rounded to one significant 
digit from 0.292 mg methylmercury/kg fish tissue). This is the 
concentration in fish tissue that should not be exceeded based on a 
total fish and shellfish consumption-weighted rate of 0.0175 kg fish/
day (17.5 g/day). On a site-specific or local level, States and 
authorized Tribes can chose to apportion all of the 0.0175 kg fish/day 
to the highest trophic level consumed for their population or modify it 
based on local or regional consumption patterns. EPA strongly 
encourages States and authorized Tribes to develop a water quality 
criterion for methylmercury using local or regional data over the 
default values if they believe that such a water quality criterion 
would be more appropriate for their target population.

VI. How Can the Fish Tissue Residue Water Quality Criterion Be 
Related to a Mercury Concentration in Water?

    EPA recognizes that a State's water quality criterion in the form 
of a fish tissue residue value may pose implementation challenges under 
traditional water quality based control programs. Under a water 
quality-based approach to controlling pollutants, NPDES permit 
compliance with water quality standards is usually determined by 
comparing the allowable concentration of a pollutant in the water 
column to the actual pollutant concentration measured in the water 
column over some specific period of time. Mechanisms to control 
pollutants in waterbodies usually involve determining the allowable 
discharge load to a waterbody by conducting TMDL and waste load 
allocation (WLA) calculations. The traditional approach for monitoring, 
measuring compliance, and ultimately controlling the discharge of a 
pollutant is based on the concentration of the pollutant in water; 
thus, a mechanism is needed to relate concentrations of methylmercury 
in fish tissue to concentrations in water. EPA has provided three 
recommended approaches in order to relate the methylmercury fish tissue 
water quality criterion to concentrations of mercury in water. Each 
approach has its own advantages, limitations, and uncertainties as 
discussed below.
    EPA's preferred approach for relating a concentration of 
methylmercury in fish tissue to a concentration of mercury in ambient 
water is to derive site-specific BAFs based on water and fish collected 
in the waterbody of concern. This recommendation is consistent with 
EPA's bioaccumulation guidance contained in the 2000 Human Health 
Methodology. Furthermore, this recommendation is consistent with the 
views expressed by the methylmercury BAF peer reviewers. See the 
Addresses section of today's Notice to obtain peer review responses 
from the Water Docket. EPA prefers the use of site-specific BAFs 
because they inherently incorporate the net effects of the biotic and 
abiotic factors at a particular location that can affect 
bioaccumulation in the aquatic food chain, and thus provide an accurate 
accounting of the uptake of methylmercury. When sampling fish and water 
to derive a site-specific BAF, one needs to consider how best to sample 
so that issues such as seasonal variability in fish exposure to 
methylmercury, spacial variability, and fish size are taken into 
account. These issues and others should also be assessed in relation to 
the fish consumption patterns of the exposed human population. EPA 
expects to publish specific guidance for deriving field-measured site-
specific BAFs in late 2001. However, until then the recently published 
procedures in the 2000 Human Health Methodology for deriving BAFs can 
be used as a general guide. In addition, the Bioaccumulation Technical 
Support Document (TSD) for the 2000 Human Health Methodology (expected 
to be published in late 2001) will provide additional information and 
guidance on deriving site-specific BAFs.
    Another approach for deriving methylmercury BAFs is to use a 
bioaccumulation model. Most bioaccumulation models are generally 
process-based or mechanistic type mathematical models that are meant to 
represent what occurs in nature. At this time, the general science of 
bioaccumulation modeling, especially for mercury, is not advanced to 
the stage where models are readily available and applicable to all 
types of pollutants and aquatic systems. Three examples of mechanistic-
type bioaccumulation models are: the Mercury Cycling Model (Tetra Tech, 
1999); EPA's aquatic food chain model AQUATOX (USEPA, 2000g); and the 
Quantitative Environmental Analysis food chain model QEAFDCHN (QEA, 
2000). There are only a few models that might be used to predict 
methylmercury bioaccumulation. Such models generally have not been 
widely used and have only been applied to mercury in a few aquatic 
ecosystems under specific environmental conditions. Of the examples 
listed above, only the Mercury Cycling Model was developed solely for 
mercury. The others have been generally developed for nonionic organic 
chemicals that bioaccumulate. They might be applied to mercury with 
substantial modifications. Most bioaccumulation models are based upon a 
chemical mass balance approach for fish or other aquatic organisms, 
which requires considerable understanding of mercury loadings to the 
environment and how mercury moves through the environment. Each model 
results in a BAF with some level of uncertainty. None of the example 
models can predict bioaccumulation without considerable site-specific 
information and at least some degree of calibration to the waterbody of 
interest, and in some cases considerable modification of the model. The 
amount and quality of data required for proper model application may 
equal or exceed that necessary to develop a site-specific methylmercury 
BAF. Other types of models could also be used if they are 
scientifically defensible. Regardless of the type of model, if a model 
is chosen, the issues discussed in the bioaccumulation guidance 
contained in the 2000 Human Health Methodology should be carefully 
considered. The derivation of site-specific parameters used in the 
model should also be documented, and some indication given of the 
uncertainty surrounding the BAFs predicted by the model.
    EPA acknowledges that derivation of site-specific field-measured 
BAFs may not be feasible in all situations. Therefore, in the absence 
of site-specific methylmercury bioaccumulation data, a possible third 
approach is to use EPA's empirically derived draft methylmercury BAFs. 
As previously discussed, as part of initial efforts to

[[Page 1356]]

derive a water column-based section 304(a) water quality criterion, EPA 
used the Agency's BAF guidance in the 2000 Human Health Methodology and 
BAF methods in Volume III, Appendix D of the Mercury Study to develop 
draft empirically derived BAFs from field data collected across the 
United States and reported in the open literature. The empirically 
derived BAFs are listed by trophic level in Table 1.

                              Table 1.--Empirically Derived BAFs for Methylmercury
----------------------------------------------------------------------------------------------------------------
                                                                    BAF trophic     BAF trophic     BAF trophic
                                                                      level 2         level 3         level 4
----------------------------------------------------------------------------------------------------------------
BAF.............................................................         160,000         680,000       2,700,000
----------------------------------------------------------------------------------------------------------------

    The BAF peer reviewers expressed concerns about the predictive 
capability of these draft BAFs and about using them to derive a section 
304(a) water quality criterion for methylmercury that would be 
accurately protective for waterbodies across the nation. However, EPA 
believes that the methylmercury BAFs in Table 1 are sufficiently 
predictive of bioaccumulation to be used in implementing a fish tissue 
based methylmercury water quality criterion in a State's or authorized 
Tribe's water quality standards in the absence of any other site-
specific bioaccumulation data. Thus, EPA will consider water quality 
standards implementation approaches that use these empirically derived 
BAFs. EPA recognizes that these methylmercury BAF values are not 
entirely representative of the methylmercury bioaccumulation potential 
in all waterbodies across the United States, and they may over- or 
underestimate site-specific bioaccumulation potential. There is 
uncertainty in using these BAFs as they collapse a very complex 
nonlinear process into a simplistic and linear approach to predicting 
bioaccumulation and assume that the biotic and abiotic process 
affecting mercury fate and bioaccumulation are similar across different 
waterbodies. The decision to publish these empirically derived BAFs is 
an Agency risk management decision made based on the need for a 
mechanism to relate a fish tissue concentration of methylmercury to a 
water column concentration. EPA has selected the geometric mean of the 
field-measured BAFs obtained from the open literature as the 
empirically derived BAFs for each trophic level. EPA believes the 
geometric mean is the central tendency value that best represents the 
wide range of environmental and biological conditions present in the 
waters of the United States. Choosing a value near the extremes of the 
distribution (e.g., 10th or 90th percentile) may introduce an 
unacceptable level of uncertainty into the CWA goal of protecting 
public health. Furthermore, EPA believes a geometric mean is most 
appropriate because the underlying processes of methylmercury 
bioaccumulation are more likely multiplicative than additive.
    Other empirical, modeling, or newly developed bioaccumulation 
prediction approaches may be used to relate concentrations of 
methylmercury in fish tissue to concentrations of methylmercury in 
water, provided the approach is scientifically defensible and 
adequately documented.
    In addition to using BAFs to relate concentrations of methylmercury 
in fish tissue to methylmercury concentrations in water, a factor is 
needed to translate methylmercury in water to its total mercury 
equivalent. NPDES permits and other water quality-based pollution 
control activities are traditionally based on the total concentration 
of the inorganic metal form, not the dissolved organic form. Many of 
the issues surrounding the uncertainty in predictability and 
transferability of methylmercury BAFs across different waterbodies also 
pertain to relating methylmercury in water to a given total mercury 
concentration. As with BAFs, EPA's preferred approach for translating 
between total and methylmercury is for States and authorized Tribes to 
measure total mercury and methylmercury and in the waterbody of 
interest. However, EPA will consider standards implemented with 
empirically derived translators. As part of exercise to develop draft 
methylmercury BAFs, EPA derived methylmercury-to-total mercury 
translator factors for rivers/streams and lakes. Like the BAFs, the 
methylmercury-to-total mercury translators were empirically derived 
based on water data collected in the field from a variety of locations 
across the United States. Depending on the available mercury water 
data, more than one translation may be necessary to translate to the 
total concentration of mercury in ambient waters. Table 2 lists the 
translator factors that could be used to translate between 
methylmercury and mercury in ambient surface waters in the absence of 
any site-specific data.

                Table 2.--Summary of Mercury Translators
------------------------------------------------------------------------
                                             Lakes and      Rivers and
               Translation                reservoirs \1\    streams \1\
------------------------------------------------------------------------
Fraction of total mercury that is                  0.60            0.37
 dissolved..............................
Fraction of total mercury that is                  0.032           0.014
 dissolved methylmercury................
Fraction of total methylmercury that is            0.61            0.49
 dissolved methylmercury................
------------------------------------------------------------------------
\1\ Values are from Section II, Table 15, of the EPA internal draft
  report National Bioaccumulation Factors for Methylmercury, available
  from the Water Docket.

VII. What Is the Relationship Between Fish Advisories and the Fish 
Tissue Residue Water Quality Criterion?

    A majority of States and authorized Tribes with fish advisory 
programs have adopted a risk-based approach to developing fish 
advisories that is similar to the approach recommended in EPA's 
Guidance for Assessing Chemical Contaminant Data for Use in Fish 
Advisories (EPA 2000 e, h). However, due to variations in State and 
Tribal fish advisory programs, some States and Tribes may not be 
adequately warning the public of health risks. A small number of States 
continue to use fish consumption advisory approaches that are 
considered by EPA to be inadequate for protecting public health. The 
use of these approaches may lead to significant

[[Page 1357]]

increased health risks for people consuming fish harvested from 
contaminated local waters. Such approaches include the inappropriate 
use of Action Levels and Tolerances developed by EPA and the Food and 
Drug Administration. These are appropriate for use in the commercial 
market place, but are considered to be inappropriate for establishing 
local advisory needs and should not be used for that purpose.
    Both today's section 304(a) human health water quality criterion 
guidance for methylmercury and EPA's recommended fish consumption limit 
for mercury (which EPA encourages States and authorized Tribes to use 
as guidance in setting fish advisories) are meant to protect humans 
from consumption of mercury-contaminated fish. The procedures for 
deriving these two values are consistent with each other, but in 
deriving the section 304(a) methylmercury water quality criterion, EPA 
used an RSC of 2.7 10-5 mg/kg-day to account for exposure 
from non-freshwater and non-estuarine fish. See section IV.B of today's 
Notice. The guidance for setting fish consumption limits (USEPA, 2000e) 
also discusses using an RSC to account for exposures other than 
noncommercially caught fish, but does not specifically require this to 
be done. The RSC guidance in the 2000 Human Health Methodology provides 
more detail and specific quantitative procedures to account for other 
exposure pathways. EPA recommends that States and authorized Tribes 
consider using an RSC to account other sources of mercury exposure when 
deriving a fish consumption limit and setting a fish advisory for 
mercury.

VIII. How Does EPA Suggest Implementing the Methylmercury Water 
Quality Criterion?

    EPA encourages States and authorized Tribes to adopt the fish 
tissue residue water quality criterion for methylmercury outlined in 
this notice into their water quality standards to protect CWA section 
101(a) designated uses related to human consumption of fish. This 
recommended water quality criterion reflects the most current and best 
science. EPA recognizes and emphasizes that States and authorized 
Tribes will need additional, specific procedures and water quality 
program guidance in order to implement water quality criteria they 
adopt based on this guidance. These procedures include, but are not 
necessarily limited to: (1) An analytical method for detecting and 
measuring concentrations in fish and water; (2) a field sampling plan 
for collecting fish and protocols for laboratory analysis and data 
interpretation; (3) a procedure for translating methylmercury 
concentrations in fish to total mercury concentrations in ambient 
surface water or effluent; (4) data quality objectives and associated 
procedures for determining attainment of the water quality criterion 
and status of designated use impairment based on fish residue data; (5) 
harmonization with fish consumption advisory programs, (6) procedures 
for determining the need for a water quality-based effluent limit 
(WQBEL) in NPDES permits for point source discharges of mercury; (7) 
procedures for developing and implementing WQBELs for NPDES permits; 
and, (8) procedures for developing targets for TMDL load and waste load 
allocations.
    To help States and authorized Tribes adopt the recommended section 
304(a) water quality criterion for methylmercury as part of their 
standards, and to implement those standards, EPA plans to begin 
development implementation procedures and guidance documents by the end 
of 2001. These will be part of a broad national implementation policy 
for this water quality criterion. The implementation policy will be 
developed with consideration of the draft Mercury Action Plan submitted 
for public comment in 1998 and expected to be revised soon. EPA expects 
States and authorized Tribes to adopt new or revised human health 
mercury water quality criteria and to use the procedures and guidance 
contained in the forthcoming implementation policy to adopt their water 
quality criteria within five years from today's publication. EPA 
generally believes that five years from the date of EPA's publication 
of new or revised section 304(a) water quality criteria guidance is a 
reasonable time by which States and Tribes should take action to adopt 
new or revised water quality criteria necessary to protect the 
designated uses of their waters. See 63 FR 68353.
    EPA recently published a new analytical method (method 1631) for 
detecting and measuring total and dissolved mercury in water and fish 
samples (USEPA, 1999b). This method is approximately 400 times more 
sensitive than EPA's previously recommended analytical method and is 
capable of measuring mercury concentrations well into the ranges 
identified in this notice for fish concentrations as well as those 
anticipated for associated water concentrations (detection limit of 0.2 
ng/L in water). This method determines the amount of total mercury, not 
methylmercury, in water and fish. This will likely result in a 
substantial increase in the number of point source discharges of 
mercury needing WQBELs in their NPDES permits.
    Among the many issues associated with implementation, State and 
Tribal water quality managers will need to identify which species to 
target for sampling, determine sample compositing procedures and 
frequency of sampling, and relate sampling and analysis procedures to 
the consumption patterns intended for protection by the water quality 
criterion. The Agency has published guidance on field sampling and 
analysis as part of the package of guidance to States and Tribes for 
issuing fish consumption advisories. EPA anticipates that this guidance 
will also be useful for implementing State or Tribal water quality 
criterion for methylmercury based on today's criterion guidance.
    Three translations are necessary to relate the methylmercury water 
quality criterion for fish tissue expressed in this notice to a total 
mercury concentration in ambient water or effluent, for NPDES or TMDL 
purposes. The first translation is to determine the fraction of 
measured mercury in fish that is methylmercury. Although this can vary 
in practice, the methylmercury fraction is typically very high in 
freshwater and estuarine fish, and approaches 100 percent for higher 
trophic level organisms. The second translation is from methylmercury 
in fish to methylmercury in water. As discussed in detail above, the 
best means of determining this relationship is through site-specific 
analysis of bioaccumulation patterns. The third translation is from 
methylmercury in water to total mercury in water. As with the BAFs, the 
preferred method to do this translation is to measure the 
concentrations of methylmercury and total mercury in ambient water.
    As mentioned, EPA believes an implementation policy is necessary 
that addresses recommendations for establishing sampling protocols and 
determining attainment of State or Tribal methylmercury water quality 
criterion, NPDES permitting and TMDL development, and source management 
and control strategies. For example, the water quality standards 
portion of this policy would address issues such as how the water 
quality standards variance and use attainability analysis processes 
could be used to address legacy contaminants. Also, EPA expects that, 
as a result of this revised methylmercury water quality criterion, 
together with the more sensitive method for detecting mercury, there 
will be an increase in the number of waterbodies

[[Page 1358]]

reported on State 303(d) lists as impaired due to mercury 
contamination. Thus, the policy would also discuss approaches for 
managing the development of TMDLs for waterbodies impaired by mercury. 
This would include approaches for addressing waterbodies where much of 
the mercury is from atmospheric sources, and how TMDLs can take into 
account ongoing efforts to address sources of mercury, such as programs 
under the Clean Air Act and pollution prevention activities.
    The policy would also address numerous issues associated with point 
source discharges of mercury such as determining the need for a WQBEL 
in NPDES permits and, where needed, developing and implementing those 
limits. EPA intends to take the following factors or assumptions into 
account when it addresses these issues: the unique properties of 
mercury; EPA's expectation that there will likely be a substantial 
increase in the number of point source discharges needing WQBELs as a 
result of the new more sensitive method; and, in most cases, the 
relatively small contribution from point source discharges to the total 
loadings of mercury to a waterbody.
    Given the ongoing atmospheric sources of mercury and the long-term 
cycling of mercury in the environment, the most effective means of 
protecting public health for the next few decades will continue to be 
the issuance of fish consumption advisories by State and Tribal 
authorities, to ensure the public knows what level of fish consumption 
from specific waters is safe. EPA also emphasizes that the science 
underlying today's recommended section 304(a) water quality criterion 
is sound and recommends that States and authorized Tribes consider 
using an appropriate RSC in establishing and issuing fish consumption 
advisories as described in the fish advisory guidance (USEPA, 2000e). 
However, effective source control and management programs need to be 
initiated and developed in the coming few years to begin the long-term 
process of recovery from the widespread mercury contamination evident 
in our aquatic environments, with the goal of reducing mercury 
contamination so that fish consumption advisories can be removed.
    EPA believes that flexibility may be appropriate as water quality 
standards based on today's methylmercury water quality criterion are 
implemented. Today's notice serves as an initiation of dialogue with 
stakeholders on recommended approaches for using today's section 304(a) 
water quality criterion guidance and managing mercury contamination in 
the aquatic environment. EPA is interested in obtaining information, 
views, suggestions, and innovative approaches from the public. EPA is 
particularly interested in specific examples or model approaches for 
management of mercury contamination at the Federal, State, Tribal, and 
local level. EPA anticipates this dialogue will be facilitated by a 
variety of means, which may include public meetings, meetings with 
stakeholders, and written correspondence and responses.

IX. Literature Cited

Akagi, H., O. Malm,Y. Kinjo, M. Harada, F.J.P. Branches, W.C. 
Pfeiffer and H. Kato (1995). Methylmercury pollution in the Amazon, 
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    Dated: December 21, 2000.
J. Charles Fox,
Assistant Administrator for Water.
[FR Doc. 01-217 Filed 1-5-01; 8:45 am]
BILLING CODE 6560-50-P