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

Note: EPA no longer updates this information, but it may be useful as a reference or resource.

[Federal Register: January 8, 2001 (Volume 66, Number 5)]
[Notices]
[Page 1344-1359]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr08ja01-55]

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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
manibusan.mary@epa.gov. 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,
Brazil. Sci. Total Environ. 175:85-95.
Becker, D. S. and G.N. Bigham. 1995. Distribution of Mercury in the
Aquatic Food Web of Onondaga Lake, New York. Water Air Soil Pollu.
80:563-571.
Bloom, N.S. 1992. On the chemical form of mercury in edible fish and
marine invertebrate tissue. Can. J. Fish. Aquat. Sci. 49:1010-1017.
Cope, W.G., J.G. Wiener and R.G. Rada. 1990. Mercury accumulation in
yellow perch in Wisconsin seepage lakes: Relation to lake
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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

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