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Notice of Draft Guidance for Implementing the January 2001 Methylmercury Water Quality Criterion

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Environmental Protection Agency (EPA).


Notice of availability and request for comments.


EPA announces the availability of draft guidance for implementing the water quality criterion for methylmercury and requests comments on the draft guidance. The draft document provides technical guidance to states, territories, and authorized tribes exercising responsibility under Clean Water Act (CWA) section 303(c) on how to use EPA's fish tissue-based methylmercury criterion recommendation in developing their own water quality standards for methylmercury and in implementing these standards in Total Maximum Daily Loads (TMDLs) and National Pollutant Discharge Elimination System (NPDES) permits. The guidance document does not impose any legally binding requirements on any entity. It provides various technical and policy approaches to implementing the criterion. These approaches are recommendations only. States, territories and authorized tribes may choose to implement other technically-sound approaches that are consistent with the CWA and EPA's implementing regulations.


Comments must be received on or before October 10, 2006.


Submit your comments, identified by Docket ID No. EPA-HQ-OW-2006-0656, by one of the following methods:

  • Follow the on-line instructions for submitting comments.
  • E-mail:
  • Mail: Water Docket, Environmental Protection Agency, Mailcode: 4101T, 1200 Pennsylvania Ave., NW, Washington, DC 20460. Please include a total of four copies.
  • Hand Delivery: EPA Docket Center (EPA/DC), EPA West, Room B102, 1301 Constitution Ave., NW., Washington, DC 20460. Please include a total of four copies. Such deliveries are only accepted during the Docket's normal hours of operation, and special arrangements should be made for deliveries of boxed information.

Instructions: Direct your comments to Docket ID No. EPA-HQ-OW-2006-0656. EPA's policy is that all comments received will be included in the public docket without change and may be made available online at, including any personal information provided, unless the comment includes information claimed to be Confidential Business Information (CBI) or other information whose disclosure is restricted by statute. Do not submit information that you consider to be CBI or otherwise protected through or The website is an “anonymous access” system, which means EPA will not know your identity or contact information unless you provide it in the body of your comment. If you send an e-mail comment directly to EPA without going through your e-mail address will be automatically captured and included as part of the comment that is placed in the public docket and made available on the Internet. If you submit an electronic comment, EPA recommends that you include your name and other contact information in the body of your comment and with any disk or CD-ROM you submit. If EPA cannot read your comment due to technical difficulties and cannot contact you for clarification, EPA may not be able to consider your comment. Electronic files should avoid the use of special characters, any form of encryption, and be free of any defects or viruses. For additional information about EPA's public docket visit the EPA Docket Center homepage at​epahome/​dockets.htm.

Docket: All documents in the docket are listed in the index. Although listed in the index, some information is not publicly available, e.g., CBI or other information whose disclosure is restricted by statute. Certain other material, such as copyrighted material, will be publicly available only in hard copy. Publicly available docket materials are available either electronically in http://Start Printed Page or in hard copy at the Water Docket, EPA/DC, EPA West, Room B102, 1301 Constitution Ave., NW, Washington, DC. The Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal holidays. The telephone number for the Public Reading Room is (202) 566-1744, and the telephone number for the Water Docket is (202) 566-2426).


The EPA Docket Center suffered damage due to flooding during the last week of June 2006. The Docket Center is continuing to operate. However, during the cleanup, there will be temporary changes to Docket Center telephone numbers, addresses, and hours of operation for people who wish to make hand deliveries or visit the Public Reading Room to view documents. Consult EPA's Federal Register notice at 71 FR 38147 (July 5, 2006) or the EPA Web site at​epahome/​dockets.htm for current information on docket operations, locations and telephone numbers. The Docket Center's mailing address for U.S. mail and the procedure for submitting comments to are not affected by the flooding and will remain the same.

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Jim Pendergast, Standards and Health Protection Division, Office of Water, (4305T), Environmental Protection Agency, 1200 Pennsylvania Ave., NW, Washington, DC, 20460; telephone number: 202-566-0398; fax number: 202-566-0409; e-mail address:

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I. General Information

A. Does this Action Apply to Me?

Entities potentially interested in today's notice are those that discharge or release mercury and methylmercury to surface waters, and federal, state, tribal, and local authorities that regulate methylmercury levels in surface water. Categories and entities interested in today's notice include but are not limited to:

CategoryExamples of potentially affected entities
State/Local/Tribal GovernmentStates, municipalities, tribes.
IndustryMining, coal-fired power generation, other industries using mercury in their processing

This table is not intended to be exhaustive. Other types of entities not listed in the table may also be interested.

B. What Should I Consider as I Prepare My Comments for EPA?

1. Submitting CBI. Do not submit this information to EPA through or e-mail. Clearly mark the part or all of the information that you claim to be CBI. For CBI information in a disk or CD ROM that you mail to EPA, mark the outside of the disk or CD ROM as CBI and then identify electronically within the disk or CD ROM the specific information that is claimed as CBI). In addition to one complete version of the comment that includes information claimed as CBI, a copy of the comment that does not contain the information claimed as CBI must be submitted for inclusion in the public docket. Information so marked will not be disclosed except in accordance with procedures set forth in 40 CFR part 2.

2. Tips for Preparing Your Comments. When submitting comments, remember to:

  • Identify the docket number and other identifying information (subject heading, Federal Register date and page number).
  • Follow directions—The agency may ask you to respond to specific questions or organize comments by referencing a Code of Federal Regulations (CFR) part or section number.
  • Explain why you agree or disagree; suggest alternatives and substitute language for your requested changes.
  • Describe any assumptions and provide any technical information and/or data that you used.
  • If you estimate potential costs or burdens, explain how you arrived at your estimate in sufficient detail to allow for it to be reproduced.
  • Provide specific examples to illustrate your concerns, and suggest alternatives.
  • Explain your views as clearly as possible, avoiding the use of profanity or personal threats.
  • Make sure to submit your comments by the comment period deadline identified.

II. Background and Today's Action

A. What Is Methylmercury and Why Are We Concerned About It?

Mercury occurs naturally in the earth's crust and cycles in the environment as part of both natural and human-induced 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 circulates in the atmosphere for up to a year, and, hence, can be widely dispersed and transported thousands of miles from sources of emission. Most of the mercury in water, soil, sediments, plants, and animals is in the form of inorganic mercury salts and organic forms of mercury (e.g., methylmercury). Methylmercury most often results from microbial activity in wetlands, the water column, and sediments and is the form of mercury that presents the greatest risk to human health. Divalent mercury, when bound to airborne particles, is readily removed from the atmosphere by precipitation and is also dry deposited. Even after it deposits, mercury commonly returns to the atmosphere either as a gas or associated with particles, and redeposits elsewhere. As mercury cycles between the atmosphere, land, and water, mercury undergoes a series of complex chemical and physical transformations, many of which are not completely understood.

Exposure to methylmercury can result in a variety of health effects in humans. Children who are exposed to low concentrations of methylmercury prenatally might be at risk of poor performance on neurobehavioral tests, such as those measuring attention, fine motor function, language skills, visual-spatial abilities, and verbal memory. (NRC 2000, USEPA 2002, USEPA 2005). The primary route by which the U.S. population is exposed to methylmercury is through the consumption of fish containing methylmercury. For most people, methylmercury exposure from consumption of fish and shellfish is not a health concern. Yet, the exposure levels at which neurological effects have been observed in children can occur via maternal consumption of fish (rather than high-dose poisoning episodes) (USEPA 2005). The risks from methylmercury in fish and shellfish depend on the amount of fish and shellfish eaten and the levels of methylmercury in the fish and shellfish. Therefore, the Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) are advising women who may become pregnant, pregnant women, nursing mothers, and young children to avoid some types of fish and eat fish and shellfish that are lower in methylmercury. You can find more information about this joint Federal advisory on EPA's Web site at​waterscience/​fish.

In 2000, the National Academy of Sciences (NAS)/National Research Council (NRC) reviewed the health studies on methylmercury (NRC 2000). In its review of the literature, NRC found neurodevelopmental effects to be the most sensitive endpoints and appropriate for establishing a Start Printed Page 45562methylmercury Reference Dose (RfD) (NRC 2000). EPA defines an RfD as “an estimate (with uncertainty spanning perhaps an order of magnitude) of a daily oral exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. On the basis of the NRC report, EPA established an RfD of 0.0001 mg/kg per day (0.0001 milligram of methylmercury per day for each kilogram of a person's body mass) in 2001 (USEPA 2002). EPA believes that exposures at or below the RfD are unlikely to be associated with appreciable risk of deleterious effects. It is important to note, however, that the RfD does not define an exposure level corresponding to zero risk; methylmercury exposure near or below the RfD could pose a very low level of risk that EPA deems to be non-appreciable. It is also important to note that the RfD does not define a bright line, above which individuals are at risk of adverse effects (USEPA 2005). NAS determined that EPA's RfD “is a scientifically justified level for the protection of public health.”

With regard to other health effects of methylmercury, some recent epidemiological studies in men suggest that methylmercury is associated with a higher risk of acute myocardial infarction, coronary heart disease, and cardiovascular disease in some populations. Other recent studies have not observed this association. The studies that have observed an association suggest that the exposure to methylmercury might attenuate the beneficial effects of fish consumption (USEPA 2005). There also is some recent evidence that exposures of methylmercury might result in genotoxic or immunotoxic effects. Other research with less corroboration suggests that reproductive, renal, and hematological impacts could be of concern. There are insufficient human data to evaluate whether these effects are consistent with methylmercury exposure levels in the U.S. population (USEPA 2005).

B. What Is the Current Methylmercury Criterion?

In a January 8, 2001, Federal Register notice (66 FR 1344), EPA announced the availability of its recommended water quality criterion for methylmercury. The methylmercury water quality criterion is derived from the methylmercury RfD (described above) and data about the target population to be protected (i.e., exposure parameters and assumptions). The equation for calculating the methylmercury fish tissue residue water quality criterion for the protection of human health is:


TRC = Fish tissue residue criterion (mg methylmercury/kg fish tissue) for freshwater and estuarine fish and shellfish

RfD = Reference Dose (based on non-cancer human health effects). For methylmercury the RfD is 0.0001 mg/kg BW-day (0.1 ug/kg BW-day)

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 and all values used in the equation are described in Water Quality Criterion for the Protection of Human Health, Methylmercury (USEPA 2001b). This equation is essentially the same equation used in the 2000 Human Health Methodology to calculate a water quality criterion for a pollutant that may cause non-cancer health effects, but is rearranged to solve for a protective concentration in fish tissue rather than in water. Thus, the equation does not include a bioaccumulation factor (BAF) or drinking water intake value (methylmercury exposure from drinking water is negligible (USEPA 2001a)). Incorporating the relevant values into the above equation, EPA obtained a fish tissue concentration (TRC) of 0.3 mg methylmercury/kg fish as the concentration in fish tissue that should not be exceeded. EPA's preference is for states and authorized tribes to use local or regional consumption rates, if these would better reflect the target populations.

C. What Is The Draft Implementation Guidance?

In the 2001 Federal Register notice of the availability of EPA's recommended water quality criterion for methylmercury, EPA stated that it would develop associated procedures and guidance for implementing the criterion. We are issuing that draft guidance today. The guidance will assist states in developing a water quality criterion for methylmercury in their water quality standards. States can either adopt EPA's recommended criterion or another criterion that is scientifically defensible and consistent with the Act and its implementing regulations. 40 CFR 131.11(a)(2).

This guidance document presents suggested approaches to criteria adoption and implementation. These approaches are recommendations and do not represent the only technically defensible approaches. The discussion in the guidance document is intended solely as guidance. This guidance does not change or, substitute for, applicable sections of the CWA or EPA's regulations; nor is it a regulation itself. Thus, it does not impose legally binding requirements on EPA, states, authorized tribes, or the regulated community and may not apply to a particular situation. EPA, state, territorial, and tribal decision makers retain the discretion to adopt approaches on a case-by-case basis that differ from this guidance where appropriate.

D. Why Did EPA Draft This Guidance?

The methylmercury criterion is expressed as a fish and shellfish tissue value, and this raises both technical and programmatic implementation questions. EPA expects that, as a result of the revised methylmercury water quality criterion, together with a more sensitive method for detecting mercury in effluent and the water column, and increased monitoring of previously unmonitored waterbodies, the number of waterbodies that states report on CWA section 303(d) lists as impaired due to methylmercury contamination might continue to increase. Development of water quality standards, NPDES permits, and TMDLs present challenges because these activities typically have been based on a water concentration (e.g., as a measure of mercury levels in effluent). This guidance addresses issues associated with states and authorized tribes adopting the new water quality criterion into their water quality standards programs and implementation of the revised water quality criterion in TMDLs and NPDES permits. Further, because atmospheric deposition serves as a large source of mercury for many waterbodies, implementation of the criterion involves coordination across various media and program areas.

E. What Does the Draft Guidance Recommend?

For states and authorized tribes exercising responsibility under CWA section 303(c), this document provides technical guidance on how they might want to use the recommended 2001 fish tissue-based criterion to develop their own water quality standards for Start Printed Page 45563methylmercury. States and authorized tribes may decide to adopt the EPA recommended methylmercury fish tissue-based criterion based on the national default fish consumption rate or translate the tissue value to a water column value through use of methylmercury BAFs. If a state or authorized tribe decides to translate the fish tissue criterion to a water column criterion, EPA recommends three approaches for relating a concentration of methylmercury in fish tissue to a concentration of methylmercury in ambient water: (1) Deriving site-specific methylmercury BAFs; (2) using bioaccumulation models; and (3) using EPA's draft default methylmercury BAFs. All three approaches have limitations, such as the amount of data necessary to develop a BAF. This guidance discusses the advantages and limitations of each approach.

States and authorized tribes may also consider calculating their own fish tissue criteria or adopting site-specific criteria for methylmercury to reflect local or regional fish consumption rates or relative source contributions. This guidance also discusses variances and use attainability analyses relating to methylmercury.

This document describes analytical methods for determining the concentrations of mercury and methylmercury in both tissue and water. These methods can detect mercury and methylmercury in tissue and water at very low levels—well below the levels of the previous criterion for mercury in the water column and the current criterion of methylmercury in fish tissue. This document also provides guidance for field sampling plans, laboratory analysis protocols, and data interpretation that is based on previously published EPA guidance on sampling strategies for contaminant monitoring. This guidance also describes how states can assess the attainment of water quality criteria and protection of designated uses by comparing sampling data to water quality criteria.

This guidance also discusses approaches for the development of TMDLs for waterbodies impaired by mercury. This includes approaches for TMDLs for waterbodies where much of the mercury is from atmospheric sources and suggestions regarding how such TMDLs can take into account ongoing efforts to address sources of mercury, such as programs under the Clean Air Act (CAA) and pollution prevention activities.

EPA's Technical Support Document for Water Quality-based Toxics Control (TSD), EPA 505/2-90-001, explains how to implement criteria expressed in terms of pollutant concentrations in water in NPDES permits. States that decide to implement the methylmercury tissue criterion as a water concentration for NPDES permits should continue to use the TSD guidance. However, for states that decide to implement the methylmercury tissue criterion directly, that is, without translating it into a water column value, the TSD doesn't provide relevant guidance. Today's draft guidance also includes a recommended approach for directly incorporating the methylmercury tissue criterion in NPDES permits.

F. Are There Particular Issues on Which EPA is Requesting Comment?

EPA requests comments only on the draft methylmercury criterion implementation guidance. EPA is not requesting comments on the 2001 methylmercury criterion itself. Although EPA solicits comment on the entire draft guidance, it is particularly interested in the following topics:

1. Implementation Approach for NPDES Permits Where the Criterion Is Implemented as a Fish Tissue Value

Today's guidance presents a recommended approach for directly incorporating the methylmercury tissue criterion in NPDES permits. This approach does not rely upon a state developing a bioaccumulation factor to convert the methylmercury tissue criterion into a water concentration equivalent. The approach recommends that facilities that use, accept or receive mercury into their wastewaters develop mercury minimization plans. For discharges that are small contributors of mercury to a watershed or do not use mercury in their processes, the approach recommends that current permit effluent levels remain constant. EPA expects that most facilities will fall into this category due to significant loadings from other sources (e.g., air deposition, abandoned mines). For discharges that are significant contributors of mercury to a watershed and use mercury in their processes, the approach recommends that permit effluent limits ensure the attainment of water quality standards. EPA expects that few dischargers should fall into this category. For new or increased discharges, the approach recommends that permit effluent limits hold watershed loadings constant using antidegradation principles.

EPA solicits comment on the recommendations for directly incorporating the methylmercury tissue criterion in NPDES permits. The draft guidance recommends that a permitting authority could reasonably conclude that reasonable potential exists if two conditions are present (1) The NPDES permitted discharger has mercury in its effluent at a quantifiable level and (2) fish tissue from the waterbody into which the discharger discharges exceeds the fish tissue water quality criterion. EPA specifically solicits comment on alternate methods, based on using other information, for determining that there is reasonable potential to exceed the water quality standard where fish tissue data show that the methylmercury tissue criterion in a water quality standard is achieved.

2. Applying Water Quality Variances on a Watershed or State-Wide Basis

Traditionally, states establish water quality variances that are specific to a pollutant and a facility. EPA recognizes that, for mercury, there are situations where a number of NPDES dischargers are located in the same area or watershed and the justification supporting granting a variance applies to all of the dischargers. Two states, Ohio and Michigan, have already developed variances that apply to multiple discharges for mercury. Today's guidance encourages states and authorized tribes to consider establishing a multiple-discharger variance for a group of dischargers collectively.

EPA solicits comment on whether it should discuss multi-discharge, watershed, or state-wide variances in the final guidance.

G. References Cited

NRC (National Research Council). 2000. Toxicological effects of methylmercury. Committee on the Toxicological Effects of Methylmercury. National Academy Press. Washington, DC.

USEPA (U.S. Environmental Protection Agency). 1991. Technical Support Document for Water Quality-based Toxics Control. EPA 505/2-90-001. U.S. Environmental Protection Agency, Office of Water Enforcement and Permits and Office of Water Regulations and Standards.

USEPA (U.S. Environmental Protection Agency). 2001a. Water quality criteria: Notice of Availability of water quality criterion for the protection of human health: Methylmercury. U.S. Environmental Protection Agency, Office of Water, Washington, DC. Fed. Regist., 66:1344.

USEPA (U.S. Environmental Protection Agency). 2001b. Water quality criterion for the protection of human health: Methylmercury. EPA-823-R-01-001. U.S. Environmental Protection Agency, Office of Water, Washington, DC.

USEPA (U.S. Environmental Protection Agency). 2002. Integrated Risk Information System (IRIS). Methylmercury. U.S. Environmental Protection Agency, Office Start Printed Page 45564of Research and Development, National Center for Environmental Assessment.

USEPA (U.S. Environmental Protection Agency). 2005. Regulatory Impact Analysis of the Clean Air Mercury Rule. Final Report. EPA-452/R-05-003. U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards, Air Quality Strategies and Standards Division, Research Triangle Park, NC.

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Dated: August 3, 2006.

Benjamin H. Grumbles,

Assistant Administrator for Water.

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[FR Doc. 06-6803 Filed 8-8-06; 8:45 am]