United States Office of Water EPA-823-F-10-001
Environmental Protection 4305T April 2010
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I Guidance for Implementing the January 2001
Methylmercury Water Quality Criterion
Summary
EPA is publishing its final Guidance for Implementing the January 2001 Methylmercury Water
Quality Criterion. This document will help protect waters and human health by giving guidance
to states, territories, and authorized tribes (states and tribes) for adopting a fish tissue-based
methylmercury water quality criterion into their water quality standards and implementing the
criterion through other water quality programs. You can download the document from EPA's
web site at www.epa.gov/waterscience/criteria/methylmercurv/index.html.
Background
Methylmercury in surface waters can enter the aquatic food chain and become stored in fish and
shellfish muscle tissue. Eating fish and shellfish contaminated with methylmercury in amounts
that exceed EPA's criterion can result hi a variety of health effects in humans. For example,
children who were exposed to low concentrations of methylmercury before they were born 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.
In January 2001, EPA published a new water quality criterion for methylmercury that, for the
first time, expresses a human health criterion as a concentration in fish and shellfish tissue
concentration rather than in the water. Adopting the fish tissue criterion into water quality
standards presents several challenges, such as implementing the fish tissue criterion in National
Pollutant Discharge Elimination System (NPDES) permit limits. In a 2001 Federal Register
announcement, EPA stated its intention to develop implementation guidance to address these
issues. Subsequently, EPA sought input from state environmental agencies to develop the
guidance. EPA released draft guidance for public comment in 2006 and developed the final
guidance to address the comments received.
About This Guidance Document
The Guidance helps states and tribes adopt and implement a methylmercury water quality
criterion expressed as a fish tissue value. It consolidates existing EPA guidance and practice
relevant to methylmercury and also includes new information, such as alternative approaches for
implementing the new methylmercury criterion where bioaccumulation data are not available for
developing a water column translation and NPDES permits must be issued, hi these cases, where
a point source discharge could cause or contribute to an exceedance of the mercury water quality
standard, the guidance recommends that the permitting authority include permit conditions
requiring the permittee to implement a mercury minimization plan tailored to the facility's
potential mercury discharge. The permktiHB authority would also require effluent monitoring to
determine whether the
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This approach does not generally require or recommend translating the fish tissue concentration
into a water column concentration using site-specific bioaccumulation factors that can be costly
to develop. However, where direct discharges of mercury to a waterbody are high, EPA
recommends that permit authorities work with mercury dischargers in the watershed to collect
data necessary to develop a total maximum daily load (TMDL), an analysis of sources and
loading capacity similar to what a TMI)L would provide, or a water column translation of the
fish tissue criterion for future permitting.
How to Get Additional Information
If you do not wish to download the guidance document from EPA’s web site, you can instead
order a copy of the document from EPA’s Water Resource Center by calling (202) 566-1729 or
emailing: center.water-resourceC epa.gov . Ask for EPA document number 823-R-10-00l. You
may also email Fred Leutner at 1eutner.fred( epa.gov or Holly Green at green.ho1lv( epa.gov for
further information.
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