The methylmercury human health criterion is a concentration of methylmercury in fish that EPA calculated to protect human health. States and tribes may use the criterion as the basis for establishing water quality standards.

• Fact Sheet: 2010 Implementation Guidance
• 2010 Methylmercury Implementation Guidance

Final Implementation Guidance

This final Guidance for Implementing the January 2001 Methylmercury Water Quality Criterion provides technical guidance to states and authorized tribes on how they may want to use the January 2001 fish tissue-based recommended water quality criterion for methylmercury in surface water protection programs (e.g., TMDLs, NPDES permitting). The guidance addresses questions related to water quality standards adoption (e.g., site-specific criteria, variances), assessments, monitoring, TMDLs, and NPDES permitting. The guidance consolidates existing EPA guidance where relevant to mercury.

• Fact Sheet: 2001 Final Methylmercury Criteria
• Federal Register Notice: 2001 Final Methylmercury Criteria
• 2001 Final Methylmercury Criteria Document

This April 2010 guidance supersedes the guidance EPA published in January 2009. The Obama Administration asked EPA to confirm the continued appropriateness and applicability of several agency actions, including the January 2009 methylmercury implementation guidance. Based on the outcome of this review, EPA improved the document's clarity, and as a result, the ability of states and tribes to protect public health from methylmercury impacts, but did not change the fundamental policy recommendations in the January 2009 document. Revisions include:

• Recognizing that states and tribes may consider using existing water column criteria (in addition to the new fish tissue criterion), on a temporary basis, to derive numeric permit limits for waters with relatively high water inputs of mercury, while allowing establishment of mercury minimization plans for all other waters to move forward.
• Providing examples of what EPA considers “appropriate” uses of draft national bioaccumulation factors (i.e., where fish tissue data are unavailable and where direct water inputs are relatively high).
• Clarifying under what circumstances EPA recommends that states and tribes translate the fish tissue criterion for implementation:
  • Where site-specific data to do so is readily available (in addition to where translation is already done).
  • Where methylmercury impairments are high priorities for action. Where direct water inputs of mercury are relatively high.
• Clarifying that where a use attainability analysis indicates that the current use is unattainable, the state or tribe will need to identify and assign the “highest attainable use.” For example, the state or tribe could refine its designated use from "fish consumption" to "mercury-limited fish consumption." That way the waterbody would still be expected to meet other pollutant criteria designed to protect fish consumption.
• Highlighting that states and tribes should include evaluation of culturally and economically diverse communities when determining local or regional fish consumption rates.
• Clarifying and strengthening the recommendation that permitting authorities find reasonable potential where fish tissue levels are close to or exceed the criterion.
• Outlining existing Clean Water Act antibacksliding provisions and including a brief example of how antibacksliding requirements would apply to a new methylmercury criterion.

EPA's Mercury homepage provides a broad range of information about mercury.

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