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TE News v.16--
New methylmercury criterion of 0.3 mg/kg in fish

To: nawqa 91pc, nawqa 94pc, nawqa 97pc, nawqa 01pc, wqspecs
Cc: nawqa nst, ahwelch, pcvanmet, rdeweese, dpkrabbe, sjryker, cory,
    mkoterba, nawqa nlt, pahamilt, egraffy, akwill, crawford, william_brumbaugh
From:  Dennis R Helsel
Date:  02/05/01 04:09 PM
Subject: New methylmercury criterion

Trace Element Synthesis News v.16
New methylmercury criterion of 0.3 mg/kg in fish

USEPA recently established a new water quality criterion for methylmercury. It is unusual in that the water quality criterion is not defined for concentrations in the water column, but for concentrations in fish. The new criterion is 0.3 mg methylmercury per kg of fish (wet weight).

The USEPA fact sheet on the new rule can be found at
http://www.epa.gov/waterscience/criteria/methylmercury/factsheet.html

This represents a decrease from the previous recommended level of 0.5 mg/kg. The criterion is not a legally-enforceable standard, but is often used as the level a State or Tribe would consider in setting advisories for fish consumption. It can be expected that more advisories will result from this new rule, and perhaps more States may issue an entire Statewide advisory for fish consumption. Information on current advisories can be found at:
http://www.epa.gov/ost/fish/listing.html

USEPA provides an approach in its fact sheet using empirical bioaccumulation factors (ratios) to relate the 0.3 mg/kg criterion to concentrations for methylmercury in water. Based on NAWQA sampling across the Nation two years ago, we can estimate a concentration using linear regression. Concentrations in fish vary with age of the fish and with species type, the percent wetlands in the basin, and the pH of the stream water. As an overall average concentration across fish species, wetlands densities and pH, 0.3 mg/kg in a 3-year old predator fish would correspond to approximately a concentration of 0.12 ng/L methylmercury in stream water. Corresponding estimates for other trophic levels, or for specific fish species, other ages of fish, and for specific locations would differ.

In another ruling last December, USEPA announced that it would develop a regulation limiting the amount of mercury which could be released by coal- and oil-fired power plants. That regulation will be proposed by December 2003, and implemented after a review period. There may be interest in looking at changes (trends) comparing today's levels of mercury in air, precip, sediment and fish with those from 5-10 years from now to judge effectiveness of these controls. More information can be found through the Trace Element Synthesis web page, or the USEPA page
http://www.epa.gov/mercury/actions.htm#utility

Finally, USEPA's research strategy for mercury is available at
http://www.epa.gov/ORD/NRMRL/mercury/
It identifies the scientific questions USEPA considers of primary importance as research needs regarding the risks to humans and wildlife posed by mercury.

Visit the TE external page at: http://water.usgs.gov/nawqa/trace/ for up to date info on regulations, publications, etc.

The TE synthesis internal page has much info for study units: http://water.usgs.gov/nawqa-only/trace/
including all the TE News. The previous four were:

v.12  Results of TE Blanks from 91 Study Units     2/09/00
v.13  Arsenic in Groundwater;  new proposed MCL    5/30/00
v.14  Changes in radchem data reporting            9/29/00
v.15  New arsenic MCL at 10 ug/L                   1/19/01

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