United States Office of Water EPA-823-F-01-026
Environmental Protection 4305 November 2001
Agency
Fact Sheet
Mercury Maps: Linking Air Deposition and Fish
Contamination on a National Scale
Summary
Mercury Maps is a tool that relates changes in mercury air deposition rates to changes in
mercury fish tissue concentration on a national scale. Mercury Maps shows:
• Where fish tissue concentrations exceed the new national methylmercury criterion;
• How fish tissue concentrations relate to air deposition rates;
• Which watersheds have air deposition is as their sole significant source of mercury;
• Which watersheds contain potentially significant sources of mercury loads other than air
deposition; and
• Estimates of mercury air deposition reductions needed to meet the new criterion.
Background
As of December 2000,41 states had issued 2,242 fish advisories for mercury In most cases,
EPA's information indicates that elevated mercury fish tissue concentrations result primarily from
atmospheric deposition. Mercury air emissions from coal-fired power plants, waste incinerators,
mercury cell chlorine manufacturing facilities, and other sources can be transported long
distances before ultimately depositing on watersheds and waterbodies. Much of the mercury
deposited within state boundaries is generated from emission sources outside the state. Mercury
Maps can be used to coordinate EPA's efforts to address mercury contamination in water quality.
wastewater permitting, and air emission programs.
Environmental and Public Health Benefits
Mercury Maps can be used to help evaluate the benefits of technology-based air emission
reduction standards. One component of an overall benefits analysis, Mercury Maps relates
reductions in air deposition rates to reductions in fish tissue concentrations, by watershed,
nationwide. Mercury Maps could also be used to perform individual Total Maximum Daily Load
(TMDL) analyses and/or to perform TMDL analyses for multiple watersheds at a time. States
could use this approach to develop state-wide approaches for addressing the fish mercury
contamination problem. While Mercury Maps addresses only effects on inland freshwater fish
and is based on the new methylmercury criterion, most state standards are water column
concentration-based. States would need to adopt fish-tissue based target levels in order to benefit
from this approach. In addition, most state fish consumption advisories are set at target levels
that are about half the criterion concentration
Technical Approach
Mercury Maps is a peer-reviewed geographic information system (GIS) tool with national data
coverages for watersheds, fish tissue concentrations, and non-air-deposition source locations.
The model used in this project is a reduced form of the watershed and aquatic ecosystem effects
models used in the 1997 Mercury Study Report to Congress. The equations from these models
have been reduced to a single equilibrium-state equation and applied directly in the GIS The
Mercury Maps model concludes that for long-term equilibrium conditions, the ratio of current to
future air deposition rates will equal the ratio of current to future fish tissue concentrations.
Estimates of percent air deposition reductions, by watershed, as generated from a regional air
deposition model would be needed to predict fish concentration reductions.
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Estimated Percent Reductions in Air Deposition Load
Necessary to Meet New Methylmercury Criterion*
S
% Reduction to Meet Crit
Cuffently Meets Criterion
10% Reduction Requred
15% Reduction Requred
! 20% Reduction Requred
25% Reduction Requred
50% Reduction Requred
75% Reduction Reqr.ared
> 75% Reduction Required
Contains Other Sources
No Georeferenced Fish Data
* States currently use water column concentration-based mercury water quality standards and would need t dopt fish tissue-based
target levels in order to use this approach for mercury TMDLs. Additional reductions would be required to meet EPA national and most
state fish advisory levels, which are often set below the methyl-mercury criterion.
Note: Watersheds highlighted yellow have “significant” mercury sources other than deposition, defined as where the total estimated load
from Publicly Owned Treatment Works (POTWs) and pulp and paper mills is greater than 5% of estimated waterbody delivered mercury
at a typical air deposition load (10 g/km2/yr), and/or where mercury cell chlor-alkali facilities, mercury mines, or significant past producer
gold mines are present. See text of report for data sources for point source dischargers and mines.
Source: National Listing of Fish and Wildlife Advisories (NLFWA) Mercury Fish Tissue Database (June, 2001).
Mercury Maps is based on the 22,000 records of fish tissue mercury concentrations in 35 states
(west coast and states in the eastern two thirds of the U.S.) from the National Listing of Fish and
Wildlife Advisories (NLFWA) Fish Tissue Database. Mercury Maps is designed to work only with
watersheds where air deposition is the sole significant source of mercury. Watersheds are
eliminated from the analysis if they contain potentially significant, but unquantified, runoff and
effluent loads from: mercury mines, large-producer gold mines, and mercury-cell chlor-alkali
facilities. Watersheds are also eliminated when the total screening level effluent load estimates
for municipal wastewater treatment plants and pulp and paper mills are above five percent of the
estimated waterbody-delivered air deposition load.
Additional Information
For further information concerning this report, please see the Mercury Maps web page at:
http://www.epa.gov/waterscience/maps. If you have any questions, please contact Paul Cocca at
the U.S. Environmental Protection Agency, Office of Water, Standards and Health Protection
Division (4305), 1200 Pennsylvania Ave., Washington, DC 20460. He may be contacted by
phone at 202/260-8614 or by email at: cocca.paul@epa.gov.
Watersheds with No Other Significant Mercury Sources
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