Scientists detected mercury contamination in every fish sampled in 291 streams across the country, according to a U.S. Geological Survey study released August 19.
Mercury, a neurotoxin, is one of the most serious contaminants
threatening environmental waters. The main source of mercury to natural
waters is mercury that is emitted to the atmosphere and deposited onto
watersheds by precipitation. However, atmospheric mercury alone does
not explain contamination in fish in freshwater streams. Naturally
occurring watershed features, like wetlands and forests, can enhance
the conversion of mercury to the toxic form, methylmercury.
Methylmercury is readily taken up by aquatic organisms, resulting in
contamination in fish.The new study:
The USGS studied mercury contamination in fish, bed sediment and
water from 291 streams across the nation, sampled from 1998 to 2005.
Atmospheric mercury is the main source to most of these streams —
coal-fired power plants are the largest source of mercury emissions in
the United States — but 59 of the streams also were potentially
affected by gold and mercury mining. Since USGS studies targeted
specific sites and fish species, the findings may not be representative
of mercury levels in all types of freshwater environments across the
About a quarter of all these fish samples were found to contain mercury at levels
exceeding the criterion for the protection of people who consume
average amounts of fish, established by the U.S. Environmental
Protection Agency. More than two-thirds of the fish exceeded the U.S.
EPA level of concern for fish-eating mammals.
“This study shows just how widespread mercury pollution has become
in our air, watersheds, and many of our fish in freshwater streams,”
said Secretary of the Interior Ken Salazar. “This science sends a clear
message that our country must continue to confront pollution, restore
our nation’s waterways, and protect the public from potential health
Some of the highest levels of mercury in fish were found in the
tea-colored or “blackwater” streams in North and South Carolina,
Georgia, Florida and Louisiana — areas associated with relatively
undeveloped forested watersheds containing abundant wetlands compared
to the rest of the country. High levels of mercury in fish also were
found in relatively undeveloped watersheds in the Northeast and the
Upper Midwest. Elevated levels are noted in areas of the Western United
States affected by mining. Complete findings of the USGS report, as
well as additional detailed studies in selected streams, are available online.
For a national listing of fish advisories from the Environmental Protection Agency, click here.
“This study improves our understanding of where mercury ends up in
fish in freshwater streams,” said USGS scientist Barbara Scudder. “The
findings are critical for decision-makers to effectively manage mercury
sources and to better anticipate concentrations of mercury and
methylmercury in unstudied streams in comparable environmental
All 50 states have mercury monitoring programs, and 48 states issued
fish-consumption advisories for mercury in 2006, the most recent year
of national-scale reporting to the EPA.
The EPA regulates mercury emissions to air, land and water. In February
2009, the EPA announced that it intends to control air emissions of
mercury from coal-fired power plants by issuing a rule under the Clean
Source: U.S. Department of the Interior
The cited USGS study
USGS: National Water-Quality Assessment (NAWQA) Program: Mercury in Stream Ecosystems
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last time modified: November 3, 2009