Fish in streams across U.S. tainted with mercury
Researchers found mercury in every fish tested in a nationwide stream survey, with some of the higher concentrations showing up in mining areas of the West.
In about a quarter of the fish, levels of the toxic metal exceeded federal standards for people who eat an average amount of fish.
“This study shows just how widespread mercury pollution has become in our air, watersheds, and many of our fish in freshwater streams,” U.S. Interior Secretary Ken Salazar said in a press release.
The study, conducted by the U.S. Geological Survey, sampled 34 fish species at 291 stream sites across the country from 1998 to 2005.
The most contaminated sample came from smallmouth bass in the Carson River in Dayton, Nev., a historic gold mining area.
Overall, high mercury levels were detected in fish from streams in the Southeast, along the East Coast and in western areas -- including Northern California -- where gold or mercury has been mined.
Coal-fired power plants are the largest source of mercury emissions in the U.S. For most of the sampled streams, atmospheric mercury is the primary source of the pollutant.
Wetlands and forests aid the conversion of mercury into its toxic form, methylmercury, which enters the aquatic food chain.
In the study, largemouth, smallmouth and spotted bass had the greatest average mercury concentrations. Brown trout, rainbow-cutthroat trout and channel catfish had the lowest.
-- Bettina Boxall
Photo: Rainbow trout. Credit: Ken Hively / Los Angeles Times