Every single fish sampled from 291 streams across the United States between 1998-2005 was contaminated with mercury, according to the US Geological Survey.
A quarter of the sampled fish contained levels of mercury higher than those deemed safe for human consumption and more than two thirds contained levels exceeding the Environmental Protection Agency’s level of concern for the protection of fish-eating mammals, says a new report from the USGS.
“This study shows just how widespread mercury pollution has become in our air, watersheds, and many of our fish in freshwater streams,” says Ken Salazar, Secretary of the US Department of the Interior (press release).
Most of the mercury that reaches waterways in the US comes from emissions by coal- power plants. Once in the atmosphere the metal gets precipitated down, and then converted to the more toxic form, methyl mercury, This is easily taken up by fish and other aquatic organisms.
This conversion process has just been elucidated in a study from Duke University in the US, presented at the conference of the American Chemical Society (ACS) in Washington, D.C.
“The exposure rate of mercury in the US is quite high,” says Heileen Hsu-Kim, a member of the Duke team (press release). “A recent epidemiological survey found that up 8 percent of women had mercury levels higher than national guidelines. Since humans are on top of the food chain, any mercury in our food accumulates in our body.”
Barbara Scudder, a scientist with the USGS, says that people should eat more fish species lower down the food chain, such as perch, bluegill or crappie.
Reuters reports that the EPA is now planning to issue new rules under the Clean Air Act to control air emissions of mercury from coal-powered power plants.
Meanwhile, in New Zealand the Green Party raised concerns about mercury levels in fish there. MP Sue Kedgley told the New Zealand Herald that “swimming with sharks could be safer than eating some varieties of fish sold in New Zealand”.