Mercury contamination found in a quarter of U.S. freshwater fish exceeds federal safe levels for human consumption, according to a study released today by the U.S. Geological Survey.
In a study by the US Geological Survey over 25% of the fish fish, sediment and water drawn from 291 rivers and streams between 1998 and 2005, carried mercury at levels above the safe standard for human consumption (0.3 parts per million wet weight), while all of the fish had detectable mercury levels.
Atmospheric deposition of mercury is responsible for the contamination of most waterways, but that alone does not account for all of it. Wetlands, forests and organic soils can enhance the conversion of mercury to highly toxic methylmercury, which accumulates in the food chain and can cause serious public health problems.
Overall, the scientists found concentrations in fish corresponded with increasing concentrations of methylmercury in the water.
Some of the highest levels of mercury in fish were found in ‘blackwater’ streams in North and South Carolina, Georgia, Florida and Louisiana, all of which have large, undeveloped, forested watersheds. Some high levels were also found in the western United States, which the scientists attributed to mining.
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First Published in August 2009
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