Scientists find high levels of Gold Rush mercury in Californian fish

Scientists at the US Geological Survey (USGS) have found high levels of mercury in bass and catfish in the Bear and South Yuba river watersheds in the Sierra Nevada of northern California.


Samples were taken from 141 fish, predominantly largemouth bass, collected during September and October 1999 from reservoirs and streams in Nevada, Placer, and Yuba counties. Mercury concentrations in the fish ranged from 0.02 to 1.5 parts per million (ppm), compared to the Food and Drug Administration’s action level for commercial fish of 1.0 ppm.

“Liquid elemental mercury, or quicksilver, was used extensively in the Bear and Yuba River watersheds since the early gold mining days,” said Charlie Alpers, USGS Research Chemist and Chief Scientist on the study. “Our fish survey is part of the first comprehensive investigation in the Sierra Nevada region of mercury distribution in water, sediment, and biota, and the potential risks to human health and ecosystems.”

“Elemental mercury, the kind you can see, is only one part of the problem,” said Jason May, USGS biologist. “It is the presence of methylmercury, the organic form of mercury that accumulates in organisms, that will be of most concern.”

The USGS’s data has been submitted to the California Environmental Protection Agency and their Office of Environmental Health and Hazard Assessment (OEHHA). Environmental health officials from Nevada, Placer, and Yuba counties will be working closely with OEHHA in order to decide whether formal notification to the public should be made concerning fish consumption.

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