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Small amounts of mercury occur naturally in the Sierra, but extensive gold mining in this area brought in much larger quantities of the toxic element. Gold miners used more than 26 million pounds of mercury in the Sierra to extract gold. As many as 8 million pounds may have escaped into watersheds through hydraulic mining and other mining processes, and some of this now remains in the gravel of streambeds, the sediments trapped behind dams, and the aquatic food chain.
Mercury reacts with bacteria to become methylmercury, a highly toxic compound that affects both humans and wildlife. Mercury exposure affects the immune, reproductive, renal, and cardiovascular systems. Because it is a developmental toxin, it is particularly hazardous for children and pregnant women. Swimming in rivers or lakes or drinking tap water does not expose people to mercury, but fish consumption is a major source of exposure. Methylmercury becomes concentrated in fish through bioaccumulation as it ascends in the food chain. In top predators like bass, mercury concentrations can be 10,000 to 100,000 times higher than in the environment.
The Office of Environmental Health Hazard Assessment has issued advisories recommending that people eat no more than one meal per month of bass or one meal per week of smaller fish from local rivers and lakes.
SYRCL is working to bring information about this important issue to the local community. In November of 2001, SYRCL and the Nevada County Resource Conservation District hosted a free public conference on mercury in the watershed, "Mercury, Mines, Rivers, and You".
Find out more:
Winter 2002 Sierra Citizen—"Everything You Wanted to Know About Mercury"
SYRCL Report: Mercury Contamination in the Yuba and Bear River Watersheds
Delta Tributaries Mercury Council
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