Mercury in Seafood

Exposure to mercury can cause a string of harmful health effects, including ginvigitis, blindness, paralysis, birth defects, and neurological and muscular disorders. The California Office of Environmental Health Hazard Assessment has issued a health advisory, recommending that adults eat only certain species of fish with low mercury contamination.  The health advisory establishes special guidelines for pregnant women and children because they are more susceptible to mercury.

Pollution in the Bay

Most of the mercury pollution in San Francisco Bay comes from historic gold mines, which operated in the Sierra Nevada Foothills during the 19th and 20th centuries. The mining industry utilized mercury’s unique chemical properties to separate gold from the raw ore. This technique is no longer used; but mercury in the soil and river sediment near old mines continues to flow into San Francisco Bay.

Other sources of mercury pollution come from improper disposal of everyday products like mercury thermometers, thermostats, fluorescent lights, and mercury-containing switches in automobiles, washing machines, and other equipment. Ensure that your products do not pollute the Bay by using RecycleWhere to find the proper disposal option.

Bioaccumulation and Biomagnification

Once mercury enters rivers and streams, microorganisms in sediment convert some of it into a more harmful substance called methyl mercury.  Methyl mercury can be readily absorbed through the skin and in the stomach.

Bioaccumulation is the process by which methyl mercury builds up in organisms like plankton, small fish, large fish and people over time. Biomagnification is the process by which methyl mercury becomes more concentrated as it passes up the food chain. This exposes those higher on the food chain, like large fish and people, to more methyl mercury than those lower on the food chain, like plankton and small fish.

Both of these processes result in methyl mercury in your fish and on your plate. Follow the California Office of Environmental Health Hazard Assessment’s safe eating guidelines for San Francisco Bay to reduce your exposure.