Bay Nature magazineOctober-December 2007


Mercury Clean-Up in San Francisco Bay

October 1, 2007

In July, the State Water Resources Control Board approved a plan to clean up mercury in San Francisco Bay, fulfilling a mandate set in 2002 when the Bay was placed on the impaired list under the Clean Water Act. According to Richard Looker of the San Francisco Bay Regional Water Quality Control Board, the Bay contains so much legacy mercury from more than a century of mining that, even if no more were to enter the system, it would take 40 years to flush out. However, about 1,200 kilograms of mercury continue to enter the system annually from rivers carrying sediment from old mines, wastewater and storm runoffs, and atmospheric depositions from oil refineries and other industrial complexes. Mercury-enriched sediment sits about a meter thick on the Bay floor. Inorganic mercury can become a serious health problem when it is converted to methyl mercury, the form most toxic to people and wildlife.

A multiyear field study on the effects of mercury on breeding waterbirds in the Bay demonstrates the complexity of the problem. Scientists from the U.S. Geological Survey, U.S. Fish & Wildlife Service, San Francisco Bay Bird Observatory, and PRBO Conservation Science found that mercury concentrations are above toxic levels for several species, with Forster’s terns at the highest risk. The terns often nest on isolated islands in salt ponds or on the margins of the Bay in shallow-water habitats high in methyl mercury. The scientists found that during the 45 days before breeding, the terns’ methyl mercury blood concentrations tripled. They also found high levels in newly hatched chicks.

Mercury in the Bay seems an intractable problem, but Looker insists there is hope. “There isn’t much we can do about the legacy of inorganic mercury in the system, but if we can learn more about when, where, and how it is converted to methyl mercury, maybe we can slow that process.”

For eight years, the advocacy group Baykeeper has fought for aggressive clean-up, arguing that “natural attenuation,” an approach suggested in earlier draft plans, is not an adequate response. “We’re at a good starting point now,” says Baykeeper program director Sejal Choksi. “But we want to see some action against the sources that are contributing mercury right now.”

To learn more, go to for the “San Francisco Bay Mercury News,” an electronic newsletter that compiles information about mercury research activities around the Bay.

About the Author

Writer Aleta George trained as a Jepson Prairie docent in 2009. In addition to writing Bay Nature's Ear to the Ground column, she has written for Smithsonian, High Country News, and the Los Angeles Times.

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