Mercury contamination, a worldwide environmental problem, has been called “public enemy No. 1” in California’s San Francisco Bay.
Mercury mining and gold recovery in the mid-1800s to late 1900s, combined with present day oil refineries, chemical manufacturing plants and wastewater treatment plants have contributed enough mercury to threaten wildlife and prompt a fish consumption advisory in the Bay Area. With so many possible sources of contamination, environmental scientists and regulatory agencies would like to know which specific sources contribute most to harmful levels of mercury in the aquatic food web.
Teasing out that information was not possible in the past, but with the use of a mercury “fingerprinting” technique, researchers from U-M, the University of California, Davis, and the San Francisco Estuary Institute, have identified the main sources of mercury in bay floor sediments and shown that small fish near the base of the food web acquire their mercury from those sediments.
“Without a clear answer to what was responsible for mercury in fish in San Francisco Bay, we needed a way to trace its origins,” says Joel Blum, who is the John D. MacArthur Professor of Geological Sciences and a professor of ecology. “This is the first study to track mercury directly from source to sediment to food web.”
While this study draws conclusions only for San Francisco Bay, the fingerprinting technique broadly can be applied, says graduate student Gretchen Gehrke, the paper’s lead author. “Mercury contamination is a problem in areas all over the world, and most of those places have multiple possible mercury sources. There’s a lot of interest in figuring out which sources are contributing the mercury that most readily gets into the food web and creates environmental and health risks.”
The findings appear in two companion papers, one in the Feb. 1 issue of the journal Geochemica et Cosmochimica Acta and the other published online Jan. 21 in Environmental Science & Technology.
Mercury is a naturally occurring element, but some 2,000 tons of it enter the global environment each year from human-generated sources. Deposited onto land or into water, mercury is picked up by some types of microorganisms, which convert a small portion of it to methylmercury, a highly toxic form that builds up in fish and the animals — and people — that eat them.
The primary way people in the United States are exposed to methylmercury is by eating fish and shellfish. Health effects include damage to the central nervous system, heart and immune system. The developing brains of young and unborn children are especially vulnerable.
The researchers hope the results will help local agencies decide where to focus their efforts to protect wildlife from exposure to mercury.
