ANN ARBOR, Mich., Jan. 25 (UPI) -- High mercury levels in fish in San Francisco Bay are a legacy of a century and a half of California gold and mercury mining, researchers say.
Scientists say mining activities in the mid-1800s to late 1900s, combined with present day oil refineries, chemical manufacturing plants and wastewater treatment plants, have contributed sufficient mercury to threaten wildlife and prompt a fish consumption advisory in the Bay Area.
Using mercury "fingerprinting" techniques, researchers from the University of Michigan, the University of California, Davis, and the San Francisco Estuary Institute, have identified the main sources of mercury in bay floor sediments, a UM release reported Tuesday.
"Without a clear answer to what was responsible for mercury in fish in San Francisco Bay, we needed a way to trace its origins," UM geology Professor Joel Blum said. "This is the first study to track mercury directly from source to sediment to food web."
The study, while focusing on San Francisco Bay, used techniques that can be applied elsewhere, one researcher said.
"Mercury contamination is a problem in areas all over the world, and most of those places have multiple possible mercury sources," UM graduate student Gretchen Gehrke said. "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 "fingerprinting" technique tagged the two main culprits in the San Francisco Bay.
"There's one distinct fingerprint coming from historic mercury mines to the south and a different fingerprint coming from historic gold mines to the north," Gehrke said.
The researchers say their results will help local agencies decide where to focus their efforts to protect wildlife from exposure to mercury.