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| Elkhorn Slough was one of two sites where UCSC researchers say they found high levels of mercury in the groundwater. |
Scientists at UCSC have discovered high levels of an ultra-toxic form of mercury in the groundwater of two coastal sites in California. The groundwater flows, they say, show a previously unknown source for what have been mysteriously high levels of mercury recently found in marine environments and in seafood.
"The big question for public health is, 'Where is all the mercury in seafood coming from?'" says Russell Flegal, professor of environmental toxicology at UCSC and a coauthor of the study. "What we have shown is that methylmercury is coming from groundwater in California at surprisingly high levels."
Sites at Stinson Beach in Marin County and Elkhorn Slough in Monterey County were found to have the high methylmercury levels. Methylmercury is a deadly form of mercury that usually shows up in the ocean food chain and on dinner tables worldwide. Mercury usually enters the environment through a process called deposition, in which airborne particles of the element float down to earth. According to the university, the amount of mercury that falls from the sky in this fashion has tripled since the industrial revolution 200 years ago.
The levels of mercury found in the two groundwater sites have a roughly equal amount of mercury as what normally rains down through the atmosphere, the researchers say. But while humans and their fossil fuel burning habits are primarily blamed for the increase in airborne mercury, the study's lead author Frank Black says the natural weathering of mercury-containing rocks is likely behind much of the heightened groundwater mercury levels.
"People have assumed that methylmercury must come from the bottom of the ocean or from surface waters flowing to the coast," said UCSC biogeochemist Adina Paytan, a coauthor of the study. "But never from groundwater."