Elephant Seals Cause Mercury Spike in Coastal Waters, Study Finds

posted: 09/08/15
by: Discovery.com Staff

Molting elephant seals are responsible for an annual spike in mercury levels off of the California coast, a University of California Santa Cruz study said.

Heavy consumers of fish, elephant seals accumulate high levels of mercury in their bodies. The toxic metal travels up the food chain in a process known as biomagnification.

As part of their annual molt, the seals shed their hair and outer layer of skin, which comes off in large "sheets," researchers explained. The mercury-rich tissues are then left to disintegrate on the beach; the resulting spike in mercury levels is up to 17 times higher than normal, rivaling mercury levels in the urbanized San Francisco Bay estuary.

Elephant seal pup in nursery pool, Sea Lion Island, Falklands.
Ed Charles/DCL

"Many studies have looked at biomagnification up the food chain, and we took that a step further to see what happens next. Mercury is an element, so it never breaks down and goes away -- it just changes forms," study first author Jennifer Cossaboon explains in a news release.

The research builds upon a previous study conducted by UC-Santa Cruz microbiology and environmental toxicology professor Russell Flegal, who first noted the mercury spike in 1981.

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"At that time, we didn't have the analytical instruments to detect mercury at the concentrations found in seawater, so we used mussels, which filter seawater, as sentinel organisms," Flegal said. "In the new study, we were able to look at seasonal changes in the water, and during the elephant seal molting season the levels of methyl mercury really took off."

Cossaboon and Flegal's research is published in the September 7 edition of the journal Proceedings of the National Academy of Sciences.


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