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Molted elephant seal skin leeching mercury into coastal waters

Previous research has linked both elephant seal molting and sea lion feces to spikes in coastal mercury levels.

By Brooks Hays
Molted elephant seal skin leeching mercury into coastal waters
Researchers suggest elephant seal molting is leading spikes in coastal mercury levels. Photo by Terry Schmitt/UPI | License Photo

SANTA CRUZ, Calif., Sept. 8 (UPI) -- Scientists say the molted skin of elephant seals is to blame for heightened mercury levels in the coastal waters of Northern California's Ano Nuevo State Reserve.

Because mercury is an element, it is never broken down. Instead, it accumulates in animals that eat plants and animals that contain mercury -- which occurs naturally and is a byproduct of manmade activities like coal production. As traces of mercury travel up the food chain, larger and larger concentrations accumulate in top predators.

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Large fish and marine mammals like tuna and seals can accrue relatively high levels of mercury. And as new research shows, the element can leech back into the surrounding environs when species like elephant seals molt.

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

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Cossaboon is one of two first authors of a new study -- published in the journal Proceedings of the Royal Society B -- linking seasonal spikes in methyl mercury levels to molting season in Northern California. Cossaboon was an undergraduate at the University of California, Santa Cruz when she began her research into molted mercury, but is now a graduate student in environmental health at San Diego State University.

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Previous research has linked both elephant seal molting and sea lion feces to spikes in mercury levels, but those studies relied on mercury levels measured in mussels.

"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," said co-author Russell Flegal, professor of microbiology and environmental toxicology at UC Santa Cruz. "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."

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Because elephant seals mostly fast during molting season, researchers were able to pin the mercury spikes on shed skin -- as opposed to feces.

Mercury levels measured in 99 percent of the elephant seals analyzed in Ano Nuevo State Reserve measured well above the threshold for neurotoxicity in humans.

"It is important, however, to be cautious in trying to use that threshold for another species," said first author Sarah Peterson, a graduate student in ecology and evolutionary biology. "We do not know what these concentrations mean for elephant seals."

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