Toxic Mercury in California Coastal Waters May be from Sea Lions and Elephant Seals

First Posted: Sep 09, 2015 08:51 AM EDT

Mercury pollution in California may be coming from a surprising source: elephant seals. Scientists have found that molting elephant seals actually shed considerable amounts of mercury into coastal waters.

Mercury is a major problem in the marine environment. The most toxic form of it, methyl mercury, is readily absorbed and accumulates in the bodies of marine organisms. The higher up the food chain you go, the more concentrated the toxin becomes. This means that mercury concentrations in top predators can be 1 to 10 million times higher than levels found in seawater.

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

The researchers looked at seasonal changes in the water. Surprisingly, in comparison to other coastal sites, the concentration of methyl mercury in the seawater at Ano Nuevo was twice as high during the breeding season and 17 times higher during the molting season. These higher concentratiosn are largely due to the elephant seals that molt there.

It's not just the elephant seals, though. Researchers found high concentrations of mercury in sea lion feces nearby. There also happens to be a large sea lion population in the area that may be also adding mercury to the coastal waters.

The findings reveal that mercury pollution is a huge problem. Because the animals take it in and then release it to the environment once more, the cycle of pollution continues. In fact, most the mercury levels in these animals exceed the threshold for clinical neurotoxicity in humans. This is particularly important to note when working on conservation efforts.

The findings are published in the journal Proceedings of the National Academy of Sciences.

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TagsMercury, Mercury Pollution, Pollution, Ocean, West Coast, Sea Lion, Seal, Marine Mammals