When elephant seals molt along the California coast, they shed more than fur. Scientists at the University of California at Santa Cruz have figured out that they're also leaving behind potentially dangerous levels of mercury—in that same fur, reports Smithsonian. It's a cycle that goes something like this: Humans put mercury in the ocean through air pollution or industrial runoff. Fish consume the mercury. Then sea lions eat the fish in open water, get the mercury in their systems, bring it back to coastal waters when it's molting season, and leave it behind in their discarded fur. Specifically, scientists found that coastal waters at Año Nuevo State Park near Santa Cruz—a popular breeding ground for seals and sea lions—had mercury levels 17 times higher than areas without seals, reports KPBS.
"I think it's important when trying to understand the global mercury cycle, that we're really looking at the whole picture," a UCSC researcher tells the Washington Post. "It's really interesting to see how wildlife can be exacerbating the cycle." The Post explains why all this is especially worrisome: Microorganisms in the ocean turn mercury into the more dangerous form of "methylmercury," a neurotoxin that can cause brain damage. This methylmercury gets passed up the food chain, becoming more concentrated in a process called biomagnification, says a post at UCSC. It was methylmercury that scientists found in the waters near the seals' breeding ground. One bright spot: Because this is a protected area off-limits to fishing, the elevated levels probably aren't a big threat to humans, notes the Post. (We can also blame seals for bringing us tuberculosis.)