Environmental mercury poisoning is commonly referred to as human-induced, but a new study pointed the figure at other mammals, seals and sea lions.

According to The Washington Post, authors of a study published in the journal Proceedings of the National Academy of Sciences detailed how the seals' fur is contributing to the mercury in California's coastal waters.

"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, who led the project as an undergraduate at the University of California - Santa Cruz (UCSC), said in a press release.

Another UCSC professor first detected heightened mercury levels off the coast of California in 1981. Russell Flegal, of microbiology and environmental toxicology department, noticed mercury in mussels where seals and sea lions, mammals known as pinnipeds, live.

"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 release. "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."

Published in June, the new study found the highest concentrations of mercury in the fur of the elephant seals that hunted their prey deep in the ocean. The lowest concentration was found in the seals that fed farther north.

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