After smoke stacks and industrial waste, researchers can add lounging seals to the list of mercury polluters.
Hair from Northern elephant seals (Mirounga angustirostris) is loaded with the toxic metal. And when shed, that hair can boost mercury levels in surrounding seawater by about 17 times, researchers report September 7 in the Proceedings of the National Academy of Sciences.
The finding may solve a long-standing mystery of why remote, seemingly pristine coastal areas where seals congregate can be hot spots for mercury pollution, harboring hazardous levels of the neurotoxicant, the authors say.
“It’s important to be aware of this phenomenon, just so we know where to identify those hot spots,” says coauthor Jennifer Cossaboon, an environmental health researcher at San Diego State University in California.
Cossaboon and colleagues at the University of California, Santa Cruz (where Cossaboon worked at the time of the study) got their first clue about seal-spread pollution from a 1970s environmental survey. The survey found unusually high levels of mercury in mussels in Año Nuevo State Reserve.
The coastal park, about 70 kilometers south of San Francisco, is far from traditional sources of mercury pollution, such as gold mines (SN: 11/30/13, p.13). But it’s a popular destination for seals.
By analyzing seawater samples from the park in 2012 and 2013, Cossaboon and colleagues noted a spike in methylmercury, the form of mercury that amasses in sea creatures. The rise coincided with the Northern elephant seals’ annual spring molt.
Seals are known to expel mercury, which they get from their prey, through their coats, Cossaboon says. After analyzing hair samples, the researchers estimated that about 4,000 adult seals shedding 54,000 kilograms of fluff per year in Año Nuevo could release 0.2 kilograms of mercury — enough to explain the pollution spike. That mercury then could be gobbled up by small marine life or seafloor-dwelling microbes and get passed up the food chain.
“It’s certainly interesting,” says marine geochemist Robert Mason of the University of Connecticut in Groton. But, he says, more research is needed to definitively link the mercury from seal hair to mercury in organisms, like mussels.
Editor’s Note: This article was updated September 25, 2015, to clarify that mercury is a neurotoxicant.