Fog ferries mercury from the ocean to land animals

SAN FRANCISCO – The government advises that people, and especially children and pregnant women, limit the amount of fish they eat. That’s because of mercury. Mercury pollution, from sources such as gold mining and power generation, ends up in the atmosphere and then the oceans, where it is transformed into methylmercury, which is as toxic as the element. Methylmercury accumulates in ocean creatures, and animals higher up in the food chain, such as tuna, tend to have higher levels of mercury. People who eat enough of those fish can experience health problems; mercury can impair development in children, infants and fetuses.

But the route of mercury pollution from air to ocean to fish is only part of the story. In 2012, researchers reported that methylmercury could be found in fog water along the central Californian coast. Now researchers are finding that the mercury, picked up from ocean water, is being deposited on land and accumulating in animals, from spiders to mountain lions.

Peter Weiss-Penzias, an atmospheric scientist at the University of California, Santa Cruz, and colleagues have been trying to trace methylmercury through the central California terrestrial food web. They started with arthropods, measuring mercury concentrations in wolf spiders, camel crickets and pill bugs. The researchers found mercury in all the arthropods, but the highest levels were in the wolf spiders, the team reported in the April Bulletin of Environmental Contamination and Toxicology. Wolf spiders are carnivorous, and they appeared to be acquiring more mercury through bioaccumulation.

“Spiders in foggy areas exceed FDA limits [for people],” Kenneth Coale, director of Moss Landing Marine Laboratories in California, quipped at a press conference Wednesday at the American Geophysical Union Fall Meeting. Coale has been studying mercury’s path from ocean to land via fog.

Other species, bigger ones, may also be affected. On Monday, Weiss-Penzias presented preliminary data showing high levels of mercury in deer in central California and in the mountain lions that eat them. A couple of mountain lions had mercury levels high enough that they could be experiencing health problems, Weiss-Penzias said. “There’s a handful that could potentially be impacted,” he told me.

Weiss-Penzias and his colleagues are still working to trace the path of toxic mercury from ocean waters to fog to land to animals, and on up the food chain. “We’re trying to connect the dots,” he said. But this research is a worrying sign that mercury pollution may be a much bigger problem than we realize, and one that can’t be solved by simply limiting the amount of tuna you eat.