Illegal gold mining causing record mercury levels in Peruvian rainforests

Scientists have found that the highest recorded levels of atmospheric mercury exist in an unlikely place — Peru's Amazon rainforest. The study, published on Wednesday in Nature Communications, pointed to illegal gold mining as the cause.

The miners use mercury, which binds to gold, to separate the precious stone from river sediments, according to the international team of researchers. The mercury is then burned off in an open fire oven, and its smoke falls onto nearby leaves and washes into the forest soil by rainfall.

The researchers collected samples of air, leaf litter, soil and green leaves from the top of trees, to determine the levels of atmospheric methylmercury, the most toxic form of mercury. They found that in one area of the forest, mercury levels rivaled those measured in industrial areas where mercury is mined. 

"We found that mature Amazonian forests near gold mining are capturing huge volumes of atmospheric mercury, more than any other ecosystem previously studied in the entire world," said Jacqueline Gerson, a postdoctoral researcher at the University of California, Berkeley said in a press release.

While the high concentrations of mercury have negative implications for the local environment — the research team worries that the mercury levels could reduce bird reproduction by 30% after finding that they had up to 12 times more mercury in their feathers than most other birds — the forest absorption is actually benefiting the overall environment. 

"These forests are doing an enormous service by capturing a huge fraction of this mercury and preventing it from getting to the global atmospheric pool," Emily Bernhardt, professor of Biology at Duke University, said. "It makes it even more important that they not be burned or deforested, because that would release all that mercury back to the atmosphere."

The scientists appreciated that gold mining was a staple of the local economy, and many artisans relied on it for their livelihood. Gerson wrote that they hope to work with local communities "to come up with ways for miners to have a sustainable livelihood and protect indigenous communities from being poisoned through air and water."

"There's a reason why people are mining," Bernhardt added. "The goal is not to get rid of mining completely, nor is it for people like us coming in from the United States to be the ones imposing solutions or determining what should happen."