Science Gazette

The Peruvian gold rush has ruined the jungles, turning them into extremely polluted mercury sinks

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In a pristine region of Peruvian Amazon, scientists report the world’s highest levels of atmospheric mercury contamination.

Illegal gold mining in the Peruvian Amazon is polluting the atmosphere with unusually high amounts of mercury in a neighboring section of virgin jungle. The greatest quantities of mercury ever recorded were found in an old-growth virgin forest, which rivaled industrial regions where mercury is mined. Birds from this region had up to twelve times more mercury in their systems than birds from less polluted locations, a degree of poisoning that should make it difficult for them to reproduce.

You definitely wouldn’t select a piece of virgin Amazonian rainforest if you had to predict which section of the planet had the greatest levels of atmospheric mercury contamination. They are, however, precisely where they are.

An international team of researchers shows that illicit gold mining in the Peruvian Amazon is creating extraordinarily high levels of atmospheric mercury pollution in the adjacent Los Amigos Biological Station in a new study published in the journal Nature Communications on Jan. 26.

The greatest quantities of mercury ever recorded were detected in an old-growth virgin forest, rivaling industrial regions where mercury is extracted. Birds in this region had up to twelve times the amount of mercury in their systems as birds in less contaminated locations.

Mercury pollution’s effect and spread have mostly been examined in aquatic systems. The first measurements of terrestrial deposits of atmospheric methylmercury, the most deadly form of mercury, are provided in this article by a team of researchers headed by Jacqueline Gerson, who performed this research as part of her Ph.D. at Duke, and Emily Bernhardt, professor of Biology.

Illegal miners use mercury, which binds to gold and forms pellets big enough to be captured in a filter, to extract gold particles from river sediments. When these pellets are burnt in open fire ovens, mercury is discharged into the atmosphere. The high temperature separates the gold from the mercury, which melts and emits smoke. Rainfall washes mercury smoke into the soil, which is either deposited on the surface of leaves or absorbed straight into the tissues of the leaves.

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Gerson and her colleagues used a big slingshot to capture samples of air, leaf litter, soil, and green leaves from the tops of trees in order to measure the mercury. They collected data from four different kinds of environments: forested and deforested, close and distant from mining, and forested and deforested. Two of the nearby wooded areas are patches of tiny, scraggly trees, and the third is Los Amigos Biological Station, a pure old-growth forest that has never been altered.

Regardless of their distance from the mining activities, deforested regions that would have acquired mercury primarily by rainfall had low mercury levels. Forested regions, which store mercury on and in their leaves, were not all created equal. The mercury levels in the four regions with scraggly trees, two near mining activity and two farther away, were comparable to global norms.

“We discovered that mature Amazonian forests near gold mining capture massive amounts of atmospheric mercury, more than any other ecosystem ever investigated in the whole globe,” said Gerson, a postdoctoral researcher at the University of California, Berkeley.

Gerson and her team calculated a parameter called leaf area index, which represents how dense the canopy is, for all forested areas.

The amount of mercury in the canopy was found to be proportional to the leaf area index: the denser the canopy, the more mercury it held. The canopy works as a catch-all for gases and particles emitted by neighboring gold-mercury pellets being burned.

The scientists analyzed the mercury deposited in the feathers of three songbird species at reserve sites close and distant from mining activities to determine how much mercury was captured in the forest canopy and finding its way through the food chain.

Los Amigos birds had three times more mercury in their feathers on average, and up to 12 times more mercury in their feathers than birds from a more distant biological station. Mercury concentrations this high might cause a 30 percent drop in the reproductive success of these birds.

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“These trees are doing an incredible job by absorbing a significant portion of this mercury and keeping it from entering the global atmospheric pool,” Bernhardt said. “This emphasizes the need of not burning or deforesting them, since this would release all of the mercury back into the atmosphere.”

Local populations rely on small-scale artisanal gold mining for a living. It is motivated by economic need, similar to the American gold rush that destroyed California in the 1850s, and it disproportionately affects indigenous people.

Bernhardt said, “This isn’t anything new or unique to this location.” “Many of the wealthiest nations of the globe where gold was accessible had previously done something quite similar, using very similar tactics. Mining is being pushed deeper into new locations as a result of increased demand.”

“There’s a reason people mine,” Gerson said. “Because mining is such an essential source of income, the objective isn’t to entirely eliminate it, nor is it for individuals like us from the United States to be the ones imposing answers or deciding what should happen.”

“The idea is to emphasize that the challenges are far broader than water pollution,” Gerson said. “We need to collaborate with local people to come up with solutions for miners to have a sustainable existence while also protecting indigenous populations from being poisoned by air and water.”

Duke Global Health Institute Dissertation Fieldwork Grant, Duke Global Health Institute Doctoral Scholar Program, Duke University Bass Connections, Duke University Center for Latin American and Caribbean Studies Tinker Research Travel Grant Award, Duke University Center for International and Global Studies Research and Training Grant, Duke University Dissertation Research International Travel Award, Geological Society of America Dissertation Research International Travel Award, Geological Society of America Dissertation Research International Travel Award, Geological Society of America Dissertation Research International Travel Award, Geological Society of Emily Bernhardt received funding from the Josiah Charles Trent Memorial Foundation Endowment Fund Grant and the Graduate Research Fellowship Program of the National Science Foundation.

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