Record amounts of mercury found in Peruvian Amazon rainforest
Illegal gold miners use mercury to bind gold particles, then separate the two metals by burning gold-mercury pellets in open fire ovens, releasing clouds of highly toxic mercury particles into the atmosphere. Credit – Melissa Marchese
Duke University – A new study has discovered that the world’s highest levels of mercury pollution have been found in an area of the Amazon rainforest in Peru.
The study, which appeared in the journal Nature Communications on Jan. 28, an international team of researchers show that illegal gold mining in the Peruvian Amazon is causing exceptionally high levels of atmospheric mercury pollution in the nearby Los Amigos Biological Station.
The spread of mercury pollution from gold mining has primarily been studied in aquatic systems. In this study, a team of researchers led by Jacqueline Gerson, who completed this research as part of her Ph.D. at Duke, and Emily Bernhardt, professor of Biology, provide the first measurements of terrestrial inputs, storage and impact of atmospheric mercury to forests and measurements of methylmercury, the most toxic form of mercury.
Illegal miners separate gold particles from river sediments using mercury, which binds to gold, forming pellets large enough to be caught in a sieve. Atmospheric mercury is released when these pellets are burned in open fire ovens. This mercury smoke ends up being washed into the soil by rainfall, deposited onto the surface of leaves, or absorbed directly into the leaves’ tissues.
To measure this mercury, Gerson and her team collected samples of air, leaf litter, soil and green leaves. They focused their collection on four types of environments: forested and deforested, near mining activity or far from mining activity. Two of the forested areas near mining activity are patches with small, scraggly trees, and the third is Los Amigos Biological Station, a pristine old-growth forest that has never been touched.
Deforested areas, that would have received mercury solely through rainfall, had low levels of mercury regardless of their distance to the mining activity. Forested areas, which accumulate mercury both on their leaves and into their leaves, weren’t all the same. The four areas with scraggly trees, two near mining activity and two further away, had levels of mercury in keeping with worldwide averages.
“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 Gerson, who is currently a postdoctoral researcher at the University of California, Berkeley.
For all forested areas, Gerson and her team measured a parameter called leaf area index, which represents how dense the canopy is. They found that mercury levels were directly related to leaf area index: the denser the canopy, the more mercury it holds. The canopy acts like a catch-all for the gases and particulates originating from the nearby burning of gold-mercury pellets.
To estimate how much of the mercury caught in the forest canopy was making its way through the food web, the team measured the mercury accumulated in feathers of three songbird species, in reserve stations near and far from mining activity.
Birds from Los Amigos had on average three times, and up to 12 times more mercury in their feathers than those from a more remote biological station. Such high concentrations of mercury could provoke a decline of up to 30 per cent in these birds’ reproductive success.
“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,” Bernhardt 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.”
Small-scale artisanal gold mining is driven by economic necessity, but it disproportionally impacts Indigenous communities.
“There’s a reason why people are mining,” Gerson said. “It’s an important livelihood, so the goal is not to get rid of mining completely…The goal is to highlight that the issues are far more vast than water pollution, and that we need 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,” Gerson said.
