The primary Amazon rainforest (the name given to areas with the least human intervention) of southeastern Peru appears untouched. Ancient trees with huge trunks grow alongside slender young trees, forming a canopy so thick that scientists sometimes get the impression that it’s night during the day.
But a recent analysis of what’s inside tree leaves and bird feathers tells a different story: The same canopy that supports possibly the richest biodiversity on the planet is also absorbing alarming levels of toxic mercury, according to a study published on Friday. (28).
Mercury is released into the air by prospectors looking for gold on the banks of rivers. They use mercury to separate the precious metal from the sediments that surround it and then burn it.
Mercury particles are released into the air, fall on leaves as dust and are washed to the forest floor by rain. Other particles are absorbed by the leaves.
From there, the mercury appears to have transferred through the food chain, reaching songbirds, which revealed mercury levels between 2 and 12 times higher than those in comparable areas further away from mining activity.
“The pattern was much stronger and more devastating than we anticipated finding,” commented biogeochemist Jacqueline Gerson of the University of California at Berkeley, who led the study as a doctoral student at Duke University. The study was published in the journal Nature Communications.
Made in the Madre de Dios region of Peru, the discovery brings new evidence of how humans are modifying ecosystems around the world with little understanding of the consequences, as species extinctions accelerate.
Scientists have long known that mercury, also released into the air by burning coal, is a dangerous neurotoxin for humans and animals.
In aquatic systems mercury can easily convert into a highly toxic form called methylmercury. When larger fish consume smaller ones, mercury is still present, accumulating in the food chain.
For this reason, pregnant women are advised to avoid eating large predatory fish such as dogfish, mackerel and swordfish.
Illegal gold mining has been increasing in the Madre de Dios region in recent years, following the rise in the price of gold on world markets. In 2016, the Peruvian government declared a health emergency in the region, after 40% of people tested in 97 villages had dangerously high levels of mercury in their bodies.
Scientists have focused primarily on human exposure to mercury in rivers, lakes and oceans. They have not been equally concerned about the presence of mercury on land, as it is less likely to convert to methylmercury. But the large volume of mercury released into the forest, added to the soil and rainy conditions, is leading to worrying levels of methylmercury in the region.
“Until now, it was thought that the exposure to methylmercury of the population of the Peruvian Amazon came from the consumption of fish,” said Jacqueline Gerson. “But it’s possible that’s not the case.”
The type of artisanal gold mining done in the Madre de Dios region is practiced in about 70 countries, often illegally or unofficially, and is the world’s largest source of mercury pollution. And it accounts for about 20% of the world’s gold production.
Julio Cusurichi Palacios, president of the Indigenous Federation of Rio Madre de Dios and Afluentes, made up of indigenous communities in the region, said the government should fight illegal mining with police force, but also promote alternative livelihoods for indigenous people and other inhabitants of the region. region.
Residents fish, harvest Brazil nuts, plant agave and corn, he said, but they need assistance “to improve and sell their produce, so they don’t think ‘there’s no market for my product, so the way is to go to the mines'” .
Gerson and his team collected soil, leaves, forest waste and other samples at three sites close to the mining activity and two more distant ones. They used a giant slingshot to harvest certain leaves, throwing a weighted rope towards the canopy and pulling branches down.
When mercury levels were revealed, the highest were in areas of protected virgin forest near the mine. These areas had 15 times more mercury than nearby clearings, probably because the thick canopy and dense vegetation had captured and stored the mercury.
Shocked by the numbers obtained, Gerson scoured the scientific literature looking for examples of forests with similar levels of mercury. The only one she found was in an industrial area of ​​Guizhou, China, polluted by mercury mining and coal burning. Some of the mercury levels detected in the healthy-looking Amazonian primary forest were even higher.
When they capture mercury, forests help keep it out of aquatic systems, said Emily Bernhardt, a professor of biogeochemistry at Duke University and a co-author of the study.
“This is one of the most biodiverse forests on the planet,” she said. “We already know that it captures tons of carbon in its biomass and its soil. Now we’ve discovered an additional and incredibly important role that it plays.”
But this service that the forest provides is not without cost. Mercury poisoning can affect the birds’ ability to orient themselves and sing and can lead to them laying fewer eggs, the scientist said, as well as reducing the chances of their eggs hatching.
Scientists have until now assumed that airborne mercury pollution from gold mining had less of a local impact, said Daniel Obrist, a professor of environmental science at Massachusetts Lowell University who studies mercury in northeastern and Arctic forests and was not involved. of the Amazon study.
“The study came to fill a very important gap in the knowledge of what happens there with small-scale mining and its consequences”, said Obrist. “Not just for global processes, but also for local communities.”
Translation by Clara Allain.
Source: Folha
