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The protected old-growth forest in the Amazon in southeastern Peru looks pristine: Ancient trees with massive trunks grow alongside young, slender trees, creating such a thick canopy that it sometimes seems like evening during the day to scientists.

But a new analysis of what’s inside the leaves of the forest and the feathers of birds tells a different story: The same canopy that supports the richest biodiversity on the planet is also absorbing alarming levels of toxic mercury, according to a study published Friday.

Mercury is released into the air by miners searching for gold on nearby river banks. They use mercury to separate the precious metal from the surrounding sediment and then burn it. Airborne particles adhere to the leaves like dust and are washed to the forest floor by rain. Other particles are absorbed into the leaf tissue. From there, the mercury seems to have transferred the food web to the songbirds; this showed mercury levels in comparable areas away from mining activity were two to 12 times higher.

“The patterns were much sharper and much more destructive than we expected to find,” said biogeochemist Jacqueline Gerson of the University of California, Berkeley, who led the research as a PhD. Student at Duke. study published in the journal Nature Communications..

Findings from Peru’s Madre de Dios region provide new evidence of how humans are changing ecosystems around the world with little understanding of the consequences as species extinction rates accelerate.

Scientists have long known that mercury, which is released into the air by burning coal, is a dangerous neurotoxin for humans and animals. In aquatic ecosystems, it can easily transform into a highly toxic form called methylmercury. While the bigger fish eat the smaller fish, the mercury sticks around and builds up the food web. That’s why doctors advise pregnant women around the world not to eat large, predatory fish such as shark, king mackerel, and swordfish.

In the Madre de Dios district, where illegal gold mining is on the rise In recent years, with the price of gold in global markets, the government declared a health emergency in 2016 as 40 percent of people tested in 97 villages had dangerously high levels of mercury in their systems.

Researchers mostly focused on human exposure to mercury in rivers, lakes, and oceans. They’re not worried about this on land, as it’s less likely to be methyl mercury. However, the rainy conditions and the sheer load of mercury entering the forest with the soil lead to corresponding levels of methyl mercury there.

Dr. “It was hypothesized that people living in the Peruvian Amazon got all their methylmercury exposure from eating fish,” Gerson said. “It may not be.”

The type of gold mining that takes place in the Madre de Dios region, called artisanal and small-scale gold mining, takes place in around 70 countries, often illegally or unofficially. largest source of mercury pollution in the world. It also accounts for about 20 percent of global gold production.

Julio Cusurichi Palacios, president of the Indigenous Federation of the Madre de Dios River and Tributaries, a group formed by Indigenous communities in the region, said the government must combat illegal mining, while simultaneously strengthening alternative livelihoods for Indigenous and other local people. He said they harvested fish, Brazil nuts, yucca and corn, but “they need help developing their wares, selling their wares; Market.'”

For research, Dr. Gerson and his team collected soil, leaves, forest litter, and other samples at three sites close to the mining activity and two further away. To collect some leaves, they used a giant slingshot to pull a weighted rope over the canopy and pull the branches down.

When mercury levels returned, the protected old-growth area near gold mining activity stood out. These areas had 15 times more mercury than nearby openings, probably because thick canopy and vegetation captured and stored the mercury.

Shocked by the numbers, Dr. Gerson continued to search the scientific literature for forest samples of similar levels. All he found was in Guizhou, China, in an industrial area contaminated by mercury mining and coal burning. Some levels in the healthy-looking old Amazon were even higher.

By capturing mercury, forests help keep it out of water systems, said Emily Bernhardt, professor of biogeochemistry at Duke University and co-author of the study.

Dr. “These are some of the most biodiverse forests on Earth,” Bernhardt said. “We already knew they were sequestering tons of carbon in their biomass and soil, and now we’ve uncovered an incredibly important additional service.”

However, the service is not free. He noted that mercury poisoning could affect the birds’ ability to navigate and sing, causing them to lay fewer eggs. It can also reduce the likelihood of their eggs hatching.

Daniel Obrist, a professor of environmental science at the University of Massachusetts Lowell who studies mercury in forests in the northeastern United States and the Arctic, said previously that scientists had assumed that airborne mercury pollution from this type of gold mining would have less impact locally. and was not included in the Amazon study.

Dr. “This fills a very important gap in understanding what’s going on in small-scale mining and what the implications are,” Obrist said. “Not just for global processes, but for local communities as well.”