Picture this: A rickety barge about the size of a garden shed is floating on the Madre de Dios river in eastern Peru. A stream of tan sludge pours off a conveyor belt on one side of the platform. Smoke from a generator belches from the other. The sound of a massive pump thuds across the water. And dangling over the side of the barge is a thick tube to suck sediment up from the riverbed.
Welcome to wildcat gold mining in the 21st century, Peruvian style.
"Somebody will dive down to the bottom of the river with a scuba suit or some kind of tube to breathe," says Bill Pan, an assistant professor in the Global Health Institute at Duke University. "They'll be on the bottom sucking up the dirt."
The miners sift through the dirt searching for flecks of gold and use a ball of mercury to extract tiny specks of the precious metal from the sludge.
In this process, tiny beads of mercury end up getting dumped back into the river along with the leftover mud.
Pan and his colleagues at Duke show in a new research paper that these illegal mining boats, along with open-pit artisanal mines, are responsible for toxic levels of mercury not just near the miners but also hundreds of miles downstream.
Over the past decade, tens of thousands of people have moved to this remote area of the Amazon jungle in hopes of striking it rich — or at least making a bit more money than they were before. Not all of them work on floating barges. Some of the miners clear trees from riverbanks and sift the soil in search of gold. The destruction of the forests has been widely documented. This new study shows the extent of the mercury contamination. And the study clearly shows the link between mining and the elevated levels of mercury in the environment.
"There's definitely a strong correlation between where the mining is occurring and where people are at risk for mercury toxicity," Pan says. "And that risk remains elevated for hundreds of miles."
A study in 2013 from the Carnegie Institution for Science found mercury in fish and people in the region at levels far above what the World Health Organization views as acceptable. Mercury exposure can lead to neurological damage. It's particularly dangerous for pregnant women and young children. Heileen Hsu-Kim, an associate professor of environmental engineering at Duke who worked on the study with Pan, says it's clear that mercury levels in fish and people have been going up as mining has expanded.
The government of Peru has attempted to crack down on illegal miners operating on the Madre de Dios. The Peruvian navy has even blown up some of the barges. But with gold prices well above $1,000 an ounce, laborers continue to flock to the boats and open-pit mines where they can earn far more than in the other jobs that are available to them in the country.
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