Mercury-based gold mining haunts Peruvian rainforests

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AGU Fall Meeting 2021

In the southeastern corner of Peru, the Madre de Dios River flows east, eventually emptying into the mighty Amazon. Verdant tropical forests grow in sandy soils speckled with gold.

Today, gold diggers felled trees in the forest, removing sediment and removing sand. To extract the precious metal from this mixture, the miners add liquid mercury, which recovers the gold and forms an amalgam with it. By burning the resulting goo, miners can burn off the mercury. Dangerous vapors rise to the sky and the gold remains behind.

In recent years, the Peruvian government has gold miners expelled protected areas of Madre de Dios, the region through which the river of the same name flows. Following these interventions, the hydrologist Evan Dethier, a postdoctoral fellow at Dartmouth College, and his colleagues have tracked forest reclamation and tracked ousted miners using satellite imagery to look for telltale signs of ongoing gold mining: sediment-laden ponds tinged with yellow punctuating the forest. They found that where the miners have been evicted, revegetation is sparse. They also found that many miners appeared to be moving elsewhere, often to the parts closest to Madre de Dios where mining is legal. Dethier will present the team’s results on December 15 at the AGU Fall 2021 meeting.

Miners work to separate gold from sand in barrels by adding liquid mercury. At the bottom, tree trunks float on the yellow and stagnant water. Credit: Jimena Diaz Leiva

Mining migrations

During the second half of the 20th century, migrants flocked from the Andes to Madre de Dios in search of work in gold mining, said Jimena Diaz Leiva, an interdisciplinary environmental scientist who recently completed her doctorate. at the University of California, Berkeley. Diaz is not involved in the new study. At the time, the Peruvian government encouraged mining, offering tax incentives and selling miners essential machinery and other mining related accessories (including mercury). A state mining bank established in 1942 called the Banco Minero del Perú was the only legal buyer of gold, with remote rural outposts that allowed miners to sell their gold without having to travel long distances, she said.

Gold mining, Diaz said, was a state-sanctioned path to a better life, allowing miners to expand their mining operations, start other businesses, and educate their children. children.

Then, in the early 2010s, Peru officially codified mining bans in rivers and protected areas, as gold prices hit record highs, Diaz said. Military intervention soon started, enshrined in law as a means of eliminating illegal mining operations in the protected parts of Madre de Dios.

By combining satellite data that can see through clouds with satellite snapshots in which fawn and actively exploited ponds can be easily spotted on a clear day, Dethier and his colleagues have reconstructed an almost weekly record of the activity of gold mining in Madre de Dios for 5 to 6 year olds. These images testify to the relative success of Operation Mercury, the government’s 2019 offer to drive miners out of protected areas: Where the government has kicked out the miners, the ponds are almost completely abandoned – shades of blue or green instead of beige mud.

“It’s a lot of deforestation and a lot of new mining ponds.”

Remote sensing data also showed that informal mining operations appear to have shifted to areas of Madre de Dios where mining is legal. There is “a lot of deforestation and a lot of new mining ponds,” Dethier said. In other words, Peru’s interventions have succeeded in removing miners from protected areas without diminishing the overall impact of mining in the region.

Affect people and landscapes

Liquid mercury used in mining can affect the health of miners and other local residents. Miners often do not take any precautions when working with liquid mercury, Diaz said. The effects are often not direct: their exposure often occurs during the combustion of amalgam fillings, which often occurs outdoors where winds can carry the harmful smoke away, offering some protection to minors while contaminating the air. Additionally, because miners have been portrayed as bad environmental actors, they associate any discussion of health effects with an environmental anti-mining agenda, she noted.

As a result, “many miners do not believe that there is really [negative] health effects, ”she said.

The indirect effects of mining operations, however, extend beyond miners. Some of the mercury ends up in mining ponds, where bacteria can turn it into a more harmful type of mercury that builds up in fish, Diaz said. Because the diet of local indigenous people relies heavily on wild fish, she said, they are much more exposed to mercury than Andean miners, who tend to adopt a land-based diet.

Mining also physically alters the landscape by removing trees, accumulating water and releasing sediment, Dethier said. This changing landscape will change how rivers work, he said, and these effects also require special attention. “It’s really an open question. What happens to this area?

—Alka Tripathy-Lang (@DrAlkaTrip), science writer

Quote: Tripathy-Lang, A. (2021), Mercury-based gold mining haunts Peruvian rainforests, Éos, 102 years old, https://doi.org/10.1029/2021EO210645. Posted on December 15, 2021.
2021. The authors. CC BY-NC-ND 3.0
Unless otherwise indicated, images are subject to copyright. Any reuse without the express permission of the copyright holder is prohibited.


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