Gold mining spreads mercury to tropical birds, study says

Royal Flycatcher
Royal Flycatcher

Tropical birds, from kingfishers to wrens to warblers, are showing signs of mercury contamination as artisanal and small-scale gold mining operations reach deeper into jungles, new research finds.

Birds living within 7 km (4 miles) of such gold mining activity were found to have mercury concentrations over four times higher than those living at other sites across the tropics of Central and South America, according to the study published Tuesday in the journal Ecotoxicology.

A Black-spotted Bare-eye
A Black-spotted Bare-eye (Phlegopsis nigromaculata) captured next to an artisanal gold mining operation in Madre de Dios, Peru. Credit: Chris Sayers/UCLA

“It’s a wake-up call for bird conservation internationally across the tropics,” said lead author Chris Sayers, a conservation biologist at the University of California Los Angeles.

Tropical bird biodiversity has been decliningin recent decades, but scientists are not fully sure why. “Based on the levels here, it’s reasonable to suggest that mercury may be playing a role,” Sayers said.

Over a 17-year period ending in 2023, dozens of scientists collected thousands of feather, blood and tissue samples from 322 bird species across nine countries in Central and South America and the West Indies, creating the world’s largest database to date on mercury concentrations in birds.

“The most important finding of our study was that mercury concentrations were nearly four times higher at sites impacted by artisanal and small-scale gold mining activities,” said Chris Sayers, lead author of the study, in a statement.

Mercury is used in gold mining as a quick way to access hard-to-reach, tiny particles of gold, as it can bind to the desired metal. When these lumps of amalgam are heated, the mercury is vaporized, leaving only the gold. The mercury vapor either goes into the ground, seeps into water or goes into the atmosphere.

In their paper, the researchers describe mercury as “a persistent pollutant that adversely impacts environmental, animal, and public health on a global scale.” In tropical birds, high mercury levels can affect their immune system, making them more susceptible to disease. As tropical birds are often an indicator of overall ecosystem health, the findings in the study suggest that mercury levels could be high in other species too, including humans – who also experience toxic effects – living near gold mining operations.

As such, it’s worth considering if it’s really necessary to use mercury in gold mining in the first place. According to the researchers, the miners argue that it is, as it makes the process quicker and more efficient. Artisanal gold mining can also be an important part of the economy in small tropical communities.

However, co-author of the study Claudia Vega said that these communities should be informed about the environmental damage caused by gold mining, although more research is needed. This study involved local researchers, an approach that could help to guide these key conversations.

“This research serves as a wakeup call for bird conservation in the neotropics while also demonstrating the efficacy of thoughtful and equitable collaboration with local stakeholders,” Sayers concluded.

Source: Water Education

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