Mercury pollution accumulated in trees could offer a new way to keep tabs on destructive gold mining operations in the Amazon rainforest.
鈥淲e could potentially see whether mining is starting to ramp up,鈥� says at Cornell University in New York.
Most small-scale gold mining operations separate gold from ore by adding liquid mercury and then burning the mixture, releasing large amounts of mercury 鈥� a potent neurotoxin 鈥� into the air. Together, these mining operations, many of which are illegal, represent the largest source of mercury pollution in the global environment, outdoing even mercury released by all of the world鈥檚 coal-fired power plants.
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While stripped forest and flooded land can be a telltale sign of mining, the mercury released by these operations is more difficult to track. It鈥檚 鈥渃ompletely invisible鈥�, says Gerson. However, trees growing nearing mining sites are known to take up the pollution.
To test whether the trees might offer a reliable way of measuring mercury, Gerson and her colleagues working in the Peruvian Amazon took cores from the trunks of wild fig trees (Ficus insipida), one of the few tropical tree species that produces seasonal growth rings. Three of the sites from which the researchers took cores were within a few kilometres of known mining activity, while two were far from any known mining.
They found mercury levels were highest in the tree cores collected from sites near mining activity, especially those from the two sites near mining towns where most mercury burning happens. The pattern of mercury concentration in the trees also closely tracked independent measures of mercury in the air at each of the sites. 鈥淭he tree is just reflecting what the atmosphere is doing,鈥� says Gerson.
This suggests the trees could be used to track mercury emissions even in remote parts of the forest that lack instruments to monitor the air. 鈥淵ou can use trees to determine where we need to have interventions,鈥� says Gerson. That could include supplying people with technology for mining without mercury or cheaper equipment that limits mercury emissions, she says.
Variations in mercury concentrations in Ficus tree rings over time could also establish a historical baseline for mercury at a given site, helping to distinguish between mercury from mining and natural background levels, says at Wake Forest University in North Carolina, a member of the research team.
鈥淵ou can start to go back and see: how did it change when the mining came?鈥� says Fernandez. 鈥淲e鈥檙e starting to see that it changed a lot.鈥� For instance, trees from two of the sites near mining activity saw a distinct rise in mercury levels after 2005.
Today, record-high prices for gold again threaten to expand mining operations, says Fernandez. Yet US federal funding for effective interventions is being slashed. For instance, Fernandez leads a research consortium focused on mercury pollution called the that just saw its funding from the US Agency for International Development terminated as part of wider cuts by the Trump administration.
This is counterproductive even for an agenda focused on 鈥淎merica First鈥�, says Fernandez. 鈥淎rtisanal gold mining is something that threatens borders. It corrupts societies. It is a global source of mercury pollution,鈥� he says.
Frontiers in Environmental Science
