Tree rings track atmospheric mercury cheaply

Research was conducted in the Peruvian Amazon and published April 8 in the journal Frontiers in Environmental Science.

Computer models suggest that atmospheric mercury can potentially travel across the globe, to be deposited back in landscapes. When it falls to the ground or in water, it can accumulate in organisms such as fish and other food sources, where it acts as a neurotoxin to both humans and wildlife.

Environmentalists and scientists may now establish biomonitoring networks with wild fig trees (Ficus insipida) in order to better understand how mercury spreads over time and space.

"We're trying to reduce emissions, especially from gold mining, as part of the United Nations Minamata Convention on Mercury, and in order to do that, we need to be able to measure it, to see the impact over time," said Jacqueline Gerson, the study's corresponding author and assistant professor of environmental and biological engineering. "This really offers a method that can be employed throughout the Global South to understand changes in mercury over time, as well as spatial indicators of mercury."

Artisanal and small-scale gold mining accounts for about 20% of all the gold produced worldwide and is the biggest single source of mercury pollution. Liquid elemental mercury is used to separate gold from ore; mercury can then enter the environment either when ore residues are dumped onto the landscape or when it is burned off, a practice employed in some 70 countries worldwide.

Previous studies have used tree rings to track mercury levels from coal combustion, particularly in Canada, but the method had not been used in the tropics for measuring mercury from gold mining.

"While the technique itself is not new," Gerson said, "we wanted to test its application in places where it's really hard to put out monitors for atmospheric concentrations, because they're costly and require energy or need to be changed a lot."

Currently, expensive active mercury monitors pump air through a device to collect mercury and require electricity, while passive air samplers use activated charcoal to collect ambient mercury and are good for remote areas but cost up to $100 each.