Forest fires affect the organic content of soil.

Studies to Investigate Fire Effects, Mercury and Water Links

Kathryn Nagy, professor of Earth and environmental sciences at the University of Illinois at Chicago (UIC), has been working for more than 10 years on the natural processes that either release mercury into water or may be able to remove it.

Methylmercury – the chemical form of the heavy metal element that's most toxic to humans – often enters human diets after fish consumption. Mercury gets methylated in watersheds by microorganisms. The methylmercury then becomes progressively more concentrated as it moves up the food chain.

"We're trying to understand more about bioavailable mercury – the mercury in water that gets methylated – and about everything that can keep it out of the water," Nagy said.

Cleaning up mercury contamination using plants or peat holds promise as an eco-friendly solution, but before that happens, more needs to be learned about the biogeochemistry at work.

Nagy is receiving $225,000 from a $700,000 National Science Foundation (NSF) collaborative grant just awarded to researchers at UIC, the University of Colorado at Boulder and the Mountain Studies Institute to study the damaging effects that forest fires have on soil organic matter, which influence the amount of mercury available for methylation. Scientists from France's Centre National de la Recherche Scientifique in Grenoble and the U.S. Geological Survey are also participating.

Fire releases into the air some but not all mercury bound to sulfur in soil organic matter. Nagy wants to characterize how fire changes the sulfur, how strong the mercury-sulfur bond is, and under what conditions the bonding can be altered.

She and her coworkers will study what happens to sulfur in soil organic matter that's washed into watersheds after a fire to learn how that may affect the process of methylating mercury. Samples will be taken from forests in parts of the Colorado Rockies before and after fires. Data will also be gathered before and after "prescribed" or controlled burns, and in simulated laboratory experiments.

Nagy is also doing related work using a $670,000 Department of Energy grant she leads to study the aftereffects of an Oak Ridge National Laboratory mercury spill that entered local surface waters and soil. The award totals about $1.2 million and involves most of the same collaborators on the NSF grant.

"A lot of biochemistry goes on in soils," she said. "Soils are complex with minerals, water, decaying organic matter and many living organisms: plants, bacteria and fungi. We're trying to learn how biochemical molecules the organisms produce can attack the mercury that is bound to natural organic matter and minerals, and release it back to the water."

Nagy hopes that by getting a better understanding of the chemical reactions that affect mercury's movement, more effective methods of decontamination can be devised.

"If we understand the organic matter structure that's chemically binding with the mercury and where it comes from, maybe that will help us understand how to use plants or peats to clean up mercury from water or soil."

The NSF grant's lead investigator is Joseph Ryan of the University of Colorado at Boulder. Other investigators are George Aiken of the USGS, Koren Nydick of the Mountain Studies Institute, and Alain Manceau of CNRS. Nagy's partners on the DOE grant include Ryan, Aiken, Manceau, and Baohua Gu of the Oak Ridge National Laboratory.

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