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Updated 10:00 AM October 31, 2007
 

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New fingerprinting method tracks mercury in environment
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With mercury polluting the air, soil and water, and becoming concentrated in fish and wildlife as it is passed up the food chain, understanding how the potent nerve toxin travels through the environment is crucial.

A new method developed at the University uses natural "fingerprints" to track mercury and the chemical transformations it undergoes. A report on the work was published Oct. 19 in the journal Science.

Mercury is a naturally occurring element, but some 150 tons of it enter the environment each year from human-generated sources in the United States, such as incinerators, chlorine-producing plants and coal-fired power plants. Mercury is deposited onto land or into water, where microorganisms convert some of it to methylmercury, a highly toxic form that builds up in fish and the animals that eat them. In wildlife, exposure to methylmercury can interfere with reproduction, growth, development and behavior and may even cause death.

Effects on humans include damage to the central nervous system, heart and immune system. The developing brains of young and unborn children are especially vulnerable.

Because of such profound and irreversible effects on health and the environment, "it's very important to understand how and where mercury transforms into its most toxic forms and how it moves around in the environment, leading to human and animal exposure," says research fellow Bridget Bergquist, first author on the paper.

"I have often dreamed of how useful it would be if we could mark individual atoms of mercury with an indelible fingerprint of key chemical reactions and use this fingerprint to follow them around in the environment," says co-author Joel Blum, who has been working on the problem for more than a decade.

Bergquist and Blum based their new tracking method on a natural phenomenon called isotopic fractionation, in which different isotopes (forms) of mercury react to form new compounds at slightly different rates, something like bicycle racers in the Tour de France. Some riders perform better in the mountainous stages of the race and are separated from the pack due to their strength; others distinguish themselves on the flat stages of race due to their superior speed.

In their work, Bergquist and Blum show that mass-dependent fractionation can be used to track mercury. Because the process is observed naturally in fish as they grow, the mercury the fish excrete must have a different isotopic composition than the mercury they take in, so mass-dependent fractionation (MDF) may reveal how much mercury fish consume, how much they excrete and how it changes during the fishes' lifetimes.

By combining two methods that provide distinct isotope signatures, Bergquist and Blum came up with a tracking tool that is more powerful than either one alone.

In one study research fellow Abir Biswas, working with Bergquist and Blum, found that mercury in coals from various coal-producing regions around the world vary in their mass-dependent and mass-independent isotopic composition. "This suggests that we may be able to use the mercury isotope studies to distinguish different sources of mercury to the atmosphere, which has far-reaching practical applications," says Blum, the John D. MacArthur Professor of Geological Sciences.

The researchers received funding from the Division of Earth Sciences of the National Science Foundation and the Turner Postdoctoral Fellowship from the Department of Geological Sciences.

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