Identifying Sources of Mercury

A group of researchers is working on a way to identify sources of environmental mercury, particularly methylmercury, by analyzing isotopes.

Mercury is a naturally occurring element, but some 2000 tons of it enter the environment each year from human-generated sources such as incinerators, chlorine-producing plants and coal-burning 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....

For the past eight years, Blum and co-workers have been trying to develop a way of reading mercury fingerprints in coal and other sources of mercury. The hope was that they could then find those same fingerprints in soil and water bodies, much as a detective matches a suspect's fingerprints to those found at a crime scene, and use them to figure out exactly what the sources of mercury pollution are in certain areas....

The fingerprinting technique relies on a natural phenomenon called isotopic fractionation, in which different isotopes (atoms with different numbers of neutrons) of mercury react to form new compounds at slightly different rates. In one type of isotopic fractionation, mass-dependent fractionation (MDF), the differing rates depend on the masses of the isotopes. In mass-independent fractionation (MIF), the behavior of the isotopes depends not on their absolute masses but on whether their masses are odd or even. Combining mass-dependent and mass-independent isotope signals, the researchers created a powerful fingerprinting tool.

Previously, Blum and coworkers investigated the possibility of using the method to identify sources of mercury contamination in fish. The coal project was more challenging because of the difficulty of extracting and concentrating mercury from coal. The researchers developed a system that slowly burns the coal under controlled conditions in a series of furnaces and then traps the mercury that is released.

If those sources could be identified, then perhaps some contamination could be reduced. Environmental mercury is a pressing issue, primarily because of its threat to humans (who ingest it while eating fish). It also is a conservation issue for many bird species, especially wood thrushes, that absorb high levels of mercury and methylmercury through their diets.