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Pollutants Zapped From the Earth

In a technical tour de force, scientists have coaxed a toxic chemical out of contaminated soil without removing or incinerating the soil. The technique, reported in the 1 April issue of the journal Environmental Science and Technology, could prove to be a cheap, efficient way to eliminate many pollutants from soil.

Using electricity to move contaminants out of soil is not a new idea, but it has taken a collaboration between the Environmental Protection Agency and Monsanto, DuPont, and General Electric to make it practical. The principle is quite simple: Electrodes stuck into the soil pull water--and contaminants--into buried containers about half a meter wide and a few meters deep. These "treatment zones" contain materials that destroy the contaminants.

Sa Ho of the Monsanto Co. in St. Louis, Missouri, and his colleagues conducted two tests at a uranium plant in Paducah, Kentucky. For about a year the researchers ran a 35-amp current through electrodes placed as deep as 14 meters, while iron filings in the treatment zones converted almost all the trichloroethylene to harmless byproducts such as salt and ethane gas. The treatment costs $45 to $80 per cubic yard, says Ho, compared to $200 to $1000 for digging up and incinerating the soil.

The approach will be particularly useful for cleaning up hard-packed soils that are difficult to treat with other methods, such as sucking air out of loose soil to extract volatile contaminants, says Paul Kostecki, an environmental scientist at the University of Massachusetts, Amherst. Others agree. "It is a really good treatment when you have very tight soil," says Elizabeth Phillips of the Department of Energy, which plans to use the technique to complete the cleanup of hard-packed soil at Paducah.