Messenger - Vol. 2, No. 1, Page 12 Fall 1992 Soil sleuths search for contaminating culprits Hot on the trail of potent pollutants in soil, Donald L. Sparks and his graduate students are attempting--with federal and industrial support--to pinpoint the exact chemical footprints of the culprits so decontamination teams can step in. Sparks, professor of soil science, uses sophisticated measurement equipment at the Brookhaven National Laboratory on Long Island to determine how tightly metal oxides and organic pollutants are held by the soil. After a specific chemical form of the pollutant is identified, he can then look at ways it could be released from the soil and can estimate the rate of release. The pollutants he is investigating include industrial solvents, heavy metals and even pesticides that were applied to growing fields over a long period of time leading to a toxic buildup. Establishing the exact identity of the pollutant is important because its movement through the soil and toxicity may vary with the chemical form. For example, chromium in a hexavalent oxidation state is highly toxic, while in a trivalent state it is less so. Arsenic in some forms moves rapidly into water-bearing areas beneath the soil surface known as aquifers, while other forms adhere to the surface itself. Sparks and his students have used electron microscopy at the National Center for Electron Microscopy (Lawrence Berkeley Lab) to identify a reaction that inhibits the transformation of the less toxic chromium to the more hazardous form. "Once we identify the contaminant exactly, the chemistry and technology may already be present for decontamination and we won't be shooting in the dark," Sparks says. For example, "If we find lead, then we try to determine whether it is in a sulfide, carbonate or some other form." he says. Sparks and his associates use high-tech hardware at Brookhaven for their detection procedure--the extended X-ray absorption fine structure spectroscopy, or EXAFS. "This is a powerful, non-invasive technique, which has not been used before to identify specific pollutants in contaminated soil," he says. "We can use it in situ and get direct information on how the metal is bound to the soil and what its valence is." A collaborative effort with the Du Pont Co. and the U.S. Department of Energy, Sparks' current project exposes his students to the most sophisticated available equipment and strengthens the quality of their research. Sparks and four colleagues in the Department of Plant and Soil Sciences share their interest in complex environmental problems with undergraduate students as well. This fall, the department introduces a new interdisciplinary major in environmental soil science in which students will take courses in physics, chemistry, biology, geology, geography and public policy, in addition to soil science and other agricultural sciences. --Cornelia Weil