Vol. 18, No. 14Dec. 10, 1998

Soil chemistry team digs environmental issues

Donald Sparks (front, right) with student researchers (from left) postdoctoral student
Robert Ford and doctoral students Kirk Scheckel and Darryl Roberts

Americans are becoming increasingly wary of what's in their drinking water, and stories of water contamination appear regularly in publications nationwide.

At the same time, advertisements for home water-filtration devices are everywhere, and supermarket shelves are being stocked more and more with spring water and other beverages that tend to keep consumers away from the tap.

Now, researchers with UD's Department of Plant and Soil Sciences-part of the College of Agriculture and Natural Resources at Townsend Hall-are conducting state-of-the-art research that promises to provide cleaner drinking water sources in the next century, and soils that are better able to prevent contamination of flora and fauna in "stressed" areas of our once-pristine planet.

The world-class research, carried out in part with a series of generous grants from the DuPont Co. and the State of Delaware over the past decade, focuses on the mechanisms by which metal contaminants from dumped or accidentally spilled industrial waste either bind to the soil or leach down into underground aquifers that provide water for people to drink.

"By predicting how metals react with soils, we can determine their form, or speciation, and how tightly they are bound to soils," said Donald L. Sparks, Distinguished Professor of Soil Chemistry, chair of the department and newly elected president of the Soil Science Society of America.

"Such information is necessary to predict the long-term fate and transport of pollutants in soils and waters, and to devise effective remediation strategies," added Sparks, who also was recently elected chair of the Soil Chemistry Division of the International Union of Soil Science.

The metals that create hazards to humans, plants, fish and wild animals include copper, lead, nickel and cadmium, Sparks said. Trace amounts of these metals occur naturally in the environment. Nickel is present in quantities of less than 50 parts per million (ppm). But, with industrial sewage sludge and chemical spills, Sparks noted, nickel levels can reach a toxic 2,550 ppm-a range that is potentially deadly to living things.

Sparks and his research group are using cutting-edge, analytical equipment at Brookhaven and Lawrence Berkeley National Laboratories to study metal reactions with soil minerals at the molecular scale. The soil chemistry program currently includes nine students working on Ph.D.s, three post-doctoral researchers and a visiting professor from Israel.

"The diversity in backgrounds greatly enriches the educational and social experiences of the group members," Sparks said.

The team has been focusing its efforts on understanding, at the molecular level, the rate and mechanisms of metal binding (sorption) reactions on soil minerals. According to data presented by Sparks and his group at a recent agricultural research awareness meeting for members of Congress, "to accurately predict the fate of contaminants in the environment, one must accurately understand sorption mechanisms." By understanding the mechanisms, Sparks added, "one can mitigate contamination of lakes, wells and other water sources."

Working at the molecular level at national laboratory facilities, Sparks' students have been concentrating on such techniques as X-ray Absorption Spectroscopy (XAS) and Scanning Force Microscopy (SFM) to study the interaction of metals and soil.

The XAS technique generates X-rays in a synchrotron, which accelerates sub-atomic particles in a circular path to near the speed of light. The X-rays help determine "the local chemical environment" of metals on the surfaces of soil particles. They also tell UD scientists how well a metal will bind, or move through the soil.

The SFM technique is used to study how metals react on the soil's surface over time. Pictures generated by SFM show dramatic peaks and valleys at the "nanometer" level-one billionth of a meter.

Working part-time at UD on his Ph.D. in environmental soil geochemistry, DuPont Co. senior process engineer James A. Dyer last year finished his master's degree in environmental civil engineering. DuPont is interested in practical applications resulting from the soil chemistry group's research for both environmental and economic reasons, he said. "The stake for DuPont is hundreds of millions of dollars in better remediation solutions," said Dyer.

In years past, he explained, industrial firms didn't know the effects of then-legal and routine waste disposal, dumping in landfills or accidental spills. With better environmental awareness in recent decades, "the standard approach has typically been excavation," he said. "But, research at Delaware and other universities helps to show us other ways to more cost-effectively and safely deal with contaminated soil." The goal, he added, is to make sure dangerous metals are not "bioavailable" to harm plant and animal organisms.

Some of the latest techniques involve leaving the soil "in situ," treating it with lime to neutralize contaminants, installing barrier walls around a site, making the unwanted elements less soluble or chemically changing them so they bind to the soil.

"Immobilization," Dyer said, "is the first priority to avoid contamination."

Post-doctoral researcher Robert G. Ford, who earned his environmental engineering Ph.D. from Clemson University in South Carolina, is at UD studying how metals interact with minerals present in soils.

"The metals could be natural or present from disposal of waste," Ford said. "We run experiments in the lab to mimic the natural environment." Soil acts like a "chemical sponge" to attract some metals, according to Ford, who has recently submitted an article about his research to the journal, Science.

"Our ultimate goal is to determine how much contaminant metal can go into crops or drinking water and affect public health," Ford said. "We look at how metals become attached to soil, how strong that attachment is, and if it is fleeting or permanent."

Ph.D. student Darryl Roberts from California Polytechnic State University is working at UD, supported by a prestigious National Science Foundation fellowship. "I'm looking at the fate of nickel on soil clays and soils using molecular scale techniques ... how nickel reactions change over time, and how time affects the subsequent release of nickel into the environment," he said.

Like Ford, Andreas Scheinost, a postdoctoral fellow from Germany, and Kirk Scheckel, a doctoral student from Iowa State University, Roberts attended sessions and presented papers at the World Congress of Soil Science and the Goldschmidt Conference in the south of France this past summer.

Other graduate students and post-doctoral researchers in the soil chemistry group come from Texas A&M, Louisiana State, The Technion, Tokyo University and the University of California's Davis campus.

"With excellent laboratory facilities at UD, and the opportunity to employ cutting-edge technologies at national laboratories, our students are able to conduct original and important research that greatly benefits society," Sparks said. "Moreover, such training enables them to be highly competitive for jobs in academe and industry." One of Sparks' recent students, for instance, Scott E. Fendorf, has accepted a faculty position at Stanford University.

-Phil Milford
Photo by Robert Cohen