Volume 8, Number 2, 1999

Soil chemistry team digs into environmental issues

Scientists in UD's Department of Plant and Soil Sciences are conducting state-of-the-art research that promises to provide cleaner drinking water and ways to immobolize contaminated soils to prevent further harm to flora and fauna.

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 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," says Donald L. Sparks, Distinguished Professor of Soil Chemistry, chairperson of the department and current 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 help us devise effective remediation strategies," adds Sparks, who was recently elected chairperson 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 says. Trace amounts of these metals occur naturally in the environment, with nickel frequently present in quantities of less than 50 parts per million (ppm). But, Sparks notes, industrial sewage sludge and chemical spills can cause nickel levels to 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 doctorates, three postdoctoral researchers and a visiting professor from Israel. "The diversity in backgrounds greatly enriches the educational and social experiences of the group members," Sparks says.

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. By understanding the mechanisms, Sparks says, "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 holds a 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 says. "The stake for DuPont is hundreds of millions of dollars in better remediation solutions," says Dyer.

In years past, he explains, 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 says. "But, research at Delaware and other universities helps to show us other safe and more cost-effective ways to deal with contaminated soil." The goal, he adds, 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 says, "is the first priority to avoid contamination."

Postdoctoral researcher Robert G. Ford, who earned his doctorate in environmental engineering 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 says. "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 says. "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 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 says.

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 postdoctoral 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.

-Phil Milford