University of Delaware
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UpDate - Vol. 16, No. 30, May 8

             UD researchers play key roles at ACS meeting
     Donald L. Sparks, Distinguished Professor of Soil
Sciences, and George W. Luther III, marine studies, were
among several dozen UD researchers who played key roles in
the American Chemical Society's 213th National Meeting in
San Francisco April 13-17.
     Sparks co-organized a prestigious geochemistry
symposium during the meeting. Along with nine of his
graduate students and postdoctoral associates, he also
presented new information-based on molecular-scale studies
of different metals in soils-that may help environmental
engineers immobilize these contaminants more effectively.
     Luther, chairperson of the entire ACS Division of
Geochemistry, coordinated all geochemistry sessions during
the meeting and presided over a poster session focusing on a
broad range of geochemical studies.
     In addition, Luther's postdoctoral student, Amy E.
Witter, described her investigations of iron complexation
with organic compounds at natural levels in western North
Atlantic ocean waters. Another study by Luther's student,
David Ruppel, and former student/part-time instructor,
Caroline Burkhard, explored the reactivity of dissolved
manganese in marine waters. Finally, Luther discussed the
reaction of iron with organic compounds isolated from marine
and cyano bacteria.
     At the soil's surface, key industrial metals including
nickel, copper, chromium, cobalt and zinc-but not lead-form
mixed metal compounds that dramatically diminish their
mobility in the natural environment, Sparks, department
chairperson, said.
     "We have been able to precisely identify the chemical
structure of these mixed metal compounds, or precipitates,
on various soil/mineral surfaces," he added. "They form
quickly, in some cases in just 15 minutes, and they seem to
be quite resistant to degradation. We believe these
complexes could be an important mechanism for metal
sequestration, to prevent them from leaching into
surrounding soil or groundwater."
     The strategy may prove useful for trapping many metal
"cations" (positively charged ions) in terrestrial as well
as aquatic systems, said graduate student Kirk G. Scheckel.
The native aluminum then complexes with nickel to form a
"mixed cation hydroxide phase," Scheckel said. "In other
words, these metals rapidly accumulate and change, creating
a kind of blanket."
     That's good news, because it suggests a way to
immobilize metals within surface precipitates, according to
another key member of Sparks' research team, Andr
Scheidegger, a graduate of the Swiss Federal Institute in
Zurich, Switzerland. Contaminants might also be removed more
easily from surface precipitates, using traditional cleanup
techniques such as soil washing. For example, Scheckel has
found that EDTA-a strong "chelator that latches onto
targeted substances like a pair of claws-removes 96 percent
of nickel from precipitates on the surface of pyrophyllite,
a clay mineral found in soils."
     Metals such as nickel form mixed metal compounds at
neutral and slightly alkaline conditions, and at relatively
low metal concentrations on the soil's surface, Sparks said.
Consequently, he noted, it should be possible to enhance the
formation of these surface precipitates by simply liming the
soil. (Unfortunately, the researchers said, lead is
characterized by larger cations-roughly twice the ionic
radius of nickel-which don't "fit" into the molecular matrix
of the precipitates.)
     Sparks' collaborator and sponsor, Noel Scrivner, a
principal division consultant with the DuPont Co.,  said UD
researchers have made a "significant contribution" to
environmental science.
     "The UD researchers have provided, for the first time,
a firm scientific explanation for why certain metals don't
seem to migrate in soils," Scrivner said. "It's a whole new
class of phenomena, and the research has been done so well
that it's absolutely definitive. I suspect it's going to put
UD's Department of Plant and Soil Sciences on the map."
     Research by Sparks and his students is supported by the
DuPont Co., the state of Delaware, the U.S. Department of
Agriculture and the U.S. Geological Survey.
     Sparks' graduate students have received numerous honors
and awards, including national and UD dissertation prizes
and five national fellowships. Former graduate student
Philip M. Jardine, for example, is now an environmental soil
chemist at Oak Ridge National Laboratory and recently
received a Presidential Early Career Award for Scientists
and Engineers and the Young Independent Scientist Award from
the U.S. Deparment of Energy.
                                          -Ginger Pinholster