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
      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