U.S. Water News Online
LINCOLN, Neb. -- A relatively simple method of mixing iron
into soil contaminated with pesticides could save millions of dollars
for those faced with cleaning up environmental spills.
"There are always going to be spills that go unreported in large
part because of the high costs associated with treating them. If a
low-cost, low-tech way of cleaning up pesticide spills can be used as
an alternative, more of them may be reported and dealt with and
that's good for the environment," said Steve Comfort, a University of
Nebraska soil environmental chemist.
As part of ongoing research on ways to clean up soil and
groundwater contaminated with potentially toxic pesticides and
ordnance compounds, Comfort and NU residue chemist Pat Shea recently
struck upon a method of mixing pesticide-contaminated soil with
fine-grained metallic iron and water. This approach can successfully
eliminate up to 99 percent of the contamination, allowing the soil to
be returned to its original site.
The NU Institute of Agriculture and Natural Resources (IANR)
researchers were able to test their treatment method on a large scale
last summer in southwest Nebraska.
The site was a farm cooperative where nearly five years ago an
accidental spill dumped more than 750 gallons of metolachlor into a
clay-lined waste lagoon at the co-op.
Metolachlor is one of the most commonly used farm herbicides in
Nebraska, most often encountered under the "Dual" trade name.
"The water table is shallow at the site and analysis of
groundwater and soil from locations near the lagoon indicated high
potential for groundwater contamination," Comfort said.
After the accidental spill, about 1,000 cubic yards of
contaminated soil were excavated from the lagoon and held at the
site, awaiting either removal or remedial treatment.
"The pesticide concentrations were high enough that they posed a
risk of sustaining groundwater contamination, as well as being
potentially toxic to surrounding plant and animal life," Shea said.
As part of their demonstration project, the IANR research chemists
placed the stockpiled, contaminated soil into long windrows using
common earthmoving equipment and then mixed three times with a
high-speed implement that its manufacturer has trademarked under the
name "microenfractionator." The device combines the actions of
homogenizing the soil, reducing the size of its particles and
aeration. A tractor is used to pull the implement through the
windrows of soil. as part of the treatment process, fine-grained iron
particles are added to the mixing operation, along with water.
"The microenfractionator provided uniform distribution of the iron
within the windrowed soil and helped make the initial pesticide
concentration more uniform," Shea said. The mixed and treated
windrows were then covered with sheets of clear plastic and kept
moist for the next three months.
Following the addition of the iron particles, along with some
other amendments, such as acetic acid and aluminum sulfate, the
metolachlor concentrations in the contaminated soil rapidly
decreased, with chemical destruction rates between 72 and 99 percent
within the first 90 days, said Comfort. Even one day after treatment,
the soil began showing measurable decreases in metolachlor
Not only did the environment benefit from this process, the
potential cost savings are huge.
Using the current, accepted practice of transporting and
incinerating the 2.5 million pounds of contaminated soil would have
cost more than $3.1 million. Using Comfort and Shea's approach was
estimated at less than $65,000, including the labor.
"The iron is the key. It shows the potential to very quickly and
effectively promote the decomposition of a wide variety of
pesticides," said Shea. An added bonus of this method is that people
can be quickly and inexpensively trained to do it, using relatively
inexpensive and readily available machinery and supplies, soil
additives, and techniques.
The IANR Agricultural Research Division research is ongoing and is
being funded and sponsored in part by NU's School of Natural Resource
Sciences and Water Center/Environmental Programs and a grant from the
U.S. Geological Survey.
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