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 niversity of Arkansas researchers Greg Thoma, Craig
Beyrouty and Duane Wolf think crabgrass deserves more respect.
In fact, the results of their greenhouse study indicate crabgrass
may be able to clean up soils heavily contaminated with petroleum.
 Soils with
oil contamination are a significant environmental problem in
many states, the researchers added, but crabgrass may provide
a low-cost, low-maintenance solution. Heavy oil contamination
typically occurs around oil wellheads, where oil has been extracted
over several years. This contamination produces a hard, black
expanse where little will grow. Thoma, Beyrouty and Wolf are
trying to reclaim this wasteland into a pine forest at a test
site in southern Arkansas.
"The
contaminated soil is asphalt-like," explains Thoma. "It
is hard and black with a thick crust layer covering a gooey,
tar-like substance that can be a foot deep."
However,
because oil is near the surface, relatively immobile, and not
an imminent threat to the environment, it is an ideal candidate
for phytoremediation. In this form of bioremediation, plants
are used to reduce or eliminate the hazards by enhancing naturally
occurring biological processes that decompose oil.
Other forms
of remediation, such as dig-and-haul or incineration, take less
time, but they require constant attention and are very costly.
Phytoremediation is a slow process, but it is low in cost and
requires very little maintenance.
The original
greenhouse study evaluated the germination, survival and growth
of five plant species -- Bermuda, rye, fescue, crabgrass and
alfalfa -- in crude-oil contaminated soils. It also looked at
the effects of several soil amendments, including inorganic fertilizer,
broiler (chicken) litter, paper mill biosolids and hardwood sawdust.
Crabgrass
had a moderate germination rate (78%) and a relatively low survival
rate (64.5%), but the plants that survived grew at a spectacular
rate and produced high root length and biomass. Although broiler
litter had a severe negative impact on germination (46%) and
survival rate (66%) of all plant species, it resulted in increased
biomass and root surface area.
Field study
of these results began at a site in southern Arkansas in January.
This research site is part of the Remediation Technologies Development
Forum (RTDF) Phytoremediation of Organics project. This national
project uses standardized protocols to look at the use of agricultural
and non-crop plants that can degrade petroleum in soil under
various climatic conditions. The 20 research sites range from
Rhode Island to California, Alaska to Arkansas. RTDF is a public-private
partnership funded by the US Environmental Protection Agency.
Beyrouty
and Wolf, professors in the crop, soil and environmental sciences
department, have worked on the greenhouse and field studies.
Thoma, associate professor of chemical engineering, is focusing
on using these data to develop a model that can be used both
as a screening tool and a guide for basic research. The model
will help in deciding if a particular application will work on
a particular site.
"Although
some models already exist, they are all intended for use with
mobile contaminants such as heavy metals, TNT, or pesticides,"
noted Thoma. "Oil and many other contaminants are immobile
and cannot currently be modeled accurately."
Instead
of assuming that the contaminant is drawn toward the plant, Thoma's
model assumes that the plant grows toward the contaminant. The
model that is under development will be environmentally sensitive
and time dependent, using a fractal generator to "grow"
virtual plant roots in virtual soil. Because it allows for modeling
different types of plants and soil contaminants, it will bridge
the gap between different kinds of phytoremediation. For example,
it can be used for modeling grasses growing in petroleum-contaminated
soil or mulberry bushes growing in a variety of contaminants.
Researchers
presented their findings at an invited symposium at Auburn University
on Jan. 21. 
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comp.uark.edu.