FAYETTEVILLE, Ark. — University 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 U.S. 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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