Evaluation of prairie grasses for reducing the environmental impact of herbicide contamination
The primary goal of this dissertation was to evaluate the use of prairie grasses for reducing the environmental impact of herbicides. Studies included: use of prairie grasses as a phytoremediation tool for contaminated soil; comparison of grass species for use in vegetative buffer strips; fate of 14C-pendimethalin in vegetated and unvegetated soil; and environmental hazards of pendimethalin contaminated soil.;Throughout this dissertation, evidence was presented that prairie grasses can increase the dissipation rate of herbicides. In one study, 78% less metolachlor and 39% less pendimethalin remaining in vegetated treatments as compared to unvegetated treatments. In a separate study, the presence of nearly all grasses tested, but specifically the prairie grasses, resulted in greater degradation of atrazine and metolachlor in rhizosphere soil as compared to unvegetated soil. Phytoremediation mechanisms likely involve plant uptake and increased soil degradation.;Prairie grasses were also shown to decrease movement of pesticides both through the soil column and into biota, thus serving as a phytostabilization agent. Nearly 20% of the metolachlor in unvegetated columns leached out of the bottom of the column after application of an artificial "rain event", while only 5% leached out of vegetated columns. It was also shown that even though vegetated columns allowed infiltration of artificial surface runoff at a much faster rate, the total amount of herbicide moving through the column was held constant, and the amount leaching through after initial applications of herbicide was reduced. Additionally, the presence of vegetation decreased the bioavailability of pendimethalin as measured by earthworm uptake and toxicity to lettuce seedlings.;Pendimethalin residues are very persistent and are likely to be present at some level following bioremediation. Therefore, a hazard evaluation was performed to determine tolerable soil concentrations of pendimethalin that could remain without risk to the biota in the environment. Even low levels of pendimethalin, 10mg/kg or less, were shown to have toxic effects on plants and earthworms, and concentrations as low as 30 mg/kg were shown to have potentially toxic effects through trophic transfer. Thus remediation would need to continue until pendimethalin is reduced to field application levels (10 mg/kg) or less.