Date of Award

8-2017

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Engineering and Earth Sciences

Committee Member

Dr. Cindy Lee, Committee Chair

Committee Member

Dr. Elizabeth Carraway

Committee Member

Dr. Lindsay Shuller-Nickles

Abstract

Pesticides are widely used around the world because, in part, they increase food production, decrease the spread of disease via insects, and protect buildings from damage due to these pests. Chiral pesticides, pesticides which contain molecules that can have at least two stereoisomers, make up about 25% of all pesticides. In order to decrease the mass of pesticides applied to the environment, only the bioactive enantiomer could be marketed as a chiral switch formula; however, if the enantiopure pesticide undergoes enantiomerization in the environment, it would defeat the purpose of marketing such a formula. The goal of this thesis is to elucidate if two chiral pesticides, metalaxyl and malathion, undergo enantiomerization in soil. Soil was collected at Lake Hartwell near Anderson, SC. The soil was characterized for metal oxide content, trace metals, particle size distribution, pH, and organic carbon. Then, the process of enantiomerization was observed under the following conditions for metalaxyl: acid-unsterilized, lime-unsterilized, acid-sterilized, and lime-sterilized. For malathion, enantiomerization was observed under the following conditions: acid-unsterilized, lime-unsterilized at ambient temperatures, and lime-unsterilized at 10°C. Chiral analysis was performed to determine if enantiomerization took place; achiral analysis was performed to determine mass balance. Racemic metalaxyl was found to have no statistically significant change in enantiomeric fraction (EF) over two weeks in any of the treatments listed above, which is consistent with previous research. Metalaxyl-M, the chiral switch formula composed of 97% of the R-enantiomer, showed statistically significant differences in both of the unsterilized treatments, which may be due to the small presence of the (+)-enantiomer, allowing any variation in EF to magnify error and cause a statistically significant difference. There was no evidence of degradation for either formulation over two weeks. The R-enantiomer for malathion demonstrated a statistically significant change in EF on day three in acid-unsterilized soil while the S-enantiomer and racemic mixture did not. There was also evidence of degradation occurring over three days. For the lime-unsterilized treatments in a 10°C environment, statistically significant differences in EF were found in all three incubations over three days. For the lime-unsterilized treatments at ambient temperature, there was a statistically significant change in EF for R-malathion but not for S-malathion. There was evidence of degradation for all incubations in both 10°C and ambient temperatures; however, degradation was much slower for the incubations in the 10°C environment. These observations support the hypothesis that metalaxyl will not undergo enantiomerization in the environment while malathion will.

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