Date of Award

12-2008

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Environmental Engineering and Science

Advisor

Kendall, Treavor A

Committee Member

Lee , Cindy M

Committee Member

Carraway , Elizabeth R

Abstract

Determining the occurrence and potential adverse effects of antibiotic pharmaceuticals released into the environment is a critical step towards responsible environmental stewardship. Under aqueous conditions typically found in soils and natural waters, the antibiotic agent sulfamethoxazole (SMX) was transformed in the presence of pyrolusite MnO2 via oxidative pathways. At least 50% loss of SMX was observed after 269 hr in acidic and basic solutions (pH 3-9). A maximum of 100% loss was recorded at pH 3 and 66% loss was recorded at circumneutral pH. Concomitantly, aqueous manganese concentrations increased to around 10 µM at pH 3 and 2 µM at pH 6 over the same time period which suggests an oxidative transformation associated with the mineral surface. Initial pseudo-first order reaction rate constants (kinit) increase with decreasing pH from 0.0039 hr-1 at pH 9 to 0.019 hr-1 at pH 3. HPLC results showed similar transformation products at different pH values. Mass spectrometry of the reaction products collected at pH 3 and 4 confirm an oxidative pathway by which oxidation and hydroxylation occurs at the aniline moiety and isoxazole ring of SMX, and hydrolysis occurs at the sulfonamide moiety. Transformation kinetics of SMX on the surface of manganite was also studied. The initial transformation of SMX on manganite was faster than on pyrolusite at pH 4 to 9; however, at pH 3, the transformation rate was much slower. The observed transformation of SMX by manganese oxides suggests that this ubiquitous component of soils and sediments likely plays an important role in the fate of this antibiotic agent in the environment.

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