PhD defense: Kiranmayi Mangalgiri

Kiranmayi Mangalgiri PhD Defense

Date: Tuesday, April 25th
Time: 1:00 pm
Location: Commons 329

Dissertation Title:  Photolytic Fate of Antibiotics in UV-based Engineered and Natural Systems

Abstract:

Antibiotics are used at high doses as feed additives in poultry operations. However, most of the antibiotics ingested by poultry are excreted unchanged. Since poultry litter is land applied as a fertilizer, antibiotics are introduced into the environment. However, the photolytic fate of antibiotics is not well characterized in agricultural systems. This dissertation was designed to address two objectives: (i) to characterize photodegradation of antibiotics in UV-based engineered systems; and, (ii) to determine the photolytic fate of antibiotics in agriculturally-relevant natural systems.

A critical review on the detection, fate, and toxicity of organoarsenical antibiotics, a relatively understudied group of feed additives in the poultry industry, justified the need to conduct photodegradation studies for this unique class of antibiotics. Irradiation experiments and UV-H2O2 treatment at 253.7 nm for two organoarsenicals, roxarsone and nitarsone, produced the pseudo-first-order fluence-based rate constants in the range of 5.30-29.7×10-5 cm2 mJ-1, and second-order rate constants for reaction with hydroxyl radicals as 3.40 (±0.45)×109 and 8.28(±0.49)×108 M-1 s-1 for roxarsone and nitarsone, respectively. Bicarbonate and dissolved organic matter (DOM) from poultry litter affected the transformation efficiency, and inorganic arsenic was detected as a major byproduct.

The role of DOM at elevated concentrations was evaluated for photolysis of four representative antibiotics at 310 - 410 nm. The dominant mechanism for ciprofloxacin degradation was direct photolysis; degradation of roxarsone, chlortetracycline, and sulfamethoxazole was sensitized to varying degrees as a function of DOM content and source due to generation of reactive species. A parallel factor analysis of fluorescence excitation emission matrices was used to describe the fate of DOM in engineered and natural systems. Four components, microbial humic-like, terrestrial humic-like, tyrosine-like, and tryptophan-like fluorescence signatures were identified. In general, the tryptophan-like component was more reactive than the humic-like components. The tyrosine-like component was recalcitrant throughout all treatment strategies. These components may be used to benchmark changes in fluorescent DOM during treatment of agricultural waste.

This dissertation reports critical knowledge on the complex photochemical fate of antibiotics in agriculturally-impacted waters for UV-based treatment processes, oxidation systems, and natural processes. The information reported here will help address public health concerns over the spread and development of antibiotic resistance.