The importance of reactive oxygen species on the aqueous phototransformation of sulfonamide antibiotics:kinetics, pathways, and comparisons with direct photolysis

Ge, Linke and Zhang, P. and Halsall, C. and Li, Y. and Chen, C.-E. and Li, J. and Sun, H. and Yao, Z. (2019) The importance of reactive oxygen species on the aqueous phototransformation of sulfonamide antibiotics:kinetics, pathways, and comparisons with direct photolysis. Water Research, 149. pp. 243-250. ISSN 0043-1354

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Abstract

Sulfonamide antibiotics (SAs) are increasingly detected as aquatic contaminants and exist as different dissociated species depending on the pH of the water. Their removal in sunlit surface waters is governed by photochemical transformation. Here we report a detailed examination of the hydroxyl radical (•OH) and singlet oxygen (1O2) mediated photooxidation of nine SAs: sulfamethoxazole, sulfisoxazole, sulfamethizole, sulfathiazole, sulfamethazine, sulfamerazine, sulfadiazine, sulfachloropyridazine and sulfadimethoxine. Both •OH and 1O2 oxidation kinetics varied depending on the dominant protonated states of the SA in question (H2SAs+, HSAs0 and SAs−) as a function of pH. Based on competition kinetic experiments and matrix deconvolution calculations, HSAs0 or SAs− (pH ∼5–8) were observed to be more highly reactive towards •OH, while SAs− (pH ∼8) react the fastest with 1O2 for most of the SAs tested. Using the empirically derived rates of reaction for the speciated forms at different pHs, the environmental half-lives were determined using typical 1O2 and •OH concentrations observed in the environment. This approach suggests that photochemical 1O2 oxidation contributes more than •OH oxidation and direct photolysis to the overall phototransformation of SAs in sunlit waters. Based on the identification of key photointermediates using tandem mass spectrometry, 1O2 oxidation generally occurred at the amino moiety on the molecule, whereas •OH reaction experienced multi-site hydroxylation. Both these reactions preserve the basic parent structure of the compounds and raise concerns that the routes of phototransformation give rise to intermediates with similar antimicrobial potency as the parent SAs. We therefore recommend that these phototransformation pathways are included in risk assessments concerning the presence and fate of SAs in waste and surface waters. © 2018 The Authors

Item Type:
Journal Article
Journal or Publication Title:
Water Research
Uncontrolled Keywords:
/dk/atira/pure/subjectarea/asjc/2300/2311
Subjects:
ID Code:
129423
Deposited By:
Deposited On:
18 Dec 2018 01:01
Refereed?:
Yes
Published?:
Published
Last Modified:
29 Oct 2020 08:32