Concentration-dependent photodegradation kinetics and hydroxyl-radical oxidation of phenicol antibiotics

Thiamphenicol and florfenicol are two phenicol antibiotics widely used in aquaculture and are ubiquitous as micropollutants in surface waters. The present study investigated their photodegradation kinetics, hydroxyl-radical ((OH)-O-.) oxidation reactivities and products. Firstly, the photolytic kinetics of the phenicols in pure water was studied as a function of initial concentrations (C-0) under UV-vis irradiation (lambda > 200 nm). It was found that the kinetics was influenced by C-0. A linear plot of the pseudo-first-order rate constant vs C-0 was observed with a negative slope. Secondly, the reaction between the phenicol antibiotics and (OH)-O-. was examined with a competition kinetic method under simulated solar irradiation (lambda > 290 nm), which quantified their bimolecular reaction rate constants of (2.13 +/- 0.02) x 10(9) M-1 s(-1) and (1.82 +/- 0.10) x 10(9) M-1 s(-1) for thiamphenicol and florfenicol, respectively. Then the corresponding (OH)-O-. oxidated half-lives in sunlit surface waters were calculated to be 90.5-106.1 h. Some main intermediates were formed from the reaction, which suggested that the two phenicols underwent hydroxylation, oxygenation and dehydrogenation when (OH)-O-. existed. These results are of importance to assess the phenicol persistence in wastewater treatment and sunlit surface waters. (C) 2014 Elsevier Ltd. All rights reserved.