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.

甲砜霉素和氟苯尼考是两种在水产养殖中广泛使用的氯霉素类抗生素，在地表水中作为微污染物普遍存在。本研究调查了它们的光降解动力学、羟基自由基（·OH）氧化反应活性及产物。首先，在紫外 - 可见光照（λ>200 nm）下，研究了氯霉素类在纯水中的光解动力学随初始浓度（C₀）的变化。发现动力学受C₀影响，拟一级速率常数与C₀的线性关系图呈现负斜率。其次，在模拟太阳光照（λ>290 nm）下，采用竞争动力学方法研究了氯霉素类抗生素与·OH之间的反应，确定了甲砜霉素和氟苯尼考的双分子反应速率常数分别为(2.13±0.02)×10⁹ M⁻¹ s⁻¹和(1.82±0.10)×10⁹ M⁻¹ s⁻¹。然后计算出在阳光照射的地表水中相应的·OH氧化半衰期为90.5 - 106.1小时。反应形成了一些主要中间体，这表明当存在·OH时，这两种氯霉素发生了羟基化、氧化和脱氢反应。这些结果对于评估氯霉素类在废水处理和阳光照射的地表水中的持久性具有重要意义。（C）2014爱思唯尔有限公司。保留所有权利。