Light-Source-Dependent Effects of Main Water Constituents on Photodegradation of Phenicol Antibiotics: Mechanism and Kinetics

Abstract

Thiamphenicol and florfenicol are two phenicol antibiotics commonly used in aquaculture. Photodegradation experiments on these phenicols were performed in aqueous solutions under irradiation of different light sources. We found under UV-vis irradiation (lamda >200 nm) they photodegraded the fastest in seawater, followed by pure water and freshwater, whereas under solar or simulated sunlight (lamda >290 nm), they photodegraded in freshwater only. The effects of Cl- (the dominant seawater constituent), humic acids (HA, main constituents in freshwater) and other water constituents on the photodegradation of the antibiotics as a function of different light sources were studied so as to interpret the light-source-dependent effects of different waters. Under UV-vis irradiation, Cl- was found to promote singlet oxygen ((1)O2) formation and accelerated the photodegradation of phenicols, whereas the phenicols did not photolyze under simulated solar irradiation, irrespective of Cl-. In contrast, the presence of HA inhibited phenicol photolysis under UV-vis irradiation through competitive photoabsorption, but HA photosensitized degradation under simulated solar irradiation. Under UV-vis irradiation, the wavelength-averaged (200-290 nm) quantum yields for thiamphenicol and florfenicol in pure water were 0.022 +/- 0.001 and 0.029 +/- 0.001, respectively. Their solar photolytic half-lives in freshwater were 186 +/- 17 h and 99 +/- 16 h, respectively. UV-vis photodegradation intermediates were identified by HPLC-MS/MS, and degradation pathways were proposed. These involve photoinduced hydrolysis, dechlorination, self-sensitized photo-oxidation processvia (1)O2, and chlorination. These results are of importance toward the goal of assessing the persistence of phenicols in wastewater treatment and the environment.

Photodegradation of sulfapyridine under simulated sunlight irradiation: Kinetics, mechanism and toxicity evolvement

“…Although HA could also enhance the photodegradation as a photosensitizer (Hassett, 2006;Vione et al, 2006;Zhan et al, 2006), the result of this experiment indicated that photosensitization might be secondary to the SPY degradation. This was corresponded with previous studies that HA could bring about light attenuation (Dimou et al, 2004(Dimou et al, , 2005Ge et al, 2009). …”

“…S5 and S6. SPY could undergo three reactions on basis of the product identifications: photoinduced hydrolysis, photo-oxidation and desulfonation, which are also common reaction types for the photodecomposition of other compounds (Ge et al, 2009;Trovó et al, 2009). The photooxidation reaction mediated via 1 O 2 generated product VI, which was transformed into VII through reduction process.…”

“…Antibiotics are a class of commonly used PPCPs used as human and veterinary medicine. Due to their pseudo-persistent nature and potential to cause antibiotic resistant bacteria and genes (Baran et al, 2006;Zhang et al, 2013;Guo et al, 2013), it is imperative to study the fate and transport of antibiotics and their impacts in the natural environment (Ge et al, 2009(Ge et al, , 2010Guo et al, 2013).…”

“…Nitrate in surface water can mediate the formation of Å OH and oxidize organic pollutants (Brezonik and Fulkerson-Brekken, 1998), however, this process has been reported to be of no help for the elimination of sulfonamides (Trovó et al, 2009). Dissolved organic matter (DOM) in nature water can promote the indirect photolysis by direct energy transference or by producing oxidants such as Å OH, HOO=O À 2 , 1 O 2 , and also can inhibit the indirect photolysis for scavenging reactive oxygen species (ROS) or competitive light absorption (Fisher et al, 2006;Ge et al, 2009;Guerard et al, 2009). Bicarbonate has been documented to affect the photodegradation of PPCPs for the yield of CO ÀÅ 3 due to reaction with Å OH, which is reactive for the easily oxidized substrates via one-electron oxidation and also can inhibit the photodegradation process of many organic pollutants (Feng and Nansheng, 2000;Lam and Mabury, 2005).…”

Degradation of the antibiotic sulfamonomethoxine sodium in aqueous solution by photo-Fenton oxidation

“…However, many factors will affect the degradation efficiency of organic pollutants in the photo-Fenton system, including pH, temperature, and the concentrations of H 2 O 2 , Fe 2+ , Cl  , dissolved organic matter (DOM) and contaminations [27,30].…”