Effects Of Surfactants On Photodegradation Of Oxytetracycline In Water

Antibiotics have been frequently detected in different environmental media(such as soils, waters, sediment) and biological samples due to their wide use as human and veterinary medicine and in aquacultures, becoming one type of emerging pollutants. In surface waters, photochemical degradation is the predominant degradation pathway for antibiotics and is affected by dissolved components in water. Surfactants have hydrophilic and hydrophobic groups and have some specific properties(e.g. they can decrease surface tension of aqueous solution). Surfactants are used in household detergents, personal care products, textile, food, architecture and pharmaceutical field, etc. Surfactants are discharged into the environmental water bodies via various ways, may coexist with antibiotics and affect the transformation behavior of antibiotics in water. Up to now, effects of surfactants on the photodecomposition of antibiotics are scarely studied, and the reaction mechanisms are poorly understood.In this study, effects of four surfactants (CTAB, SDBS, SDS and Tween80) on the photodegradation of oxytetracycline(OTC) were studied. It was found that under simulated solar irradiation, photodegradation reactions of OTC in pure water and surfactant solutions at pH7.5all followed the pseudo-first-order kinetics and apparent photodegradation rate constants of OTC in CTAB, SDBS, SDS and Tween80solutions were0.0146,0.0054,0.0048and0.0035min-1, which were1.35～5.62times that in pure water (0.0026min-1). Quantum yields of OTC in CTAB, SDBS, SDS and Tween80solutions were1.89～6.36times that in pure water. CTAB could enhance the photolysis of OTC most distinctly. With the increase of CTAB concentrations and pH, OTC could photodegrade more quickly. Under alkaline conditions, CTAB facilitated the photolysis of OTC, while CTAB didnt enhance the photodegradation of OTC under acid conditions. Due to the different dissociation species of OTC at different pH and CTAB being cationic, CTAB might influence the photodegradation of OTC through electrostatic interactions between CTAB and OTC. Under natural sunlight, CTAB could improve the photodegradation of OTC both in pure and fresh water, which indicated that in real environment the coexistence of surfactants might have influences on the photolysis of OTC.Reactive oxygen species (·OH,1O2, etc.) quenching or sensitization experiments indicated that OTC can react with singlet oxygen(1O2). but concentrations of1O2and hydroxyl radical(·OH) generated by the photolysis of OTC were low, which made little contribution on the photodegradation of OTC. CTAB accelerated the photodegradation of OTC not by generating ROS (.OH,1O2). However, the existence of CTAB is in favor of the reaction of OTC with1O2and O2. This study can help understand the photochemical behavior of OTC with the coexistence of surfactants and provide some information for the environmental risk assessment of antibiotics.