Effects of Dissolved Organic Matters on Photodegradation of Two Typical Androgens
|School||Dalian University of Technology|
|Keywords||DOM Androgens Phoyolysis ROS|
Androgens as one kind of typical EDCs are frequently detected in surface waters. Previous studies demonstrated that they could induce biological toxicity and endocrine disrupting effects. Therefore, it is necessary to investigate their environmental behaviors and toxicological effects for evaluating the ecological risk of androgens. Photochemical transformation is an important transformation pathway for organic pollutants in surface waters. The photochemical behaviors of organic pollutants are affected by dissolved organic matter (DOM), which are widely distributed in the water environment. The effects of DOM on the transformation are associated with the structure of compounds and the sources of DOM. In this study, two androgens,17β-trenbolone and testosterone, four commercial DOMs (SRT-、NAHA, LHA、ESHA) and two DOMs extracted from livestock manure are selected to investigate the effects of DOM on the photodegradation of androgens.Photodegradation experiments results show that both of two androgens photodegrade under stimulated sunlight following pseudo first-order kinetics. According to quantum yields measured, the half-lives under natural solar were15-29.4hours and3.64-7.18days for17β-trenbolone and testosterone respectively. The half-lives change over seasonal illumination intensity as the following order:winter> autumn> spring> summer. The photodegradation of testosterone is affected by dissolved oxygen.DOM extracted from livestock manures decreased the photodegradation rates of two androgens through competitive light absorption. All the commercial DOMs inhibit direct photolysis of17β-trenbolone due to light shielding effects. Meanwhile, static state quenching also makes a contribution to the photolysis inhibition of17β-trenbolone by LHA and ESHA. The commercial DOMs could inhibit the photodegradation of testosterone through competitive light absorption, however, indirect photolysis of testosterone also occure in the irradiated solutions with DOMs. Owing to the dual effects by light screening and photosensitization, SRFA and LHA have no obvious effect on the apparent photolysis of testosterone, but NAHA、ESHA accelerate the photodegradation rate of testosterone.Reactive oxygen species (ROS) quencing experiment and EPR results demonstrate that testosterone can undergo photooxidation by hydroxyl radicals and singlet oxygen and photosensitization induced by triplet excited states DOM, and singlet oxygen is the major ROS photogenerated by DOMs.