Effects Of Aqueous Dissolved Organic Matters On Photodegradation Of Four Typical Antidepressant Drugs

Antidepressant pharmaceuticals as a new class of pollutants in the environment are detected frequently. Some research work demonstrated that they could induce biological toxicity and disruptive endocrine system, which are harm to human health and ecological system seriously. Therefore, it’s necessary to investigate their environmental behaviors and toxicological effects for evaluating the ecological risk. Photochemical transformation is an important transformation pathway for toxic organic pollutants in surface waters. The photochemical behavior of organic pollutants can be influenced by dissolved organic matters (DOM). In this study, four antidepressant drugs as Bupropion, Citalopram, Sertraline, and Venlafaxine are selected for investigating the photodegradation dynamics and the effects caused by DOM and pH, so as to better understand their environmental photochemical behavior under stimulated sunlight.Photodegradation experiments of four target conpounds show that all drugs could photodegrade under stimulated sunlight, following pseudo first-order kinetics. Except that the behavior of Sertraline is correlated to DO in solutions. According to quantum yields reached by experiments, we calcultate the half-lifives under natural solar as:8.2-21.4d (Bupropion),5.2-13.3d (Citalopram),6.32-15.9y (Sertraline),59.6-145d (Venlafaxine). And products of Bupropion is HO-Bupropion, meanwhile, Bupropion has a photoisomerization process. Photodegradation products of Citalopram are Citalopram N-oxide, methylcitalopram and N-desmethylcitalopram, N-desmethylation is a primary degradation path. Sertraline produced by hydroxylation and desmethylamination. Venlafaxine produced by N-desmethylation and hydroxylation, N-desmethylation is also the primary path.Both Citalopram and Venlafaxine could photolysis in the presence of Suwannee River fulvic acid (SRFA) or humic acid (SRHA), and DOM has much influence on the photodegradation of target compounds. SRFA and SRHA could stimulate photodegradation of Venlafaxine, as well as the effect of SRHA is stronger than SRFA. SRHA could restrain photodegradation of Citalopram, owing to it has dual effects by light masking or photosensitization, light masking being more effective.The effects of SRFA and SRHA on the photodegradation of Bupropion at different pH were investigated by simulated sunlight experiments. The results show that Bupropion photodegrades faster in the presence of either SRFA or SRHA. However, the effects of the two DOM are dependent on solution pH. In the pH range5~9, Bupropion can undergo photooxidation and photosensitization induced by hydroxyl radicals and triplet excited states DOM, respectively, which are photogenerated by DOM. At pH>9, photosensitization is the major transformation pathway of Bupropion. The role of singlet state oxygen can be neglected. The photosenatizing ability of3SRHA*to Bupropion is stronger than that of3SRFA*.