Degradation of venlafaxine using TiO2/UV process: Kinetic studies, RSM optimization, identification of transformation products and toxicity evaluation

The photochemical degradation of the antidepressant drug venlafaxine (VNF) by UV/TiO2 process was investigated in the present study. Prescreening experiments were conducted to study the effects of main parameters affecting the photocatalytic process. In addition, the effects and interactions of most influenced parameters were evaluated and optimized by using a central composite design model and a response surface methodology. Results indicated that VNF was quickly removed in all the irradiation experiments and its degradation was mainly affected by the studied variables (catalyst dose, initial VNF concentration and pH), as well as their interaction effects. Parallel to kinetic studies, the transformation products (TPs) generated during the treatment was investigated using LC coupled to low and high resolution mass spectrometry. Based on identification of the main TPs, tentative transformation pathways were proposed, including hydroxylation, demethylation and dehydration as major transformation routes. The potential risk of VNF and its TPs to aqueous organisms was also investigated using Microtox bioassay before and during the processes. The obtained results showed an increment in the acute toxicity in the first stages and a continuously decreasing after then to very low values reached within 240 min of the photocatalytic treatment, demonstrating that UV/TiO2 can lead to the elimination of parent compound and the detoxification of the solution. (C) 2016 Elsevier B.V. All rights reserved.