Photochemical environmental persistence of venlafaxine in an urban water reservoir: A combined experimental and computational investigation.

The photochemical behavior of venlafaxine (VNX) in surface water was investigated using a hybrid theoretical-experimental-kinetic modeling approach. In addition to the direct photolysis quantum yield, the rate constants of the reactions between VNX and reactive photo-induced species (hydroxyl radicals, HO·; singlet oxygen, 1O 2 ; and triplet excited states of chromophoric dissolved organic matter, 3CDOM*) in sunlit water were measured under simulated solar radiation using competition kinetics. To elucidate possible degradation products, first-principles calculations were applied, followed by toxicity estimation by quantitative structure-activity relationship (QSAR) calculations. Furthermore, kinetic simulations of VNX persistence in an urban water reservoir of the São Paulo Metropolitan Region, Brazil, were performed. The results indicate low direct photolysis of VNX, with Φ VNX = (1.06 ± 0.18) × 10−2 mol Einstein−1. The measured values of the second-order reaction rate constants are k VNX, 3CDOM* = (3.98 ± 0.28) × 109 L mol−1 s−1 and k VNX,1O2 = (2.09 ± 0.17) × 107 L mol−1 s−1, which are lower than k VNX, HO· obs = (6.92 ± 0.37) × 109 L mol−1 s−1 and k VNX, HO· theo = 4.98 × 109 L mol−1 s−1. O-desmethylvenlafaxine, the most thermodynamically stable metabolite predicted by theoretical calculations, revealed potentially greater toxicity and, therefore, higher environmental risk to aquatic ecosystems. The estimated half-lives for VNX range from 9 to 62 days, depending on the season, local weather conditions and water quality parameters, the effects of which can be satisfactorily simulated with the aid of the modified photochemical fate model proposed in this work. [Display omitted] [ABSTRACT FROM AUTHOR]