Optimized Photo-Fenton degradation of psychoactive pharmaceuticals alprazolam and diazepam using a chemometric approach—Structure and toxicity of transformation products

Highlights: • Degradation of benzodiazepines Alprazolam and Diazepam using Photo-Fenton. • Central composite design for process optimization. • Identification of transformation products with LC–MS/MS. • Toxicity abatement and mineralization study. The objectives of the present study were: a) to evaluate the photocatalytic degradation of two benzodiazepine pharmaceuticals, alprazolam and diazepam, using Photo-Fenton, b) to optimize the experimental parameters through a central composite experimental design, c) to assess their mineralization and toxicity variations and d) to identify the transformation products during the process and to propose transformation pathways. Response Surface Methodology proved to be a useful tool for the optimization of the degradation process as the statistical coefficients (R² = 0.967 for alprazolam and R² = 0.929 for diazepam) showed satisfactory values confirming the adequate correlation between the predicted models and experimental values. Two sets of experimental conditions were proposed taking into consideration criteria related to the reaction rate and the minimum use of iron. Toxicity of the system varied with time after the treatment, indicating the gradual production of transformation products which differ in their toxic potential. Fifteen and twenty-three photocatalytic degradation products were identified for ALP and DZP respectively using LC-(ESI)MS/MS. In the case of ALP, the main degradation reactions included, phenyl-group removal and the opening of the 7-membered ring, while for DZP, degradation occurred through hydroxylation, formation of benzophenone and the opening of the 7-membered cyclic group.