Photodegradation of gemfibrozil in aqueous solution under UV irradiation: kinetics, mechanism, toxicity, and degradation pathways

The lipid regulator gemfibrozil (GEM) has been reported to be persistent in conventional wastewater treatment plants. This study investigated the photolytic behavior, toxicity of intermediate products, and degradation pathways of GEM in aqueous solutions under UV irradiation. The results demonstrated that the photodegradation of GEM followed pseudo-first-order kinetics, and the pseudo-first-order rate constant was decreased markedly with increasing initial concentrations of GEM and initial pH. The photodegradation of GEM included direct photolysis via 3GEM* and self-sensitization via ROS, where the contribution rates of degradation were 0.52, 90.05, and 8.38 % for ·OH, 1O2, and 3GEM*, respectively. Singlet oxygen (1O2) was evidenced by the molecular probe compound, furfuryl alcohol (FFA), and was identified as the primary reactive species in the photolytic process. The steady-state concentrations of 1O2 increased from (0.324 ± 0.014) × 10−12 to (1.021 ± 0.040) × 10−12 mol L−1, as the initial concentrations of GEM were increased from 5 to 20 mg L−1. The second-order rate constant for the reaction of GEM with 1O2 was calculated to be 2.55 × 106 M−1 s−1. The primary transformation products were identified using HPLC-MS/MS, and possible photodegradation pathways were proposed by hydroxylation, aldehydes reactions, as well as the cleavage of ether side chains. The toxicity of phototransformation product evaluation revealed that photolysis potentially provides a critical pathway for GEM toxicity reduction in potable water and wastewater treatment facilities.