Environmental fate and ecotoxicity of diclofenac degradation products generated by photo-assisted advanced oxidation processes

Abstract

Diclofenac (DCF), a widely used non-steroidal anti-inflammatory drug (NSAID), poses environmental concerns due to its persistence, bioaccumulation potential, and transformation into toxic byproducts during oxidative and chlorination processes. This study investigated the photodegradation of DCF, both directly and in the presence of oxidants, to characterize the resulting degradation products and assess their potential environmental impact.The highest efficiency for direct UV photodegradation of DCF was observed at pH 5, while the addition of oxidants significantly accelerated the degradation rate. Among the advanced oxidation processes (AOPs) examined, the H₂O₂/UV system, with a DCF:H₂O₂ molar ratio of 1:30, exhibited the most effective performance in terms of DCF removal and total organic carbon (TOC) reduction. However, ecotoxicity assessments using Alivibrio fischeri, Daphnia magna, and Lemna minor revealed that AOPs generally increased the toxicity of the resulting solutions compared to untreated DCF.Toxicity analyses showed that post-reaction mixtures from AOPs involving NaOCl exhibited the highest toxic effects, consistent with forming specific transformation products identified as highly toxic by ECOSAR modeling. Additionally, the analysis of the physicochemical properties of DCF and its transformation products, including solubility and organic matter affinity, suggests a limited potential for long-range transport. These compounds are more likely to bind to sediments, reducing their mobility in groundwater.