Hazardous radical-coupled transformation products of benzophenone-3 formed during manganese dioxide treatment

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

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.

Hybrid radical coupling during MnO2-mediated transformation of a mixture of organic UV filters: Chemistry and toxicity assessment

Manganese oxide (MnO2) is one of the most abundant metal oxides, and it is renowned for its ability to degrade various phenolic micropollutants. However, under MnO2-mediated transformation, BP-3 transforms into 12 different radical-coupled transformation products (TPs) out of 15 identified TPs. These radical-coupled TPs are reported with adverse environmental impacts. This study explored the effects of MnO2 on organic UV filter mixtures and different water constituents (i.e., bicarbonate ion (HCO3-), humic acid (HA) and halide ions) in terms of degradation efficiency and transformation chemistry. When a mixture of benzophenone-3 (BP-3) and avobenzone (AVO) underwent transformation by MnO2, hybrid radical-coupled TPs derived from both organic UV filters were generated. These hybrid radical-coupled TPs were evaluated by an in silico prediction tool and Vibrio fischeri bioluminescence inhibition assay (VFBIA). Results showed that these TPs were potentially toxic to aquatic organisms, even more so than their parent compounds. The higher the concentration of HCO3-, HA, chloride ion (Cl-) and bromide ion (Br-), the greater the reduction in the efficiencies of degrading BP-3 and AVO. Contrastingly, in the presence of iodide ion (I-), degradation efficiencies of BP-3 and AVO were enhanced; however, iodinated TPs and iodinated radical-coupled TPs were formed, with questionable toxicity. This study has revealed the environmental risks of hybrid radical-coupled TPs, iodinated TPs and iodinated radical-coupled TPs when the organic UV filters BP-3 and AVO are transformed by MnO2.