Optimization of nimesulide oxidation via a UV-ABC/H2O2 treatment process: Degradation products, ecotoxicological effects, and their dependence on the water matrix.

Nimesulide (Nim) degradation in ultrapure water (UW) and municipal sewage (MS) via UV-ABC/H2O2 was investigated. The variables included in the experimental design were time, initial Nim, and initial H2O2 concentrations. Resulting decreases in Nim concentration (monitored by high performance liquid chromatography (HPLC) using a photodiode array detector operating at a maximum UV absorbance of 300 nm), mineralization (from total organic carbon (TOC) measurements), and ecotoxicity (assays employing the bioindicators Daphnia similis, Artemia salina, and Allium cepa) were also studied. Degradation rates of 90% or higher were found for 15-20 min reaction times, employing combinations of [H2O2] = 50-150 mg L-1 and [Nim] = 8.5-15 mg L-1 prepared with MS. Mineralization rates of 70% and higher were attained within 60 min of reaction for [Nim] = 15 mg L-1 prepared in MS with [H2O2] = 100 mg L-1. Nim by-products were detected and possible degradation pathways proposed. Ecotoxicity evaluation using A. salina, D. similis, and A. cepa revealed that the treated samples had significantly lower toxicity. Exposure to treated samples resulted in survival rates of 79% for A. salina and over 90% for D. similis. No root growth inhibition was observed in A. cepa exposed to treated samples, whereas exposure to untreated samples inhibited root growth by 60%. Statistical analysis revealed elimination of cytotoxicity and reduction of genotoxicity against A. cepa. The results showed that the UV-ABC/H2O2 process can be employed as a pre- or post-treatment method to remove Nim from contaminated wastewater.