Photodegradation of sulfamethazine, sulfamethoxypiridazine, amitriptyline, and clomipramine drugs in aqueous media

The photochemical transformation of two antibacterial sulfonamides, namely sulfamethazine (SMT) and sulfamethoxypyridazine (SMP), and two tricyclic antidepressants, namely amitriptyline (AMT) and clomipramine (CMP) were investigated. Experiments conducted in river water under artificial sunlight irradiation show an acceleration of the degradation for SMT, SMP, and CMP of a factor 1.6–7.7 by comparison to purified water. This acceleration is, at least partially, due to photosensitized reactions which can occur in river water. The photodegradation of CMP was particularly fast. In addition, no degradation was observed for AMT in purified water while photosensitized reaction occurs. Under ultra-violet (254 nm) irradiation in purified water, the four drugs were degraded. Calculated quantum yields of photodegradation were of 4.3 × 10−3, 5.1 × 10−3, 7.6 × 10−3, and 65.0 × 10−3 respectively for SMT, SMP, AMT, and CMP. UV coupled with hydrogen peroxide (UV/H2O2) was used as an advanced oxidation process for water depollution. The calculated second order rate constants of reaction with hydroxyl radicals were of 5.0 × 109, 5.0 × 109, 8.0 × 109 and 9.5 × 109 L mol−1 s−1 for SMT, SMP, AMT and CMP, respectively. Finally, the structures of photoproducts were proposed according to LC–MS/MS analyses. The elimination of SO2 was the main photochemical process for SMT and SMP. In the case of AMT and CMP, hydration and hydroxylation, respectively, were observed.