Oxidative transformation of oxcarbazepine by Cl₂, ClO₂ and O₃: characteristics and pathways

In this research, the degradation efficiency, mechanism and intermediates’ toxicities of oxcarbazepine (OXC) upon chlorination, chlorine dioxide oxidation and ozonation were investigated. Results showed that three degradation approaches followed second-order kinetics, and ozonation had the highest removal efficiency both of OXC and dissolved organic carbon (DOC). Reaction intermediates were evaluated by ultra performance liquid chromatography in combination with time-of-flight mass spectrometry (UPLC-Q-TOF-MS). Totals of 11, six and 10 intermediates were detected during the oxidation processes of chlorination, chlorine dioxide oxidation and ozonation, respectively. Although three oxidation approaches had similar pathways in N-heterocyclic ring cleavage and reorganization, ozonation was much more focused on attacking by hydroxyl radicals (OH^•), while chlorination had significant Cl-substitution by-products. Chlorine dioxide oxidation brought about fewer degradation by-products than the other two approaches. The above-mentioned oxidation intermediates according to EPA TEST were predicted to be more toxic than OXC, especially those from chlorination. Further test results of the eco-toxicities of oxidized mixtures to the bioluminescent marine bacterium Vibrio fischeri demonstrated the chlorinated samples could lead to the accumulation of toxic transformation products, while chlorine dioxide oxidation and ozonation had detoxication impacts during these processes.