Degradation of anticancer drug capecitabine in aquatic media by three advanced oxidation processes: Mechanisms, toxicity changes and energy cost evaluation

Abstract

Degradation of capecitabine was conducted using electrochemical oxidation, UV/H2O2 oxidation, and ozonation. Capecitabine was efficiently degraded by three advanced oxidation processes. The degradation rates of capecitabine achieved approximately 99.0% after 4 min of ozonation, 12 min of electrochemical oxidation, and 30 min of UV/H2O2 oxidation. The mineralization rate obtained was merely 10.3% for ozonation at 60 min, compared to 91.7% for electrochemical oxidation and 55.3% for UV/H2O2 oxidation. Capecitabine was degraded by oxidation, defluorination, hydrogenation, hydrolysis, ring and bond cleavage. Thus, multiple intermediates were generated during the degradation process, such as F-, formic acid, acetic acid, oxalic acid, and other intermediate metabolites with lager molecules. A total of eighteen metabolites, except for F- and carboxylic acids, were identified by QTOF-HRMS, where six of them could only be detected by the electrochemical oxidation process, two of them were by the UV/H2O2 oxidation process, and one of them by the ozonation process. Electrochemical oxidation was the only process that could achieve over 90% removal of cytotoxicity and genotoxicity, and the metabolites were non-genotoxic after 60 min of reaction. The number of live cells decreased with the increasing reaction time in ozonation, demonstrating the higher toxicity of the intermediates in ozonation. Energy cost evaluation results suggested that the lowest energy consumption was achieved at 1.8 kWh/m3 for 90% of capecitabine degradation with the O3 dosage of 250 mg/h. Energy consumptions for 50% removal of cytotoxicity were 21.3 and 6.3 kWh/m3 in electrochemical oxidation and UV/H2O2 oxidation, respectively. The highest energy cost for 50% of genotoxicity removal was observed in electrochemical oxidation, while ozonation was identified as the most cost-effective process.