Elucidation of colchicine degradation pathways under UVC, UVC/H2O2 and UVC/S2O82- processes: proposed transformation products identification, mechanistic insights and in silico evaluation.

Colchicine (COL), an alkaloid widely consumed during the COVID-19 pandemic, is inefficiently removed by conventional wastewater treatment plants, leading to environmental exposure to the parent compound and its transformation products (TPs). This study evaluated the degradation of COL under UVC, UVC/H2O2, and UVC/S2O82- processes, focusing on degradation kinetics, TPs formation, degradation mechanisms, and toxicological and environmental relevance. Use of UVC achieved over 90% COL removal within 12 min (k = 0.22 min-1), while the oxidant-assisted processes enhanced degradation rates by 2.3 and 2.6 times, involving sulfate (SO4•-) and hydroxyl (HO•) radicals, respectively. Six TPs were identified, including process-specific and isomeric species, some reported for the first time, predominantly formed via O-demethylation, ether bond cleavage, and sulfate radical-mediated oxidation at the amide nitrogen. Photolytic, electron transfer, and hydrogen abstraction mechanisms were proposed. In silico (Q)SAR assessments revealed that all the TPs exhibited higher mobility and similar persistence, compared to COL, suggesting an increased potential for groundwater contamination. Most of the TPs were predicted to be non-biodegradable and inefficiently removed by conventional activated sludge treatment. Several TPs retained carcinogenic potential comparable to COL, particularly those formed under UVC/H2O2 and UVC/S2O82-. Overall, oxidant-assisted UVC processes promoted more effective degradation of both COL and its TPs, compared to photolysis alone.