Degradation pathways and in silico ecotoxicity assessment of meropenem by-products generated by electrochemical oxidation

Hospital effluents are a recognized source of recalcitrant antibiotics, such as meropenem (MRP), a last-resort carbapenem whose environmental occurrence poses significant risks to antimicrobial resistance. Although electrochemical oxidation effectively removes such compounds, the fate of the transformation products (TPs) generated during treatment and their ecotoxicological implications remain largely unexplored. This study investigates the electrochemical degradation of MRP in synthetic hospital wastewater using boron-doped diamond (BDD) and mixed-metal oxide (MMO) anodes at varying current densities. BDD anodes achieved complete MRP removal within 10–30 min and TOC reductions above 67% at 50 mA cm −2 , driven predominantly by surface-generated hydroxyl radicals, as confirmed by radical scavenger experiments. In contrast, MMO anodes showed lower mineralization efficiency and greater accumulation of chlorine species and chloramines. High-resolution LC-ESI-QTOF-MS enabled the identification of twenty TPs (P1-P20) and the proposal of a comprehensive degradation pathway involving β-lactam ring opening, dehydrogenation, side-chain cleavage, C-S bond scission, and progressive fragmentation to low-molecular-mass products. In silico ecotoxicity screening using ECOSAR and T.E.S.T. suggested that most TPs are predicted to fall within lower toxicity categories for aquatic organisms, with limited bioaccumulation and mutagenicity potential, whereas a few mid-chain intermediates were predicted to display comparatively higher toxicity associated with conjugated electrophilic motifs. Overall, BDD-based electrochemical oxidation steered MRP transformation towards products with predicted equal or lower ecotoxicological concern, suggesting potential for the treatment of carbapenem-containing hospital effluents. This work is distinguished by its integrated assessment of electrode-specific degradation behaviour, transformation products, chloramine speciation, and predicted ecotoxicological risks during meropenem treatment in synthetic hospital wastewater.