Beyond degradation: LC-HRMS based tracking of transformation products and toxicity during photocatalytic removal of ceftazidime via advanced oxidation processes

High-resolution mass spectrometry combined with liquid chromatography (LC-HRMS) was employed to comprehensively investigate transformation pathways and transformation products (TPs) formation during the degradation of ceftazidime (CAZ). The degradation of CAZ was investigated using advanced oxidation processes (AOPs), including heterogeneous TiO₂ photocatalysis, MOF-based photocatalysis, and homogeneous treatments with hydrogen peroxide (HP) or persulfate (PS). TiO₂-mediated photocatalysis achieved complete CAZ removal within 60 min, with reaction rates enhanced by increased catalyst loading or oxidant addition, whereas excessive HP concentration slowed degradation. MOF-based photocatalysis showed limited activity, although oxidants improved reaction kinetics. Homogeneous photocatalytic treatments also efficiently degraded CAZ, with higher iron or oxidant concentrations accelerating the process. LC-HRMS analysis enabled the confident elucidation of nineteen TPs, eighteen of which are reported here for the first time for ceftazidime degradation, classified as N-alkylated pyridinium derivatives, aminothiazole-ring derivatives, and alkyl sulfates. Accurate-mass measurements and HRMS-based structural interpretation revealed key transformation pathways during CAZ oxidation. Total organic carbon (TOC) measurements indicated superior mineralization with TiO₂, followed by homogeneous treatments. ECOSAR-based toxicity predictions suggested low ecotoxicity for most TPs, except the parent compound and TP273, which exhibited potential toxicity toward Daphnia magna . Overall, photocatalytic AOPs effectively degrade CAZ and its TPs, with HRMS-supported TP elucidation demonstrating that TiO₂-based heterogeneous photocatalysis providing the highest mineralization and lowest predicted ecotoxicity.