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
eighteen TPs, seventeen 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 measure-
ments and HRMS-based structural interpretation revealed key transformation pathways during CAZ oxidation.
Total organic carbon (TOC) measurements indicated superior mineralization with TiO₂, followed by homoge-
neous 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 het-
erogeneous photocatalysis providing the highest mineralization and lowest predicted ecotoxicity.