Degradation of antibiotic Cephalosporin C in different water matrices by ionizing radiation: Degradation kinetics, pathways, and toxicity

Abstract

Cephalosporin antibiotics are ubiquitous emerging pollutants in various aquatic environments due to their extensive production and application. Herein, the radiolytic degradation of antibiotic Cephalosporin C (CEP-C) in different water matrices was comprehensively investigated using gamma radiation at various experimental conditions. The results revealed that CEP-C oxidation obeyed pseudo first-order kinetics, and 100%, 94.9%, 67.0%, 44.6% and 34.5% removal of CEP-C with 10–200 mg/L was achieved at 0.4 kGy, respectively. The degradation was faster at higher absorbed dose and acidic conditions (pH = 3.5). The inorganic anions, including SO42−, NO3−, and HCO3−, had negative influence on the degradation of CEP-C, the corresponding rate constant decreased from 4.603 to 3.667, 1.677 and 2.509 kGy−1 respectively in the presence of SO42−, NO3−, and HCO3−. The analysis of intermediate products indicated that CEP-C was oxidized to generate about 10 intermediate products. Besides, it was inferred that the thioether sulfur oxidation, β-lactam ring opening, acetyl dissociation from dihydrothiazine ring and D-α-aminohexylamide group abscission were the major reaction mechanisms of CEP-C degradation by gamma radiation. Importantly, the antibacterial activity of CEP-C could be completely vanished by gamma radiation alone, while more toxic intermediate products might be formed. Addition of hydrogen peroxide and peroxymonosulfate could significantly improve the CEP-C degradation, and reduce the toxicity of intermediates of CEP-C degradation. Similar degradation behavior was observed in the groundwater and wastewater, implying that ionizing radiation can be used for degradation of Cephalosporin in water and wastewater.