Degradation of antibiotic cephalosporin C in aqueous solution and elimination of antimicrobial activity by gamma irradiation

The serious threat of antimicrobial resistance to human health and ecological environment has aroused the development of potential technologies to abate antibiotics from aqueous solution. This work shows that ionizing irradiation was efficient to degrade the broad-spectrum beta-lactams antibiotic, cephalosporin C (CEP-C) in aqueous solution and eliminate the antimicrobial activity. As exposed to gamma irradiation, a complete removal of CEP-C was achieved at 0.4-2.0 kGy with the initial CEP-C concentrations of 0.02-0.2 mM, while the TOC reduction at 2 kGy reached 5-28%. The CEP-C degradation rate declined with increasing the initial CEP-C concentrations and maintained at the similar levels in the pH range of 3.5-9.5. The rate constant of CEP-C degradation was reduced by around 2.2 times in the presence of t-BuOH, suggesting that (OH)-O-center dot is mainly responsible for CEP-C degradation. The intermediates formed did not exhibit the antimicrobial activity. Positive correlation between the CEP-C removal and the loss of antimicrobial activity against S. aureus and E. coli was observed in both deionized water and underground water. However, the acute toxicity increased until 5 kGy and declined with further increasing the absorbed doses. Byproducts with opened beta-lactam ring and dihydrothiazine ring, as well as formic acid, acetic acid and sulfate were detected, indicating that the active position of CEP-C was destroyed by gamma irradiation.