Degradation kinetics and mechanism of antibiotic ceftiofur in recycled water derived from a beef farm.

Ceftiofur is a third-generation cephalosporin antibiotic that has been widely used to treat bacterial infections in concentrated animal feeding operations (CAFOs). Land application of CAFO waste may lead to the loading of ceftiofur residues and its metabolites to the environment. To understand the potential contamination of the antibiotic in the environment, the degradation kinetics and mechanisms of ceftiofur in solutions blended with and without the recycled water derived from a beef farm were investigated. The transformation of ceftiofur in aqueous solutions in the presence of the CAFO recycled water was the combined process of hydrolysis and biodegradation. The total degradation rates of ceftiofur at 15 °C, 25 °C, 35 °C, and 45 °C varied from 0.4-2.8×10(-3), 1.4-4.4×10(-3), 6.3-11×10(-3), and 11-17×10(-3) h(-1), respectively, in aqueous solutions blended with 1 to 5% CAFO recycled water. Hydrolysis of ceftiofur increased with incubation temperature from 15 to 45 °C. The biodegradation rates of ceftiofur were also temperature-dependent and increased with the application amounts of the recycled CAFO water. Cef-aldehyde and desfuroylceftiofur (DFC) were identified as the main biodegradation and hydrolysis products, respectively. This result suggests that the primary biodegradation mechanism of ceftiofur was the cleavage of the β-lactam ring, while hydrolytic cleavage occurred at the thioester bond. Unlike DFC and ceftiofur, cef-aldehyde does not contain a β-lactam ring and has less antimicrobial activity, indicating that the biodegradation of ceftiofur in animal wastewater may mitigate the potentially adverse impact of the antibiotic to the environment.