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TP5 Ecotoxicity and Environmental Chemistry Antibiotics
(283) Environmental Fate of the Veterinary Antimicrobial Ceftiofur (Excenel®, Naxcel®).
Smolenski, Walter1, Hummel, Bernard1, Lesman, Steven1, 1 Pfizer Animal Health, Kalamazoo, MI, USA
ABSTRACT- Ceftiofur (CF) is a late-generation cephalosporin used solely for veterinary purposes and is the active ingredient in Excenel® and Naxcel®. The fate of antibiotics excreted by food animals is of environmental concern. Degradation of active molecules provides less opportunity for detrimental environmental effects to occur. Ceftiofur residues excreted from cattle are inactive in feces but active in urine. Urine residues become inactive when mixed with feces. Ceftiofur is light sensitive, and aqueous hydrolysis occurs with a 8 day half-life (t) at pH 7. Ceftiofur has a Koc in soil of 276. Methods: For biodegradation studies, 14C-Ceftiofur was added to 4 soils at 5 ppm and incubated at 20°C. Mineralization to 14CO2 was measured, ceftiofur and production of metabolites analyzed by LC/MS. An assay that converted active metabolites including ceftiofur to a common metabolite, desfuroylceftiofur (DFC) and then stabilized by conversion to DFC-acetamide (DCA) was used to measure total active residue. Results: The t of ceftiofur and active metabolites (DCA) ranged from 0.1 to 1.9 h. and 0.2 to 2.4 h, respectively. All radioactive metabolites were transient without accumulation. The ultimate fate of the carbon in the molecule was mineralization to 14CO2. At only 3 days 14CO2 recovery in 3 soils was >12%, and by 120 days mean recovery increased to 54%. The overall mass balance of 14CO2, soil-bound and extractable radioactivity was 99%. Conclusion: Ceftiofur is rapidly inactivated and transformed in aerobic soil systems, and ultimately mineralized to CO2. All metabolites detected were transient and did not accumulate. With the short residence time of the molecule and its metabolites in soil and other environments, the likelihood for environmental effects to occur is low.
Key words: biodegradation, antibiotic, ceftiofur, soil
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