Aerobic biodegradation of (14C)‐sarafloxacin hydrochloride in soil

Abstract

AbstractThe aerobic biodegradation of sarafloxacin hydrochloride, a fluoroquinolone antibiotic registered for use against poultry diseases, was tested in three soils: loam, silt loam, and sandy loam. Sarafloxacin treatment demonstrated mineralization to 14CO2 amounting to 0.58%, 0.49%, and 0.57% in loam, silt loam, and sandy loam soils, respectively, at the termination of the test. The extractability of sarafloxacin from soil in acetonitrile and water (ACN:H2O, 1:1, v/v) was less than 1% of the applied radioactivity. This was followed by extraction with pipemidic acid (a quinolone with structural similarity to sarafloxacin) and KOH (PIP:KOH), which resulted in ∼25% extractability in loam, ∼73% in silt loam, and ∼80% in sandy loam soils, with extractability increasing with decreasing organic matter content (5.8%, 2.5%, and 1.3%, respectively, for the three soils). The high‐performance liquid chromatography (HPLC) analysis of ACN:H2O extractable radioactivity showed several components, all of which were less than 1% of the applied radioactivity. Hence, no attempt was made to characterize these components. The HPLC analysis of PIP:KOH extracts demonstrated two major components, one with a retention time of ∼4 to 5 min (designated polar component), the other component, sarafloxacin, with a retention time of ∼35 min. The components present in ACN:H2O or PIP:KOH extracts were not significantly different at day zero or at termination, prompting experiments that resulted in the following observations. Sarafloxacin standard exposed to extraction solvents (PIP:KOH and ACN:H2O) showed no degradation, suggesting stability of the test article in extraction solvents. Component profiles in sterile soils were similar to those in nonsterile soils, suggesting that the formation of the polar degradate component of sarafloxacin is an abiotic phenomenon. Experiments conducted with sand spiked with sarafloxacin showed very little or no transformation, suggesting that the degradation is a soil‐related phenomenon. The polar component was converted to sarafloxacin when the extracts were subjected to acid hydrolysis.