Aerobic biodegradation of virginiamycin in soil

Aerobic biodegradation of virginiamycin was examined in six different soil types over a 64‐d incubation period. The following test conditions were examined in parallel for each soil type: (1) [ 14 C]virginiamycin at 0.5 mg carbon/50 g soil amended with 9.5 mg carbon as unlabeled glucose/50 g soil; and (2) [ 14 C]glucose at 10 mg carbon/50 g soil was used as the reference chemical. The amounts of 14 CO 2 and [ 14 C]volatile products released upon biodegradation of [ 14 C]virginiamycin and [ 14 C]glucose were collected over the duration of the study. Three of the six soils were extracted at the end of the study, and the extracts were analyzed by HPLC to examine the fate of the parent drug. A mass balance of the applied activity was also determined for each soil type. Virginiamycin was found to biodegrade in each soil type tested, and the calculated mineralization half‐lives ranged from 87 to 173 days for three of the six soils tested with first‐order rate constants of 0.004 to 0.008 day −1 . Despite slow mineralization, extensive breakdown of virginiamycin into a series of minor components aerobically with no single degradation product present at >10% of the initial virginiamycin concentration was observed in the remaining three soils. The mass balance of the applied activity of [ 14 C]virginiamycin was in the range 86 to 101% and that of applied [ 14 C]glucose was 91 to 100%. Based on the results, virginiamycin upon entry into the environment is expected to undergo extensive biotransformation in the presence of soil microorganisms.