Adsorption and Degradation of Veterinary Antibiotics in Soils Under Different Redox Conditions.

Widespread application of biosolids to agricultural fields has raised the environmental concern over the risk associated with veterinary antibiotics. The current understanding of these antibiotic compounds in soil is very limited. In this study, experiments were carried to examine the sorption and degradation behavior of tylosin in a biosolids-impacted soil. Six 150-g soil samples with each were mixed with 1500 mL of 0.01 M CaCl₂ solution in a laboratory microcosm. Redox potential of the six microcosms were adjusted and marinated at -200, 50, 150, 300, and 500 mV using air/N2 ratio. A fixed tylosin concentrated was injected into each microcosm, and the suspension was collected from each flask at different time intervals. It was found that the rate of tylosin disappearing (not recovered) was different at different redox potential. The faster rate of tylosin disappearing was observed at 50~300 mV than at -200 and 500 mV. During 1 to 5 days, the greatest loss of tylosin was 45% at 300mv, whereas after 5 days, the greatest loss was 82% at 50 and 150 mV. These results will be compared with those obtained under microbial control using sodium azide, and the implication will be discussed.