Effects of veterinary antibiotics on atrazine degradation in soi

The presence of veterinary antibiotics (VAs) in manure applied to agricultural lands may decrease agrichemical degradation by inadvertently altering soil microbial communities or function. Reduced soil microbial degradation of the commonly used herbicide atrazine (ATZ) could increase frequency of detection and concentration of ATZ in water resources. Therefore, the objectives of this study were to investigate the influence of two VAs, sulfamethazine (SMZ) and oxytetracycline (OTC), on ATZ degradation and activities of the soil microbial enzymes dehydrogenase (DH) and beta- glucosidase (beta-glu) in soil and soil amended with 5% swine manure. Sandy loam soil and swine manure were used to conduct two side-by-side incubation experiments, one to analyze for 14C-ATZ degradation and the other to measure enzyme activity (no radio-labeled ATZ). Samples were incubated in the dark at 25°C and destructively sampled over a 96 day incubation period. No significant differences between treatments in the soil incubation study were observed for the quantity of ATZ remaining in soil. The distribution of ATZ and its metabolites remaining in the soil were slightly, but not significantly different. After 96 days, approximately half as much ATZ was mineralized to 14CO 2 in samples treated with 100 mug SMZ kg-1 relative to the ATZ only control. The apparent half-life of ATZ in the soil incubation experiment ranged from 10.6 to 13.5 days.;The addition of manure dramatically changed the behavior of ATZ in soil. In the presence of manure, ATZ degradation decreased by nearly 20% and increased the half-life of ATZ by approximately 20 days. The addition of manure resulted in over 50% more ATZ remaining, a reduction in DDA by nearly half, and the complete absence of DEA in soil. Atrazine mineralization was reduced by nearly 50% in manure-amended soil. However, the VA treatment did not significantly affect ATZ degradation in manure-amended soil. beta-glu activity was significantly influenced by VA type and concentration in the soil incubation study; the least overall beta-glu activity was observed in 100 mug kg-1 SMZ treated soil and the greatest activity was observed in 100 mug kg -1 OTC treated soil. beta-glu activity was repressed in manure-amended soils and elevated in VA treated soils (no ATZ or manure) relative to the ATZ only control. Veterinary antibiotics did not significantly influence DH activity in soil, yet the addition of manure stimulated DH activity. A complicated interaction effect between treatment and time was observed for both beta-glu and DH enzymatic activity in soil and manure amended soil. Microbial turnover, utilization of manure, VAs, and ATZ as carbon sources, as well as sensitivity of different groups within microbial consortia to ATZ/VAs are possible explanations for the interaction of treatment and time. It appears the application of VAs to agricultural fields does not significantly reduce ATZ degradation in soil at the investigated concentrations. However, the input of manure significantly increased the length of time ATZ will remain in soil. Further research investigating different VA types and concentrations, additional manure sources, and ATZ adapted soils is warranted. The results of this research will influence management decisions which could mitigate negative impacts associated with ATZ and VA co-application to soils.