Effect of Veterinary Antibiotics On Atrazine Degradation.

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 and oxytetracycline, on ATZ degradation in soil and activities of the soil microbial enzymes dehydrogenase and β-glucosidase. A sandy loam soil was collected from a fallow field (0-10 cm depth) that had not received ATZ application for at least 25 years. This soil was 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); ATZ was added to all samples to achieve an initial concentration of 500 mg/kg. Sulfamethazine (SMZ) or oxytetracycline (OTC) was added to the soil directly through solution addition or via incorporation of VA amended swine manure at  initial concentrations of 100 mg/kg (manure and non-manure experiments) and 1000 mg/kg (non-manure experiment).  Samples were incubated in the dark at 25^oC and destructively sampled after 0, 1, 2, 7, 14, 28, and 96 days of incubation.  On a biweekly basis moisture content was adjusted to maintain 60% water-filled pore space and CO₂ traps were replaced.  Atrazine and the ATZ metabolites deethylatrazine and deisopropylatrazine were extracted from the soil and quantified using high performance liquid chromatography.  Atrazine degradation data and the fitting of kinetic models to these results will be presented along with enzyme activity data.  The results of this research will influence management decisions which could mitigate negative impacts associated with ATZ and VA co-application to soils.