Veterinary antibiotic sorption to agroforestry buffer, grass buffer and cropland soils
Veterinary antibiotics are used to treat infectious animal diseases and enhance animal growth. In Missouri, the increased growth of confined animal feeding operations (CAFOs) and the need to dispose of manure generated by CAFOS may be problematic due to co-application of antibiotics during land application of manure. Surface runoff events from claypan or claypan-like soils are relatively frequent; thus, there is a need to develop and evaluate the use of vegetative buffer strips (VBS) as management tools to reduce antibiotic transport to surface water resources. The objectives of this study were to (1) investigate oxytetracycline (OTC) and sulfadimethoxine (SDT) sorption to agroforestry (tree/grass) buffer, grass buffer, and cropland soils, (2) evaluate differences in antibiotic sorption between soils collected from different vegetative species, and (3) elucidate relationships between soil properties and antibiotic sorption. Sorption/desorption isotherms generated using batch techniques were well-fitted by the Freundlich isotherm model (r2 [greater than] 0.80). Oxytetracycline was strongly adsorbed by all soils, and the antibiotic was not readily desorbed; hysteresis was observed between all adsorption and desorption isotherms. Solid-solution distribution coefficients (Kd) values of OTC are an order of magnitude greater than those of SDT. Statistical analyses indicate that OTC Kd values are significantly greater for VBS soils relative to cropland soil, and STD Kd values are significantly greater for agroforestry soils as compared to other soils studied. Regression analyses correlating antibiotic sorption to soil properties are in progress. Results indicate that agroforestry and grass buffers may effectively mitigate antibiotic loss from agroecosystems due to enhanced antibiotic sorption properties.