Selected veterinary pharmaceuticals in agricultural water and soil from land application of animal manure

Veterinary pharmaceuticals are commonly administered to animals for disease control, and added into feeds at subtherapeutic levels to improve feeding efficiency. As a result of these practices, a certain fraction of the pharmaceuticals are excreted into animal manures. Land application of these manures contaminates soils with the veterinary pharmaceuticals, which can subsequently lead to contamination of surface and groundwaters. Information on the occurrence and fate of pharmaceuticals in soil and water is needed to assess the potential for exposure of at-risk populations and the impacts on agricultural ecosystems. In this study, we investigated the occurrence and fate of four commonly used veterinary pharmaceuticals (amprolium, carbadox, monensin, and tylosin) in a farm in Michigan. Amprolium and monensin were frequently detected in nearby surface water, with concentrations ranging from several to hundreds of nanograms per liter, whereas tylosin or carbadox was rarely found. These pharmaceuticals were more frequently detected in surface runoffduring nongrowing season (October to April) than during growing season (May to September). Pharmaceuticals resulting from postharvest manure application appeared to be more persistent than those from spring application. High concentrations of pharmaceuticals in soils were generally observed at the sites where the respective concentrations in surface water were also high. For monensin, the ratios of soil-sorbed to aqueous concentrations obtained from field samples were within the order of the distribution coefficients obtained from laboratory studies. These results suggest that soil is a reservoir for veterinary pharmaceuticals that can be disseminated to nearby surface water via desorption from soil, surface runoff, and soil erosion.