Veterinary Pharmaceuticals in Agricultural Water and Soil Resulting from Animal Feeding Operations

Veterinary antibiotics are commonly administered to animals for disease control and added into feeds at subtherapeutic levels to improve the feeding efficiency. During these utilizations, a certain fraction of antibiotics is excreted into animal manures, and the subsequent land application of these manures disseminates pharmaceuticals into soil and water. Information on the occurrence and distribution of antibiotics in agricultural ecosystems is needed to assess the exposures and impacts of the chemicals. In this study, we investigated the occurrence and fate of four commonly used veterinary antibiotics (amprolium, carbadox, monensin and tylosin) in an animal farm. A sensitive and robust analytical method was established to simultaneously measure these pharmaceuticals in water and soil by coupling single-cartridge solid-phase extraction with analysis of liquid chromatograph equipped with tandem mass spectrometry. Among these four antibiotics, amprolium and monensin were frequently detected in soil and water with concentrations ranging from several to hundreds of ppt (ng/kg). No tylosin and carbadox were observed above detection limits. High concentrations of antibiotics in soils were generally observed in the sites where the respective concentrations in water were high. The observed ratios of soil-sorbed to aqueous concentrations were within the order of the distribution coefficients obtained from laboratory studies. This suggests that soil is a sink for veterinary drugs that are disseminated into the surrounding media through desorption from the soil and/or via a surface runoff.