Environmental Occurrence of Antibiotics in Dairy Farming

Intense animal husbandry is of growing concern as a potential contamination source of a variety of emerging contaminants including pathogens, naturally occurring and synthetic steroid hormones, and various pharmaceuticals, particularly antibiotics. For example, more than twenty million pounds of antibiotics are sold for use in animal husbandry with 95% going towards therapeutic use. Here, we focus on the application and potential environmental occurrence of pharmaceuticals on dairies. Using two dairy farms in California as study sites, we conducted four seasonal samplings along three environmental pathways – 1) from flush lanes to lagoon waters to shallow groundwater, 2) from manure application to shallow groundwater beneath the associated fields, and 3) through leaching from surface soil to soil cores to shallow groundwater beneath the dairies. Concentrations of pharmaceuticals were determined using solid-phase extraction and liquid chromatography – tandem mass spectrometry with positive electrospray ionization. In the wastewater stream, sulfonamides, tetracyclines and their degradation products, lincomycin, trimethoprim, and ibuprofen were detected. Along the pathway 1), in groundwater immediately downgradient of the lagoons, sulfonamides and lincomycin were present. Along the pathway 2), in groundwater beneath the associated fields that receive manure, sulfonamides were detected. Along the pathway 3), in surface solid samples, sulfonamides, tetracyclines and their degradation products, and erythromycin were detected, and deeper in soil cores from 0 to 30 cm, sulfonamides and tetracycline were detected. In groundwater beneath dairy facilities, sulfonamides and lincomycin were detected. Sulfonamides were most frequently detected in groundwater immediately downgradient of lagoons, the field that receives manure, and wells in corral area indicating that they reach shallow groundwater through all of the three pathways.