Use and Environmental Occurrence of Antibiotics in Dairy Farms with Manured Forage Fields.

There is growing concern about the impact of antibiotics released from concentrated animal feeding operations (CAFOs) on terrestrial and aquatic organisms. A significant fraction of antibiotics administered on animals is typically excreted in feces and urine. Manure solids and liquid manure water are land-applied as soil amendment and for fertilization. This study investigates the use and occurrence of antibiotics in dairy CAFOs and their potential transport into first-encountered groundwater. On two dairies we conducted four seasonal sampling campaigns across various animal production and waste management systems along respective environmental pathways: application to animals, excretion to surfaces, manure collection systems, soil, and shallow groundwater. Concentrations of antibiotics were determined using on line solid phase extraction (OLSPE) and liquid chromatography-tandem mass spectrometry (LC/MS/MS) with electrospray ionization (ESI) for water samples, and accelerated solvent extraction (ASE) LC/MS/MS with ESI for solid samples. A wide range of antibiotics was applied at both farms leading to excretion of several hundred grams per farm-day. Sulfonamides, tetracyclines and their epimers/isomers, and lincomycin were most frequently detected. Yet, despite decades of use, antibiotic occurrence was largely limited to within farm boundaries. Lagoons, hospital pens, and calf hutches were the sites with most frequent antibiotic detections. When detected below ground, tetracyclines were mainly found in soils while sulfonamides were found in shallow groundwater reflecting key differences in their physicochemical properties. In manure lagoons, ten compounds were detected including tetracyclines and trimethoprim. Of these ten, sulfadimethoxine, sulfamethazine, and lincomycin were found in shallow groundwater directly downgradient from the lagoons. Antibiotics were sporadically detected in field surface materials on fields with manure applications, but below the detection limit in sandy soils. Sulfadimethoxine and sulfamethazine were detected in shallow groundwater near the flood irrigation gates (top of field), but at highly attenuated levels not attributable to dilution with irrigation water.