Sorption, Leaching and Surface Runoff of Rangeland Veterinary Pharmaceuticals From Soil Boxes.

The extensive use of veterinary pharmaceuticals in animal husbandry has raised environmental concerns due to the large percentage of administered doses that pass unaltered with the animals waste.  Recent studies have focused on pharmaceutical use in concentrated animal feed operations (CAFOs) but there is limited information on the fate and transport of these veterinary medicines in rangeland ecosystems. In the current study soil boxes (0.3 m wide, 1.22 m long, and 0.3 m high; 7% slope) packed with Yolo silt loam or Auburn-Argonaut gravely loam soil were used to evaluate leaching of three common veterinary pharmaceuticals (oxytetracycline, chlortetracycline, and ivermectin) used in rangeland beef cattle. Cow manure (1 kg, 80% moisture) spiked with 200 µg of the  antibiotics was applied on each grassed soil box. Soil boxes were then irrigated at a 1 L/min flow rate for three irrigation events. Pharmaceutical concentrations in runoff and leachate water were quantified by high performance liquid chromatography coupled with ion trap mass spectroscopy. Prior to analysis, the water samples were purified by tandem solid-phase extraction. After three weeks of irrigation 0.7-4.2% of the spiked amount of antibiotics were leached from the soil boxes. Amounts of antibiotics in runoff water were 2 to 10 times higher than those found in the leachate water. Detected amounts of ivermectin, oxytetracycline, and chlortetracycline in runoff water were 1.0-1.4, 1.8-4.1, and 3.8-6.6 µg, respectively. Soil type had little effect on the amount of leached ivermectin and chlortetracycline. However, the amount of oxytetracycline leached from Yolo soil was more than three times higher than that from the Auburn-Argonaut soil.