Transport mechanisms for veterinary pharmaceuticals from beef cattle feedyards to wetlands: Is aerial deposition a contributing source?

Veterinary pharmaceuticals from beef cattle feedyards have, with increasing frequency; been identified as contaminants in aquatic systems. Transport of these pharmaceuticals has generally been assumed to be via manure land application, surface runoff, or groundwater percolation. However, veterinary pharmaceuticals in airborne particulate matter downwind of beef cattle feedyards have recently been documented, indicating that aerial transport and deposition are a potential transport mechanism in arid and semi-arid environments. In this study, 35 hydrologically discrete playa wetlands within 15 km of beef cattle feedyards were examined for occurrence of six steroid hormones and eight antibiotics. 17 alpha-trenbolone, estrone, estradiol, tetracycline, chlortetracycline, oxytetracycline, tylosin, and monensin were all detected in either water or sediment samples. Concentrations for the majority of analytes were < 15 ng/g in sediment and < 70 ng/L in water. Tylosin and monensin were detected at highest concentrations in water, at 3 and 84 mu g/L, respectively. A correlation between distance from the nearest beef cattle feedyard and concentration of monensin in playa water was observed, similar to correlations observed between pharmaceutical concentrations and distance from feedyard among air samples collected downwind of feedyards. This study suggests that airborne transport and deposition of pharmaceutical-laden particulate matter are a possible contributor to pharmaceutical concentrations in aquatic systems. Aerial deposition of pharmaceutical-laden particulate matter, not typically included in risk assessments, is of yet poorly characterized but may play a significant role in pharmaceutical transport in arid and semi-arid locations and deserves further investigation.