Occurrence of a veterinary antibiotic in streams in a small catchment area with livestock farms

The release of pharmaceuticals into the aquatic environment and their occurrence in surface waters has become an increasing concern in recent years. In this study we investigated the occurrence of oxytetracycline (OTC), one of the most widely used veterinary antibiotics, in stream waters in a small catchment area with many livestock farms. OTC was detected in the concentration range of 2 ng/L to 68 μg/L. Increasing trends in OTC concentrations and daily loads during winter were observed, which correspond to the common veterinary practice of using higher dosages of antibiotics as prophylaxis against disease in winter. High concentrations of OTC in stream water were observed in the vicinity of a livestock farm. There, the daily OTC load rate was in a reasonable range when the number of animals, the additive rate of antibiotics to fodder, and the OTC removal efficiency in activated sludge processes were estimated.

OTC concentrations in a river basin with livestock farms were as high as 68 μg/L. The highest concentration was observed in a small stream that abuts a swine farm (sampling point S1). OTC concentrations and daily OTC loads decreased as water flowed downstream, probably as a result of decomposition or adsorption to sediment, or both. OTC concentrations at downstream sampling points ranged from 2 to 200 ng/L, and concentrations at sampling point S9 (the farthest downstream point) ranged from 10 to 50 ng/L. The OTC concentration did not increase after a rain, a fact that may suggest that the application of manure to land is not related to the occurrence of veterinary medicine in the river. The OTC concentration and daily rate increased in winter, probably due to greater use for prophylaxis against infection in livestock.