Concentration and Environmental Loading of Veterinary Antibiotics in Agricultural Irrigation Ditches

Abstract

The concentration of veterinary antibiotics in aqueous and sediment matrices was measured in agricultural irrigation ditches bordering several animal-feeding operations (AFOs) and then compared to its concentration in the watershed. Analytical determination in aqueous samples was based on solid phase extraction (SPE) and appropriate buffer solutions were used to extract residuals in sediment samples. Separation and detection of extracted veterinary antibiotics were performed with high performance liquid chromatograph tandem mass spectrometry (HPLC/MS/MS). In general, higher concentrations of antibiotic were observed in the aqueous phase of irrigation ditches, with the highest concentration of erythromycin hydrochloride (ETM-H 2 O) of 0.53 μg L -1 , than in aqueous watershed samples. In contrast, higher concentrations were measured in river sediment than in irrigation ditch sediment with the highest concentration of oxytetracycline of 110.9 μg kg -1 . There was a high calculated correlation ( > 0.95) between precipitation and measured concentration in aqueous samples from the irrigation ditches for five of the ten targeted veterinary antibiotics, indicating that surface runoff could be an important transport mechanism of veterinary antibiotics from field to environment. Further, environmental loading calculation based on measured concentrations in aqueous samples and flow information clearly showed that irrigation ditches were 18 times greater than river. This result suggests the likelihood that veterinary antibiotics can be transported via irrigation ditches to the watershed. The transport via surface runoff and likely environmental loading via irrigation ditches examined in this study helps identify the pathway of veterinary antibiotics residuals in the environment.