Occurrence of antibiotics in an agricultural watershed in south-central Idaho

Authors: Dungan, Robert - Rob; SNOW, DANIEL - University Of Nebraska; Bjorneberg, David - Dave

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/4/2017
Publication Date: 11/16/2017
Citation: Dungan, R.S., Snow, D.D., Bjorneberg, D.L. 2017. Occurrence of antibiotics in an agricultural watershed in south-central Idaho. Journal of Environmental Quality. 46:1455-1461. https://doi.org/10.2134/jeq2017.06.0229.
DOI: https://doi.org/10.2134/jeq2017.06.0229

Interpretive Summary: In this study we investigated the occurrence of 21 veterinary and human antibiotics and a growth promotor (ractopamine) in irrigation return flows of an intensively managed agricultural watershed in south-central Idaho. Irrigation return flows are essentially drainage ditches that collect runoff from surrounding fields and can transport sediment, nutrients, pathogens, and organic compounds to surface waters. Only 9 pharmaceutical compounds (8 antibiotics and ractopamine) were detected at frequencies ranging from 3.1 to 62.5%, with monensin having the highest rate of detection. Monensin is an ionophore exclusively used in cattle and poultry industries to prevent coccidiosis and increase weight gain and milk production efficiency. Aqueous concentrations of the antibiotics were estimated to range from 0.003 ng/L for tylosin to 249 ng/L for oxytetracycline. And while monensin had a low time-weighted concentration (0.24 ng/L), the fact that it was the most frequently detected compound suggests that a portion of the pharmaceuticals were entering the return flows as runoff from animal manure-treated fields during the irrigation season. In addition, pharmaceuticals were also detected at a background site that consisted of diverted Snake River water that is the source of irrigation water for the watershed. Therefore, antibiotics, as well as ractopamine, are likely being applied to soils and transported with runoff to irrigation return flows. This study provides additional evidence that surface waters within agricultural watersheds contain low-level pharmaceuticals associated with veterinary and human uses.

Technical Abstract: The polar organic compound integrative sampler (POCIS) is a tool that has been effectively used to passively sample organic pollutants in water. In this study, POCIS were used to investigate the occurrence of 21 veterinary and human antibiotics and a beta agonist (ractopamine) in irrigation return flows of an intensively managed agricultural watershed in south-central Idaho. Erythromycin-H2O, monensin, oxytetracycline, ractopamine, sulfadimethoxine, sulfamethazine, sulfamethoxazole, trimethoprim, and tylosin were detected at frequencies ranging from 3.1 to 62.5%, with monensin having the highest rate of detection. Based on uptake rates from published literature, aqueous concentrations were estimated to range from 0.003 ng L-1 for tylosin to 249 ng L-1 for oxytetracycline. While monensin had the lowest time-weighted average concentration (0.24 ng L-1), the fact that it was the most frequently detected compound suggests that a portion of the pharmaceuticals were entering the return flows as runoff from animal manure-treated fields during the irrigation season. The same pharmaceuticals (except oxytetracycline, sulfamethazine, and tylosin) were also detected at a background site that consisted of diverted Snake River water that is the source of irrigation water for the watershed. Therefore, antibiotics, as well as ractopamine, are likely being applied to soils and transported with runoff to irrigation return flows. This study provides additional evidence that surface waters within agricultural watersheds contain low-level pharmaceuticals associated with veterinary and human uses.