The distribution of veterinary antibiotics in the river system in a livestock-producing region and interactions between different phases.

The occurrence of six common antibiotics in the surface water, sediment, and suspended particulate matter (SPM) of the Jiyun River, a typical river in the livestock-producing region in Beijing, northern China, was investigated. The results revealed that the antibiotics were widely distributed in the studied area. The aqueous samples were contaminated by the antibiotics, and the target antibiotics presented in highest levels were sulfonamides, with maximum concentrations of 230 and 385 ng/L for sulfadiazine and sulfamethoxazole, respectively. Oxytetracyline, one of the tetracylines, was the most frequently detected compound in the particulate phase with maximum concentration of 121 and 130 ng/g in the sediment and SPM, respectively. The total antibiotic concentration in the water was higher in the tributary than that in the main river, demonstrating that the tributaries were discharging antibiotics into the main river. In addition, the partition coefficients of sediment-water (Kp(S)) and the SPM-water (Kp(SPM)) were calculated. Overall, the Kp(S) decreases with an increase in the contents of SPM. In terms of the interaction between SPM and water, linear relationship between logarithm of Kp(SPM) (log Kp(SPM)) and the logarithm of molecular weight (log MW) was obtained, suggesting that large and heavy molecules are more likely to be attracted to suspended particulates, eventually leading to their enrichments in bed sediments.