Wastewater treatment plants (WWTPs) are regarded as one of the most important sources of antibiotics in the environment. The occurrence, seasonal variation and removal efficiency of 21 antibiotics and 10 metabolites, including five sulfonamides and three of their metabolites, six quinolones, two macrolides, two β-Lactams and five tetracyclines and seven of their metabolites, were investigated in five WWTPs in different seasons in the Jiulongjiang River Region, South China. 16 antibiotics and 6 metabolites in summer and 14 antibiotics and 6 metabolites in winter were found, respectively. The most frequently detected antibiotics were sulfamethazine, sulfamethoxazole, n-acetyl sulfamethazine, n-acetyl sulfamethoxazole, ofloxacin, cephalexin monohydrate and cephradine; of these, the concentration of cephradine was the highest in most of the influent and effluent samples. The highest level of total antibiotics was found in Longyan City WWTPs, where there are more population and swine farms. Seasonal variation of the antibiotics in wastewater samples was also studied. The concentrations of antibiotics in winter were higher than those in summer. The antibiotics could not be removed completely by the WWTPs, and the mean removal efficiency ranged from -71.6 to 56.3%. Of all the antibiotics, the tetracyclines were removed comparatively more efficiently, probably due to their adsorption to sludge. The low removal efficiency of antibiotics in WWTPs could be one of the important reasons for the presence of antibiotics in the environment in Jiulongjiang Region.

In this study, the occurrence and sources of five cataloged antibiotics and metabolites were studied in Jiulongjiang River basin, south China. Nineteen antibiotics and 13 metabolites were detected in water samples from 16 river sampling sites, wastewater from 5 swine-raising facilities, and effluent from 5 wastewater treatment plants (WWTPs). The results showed that 12 antibiotics and 6 metabolites were detected in river water samples. Sulfonamides (SAs) and their metabolites were detected at high concentrations (8.59-158.94 ng/L). Tetracyclines (TCs) and their metabolites were frequently detected in swine wastewater, and the maximum concentration was up to the level in milligram per liter. Macrolides (MLs) and β-lactams (β-Ls) were found in all WWTP effluent samples and some river samples, while they were never found in any of the swine wastewater samples. SAs and quinolones (QNs) were detected in all samples. Hierarchical cluster analysis of 16 surface water samples was applied to achieve the spatial distribution characteristics of antibiotics in the Jiulongjiang River. As a result, two categories were obviously obtained. Principal component analysis and redundancy analysis showed that TCs and SAs as well as their metabolites were the major antibiotics in Jiulongjiang River, and they mainly originated from swine wastewater, while the QNs, MLs, and β-Ls in the Jiulongjiang River came from WWTP effluent.