The occurrence of quinolone and imidazole antibiotics in rivers in Central Taiwan

The occurrence of antibiotics in aquatic environments has been of increasing concern around the world due to their ability to alter the structure of microbial communities and to promote the development of antimicrobial-resistant pathogens. Six major rivers in Central Taiwan were investigated for the occurrence of the eight most frequently prescribed quinolone and imidazole antibiotics using solid-phase extraction followed by high performance liquid chromatography-electrospray ionization-tandem mass spectrometry. Nalidixic acid, flumequine, ofloxacin, dimetridazole, and metronidazole were detected at 0.8-192ng/L in the water samples. The three most frequently detected antibiotics at all sampling sites were metronidazole, nalidixic acid, and flumequine (detection frequency (n=24) 19 sites). The highest concentration of flumequine was detected at 192 +/- 6.5ng/L in the Old Zhuoshui River. Compared to the available predicted no-effect concentration data, the risk quotients of flumequine and ofloxacin were estimated to be close to one. The Old Zhuoshui and Beigang Rivers were shown to be the two most contaminated rivers with the nearby animal husbandries being the important source of contamination. The information provided here warrants future attention and is useful for the development of regulation and remediation strategies.