Preliminary occurrence studies of antibiotic residues in Hong Kong and Pearl River Delta.

An improved liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated to investigate the occurrence of selected antibiotic residues in Hong Kong and Pearl River Delta. LC and MS parameters were optimized to produce the maximum analytical responses for each compound. The established method targeted five groups of antibiotics, namely, macrolides, sulfonamides, tetracyclines, quinolones, and amphenicols. The method was validated for three types of environmental water matrices, namely, reservoir, river, and estuarine waters. Low detection limits of 0.17-0.18 ng/L for macrolides, 0.22-0.34 ng/L for quinolones, 0.67-1.65 ng/L for tetracyclines, and 0.27-0.56 ng/L for sulfonamides were obtained. No apparent interferences were observed in the chromatograms of all antibiotics groups. The developed method was preliminarily used to analyze water samples collected from Yuen Long River in New Territories, Hong Kong and four sites along the Pearl River Delta. Results showed that high level of tetracycline was found among the groups tested in the local river samples. In Pearl River Delta, we identified significant levels of erythromycin, roxithromycin, and sulfadiazine in Shenzhen Reservoir.