Antibiotics in the coastal environment of the Hailing Bay region, South China Sea: Spatial distribution, source analysis and ecological risks

Highlights: • Thirty-eight antibiotics were systematically investigated in marine environment. • The distribution of antibiotics was significantly correlated with COD and NO₃–N. • Untreated domestic sewage was the primary source of antibiotics. • Fluoroquinolones showed a strong sorption capacity onto sediments. • Oxytetracycline, norfloxacin and erythromycin–H₂O indicated high risks. - Abstract: In this study, the occurrence and spatial distribution of 38 antibiotics in surface water and sediment samples of the Hailing Bay region, South China Sea, were investigated. Twenty-one, 16 and 15 of 38 antibiotics were detected with the concentrations ranging from <0.08 (clarithromycin) to 15,163 ng/L (oxytetracycline), 2.12 (methacycline) to 1318 ng/L (erythromycin–H₂O), <1.95 (ciprofloxacin) to 184 ng/g (chlortetracycline) in the seawater, discharged effluent and sediment samples, respectively. The concentrations of antibiotics in the water phase were correlated positively with chemical oxygen demand and nitrate. The source analysis indicated that untreated domestic sewage was the primary source of antibiotics in the study region. Fluoroquinolones showed strong sorption capacity onto sediments due to their high pseudo-partitioning coefficients. Risk assessment indicated that oxytetracycline, norfloxacin and erythromycin–H₂O posed high risks to aquatic organisms