Presence and environmental risk assessment of selected antibiotics in coastal water adjacent to mariculture areas in the Bohai Sea.

The presence and concentrations of 25 antibiotics in Dalian coastal water of the Bohai Sea were investigated using solid-phase extraction coupled with high-performance liquid chromatography tandem mass spectrometry. Results showed that antibiotics were widely detected in this region with total concentration ranging from 22.6 to 2402.4 ng/L. Enrofloxacin and trimethoprim were 100% detected followed by sulfamethoxazole with a detection rate of 90.9%. No significant correlations were found between antibiotics concentrations and sample parameters such as dissolved organic carbon, salinity, and distance from the coast, suggesting that concentrations and distributions of the antibiotics in this area were source-dependent. Antibiotic concentration in the sample from an offshore cage-culture area was the highest. Based on composition profiles, mariculture was supposed to be an important source of antibiotics. According to the assessment, individual antibiotic posed low to moderate risk, while the antibiotic mixture presented high risk. Enrofloxacin, clarithromycin and sulfamethoxazole, the top three contributors to the mixture risk quotients for each site, need priority control in this area. Besides, levels of enrofloxacin were high enough to exert a selective pressure on bacteria that may lead to an increase in the prevalence of resistance.