Occurrence and distribution of antibiotics in the Beibu Gulf, China: impacts of river discharge and aquaculture activities.

The occurrence and distribution of eleven selected antibiotics belonging to three groups were investigated in the Beibu Gulf. In addition, the potential effects of water discharged from four rivers and aquaculture activities were analyzed. Erythromycin-H₂O, sulfamethoxazole and trimethoprim were the most frequently detected compounds, with mean concentrations ranging from 0.51 to 6.30 ng L⁻¹. The concentrations of the rivers were generally higher than those of the gulf, implying that river discharge has an important effect on the Beibu Gulf. The concentrations of erythromycin-H₂O, sulfamethoxazole and sulfadimidine in the vicinity of aquaculture activities were higher, suggesting that a higher intensity of aquaculture activities could contribute to increasing levels of antibiotics in the environment. According to MEC (measured environmental concentration)/PNEC (predicted no-effect concentration), erythromycin, sulfamethoxazole and clarithromycin may present possible environmental risk to Pseudokirchneriella subcapitata, Synechococcus leopoliensis and P. subcapitata, respectively; therefore, attention should be given to the long-term ecological effects caused by the continuous discharge of antibiotics in the Beibu Gulf.