A Comprehensive Contamination Investigation of Bohai Bay Seawater: Antibiotics Occurrence, Distribution, Ecological Risks and Their Interactive Factors.

A comprehensive, large-scale coastal investigation of antibiotics in seawater from Bohai Bay is lacking. Therefore, in this study, we investigated the occurrence and ecological risks of 45 antibiotics belonging to 5 classes in seawater from Bohai Bay, as well as their inter-relation with trace elements and other contaminants. The results show that tetracyclines (TCs) were detected in the highest concentration among the five classes (in the range of 0.6−2.0 μg/L). The total concentrations of the five classes of antibiotics were detected in the following order: tetracyclines (TCs) > quinolones (QAs) > sulfonamides (SAs) > macrolides (MAs) > lactams (LAs). Higher antibiotic concentrations were detected at the sampling sites closest to the coast or the shipping port. Among seven trace elements, four were quantitatively detected, with Zn representing the highest concentration. Antibiotic residuals were found to be positively correlated with total organic carbon (TOC), conductivity (Ec) and suspended solids (SS); pH and NH4+-N usually showed a negative correlation with antibiotics; TN and TP also exhibited relationships with antibiotics. The risk quotient (RQ) was calculated for different antibiotics at different sites. It was found that antibiotics pose higher risks to algae than to invertebrates or fish; sulfamethoxazole, enrofloxacin and ofloxacin were all found to pose high risk to algae at some of the sampling sites. Structural equation model (SEM) results show that trace elements, antibiotic levels and EC50 are the main factors affecting the ecological risks of antibiotics.