Occurrences of antibiotics and antimicrobial resistance in combined and separate sewage overflow effluents of Shanghai, China.

Antibiotic contamination and antimicrobial resistance (AMR) are extremely serious worldwide. Overflow effluents from sewage and drainage systems are important sources of antibiotics and AMR for urban water bodies. However, there are few reports on the occurrence, characteristics, and interactions between such wastewater and environmental factors. This study provided important data support. Herein, this paper explored the occurrences of antibiotics, ARGs, and microbial communities in the overflow effluents from different functional areas of Shanghai, and compared them between combined sewage overflow (CSO) and separate sewage overflow (SSO). The results showed that the total concentration of antibiotics ranged from 3.97 to 401.37 ng/L, with quinolones being the predominant type. The antibiotics in CSO effluents (188.36 ng/L) were approximately 1.29 times that of SSO (146.35 ng/L). The abundance of ARGs and microbial communities of CSO (346 and 28,543 species) was approximately 1.01 and 1.04 times that of SSO (344 and 27,424 species), respectively, similar to the concentration characteristics of antibiotics, but this trend was opposite among the receiving waters. The hospital perimeter and industrial park were the most severely polluted and least polluted areas respectively. The detected antibiotics and ARGs were all related to commonly used clinical medicines, and the dominant microorganisms species were mostly related to human and animal diseases. Antibiotic efflux and antibiotic target alteration were the main resistance mechanisms. The fate of antibiotics and AMR was closely related to conventional environmental pollutants such as suspended solid (SS), NH3-N, total phosphorus (TP), etc. Finally, this study provided some basic data and practical suggestions for the urban overflow pollution control.