Diverse and abundant antibiotics and antibiotic resistance genes in an urban water system

The widespread use of antibiotics has resulted in pollution associated with antibiotics and antibiotic resistance genes (ARGs) in urban water systems, threatening the public health and the ecological security. In this study, the patterns of the diversity and abundance of the antibiotics and ARGs in a typical city (Kunming, China) were analyzed by monitoring their presence in the tap water, the land block sewage discharge units, the sewage pipes, the influent of WWTP, the effluent of WWTP, and the urban river channel. The results showed that although the average concentration of total antibiotics in tap water was 10 ng/L, the concentrations reached hundreds or even thousands of ng/L in all the other sections, indicating antibiotics entering water system through human or pets discharge. The relative abundances of ARG copies to 16S rRNA gene copies in the effluent of WWTP, the urban river channel which was the downstream of WWTP were higher than those of the sewage pipes, increasing risk of ARG transfer after treatment by WWTP. In general, the relative abundance of ARGs in spring was higher than that in winter. There was no significant correlation between antibiotics concentrations and their corresponding ARGs, except for a correlation between tetracyclines and tet-resistance genes. Due to the existence of transposases, the urban water system is exposed to a widespread risk of horizontal transfer of ARGs.