The Behavior Of Antibiotic Resistance Genes In Urban Drinking Water Treatment Systems

Nowadays, the emerging pollution of antibiotic resistance genes (ARGs) in water environment has been considered as a new threat to human health. ARGs exist in surface water cannot be completely eliminated in drinking water treatment plant (DWTP) and the mobile gene elements (MGEs), e.g. transposes and intI-1 are of great importance in the exchange of resistance as well as contribute to resistance retention and dissemination. Thus, the enrichment of ARGs may occur during the drinking water supply systems and threat human body eventually.A total of 285 ARGs,8 transposes and intI-1 were detected utilizing advanced high-throughput quantitative PCR techniques in the water samples of two DWTPs and residential areas. ARGs were mainly divided into 8 subtypes, including aminoglycoside; beta-lactam; FCA; MLSB; other/efflux; sulfonamide; tetracycline; vancomycin resistance genes. DWTP-1 employs the combination of ozone/biological activated carbon (BAC) treatment while DWTP-2 uses conventional drinking water treatment methods.The result manifested that the effluents of DWTP remain ARGs residues and the total concentrations of different kinds of ARGs exceeded 105 copies/L. The removal efficiency of ARGs in DWTP-1 (1.89log) was lower than DWTP-2 (2.46log), which indicated that the advanced drinking water treatment processes may not remove ARGs effectively compared with traditional treatment processes. Biological activated carbon (BAC) treatment process can accumulate ARGs remarkably during the DWTP (P<0.05). The average relative abundance of ARGs in the effluent of BAC was approximately 1 order of magnitude higher than previous treatment process. Besides, the number of detected ARGs rose from 103 to 203 after BAC process.The ARGs have accumulated remarkably after the drinking water pipeline transportation(P<0.01), among which beta-lactam resistance genes have the highest enrichment and went up from 7.10×106 copies/L in the effluent of DWTPs to 7.59×108 copies/L in tap water. The results indicated that the distribution systems may serve as ARGs reservoir and we should pay more attention to the important role of drinking water pipeline transportation. The average concentration of ARGs in drinking water at room temperature (1.63×108 copies/L) declined slightly after heat treatment process(7.57×107 copies/L), no significant corrections were observed between them (P>0.05).Aminoglycoside, MLSB, other/efflux, sulfonamide and tetracycline resistance genes have significant correlations with transposes and intl-1 (P<0.05) in DWTP-1, especially sulfonamide and tetracycline resistance genes (P<0.001). Except for sulfonamide, other subtypes of ARGs have significant correlations with intI-1 (P<0.05) in DWTP-2. This is the first study to investigate the behavior of ARGs in drinking water treatment systems utilizing advanced high-throughput quantitative techniques and provides beneficial reference to the ARGs pollution in water environment in China.