Chlorination-induced spread of antibiotic resistance genes in drinking water systems

Chlorine, the most widely utilized disinfectant for drinking water globally, has recently been implicated in facilitating the spread of antibiotic resistance genes (ARGs), raising concerns about its underestimated environmental and ecological risks. However, given the current fragmented research focus and results, a comprehensive understanding of the potential mechanisms and influencing factors behind chlorination-promoted ARGs transmission in drinking water systems is crucial. This work is the first to systematically review the variations in abundance, transmission mechanisms, influencing factors, and mitigation strategies related to ARGs during the chlorination process. The results indicated that chlorination could induce genetic mutations and promote horizontal gene transfer through multiple pathways, including increased reactive oxygen species, enhanced membrane permeability, stimulation of the SOS response, and activation of efflux pumps. In addition, this work delves into significant discoveries regarding the factors affecting ARG transmission in drinking water, such as chlorine concentration, reaction time, disinfection byproducts, pipe materials, biofilms, and the water matrix. A series of effective strategies from water source to point-of-use were proposed aimed at mitigating ARGs transmission risks in the drinking water system. Finally, we address existing challenges and outline future research directions to overcome these bottlenecks. Overall, this review aims to advance our understanding of the role of chlorination in the dissemination of ARGs and to inspire innovative research ideas for optimizing disinfection techniques, minimizing the risks of antibiotic resistance transmission, and enhancing the safety of drinking water.