How does zinc oxide and zero valent iron nanoparticles impact the occurrence of antibiotic resistance genes in landfill leachate?
Landfill leachate has been identified as a significant reservoir of antibiotic resistance genes (ARGs). Metallic nanoparticles (M-NPs) increasingly incorporated into various consumer products are eventually disposed in landfill and leached into leachate. However, little is known about the impact of M-NPs on the occurrence of ARGs in leachate. Here, we investigated the changes of ARGs for 56 days in leachate exposed to different concentrations of two representative M-NPs, i.e. zinc oxide (ZnO) and zero valent iron (Fe0) NPs. The results showed that ZnO NPs exposure increased ARGs abundances, and Fe0 NPs exposure decreased ARGs abundances. Most of ARGs abundances were significantly associated with mobile genetic elements (MGEs). Furthermore, the presence of ZnO and Fe0 NPs induced the obvious changes of bacterial community. Network analysis revealed significant bacteria-ARGs co-occurrence patterns, indicating that the shifted bacterial community was an important factor explaining the changed ARG patterns. Structural equation models suggested that ZnO NPs exposure increased the abundances of ARGs by dominantly driving changes of bacterial community, followed by the increase of MGEs, whereas the decreased abundances of ARGs was mainly associated with the reduction of MGEs mediated by Fe0 NPs. These findings can provide theoretical reference for future evaluating public health risks of M-NPs and promote the mechanistic understanding of M-NPs-induced ARGs dissemination or attenuation in the environment.