Peikun Yuan, Yang Wang, Ping Zhang, Pin Gao
Microplastics (MPs) and antibiotic resistance genes (ARGs) are classified as emerging pollutants, that are frequently detected in municipal wastewater treatment plants, posing substantial risks to global public health. This study investigated the fate and dissemination profiles of intracellular ARGs (i-ARGs) and extracellular ARGs (e-ARGs) in nitrifying sludge systems. Microplastic-induced stress promoted the overall enrichment of ARGs in nitrifying sludge, with polylactic acid microplastics (PLA-MPs) selectively enriching i-tetX. Exposure to polyvinyl chloride microplastics (PVC-MPs) triggered reactive oxygen species generation, which drove the enrichment of e-tetC, a resistance determinant associated with efflux pump-mediated resistance mechanisms. Under stress of PVC-MPs, e-ARGs and e-intI1 accounted for 9.9% of the total ARGs and intI1, which is significantly higher than that observed for polyethylene microplastics (PE-MPs, 4.6%) and PLA-MPs (5.2%). Furthermore, i-ARGs and e-ARGs exhibited distinct distribution patterns in the nitrifying sludge system. Most functional bacteria enriched in nitrifying sludge contributed to the accumulation of both i-ARGs and e-ARGs. PLS-PM results revealed that i-intI1 and functional bacterial communitiy was the predominant factor driving accumulation of i-ARGs under exposure to PLA-MPs. For PE-MPs, e-ARGs were primarily derived from i-ARGs (path coefficient = 6.138, P < 0.05). In contrast, e-intI1 was the dominant factor influencing e-ARG accumulation under stress of PVC-MPs (path coefficient = 1.935). Overall, these findings indicate that microplastic type is a critical factor governing the divergent transmission pathways of i-ARGs and e-ARGs in nitrifying sludge. This observation underscores the necessity of conducting polymer-specific assessment of ARG-associated ecological risks for biological wastewater treatment systems.