Polyvinyl chloride microplastics disrupt spatial purification gradients and amplify antibiotic resistance risks in sulfamethoxazole-stressed constructed wetlands

PVC MPs disrupt the spatial purification gradient in constructed wetlands. • PVC MPs accelerate the collapse of denitrification and inhibit sulfamethoxazole removal. • PVC MPs intensify the deterministic community assembly and fragment microbial co-occurrence networks. • PVC MPs reverse the attenuation trend of ARGs and enrich ARG-harboring pathogens. Co-occurrence of antibiotics and microplastics (MPs) in constructed wetlands (CWs) poses substantial threats to stable pollutant removal performance. However, their long-term combined impacts on the functional integrity of CWs along spatial flow paths remain poorly understood. Although the individual effects of sulfamethoxazole (SMX) on CWs have been extensively documented, this study established replicated continuous-flow horizontal subsurface flow CWs fed with SMX-spiked wastewater to systematically investigate effects of polyvinyl chloride (PVC) MPs on pollutant removal and microbial community assembly. The results showed that PVC MPs exerted negligible effects on overall removal of organic carbon and ammonia, but significantly accelerated decline in denitrification and SMX degradation along the flow direction. Relative to the SMX-only control system, the final removal efficiencies of total nitrogen and SMX in the microplastic exposure system were 6.0% and 15.3% lower, respectively. PVC MPs disrupted the inherent spatial purification gradient along flow direction, triggered unexpected pollutant accumulation and concentration inversion, and intensified deterministic process of microbial community assembly. This shift suppressed proliferation of core functional denitrifying taxa (e.g., Zoogloea and Comamonas ), while favoring growth of stress-tolerant generalist taxa. Functional metagenomic prediction revealed that these taxonomic shifts were accompanied by disruption of spatial functional gradients associated with carbon and nitrogen metabolic pathways. PVC MPs amplified ecological risks by converting the downstream section of CWs into hotspots for antibiotic resistance genes (ARGs), resulting in upregulated expression of genes related to cell motility and membrane transport, which facilitated horizontal gene transfer of sul1 , sul2 , and intI1 . This MP-induced selective pressure drove enrichment of potential ARG-carrying pathogens in the outlet zone. These findings provide novel mechanistic insights for risk assessment of MP-antibiotic co-contamination in engineered CW systems. Download: Download high-res image (212KB) Download: Download full-size image