Co-exposure effects of polystyrene nanoplastics and silver nanoparticles in constructed wetlands: Microbial and macrophyte responses

Nano-sized plastics (NPs) derived from plastic debris widely co-existing with engineering nanomaterials in wastewater may alter their mixture toxicological impacts, thus potentially threatening pollutant removal. This study showed that co-exposure of silver nanoparticles (nAg) and polystyrene NPs (nPS) significantly distributed electron transport chain systems, and subsequently hindered the ATP formation, owing to higher ROS generation. Combined group showed higher inhibition NH-N transformation than single exposure. In contrast, average NO-N effluent concentration significantly increased by 43.8 % and 17.37 % in nPS groups, which were lower than other groups, consistent with the variations of denitrifying enzymes such as NAR and NIR activity. Moreover, synergistic disturbance was observed on plant antioxidant enzyme systems and biosynthesis of leaf chlorophyll. Dynamic succession and functional profile of microbials based on the obtained sequences showed that the individual and joint accumulation was confirmed as the deterministic disturbance factor that contributed to the decrease in microbial diversity and changes in microbial composition, and enriched certain functional microbes (e.g., denitrifiers and nitrifiers) in CWs. Joint accumulation of nAg and nPS reduced Nitrosomonas abundance by 1.30 folds whereas canonical denitrifiers Thauera, Flavobacterium and Zoogloea significantly enriched in nAg and nAg+nPS groups and denitrifying enzyme-coding genes were also potentially enriched, suggesting potential positive impact of low levels NPs treatment on denitrification processes. Our study highlights co-existing NPs induced ecotoxicological effects in microbiota dynamics, plant growth, and functioning genes in CWs, and provides important insights into how functional microbial communities and wetland plants response to the long-term environmental disturbance of joint plastic exposure.