A comprehensive study on the exposure of nanoplastics to constructed wetland ecological systems: Macrophyte physiology and microbial enzymology, community composition and metabolic functions

The increasing emissions of nanoplastics inevitably pose a potential threat to constructed wetland (CWs) ecosystems. However, to our knowledge, the studies on the impact of nanoplastics on CWs were mainly for the effect on nitrogen removal, but comprehensive research on wetlands is still lacking. Thus, we revealed the overall effects of polystyrene nanoparticles (PSNPs) on wastewater treatment performance, and separate exploration of macrophytes and microbes. Results showed that although 1 and 10 mg/L PSNPs had little influences on COD removal, they caused serious suppression in TN removal, and 10 mg/L PSNPs negatively affected the NH4+-N and TP removal. These suppressions were due to the accumulation of>97% PSNPs attached to the sand biofilm, which proved that CWs could effectively remove nanoplastics. As for macrophyte physiology, PSNPs significantly affected the activities of superoxide dismutase, catalase, peroxidase, and the content of malondialdehyde in each phase. The major photosynthetic pigment biosynthesis was inhibited with 10 mg/L PSNPs. Furthermore, the soil catalase activities and the relative abundances of main antioxidant enzymes were obviously impacted. Caused by excess nanoplastic-induced ROS, almost all activities of dehydrogenase, phosphatase, ammonia monooxygenase, nitrate reductase were significantly inhibited. As for metagenomics analysis, taxonomy annotation revealed that PSNPs negatively affected the major functional bacteria involved in global geochemical nitrogen, phosphorus and sulfur cycle. Functional annotation analysis revealed that some indispensable metabolism pathways (oxidative phosphorylation, pyruvate metabolism, ABC transporter, two-component system, biofilm formation, etc.) were also inhibited. Additionally, nanoplastics reduced the overall pattern of genes related to nitrogen metabolism and partial genes in glucose degradation. Overall, our results comprehensively indicate that nanoplastic is a potential danger to wetland ecosystems and should receive more attention.