Study On Ecological Effects Of Typical Nanoplastics (PS NPs) In Iris Pseudacorus Constructed Wetland

The industrial production of polystyrene nanoparticles（PS NPs）and the crushing and degradation of polystyrene plastics have increased the environmental release of PS NPs.Studies have shown that PS NPs can enter the sewage treatment system through the sewage pipe network,affecting the endogenous respiration and methane production capacity of activated sludge,and reducing the treatment efficiency.In addition,PS NPs also induce excessive production of active oxygen,which has a negative impact on the metabolism of microorganisms and plants.Constructed wetland is an ecological treatment technology that is coordinated by substrates,microorganisms and plants.It has a good effect on the removal of conventional pollutants and other new pollutants such as nanoparticles.However,there are still few reports on the ecological effects and migration and removal effects of PS NPs in constructed wetlands.Therefore,investigating the impact of PS NPs on constructed wetland ecosystems and clarifying the environmental effects of PS NPs have important theoretical value and practical significance.In this study,three vertical flow constructed wetlands planted with Iris.pseudacorus were built,which were the control group（CK）without PS NPs,1 mg/L PS NPs exposure group（VF1）and 10 mg/L PS NPs exposure group（VF10）,respectively.The effects of different concentrations of PS NPs exposure on the decontamination performance,substrate enzyme activity,plant physiological characteristics and microbial community structure of constructed wetlands were investigated.The ecological effects of long-term exposure of PS NPs to constructed wetlands and the feasibility of constructed wetland ecological technology to remove this nanoplastic pollution were analyzed.The main conclusions were as follows:This study investigated the effects of exposure to two concentrations（1 mg/L,10 mg/L）of PS NPs on the decontamination performance of vertical flow constructed wetlands.The results showed that the vertical flow constructed wetland effectively reduced the nanoplastic pollution in sewage,and the removal rate of PS NPs in the VF1 and VF10 wetlands were both over 97%.Under PS NPs exposure,the removal of chemical oxygen demand（COD）and total phosphorus（TP）in the vertical flow constructed wetland was not significantly affected,but the removal of total nitrogen（TN）was inhibited,which interfered with the nitrogen removal process and showed a concentration effect.Under 1 mg/L PS NPs exposure,the removal of NH₄⁺-N had no significant effect,but the concentration of NO₃^--N accumulated in a large amount;under 10 mg/L PS NPs exposure,the removal of NH₄⁺-N was inhibited,while the removal of NO₃^--N had no significant effect.This study investigated the effects of exposure to two concentrations of PS NPs on the activity of substrate enzymes in vertical flow constructed wetlands.The results showed that PS NPs have varying degrees of influence on the activities of substrate enzymes involved in carbon,nitrogen,and phosphorus cycles.After exposure to 1 and 10 mg/L PS NPs,the dehydrogenase（DHA）and neutral phosphatase（NP）activities of the two wetlands decreased,and the higher the concentration,the stronger the inhibitory effect.Combined with the analysis of NMDS and Anosim,the key enzyme activities of the nitrogen cycle of the three wetlands were significantly different,and the changes in these enzyme activities further affected the nitrogen removal process of the wetlands:Compared with the control group,the urease（URE）activities of VF1and VF10 wetlands all decreased,indicating that the conversion of organic nitrogen to inorganic nitrogen was inhibited;In VF10 wetland,the activities of ammonia monooxygenase（AMO）,hydroxylamine oxidoreductase（HAO）,and nitrite oxidoreductase（NXR）were all reduced,mainly inhibiting nitrification,while the three enzyme activities in VF1 wetland decreased slightly,and the nitrification process was not significantly affected;the nitrate reductase（NAR）and nitrite reductase（NIR）activities of the two wetlands of VF1 and VF10 were significantly decreased,which mainly inhibited denitrification.In addition,catalase（CAT）activity showed a significant increase first and then a gradual decrease trend under PS NPs exposure,indicating that PS NPs produced oxidative stress and the antioxidant system was damaged.This study investigated the effects of PS NPs exposure to two concentrations on the antioxidant system and photosynthesis of plants in vertical flow constructed wetlands.The results showed that in the initial stage of PS NPs exposure,the activities of superoxide dismutase（SOD）,peroxidase（POD）and catalase（CAT）in the leaves of Iris.pseudacorus were all promoted,and the antioxidant system of wetland plants was stimulated.The defensive effect of plants was more obvious under higher concentration exposure.In the later period of exposure,the activities of POD and CAT of plants under low-concentration exposure（VF1）were promoted,and the SOD activity decreased to 88.28%of the control;the activities of SOD and CAT of plants under high-concentration exposure（VF10）decreased even more and decreased to 82.39%,76.43%of the control,respectively.The antioxidant system was damaged,in addition,PS NPs stress increased the content of malondialdehyde（MDA）in leaves and increased the degree of membrane lipid peroxidation.During the entire test period,PS NPs exposure did not affect photosynthetic pigment synthesis significantly.The content of chlorophyll a（Chl a）,chlorophyll b（Chl b）,total chlorophyll（total Chl）,and carotenoids（Car）of Iris.pseudacorus had no obvious change compared with the control group.This study also investigated the effects of PS NPs exposure to two concentrations on the morphology of microbial membranes and the structure of microbial community.The results showed that nano-scale particles appeared on the surface of the biofilm after PS NPs exposure,and the accumulation of PS NPs in VF10 wetland was higher.These particles aggregated on the surface of the biofilm might change the living environment of microorganisms,thereby affecting the decontamination performance of constructed wetlands.In addition,the microbial community structure changed significantly after PS NPs exposure.Compared with the control group,the proportion of the main bacteria removing nitrigon and phosphorus in the two exposure groups decreased to varying degrees in phylum,class,and genus levels.In summary,the constructed wetlands effectively removed the influent PS NPs.PS NPs exposure had no significant effect on the removal of COD and TP in VF1 and VF10 wetlands,but it had an impact on the nitrogen conversion process and the nitrigon removal effect.PS NPs produced oxidative stress,which affected wetland substrate enzyme activities and plant antioxidant systems.In addition,the relative abundance of functional bacteria that participated in the carbon,nitrogen,phosphorus,and sulfur cycles in the constructed wetland decreased,which in turn affected the material cycle process of the constructed wetland system.