Study On The Ecological Effects Of Typical Perfluoroalkyl Substances In Constructed Wetland

The unique physicochemical properties of perfluoroalkyl substances（PFASs）have led to their widespread use in industrial manufacturing.Due to its environmental persistence and various ecological toxicity,perfluorooctanoic acid（PFOA）,a representative substance of long-chain PFASs,was officially included in the Stockholm Convention on Persistent Organic Pollutants in 2019.In order to meet the industrial needs,short-chain PFASs represented by perfluorobutyric acid（PFBA）came into being and gradually replaced long-chain PFASs in actual production.Over the past decades,a large number of PFASs have been released into the environment with the production,transportation,use and disposal of the products concerned,which have been detected in a variety of environmental media so far,posing an environmental and health risk that cannot be ignored.As PFASs discharged from various pollution sources inevitably flow into urban sewage systems through water recycling systems and sewage networks,constructed wetland,a common ecological treatment technology for treating the sewage,are bound to accept PFASs carried in the sewage.Therefore,studying the ecological effects of PFBA and PFOA in constructed wetland is of scientific significance to explore the sustainable development of constructed wetland.In this study,three groups of vertical submerged constructed wetlands CW1-3 were constructed under laboratory conditions,of which CW1 was the control group,and PFBA and PFOA were added to the feed water of CW2 and CW3 respectively after the start of the dosing period.90-day experiments were conducted after the wetlands were stabilized,divided into three stages:before dosing（-30-0d）,1 mg/L exposure（0-30d）and 10 mg/L exposure（30-60d）.The ecological effects of PFBA and PFOA in the constructed wetland were evaluated by examining the conventional water quality indicators,substrate enzyme activity,plant antioxidant system and microbial community characteristics at different stages.The main findings are as follows:In this study,the effects of PFBA and PFOA on the decontamination performance of constructed wetlands were investigated at different exposure concentrations.The results showed that in terms of organic removal,the three groups of wetlands always maintained high COD removal efficiency（88.29%-92.51%）,PFBA and PFOA at 1 mg/L and 10 mg/L exposure concentrations had no significant effect on the COD removal capacity of constructed wetlands.In terms of nitrogen removal,PFOA had a greater effect on the constructed wetland,causing significant inhibition of nitrogen removal performance at both 1 mg/L and 10 mg/L exposure concentrations,with NH₄⁺-N and TN removal rates decreasing by 23.99%and13.21%,respectively.In terms of phosphorus removal performance,PFOA at 1 mg/L exposure concentration show a significant effect and the average TP removal rate decreased by 8.58%compared with the control group;the effect of PFBA on the phosphorus removal ability of the wetland only existed at an exposed concentration of 10 mg/L.In this study,the effects of PFOA and PFBA on the enzymatic activities of constructed wetland substrates were investigated at different exposure concentrations.The results showed that DHA activity was significantly inhibited with the rates ranging from 94.72%to 98.47%at different concentrations.The enzyme activities related to nitrogen cycle were affected by the effects to different degrees.Among them,PFOA always showed inhibitory effects on AMO and NAR,with the percentage of inhibition ranging from 12.56%to 16.12%and 11.03%to37.13%,respectively;PFBA showed opposite toxic effects on AMO and NAR at different concentrations in which 1 mg/L exposed concentration activated AMO and inhibited NAR activity;while 10 mg/L exposed concentration activated NAR and the AMO activity was inhibited.PFBA and PFOA both showed activating effects on URE,with activation rates ranging from 13.43%to 34.37%;NP activity was always inhibited,with PFBA showing the strongest inhibitory effect at 1 mg/L exposure,with an inhibition rate of 42.11%.In this study,the effects of PFOA and PFBA on the antioxidant system of wetland plants were investigated at different exposure concentrations.The results showed that the exposure to PFBA and PFOA caused stress to the plants,resulting in oxidative stress.The superoxide dismutase and peroxidase activities were increased by 17.23%-28.13%and 10.49%-14.17%at10 mg/L PFBA and PFOA exposure,respectively.Catalase activity increased by 44.65%at 1mg/L PFBA exposure,and partial inactivation of catalase occurred after the exposure concentration was increased to 10 mg/L;PFOA did not show a significant stress effect.In addition,PFBA and PFOA induced lipid peroxidation reactions with a maximum increase of30.35%in malondialdehyde content.Chlorophyll content in plant leaves showed a significant decrease at the 10 mg/L exposure stage,with the total chlorophyll content in the PFBA and PFOA groups being 85.80%and 61.61%of the control group,respectively.In this study,the effects of PFOA and PFBA on the diversity and structural composition of microbial communities in constructed wetlands at different exposure concentrations were investigated.The results showed that the dominant phyla in the constructed wetland were Proteobacteria,Bacteroidetes,Firmicutes,Actinobacteria and Acidobacteria.PFOA exposure reduced the richness and diversity of the wetland microbial community,and significantly suppressed the flora of the phyla other than Proteobacteria and Bacteroidetes.The similarity of structural composition at the genus level increased between the two dosing groups at the end of the experiment,indicating that the effects of PFBA and PFOA on microbial community structure were similar.