Microbial Community Response To Perfluoroalkyl Substances In The Xiaoqing River Basin And Estuary Area

Per and polyfluoroalkyl substances(PFAS),are a group of compounds that parts or all of the hydrogen atoms in the carbon chain are replaced by fluorine atoms.They are used in a wide range of industries and are therefore widely distributed in the environment as persistent organic pollutants(POPs).Microbial communities are the cornerstone of natural ecosystems and play an essential role in maintaining the stability of the ecosystem through material and energy cycling.Currently,studies on microbial community response to PFAS contamination are still incomplete.There is a lack of comprehensive consideration of the effects between seasons,habitats,and microbial species on the variability of microbial communities under PFAS contamination.The laboratory simulation system is too simplified compared to the in-situ environment,and hard to find research focused on the particle-attached communities in the water phase.Based on the current issues in the impact of PFAS on microbial community research,this thesis investigates the variation of microbial communities in PFAS-contaminated point sources,under Perfluorooctanoic acid(PFOA)contamination in the laboratory simulations,and the validation of biomarkers from the simulations in estuarine areas.This thesis presents the results of a study on the variation of microbial communities under the influence of the PFAS point source,in laboratory simulations,and the validation of biomarkers in the estuary.The main findings of this paper are as follows:(1)A comprehensive analysis of microbial community variation in PFAS point source areas clarifies that seasonal changes cause microbial communities different responses to PFAS contamination and different types of microbial communities(bacteria,fungi,microeukaryotes)also show different responses to PFAS contamination.However,at the spatial scale,no significant differences between the upstream and downstream communities of the PFAS point source.It suggests that strong environmental factors cover the PFAS effect on community variation.In the linear discriminant analysis,some biomarkers(e.g.Peridiniopsis,Syncephalis)are well correlated with PFAS concentrations.We suggest that the biomarkers in the water phase(e.g.Peridiniopsis)may originate from the co-emissions of fluorocarbon plant waters,while biomarkers in the sediment phase(e.g.Syncephalis)are more likely to indicate real environmental effects from PFAS contamination.In Non-metric multidimensional scaling(NMDS)analyses,the microbial communities between the upstream and downstream of the point source were more variable in the wet season than in the dry season.It is necessary to include two or more seasonal samples in field studies of the effects of PFAS on environmental microbial.In the Alpha diversity analysis,bacteria showed greater variation than microeukaryotes in the water phase,and bacterial community composition in the sediment phase was stable in both the dry and wet seasons,while fungi showed more seasonal differences.(2)In microcosm simulations of PFOA transport in riverine and marine environments and effects on bacterial communities,it was found that microbial communities in microcosm experiments were more stable and tolerant than in simple simulations.In the comparison of river and sea microcosm systems,PFOA accumulates more rapidly in the sea system sediment phase.Besides,bacterial community Alpha diversity and PFOA concentrations were significantly correlated in the marine simulated system.In the linear discriminant analysis,Flavobacteriacea both significantly exist in the river and sea PFOA-added systems.It suggests Flavobacteriacea have the potential as a PFOA biomarker.In time scale difference(Metastat)analysis,some significant differences genera,e.g.Desulfoprunum,Dinghuibacter,and Terrimonas,were repeatedly shown in the experimental(PFOA added)and blank groups,and they were not specific indicators of PFOA contamination.While Actibacter and Limnobacter were suitable to become the stable middle-long-term PFOA indicators after high-level PFOA pollution.(3)The microbial community variations show seasonal difference effects in the water phase,particle-attached phase,and free-living phase.The variation of river runoff and temperature difference was considered the main reason for seasonal difference results.In the percentage of similarity analysis,a kind of Cyanobacteria and Acinetobacter were the main contributing genera to the seasonal variation in microbial community structure at the taxonomic level of the bacterial community genus.In the Lefse analysis,unique biomarkers were found in the sediment,particle-attached and free-living bacterial communities,suggesting that each of these three communities was specific and responded differently to PFAS.In Canonical Correlation Analysis(CCA),PFAS concentrations were found to explain more of the bacterial community in the river’s upper reaches.It may due to the lower salt concentrations in upstream than offshore areas.The correlation analysis of the top ten dominant phyla and genera in the particle-attached bacterial community with PFAS concentrations revealed that Cyanobacteria,Proteobacteria,Verrucomicrobia,Armatimonadetes phylum,and Alsobacter genus relative abundance were significantly correlated with suspended particulate PFAS concentrations.Besides,the phylum,Legionella,and Thermomonas in the dry season bacterial community were significantly correlated with PFAS concentrations in water.This suggests that the bacterial community composition in the particulate phase may be strongly influenced by PFAS contamination.Therefore,more attention needs to be paid to particle-attached phase bacterial communities in future studies.