The Pollution Characteristics Of Emerging Per-and Polyfluoroalkyl Substances In Water Environment In The Loess Plateau And Mechanism Of Bioaccumulation And Transformation In Plants

Per-and polyfluoroalkyl substances?PFASs?are comprised of a range of chemicals that are characterized by a perfluorinated carbon chain attached to various functional groups,and are characterized by their special properties,such as high chemical and thermal stability and excellent surface activity.PFASs have been widely used in fire-gighting foams,food packaging,super surfactants and mist suppressant for the hard chrome plating industry.Extensive application invetitably leads to the discharge of PFASs into the environment,and they have been widely detected in water,soil,atmosphere,organisms and humans.Toxicological studies demonstrate that perfluorooctane sulfonate?PFOS?and perfluorooctanoate?PFOA?and long chain perfluoroalkyl acids?PFAAs?have adverse effects on human health,leading to the regulations and phase-out of them in many countries.Whereas,the huge market demand promotes the development of numerous fluorinated alternatives with similar chemical properties and structures to replace PFOA and PFOS,such as polyfluoroalkyl ether sulfonates?PFESAs?,perfluorophosphinates?C6/C6 and C8/C8 PFPi As?and polyfluoroalkylated phosphate mono-and diesters?mono PAP and di PAP?.Although there are only a few of toxicological studies on these emerging PFASs,the available results demonstrated that these emerging PFASs displayed similar or even greater toxic effects on human health.Howerer,little knowledge is known on these emerging PFASs.To accurately assess the pollution characteristics and environmental behaviors,the spatial distribution and profiles,sources,and replacing characteristics in surface water in Wei and Fen river basins in central and western China and groundwater in Loess Plateau were investigated in the present study.Due to the relatively high solubility of PFASs in water,it is proposed that PFASs are liable to transfer to other environmental compartments through water.Farmland irrigation with surface water or/and groundwater may result in PFASs enter into soil,and accumulated by plant,which are potential sources of PFASs for human.On the basis of a comprehensive understanding of the environmental pollution characteristics of the emerging PFASs,systematically explored their uptake,translocation and transformation behavior in plant.In addition,pot experiments were applied to investigate the bioavailability of emerging PFASs in soil and their bioaccumulation in soil-plant system,which may provide useful information to evaluate the novel PFASs risks to the environment and human health in the present study.The major results and conclusions obtained in this thesis are as follows:?1?The occurrence and replacing trend of the legacy and novel fluorinated alternatives waer examined in the surface water from Fen and Wei rivers,which are the two major rivers located in the underdeveloped and ecology vulnerable areas of western China.Results showed that the contamination of legacy and emerging PFASs in both river basins was widespread,and mainly caused by industrial activities.In both rivers,perfluorohexane sulfonic acid?PFHx S?,as a substitute for perfluorooctane sulfonic acid?PFOS?,was predominant in the urban areas.In the Fen River,more substitutes of PFOS,such as 6:2 fluorotelomer sulfonate?6:2 FTS?and 6:2 chlorinated polyfluorinated ether sulfonate?6:2 Cl-PFESA?,were distinct,while significant replacing for PFOA with short-chain perfluoroalkyl carboxylic acids?C4-C7?and Ammonium salt of 4,8-dioxa-3H-per-fluorononanoate?ADONA?was observed in Wei River.Besides,advanced oxidation experiment indicated that there were unknown PFASs which could be the precursors of perfluorocarboxylic acids in Wei River.Isomeric analyses indicated that there was contribution of telomerization related sources for PFOA in both rivers,whereas PFOS was mainly from ECF.The estimated total mass discharge of PFASs derived from Wei and Fen River to the Yellow river were239 and 62.6 kg/year,respectively.?2?In this study,legacy and novel per/polyfluoroalkyl substances?PFASs?were measured in groundwater samples collected from Loess Plateau of China to understand their occurrence,sources and health risks.The total concentration of PFASs ranged from 2.78-115 ng/L,with perfluorooctanoic acid?PFOA?as the dominant compound.Many emerging PFASs,including 6:2 fluorotelomer sulfonates?FTS?,6:2 chlorinated polyfluorinated ether sulfonic acid?Cl-PFESAs?,ammonium 4,8-dioxa-3H-perfluorononanoate?ADONA?,and hexafluoropropylene oxide?HFPO?homologues were frequently detected in 96.7-100%of the samples.Multiple source apportionment analyses indicated that the PFASs in the groundwater mainly originated from industrial activities,but agricultural activities also made contributions in rural areas.Total oxidizable precursor?TOP?assay indicated that there were substantial unknown precursors of perfluoroalkyl acids?PFAAs?in the groundwater samples.The total concentration of PFASs decreased with the well depth,while the PFAA-precursors displayed contrasting vertical profile trend,which might be due to the suppressed microbial transformation in the groundwater.The potential human health risk caused by PFASs exposure via drinking groundwater in the Loess Plateau was low,except one site which was close to the industry bases.?3?As emerging alternatives of legacy perfluoroalkyl substances,perfluorophosphinates?PFPi As?and perfluorophosphonates?PFPAs?are widely applied in industrial and agricultural fields and are supposed to be large partitioned to soil and highly persistent.It is of particular interest to understand their transfer from roots to shoots and transformation in plants,such as wheat.The results of hydroponically experiments indicated that C6/C6 PFPi A,C8/C8 PFPi A,perfluorooctanophosphonic acid?PFOPA?,and perfluorohexaphosphonic acid?PFHx PA?were quickly adsorbed on the epidermis of wheat root,which was driven by their hydrophobicity.A small fraction of the accumulated PFPi As and PFPAs in the wheat root was subjected to absorption via an active process dependent on H⁺-ATPase.PFHx PA,which has the smallest molecular weight and medium hydrophilicity,displayed the strongest absorption efficiency via the water and anion channels,and had the highest translocation potential from roots to shoots in wheat,respectively,as well as 1H-perfluorohexane?1H-PFHx?and 1H-perfluorooctane?1H-PFO?,which were regulated by cytochromes P450 in wheat root.Exposure to PFPi As in roots ultimately caused the accumulation of more persistent PFPAs in the above-ground parts of plants.?4?As emerging alternatives of legacy perfluoroalkyl substances,6:2 FTS,6:2 Cl-PFESA,and PFPi As are supposed to be partitioned to soil and highly persistent in the environment.The uptake of novel PFASs by plants represents a potential pathway for their transfer in the food chain.In this study,the bioavailability of these four novel PFASs in soil and the bioaccumulation characteristics in greenhouse-grown wheat?Triticum aestivum L.?,maize?Zea mays L.?,soybean?Glycine max L.Merrill?,and pumpkin?Cucurbita maxima L.?were investigated.The results indicated that these novel PFASs with higher hydrophobicity were more easily sequestrated in soil,and the fractions extracted by methanol could well describe their bioavailability,which could be simulated by low-molecular-weight organic acids at rhizospheric concentrations.A negative relationship was found between root soil concentration factors?RSCFs?and hudrophobicity(log K_ow)of the target PFASs.This correlation was also found in the translocation factors?TF?from roots to shoots.Furthermore,the uptake and transfer of the target PFASs were regulated by the protein contents in plant roots and shoots.