Partition Mechanisms Of Typical Per/Polyfluoroalkyl Substances In The Aquatic Environment And Aqueous Aerosol

Due to the distinctive physico-chemical stability,hydrophobic-oleophobic property and surface activity,per-and polyfluoroalkyl substances（PFASs）have been wildly applied in various industrial areas and daily life.Extensive consumption result in the inevitable emissions to the environment.Numerous monitoring studies have reported the occurrence of PFASs in varied multiple environmental mediums like rivers,oceans,sediments,dust,organisms and even in human blood.As a result of strong stability of fluorinated aliphatic carbon skeleton,PFASs are not readily decomposable by physical,chemical,and biological mechanisms and could form persistent pollution.Many studies proved that legacy PFASs such as perfluorooctane sulfonate（PFOS）and perfluorooctanoic acid（PFOA）to be reproductive toxic and neurotoxic.Concerns about the persistence and toxicities drove government agencies and organizations to limit the production and emission of these legacy PFAS compounds.The large market demand inevitably prompted the development and trade of many poly or perfluorinated alternatives,leading to the frequent detection in the water environment.Hexafluoropropylene oxide dimer acid（HFPO-DA,with the trade name Gen X）and6:2 chlorinated polyfluorinated ether sulfonate（6:2 Cl-PFESA,with the trade name F-53B）were the prominent alternatives.Although these alternatives have been widely used in our country and abroad,the reports about the occurrence and distribution in multiple environmental mediums were still limited,and the data are not enough to clarify their ecological and environmental risks.In fact,aquatic environment is thought to be the most important sink of PFASs.Ionic PFASs are at equilibrium with their conjugate bases in natural aqueous systems.In theory,the conjugate bases of anionic PFASs have negligible vapor pressure resulting in extremely low air-water partition coefficients.However,it is found that ionic PFASs are still the dominant PFASs in atmospheric particulate matters and precipitations.Therefore,the transport mechanism of ionic PFASs between aquatic and atmosphere environment has aroused widespread concern in the academia.In addition,the chemical structures of novel alternatives are modified from legacy PFASs for the sake of reducing bioaccumulation and persistence.For example,an ether linkage has been inserted into the fluorinated aliphatic carbon skeleton of Gen X and F-53B.The modification of the chemical structures could change the distribution,transport and fate in environment.Investigating the effects of chemical structures on the distribution and transport in aquatic environment of PFASs is of great significance for illustrating the environmental fate of PFASs.Besides the chemical structures of the PFASs,other factors might also distinctly affect their environmental behavior.In natural waters,there are many components,such as inorganic salts,dissolved organic matters（DOM）,and surfactants,which are well documented to affect the transport and fate of many contaminants.The following works are carried out and the main conclusions are as follows in this dissertation.（1）26 emerging and legacy PFASs were measured in the surface water（including dissolved phase and suspended particulate matter）and sediments taken from Hai River basin,China.The total concentrations of PFASs（∑PFASs）ranged from 1.74 to 172ng/L,with perfluorooctanonate（PFOA）as the dominant compound（15.2%of the∑PFASs,median value）.Emerging PFASs,such as dimer acid of hexafluoropropylene oxide dimer acid（HFPO-DA）and trimer acid（HFPO-TA）,were widely detected in water samples.Specifically,chlorinated polyfluorinated ether sulfonate（F-53B）was observed to be predominant in sediment samples.A receptor model,Unmix,was introduced to identify the sources of PFASs in the surface water,and the results indicated that fire-fighting foam/fluoropolymer processing aids（36.6%）were the dominant source.The field-based sediment-water（organic carbon normalized）coefficients,K_oc,were correlated to the carbon chain lengths of the PFASs.A technique coupling one-way analysis of variance with chemical mass balance model was developed to trace the manufacturing sources of PFOA.Electrochemical fluorination（ECF）was the major PFOA manufacturing source in Hai River Basin with considerable contribution by telomerization.For the first time,the isomers of perfluorooctane sulfonamide（PFOSA）were quantified in the environmental samples.The lower proportion of branched（br-）PFOSA isomers and higher percentage of br-perfluorooctane sulfonate（PFOS）isomers in the water samples relative to their corresponding commercial products,provided more direct evidences that br-PFOSA isomers were biotransformed more easily than n-PFOSA,explaining the observed enrichment of br-PFOS in the aquatic environment.（2）In this study,the enrichment behaviors of 12 legacy and emerging PFASs in aqueous aerosol（AA）in both single solute and mixed solutions were investigated.The enrichment factors（EF）displayed a general increasing trend with the fluorinated carbon chain length.For the first time,a robust Quantitative Structure-Property Relationship（QSPR）model coupled with partial least-square method was established with fifteen quantum chemical descriptors.Four molecular descriptors,including dipole moment（μ）,molecular weight（MW）,the maximal value of the molecular surface potential(V_s,max)and molecular volume（V）were identified as the key structural variables affecting the PFASs enrichment.Inorganic salts and humic acid（HA）which are common in seawater,facilitated the PFASs enrichment as a result of enhanced hydrophobicity and the bridging effect caused by divalent cations.The typical cationic and anionic surfactants,cetyltrimethylammonium bromide and sodium dodecyl sulfate,both inhibited the enrichment due to the competition between PFASs and surfactants.It is interesting that 6:2 chlorinated polyfluorinated ether sulfonate（F-53B）had the highest EF among the 12 PFASs,implying its strong potential of atmosphere transport.（3）Natural and engineered nanoparticles,such as nano maghemite（NM）,are ubiquitous in the water environment.These nanoparticles could absorb pollutants like PFASs due to large surface area and diverse surface properties.Thus,the nanoparticles have important effects on the transport behavior of PFASs from water to atmosphere environment.In this study,the effects of NM on the enrichment of PFASs in AA were investigated.The results indicated that the EF of PFASs（long-chain PFASs in particular）were increased by NM under environmental conditions（0.5 mg/L）,and EF of each long-chain PFAS increased 0.60 on average.The EF of PFASs raised with the NM concentration increasing resulting from the adsorption between NM and PFASs.NM could carry PFASs into AA that promoted the enrichment of PFASs in aqueous aerosol.Batch experiment was conducted to investigate the adsorption of PFASs on NM.Significant adsorption of long-chain PFASs on NM were observed.And with the length of carbon chain growing,the adsorption capacity of NM on PFASs increased.These results suggested that hydrophobic interaction play an important role in the adsorption of NM and PFASs.Meanwhile,NM is positively charged in aqueous solution,therefore,there could be electrostatic interaction between the NM and PFASs in the adsorption process.The electrostatic interaction between the NM and PFASs was proved indirectly by comparing the adsorption of PFASs on negatively charged nano Ti O_2.Phosphate could change the the charge of NM,and the addition of phosphate reduced the adsorption of PFASs on NM.This also proves the electrostatic interaction between NM and PFASs.