| Perfluorinated compounds(PFCs) is a new kind of persistent organic pollutants(POPs) that exhibits environmental persistence,long range transport ability,bio-concentration,food web accumulation and ecological toxicity.After more than fifty years of production and use, those chemicals have been found every where in the global ecosystem.Due to their higher solubility and liberation degree,the majority of this class of chemicals discharged historically accumulates in the environmental water bodies.That means the global ocean may play an important role in their environmental behaviors.Perfluorooctane sulfonate(PFOS) and perfluorooctanoate(PFOA) may be adsorbed on the sea surface attributed to their superior surface activity,implying that the sea surface microlayer(SML) may play a special role in oceanic environmental system.PFCs enriched in SML may be a potential regenerative source, by which PFCs may transfer into atmosphere from ocean water and undergo long-range atmospheric transport.Moreover,SML is the habitat for fish eggs and its emboys,which may find a profound influence on the reproduction of oceanic ecosystem.Studies on the PFCs' distribution in SML not only favor to understand PFCs' environmental distribution,but also favor to find clues for the studies of air/water cycling and transport of those chemicals.In the mean time,better understanding to PFCs' distribution is the foundation for futher studies, such as SML-biota's exposures.Through environmental investigation,laboratory simulation and laboratory surface tension measurements,the enrichment phenomena and isomeric and homologous distribution features of PFOS,PFOA and perfluorononanoate(PFNA) in SML were observed and discussed in the present work.The main experimental results and conclusions are as follow.(1) The investigation revealed that Dalian coastal sea is generally polluted by PFCs. Concentrations of PFOS and PFOA in surface water ranged＜0.10～2.25ng/L and 0.17～37.55ng/L.The pollution levels were higher than that in South China Sea,comparable to Korea coastal sea,but lower than those in Japanese coastal lines and Tokyo bay.(2) PFCs were found elevated in SML from corresponding subsurface water(SSW).The enrichment factors(EFs) in SML collected with glass plate method for PFOS were as high as 23.5～108.6 at three near-shore sites.Concentrations in surface water(SW) was also generally higher than corresponding SSW samples,giving Csw/Cssw mean ratios of 1.5 and 1.4 for PFOS and PFOA in Dalian coastal sea,respectively. (3) Both PFOS branched and linear isomers were found generally elevated in SML from SSW.Especially,the concentration of the total branched monoperfluoromethyl substituted isomers(M-PFOS) was found higher than that of linear isomer(L-PFOS) in SML.The M-PFOS' EFs in SML collected with stainless steel screen ranged from 4 to 127,with a higher geometric mean of 19.Comparatively,the L-PFOS' EFs ranged from 3 to 57,with a lower geometric mean of 7.The branched M-PFOS to L-PFOS concentration ratios in SML ranged from 0.8 to 2.0 with a geometric mean of as high as 1.2,which was much higher than that in SSW and the estimated mean value of 0.43 in PFOS products as the original pollutants source.The findings of this work provided new clues that can be used in SML-mediated marine aerosol transport estimation and implied unique isomeric exposures to microlayer-biota.(4) PFOA and PFNA concentrations in SML collected with a stainless steel screen(with a depth of 200 um) ranged 1.92～17.66 ng/L(geomean 4.27 ng/L) and 0.40～9.30 ng/L (geomean 1.38ng/L).The geomeans of EFs were 2.5(1.0～17) and 8.2(2.1～42).PFNA to PFOA mean ratio was 0.33 that was significantly higher than the value of 0.10 in SSW.(5) Laboratory simulation revealed that both screen and glass plate methods can be used to measure the EFs for PFOA in SML with a good linearity.The EFs geomeans werel.16 (r2=0.987) for glass plate method and 5.25(r2=0.994) for screen method with a sampling depth of 50±10um and 200um,respectively.Due to the higher sampling efficiency and sensitivity,stainless screen method was quantified as more adaptive method for perfluorinated surfactants microlayer collection.Sulfonate surfactants show higher enrichment factors in SML than carbonate ones with the same carbon number.With chain length increase, homologues' EFs increase in exponential trend.Branched to linear PFOS isomer ratio(1.04) was higher than that(0.38) in sea bulk water in the simulation.Experiment results confirmed branched PFOS isomers can exhibit higher enrichmental ability than linear ones,implying that branched PFCs isomers may show priority through marine aerosol transport.(6) Surface tension measurements and classical thermodynamic theory of surface adsorption indicate that the adsorption of PFOA on seawater/air interface can be characterized by Longmuir surface enrichment factors of extremely dilute solution.Temperature and salinity are the two major thermodynamic factors that affect their adsorptions in SML.When temperature rises,surface adsorptions decrease;while salinity increases,adsorptions increase. The variations of PFCs' concentration and pH in actual environmental levels have less influence on PFSs' EFs in SML. |
