Perfluorooctane Sulfonate Isomers Research Articles

Isomer-Specific Biotransformation of Perfluorooctane Sulfonamide in Sprague–Dawley Rats

Great variability exists in perfluorooctane sulfonate (PFOS) isomer patterns in human and wildlife samples, including unexpectedly high percentages (e.g., >40%) of branched isomers in human sera. Previous in vitro tests showed that branched PFOS-precursors were biotransformed faster than the corresponding linear isomer. Thus, high percentages of branched PFOS may be a biomarker of PFOS-precursor exposure in humans. We evaluated this hypothesis by examining the isomer-specific fate of perfluorooctane sulfonamide (PFOSA), a known PFOS-precursor, in male Sprague-Dawley rats exposed to commercial PFOSA via food for 77 days (83.0 ± 20.4 ng kg(-1) day(-1)), followed by 27 days of depuration. Elimination half-lives of the two major branched PFOSA isomers (2.5 ± 1.0 days and 3.7 ± 1.2 days) were quicker than for linear PFOSA (5.9 ± 4.6 days), resulting in a depletion of branched PFOSA isomers in blood and tissues relative to the dose. A corresponding increase in the total branched isomer content of PFOS, the ultimate metabolite, in rat serum was not observed. However, a significant enrichment of 5m-PFOS and a significant depletion of 1m-PFOS were observed, relative to authentic electrochemical PFOS. The data cannot be directly extrapolated to humans, due to known differences in the toxicokinetics of PFOS in rodents and humans. However, the results confirm that in vivo exposure to commercially relevant PFOS-precursors can result in a distinct PFOS isomer profile that may be useful as a biomarker of exposure source.

Impact of Treatment Processes on the Removal of Perfluoroalkyl Acids from the Drinking Water Production Chain

The behavior of polyfluoralkyl acids (PFAAs) from intake (raw source water) to finished drinking water was assessed by taking samples from influent and effluent of the several treatment steps used in a drinking water production chain. These consisted of intake, coagulation, rapid sand filtration, dune passage, aeration, rapid sand filtration, ozonation, pellet softening, granular activated carbon (GAC) filtration, slow sand filtration, and finished drinking water. In the intake water taken from the Lek canal (a tributary of the river Rhine), the most abundant PFAA were PFBA (perfluorobutanoic acid), PFBS (perfluorobutane sulfonate), PFOS (perfluorooctane sulfonate), and PFOA (perfluorooctanoic acid). During treatment, longer chain PFAA such as PFNA (perfluorononanoic acid) and PFOS were readily removed by the GAC treatment step and their GAC effluent concentrations were reduced to levels below the limits of quantitation (LOQ) (0.23 and 0.24 ng/L for PFOS and PFNA, respectively). However, more hydrophilic shorter chain PFAA (especially PFBA and PFBS) were not removed by GAC and their concentrations remained constant through treatment. A decreasing removal capacity of the GAC was observed with increasing carbon loading and with decreasing carbon chain length of the PFAAs. This study shows that none of the treatment steps, including softening processes, are effective for PFAA removal, except for GAC filtration. GAC can effectively remove certain PFAA from the drinking water cycle.The enrichment of branched PFOS and PFOA isomers relative to non branched isomers during GAC filtration was observed during treatment. The finished water contained 26 and 19 ng/L of PFBA and PFBS. Other PFAAs were present in concentrations below 4.2 ng/L The concentrations of PFAA observed in finished waters are no reason for concern for human health as margins to existing guidelines are sufficiently large.

Increasing levels of long-chain perfluorocarboxylic acids (PFCAs) in Arctic and North Atlantic marine mammals, 1984–2009

Temporal variations in concentrations of perfluorinated carboxylic acids (PFCAs) and sulfonic acids (PFSAs), including perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) structural isomers, were examined in livers of pilot whale ( Globicephala melas), ringed seal ( Phoca hisida), minke whale ( Balaenoptera acutorostrata), harbor porpoise ( Phocoena phocoena), hooded seal ( Cystophora cristata), Atlantic white-sided dolphin ( Lagenorhynchus acutus) and in muscle tissue of fin whales ( Balaenoptera physalus). The sampling spanned over 20 years (1984–2009) and covered a large geographical area of the North Atlantic and West Greenland. Liver and muscle samples were homogenized, extracted with acetonitrile, cleaned up using hexane and solid phase extraction (SPE), and analyzed by liquid chromatography with negative electrospray tandem mass spectrometry (LC-MS/MS). In general, the levels of the long-chained PFCAs (C9–C12) increased whereas the levels of PFOS remained steady over the studied period. The PFOS isomer pattern in pilot whale liver was relatively constant over the sampling years. However, in ringed seals there seemed to be a decrease in linear PFOS (L-PFOS) with time, going from 91% in 1984 to 83% in 2006.

Placental transfer of perfluorinated compounds is selective – A Norwegian Mother and Child sub-cohort study

Perfluorinated compounds (PFCs) comprise a large group of man-made fluorinated chemicals used in a number of consumer products and industrial applications. PFCs have shown to be persistent, bio-accumulative and widespread in the environment. Animal studies have demonstrated hepatotoxicity, immunotoxicity, developmental toxicity as well as hormonal effects. We investigated prenatal exposure to several PFCs and detected up to seven different PFCs in 123 paired samples of human maternal and cord blood, from a subcohort of the Norwegian Mother and Child Cohort Study (MoBa). The maternal and foetal levels were significantly correlated for all PFCs tested with median PFC concentrations in cord blood ranging between 30 and 79% of the maternal concentrations, demonstrating placental passage. The composition of the different PFCs varied between cord and maternal blood, with a higher proportion of shorter chained PFCs together with a higher amount of the branched isomers of perfluorooctane sulfonate (PFOS) in cord blood. Additionally, the sulfonate group seems to impede transfer efficiency. This indicates a selective placental passage of the different PFCs and hence a specific foetal exposure.

Isomer Profiles of Perfluorochemicals in Matched Maternal, Cord, and House Dust Samples: Manufacturing Sources and Transplacental Transfer

Background: Perfluorochemicals (PFCs) are detectable in the general population and in the human environment, including house dust. Sources are not well characterized, but isomer patterns should enable differentiation of historical and contemporary manufacturing sources. Isomer-specific maternal–fetal transfer of PFCs has not been examined despite known developmental toxicity of perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) in rodents.Objectives: We elucidated relative contributions of electrochemical (phased out in 2001) and telomer (contemporary) PFCs in dust and measured how transplacental transfer efficiency (TTE; based on a comparison of maternal and cord sera concentrations) is affected by perfluorinated chain length and isomer branching pattern.Methods: We analyzed matching samples of house dust (n = 18), maternal sera (n = 20), and umbilical cord sera (n = 20) by isomer-specific high-performance liquid chromatography tandem mass spectrometry.Results: PFOA isomer signatures revealed that telomer sources accounted for 0–95% of total PFOA in house dust (median, 31%). This may partly explain why serum PFOA concentrations are not declining in some countries despite the phase-out of electrochemical PFOA. TTE data indicate that total branched isomers crossed the placenta more efficiently than did linear isomers for both PFOS (p < 0.01) and PFOA (p = 0.02) and that placental transfer of branched isomers of PFOS increased as the branching point moved closer to the sulfonate (SO3–) end of the molecule.Conclusions: Results suggest that humans are exposed to telomer PFOA, but larger studies that also account for dietary sources should be conducted. The exposure profile of PFOS and PFOA isomers can differ between the mother and fetus—an important consideration for perinatal epidemiology studies of PFCs.

Isomer‐specific accumulation of perfluorooctane sulfonate in the liver of chicken embryos exposed in ovo to a technical mixture

Prior to its recent phaseout, perfluorooctane sulfonate (PFOS) was produced by electrochemical fluorination processes, which yielded technical mixtures composed of linear isomer (∼65-79%) and several branched isomers (∼21-35%). Because PFOS can biomagnify in wildlife, birds that occupy higher trophic levels are at increased risk of exposure. We hypothesized that the pharmacokinetic properties of PFOS are isomer-specific in developing chicken (Gallus gallus domesticus) embryos exposed to technical grade PFOS (T-PFOS). In the present study, T-PFOS was composed of 62.7% linear isomer (L-PFOS), and 37.3% branched isomer, including six mono(trifluoromethyl)-branched isomers and four bis(trifluoromethyl)-branched isomers. Concentrations of 0.1, 5, or 100 µg/g of T-PFOS were injected into the air cell of chicken eggs prior to incubation. After pipping, compared with T-PFOS, the PFOS isomer profile in embryonic liver tissue for the 0.1 µg/g dose group showed 21% enrichment in the proportion of L-PFOS with a corresponding decrease in the proportion of branched isomers. Not all branched isomers were discriminated against at equal rates. The proportion of two mono(trifluoromethyl)-branched isomers and three bis(trifluoromethyl)-branched isomers decreased to a greater degree than other branched isomers. In contrast, the mono-branched isomer, P6MHpS, was overrepresented in the low-dose group. In the higher dose groups, L-PFOS was still enriched but only by approximately 10%, which indicated a dose-dependent change in isomer composition relative to T-PFOS. These results show that accumulation of PFOS in chicken embryo livers is dependent on the presence and position of branches on the alkyl backbone. This supports the hypothesis that the pharmacokinetics of PFOS are isomer-specific in biota, and may help explain why wildlife PFOS burdens are dominated by L-PFOS relative to T-PFOS mixtures.

Perfluorinated Compounds in Infiltrated River Rhine Water and Infiltrated Rainwater in Coastal Dunes

Different studies have shown that surface waters contain perfluorinated compounds (PFCs) in the low ng/L range. Surface waters are used to produce drinking water and PFCs have been shown to travel through the purification system and form a potential threat to human health. The specific physicochemical properties of PFCs cause them to be persistent and some of them to be bioaccumulative and toxic in the environment. This study investigates the evolvement of PFC concentrations in Rhine water and rainwater during dune water infiltration processes over a transect in the dune area of the western part of The Netherlands. The difference between infiltrated river water and rainwater in terms of PFC composition was investigated. Furthermore, isomer profiles were investigated. The compound perfluorobutanesulfonate (PFBS) was found at the highest concentrations of all PFCs investigated, up to 37 ng/L in infiltrated river water (71 ± 13% of ΣPFCs). This is in contrast with the predominant occurrence of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS) reported in literature. The concentrations of PFBS found in infiltrated river Rhine water were significantly higher than those in infiltrated rainwater. For perfluorohexanesulfonate (PFHxS) the opposite was found: infiltrated rainwater contained more than infiltrated river water. The concentrations of PFOA, perfluorohexanoic acid (PFHxA), perfluoroheptanoic acid (PFHpA), PFBS, PFOS, and PFHxS in infiltrated river water showed an increasing trend with decreasing age of the water. The relative contribution of the branched PFOA and PFOS isomers to total concentrations of PFOA and PFOS showed a decreasing trend with decreasing age of the water.

Linear and Branched Perfluorooctane Sulfonate Isomer Patterns in Herring Gull Eggs from Colonial Sites Across the Laurentian Great Lakes

Linear and branched (six mono(trifluoromethyl) and four di(trifluoromethyl)) isomers of the bioaccumulative contaminant perfluorooctane sulfonate (PFOS) were analyzed for and the spatial patterns examined in individual herring gull (Larus argentatus) eggs (n = 13 per site) collected (in 2007) from 15 colonies across the Laurentian Great Lakes of North America. Linear PFOS (n-perfluoro-1-octanesulfonate (L-PFOS)) consistently dominated the isomer pattern in all eggs, comprising between 95.0% and 98.3% of the summation sigmaPFOS concentration. L-PFOS was highly enriched in the gull eggs as the summation sigmabranched-PFOS to L-PFOS isomer concentration ratios were very constant (overall average 0.038 +/- 0.001) and much lower compared to technical PFOS (range 0.27-0.54). The highest proportions of L-PFOS were generally observed in the eggs from the lower lakes (Erie and Ontario) colonies. All six mono(trifluoromethyl) branched isomers, or perfluoro-n-methyl-heptanesulfonates where n describes the carbon of the hydrocarbon chain were there is trifluoromethyl substitution relative to the sulfonate terminal group, were detected in the eggs from all the colonies. For example, P1MHpS is perfluoro-1-methyl-heptanesulfonate. Comparable to technical PFOS (T-PFOS), the percentage of the mono(trifluoromethyl) isomer to summation sigmaPFOS concentration decreased as the branch substitution was located closer to the sulfonate group, that is, P6MHpS (0%-2.5%), P5MHpS (0.43%-1.18%), P4MHpS (0.25%-0.69%), and P3MHpS (0.32%-0.74%). Although at even lower fractional composition than the mono(trifluoromethyl) isomers, of the di(trifluoromethyl) isomers, detected in >60% of the individual eggs per site was P35DMHxS and P45DMHxS for Toronto Harbour (Lake Ontario), P35DMHxS for Chantry (Lake Huron) and Fighting Island (Detroit River), and P45DMHxS for Gull Island (Lake Michigan). Relative to T-PFOS, and independent of colonial location, the high and consistent enrichment of L-PFOS in gull eggs is likely a function of several processes including PFOS or precursor sources, and isomer-specific PFOS or precursor exposure, accumulation, biotransformation, retention and/or elimination. The results of this study suggests that the apparent dilution of the mono(fluoromethyl) isomers from environmental processes that occur prior to final accumulation in herring gull eggs, is independent of the mono(fluoromethyl) isomer structure.

Isomer-Specific Biotransformation Rates of a Perfluorooctane Sulfonate (PFOS)-Precursor by Cytochrome P450 Isozymes and Human Liver Microsomes

The exposure sources of perfluorooctane sulfonate (PFOS) in humans and wildlife are not well characterized. Human biomonitoring data show that PFOS profiles may consist of up to approximately 50% branched isomers, despite the fact that historical direct manufacturing of PFOS generally resulted in products containing no more than approximately 30% branched isomers. These observations cannot be explained based on what is known about the pharmacokinetics of branched PFOS isomers; thus, here we examined the relative isomer-specific biotransformation rates of a model PFOS-precursor (N-ethylperfluorooctane sulfonamide, NEtFOSA) with human microsomes and recombinant human cytochrome P450s (CYPs) 2C9 and 2C19. Using solid phase microextraction-gas chromatography-electron capture detection to monitor NEtFOSA disappearance, and liquid chromatography-tandem mass spectrometry to monitor product formation, we showed that, in general, human microsomes and CYP isozymes transformed the branched isomers more rapidly than linear NEtFOSA. Among branched isomers, perfluoroalkyl branching geometry significantly influenced the rate of biotransformation. As a result, PFOS isomer patterns in biota exposed predominantly to precursors could be much different than expected from the isomer pattern of the precursor. While these data are suggestive that the relatively high abundance of branched PFOS isomers present in some humans, or wildlife, may be explained by substantial exposure to PFOS-precursors, in vivo studies with other relevant PFOS-precursors are warranted to validate this as a biomarker of exposure source.

Perfluorooctane Sulfonate (PFOS) Precursors Can Be Metabolized Enantioselectively: Principle for a New PFOS Source Tracking Tool

Perfluorooctane sulfonate (PFOS) is the most prominent perfluoroalkyl substance found in the serum of humans and wildlife, yet the major routes by which exposure occurs are not clear. An important issue facing both the scientific and chemical regulatory communities is the extent to which PFOS concentrations in biota are attributable to direct exposure versus metabolism of PFOS-precursors (higher molecular weight derivatives that can be biotransformed to PFOS). Given that certain branched PFOS-precursors are chiral, we hypothesized that nonracemic proportions of PFOS isomers in biological samples could be used as a marker of significant exposure to PFOS-precursors. In this proof-of-principle study we examined the enantiomer-specific biotransformation of a high-purity model PFOS-precursor isomer: C(6)F(13)C*F(CF(3))SO(2)N(H)CH(2)(C(6)H(4))OCH(3) (named 1m-PreFOS hereafter, and whereby * indicates the chiral carbon center). A method for the enantiospecific separation of a compound with a long perfluoroalkyl chain and a chiral center was developed and applied to evaluate the enantioselectivity of 1m-PreFOS biotransformation in human liver microsomes. Gradient elution in reversed-phase mode on a Chiralpak IC column permitted the near-baseline separation of the two enantiomers (E1 and E2, nomenclature based on retention order) in 65 min. Microsome incubations demonstrated that E1 and E2 were metabolized at significantly different rates; k(E1) = 6.5(+/-0.3) x 10(-2) min(-1) (half-life = 10.6 min) and k(E2) = 5.2(+/-0.3) x 10(-2) min(-1) (half-life = 13.3 min), respectively. These results suggest that tracking of PFOS exposure sources by enantiomeric fractionation is feasible, and that new analytical methods for the enantioselective analysis of PFOS isomers in human and environmental samples should be developed.

Branched Perfluorooctane Sulfonate Isomer Quantification and Characterization in Blood Serum Samples by HPLC/ESI-MS(/MS)

Perfluorooctane sulfonate (PFOS) is a global contaminant and is currently among the most prominent contaminants in human blood and wildlife samples. Although "total PFOS" (SigmaPFOS) analytical methods continue to be the most commonly used for quantification, recent analytical method developments have made it possible to resolve the various isomers of PFOS by HPLC-MS/MS. Characterized technical PFOS standards (i.e., containing a mixture of PFOS isomers) are now available that enable isomer specific quantification of PFOS, however the advantages of such an analysis have notyet been examined systematically. Herein, PFOS isomers have been individually quantified for the first time in real samples and the results are compared to a traditional SigmaPFOS method; the influence of analytical standards and isomer specific electrospray and MS/ MS behavior were also investigated. The two human serum standard reference materials chosen for analysis contained dramaticallydifferent PFOS isomer profiles (approximately 30-50% total branched isomers) emphasizing that isomer patterns should not be ignored and may provide useful information on exposure sources (i.e., direct exposure to PFOS vs indirect exposure from PFOS-precursors). Depending on the sample and the particular MS/MS transition chosen for SigmaPFOS analysis (i.e., 499-->80 or 499-->99), SigmaPFOS concentrations may be over- or underestimated compared to the isomer specific analysis. Differences in the extent of in-source fragmentation and MS/MS dissociation contributed to the systematic analytical bias. It was also shown that SigmaPFOS data are prone to interlaboratory variation due to various choices of PFOS standards and instrumental conditions used. In the future, for either SigmaPFOS or isomer specific PFOS analyses, we suggest that accuracy can be maximized and interlaboratory discrepancies minimized by using a common chemically pure technical PFOS standard characterized by 19F NMR.

Comment on “Linear and Branched Perfluorooctane Sulfonate Isomers in Technical Product and Environmental Samples by In-Port Derivatization-Gas Chromatography-Mass Spectrometry”

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Effects of 18 Perfluoroalkyl Compounds on mRNA Expression in Chicken Embryo Hepatocyte Cultures

Many studies have characterized the effects of perfluoroalkyl compounds (PFCs) in mammalian species, but limited information exists on the effects of PFCs in birds. PFCs have been detected in serum and liver of avian wildlife worldwide. While the molecular mechanisms have yet to be elucidated in detail, PFCs alter lipid metabolism through peroxisome proliferation, xenobiotic metabolism by activating the cytochrome P450 (CYP) system, and serum cholesterol levels by inducing or repressing key genes. Here, we employed a simple messenger RNA (mRNA) screening method using quantitative PCR to assess the effects of PFCs on mRNA expression in chicken embryo hepatocytes (CEH). CEH cultures were treated with perfluoroalkyl sulfonates and perfluoroalkyl carboxylates of varying chain lengths and linear or technical grade potassium perfluoro-1-octane sulfonate (L-PFOS and T-PFOS). T-PFOS comprised 80% perfluorooctane sulfonate isomers (62% linear) and various PFCs and inorganic salts. Relative mRNA expression levels of the following genes were examined: acyl-CoA oxidase (ACOX), liver fatty acid-binding protein (L-FABP), CYP1A4/1A5 and CYP4B1, 3-hydroxy-3-methylglutaryl-Coenzyme A (HMG-CoA) reductase, and sterol regulatory element-binding protein 2 (SREBP2). Compared to L-PFOS, T-PFOS altered the mRNA expression level of more genes and produced greater fold changes. L-FABP was upregulated by PFCs greater than or equal to eight carbons, while CYPs were upregulated by PFCs less than or equal to eight carbons. ACOX, HMG-CoA, and SREBP2 showed little to no change following PFC exposure. This study is the first to expose CEH cultures to multiple PFCs in vitro and demonstrates that exposure to PFC solutions of different isomeric content or chain length causes variable transcriptional responses.

Ab initio study of the structural, electronic, and thermodynamic properties of linear perfluorooctane sulfonate (PFOS) and its branched isomers

Structural, electronic, and thermodynamic properties of linear perfluorooctane sulfonate (PFOS) and its trifluoromethyl-branched isomers (i.e. 1-CF 3– to 6-CF 3–PFOS) were theoretically studied by means of ab initio density functional theory (DFT) calculations with the B3LYP functional and a 6-31++G(d,p) basis set. The anionic form of linear PFOS and its trifluromethyl-branched isomers were considered for the initial construction of the computational models; subsequently, H +, Li +, and Na + were added as counter-ions to study their effect on the properties under investigation. Insignificant changes with respect to the anions were observed in the structure of both the protonated and salt forms due to the presence of these counter-ions. However, important differences in the electrostatic potential maps as well as HOMO and LUMO molecular orbitals were observed for the various forms of PFOS. The linear and branched PFOS ions were identified as the most suitable compounds for interacting with charged species. Furthermore, in the linear anion, it was observed that the LUMO orbital is diffused along the whole fluoro-carbon chain, whereas it is localized to the region close to the ternary carbon in the 4-CF 3–PFOS, 5-CF 3–PFOS, and 6-CF 3–PFOS isomers. The higher accessibility of the LUMO orbital in these branched anions suggests that they have a higher probability of reacting with free radicals when compared with the linear counterpart. This behavior is reflected in the experimental observation that only the branched PFOS isomers were susceptible to reductive defluorination by reduced vitamin B 12 as we previously reported. The relative stability of the linear and branched PFOS in their different forms computed by comparing their calculated Gibbs free energy showed that 1-CF 3–, 6-CF 3–, and linear PFOS are the most favorable structures from a thermodynamic point of view.

Linear and Branched Perfluorooctane Sulfonate Isomers in Technical Product and Environmental Samples by In-Port Derivatization-Gas Chromatography-Mass Spectrometry

Perfluorooctane sulfonate (PFOS) is found globally as an environmental contaminant and is highly bioaccumulative in exposed biota including humans. However, there is a dearth of environmental information on the isomeric profile of PFOS, especially in biological samples, which requires suitable analysis methods for the identification and quantification of ultratrace amounts. In the present study, a novel method was developed that incorporates clean up by solid-phase extraction (SPE) WAX cartridges and in-port derivatization-gas chromatography-mass spectrometry (GC/MS) to identify and quantitatively determine linear PFOS (L-PFOS) and branched (monotrifluoromethyl and bistrifluoromethyl) isomers in PFOS technical product and in environmentally relevant biological samples. Tetrabutylammonium hydroxide (TBAH) was used for derivatization via an in situ pyrolytic alkylation reaction that occurred in the GC injector and generated butyl PFOS isomer derivatives. In addition to L-PFOS, ten branched PFOS isomers were identified in the technical product. The environmental relevance of branched PFOS isomers in addition to L-PFOS was evidenced by the presence of six branched and L-PFOS in representative herring gull and double-crested cormorant egg, and polar bear liver and plasma samples from the Great Lakes and Arctic, respectively. For all PFOS isomers in the technical product and biota samples the method demonstrated high sensitivity with the limit of detection (LOD) ranging from 0.05 to 0.25 ng/mL, with exception of L-PFOS where the LOD was 1.46 ng/mL. For the biotic samples, the method detection limits (MDLs) were slightly higher than the LODs and ranged from 0.09 to 0.46 ng/g wet weight (w.w.) with exception of L-PFOS (MDL = 6.87 ng/g w.w.).

Dietary Predictors and Plasma Concentrations of Perfluorinated Compounds in a Coastal Population from Northern Norway

Dietary intake, age, gender, and body mass index were investigated as possible predictors of perfluorinated compounds in a study population from northern Norway (44 women and 16 men). In addition to donating a blood sample, the participants answered a detailed questionnaire about diet and lifestyle. Perfluorooctane sulfonate (PFOS) (29 ng/mL), perfluorooctanoate (PFOA) (3.9 ng/mL), perfluorohexane sulfonate (PFHxS) (0.5 ng/mL), perfluorononanoate (PFNA) (0.8 ng/mL), and perfluoroheptane sulfonate (PFHpS) (1.1 ng/mL) were detected in more than 95% of all samples. Of the dietary items investigated, fruit and vegetables significantly reduced the concentrations of PFOS and PFHpS, whereas fatty fish to a smaller extent significantly increased the levels of the same compounds. Men had significantly higher concentrations of PFOS, PFOA, PFHxS, and PFHpS than women. There were significant differences in PFOS isomer pattern between genders, with women having the largest proportion of linear PFOS. PFOS, PFHxS, and PFHpS concentrations also increased with age.

Fractionation and Bioaccumulation of Perfluorooctane Sulfonate (PFOS) Isomers in a Lake Ontario Food Web

The environmental ubiquity of perfluorooctane sulfonate (PFOS) is well-known. However, little is known about the environmental fate of individual PFOS isomers. In this study, we investigated the fractionation and the bioaccumulation of PFOS isomers in water, sediment and biota collected from Lake Ontario. A total of six isomers, three perfluoro-monomethyl-substituted compounds, and three perfluoro-dimethyl isomers in addition to the linear PFOS (L-PFOS) were detected in water, sediment and biota. L-PFOS represented a much higher proportion of total PFOS (sum of linear and branched) in all organisms (>88%) compared to its proportion in technical PFOS (77%). The predominance of L-PFOS suggests a reduced uptake of branched isomers, a more rapid elimination of the branched isomers and/or a selective retention of the L-PFOS. The PFOS isomer profile found in biota was very similar to sediment, even for pelagic organisms such as zooplankton, suggesting greater partitioning of L-PFOS to biota and to sediment. The bioaccumulation factor (BAF) for L-PFOS between lake trout (whole fish) and water was estimated to be 3.4 x 10(4) L/kg compared with 2.9 x 10(3) L/kg for the monomethyl-substituted group (MM-PFOS). The remarkable difference between L-PFOS and branched isomer BAFs is due to an enrichment of branched isomers in water. The trophic magnification factor of L-PFOS (4.6 +/- 1.0) was greater than MM-PFOS isomers (1.3 +/- 0.17 to 2.6 +/- 0.51), whereas dimethyl-PFOS showed no biomagnification. The results illustrate the important influence of molecular structure on the bioaccumulation of perfluoroalkyl sulfonates.

Reductive Defluorination of Perfluorooctane Sulfonate

Perfluorooctane sulfonate (PFOS) is under increased scrutiny as an environmental pollutant due to recent reports of its worldwide distribution, environmental persistence, and bioaccumulation potential. The susceptibility of technical PFOS and PFOS branched isomers to chemical reductive dehalogenation with vitamin B12 (260 microM) as catalyst and Ti(III)-citrate (36 mM) as bulk reductant in anoxic aqueous solution at 70 degrees C and pH 9 was evaluated in this study. Defluorination was confirmed by fluoride release measurements of 18% in technical PFOS, equivalent to the removal 3 mol F-/mol PFOS, and 71% in PFOS branched isomers equivalent to the removal of 12 mol F-/mol PFOS. Degradation of PFOS was further confirmed by monitoring the disappearance of PFOS compounds with reaction time by suppressed conductivity ion chromatography, LC-MS/MS, and 19F NMR studies. The PFOS compounds differed in their susceptibility to reductive degradation by vitamin B12Ti(III) citrate. Chromatographic peaks corresponding to branched PFOS isomers disappeared whereas the peak corresponding to linear PFOS was stable. To our knowledge this is the first report of reductive dehalogenation of PFOS catalyzed by a biomolecule.

Identification and pattern of perfluorooctane sulfonate (PFOS) isomers in human serum and plasma

Human serum and plasma from Sweden ( n = 17), the United Kingdom (the UK) ( n = 13) and Australia ( n = 40) were analyzed by high performance liquid chromatography coupled to mass spectrometry. The objective was to identify different perfluorooctane sulfonate (PFOS) isomers. Similar isomer patterns typical for the electrochemical fluorination (ECF) process were found for all samples. The linear PFOS (L-PFOS) was the major isomer found (58–70%) followed by the monosubstituted PFOS isomers 1/6-CF 3-PFOS (18–22%) and 3/4/5-CF 3-PFOS (13–18%). Disubstituted isomers were also detected. The percentage of L-PFOS found in the serum and plasma samples was lower compared to a standard PFOS product (76–79%). The pattern of PFOS isomers in human serum and plasma may be suggestive concerning potential isomeric discrimination since PFOS is only produced by ECF. Possibilities for such isomer discrimination are discussed. Significant higher content of L-PFOS (68%) in Swedish samples compared to Australia and the UK (59%) was also found, which may suggest differences in exposure sources for humans.