PFOS Isomers Research Articles

A rapid method for the determination of perfluoroalkyl substances including structural isomers of perfluorooctane sulfonic acid in human serum using 96-well plates and column-switching ultra-high performance liquid chromatography tandem mass spectrometry

To facilitate high-throughput analysis suitable for large epidemiological studies we developed an automated column-switching ultra-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method for determination of perfluorocarboxylic acids (PFCAs; C5, C6, C7, C8, C9, C10, C11, C12, and C13), perfluoroalkyl sulfonic acids (PFSAs; C4, C6, C8, and C10), perfluorooctane sulfonamide (PFOSA), and five groups of structural perfluorooctane sulfonic acid (PFOS) isomers in human serum or plasma. The analytical procedure involves rapid protein precipitation using 96-well plates followed by an automated sample clean-up using an on-line trap column removing many potentially interfering sample components while through the mobile phase gradient the target analytes are eluted onto the analytical column for further separation and subsequent mass detection. The method was linear (R(2)<0.995) at concentrations ranging from 0.01 to 60ngmL(-1) with method detection limits ranging between 0.01 and 0.17ngmL(-1) depending on the analyte. The developed method was precise, with repeatability (n=7) and reproducibility (n=103) coefficients of variation between 2% and 20% for most compounds including PFOS (2% and 8%) and its structural isomers (2-6% and 4-8%). The method was in conformity with a standard reference material. The column-switching HPLC-MS/MS method has been successfully applied for the determination of perfluoroalkyl substances including structural PFOS isomers in human plasma from an epidemiological study.

Comparative theoretical investigation on the isomerization energies of long-chain perfluoroalkanes: A case study with perfluorooctane sulfonic acid congeners

AbstractThe gas and solution phase relative thermodynamic stabilities of the 89 perfluorooctane sulfonic acid (PFOS) congeners play an important role in assessing whether synthetic conditions for commercial mixtures are under thermodynamic or kinetic control, and in calculating various physico-chemical properties for these important industrial compounds and environmental contaminants. In the present study, 4,272 gas and solvent phase (water and n-octanol) calculations were conducted at various levels of semiempirical (PM6), density functional (B3LYP, B97D, PBE1PBE [PBE0], and M062X functionals with the 6-311++G(d,p) basis set), and second order Moller-Plesset perturbation (MP2/6-311++G(d,p)//B3LYP/6-311++G(d,p)) theory and the SMD, IEFPCM-UFF, and CPCM implicit solvation models on the 89 PFOS congeners in both their acid and anionic forms. The B3LYP functional consistently and incorrectly predicts substantially increasing thermodynamic stability of PFOS isomers with increasing linearity of the perfluoroalkyl chains. By comparison, PM6, M062X, and MP2 calculations more closely reflect the expected patterns of thermodynamic stability for branched versus linear PFOS congeners.

Perfluorooctane sulfonate toxicity, isomer‐specific accumulation, and maternal transfer in zebrafish (Danio rerio) and rainbow trout (Oncorhynchus mykiss)

Perfluorooctane sulfonate (PFOS; C(8)F(17)SO(3) (-)) bioaccumulation and toxicity have been demonstrated in both aquatic and terrestrial organisms. The majority of investigations have examined total PFOS concentrations in wildlife and in toxicity testing, but isomer-specific monitoring studies are less common, and no laboratory-based study of PFOS isomer accumulation in fish has been reported. The present study examined accumulation and maternal transfer of PFOS isomers in zebrafish and tissue-specific accumulation of PFOS isomers in trout parr. A median lethal dose (LC50) of 22.2 and 2.5 mg/L was calculated for adult zebrafish and trout parr, respectively. A two-week PFOS exposure resulted in tissue-specific PFOS accumulation in trout, with maximum concentrations identified in the liver tissue (>50 microg/g). Prior exposure to PFOS as alevin did not affect the accumulation of PFOS in tissues later in life. In both species, accumulation of branched PFOS isomers generally occurred to a lesser extent than linear PFOS, which may explain the relative deficiency of branched PFOS isomers in some aquatic species in the field. Analysis of exposed trout tissues indicated that isomer discrimination may occur at the level of elimination or uptake and elimination processes in the kidney or gill, respectively. When zebrafish underwent a reproductive cycle in the presence of PFOS, approximately 10% (wt) of the adult PFOS body burden was transferred to the developing embryos, resulting in a higher total PFOS concentration in eggs (116 +/- 13.3 microg/g) than in the parent fish (72.1 +/- 7.6 microg/g). The isomer profile in eggs was not significantly different from that of adults, suggesting that the maternal transfer of branched and linear PFOS isomers in fish is largely nonisomer specific.

Disposition of perfluorinated acid isomers in sprague‐dawley rats; Part 1: Single dose

Perfluorinated acids (PFAs) and their precursors (PFA-precursors) exist in the environment as linear and multiple branched isomers. These isomers are hypothesized to have different biological properties, but no isomer-specific data are currently available. The present study is the first in a two-part project examining PFA isomer-specific uptake, tissue distribution, and elimination in a rodent model. Seven male Sprague-Dawley rats were administered a single gavage dose of approximately 500 microg/kg body weight perfluorooctane sulfonate (C(8)F(17)SO(3)(-), PFOS), perfluorooctanoic acid (C(7)F(15)CO(2)H, PFOA), and perfluorononanoic acid (C(8)F(17)CO(2)H, PFNA) and 30 microg/kg body weight perfluorohexane sulfonate (C(6)F(13)SO(3)(-), PFHxS). Over the subsequent 38 d, urine, feces, and tail-vein blood samples were collected intermittently, while larger blood volumes and tissues were collected on days 3 and 38 for isomer analysis by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). For all PFAs, branched isomers generally had lower blood depuration half-lives than the corresponding linear isomer. The most remarkable exception was for the PFOS isomer containing an alpha-perfluoromethyl branch (1m-PFOS), which was threefold more persistent than linear PFOS, possibly due to steric shielding of the hydrophilic sulfonate moiety. For perfluoromonomethyl-branched isomers of PFOS, a structure-property relationship was observed whereby branching toward the sulfonate end of the perfluoroalkyl chain resulted in increased half-lives. For PFHxS, PFOA, and PFOS, preferential elimination of branched isomers occurred primarily via urine, whereas for PFNA preferential elimination of the isopropyl isomer occurred via both urine and feces. Changes in the blood isomer profiles over time and their inverse correlation to isomer elimination patterns in urine, feces, or both provided unequivocal evidence of significant isomer-specific biological handling. Source assignment based on PFA isomer profiles in biota must therefore be conducted with caution, because isomer profiles are unlikely to be conserved in biological samples.

Disposition of perfluorinated acid isomers in sprague‐dawley rats; Part 2: Subchronic dose

Two major industrial synthetic pathways have been used to produce perfluorinated acids (PFAs) or their precursors: Telomerization and electrochemical fluorination (ECF). Products of telomer and ECF origin can be distinguished by structural isomer profiles. A mixture of linear and branched perfluoroalkyl isomers is associated with ECF. Telomer products characteristically consist of a single perfluoroalkyl geometry, typically linear. In biota, it is unclear if the isomer profile is conserved relative to the exposure medium and hence whether PFA isomer profiles in organisms are useful for distinguishing environmental PFA sources. A companion study suggested isomer-specific disposition following a single oral gavage exposure to rats. To confirm these findings under a more realistic subchronic feeding scenario, male and female rats were administered PFA isomers by diet for 12 weeks, followed by a 12-week depuration period. The diet contained 500 ng/g each of ECF perfluorooctanoate (PFOA, approximately 80% n-PFOA), ECF perfluorooctane sulfonate (PFOS, approximately 70% n-PFOS), and linear and isopropyl perfluorononanoate (n- and iso-PFNA). Blood sampling during the exposure phase revealed preferential accumulation of n-PFOA and n-PFNA compared to most branched isomers. Female rats depurated all isomers faster than males. Both sexes eliminated most branched perfluorocarboxylate isomers more rapidly than the n-isomer. Elimination rates of the major branched PFOS isomers were not statistically different from n-PFOS. Two minor isomers of ECF PFOA and one branched PFOS isomer had longer elimination half-lives than the n-isomers. Although extrapolation of these pharmacokinetics trends in rats to humans and wildlife requires careful consideration of dosage level and species-specific physiology, cumulative evidence suggests that perfluorocarboxylate isomer profiles in biota may not be suitable for quantifying the relative contributions of telomer and ECF sources.

Mass spectral studies of perfluorooctane sulfonate derivatives separated by high‐resolution gas chromatography

The mass spectral characteristics of perfluorooctane sulfonate (PFOS, C(8)F(17)SO(3)-) isomers present in technical PFOS were obtained using high-resolution gas chromatography (HRGC) combined with mass spectrometry (MS). To make PFOS amenable to HRGC separation, a simple derivatization procedure was developed. The method involved the conversion of PFOS into the iso-propyl ester using iso-propanol as the derivatization reagent under acidic conditions. Mass spectra were generated employing electron ionization (EI) and negative chemical ionization (NCI). Interpretation of fragment ions was possible due to the use of deuterium-labeled iso-propanol as derivatization reagent, which induced mass shifts in the electron ionization (EI) and negative chemical ionization (NCI) mass spectra. HRMS allowed the accurate mass measurement of important EI fragments and confirmed the derivatization reaction as well as the proposed fragmentation pathway involving rearrangement. Moreover, the high resolution provided by HRGC enabled the separation of eleven PFOS isomers present in the technical product. This is an improvement over the previously reported high-performance liquid chromatography (HPLC) separation. A complete identification of all isomers was not possible due to lack of pure reference materials. Finally, the developed derivatization procedure was successfully applied to perfluoroalkyl carboxylates (PFCA) and corresponding fragmentation involving rearrangement of the derivatized PFCA was observed. The described qualitative derivatization offers a promising alternative technique for the separation and identification of isomers of perfluoroalkyl sulfonates and carboxylates by HRGC/MS.

Polyfluorinated chemicals in a spatially and temporally integrated food web in the Western Arctic

This study reports on an investigation of the presence of polyfluorinated chemicals in a spatially and temporally integrated set of biological samples representing an Arctic food web. Zooplankton, Arctic cod, and seal tissues from the western Canadian Arctic were analyzed for perfluoroalkyl sulfonates [PFAS], perfluorocarboxylates [PFCAs], and other polyfluorinated acids. Perfluorooctane sulfonate [PFOS] was found in all samples [0.20–34 ng/g] and in the highest concentrations. PFCAs from nine to 12 carbons were quantified in most of the samples [0.28–6.9 ng/g]. PFCAs with carbon chain lengths of eight or less were not detected. Likewise, 8-2 fluorotelomer acid [8-2 FTA] and 8-2 fluorotelomer unsaturated acid [8-2 FTUA], products of fluorotelomer environmental transformation, were not detected. 2H,2H,3H,3H, heptadecafluoro decanoic acid [7-3 Acid], an additional metabolite from fluorotelomer biological transformation, was detected only in seal liver tissue [0.5–2.5 ng/g]. The ratios of branched to linear PFOS isomers in fish and seal tissue were not similar and did not match that of technical PFOS as manufactured. No branched PFCA isomers were detected in any samples. It is concluded that differing pharmacokinetics complicate the use of branched to linear ratios of PFCAs in attributing their presence to a specific manufacturing process. A statistical analysis of the data revealed significant correlations between PFOS and the PFCAs detected as well as among the PFCAs themselves. The 7-3 Acid was not correlated with either PFCAs or PFAS, which suggests that it may have a different exposure pathway.

Structural identification of isomers present in technical perfluorooctane sulfonate by tandem mass spectrometry

The structures of isomeric by-products of technical perfluorooctane sulfonate (PFOS, C8F17SO3-) were characterized by high-performance liquid chromatography coupled to mass spectrometry. Ion trap (IT) as well as triple quadrupole (TQ) tandem mass spectrometry (MS/MS) identified ten PFOS isomers with best results being achieved by ion trap MS/MS. In addition to the linear isomer, the main by-products were isomers with geminal diperfluoromethyl groups and perfluoromethyl-substituted compounds. Purified fractions of the perfluoromethyl isomers allowed the elucidation of structures and the assignment of the retention times of perfluoroisopropyl-, 5-perfluoromethyl-, 4-perfluoromethyl-, 3-perfluoromethyl- and 1-perfluoromethyl-PFOS. The concentration of 2-perfluoromethyl-PFOS was too low in technical PFOS for a proper identification. Retention times of the geminal substituted diperfluoromethyl isomers could not be properly assigned due to co-elutions. The number and position of the CF3 groups can be derived from the MS/MS spectra, which allow an unequivocal identification of the isomers. TQ-MS/MS also allowed us to identify most of the isomers.