Temporal trends of perfluorooctanesulfonate isomer and enantiomer patterns in archived Swedish and American serum samples

Serum concentrations of legacy, alternative, and precursor per- and polyfluoroalkyl substances: a descriptive analysis of adult female participants in the MIREC-ENDO study

BACKGROUND

Several legacy and emerging per- and polyfluoroalkyl substances (PFAS) have been regulated around the world. There is growing concern over the proliferation of alternative PFAS, as well as PFAS precursors. Biomonitoring data for PFAS are critical for assessing exposure and human health risk.

METHODS

We collected serum samples from 289 adult female participants in a 2018-2021 follow-up study of the Maternal-Infant Research on Environmental Chemicals (MIREC) Canadian pregnancy cohort. Samples were analyzed for 40 PFAS using ultra-performance liquid chromatography-tandem mass spectrometry. For those compounds with > 50% detection, as well as the sum of these compounds, we describe serum concentrations and patterns of exposure according to sociodemographic and obstetrical history characteristics.

RESULTS

17 out of 40 PFAS were detected in > 50% of samples with 7 of these detected in > 97% of samples. Median [95th percentile] concentrations (µg/L) were highest for PFOS (1.62 [4.56]), PFOA (0.69 [1.52]), PFNA (0.38 [0.81]), and PFHxS (0.33 [0.92]). Geometric mean concentrations of PFOA and PFHxS were approximately 2-fold lower among those with more children (≥ 3 vs. 1), greater number of children breastfed (≥ 3 vs. ≤ 1), longer lifetime duration of breastfeeding (> 4 years vs. ≤ 9 months), and shorter time since last pregnancy (≤ 4 years vs. > 8 years). We observed similar patterns for PFOS, PFHpS, and the sum of 17 PFAS, though the differences between groups were smaller. Concentrations of PFOA were higher among "White" participants, while concentrations of N-MeFOSE, N-EtFOSE, 7:3 FTCA, and 4:2 FTS were slightly higher among participants reporting a race or ethnicity other than "White". Concentrations of legacy, alternative, and precursor PFAS were generally similar across levels of age, education, household income, body mass index, and menopausal status.

CONCLUSIONS

We report the first Canadian biomonitoring data for several alternative and precursor PFAS. Our findings suggest that exposure to PFAS, including several emerging alternatives, may be widespread. Our results are consistent with previous studies showing that pregnancy and breastfeeding are excretion pathways for PFAS.

Investigating the degradation potential of microbial consortia for perfluorooctane sulfonate through a functional "top-down" screening approach

Perfluorooctane sulfonate (PFOS) is a prominent perfluorinated compound commonly found in the environment, known to pose various risks to human health. However, the removal of PFOS presents significant challenges, primarily due to the limited discovery of bacteria capable of effectively degrading PFOS. Moreover, single degradation bacteria often encounter obstacles in individual cultivation and the breakdown of complex pollutants. In contrast, microbial consortia have shown promise in pollutant degradation. This study employed a continuous enrichment method, combined with multiple co-metabolic substrates, to investigate a microbial consortium with the potential for PFOS degradation. By employing this methodology, we effectively identified a microbial consortium that demonstrated the capacity to reduce PFOS when exposed to an optimal concentration of methanol. The consortium predominantly comprised of Hyphomicrobium species (46.7%) along with unclassified microorganisms (53.0%). Over a duration of 20 days, the PFOS concentration exhibited a notable decrease of 56.7% in comparison to the initial level, while considering the exclusion of adsorption effects. Furthermore, by comparing the predicted metabolic pathways of the microbial consortium with the genome of a known chloromethane-degrading bacterium, Hyphomicrobium sp. MC1, using the KEGG database, we observed distinct variations in the metabolic pathways, suggesting the potential role of the unclassified microorganisms. These findings underscore the potential effectiveness of a "top-down" functional microbial screening approach in the degradation of stubborn pollutants.

Inconsistencies in the EU regulatory risk assessment of PFAS call for readjustment

Recognition of per- and polyfluoroalkyl substances (PFAS) as widespread environmental pollutants and a consequent risk to human health, has recently made the European Union (EU) adopt several regulatory measures for their management. The coherence of these measures is challenged by the diversity and the ubiquitous occurrence of PFAS, which also complicates the EU's endeavor to advance justified, harmonized, and transparent approaches in the regulatory assessment of chemical risks. Our study critically reviews the European approach for the risk assessment of PFAS, by applying a comparative analysis of the current and pending regulatory thresholds issued for these chemicals in water bodies, drinking water, and certain foodstuffs. Our study shows that the level of health protection embedded in the studied thresholds may differ by three orders of magnitude, even in similar exposure settings. This is likely to confuse the common understanding of the toxicity and health risks of PFAS and undermine reasonable decision-making and the equal treatment of different stakeholders. We also indicate that currently, no consensus exists on the appropriate level of required health protection regarding PFAS and that the recently adopted tolerable intake value in the EU is too cautious. Based on our analysis, we propose some simple solutions on how the studied regulations and their implicit PFAS thresholds or their application could be improved. We further conclude that instead of setting EU-wide PFAS thresholds for all the environmental compartments, providing the member states with the flexibility to consider case-specific factors, such as regional background concentrations or food consumption rates, in their national regulatory procedures would likely result in more sustainable management of environmental PFAS without compromising the scientific foundation of risk assessment, the legitimacy of the EU policy framework and public health.

Environmental exposure to legacy and emerging per- and polyfluoroalkyl substances and endometriosis in women of childbearing age

Per- and polyfluoroalkyl substances (PFAS) are man-made chemicals known for their adverse effects on humans. Growing concern has risen regarding the reproductive toxicity of PFAS, but whether PFAS affect endometriosis remains to be explored. This hospital-based case-control study included 240 laparoscopic-confirmed endometriosis cases and 334 normal controls in China from 2014 to 2018. Concentrations of thirty-three legacy and emerging PFAS were measured in the plasma samples. Associations between single PFAS and endometriosis were estimated by binary logistic regression. The elastic net regression (ENR) model was used to identify dominant PFAS related to endometriosis. The joint effect of the PFAS mixture on endometriosis was assessed by principal component analysis (PCA), Bayesian kernel machine regression (BKMR), and quantile-based g-computation (q-gcomp). In the single-PFAS model, significant positive associations of PFOA [adjusted odds ratio (95 % CI): 1.22 (1.00, 1.51)], total PFOS [1.19 (1.05, 1.34)] and two branched PFOS isomers [1.16 (1.09, 1.22) for 1m-PFOS; 1.18 (1.04, 1.34) for 6m-PFOS] with increased endometriosis odds were observed. Mixture models showed that the joint effect of PFAS mixture on endometriosis was significant [1.24 (1.05, 1.48)], mainly driven by 1m-PFOS. The PFOS isomers profile suggested a PFOS precursor biotransformation source of 1m-PFOS in our population. Our study suggests that branched isomers of PFOS may be associated with endometriosis.

Simulation modelling the structure related bioaccumulation and biomagnification of per- and polyfluoroalkyl substances in aquatic food web

Until now, there is no bioaccumulation model to predict bioaccumulation of polyfluoroalkyl substances (PFASs) in aquatic organisms due to their unique amphiphilic properties. For the first time, protein contents instead of lipid contents of organisms were used in bioaccumulation models to predict the concentrations and reveal the accumulation mechanisms of PFASs in various aquatic organisms, based on the available data. Comparison between the modeled and measured results indicated the models were promising to predict the PFAS concentrations in the fishes at different trophic levels very well, as well as their bioaccumulation factors (BAF) and trophic magnification factors (TMF) of PFASs in fish. Both water and sediment are important exposure sources of PFASs in aquatic organisms. As the two main uptake pathways, the contribution of gill respiratory decreases while that of dietary intake increases with the chain length of PFASs increasing. Fecal excretion and gill respiration are the main pathways for fish to eliminate PFASs, and their relative contributions increase and decrease respectively with chain length. The short-chain (C6-C8) perfluoroalkyl acids (PFAAs) are greatly eliminated via gill respiratory quickly, leading to their very low BAFs. As the carbon chain length increases, dietary intake becomes dominant in the uptake, while elimination is mainly through fecal excretion with relatively low rates, especially in the fishes with high protein contents. For the very long chain (C12-C16) PFASs, they are very difficult to excrete with a low total elimination rate constant (k_e = 0.463-0.743 d^-1), thus leading to their high BAFs and TMFs. The high intake rate but low elimination rate, as well as the high water and sediment concentrations together contribute to the highest accumulated concentration perfluorooctane sulfonic acid in the fish of Taihu Lake.

Quantifying Indirect Contribution from Precursors to Human Body Burden of Legacy PFASs Based on Paired Blood and One-Week Duplicate Diet

The restriction on legacy perfluoroalkyl substances (PFASs) has led to increasing application and contamination of their precursors and novel alternatives. However, the indirect contribution from precursors has not been well characterized. In this study, 24 PFASs were measured in the paired human blood and urine from general volunteers (n = 20), as well as their corresponding exposure matrices (7 day duplicate diet, drinking water and dust). Perfluorooctanoic acid (PFOA) was predominant, followed by 6:2 chlorinated polyfluoroalkyl ether sulfonate (6:2 Cl-PFESA), contributing 21.6-47.0 and 6.6-20.0% of the total concentrations, respectively. Total oxidable precursor (TOP) assay and isomeric analysis coupled with a toxicokinetic model suggested that around 19% of perfluorooctane sulfonate (PFOS) in human was contributed by its precursors. The strong correlation between the estimated daily intake (EDI) and human blood concentration for 6:2 Cl-PFESA suggested that it was mainly contributed by direct exposure. The bioavailability of 6:2 Cl-PFESA in the food matrices was estimated as 18.6% by comparing the estimated and measured blood concentrations, implying that human exposure might be overestimated if the bioavailability of PFASs in food was not considered. Assuming that they had a similar bioavailability, it was estimated that ca. 20% of PFOS body burden was from indirect exposure to its precursors, which was supported by TOP assay.

Time trends of perfluoroalkyl substances in blood in 30-year old Norwegian men and women in the period 1986-2007

Biomonitoring studies are helpful tools and can increase our knowledge on time trends in human blood concentrations of PFASs: how they relate to emission trends and the potential prenatal exposure for future generations. In this study, serum was sampled in cross-sections of men and women who were 30 years old in each of the years 1986, 1994, 2001, and 2007 in Northern Norway and analyzed for 23 PFASs. Differences in serum concentrations across sampling years were investigated graphically and with significance testing and compared with those observed in our previous longitudinal study using repeated individual measurements in older men in the same years. The results demonstrate overall increasing blood burdens of PFASs in men and women in reproductively active ages during 1986-2001 and decreases until 2007. However, longer chained PFASs were still increasing in 2007 indicating divergent time trends between the different PFASs, underlining the importance of continued biomonitoring. Comparisons between 30-year-old men and older men within the same population demonstrated variation in time trends in the exact same years, underlining that biomonitoring studies must regard historic exposures and birth cohort effects.

Uptake, Acropetal Translocation, and Enantioselectivity of Perfluorooctane Sulfonate in Maize Coexisting with Copper

Plant uptake and translocation of perfluorooctane sulfonate (PFOS) are critical for food safety and raise major concerns. However, those processes are associated with many undisclosed mechanisms, especially when PFOS coexist with heavy metals. In this study, we investigated the effect of copper (Cu) on PFOS distribution in maize tissues by assessing the PFOS concentration and enantioselectivity. The presence of <100 μmol/L Cu exerted a limited effect on PFOS bioaccumulation, while >100 μmol/L Cu damaged the root cell membrane and increased root permeability, resulting in a higher PFOS concentration in roots. The suppression of acropetal translocation might be attributed to Cu inhibition of carrier proteins. The enantiomer fraction (EF) of 1m-PFOS at <100 μmol/L Cu was higher than that in a commercial product (0.5). Racemic PFOS was detected at >100 μmol/L Cu in roots and the EF variation changed from positive to negative in shoots. These EF results evidenced the existence of a protein-mediated uptake pathway. Besides, this study indicated the challenge of chiral signature application in PFOS source identification, given the effects of heavy metals and plants on PFOS enantioselectivity. The findings provide insight into PFOS bioaccumulation in plants cocontaminated with Cu and will facilitate environmental risk assessment.

Human Biomonitoring (HBM)-I values for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) - Description, derivation and discussion

In 2016, the German Human Biomonitoring Commission (HBM-C) published a statement on its decision to develop HBM-I values for Perfluorooctanoic acid (PFOA) and Perfluorooctanesulfonic acid (PFOS) (Bundesgesundheitsbl 2016, 59:1364 DOI 10.1007/s00103-016-2437-1). The HBM-I value corresponds to the concentration of a substance in a human biological material below which no adverse health effects are expected, according to current knowledge and assessment by the HBM-C, and, consequently, there is no need for action. Evidence for associations between PFOA- and PFOS-body burden and health outcomes was found for fertility and pregnancy, weights of newborns at birth, lipid metabolism, immunity, sex hormones and age at puberty/menarche, thyroid hormones, onset of menopause as well as uric acid metabolism. Significant contrasts were reported for human blood plasma concentrations between 1 and 10 ng PFOA/mL, and 1-15 ng PFOS/mL, respectively. Within the reported ranges, the HBM-C has decided to set the HBM-I-values at 2 ng PFOA/mL and 5 ng PFOS/mL blood plasma. The underlying pathomechanisms do not appear to be sufficiently clarified to provide an unambiguous explanation of the effects observed. Consistency of toxicological and epidemiological data has been considered. The available data do not indicate an unequivocal proof of a genotoxicity of PFOA and PFOS.

Exposure characteristics for congeners, isomers, and enantiomers of perfluoroalkyl substances in mothers and infants

Per- and polyfluoroalkyl substances (PFASs) are ubiquitous in the environment, making it inevitable for humans to be exposed to these pollutants. The exposure begins while in utero and continues in infancy, during the potentially most sensitive early stages of life. This review summarizes the current knowledge on pre- and neo-natal exposures based on more than 200 articles published from 2000 to date. All relevant biological matrices used in the cited studies were included, such as maternal blood, umbilical cord blood, breast milk, placenta, amniotic fluid, fetal organs, newborns' dried blood spots, and infant serum. We show that such exposures are geographically global with significant discrepancies among countries and continents, and that while the levels of major legacy PFASs (PFOS and PFOA) have declined since 2000, those of others may have not. We also show that levels of PFOS and PFOA exceed those of some major environmental toxins, such as p,p'-DDE, BDE-47, PCB-153, PBB-153, and OH-PBDEs in maternal blood. Given that the behavior and potential effects have an origin in molecular structure, biomonitoring and research at the levels of isomers and enantiomers are critically important. Through critical analysis of these works, we summarize the major achievements, consensus, and the deficiencies of existing research. To our knowledge, this is the first review on the overall internal exposure status of mothers and infants to PFASs during pregnancy and lactation.

Risk to human health related to the presence of perfluoroalkyl substances in food

The European Commission asked EFSA for a scientific evaluation on the risks to human health related to the presence of perfluoroalkyl substances (PFASs) in food. Based on several similar effects in animals, toxicokinetics and observed concentrations in human blood, the CONTAM Panel decided to perform the assessment for the sum of four PFASs: PFOA, PFNA, PFHxS and PFOS. These made up half of the lower bound (LB) exposure to those PFASs with available occurrence data, the remaining contribution being primarily from PFASs with short half-lives. Equal potencies were assumed for the four PFASs included in the assessment. The mean LB exposure in adolescents and adult age groups ranged from 3 to 22, the 95th percentile from 9 to 70 ng/kg body weight (bw) per week. Toddlers and 'other children' showed a twofold higher exposure. Upper bound exposure was 4- to 49-fold higher than LB levels, but the latter were considered more reliable. 'Fish meat', 'Fruit and fruit products' and 'Eggs and egg products' contributed most to the exposure. Based on available studies in animals and humans, effects on the immune system were considered the most critical for the risk assessment. From a human study, a lowest BMDL 10 of 17.5 ng/mL for the sum of the four PFASs in serum was identified for 1-year-old children. Using PBPK modelling, this serum level of 17.5 ng/mL in children was estimated to correspond to long-term maternal exposure of 0.63 ng/kg bw per day. Since accumulation over time is important, a tolerable weekly intake (TWI) of 4.4 ng/kg bw per week was established. This TWI also protects against other potential adverse effects observed in humans. Based on the estimated LB exposure, but also reported serum levels, the CONTAM Panel concluded that parts of the European population exceed this TWI, which is of concern.

Enantioselectivity in transplacental transfer of perfluoro-1-methylheptanesulfonate (1m-PFOS): Human biomonitoring and in silico study

Perfluorooctane sulfonates (PFOS) are one of the most prominent perfluoroalkyl contaminants in humans and wildlife. Currently, information regarding enantiomer-specific exposure to PFOS in humans through transplacental transfer is lacking. This study examined 32 matched maternal serum, cord serum and placenta samples collected from mother-infant pairs in Wuhan, China. The enantiomer fraction (EF) value of perfluoro-1-methylhptanesulfonate (1m-PFOS) was lower in cord sera (0.362 ± 0.062, n = 23) compared to maternal sera (0.422 ± 0.048, n = 21) and placenta (0.410 ± 0.060, n = 16). Evaluations of the difference between EF_1m-PFOS suggested enantioselective transplacental transfer of 1m-PFOS. In silico evaluation of the binding affinity of 1m-PFOS to human serum albumin (HSA) showed that the two 1m-PFOS enantiomers enantioselectively interacted with the HSA. This result hints the enantioselective carrier protein affinity may be a key factor for stereoselective 1m-PFOS transplacental transfer. The percentage of branched PFOS (%br-PFOS) and EF_1m-PFOS was correlated in maternal sera, but not in cord sera and placentas. These data indicated that %br-PFOS and EF_1m-PFOS may be less reliable in identifying PreFOS exposure when it comes to complex biological processes, such as transplacental transport. This study could expand our understanding of stereoselective placental contaminant transfer in humans.

Longitudinal trends in perfluoroalkyl and polyfluoroalkyl substances among multiethnic midlife women from 1999 to 2011: The Study of Women's Health Across the Nation

BACKGROUND

Limited information exists regarding longitudinal trends in midlife women's exposure to perfluoroalkyl and polyfluoroalkyl substances (PFAS). Further, little is known about how patterns of exposure differ by race/ethnicity and reproductive characteristics including parity and menopause.

OBJECTIVE

We aimed to examine temporal variations in serum PFAS concentrations among midlife women from the Study of Women's Health Across the Nation.

METHODS

Serum concentrations of 11 PFAS homologues were measured in 75 White, Black and Chinese women with blood samples collected in 1999-2000, 2002-2003, 2005-2006, and 2009-2011. Rates of changes in PFAS concentrations were calculated assuming a first-order elimination model. Associations between PFAS concentrations and race/ethnicity, menstruation and parity were evaluated with linear mixed models, adjusting for age, body mass index and study site.

RESULTS

Serum concentrations of linear-chain perfluorooctanoic acid (n-PFOA), linear- and branched-chain perfluorooctane sulfonic acid (n-PFOS and sm-PFOS) decreased significantly (-6.0%, 95% CI: -8.3%, -3.6% per year for n-PFOA; -14.8%, 95% CI: -17.3%, -12.3% per year for n-PFOS; -16.9%, 95% CI: -19.1%, -14.6% per year for sm-PFOS); whereas perfluorononanoic acid (PFNA) increased (16.0%, 95% CI: 10.6%, 21.6% per year). Detection rates of perfluorodecanoic acid (PFDeA) and perfluoroundecanoic acid (PFUA) doubled. Temporal trends varied significantly by race/ethnicity. Chinese women tended to have consistently higher PFNA concentrations at each follow-up visit, compared with White and Black women. Serum PFHxS concentrations significantly decreased in White and Black women, but not in Chinese. Menstruating women consistently had lower concentrations. Parity was associated with lower concentrations at baseline but the differences between nulliparous and parous women became smaller over time.

CONCLUSIONS

Our results suggest longitudinal declines in serum concentrations of legacy PFAS and increases in serum concentrations of emerging compounds from 1999 to 2011 in midlife women. Temporal trends in PFAS concentrations are not uniform across race/ethnicity and parity groups.

Investigating isomers/enantiomers of perfluorooctanoic acid in river water by gas chromatography-mass spectrometry with chiral derivatization

Perfluorooctanoic acid (PFOA) in environmental media contains numerous isomers/enantiomers because of the PFOA manufacturing process and biological degradation of PFOA precursors. Few methods for analyzing PFOA enantiomers have been described. A simple derivatization method using (S)-1-phenethyl chloride that was developed to allow PFOA isomers/enantiomers to be separated by gas chromatography and analyzed by electron-capture negative ionization mass spectrometry is described here. PFOA standards were analyzed, and enantiomers of the chiral isomers perfluoro-3-methyl-heptanoic acid, perfluoro-4-methyl-heptanoic acid, and perfluoro-3,5-dimethyl-hexanoic acid were separated using an HP-5MS column. Linear PFOA and perfluoro-6-methyl-heptanoic acid were chromatographically separated from these enantiomers. The linear ranges (giving correlation coefficients r > 0.997) of the calibration curves for the isomers were 0.010-3.00 ng/mL. PFOA isomer/enantiomer concentrations in river water were determined using the method. The method separated the enantiomers of perfluoro-3-methyl-heptanoic acid and perfluoro-4-methyl-heptanoic acid, the isomers of perfluoro-6-methyl-heptanoic acid, and linear PFOA in river water. No significant differences were found between the PFOA enantiomer/isomer compositions of the sample and technical PFOA. Enantiomer ratios can provide information about the sources and transport of pollutant isomers/enantiomers in the environment. Enantiomeric separation requires effective separation techniques. Our method achieved chiral separation using a non-chiral GC column that is often used in general analytical laboratories. The method could be used to investigate the sources and fates of PFOA and the isomers/enantiomers of other potentially toxic persistent pollutants in the environment and the risks posed to humans.

Isomer-specific biotransformation of perfluoroalkyl sulfonamide compounds in aerobic soil

As an important reservoir of pollutants, soil may play a critical role in altering isomer ratios of perfluorooctane sulfonate (PFOS) or PFOS precursors (PrePFOS) via microbial processes, but this possibility has not yet been investigated, as well as the feasibility of using PFOS isomer ratio for source tracking in PFOS contaminated sites. In the present study, N‑ethyl perfluorooctane sulfonamide ethanol (EtFOSE) of the technical grade was incubated in soil microcosms for 105 days to examine isomer-specific transformation processes. Experimental data combined with a mathematical model suggest new biotransformation pathways leading to PFOS, including a direct pathway to produce PFOS via hydrolysis of the sulfonamide bond. A similar rate of biotransformation was observed for EtFOSE with an estimated half-life of 8.7 and 9.6 days for the branched and linear isomers, respectively, without statistical difference. Two transformation intermediates, N‑ethyl perfluorooctanoic acid (EtFOSAA) and perfluorooctane sulfonamide (FOSA), also showed preferential biotransformation of branched isomers. On the contrary, one intermediate N‑ethyl perfluorooctane sulfonamide (EtFOSA) showed the preferred transformation of the linear isomer with an estimated half-life of 80.8 and 11.2 days for the branched and linear isomers, respectively. As PFOS is likely to be generated through more than one pathway or one precursor, its final isomer ratio is collectively determined by several upstream reactions, each having specific isomer-specific transformation kinetics. Though the soil showed enrichment of branched PFOS isomers during the 4-month incubation, compared to PFOS standards, some uncertainty arises in concluding preferential generation of branched PFOS from its precursors, due to the lack of standards for branched PreFOS. The complexity of isomer-specific biotransformation only reinforced the challenge of applying the PFOS isomer ratio for source tracking in environmental microbial systems.

Enantioselectivity in biotransformation and bioaccumulation processes of typical chiral contaminants

Chirality is a critical topic in the medicinal and agrochemical fields. One quarter of all agrochemicals was chiral in 1996, and this proportion has increased remarkably with the introduction of new compounds over time. Despite scientists have made great efforts to probe the enantiomeric selectivity of chiral chemicals in the environment since early 1990s, the different behaviours of individual enantiomers in biologically mediated processes are still unclear. In the present review, we highlight state-of-the-knowledge on the stereoselective biotransformation and accumulation of chiral contaminants in organisms ranging from invertebrates to humans. Chiral insecticides, fungicides, and herbicides, polychlorinated biphenyls (PCBs), pharmaceuticals, flame retardants hexabromocyclododecane (HBCD), and perfluorooctane sulfonate (PFOS) are all included in the target compounds. Key findings included: a) Changes in the enantiomeric fractions in vitro and in vivo models revealed that enantioselectivity commonly occurs in biotransformation and bioaccumulation. b) Emerging contaminants have become more important in the field of enantioselectivity together with their metabolites in biological transformation process. c) Chiral signatures have also been regarded as powerful tools for tracking pollution sources when the contribution of precursor is unknown. Future studies are needed in order to understand not only preliminary enrichment results but also detailed molecular mechanisms in diverse models to comprehensively understand the behaviours of chiral compounds.

Risk to human health related to the presence of perfluorooctane sulfonic acid and perfluorooctanoic acid in food

The European Commission asked EFSA for a scientific evaluation on the risks to human health related to the presence of perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) in food. Regarding PFOS and PFOA occurrence, the final data set available for dietary exposure assessment contained a total of 20,019 analytical results (PFOS n = 10,191 and PFOA n = 9,828). There were large differences between upper and lower bound exposure due to analytical methods with insufficient sensitivity. The CONTAM Panel considered the lower bound estimates to be closer to true exposure levels. Important contributors to the lower bound mean chronic exposure were 'Fish and other seafood', 'Meat and meat products' and 'Eggs and egg products', for PFOS, and 'Milk and dairy products', 'Drinking water' and 'Fish and other seafood' for PFOA. PFOS and PFOA are readily absorbed in the gastrointestinal tract, excreted in urine and faeces, and do not undergo metabolism. Estimated human half-lives for PFOS and PFOA are about 5 years and 2-4 years, respectively. The derivation of a health-based guidance value was based on human epidemiological studies. For PFOS, the increase in serum total cholesterol in adults, and the decrease in antibody response at vaccination in children were identified as the critical effects. For PFOA, the increase in serum total cholesterol was the critical effect. Also reduced birth weight (for both compounds) and increased prevalence of high serum levels of the liver enzyme alanine aminotransferase (ALT) (for PFOA) were considered. After benchmark modelling of serum levels of PFOS and PFOA, and estimating the corresponding daily intakes, the CONTAM Panel established a tolerable weekly intake (TWI) of 13 ng/kg body weight (bw) per week for PFOS and 6 ng/kg bw per week for PFOA. For both compounds, exposure of a considerable proportion of the population exceeds the proposed TWIs.

Risk to human health related to the presence of perfluorooctane sulfonic acid and perfluorooctanoic acid in food

The European Commission asked EFSA for a scientific evaluation on the risks to human health related to the presence of perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) in food. Regarding PFOS and PFOA occurrence, the final data set available for dietary exposure assessment contained a total of 20,019 analytical results (PFOS n = 10,191 and PFOA n = 9,828). There were large differences between upper and lower bound exposure due to analytical methods with insufficient sensitivity. The CONTAM Panel considered the lower bound estimates to be closer to true exposure levels. Important contributors to the lower bound mean chronic exposure were 'Fish and other seafood', 'Meat and meat products' and 'Eggs and egg products', for PFOS, and 'Milk and dairy products', 'Drinking water' and 'Fish and other seafood' for PFOA. PFOS and PFOA are readily absorbed in the gastrointestinal tract, excreted in urine and faeces, and do not undergo metabolism. Estimated human half-lives for PFOS and PFOA are about 5 years and 2-4 years, respectively. The derivation of a health-based guidance value was based on human epidemiological studies. For PFOS, the increase in serum total cholesterol in adults, and the decrease in antibody response at vaccination in children were identified as the critical effects. For PFOA, the increase in serum total cholesterol was the critical effect. Also reduced birth weight (for both compounds) and increased prevalence of high serum levels of the liver enzyme alanine aminotransferase (ALT) (for PFOA) were considered. After benchmark modelling of serum levels of PFOS and PFOA, and estimating the corresponding daily intakes, the CONTAM Panel established a tolerable weekly intake (TWI) of 13 ng/kg body weight (bw) per week for PFOS and 6 ng/kg bw per week for PFOA. For both compounds, exposure of a considerable proportion of the population exceeds the proposed TWIs.

Association among total serum isomers of perfluorinated chemicals, glucose homeostasis, lipid profiles, serum protein and metabolic syndrome in adults: NHANES, 2013-2014

Perfluorinated chemicals (PFCs) have been used widely in consumer products manufacture. Recent in vitro as well as animal studies have found that there are different toxicity and pharmacokinetic profiles between isomers of perfluorooctanoic acid (PFOA) and/or perfluorooctane sulfonate (PFOS). However, the differential effects of linear or branched PFOA/PFOS isomers on human beings have never been reported. Herein, we examined 1871 adult subjects (age older than 18 years) from the National Health and Nutrition Examination Survey (NHANES) 2013-2014 to determine the association between the isomers of PFOA/PFOS and serum biochemistry profiles, including glucose, lipids, protein and components of metabolic syndrome (MS). The results showed that for PFOA, increased linear PFOA was associated with increases in total cholesterol, serum albumin and an enhancement of β cell function as well as a decrease in the serum globulin. Increased branched PFOA was significantly associated with increased fasting glucose. All isomers of PFOA were positively associated with high-density lipoprotein-cholesterol (HDL-C) and negatively associated with glycohemoglobin (HbA1C). The branched PFOS was positively associated with β cell function and inversely associated with serum globulin. Both linear and branched isomers of PFOS were positively associated with the total protein and albumin. The increased branched PFOA was associated with less HDL-C insufficiency defined by the National Cholesterol Education Program Third Adult Treatment Panel (NCEP-ATP III) MS criteria, whereas the increased concentrations of serum total and linear PFOS were associated with less hypertriglyceridemia by the NCEP-ATP III. In conclusion, serum isomers of PFOA and PFOS were associated with glucose homeostasis, serum protein as well as lipid profiles; they were also indicators of MS. This may suggest that there is a distinct difference in the toxicokinetics of the isomers of PFOA and PFOS. Further clinical and animal studies are warranted to clarify the putative causal relationships between isomers and biochemical alterations.

Serum perfluoroalkyl acids (PFAAs) and associations with behavioral attributes

The ubiquitous use of poly- and perfluoroalkyl substances (PFASs) in a variety of industrial and consumer products has resulted in chronic exposure in most industrialized nations, and led to measurable concentrations in blood and other tissues in humans across all life stages; however, behavioral attributes that relate to exposure are not well studied. To further investigate how behavior may relate to PFAS exposure, 37 adults were recruited from central North Carolina. Participants provided blood samples and behavioral questionnaires were administered, asking questions about a variety of household, dietary, and behavioral outcomes. Six PFAAs, including PFHxA (geometric mean: 0.14 ng/mL), PFOA (1.57 ng/mL), PFNA (0.67 ng/mL), PFDA (0.28 ng/mL), PFHxS (3.17 ng/mL) and PFOS (4.96 ng/mL) were detected in >50% of the samples. Generally, males had higher serum levels than females across all chemicals, and levels were very similar to NHANES levels; however, PFHxS and PFDA levels were higher in our study population. Several personal characteristics and behaviors were associated with serum PFAS levels. Reported use of filtration devices was associated with lower levels of PFOA (28% lower, p = 0.03), but higher levels of PFHxA (122% higher, p = 0.04). Serum PFHxS levels were also elevated in individuals that vacuumed less often, and in individuals that reported consuming more microwavable foods. These results suggest that personal behaviors may be important determinants of PFAS exposures.

Temporal Shifts in Poly- and Perfluoroalkyl Substances (PFASs) in North Atlantic Pilot Whales Indicate Large Contribution of Atmospheric Precursors

Poly- and perfluoroalkyl substances (PFASs) are persistent, bioaccumulative anthropogenic compounds associated with adverse health impacts on humans and wildlife. PFAS production changed in North America and Europe around the year 2000, but impacts on wildlife appear to vary across species and location. Unlike other mammal species, cetaceans lack the enzyme for transforming an important intermediate precursor (perfluorooctane sulfonamide: FOSA), into a prevalent compound in most wildlife (perfluorooctanesulfonate: PFOS). Thus, their tissue burden differentiates these two compounds while other mammals contain PFOS from both direct exposure and precursor degradation. Here we report temporal trends in 15 PFASs measured in muscle from juvenile male North Atlantic pilot whales (Globicephala melas) harvested between 1986 and 2013. FOSA accounted for a peak of 84% of the 15 PFASs around 2000 but declined to 34% in recent years. PFOS and long-chained PFCAs (C9-C13) increased significantly over the whole period (2.8% yr-1 to 8.3% yr-1), but FOSA declined by 13% yr-1 after 2006. Results from FOSA partitioning and bioaccumulation modeling forced by changes in atmospheric inputs reasonably capture magnitudes and temporal patterns in FOSA concentrations measured in pilot whales. Rapid changes in atmospheric FOSA in polar and subpolar regions around 2000 helps to explain large declines in PFOS exposure for species that metabolize FOSA, including seafood consuming human populations. This work reinforces the importance of accounting for biological exposures to PFAS precursors.

Isomer-Specific Distribution of Perfluoroalkyl Substances in Blood

Perfluoroalkyl substances (PFASs) such as perfluorohexanesulfonate (PFHxS), perfluorooctanoate (PFOA), perfluorooctanesulfonate (PFOS) and PFOS-precursors are routinely measured in human plasma and serum, but their relative abundance in the blood cell fraction has not been carefully examined, particularly at the isomer-specific level. Human plasma and whole blood were collected and partitioning behaviors of PFASs and their isomers between plasma and blood cells were investigated. In human samples, mass fraction in plasma (Fp) for PFASs increased among perfluoroalkyl carboxylates as the carbon chain length increased from C6 (mean 0.24) to C11 (0.87), indicating preference for the plasma fraction with increasing chain length. However, among perfluoroalkyl sulfonates, PFHxS (mean 0.87) had a slightly higher Fp than PFOS (0.85). In vitro assays with spiked Sprague-Dawley rat blood were also conducted, and the results showed that PFOS-precursors had lower Fp values than perfluoroalkyl acids, with perfluoroctanesulfonamide having the lowest Fp (mean 0.24). Consistently, linear isomers of PFOS and PFOS-precursors had lower mean Fp than their corresponding total branched isomers. Multiplying by a factor of 2 is not a reasonable method to convert from whole blood to plasma PFAS concentrations, and current ratios could be used as more accurate conversion factors.

Impacts of daily intakes on the isomeric profiles of perfluoroalkyl substances (PFASs) in human serum

Perfluoroalkyl substances (PFASs) have been well studied in human daily intake for assessment of potential health risks. However, little is known about the isomeric compositions of PFASs in daily intake and their impacts on isomeric profiles in humans. In this study, we investigated the occurrence of PFASs with isomeric analysis in various human exposure matrices including foodstuffs, tap water and indoor dust. Perfluorooctanesulfonate (PFOS) and/or perfluorooctanoate (PFOA) were predominant in these exposure matrices collected in Tianjin, China. In fish and meat, linear (n-) PFOA was enriched with a percentage of 92.2% and 99.6%, respectively. Although n-PFOS was higher in fish (84.8%) than in technical PFOS (ca. 70%), it was much lower in meat (63.1%) and vegetables (58.5%). Dietary intake contributed >99% of the estimated daily intake (EDI) for the general population. The isomeric profiles of PFOA and PFOS in human serum were predicted based on the EDI and a one-compartment, first-order pharmacokinetic model. The isomeric percentage of n-PFOA in the EDI (98.6%) was similar to that in human serum (predicted: 98.2%, previously measured: 99.7%) of Tianjin residents. The results suggest direct PFOA intake plays an important role in its isomeric compositions in humans. For PFOS, the predicted n-PFOS (69.3%) was much higher than the previously measured values (59.2%) in human serum. This implies that other factors, such as indirect exposure to PFOS precursors and multiple excretion pathways, may contribute to the lower percentage of n-PFOS in humans than of technical PFOS.

Isomers/enantiomers of perfluorocarboxylic acids: Method development and detection in environmental samples

Perfluoroalkyl substances are globally distributed in both urban and remote settings, and routinely are detected in wildlife, humans, and the environment. One of the most prominent and routinely detected perfluoroalkyl substances is perfluorooctanoic acid (PFOA), which has been shown to be toxic to both humans and animals. PFOA exists as both linear and branched isomers; some of the branched isomers are chiral. A novel GC-NCI-MS method was developed to allow for isomer/enantiomer separation, which was achieved using two columns working in tandem; a 30-m DB-5MS column and a 30-m BGB-172 Analytik column. Samples were derivatized with diazomethane to form methyl esters of the PFOA isomers. In standards, at least eight PFOA isomers were detected, of which at least four were enantiomers of chiral isomers; one chiral isomer (P3) was sufficiently separated to allow for enantiomer-fraction calculations. Soil, sediment and plant samples from contaminated locations in Alabama and Georgia were analyzed. P3 was observed in most of these environmental samples, and was non-racemic in at least one sediment, suggesting the possibility of chirally selective generation from precursors or enantioselective sorption. In addition, the ratio of P3/linear PFOA was inversely related to distance from source, which we suggest might reflect a higher sorption affinity for the P3 over the linear isomer. This method focuses on PFOA, but preliminary results suggest that it should be broadly applicable to other chiral and achiral perfluorocarboxylic acids (PFCAs); e.g., we detected several other homologous PFCA isomers in our PFCA standards and some environmental samples.

Perfluoroalkyl substances (PFAS) including structural PFOS isomers in plasma from elderly men and women from Sweden: Results from the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS)

Per- and polyfluoroalkyl substances (PFASs) are a class of compounds with unique chemical properties that have been shown useful in a wide variety of applications because they provide materials with reduced surface tension and exceptional non-stick properties. PFASs are commonly found in impregnation materials, coatings of papers and textiles, fire-fighting foams, pesticides, and cleaning agents. The potential for human exposure to PFASs is high because of their widespread distribution. The aim of this study was to investigate levels of PFASs in men and women from Sweden and to assess the influence of gender and parity among women. Levels of 13 PFASs were determined in plasma samples collected during 2001-2004 from 1016 (507 women) 70year-old participants from the population-based Prospective Study of the Vasculature in Uppsala Seniors (PIVUS). The PFASs studied were nine perfluorinated carboxylic acids (PFCAs), four perfluorinated sulfonic acids (PFSAs) and perfluorooctane sulfonamide (PFOSA). In addition, structural isomers of perfluorooctane sulfonic acid (PFOS) were determined in a subset of 398 individuals. The detection rates were high and the majority of the studied compounds were detected in more than 75% of the participants. Levels of the selected analytes were found to be similar to other studies of non-occupationally exposed populations. Gender differences were observed in levels of PFHpA which was higher in men, while PFHxS was higher in women. Parity among women was shown to have a minor effect on PFAS concentrations and we found primi- and multiparous women to have slightly lower levels of PFUnDA when compared to nulliparous women.

Influence of contaminated drinking water on perfluoroalkyl acid levels in human serum--A case study from Uppsala, Sweden

In 2012 a contamination of drinking water with perfluoroalkyl acids (PFAAs) was uncovered in the City of Uppsala, Sweden. The aim of the present study was to determine how these substances have been distributed from the contamination source through the groundwater to the drinking water and how the drinking water exposure has influenced the levels of PFAAs in humans over time. The results show that PFAA levels in groundwater measured 2012-2014 decreased downstream from the point source, although high ΣPFAA levels (>100ng/L) were still found several kilometers from the point source in the Uppsala aquifer. The usage of aqueous film forming fire-fighting foams (AFFF) at a military airport in the north of the city is probably an important contamination source. Computer simulation of the distribution of PFAA-contaminated drinking water throughout the City using a hydraulic model of the pipeline network suggested that consumers in the western and southern parts of Uppsala have received most of the contaminated drinking water. PFAA levels in blood serum from 297 young women from Uppsala County, Sweden, sampled during 1996-1999 and 2008-2011 were analyzed. Significantly higher concentrations of perfluorobutane sulfonic acid (PFBS) and perfluorohexane sulfonic acid (PFHxS) were found among women who lived in districts modeled to have received contaminated drinking water compared to unaffected districts both in 1996-1999 and 2008-2011, indicating that the contamination was already present in the late 1990s. Isomer-specific analysis of PFHxS in serum showed that women in districts with contaminated drinking water also had an increased percentage of branched isomers. Our results further indicate that exposure via contaminated drinking water was the driving factor behind the earlier reported increasing temporal trends of PFBS and PFHxS in blood serum from young women in Uppsala.

Temporal changes (1997-2012) of perfluoroalkyl acids and selected precursors (including isomers) in Swedish human serum

Concentrations (including isomer patterns) and temporal changes (1997-2012) of perfluoroalkyl acids (PFAAs) and selected perfluorooctane sulfonate (PFOS) and perfluoroalkyl carboxylic acid (PFCA) precursors were determined in serum samples from Swedish women. Perfluorooctane sulfonamide (FOSA) and perfluorooctane sulfonamidoacetic acid (FOSAA), as well as its N-methyl and N-ethyl derivatives (MeFOSAA and EtFOSAA) were consistently detected. Highest PFOS precursor concentrations were found for EtFOSAA (before year 2000) or MeFOSAA and FOSAA (after 2000). Disappearance half-lives for all PFOS precursors were shorter compared to PFOS. 4:2/6:2 and 6:2/6:2 polyfluoroalkyl phosphate diesters (diPAPs) were detected in <60% of the samples, whereas 6:2/8:2 and 8:2/8:2 diPAPs were detected in >60% of the samples, but showed no significant change in concentrations over time. Linear and sum-branched isomers were quantified separately for three PFAAs and three precursors. Significant changes between 1997 and 2012 in the % linear isomer were observed for PFOA and FOSA (increase) and PFOS (decrease).

Perfluorooctane sulfonate: a review of human exposure, biomonitoring and the environmental forensics utility of its chirality and isomer distribution

Perfluorooctane sulfonate (PFOS) found extensive use for over 60 years up until its restriction in the early 2000s, culminating in its listing under the Stockholm Convention on Persistent Organic Pollutants (POPs) in 2009. Efforts to minimise human body burdens are hindered by uncertainty over their precise origins. While diet appears the principal source for the majority of western populations (with other pathways like dust ingestion, drinking water and inhalation also important contributors); the role played by exposure to PFOS-precursor compounds followed by in vivo metabolism to PFOS as the ultimate highly stable end-product is unclear. Such PFOS-precursor compounds include perfluorooctane sulfonamide derivates, e.g., perfluorooctane sulfonamides (FOSAs) and sulfonamidoethanols (FOSEs). Understanding the indirect contribution of such precursors to human body burdens of PFOS is important as a significant contribution from this pathway would render the margin of safety between the current exposure limits and estimates of external exposure to PFOS alone, narrower than hitherto appreciated. Estimates derived from mathematical modelling studies, put the contribution of so-called "precursor exposure" at between 10% and 40% of total PFOS body burdens. However, there are substantial uncertainties associated with such approaches. This paper reviews current understanding of human exposure to PFOS, with particular reference to recent research highlighting the potential of environmental forensics approaches based on the relative abundance and chiral signatures of branched chain PFOS isomers to provide definitive insights into the role played by "precursor exposure".