Analysis of structure–cytotoxicity in vitro relationship (SAR) for perfluorinated carboxylic acids

Proteomic and cardiac dysregulation by representative perfluoroalkyl acids of different chemical speciation during early embryogenesis of zebrafish

Perfluoroalkyl acids (PFAAs) of different chemical speciation were previously found to cause diverse toxicity. However, the toxicological mechanisms depending on chemical speciation are still largely unknown. In this follow-up study, zebrafish embryos were acutely exposed to only one concentration at 4.67 μM of the acid and salt of representative PFAAs, including perfluorooctanoic acid (PFOA), perfluorobutane carboxylic acid (PFBA), and perfluorobutanesulfonic acid (PFBS), till 96 h post-fertilization (hpf), aiming to gain more mechanistic insights. High-throughput proteomics found that PFAA acid and salt exerted discriminative effects on protein expression pattern. Bioinformatic analyses based on differentially expressed proteins underlined the developmental cardiotoxicity of PFOA acid with regard to cardiac muscle contraction, vascular smooth muscle contraction, adrenergic signaling in cardiomyocytes, and multiple terms related to myocardial contraction. PFOA salt and PFBS acid merely disrupted the cardiac muscle contraction pathway, while cardiac muscle cell differentiation was significantly enriched in PFBA acid-exposed zebrafish larvae. Consistently, under PFAA exposure, especially PFOA and PFBS acid forms, transcriptional levels of key genes for cardiogenesis and the concentrations of troponin and epinephrine associated with myocardial contraction were significantly dysregulated. Moreover, a transgenic line Tg (my17: GFP) expressing green fluorescent protein in myocardial cells was employed to visualize the histopathology of developing heart. PFOA acid concurrently caused multiple deficits in heart morphogenesis and function, which were characterized by the significant increase in sinus venosus and bulbus arteriosus distance (SV-BA distance), the induction of pericardial edema, and the decrease in heart rate, further confirming the stronger toxicity of PFOA acid than the salt counterpart on heart development. Overall, this study highlighted the developmental cardiotoxicity of PFAAs, with potency ranking PFOA > PFBS > PFBA. The acid forms of PFAAs induced stronger cardiac toxicity than their salt counterparts, providing an additional insight into the structure-toxicity relationship.

Significant Variability in the Developmental Toxicity of Representative Perfluoroalkyl Acids as a Function of Chemical Speciation

Current toxicological data of perfluoroalkyl acids (PFAAs) are disparate under similar exposure scenarios. To find the cause of the conflicting data, this study examined the influence of chemical speciation on the toxicity of representative PFAAs, including perfluorooctanoic acid (PFOA), perfluorobutane carboxylic acid (PFBA), and perfluorobutanesulfonic acid (PFBS). Zebrafish embryos were acutely exposed to PFAA, PFAA salt, and a pH-negative control, after which the developmental impairment and mechanisms were explored. The results showed that PFAAs were generally more toxic than the corresponding pH control, indicating that the embryonic toxicity of PFAAs was mainly caused by the pollutants themselves. In contrast to the high toxicity of PFAAs, PFAA salts only exhibited mild hazards to zebrafish embryos. Fingerprinting the changes along the thyroidal axis demonstrated distinct modes of endocrine disruption for PFAAs and PFAA salts. Furthermore, biolayer interferometry monitoring found that PFOA and PFBS acids bound more strongly with albumin proteins than did their salts. Accordingly, the acid of PFAAs accumulated significantly higher concentrations than their salt counterparts. The present findings highlight the importance of chemical forms to the outcome of developmental toxicity, calling for the discriminative risk assessment and management of PFAAs and salts.

Per- and polyfluoroalkyl substances in umbilical cord serum and body mass index trajectories from birth to age 10 years: Findings from a longitudinal birth cohort (SMBCS)

BACKGROUND

Prenatal exposure to per- and polyfluoroalkyl substances (PFAS) has been linked to low birth weight but higher childhood weight and obesity. However, little is known regarding the associations between PFAS exposure and dynamic body mass index (BMI) trajectories, particularly from birth through preadolescence.

OBJECTIVE

To evaluate the associations of cord serum PFAS concentrations with BMI trajectories from birth to age 10 years and longitudinal BMI in different periods.

METHODS

Based on 887 mother-child pairs in the longitudinal prospective birth cohort, we measured 12 PFAS congeners in cord serum and calculated BMI with anthropometric indicators at 9 follow-up time points from birth to age 10 years. The BMI trajectories were identified using group-based trajectory model (GBTM). To estimate the associations of cord serum PFAS levels with BMI trajectories and longitudinal changes in BMI, logistic regression models, linear mixed models, Bayesian kernel machine regression, and quantile-based g-computation models (QGC) were used.

RESULTS

The median concentrations of 10 PFAS congeners included in statistical analysis ranged from 0.047 to 3.623 μg/L. Two BMI trajectory classes were identified by GBTM, characterized by high group and low group. In logistic regression models, five PFAS congeners (PFBA, PFHpA, PFHxS, PFHpS, and PFDoDA) were associated with the higher probability of being in high BMI trajectory group (odds ratio, OR: 1.21 to 1.74, p < 0.05). Meanwhile, higher PFAS mixture were related to elevated odds for the high group in both BKMR models and QGC models, with PFHpA and PFHpS being the two most important drivers jointly. In the sex-stratified analysis, the positive associations remained significant exclusively among males. In the longitudinal analysis, PFUnDA and PFDoDA were associated with increased BMI from birth to age 10 years. Furthermore, PFBS and PFHpA were negatively related to BMI throughout infancy and toddlerhood (from birth to age 3 years), whereas PFDoDA confirmed a positive association with mid-childhood (from age 6 to 10 years) BMI.

CONCLUSIONS

Prenatal PFAS exposure was positively associated with BMI trajectories from birth to preadolescence and longitudinal BMI in various periods. Future research could use better trajectory modeling strategies to shape more complete growth trajectories and explore the relationship between BMI trajectories and adulthood health.

Adverse PFAS effects on mouse oocyte in vitro maturation are associated with carbon-chain length and inclusion of a sulfonate group

OBJECTIVES

Per- and polyfluoroalkyl substances (PFAS) are man-made chemicals that are widely used in various products. PFAS are characterized by their fluorinated carbon chains that make them hard to degrade and bioaccumulate in human and animals. Toxicological studies have shown PFAS toxic effects: cytotoxicity, immunotoxicity, neurotoxicity, and reproductive toxicity. However, it is still unclear how the structures of PFAS, such as carbon-chain length and functional groups, determine their reproductive toxicity.

METHODS AND RESULTS

By using a mouse-oocyte-in-vitro-maturation (IVM) system, we found the toxicity of two major categories of PFAS, perfluoroalkyl carboxylic acid (PFCA) and perfluoroalkyl sulfonic acid (PFSA), is elevated with increasing carbon-chain length and the inclusion of the sulfonate group. Specifically, at 600 μM, perfluorohexanesulfonic acid (PFHxS) and perfluorooctanesulfonic acid (PFOS) reduced the rates of both germinal-vesicle breakdown (GVBD) and polar-body extrusion (PBE) as well as enlarged polar bodies. However, the shorter PFSA, perfluorobutanesulfonic acid (PFBS), and all PFCA did not show similar adverse cytotoxicity. Further, we found that 600 μM PFHxS and PFOS exposure induced excess reactive oxygen species (ROS) and decreased mitochondrial membrane potential (MMP). Cytoskeleton analysis revealed that PFHxS and PFOS exposure induced chromosome misalignment, abnormal F-actin organization, elongated spindle formation, and symmetric division in the treated oocytes. These meiotic defects compromised oocyte developmental competence after parthenogenetic activation.

CONCLUSIONS

Our study provides new information on the structure-toxicity relationship of PFAS.

Distributions and sources of traditional and emerging per- and polyfluoroalkyl substances among multiple environmental media in the Qiantang River watershed, China

The presence of per- and polyfluoroalkyl substances (PFASs) in the food chain poses a threat to human health. Water and the atmosphere are the major transport pathways for PFASs in the environment, while water, soil and sediment are sinks. Herein, the concentrations and distributions of traditional and emerging PFASs in multi-environmental media samples in the Qiantang River watershed were comprehensively investigated. Twenty-five PFASs, including seven emerging PFASs, were identified. The concentrations in water, soil, sediment and PM_2.5 ranged from 3.58 to 786 ng L^-1, 0.72 to 12.3 ng g^-1, 0.73 to 6.60 ng g^-1, and 93.9 to 255 pg m^-3, respectively, with mean concentrations of 149 ng L^-1, 4.70 ng g^-1, 4.31 ng g^-1, and 156 pg m^-3. Perfluorooctanoic acid (PFOA) was the dominant contaminant in water, soil, and sediment, and perfluoropentanoic acid (PFPeA) was the dominant contaminant in PM_2.5. Hexafluoropropylene oxide-dimer acid (HFPO-DA) and 6 : 2 chlorinated polyfluorinated ether sulfonate (6 : 2 Cl-PFESA), as substitutes for PFOA and perfluorooctane sulfonate (PFOS), were detected, indicating the gradual replacement of traditional PFOA and PFOS in this area. Perfluoro-3,6-dioxaheptanoic acid (NFDHA), as a component of the aqueous film-forming foam FN-3, was first detected in this area. Short-chain PFASs were mainly distributed in water and PM_2.5, while long-chain PFASs were distributed in the solid phase, such as soil, sediment, and PM_2.5. Based on principal component analysis (PCA), the major PFAS sources were emulsifiers from fluorine polymerization and surface-active agents from the textile, papermaking, leather, and other industries. In addition, correlation analysis showed that water was the main source and transport pathway of short-chain perfluoroalkyl carboxylic acid (PFCA), HFPO-DA, and NFDHA in this area, while the atmosphere combined with PM_2.5 was the main transport pathway for both short- and long-chain PFCAs, PFOS, and 6 : 2 Cl-PFESA.

Occurrence and removal of poly/perfluoroalkyl substances (PFAS) in municipal and industrial wastewater treatment plants

The presence of poly- and perfluoroalkyl substances (PFAS) has caused serious problems for drinking water supplies especially at intake locations close to PFAS manufacturing facilities, wastewater treatment plants (WWTPs), and sites where PFAS-containing firefighting foam was regularly used. Although monitoring is increasing, knowledge on PFAS occurrences particularly in municipal and industrial effluents is still relatively low. Even though the production of C8-based PFAS has been phased out, they are still being detected at many WWTPs. Emerging PFAS such as GenX and F-53B are also beginning to be reported in aquatic environments. This paper presents a broad review and discussion on the occurrence of PFAS in municipal and industrial wastewater which appear to be their main sources. Carbon adsorption and ion exchange are currently used treatment technologies for PFAS removal. However, these methods have been reported to be ineffective for the removal of short-chain PFAS. Several pioneering treatment technologies, such as electrooxidation, ultrasound, and plasma have been reported for PFAS degradation. Nevertheless, in-depth research should be performed for the applicability of emerging technologies for real-world applications. This paper examines different technologies and helps to understand the research needs to improve the development of treatment processes for PFAS in wastewater streams.

Potency Ranking of Per- and Polyfluoroalkyl Substances Using High-Throughput Transcriptomic Analysis of Human Liver Spheroids

Per- and polyfluoroalkyl substances (PFAS) are some of the most prominent organic contaminants in human blood. Although the toxicological implications of human exposure to perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) are well established, data on lesser-understood PFAS are limited. New approach methodologies (NAMs) that apply bioinformatic tools to high-throughput data are being increasingly considered to inform risk assessment for data-poor chemicals. The aim of this study was to compare the potencies (ie, benchmark concentrations: BMCs) of PFAS in primary human liver microtissues (3D spheroids) using high-throughput transcriptional profiling. Gene expression changes were measured using TempO-seq, a templated, multiplexed RNA-sequencing platform. Spheroids were exposed for 1 or 10 days to increasing concentrations of 23 PFAS in 3 subgroups: carboxylates (PFCAs), sulfonates (PFSAs), and fluorotelomers and sulfonamides. PFCAs and PFSAs exhibited trends toward increased transcriptional potency with carbon chain-length. Specifically, longer-chain compounds (7-10 carbons) were more likely to induce changes in gene expression and have lower transcriptional BMCs. The combined high-throughput transcriptomic and bioinformatic analyses support the capability of NAMs to efficiently assess the effects of PFAS in liver microtissues. The data enable potency ranking of PFAS for human liver cell spheroid cytotoxicity and transcriptional changes, and assessment of in vitro transcriptomic points of departure. These data improve our understanding of the possible health effects of PFAS and will be used to inform read-across for human health risk assessment.

Potency Ranking of Per- and Polyfluoroalkyl Substances Using High-Throughput Transcriptomic Analysis of Human Liver Spheroids

Per- and polyfluoroalkyl substances (PFAS) are some of the most prominent organic contaminants in human blood. Although the toxicological implications of human exposure to perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) are well established, data on lesser-understood PFAS are limited. New approach methodologies (NAMs) that apply bioinformatic tools to high-throughput data are being increasingly considered to inform risk assessment for data-poor chemicals. The aim of this study was to compare the potencies (ie, benchmark concentrations: BMCs) of PFAS in primary human liver microtissues (3D spheroids) using high-throughput transcriptional profiling. Gene expression changes were measured using TempO-seq, a templated, multiplexed RNA-sequencing platform. Spheroids were exposed for 1 or 10 days to increasing concentrations of 23 PFAS in 3 subgroups: carboxylates (PFCAs), sulfonates (PFSAs), and fluorotelomers and sulfonamides. PFCAs and PFSAs exhibited trends toward increased transcriptional potency with carbon chain-length. Specifically, longer-chain compounds (7-10 carbons) were more likely to induce changes in gene expression and have lower transcriptional BMCs. The combined high-throughput transcriptomic and bioinformatic analyses support the capability of NAMs to efficiently assess the effects of PFAS in liver microtissues. The data enable potency ranking of PFAS for human liver cell spheroid cytotoxicity and transcriptional changes, and assessment of in vitro transcriptomic points of departure. These data improve our understanding of the possible health effects of PFAS and will be used to inform read-across for human health risk assessment.

Distribution, behaviour, bioavailability and remediation of poly- and per-fluoroalkyl substances (PFAS) in solid biowastes and biowaste-treated soil

Aqueous film-forming foam, used in firefighting, and biowastes, including biosolids, animal and poultry manures, and composts, provide a major source of poly- and perfluoroalkyl substances (PFAS) input to soil. Large amounts of biowastes are added to soil as a source of nutrients and carbon. They also are added as soil amendments to improve soil health and crop productivity. Plant uptake of PFAS through soil application of biowastes is a pathway for animal and human exposure to PFAS. The complexity of PFAS mixtures, and their chemical and thermal stability, make remediation of PFAS in both solid and aqueous matrices challenging. Remediation of PFAS in biowastes, as well as soils treated with these biowastes, can be achieved through preventing and decreasing the concentration of PFAS in biowaste sources (i.e., prevention through source control), mobilization of PFAS in contaminated soil and subsequent removal through leaching (i.e., soil washing) and plant uptake (i.e., phytoremediation), sorption of PFAS, thereby decreasing their mobility and bioavailability (i.e., immobilization), and complete removal through thermal and chemical oxidation (i.e., destruction). In this review, the distribution, bioavailability, and remediation of PFAS in soil receiving solid biowastes, which include biosolids, composts, and manure, are presented.

Non-targeted metabolomics of multiple human cells revealing differential toxic effects of perfluorooctanoic acid

Differences in toxic effects of contaminants among human cells are essential for evaluating their health risks to humans. In this study, non-targeted metabolomics of multiple human cell lines (A549 (lung), DLD-1 (intestine) and L-02 (liver) cells) was used to address the differential toxicity of perfluorooctanoic acid (PFOA). The number of differential metabolites (DMs) identified in the PFOA-treated A549 cells (67) was highest, followed by DLD-1 (12) and L-02 cells (10). The categorization of DMs was almost uniquely specific to each of cell lines. PFOA significantly promoted linoleic acid metabolism in L-02 cells whereas this metabolism was inhibited in the PFOA-treated A549 cells. The levels of interleukin (IL)-1β, IL-6, IL-8 and IL-13 were about 1.5 times higher in the PFOA-treated A549 and L-02 cells than in the controls. PFOA stimulated the biosynthesis of arginine and the metabolism of vitamin B6 in A549 cells. Arginine and vitamin B6 supplemented into cell culture effectively decreased the levels of IL-6 and IL-8. The inhibition of purine metabolism by PFOA resulted in the arrestation of DLD-1 cells at the G₀/G₁-phase. Our results suggest that the differential toxicity of PFOA related to exposure pathways could be elucidated by metabolic profiles specific to various human cells.

Comparison of zebrafish in vitro and in vivo developmental toxicity assessments of perfluoroalkyl acids (PFAAs)

Perfluoroalkyl acids (PFAAs) are persistent environmental contaminants that are associated with various adverse health outcomes. Perfluorooctanoic acid (PFOA) is one of the most prominently detected PFAAs in the environment, which is now replaced with shorter chain carbon compounds including perfluorohexanoic acid (PFHxA) and perfluorobutyric acid (PFBA). The aim of this study was to compare the toxicity of four PFAAs as a function of chain length and head group (carboxylate versus sulfonate) with in vitro and in vivo zebrafish assessments, which were subsequently compared to other cell and aquatic models. Mortality rate increased with chain length (PFOA > PFHxA ≫ PFBA) in both whole embryo/larvae and embryonic cell models. The sulfonate group enhanced toxicity with perfluorobutane sulfonate (PFBS) showing higher toxicity than PFBA and PFHxA in both larvae and cells. Toxicity trends were similar among different aquatic models, but sensitivities varied. Discrepancies with other zebrafish studies were confirmed to be associated with a lack of neutralization of acidic pH of dosing solutions in these other investigations, demonstrating the need for rigor in reporting pH of exposure solutions in all experiments. The zebrafish embryonic cell line was also found to be similar to most other cell lines regardless of exposure length. Overall, results agree with findings in other cell lines and organisms where longer chain length and sulfonate group increase toxicity, except in investigations not neutralizing the exposure solutions for these acidic compounds.

Effect of Perfluorooctanoic Acid on the Epigenetic and Tight Junction Genes of the Mouse Intestine

Perfluorooctanoic acid (PFOA) has been implicated in various toxicities including neurotoxicity, genotoxicity, nephrotoxicity, epigenetic toxicity, immunotoxicity, reproductive toxicity, and hepatotoxicity. However, information on the accumulation of PFOA in the intestine and its toxic effects on intestinal epigenetics and tight junction (TJ) genes is sparse. CD1 mice were dosed with PFOA (1, 5, 10, or 20 mg/kg/day) for 10 days, and its accumulation and induced alterations in the expression of epigenetic and tight junction genes in the small intestine and colon were evaluated using LC-MS and qPCR techniques. PFOA reduced the expression levels of DNA methyltransferases (Dnmt1, Dnmt3a, Dnmt3b) primarily in the small intestine whereas, in the colon, a decrease was observed only at high concentrations. Moreover, ten-eleven translocation genes (Tet2 and Tet3) expression was dysregulated in the small intestine, whereas in the colon Tets remained unaffected. The tight junction genes Claudins (Cldn), Occludin (Ocln), and Tight Junction Protein (Tjp) were also heavily altered in the small intestine. TJs responded differently across the gut, in proportion to PFOA dosing. Our study reveals that PFOA triggers DNA methylation changes and alters the expression of genes essential for maintaining the physical barrier of intestine, with more profound effects in the small intestine compared to the colon.

Combined effects and toxicological interactions of perfluoroalkyl and polyfluoroalkyl substances mixtures in human liver cells (HepG2)

The combined effects and toxicological interactions of perfluoroalkyl and polyfluoroalkyl substances (PFAS) mixtures remain largely unknown even though they occur as complex mixtures in the environment. This study investigated the toxicity of individual and combined PFAS to human liver cell line (HepG2). The Combination Index (CI)-isobologram equation method was used to determine the toxicological interactions of PFAS in binary, ternary and multi-component mixtures. The results indicated that the cytotoxicity of individual PFAS to HepG2 cells increased with increasing carbon chain lengths when separated into non-sulfonated and sulfonated groups. The respective cytotoxicity of PFAS is in the order of PFDA > PFNA > PFOA > PFHpA for perfluoroalkyl carboxylic acids and in the order of PFOS > PFHxS for perfluoroalkane sulfonic acids. The toxicological interaction of PFOS and PFOA with other PFAS clearly showed a different pattern of combined toxicity in HepG2 Cells. The binary, ternary, and multi-component combinations of PFOS with PFOA, PFNA, PFDA, PFHxS, and PFHpA displayed synergistic interactions for almost all inhibitory effect levels tested, whereas, either synergistic or antagonistic effect was observed in mixtures with PFOA. Overall, the pattern of interactions of PFAS mixtures is predominated by synergism, especially at low to medium effect levels; the exceptions to this were the antagonistic interactions found in mixture with PFOA, PFHxS, and PFHpA. These cytotoxicity results may have an implication on the health risk assessment of PFAS mixtures.

Spatiotemporal distribution and isomer profiles of perfluoroalkyl acids in airborne particulate matter in Chengdu City, China

Airborne particulate matter (APM) was collected in four seasons at five different areas of the city of Chengdu, China to study the spatial and seasonal contamination pattern of perfluoroalkyl acids (PFAAs). The results showed that ∑PFAA concentrations in Downtown Chengdu (mean value: 297 ± 238 pg/m³) were higher than concentrations in suburban areas. The highest concentrations of PFAAs occurred during spring (97.5-709 pg/L; arithmetic mean concentration: 297 ± 191 pg/L) while the lowest concentration occurred during autumn (9.27-105 pg/L; arithmetic mean concentration 41.1 ± 24.8 pg/L). Perfluorooctanoic acid (PFOA) was the main PFAA quantified during winter, summer and autumn, and perfluorononanoic acid (PFNA) was the predominant PFAA in spring. Relative humidity (RH) and average daily precipitation (PRE) showed significant negative correlations with PFAA concentrations in winter and summer, suggesting that they played an important role in controlling PFAA concentrations in APM. The linear structural isomer of PFOA (n-PFOA) was the most abundant isomer in APM in Chengdu, with the average proportion of 85.6% ± 6.13%, higher than the proportion in ECF PFOA commercial products (74.3-77.6%). However, the consistent fingerprint of branched PFOA in the APM implies that ECF PFOA makes a significant contribution to the PFOA in APM. PFOS in the APM collected throughout the year had a mean proportion of 54.0 ± 8.81% of n-PFOS. This proportion of n-PFOS is lower than commercial ECF products (62.9-78.2%), suggesting an additional proportion of branched PFOS isomers in APM in Chengdu.

In vitro and in silico modeling of perfluoroalkyl substances mixture toxicity in an amphibian fibroblast cell line

Poly and perfluoroalkyl substances (PFAS) are a large group of emerging organic pollutants that can persist in the environment and bioaccumulate in biota. They are found in complex mixtures, and although the exact number of PFAS is unknown, it has been estimated to be in the thousands. The objective of this study was two-fold. First, we examined the cytotoxicity of PFAS singly and in binary mixtures using an amphibian fibroblast cell line. Second, we used this experimental data to develop quantitative structure-activity relationship (QSAR) models for single and binary mixtures. We tested the cytotoxicity of four common PFAS: perfluorooctane sulfonate (PFOS); perfluorooctanoic acid (PFOA); perfluorohexane sulfonate (PFHxS); and perfluorohexanoic acid (PFHxA). PFOS was the most toxic and PFHxA the least cytotoxic. Binary mixtures allowed for the construction of isobolograms to test for additivity, synergism, or antagonism. Using this data, QSAR modeling was used for predicting the toxicity of 24 single and 1380 binary mixtures (theoretically generated). Overall, our experimental and modeling results showed that mixtures were approximately additive, with the exception of PFOS and PFOA, which were found to be weakly synergistic. This data shows that certain mixtures of PFAS may have increased toxicity potential above what the simple sum of PFAS concentrations would suggest. More studies are needed that test the toxicity of PFAS mixtures.

Effect of perfluorodecanoic acid on pig oocyte viability, intracellular calcium levels and gap junction intercellular communication during oocyte maturation in vitro

Perfluorodecanoic acid (PFDA) is a synthetic perfluorinated compound, which has been reported to exert adverse effects on somatic cells. However, its effects on germ cells have not been studied to date. The aim of the present study was to analyze the effects of PFDA on the viability, intracellular calcium levels and gap junction intercellular communication (GJIC) during porcine oocyte maturation in vitro. PFDA negatively impacted oocyte viability (medium lethal concentration, LC₅₀ = 7.8 μM) and maturation (medium inhibition of maturation, IM₅₀ = 3.8 μM). Oocytes exposed to 3.8 μM PFDA showed higher levels of intracellular calcium relative to control oocytes. In addition, GJIC among the cumulus cells and the oocyte was disrupted. The effects of PFDA on oocyte calcium homeostasis and intercellular communication seem to be responsible for the inhibition of oocyte maturation and oocyte death. In addition, since the deleterious effects of PFDA on oocyte viability, maturation and GJIC are significantly stronger than the previously reported effects of another widely used perfluorinated compound (Perfluorooctane sulfonate) in the same model, the use of PFDA in consumer products is questioned.

Perfluorohexanoic acid toxicity, part I: Development of a chronic human health toxicity value for use in risk assessment

Perfluorohexanoic acid (PFHxA) is a short-chain, six-carbon perfluoroalkyl acid (PFAA) and is a primary impurity, degradant, and metabolite associated with the short-chain fluorotelomer-based chemistry used globally today. The transition to short-chain fluorotelomer-based products as a cornerstone in replacement fluorochemistry has raised questions regarding potential human health risks associated with exposure to fluorotelomer-based substances and therefore, PFHxA. Here, we present a critical review of data relevant to such a risk assessment, including epidemiological studies and in vivo and in vitro toxicity studies that examined PFHxA acute, subchronic, and chronic toxicity. Key findings from toxicokinetic and mode-of-action studies are also evaluated. Sufficient data exist to conclude that PFHxA is not carcinogenic, is not a selective reproductive or developmental toxicant, and does not disrupt endocrine activity. Collectively, effects caused by PFHxA exposure are largely limited to potential kidney effects, are mild and/or reversible, and occur at much higher doses than observed for perfluorooctanoic acid (PFOA). A chronic human-health-based oral reference dose (RfD) for PFHxA of 0.25 mg/kg-day was calculated using benchmark dose modeling of renal papillary necrosis from a chronic rat bioassay. This RfD is four orders of magnitude greater than the chronic oral RfD calculated by the U.S. Environmental Protection Agency for PFOA. The PFHxA RfD can be used to inform public health decisions related to PFHxA and fluorotelomer precursors for which PFHxA is a terminal degradant. These findings clearly demonstrate that PFHxA is less hazardous to human health than PFOA. The analyses presented support site-specific risk assessments as well as product stewardship initiatives for current and future short-chain fluorotelomer-based products.

Evaluation of Single and Joint Toxicity of Perfluorinated Carboxylic Acids and Copper to Metal-Resistant Arthrobacter Strains

Perfluorocarboxylic acid compounds (PFCAs) and copper have been regarded as ubiquitous environmental contaminants in aquatic ecosystems worldwide. However, data on their possible joint toxic effects on microorganisms are still lacking. To study the combined effects of four PFCAs with different carbon chain lengths and copper, a series of experiments were conducted to explore the acute toxicity of these PFCAs in the absence and presence of copper on a metal-resistant Arthrobacter strain GQ-9 by microcalorimetry. The thermokinetic parameters, including growth rate constant (k), inhibitory ratio (I), and half inhibitory concentration (IC₅₀), were calculated and compared using the data obtained from the power-time curves. Our work revealed that GQ-9 is more resistant to perfluorooctanoic acid (PFOA) than Escherichia coli. The single and joint toxicity of PFCAs with copper are dose- and carbon chain length-dependent. The longer the carbon chain length of PFCAs, the higher the toxicity. In addition, PFCAs interacted synergistically with copper. This work could provide useful information for the risk assessment of co-exposure to perfluorinated compounds and heavy metals in natural environments.

Efficiency of maternal-fetal transfer of perfluoroalkyl and polyfluoroalkyl substances

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) can be transferred from a mother to her fetus during pregnancy and adversely affect fetal development. However, the efficiency and influencing factors of PFASs maternal-fetal transfer remain unclear. We measured the levels of six perfluoroalkylcarboxylates, three perfluoroalkylsulfonates, and one sulfonamide in 369 pairs of maternal and umbilical cord serum and examined the transplacental transfer efficiency (TTE) of PFASs by the functional group and carbon chain length in a prospective birth cohort in Shandong, China. All ten PFASs were detected in both maternal and umbilical cord serum in nearly all samples. Maternal and cord levels were closely correlated (the correlation coefficient [r] ranging from 0.485 to 0.908) in most PFASs except perfluorobutane sulfonic acid (PFBS) (r = 0.159). TTE was significantly affected by the functional group and carbon chain length. Compared to perfluoroalkylcarboxylates, perfluoroalkylsulfonates had a lower ratio of maternal to fetal transfer. A U-shaped relationship between carbon chain length and TTE was observed for perfluoroalkylcarboxylates while a monotonic descending trend was identified between TTE and the increasing carbon chain length for perfluoroalkylsulfonates. PFASs can readily pass through the placenta. The functional group and carbon chain length are important determinants for the TTE of PFASs.

Perfluoroalkyl substances in umbilical cord serum and gestational and postnatal growth in a Chinese birth cohort

Although animal studies have found that perfluoroalkyl substances (PFASs) affect gestational and postnatal growth, the epidemiological findings are limited and not in agreement. We explored the associations of PFAS concentrations in umbilical cord blood with gestational and postnatal growth in China. Three hundred thirty-seven singleton newborns and their mothers were recruited from November 2013 to December 2015 in Zhoukou City, China. Umbilical cord blood was collected to measure eleven PFASs by liquid chromatography-mass spectrometry. The index of gestational and postnatal growth contained fetal weight, length, and head circumference. These were obtained at birth and at the follow-up investigation (mean 19 months). Exposed to higher perfluorooctanoic acid (PFOA) were connected with reduced length at birth (p for trend = 0.01) and decreased postnatal weight (β = -429.2 g; 95% CI: -858.4, -0.121 for 2nd VS. 1st). Exposed to perfluoroundecanoic acid (PFUdA) were positively associated with indications of gestational growth and postnatal growth (p for trend = 0.02 for birth length; p for trend = 0.04 for postnatal length). Exposed to higher perfluorododecanoic acid (PFDoA) were associated with lower birth weight (β = -122.9 g, 95% CI: -244.7 to -1.2 for 2nd VS. 1st), but higher postnatal length (p for trend = 0.03). Neonates in the highest exposure group of per-fluorohexanesulfonate (PFHxS) showed decreased birth length (β = -0.33 cm, 95% CI: -0.68 to -0.01, for 2nd VS. 1st), but increased postnatal head circumference (p for trend = 0.04). Increased PFOA concentrations was associated with shorter birth length only in girls (p for trend = 0.04), suggesting that the effect of PFASs on gestational growth were different between boys and girls. In utero exposure to PFASs may affect gestational and postnatal growth.

Mechanism of bisphenol AF-induced progesterone inhibition in human chorionic gonadotrophin-stimulated mouse Leydig tumor cell line (mLTC-1) cells

Bisphenol AF (BPAF) has been shown to inhibit testicular steroidogenesis in male rats. However, the precise mechanisms related to the toxic effects of BPAF on reproduction remain poorly understood. In the present study, a mouse Leydig tumor cell line (mLTC-1) was used as a model to investigate the mechanism of steroidogenic inhibition and to identify the molecular target of BPAF. Levels of progesterone and the concentration of cyclic adenosine monophosphate (cAMP) in cells exposed to BPAF were detected, and expression of key genes and proteins in steroid biosynthesis was assessed. The results showed that BPAF exposure decreased human chorionic gonadotrophin (hCG)-stimulated progesterone production in a dose-dependent manner. The 24-h IC₅₀ (half maximal inhibitory concentration) value for BPAF regarding progesterone production was 70.2 µM. A dramatic decrease in cellular cAMP concentration was also observed. Furthermore, BPAF exposure inhibited expression of genes and proteins involved in cholesterol transport and progesterone biosynthesis. Conversely, the protein levels of steroidogenic acute regulatory protein (StAR) were not altered, and those of progesterone were still decreased upon 22R-hydroxycholesterol treatment of cells exposed to higher doses of BPAF. Together, these data indicate that BPAF exposure inhibits progesterone secretion in hCG-stimulated mLTC-1 cells by reducing expression of scavenger receptor class B type I (SR-B1) and cytochrome P450 (P450scc) due to the adverse effects of cAMP. However, StAR might not be the molecular target in this process.

Comprehensive insights into the interaction mechanism between perfluorodecanoic acid and human serum albumin

In this investigation, we explored the toxic effects of perfluorodecanoic acid (PFDA) on human serum albumin (HSA), established the interaction mode of PFDA with HSA, and provided a new strategy for the evaluation of toxicity of PFDA on functional proteins.

Perfluorohexadecanoic acid increases paracellular permeability in endothelial cells through the activation of plasma kallikrein-kinin system

Per- and polyfluoroalkyl substances (PFASs) are ubiquitous and high persistent in human blood, thus potentially inducing a myriad of deleterious consequences. Plasma kallikrein-kinin system (KKS), which physiologically regulates vascular permeability, is vulnerable to exogenous stimulators, like PFASs with long-chain alkyl backbone substituted by electronegative fluorine. The study on the interactions of PFASs with the KKS and the subsequent effects on vascular permeability would be helpful to illustrate how the chemicals penetrate the biological vascular barriers to reach different tissues. In present study, three representative PFASs, including perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA) and perfluorohexadecanoic acid (PFHxDA), were investigated for their effects on the activation of the KKS, paracellular permeability in human retina endothelial cells (HRECs) and integrity of the adherens junctions. In contrast to either PFOS or PFOA, PFHxDA efficiently triggered KKS activation in a concentration-dependent manner based on protease activity assays. The plasma activated by PFHxDA significantly increased paracellular permeability of HRECs through the degradation of adherens junctions. As evidenced by the antagonistic effect of aprotinin, PFHxDA-involved effects on vascular permeability were mediated by KKS activation. The results herein firstly revealed the mechanistic pathway for PFHxDA induced effects on vascular endothelial cells. Regarding the possible structure-related activities of the chemicals, this finding would be of great help in the risk assessment of PFASs.

Elevation of intracellular calcium and oxidative stress is involved in perfluorononanoic acid–induced neurotoxicity

Perfluorononanoic acid (PFNA) is one of the major perfluorinated compounds found in both biological and abiotic samples and has recently been demonstrated to cause neurobehavioral defects in mammals. In this study, pheochromocytoma-12 (PC12) cells were exposed to various doses of PFNA to explore the cytotoxicity of PFNA to neurons and the possible mechanisms underlying these effects. The results showed that exposure to PFNA dose-dependently decreased the viability of PC12 cells and increased the release of lactate dehydrogenase into cell culture media. Exposure to PFNA increased the malondialdehyde content and decreased the total antioxidant capacity and glutathione peroxidase activity in PC12 cell culture supernatants. Exposure to PFNA increased the intracellular calcium level and upregulated the Ca2+/calmodulin-dependent protein kinase II (CaMKII) expression in PC12 cells. PFNA also decreased Bcl-2 expression and increased Bax expression in PC12 cells. These results suggested that exposure to PFNA elevated the intracellular calcium level and activated the CaMKII signaling pathway, which may aggravate oxidative stress in PC12 cells and lead to cell damage or cell apoptosis.

Structure-Dependent Hematological Effects of Per- and Polyfluoroalkyl Substances on Activation of Plasma Kallikrein-Kinin System Cascade

Per- and polyfluoroalkyl substances (PFASs) are a global concern because of their ubiquitous occurrence and high persistence in human blood, and increasing amounts of unidentified fluorinated compounds are now becoming new exposure issues. This study aims to investigate the structure-related effects of PFASs on the activation of the plasma kallikrein-kinin system (KKS). The effects of 20 PFASs and the related long-chain aliphatic compounds were screened, and their binding affinities for the initial zymogen, Hagmen factor XII (FXII) in the KKS, were evaluated by molecular docking analysis. PFASs were demonstrated to activate the KKS in a structure-dependent mode. More specifically, PFASs with longer carbon chain length, higher fluorine atom substitution degree, and terminal acid group exhibited relatively higher activities in activating the KKS. The binding affinities of PFASs with FXII determined their capabilities for inducing KKS activation. The alternative binding modes of PFASs with FXII, together with van der Waals and hydrogen bonds, specifically accommodated the distinctive chemical structures. To our knowledge, PFASs, for the first time, were found to induce the activation of the KKS in plasma, and their chemical structure-related effects would be extremely important for risk assessment on emerging PFASs in addition to the listing in Stockholm Convention.

Effects of prenatal exposure to perfluoroalkyl acids on prevalence ofallergic diseases among 4-year-old children

Perfluoroalkyl acids (PFAAs) are ubiquitous chemicals extremely resistant and widespread throughout the environment, frequently being detected in human blood samples. Animal studies have revealed that exposure to PFAAs results in immunotoxicity. However, the association between PFAAs, especially long-chain PFAAs, and allergies in humans is not well established. We examined whether prenatal exposure to PFAAs is associated with allergic diseases among 4-year-old children in a large-scale prospective birth cohort in Hokkaido, Japan. In total, 1558 mother-child pairs were included in this study and prenatal levels of eleven PFAAs were measured in maternal plasma samples obtained between 28 and 32weeks of pregnancy by using ultra-performance liquid chromatography-tandem mass spectrometry. Participant demographic and characteristic information were obtained from self-administered pre- and postnatal questionnaires and medical birth records. Infant allergies were assessed using the Japanese version of the International Study of Asthma and Allergies in Childhood (ISAAC) Phase Three questionnaire, which was administered 4years post-delivery. Symptoms included eczema, wheezing and rhinoconjunctivitis with a prevalence of 19.0%, 18.7%, and 5.4%, respectively. Associations of PFAA quartiles with allergic outcomes were examined using logistic models. Adjusted odds ratios (ORs) in the 4th quartile vs. 1st quartile (Q4 vs. Q1) for total allergic diseases (including at least one allergic outcome) significantly decreased for perfluorododecanoic acid (PFDoDa) (Q4 vs. Q1 OR: 0.621; 95% confidence interval (CI): 0.454, 0.847) and perfluorotridecanoic acid (PFTrDA) (Q4 vs. Q1 OR: 0.712; 95% CI: 0.524, 0.966) in all children. We obtained similar results when examining the association between PFAAs and eczema. The adjusted OR (Q4 vs. Q1) for wheezing in relation to higher maternal PFHxS levels was 0.728 (95% CI: 0.497, 1.06) in all children. In conclusion, prenatal exposure to long-chain PFAAs, such as PFDoDa and PFTrDA may have an immunosuppressive effect on allergic diseases in 4-year-old children.

Effects of bisphenol analogues on steroidogenic gene expression and hormone synthesis in H295R cells

The use of Bisphenol A (BPA) has been regulated in many countries because of its potential adverse effects on human health. As a result of the restriction, structural anologues such as bisphenol S (BPS) and bisphenol F (BPF) have already been used for industrial applications as alternatives to BPA. Bisphenol AF (BPAF) is mainly used as a crosslinker in the synthesis of specialty fluoroelastomers. These compounds have been detected in various environmental matrices and human samples. Previous studies have shown that these compounds have potential endocrine disrupting effects on wildlife and mammals in general. However, the effects on adrenocortical function and the underlying mechanisms are not fully understood. In the present study, the H295R cell line was used as a model to compare the cell toxicity and to investigate the potential endocrine disrupting action of four BPs (including BPA, BPS, BPF, and BPAF). The half lethal concentration (LC50) values at 72 h exposure indicated that the rank order of toxicities of the chemicals was BPAF > BPA > BPS > BPF. The hormone results demonstrated that BPA analogues, such as BPF, BPS and BPAF were capable of altering steroidogenesis in H295R cells. BPA and BPS exhibited inhibition of hormone production, BPF predominantly led to increased progesterone and 17β-estradiol levels and BPAF showed induction of progesterone and reduction of testosterone. Inhibition effects of BPA and BPAF on hormone production were probably mediated by down-regulation of steroidogenic genes in H295R cells. However, the mechanisms of the endocrine interrupting action of BPF and BPS are still unclear, which may have additional mechanisms that have not been detected with BPA.

Placental Transfer of Perfluoroalkyl Substances and Associations with Thyroid Hormones: Beijing Prenatal Exposure Study

Perfluoroalkyl substances (PFASs) have been detected in wildlife and human samples worldwide. Toxicology research showed that PFASs could interfere with thyroid hormone homeostasis. In this study, eight PFASs, fifteen PFAS precursors and five thyroid hormones were analyzed in 157 paired maternal and cord serum samples collected in Beijing around delivery. Seven PFASs and two precursors were detected in both maternal and cord sera with significant maternal-fetal correlations (r = 0.336 to 0.806, all P < 0.001). The median ratios of major PFASs concentrations in fetal versus maternal serum were from 0.25:1 (perfluorodecanoic acid, PFDA) to 0.65:1 (perfluorooctanoic acid, PFOA). Spearman partial correlation test showed that maternal thyroid stimulating hormone (TSH) was negatively correlated with most maternal PFASs (r = −0.261 to −0.170, all P < 0.05). Maternal triiodothyronin (T3) and free T3 (FT3) showed negative correlations with most fetal PFASs (r = −0.229 to −0.165 for T3; r = −0.293 to −0.169 for FT3, all P < 0.05). Our results suggest prenatal exposure of fetus to PFASs and potential associations between PFASs and thyroid hormone homeostasis in humans.

Structure-dependent binding and activation of perfluorinated compounds on human peroxisome proliferator-activated receptor γ

Perfluorinated compounds (PFCs) have been shown to disrupt lipid metabolism and even induce cancer in rodents through activation of peroxisome proliferator-activated receptors (PPARs). Lines of evidence showed that PPARα was activated by PFCs. However, the information on the binding interactions between PPARγ and PFCs and subsequent alteration of PPARγ activity is still limited and sometimes inconsistent. In the present study, in vitro binding of 16 PFCs to human PPARγ ligand binding domain (hPPARγ-LBD) and their activity on the receptor in cells were investigated. The results showed that the binding affinity was strongly dependent on their carbon number and functional group. For the eleven perfluorinated carboxylic acids (PFCAs), the binding affinity increased with their carbon number from 4 to 11, and then decreased slightly. The binding affinity of the three perfluorinated sulfonic acids (PFSAs) was stronger than their PFCA counterparts. No binding was detected for the two fluorotelomer alcohols (FTOHs). Circular dichroim spectroscopy showed that PFC binding induced distinctive structural change of the receptor. In dual luciferase reporter assays using transiently transfected Hep G2 cells, PFCs acted as hPPARγ agonists, and their potency correlated with their binding affinity with hPPARγ-LBD. Molecular docking showed that PFCs with different chain length bind with the receptor in different geometry, which may contribute to their differences in binding affinity and transcriptional activity.

Evaluation of perfluorooctanoate for potential genotoxicity

Perfluorooctanoate (PFOA) is a fully fluorinated eight-carbon fatty acid analog with exceptional stability toward degradation that has been used as an industrial surfactant and has been detected in environmental and biological matrices. Exposures to PFOA in the workplace and in the environment have continuously stimulated investigations into its potential human health hazards. In this article, the results of fifteen unpublished genotoxicity assays conducted with perfluorooctanoate (as either the linear or linear/branched ammonium salt (APFO) or the linear/branched sodium salt) are reported and include: seven mutation assays (three in vitro reverse mutation assays with histidine auxotrophic strains of Salmonella typhimurium, two in vitro reverse mutation assays with the tryptophan auxotrophic Escherichia coli WP2uvr strain, one in vitro mitotic recombination (gene conversion) assay with Saccharomyces cerevisiae D4, and an in vitro Chinese hamster ovary (CHO) HGPRT forward mutation assay); seven studies to assess potential for chromosomal damage (three in vitro CHO chromosomal aberration studies, an in vitro human whole blood lymphocyte chromosomal aberration study, and three in vivo mouse micronucleus assays); and an in vitro C3H 10T1/2 cell transformation assay. Although PFOA has not been demonstrated to be metabolized, all in vitro assays were conducted both in the presence and in the absence of a mammalian hepatic microsomal activation system. These assays were originally described in twelve contract laboratory reports which have been available via the United States Environmental Protection Agency public docket (Administrative Record 226) for over a decade; however, the details of these assays have not been published previously in the open scientific literature. With the exception of limited positive findings at high and cytotoxic concentrations in some assay trials which reflected the likely consequence of cytotoxic disruption of normal cellular processes and not a specific genotoxic effect, the results of the studies presented in this paper and other published results clearly demonstrate the absence of direct mutagenic or genotoxic risk associated with PFOA. This finding is consistent with the physical/chemical characteristics of PFOA and is supported by other published genotoxicity studies.

Perfluorinated chemicals: differential toxicity, inhibition of aromatase activity and alteration of cellular lipids in human placental cells

The cytotoxicity of eight perfluorinated chemicals (PFCs), namely, perfluorobutanoic acid (PFBA), perfluorohexanoic acid (PFHxA), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorododecanoic acid (PFDoA), perfluorobutanesulfonate (PFBS), perfluorohexanesulfonate (PFHxS) and perfluorooctanesulfonate (PFOS) was assessed in the human placental choriocarcinoma cell line JEG-3. Only the long chain PFCs--PFOS, PFDoA, PFNA, PFOA--showed significant cytotoxicity in JEG-3 cells with EC50 values in the range of 107 to 647 μM. The observed cytotoxicity was to some extent related to a higher uptake of the longer chain PFCs by cells (PFDoA>PFOS≫PFNA>PFOA>PFHxA). Moreover, this work evidences a high potential of PFOS, PFOA and PFBS to act as aromatase inhibitors in placental cells with IC50s in the range of 57-80 μM, the inhibitory effect of PFBS being particularly important despite the rather low uptake of the compound by cells. Finally, exposure of JEG-3 cells to a mixture of the eight PFCs (0.6 μM each) led to a relative increase (up to 3.4-fold) of several lipid classes, including phosphatidylcholines (PCs), plasmalogen PC and lyso plasmalogen PC, which suggests an interference of PFCs with membrane lipids. Overall, this work highlights the ability of the PFC mixture to alter cellular lipid pattern at concentrations well below those that generate toxicity, and the potential of the short chain PFBS, often considered a safe substitute of PFOS, to significantly inhibit aromatase activity in placental cells.

Trophic magnification and isomer fractionation of perfluoroalkyl substances in the food web of Taihu Lake, China

Biomagnification of perfluoroalkyl substances (PFASs) are well studied in marine food webs, but related information in fresh water ecosystem and knowledge on fractionation of their isomers along the food web are limited. The distribution, bioaccumulation, magnification, and isomer fractionation of PFASs were investigated in a food web of Taihu Lake, China. Perfluorooctanesulfonate (PFOS) and perfluorocarboxylates (PFCAs) with longer carbon chain lengths, such as perfluorodecanoate (PFDA) and perfluoroundecanoate (PFUnA), were predominant in organisms, while perfluorohexanoate (PFHxA) and perfluorooctanoate (∑PFOA) contributed more in the water phase. The consistent profile signature of PFOA isomers in water phase with 3M electrochemical fluorination (ECF) products suggests that ECF production of PFOA still exists in China. Linear proportions of PFOA, PFOS and perfluorooctane sulfonamide (PFOSA) in the biota were in the range of 91.9-100%, 78.6-95.5%, and 72.2-95.5%, respectively, indicating preferential bioaccumulation of linear isomers in biota. Trophic magnification factors (TMFs) were estimated for PFDA (2.43), perfluorododecanoate (PFDoA) (2.68) and PFOS (3.46) when all biota were included, suggesting that PFOS and long-chained PFCAs are biomagnified in the fresh water food web. The TMF of PFOS isomers descended in the order: n-PFOS (3.86) > 3+5m-PFOS (3.35) > 4m-PFOS (3.32) > 1m-PFOS (2.92) > m2-PFOS (2.67) > iso-PFOS (2.59), which is roughly identical to their elution order on a FluoroSep-RP Octyl column, suggesting that hydrophobicity may be an important contributor for isomer discrimination in biota.

Structure-activity relationships for perfluoroalkane-induced in vitro interference with rat liver mitochondrial respiration

Perfluorinated alkyl acids (PFAAs) represent a broad class of commercial products designed primarily for the coatings industry. However, detection of residues globally in a variety of species led to the discontinuation of production in the U.S. Although PFAAs cause activation of the PPARα and CAR nuclear receptors, interference with mitochondrial bioenergetics has been implicated as an alternative mechanism of cytotoxicity. Although the mechanisms by which the eight carbon chain PFAAs interfere with mitochondrial bioenergetics are fairly well described, the activities of the more highly substituted or shorter chain PFAAs are far less well characterized. The current investigation was designed to explore structure-activity relationships by which PFAAs interfere with mitochondrial respiration in vitro. Freshly isolated rat liver mitochondria were incubated with one of 16 different PFAAs, including perfluorinated carboxylic, acetic, and sulfonic acids, sulfonamides and sulfamido acetates, and alcohols. The effect on mitochondrial respiration was measured at five concentrations and dose-response curves were generated to describe the effects on state 3 and 4 respiration and respiratory control. With the exception of PFOS, all PFAAs at sufficiently high concentrations (>20μM) stimulated state 4 and inhibited state 3 respiration. Stimulation of state 4 respiration was most pronounced for the carboxylic acids and the sulfonamides, which supports prior evidence that the perfluorinated carboxylic and acetic acids induce the mitochondrial permeability transition, whereas the sulfonamides are protonophoric uncouplers of oxidative phosphorylation. In both cases, potency increased with increasing carbon number, with a prominent inflection point between the six and eight carbon congeners. The results provide a foundation for classifying PFAAs according to specific modes of mitochondrial activity and, in combination with toxicokinetic considerations, establishing structure-activity-based boundaries for initial estimates of risk for noncancer endpoints for PFAAs for which minimal in vivo toxicity testing currently exists.

Environmental toxicity of PFCs: an enhanced integrated biomarker assessment and structure-activity analysis

Perfluorinated chemicals (PFCs) are a group of compounds with varying carbon chains and functional groups. Currently, available toxicity studies of PFCs are limited mainly to dominant species. While many other PFCs are detected in the environment and biota, it is important to extend toxicity studies to different types of PFCs to better assess their environmental and ecological impacts. In the present study, the environmental toxicity of perfluorooctanesulfonate, perfluoroocanoic acid, perfluorononanoic acid, and perfluorodecanoic acid were evaluated in green mussel, Perna viridis, using a new and improved integrated biomarker approach, the enhanced integrated biomarker response (EIBR) system, with biomarkers from multiple biological levels. Structure-activity relationships were also examined based on the biomarker results. The results show that the 4 PFCs have distinct toxicity patterns and the integrative toxicity, in terms of the EIBR value, is governed by the fluorinated chain length. In addition to commonly recognized chain length and functional group effects, several structural factors are also involved in the toxic actions of PFCs, including hydrophobicity and molecular size, and so on. By integrating biomarkers from multiple biological levels with weight-of-evidence, the proposed EIBR provides a new perspective and an ecologically relevant assessment of the environmental toxicity of the pollutants. The results of EIBR and structure-activity analysis are also useful to predict toxic behaviors of other PFCs in the group and facilitate the decision-making process.

In vitro toxicological characterization of perfluorinated carboxylic acids with different carbon chain lengths

Perfluorooctanoic acid (PFOA) is in use for the production of fluoropolymers (PFT). Due to its toxic properties it was proposed to replace the substance in its industrial applications by homologous compounds with shorter carbon chain length that were supposed to be less toxic compared to PFOA, however, the smaller PFOA homologs are poorly characterized so far. In this study we have conducted a comparative analysis of the toxicity of perfluorinated carboxylic acids (PFCA) with a carbon chain length ranging from four to twelve carbon atoms. By using the human hepatocarcinoma cell line HepG2 as an in vitro model for human hepatocytes we could show a positive correlation between the carbon chain length of the respective PFCA and its cytotoxicity. There was, however, no indication of an apoptotic mechanism for cytotoxicity. All PFCA under investigation were negative in two independent genotoxicity assays. As PFOA, being a well-known peroxisome proliferator, the other PFCA tested in this study were also shown to activate human peroxisome proliferator-activated receptor alpha (PPARα) with PFOA having the highest potential of PPARα activation. Moreover, the compounds showed weak potential to activate PPARγ and hardly activated PPARδ. Taken together, the in vitro study revealed that PFCA with a shorter carbon chain length seem to be less toxic than PFOA.

Occurrence of perfluoroalkyl acids including perfluorooctane sulfonate isomers in Huai River Basin and Taihu Lake in Jiangsu Province, China

The spatial distribution of 10 perfluoroalkyl acids including linear and branched (six monotrifluoromethyl isomers) perfluorooctane sulfonate (PFOS) in surface water was investigated in Huai River Basin and Taihu Lake in Jiangsu Province, China. In the water samples from Huai River Basin, perfluorooctanoic acid (PFOA) and PFOS were the predominant compounds (mean 18 ng/L and 4.7 ng/L, respectively), while in samples from Taihu Lake, PFOA, perfluorohexanoic acid (PFHxA), and PFOS were the predominant compounds (mean 56 ng/L, 19 ng/L, and 15 ng/L, respectively). Branched PFOS (Br-PFOS) isomers accounting for 48.1% to 62.5% of total PFOS were enriched in all samples from Taihu Lake, compared to technical electrochemical fluorination (ECF) PFOS (Br-PFOS ∼30.0%), while the similar phenomena were not found in samples from Huai River Basin (Br-PFOS 29.0-35.0%). Principal component analysis (PCA) on the percentages of the individual isomer showed that the first two components accounted for 78.4% and 15.3% of the overall observed data variance. Samples from Huai River Basin were grouped together with the ECF PFOS standard suggesting the profiles were similar, while samples from Taihu Lake were grouped by themselves, suggesting that isomer profiles in these samples were different from that of Huai River Basin. The obvious difference in isomer profiles probably results from the different environmental behaviors of PFOS isomers and/or unknown sources (PFOS or PFOS precursors).

In vitro and in vivo studies of the toxic effects of perfluorononanoic acid on rat hepatocytes and Kupffer cells

This study investigated the toxic effects of perfluorononanoic acid (PFNA), a persistent organic pollutant, on rat hepatocytes and Kupffer cells in vitro and in vivo. The results showed that administration of 5μM PFNA increased the viabilities of the hepatocytes and the Kupffer cells. An exposure of 50μM PFNA did not alter the viabilities of both cells, as well as the release of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) from the primary cultured hepatocytes or the hepatocytes co-cultured with Kupffer cells. An exposure of 100μM PFNA only decreased the viability of the hepatocytes. The administration of PFNA changed the hepatocyte expression of several genes related to lipid metabolism in vitro and in vivo. Oil Red O Staining revealed that 5mg PFNA/kg/D treatment lead to dramatic accumulation of lipids in rat liver. At the same dose PFNA damaged hepatocytes histopathologically. Up-regulated expressions of the inflammatory cytokines occurred in the Kupffer cells treated with 50μM PFNA and in the livers of the rat receiving a 5mg PFNA/kg/D treatment. In addition, these cytokines also increased in serum of the rat receiving higher dose of PFNA. In summary, on the one hand, PFNA exposure affected the viability of the hepatocytes, hepatic lipid metabolism and lead to lipid accumulation in liver. On the other hand, for the first time, PFNA exposure was demonstrated to affect the viability of the Kupffer cells as well as their expression of cytokines, which involved in regulation of various liver functions. Therefore, we conclude that both the hepatocyte and the Kupffer cell contribute to the observed hepatotoxicity of PFNA.

Levels, temporal trends, and tissue distribution of perfluorinated surfactants in freshwater fish from Asian countries

Perfluorinated surfactants (PFSs) in Asian freshwater fish species were analyzed to investigate tissue distribution, temporal trends, extent of pollution, and level of PFS exposure through food intake. Freshwater fish species, namely carp, snakehead, and catfish, were collected in Japan, Vietnam, India, Malaysia, and Thailand, and 10 PFSs, including perfluorooctanesulfonate (PFOS) and perfluorooctanoate, were analyzed by liquid chromatography-tandem mass spectrometry. PFSs in carp in Tokyo were more concentrated in kidneys (Σ10 PFSs = 257 ± 95 ng/g wet weight [ww]) and livers (119 ± 36 ng/g ww) than in ovaries (43 ± 2 ng/g ww) and muscles (24 ± 17 ng/g ww). Concentrations of PFOS and its precursor, perfluorooctane sulfonamide, in livers of carp and in waters in Tokyo showed a dramatic decrease during the last decade, probably because of 3 M's phasing-out of the manufacture of perfluorooctanesulfonyl-fluoride-based products in 2000. In contrast, continuing contamination by long-chain perfluorocarboxylates (PFCAs) with ≥ 9 fluorinated carbons was seen in multiple media, suggesting that these compounds continue to be emitted. PFS concentrations in freshwater fish species in tropical Asian countries were generally lower than those in developed countries, such as Japan, e.g., for PFOS in muscle, Vietnam < 0.05-0.3 ng/g ww; India < 0.05-0.2 ng/g ww; Malaysia < 0.05-0.2 ng/g ww; Thailand < 0.05 ng/g ww; and Japan (Tokyo) = 5.1-22 ng/g ww. Daily intake of short-chain PFCAs with ≤ 8 fluorinated carbons from freshwater fish species in Japan was approximately one order of magnitude lower than that from drinking water, whereas daily intake of PFOS and long-chain PFCAs with ≥ 9 fluorinated carbons from freshwater fish species was comparable with or greater than that from drinking water. Because the risk posed by exposure to these compounds through intake of fish species is a matter of concern, we recommend the continued monitoring of PFS levels in Asian developing countries.

Prediction of aqueous solubility, vapor pressure and critical micelle concentration for aquatic partitioning of perfluorinated chemicals

The majority of perfluorinated chemicals (PFCs) are of increasing risk to biota and environment due to their physicochemical stability, wide transport in the environment and difficulty in biodegradation. It is necessary to identify and prioritize these harmful PFCs and to characterize their physicochemical properties that govern the solubility, distribution and fate of these chemicals in an aquatic ecosystem. Therefore, available experimental data (10-35 compounds) of three important properties: aqueous solubility (AqS), vapor pressure (VP) and critical micelle concentration (CMC) on per- and polyfluorinated compounds were collected for quantitative structure-property relationship (QSPR) modeling. Simple and robust models based on theoretical molecular descriptors were developed and externally validated for predictivity. Model predictions on selected PFCs were compared with available experimental data and other published in silico predictions. The structural applicability domains (AD) of the models were verified on a bigger data set of 221 compounds. The predicted properties of the chemicals that are within the AD, are reliable, and they help to reduce the wide data gap that exists. Moreover, the predictions of AqS, VP, and CMC of most common PFCs were evaluated to understand the aquatic partitioning and to derive a relation with the available experimental data of bioconcentration factor (BCF).

Hydrophobicity-dependent QSARs to predict the toxicity of perfluorinated carboxylic acids and their mixtures

Perfluorinated carboxylic acids (PFCAs) have wide industrial applications because of their unique physicochemical characteristics. However, data on the toxicity of much of this chemical class is lacking, particularly with regard to mixture toxicity. In this study, the toxicity of individual PFCAs and their mixtures to Photobacterium phosphoreum were observed. There was a tendency of increasing toxicity from C3 to C14 PFCA and a tendency of decreasing toxicity from C14 to C18 PFCA because of "the maximum tolerance of the cell membrane". Using the equivalent logK(OW) (octanol-water partition coefficient) and logK(SD) (C(18)-Empore™ disks/water partition coefficient), two linear quantitative structure-activity relationship (QSAR) models were formulated. This indicated both K(SD) and K(OW) can describe the hydrophobicity of a single chemical. However, for the PFCA mixtures, K(MD) is the more reasonable parameter than K(owmix) to describe the hydrophobicity because only the equivalent logK(MD) could be used to predict the mixture toxicity.