Repeated dose and reproductive/developmental toxicity of perfluorododecanoic acid in rats

The perils of poly- and perfluorinated chemicals on the reproductive health of humans, livestock, and wildlife

Poly- and perfluoroalkyl substances (PFAS) are a prominent class of persistent synthetic compound. The widespread use of these substances in various industrial applications has resulted in their pervasive contamination on a global scale. It is therefore concerning that PFAS have a propensity to accumulate in bodily tissues whereupon they have been linked with a range of adverse health outcomes. Despite this, the true extent of the risk posed by PFAS to humans, domestic animals, and wildlife remains unclear. Addressing these questions requires a multidisciplinary approach, combining the fields of chemistry, biology, and policy to enable meaningful investigation and develop innovative remediation strategies. This article combines the perspectives of chemists, soil scientists, reproductive biologists, and health policy researchers, to contextualise the issue of PFAS contamination and its specific impact on reproductive health. The purpose of this article is to describe the challenges associated with remediating PFAS-contaminated soils and waters and explore the consequences of PFAS contamination on health and reproduction. Furthermore, current actions to promote planetary health and protect ecosystems are presented to instigate positive social change among the scientific community.

Expanded Systematic Evidence Map for Hundreds of Per- and Polyfluoroalkyl Substances (PFAS) and Comprehensive PFAS Human Health Dashboard

BACKGROUND

Per- and polyfluoroalkyl substances (PFAS) encompass a class of chemically and structurally diverse compounds that are extensively used in industry and detected in the environment. The US Environmental Protection Agency (US EPA) 2021 PFAS Strategic Roadmap describes national research plans to address the challenge of PFAS.

OBJECTIVES

Systematic Evidence Map (SEM) methods were used to survey and summarize available epidemiological and mammalian bioassay evidence that could inform human health hazard identification for a set of 345 PFAS that were identified by the US EPA's Center for Computational Toxicology and Exposure (CCTE) for in vitro toxicity and toxicokinetic assay testing and through interagency discussions on PFAS of interest. This work builds from the 2022 evidence map that collated evidence on a separate set of ∼ 150 PFAS. Like our previous work, this SEM does not include PFAS that are the subject of ongoing or completed assessments at the US EPA.

METHODS

SEM methods were used to search, screen, and inventory mammalian bioassay and epidemiological literature from peer-reviewed and gray literature sources using manual review and machine-learning software. For each included study, study design details and health end points examined were summarized in interactive web-based literature inventories. Some included studies also underwent study evaluation and detailed extraction of health end point data. All underlying data is publicly available online as interactive visuals with downloadable metadata.

RESULTS

More than 13,000 studies were identified from scientific databases. Screening processes identified 121 mammalian bioassay and 111 epidemiological studies that met screening criteria. Epidemiological evidence (available for 12 PFAS) mostly assessed the reproductive, endocrine, developmental, metabolic, cardiovascular, and immune systems. Mammalian bioassay evidence (available for 30 PFAS) commonly assessed effects in the reproductive, whole-body, nervous, and hepatic systems. Overall, 41 PFAS had evidence across mammalian bioassay and epidemiology data streams (roughly 11% of searched chemicals).

DISCUSSION

No epidemiological and/or mammalian bioassay evidence were identified for most of the PFAS included in our search. Results from this SEM, our 2022 SEM on ∼ 150 PFAS, and other PFAS assessment products from the US EPA are compiled into a comprehensive PFAS dashboard that provides researchers and regulators an overview of the current PFAS human health landscape including data gaps and can serve as a scoping tool to facilitate prioritization of PFAS-related research and/or risk assessment activities. https://doi.org/10.1289/EHP13423.

Alcohols radicals can efficiently reduce recalcitrant perfluorooctanoic acid

Alcohols are commonly used as eluents for the regeneration of per/poly-fluoroalkyl substances (PFASs) adsorbents, but their potential effects on the subsequent treatment of these eluates have not been fully explored. This work investigated the effect of alcohols on perfluorooctanoic acid (PFOA) degradation by persulfate (PS) based advanced oxidation processes. The results showed that ethanol significantly promoted PFOA degradation in thermal/PS system. Under anoxic conditions, 25.5±1.4% or 91.2±1.6% of PFOA was degraded within 48 h in the absence or presence of ethanol. Electron paramagnetic resonance (EPR) detection, free radical quenching experiments, and chemical probe studies clearly demonstrated that the sulfate radicals (SO4•-) generated from PS activation would react with ethanol to form alcohol radicals, which could efficiently degrade PFOA. The transformation pathways of PFOA were proposed based on degradation products analysis and density function theory (DFT) calculation. The reaction between SO4•- and other alcohols could also induce the formation of alcohol radicals and facilitate to the degradation of PFOA. This work represents the positive roles of alcohols in the degradation of PFASs, providing new insights into developing simple and efficient treatments for PFASs eluate or PFAS-contaminated water.

Effects of perfluorooctanoic acid on endoplasmic reticulum stress and lipid metabolism-related genes in human pancreatic cells

Perfluorooctanoic acid (PFOA) is environmentally persistent and has been classified by The International Cancer Research Agency (IARC) as a possible human pancreatic carcinogen. In this study, the epigenetic alteration, the changes in the expression levels of endoplasmic reticulum stress-related and metabolism-related genes, as well as DNA methyltransferase expression were investigated using RT-PCR and ELISA assays. PFOA induced a significant increase in the methylation ratio (5-mC%), impacted DNA methylation maintenance gene expression and decreased lipid metabolism-related genes except for PPARγ (≥ 13-fold increase). While PFOA induced the expression of ATF4 (≥ 5.41-folds), CHOP (≥ 5.41-folds) genes, it inhibited the expression of ATF6 (≥ 67.2%), GRP78 (≥ 64.3%), Elf2α (≥ 95.8%), IRE1 (≥ 95.5%), and PERK (≥ 91.7%) genes. It is thought that epigenetic mechanisms together with disruption in the glucose-lipid metabolism and changes in endoplasmic reticulum stress-related genes may play a key role in PFOA-induced pancreatic toxicity.

Consideration of pathways for immunotoxicity of per- and polyfluoroalkyl substances (PFAS)

BACKGROUND

Per- and polyfluoroalkyl substances (PFAS) are of public health concern, because of their ubiquitous and extremely persistent occurrence, and depending on their structure, their bio-accumulative, mobile and toxic properties. Human health effects associated with exposure to PFAS include adverse effects on the immune system. In 2020, EFSA (the European Food Safety Authority) defined adverse effects on the immune system as the most critical effect for human health risk assessment, based on reduced antibody responses to childhood vaccines and similar effects observed in experimental animal studies. Likewise, the U.S. EPA (Environmental Protection Agency) considers PFAS-induced immunotoxicity, especially in children, as the critical effect for risk assessment. However, the mechanisms by which antibody concentrations are impacted are not completely understood. Furthermore, other targets of the immune system functions have been reported in the literature.

OBJECTIVE

The aim of this review is to explore PFAS-associated immune-related effects. This includes, relevant mechanisms that may underlie the observed effects on the immune system, immunosuppression as well as immunoenhancement, such as i) modulation of cell signalling and nuclear receptors, such as NF-κB and PPARs; ii) alteration of calcium signalling and homoeostasis in immune cells; iii) modulation of immune cell populations; iv) oxidative stress and v) impact on fatty acid metabolism & secondary effects on the immune system.

METHODS

A literature research was conducted using three databases (Web of Science, PubMed, and Scopus), which were searched in July 2021 for relevant studies published in the time frame from 2018 to 2021. In total, 487 publications were identified as potentially eligible and following expert-based judgement, articles relevant for mechanisms of PFAS induced immunotoxicity are discussed.

CONCLUSIONS

Taken together, we show that there is substantial evidence from both in vitro and in vivo experimental as well as epidemiological studies, supporting that various PFAS, not only PFOA and PFOS, affect multiple aspects of the immune system. Timing of exposure is critical, because the developing immune system is especially vulnerable to toxic insults, resulting in a higher risk of particularly adverse immune effects but also other organs later in life.

Internal relative potency factors based on immunotoxicity for the risk assessment of mixtures of per- and polyfluoroalkyl substances (PFAS) in human biomonitoring

Relative potency factors (RPFs) for per- and polyfluoroalkyl substances (PFAS) have previously been derived based on liver effects in rodents for the purpose of performing mixture risk assessment with primary input from biomonitoring studies. However, in 2020, EFSA established a tolerable weekly intake for four PFAS assuming equal toxic potency for immune suppressive effects in humans. In this study we explored the possibility of deriving RPFs for immune suppressive effects using available data in rodents and humans. Lymphoid organ weights, differential blood cell counts, and clinical chemistry from 28-day studies in male rats from the National Toxicology Program (NTP) were combined with modeled serum PFAS concentrations to derive internal RPFs by applying dose-response modelling. Identified functional studies used diverse protocols and were not suitable for derivation of RPFs but were used to support immunotoxicity of PFAS in a qualitative manner. Furthermore, a novel approach was used to estimate internal RPFs based on epidemiological data by dose-response curve fitting optimization, looking at serum antibody concentrations and key cell populations from the National Health and Nutrition Examination Survey (NHANES). Internal RPFs were successfully derived for PFAS based on rat thymus weight, spleen weight, and globulin concentration. The available dose-response information for blood cell counts did not show a significant trend. Immunotoxic potency in serum was determined in the order PFDA > PFNA > PFHxA > PFOS > PFBS > PFOA > PFHxS. The epidemiological data showed inverse associations for the sum of PFOA, PFNA, PFHxS, and PFOS with serum antibody concentrations to mumps and rubella, but the data did not allow for deduction of reliable internal RPF estimates. The internal RPFs for PFAS based on decreased rat lymphoid organ weights are similar to those previously established for increased rat liver weight, strengthening the confidence in the overall applicability of these RPFs.

Association of serum per- and polyfluoroalkyl substances and gestational anemia during different trimesters in Zhuang ethnic pregnancy women of Guangxi, China

BACKGROUND

Gestational anemia is a complication of pregnancy, and a low level of hemoglobin (Hb) has been linked to adverse pregnancy outcomes. Previous studies reported that PFASs were more strongly associated with Hb than red blood cells, indicating that Hb is more susceptible to the effect of PFASs. However, the evidences regarding the effects of per- and polyfluoroalkyl substances (PFASs) on gestational anemia are currently limited. Therefore, it is important to explore the effects of PFASs on anemia in Chinese pregnant women.

METHODS

A total of 821 pregnant women were recruited between June 2015 and April 2019 in the Guangxi Zhuang Birth Cohort. The concentrations of PFASs were assessed in maternal serum before 12 gestational weeks. To determine both individual and combined associations of PFASs exposure with anemia in the three stages of pregnancy, binary logistic regression, Bayesian kernel machine regression (BKMR), and weighted quantile sum (WQS) regression models were employed.

RESULTS

In single-pollutant analysis, maternal exposure to perfluorododecanoic acid (PFDoA) and perfluoroheptanoic acid (PFHpA) were associated with anemia in the first trimester, exposure to PFHpA and perfluorobutanesulfonic acid (PFBS) were associated with anemia in the second trimester, and exposure to perfluorodecanoic acid (PFDA) and perfluorononanoic acid (PFNA) were associated with anemia in the third trimester. Notably, perfluoroundecanoic acid (PFUnA) had a nonlinear association with anemia in the third trimester. In multiple-pollutant analysis, a positive association of PFDoA with anemia in the first trimester and a negative association of PFBS with anemia in the second trimester were confirmed by BKMR. Exposure to PFASs mixture was not associated with anemia in all three trimesters. In WQS, there was a significantly negative association between the PFAS mixture and anemia in the second trimester.

CONCLUSION

Maternal exposure to PFASs is associated with gestational anemia in different trimesters.

Perfluorooctanoic acid exposure in vivo perturbs mitochondrial metabolic during oocyte maturation

Perfluorooctanoic acid (PFOA), a member of a group of polyfluorinated and perfluorinated alkyl substances (PFAS), is associated with adverse pregnancy outcomes in mammals. However, the effects of in vivo exposure to PFOA on the female reproductive system and the underlying mechanisms remain unclear. In our study, we constructed a mouse model to investigate whether low-dose PFOA (1 mg/kg/day) or high-dose PFOA (5 mg/kg/day) affect meiosis maturation of oocytes and the potential mechanisms that may be associated with oocyte maturation disorder. Our results indicate that low-dose and high-dose PFOA can lead to impaired oocyte maturation, which is manifested by decreased rate of embryonic foam rupture and first polar body extrusion. Moreover, PFOA exposure harmed the mitochondrial metabolic, resulting in low levels of ATP contents, high reactive oxygen species, aberrant mitochondrial membrane potential. In addition, the proportion of DNA damage marker γ-H2AX was also significantly increased in PFOA exposure oocytes. These changes lead to abnormal arrangements of the spindle and chromosomes during oocyte maturation. In conclusion, our results for the first time illustrated that exposure to PFOA in vivo in female mice impaired the meiosis maturation of oocytes, which provided a basis for studying the mechanism of PFOA reproductive toxicity in female mammals.

Association between prenatal exposure to perfluoroalkyl substances and anogenital distance in female neonates

BACKGROUND

Perfluoroalkyl substances (PFASs) have been reported to exert reproductive toxicity. Anogenital distance (AGD) is a biomarker of intrauterine androgen exposure and an indicator of genital development. An animal study reported that female neonatal rats exposed to perfluorooctanoic acid or perfluorooctane sulfonate (PFOS) during postnatal days 1-5 exhibited a longer AGD, while epidemiological studies have shown inconsistent results. This study aimed to examine the effects of prenatal exposure to PFASs on the AGD in female neonates.

METHODS

PFAS levels were measured in plasma samples obtained from pregnant women at 12-16 gestational weeks using high-performance liquid chromatography/mass spectrometry. The AGD of each female neonate was measured within 3 days after delivery. The anogenital index (AGI), calculated as AGD divided by weight, was also determined. A total of 362 motherinfant pairs were included in this study. A multivariate linear regression model was used to examine the association between prenatal ln-transformed concentrations of PFASs and AGD/AGI. In addition, weighted quantile sum regression (WQSR) and Bayesian kernel machine regression (BKMR) models were used to assess the overall effects of a mixture of PFASs on the AGD/AGI and to identify important contributors to the overall effect.

RESULTS

There was a consistent pattern of association between maternal PFAS concentrations and increased AGDanus to posterior fourchette (AF), AGDanus to clitoris (AC), and AGIAF lengths at birth. Statistical significance was found between maternal ln-transformed concentrations of perfluorohexane sulfonate (PFHxS), perfluorododecanoic acid, and perfluorotridecanoic acid and AGDAF, with β values (95% confidence interval [CI]) of 0.83 (0.16, 1.51), 0.32 (0.05, 0.59), and 0.25 (0.00, 0.51) mm, respectively; between PFOS and AGDAC, with a β value (95% CI) of 0.63 (0.04, 1.21) mm; and between PFHxS and AGIAF, with a β value (95% CI) of 0.22 (0.02, 0.43) mm/kg. Similarly, the WQSR and BKMR models showed that an increase in the AGDAF/AGIAF at birth was associated with co-exposure to a mixture of PFASs.

CONCLUSION

High maternal concentrations of PFASs were associated with increased AGD in female neonates, indicating that PFASs may impair reproductive development in female offspring in early life.

Internal Relative Potency Factors for the Risk Assessment of Mixtures of Per- and Polyfluoroalkyl Substances (PFAS) in Human Biomonitoring

BACKGROUND

In human biomonitoring, blood is often used as a matrix to measure exposure to per- and polyfluoroalkyl substances (PFAS). Because the toxicokinetics of a substance (determining the steady-state blood concentration) may affect the toxic potency, the difference in toxicokinetics among PFAS has to be accounted for when blood concentrations are used in mixture risk assessment.

OBJECTIVES

This research focuses on deriving relative potency factors (RPFs) at the blood serum level. These RPFs can be applied to PFAS concentrations in human blood, thereby facilitating mixture risk assessment with primary input from human biomonitoring studies.

METHODS

Toxicokinetic models are generated for 10 PFAS to estimate the internal exposure in the male rat at the blood serum level over time. By applying dose-response modeling, these internal exposures are used to derive quantitative internal RPFs based on liver effects.

RESULTS

Internal RPFs were successfully obtained for nine PFAS. Perfluorobutanoic acid (PFBA), perfluorohexanoic acid (PFHxA), perfluorononanoic acid (PFNA), perfluorododecanoic acid (PFDoDA), perfluorooctane sulfonic acid (PFOS), and hexafluoropropylene oxide-dimer acid (HFPO-DA, or GenX) were found to be more potent than perfluorooctanoic acid (PFOA) at the blood serum level in terms of relative liver weight increase, whereas perfluorobutane sulfonic acid (PFBS) and perfluorohexane sulfonic acid (PFHxS) were found to be less potent. The practical implementation of these internal RPFs is illustrated using the National Health and Nutrition Examination Survey (NHANES) biomonitoring data of 2017-2018.

DISCUSSION

It is recommended to assess the health risk resulting from exposure to PFAS as combined, aggregate exposure to the extent feasible. https://doi.org/10.1289/EHP10009.

Exposure to per- and Polyfluoroalkyl Substances and Markers of Liver Injury: A Systematic Review and Meta-Analysis

BACKGROUND

Experimental evidence indicates that exposure to certain pollutants is associated with liver damage. Per- and polyfluoroalkyl substances (PFAS) are persistent synthetic chemicals widely used in industry and consumer products and bioaccumulate in food webs and human tissues, such as the liver.

OBJECTIVE

The objective of this study was to conduct a systematic review of the literature and meta-analysis evaluating PFAS exposure and evidence of liver injury from rodent and epidemiological studies.

METHODS

PubMed and Embase were searched for all studies from earliest available indexing year through 1 December 2021 using keywords corresponding to PFAS exposure and liver injury. For data synthesis, results were limited to studies in humans and rodents assessing the following indicators of liver injury: serum alanine aminotransferase (ALT), nonalcoholic fatty liver disease, nonalcoholic steatohepatitis, or steatosis. For human studies, at least three observational studies per PFAS were used to conduct a weighted z-score meta-analysis to determine the direction and significance of associations. For rodent studies, data were synthesized to qualitatively summarize the direction and significance of effect.

RESULTS

Our search yielded 85 rodent studies and 24 epidemiological studies, primarily of people from the United States. Studies focused primarily on legacy PFAS: perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), perfluorononanoic acid (PFNA), and perfluorohexanesulfonic acid. Meta-analyses of human studies revealed that higher ALT levels were associated with exposure to PFOA (z-score= 6.20, p<0.001), PFOS (z-score= 3.55, p<0.001), and PFNA (z-score= 2.27, p=0.023). PFOA exposure was also associated with higher aspartate aminotransferase and gamma-glutamyl transferase levels in humans. In rodents, PFAS exposures consistently resulted in higher ALT levels and steatosis.

CONCLUSION

There is consistent evidence for PFAS hepatotoxicity from rodent studies, supported by associations of PFAS and markers of liver function in observational human studies. This review identifies a need for additional research evaluating next-generation PFAS, mixtures, and early life exposures. https://doi.org/10.1289/EHP10092.

Per- and poly-fluoroalkyl substances (PFAS) and female reproductive outcomes: PFAS elimination, endocrine-mediated effects, and disease

Per- and poly-fluoroalkyl substances (PFAS) are widespread environmental contaminants frequently detected in drinking water supplies worldwide that have been linked to a variety of adverse reproductive health outcomes in women. Compared to men, reproductive health effects in women are generally understudied while global trends in female reproduction rates are declining. Many factors may contribute to the observed decline in female reproduction, one of which is environmental contaminant exposure. PFAS have been used in home, food storage, personal care and industrial products for decades. Despite the phase-out of some legacy PFAS due to their environmental persistence and adverse health effects, alternative, short-chain and legacy PFAS mixtures will continue to pollute water and air and adversely influence women's health. Studies have shown that both long- and short-chain PFAS disrupt normal reproductive function in women through altering hormone secretion, menstrual cyclicity, and fertility. Here, we summarize the role of a variety of PFAS and PFAS mixtures in female reproductive tract dysfunction and disease. Since these chemicals may affect reproductive tissues directly or indirectly through endocrine disruption, the role of PFAS in breast, thyroid, and hypothalamic-pituitary-gonadal axis function are also discussed as the interplay between these tissues may be critical in understanding the long-term reproductive health effects of PFAS in women. A major research gap is the need for mechanism of action data - the targets for PFAS in the female reproductive and endocrine systems are not evident, but the effects are many. Given the global decline in female fecundity and the ability of PFAS to negatively impact female reproductive health, further studies are needed to examine effects on endocrine target tissues involved in the onset of reproductive disorders of women.

Determination of Perflourooctanoic Acid Toxicity in a Human Hepatocarcinoma Cell Line

BACKGROUND

Perfluorooctanoic acid (PFOA) is used in different industrial and commercial products. Research shows the presence of PFOA in home dusts, tap and surface water, and in biological samples. The International Agency for Research on Cancer (IARC) has classified PFOA as a possible carcinogen for humans. The liver is thought to be a target organ of PFOA accumulation and toxicity.

OBJECTIVE

Some studies have found toxic effects on the liver and related mechanisms; however, more studies are needed to better understand PFOA - induced hepatotoxicity.

METHODS

In the present study, a human hepatocarcinoma cell line was exposed to PFOA for 24 hours and cell viability, apoptosis, the oxidative system and immune response were evaluated.

RESULTS

While apoptosis was the main cell death pathway at low concentration (86.5%), the necrotic cell fraction increased with higher concentrations (46.7%). Significant changes in the reactive oxygen species (5.3-folds) glutathione (GSH) (1.7-folds) and catalase (CAT) (1.4-folds) levels were observed, as well as changes to interleukin-6 (≤1.8-fold) and interleukin-8 levels (35-40%).

CONCLUSIONS

In light of the data, PFOA is potentially hepatotoxic through the investigated pathways. The results represent a background for future in vivo mechanistic studies.

COMPETING INTERESTS

The authors declare no competing financial interests.

Suggestions for Improving the Characterization of Risk from Exposures to Per and Polyfluorinated Alkyl Substances

Many state and federal environmental and health agencies have developed risk-based criteria for assessing the risk of adverse health effects of per- and polyfluorinated alkyl substances (PFAS) exposure to humans and the environment. However, the criteria that have been developed vary; drinking water criteria developed for perfluorooctanoic acid, for example, can vary by up to 750 fold. This is due to differences and variability in the data and information used, study/endpoint selection, assumptions and magnitude of uncertainty factors used in the absence and extrapolation of critical effect data, differences in underlying approaches to addressing exposure within criteria development, and/or policy decisions on levels of acceptable risk. We have critically evaluated the methods used to develop these criteria while focusing on derivation and application of drinking water criteria and discuss a range of improvements to risk-characterization practice recently presented at a Focused Topic Meeting on PFAS conducted by the Society of Environmental Toxicology and Chemistry in Durham, North Carolina, USA, 12 to 15 August 2019. We propose methods that consider maximizing the use of disparate data streams, seeking patterns, and proposing biologically based approaches to evidence integration toward informed criteria development. Environ Toxicol Chem 2021;40:883-898. © 2020 SETAC.

Risk Assessment of Per- and Polyfluoroalkyl Substance Mixtures: A Relative Potency Factor Approach

Per- and polyfluoroalkyl substances (PFAS) often occur together as contamination in exposure media such as drinking water or food. The relative potency factor (RPF) methodology facilitates the risk assessment of mixture exposure. A database of liver endpoints was established for 16 PFAS, using data with the same species (rat), sex (male), and exposure route (oral) and comparable exposure duration (42-90 d). Dose-response analysis was applied to derive the relative potencies of 3 perfluoroalkyl sulfonic acids (perfluorobutane sulfonic acid, perfluorohexane sulfonic acid, perfluorooctane sulfonic acid), 8 perfluoroalkyl carboxylic acids (perfluorobutanoic acid, perfluorohexanoic acid, perfluorononanoic acid, perfluoroundecanoic acid, perfluorododecanoic acid, perfluorotetradecanoic acid, perfluorohexadecanoic acid, perfluorooctadecanoic acid), 2 perfluoroalkyl ether carboxylic acids (tetrafluoro-2-[heptafluoropropoxy]propanoic acid, 3H-perfluoro-3-[(3-methoxy-propoxy)propanoic acid]), and 2 fluorotelomer alcohols (6:2 FTOH, 8:2 FTOH) compared to perfluorooctanoic acid (PFOA), based on liver effects. In addition, the RPFs of 7 other perfluoroalkyl acids were estimated based on read-across. This resulted in the relative potencies of 22 PFAS compared to the potency of index compound PFOA. The obtained RPFs can be applied to measured PFAS quantities, resulting in the sum of PFOA equivalents in a mixture. This sum can be compared with an established PFOA concentration limit (e.g., in drinking water or food) or an external health-based guidance value (e.g., tolerable daily intake, acceptable daily intake, or reference dose) to estimate the risk resulting from direct oral exposure to mixtures. Assessing mixture exposure is particularly relevant for PFAS, with omnipresent exposure in our daily lives. Environ Toxicol Chem 2021;40:859-870. © 2020 SETAC.

Endocrine Disruptor Potential of Short- and Long-Chain Perfluoroalkyl Substances (PFASs)-A Synthesis of Current Knowledge with Proposal of Molecular Mechanism

Endocrine disruptors are a group of chemical compounds that, even in low concentrations, cause a hormonal imbalance in the body, contributing to the development of various harmful health disorders. Many industry compounds, due to their important commercial value and numerous applications, are produced on a global scale, while the mechanism of their endocrine action has not been fully understood. In recent years, per- and polyfluoroalkyl substances (PFASs) have gained the interest of major international health organizations, and thus more and more studies have been aimed to explain the toxicity of these compounds. PFASs were firstly synthesized in the 1950s and broadly used in the industry in the production of firefighting agents, cosmetics and herbicides. The numerous industrial applications of PFASs, combined with the exceptionally long half-life of these substances in the human body and extreme environmental persistence, result in a common and chronic exposure of the general population to their action. Available data have suggested that human exposure to PFASs can occur during different stages of development and may cause short- or/and long-term health effects. This paper synthetizes the current literature reports on the presence, bioaccumulation and, particularly, endocrine toxicity of selected long- and short-chain PFASs, with a special emphasis on the mechanisms underlying their endocrine actions.

Application of a Framework for Grouping and Mixtures Toxicity Assessment of PFAS: A Closer Examination of Dose-Additivity Approaches

Environmental occurrence and biomonitoring data for per- and polyfluoroalkyl substances (PFAS) demonstrate that humans are exposed to mixtures of PFAS. This article presents a new and systematic analysis of available PFAS toxicity study data using a tiered mixtures risk assessment framework consistent with United States and international mixtures guidance. The lines of evidence presented herein include a critique of whole mixture toxicity studies and analysis of dose-response models based on data from subchronic oral toxicity studies in rats. Based on available data to-date, concentration addition and relative potency factor methods are found to be inappropriate due to differences among sensitive effects and target organ potencies and noncongruent dose-response curves for the same effect endpoints from studies using the same species and protocols. Perfluorooctanoic acid and perfluorooctane sulfonic acid lack a single mode of action or molecular initiating event and our evaluation herein shows they also have noncongruent dose-response curves. Dose-response curves for long-chain perfluoroalkyl sulfonic acids (PFSAs) also significantly differ in shapes of the curves from short-chain PFSAs and perfluoroalkyl carboxylic acids evaluated, and additional differences are apparent when curves are evaluated based on internal or administered dose. Following well-established guidance, the hazard index method applied to perfluoroalkyl carboxylic acids and PFSAs grouped separately is the most appropriate approach for conducting a screening level risk assessment for nonpolymeric PFAS mixtures, given the current state-of-the science. A clear presentation of assumptions, uncertainties, and data gaps is needed before dose-additivity methods, including hazard index , are used to support risk management decisions. Adverse outcome pathway(s) and mode(s) of action information for perfluorooctanoic acid and perfluorooctane sulfonic acid and for other nonpolymer PFAS are key data gaps precluding more robust mixtures methods. These findings can guide the prioritization of future studies on single chemical and whole mixture toxicity studies.

Parental plasma concentrations of perfluoroalkyl substances and In Vitro fertilization outcomes

Perfluoroalkyl substances (PFAS) are known to be endocrine-disrupting compounds, but are nevertheless widely used in consumer and industrial products and have been detected globally in human and wildlife. Data from animal and epidemiological studies suggest that PFAS may affect human fertility. This led us to consider whether maternal or paternal plasma PFAS had effects on in vitro fertilization (IVF) outcomes. The study population consisted of 96 couples who underwent IVF treatment in 2017 due to tubal factor infertility. The concentrations of 10 PFAS in blood samples from both male and female partners were measured. Poisson regression with log link was performed to evaluate the association between the tertiles of PFAS concentrations and numbers of retrieved oocytes, mature oocytes, two-pronuclei (2 PN) zygotes, and good-quality embryos, while multiple linear regression models were used to investigate the correlation between plasma PFAS and semen parameters. Multivariable logistic regression was used to evaluate the association between the tertiles of PFAS concentrations and clinical outcomes. It was found that maternal plasma concentrations of perfluorooctanoic acid (PFOA) were negatively associated with the numbers of retrieved oocytes (p_trend = 0.023), mature oocytes (p_trend = 0.015), 2 PN zygotes (p_trend = 0.014), and good-quality embryos (p_trend = 0.012). Higher paternal plasma PFOA concentrations were found to be significantly associated with reduced numbers of 2 PN zygotes (p_trend = 0.047). None of the maternal or paternal PFAS were significantly associated with the probability of implantation, clinical pregnancy, or live birth. To our knowledge, the present study is the first to assess the association between parental exposure to PFAS and IVF outcomes. Our results suggest the potential reproductive effects of PFAS on both men and women, and that exposure to PFAS may negatively affect IVF outcomes. Future studies, particularly with large sample size cohorts, are needed to confirm these findings.

Male reproductive toxicity involved in spermatogenesis induced by perfluorooctane sulfonate and perfluorooctanoic acid in Caenorhabditis elegans

As a persistent organic pollutant, perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) have gained increasing research attention over recent years because of their potential risk to humans and the environment. In this paper, we investigated the reproductive toxicity of these pollutants using a C. elegans model to evaluate spermatogenesis throughout the entire developmental cycle of him-5 mutant by exposing to 0.001, 0.01, and 0.1 mmol/L PFOS or PFOA for 48 h. Experimental results suggested that PFOS and PFOA exposure led to reductions in brood size, germ cell number, spermatid size, and motility, and increases in rate of malformation spermatids. Analysis of variance (ANOVA) showed that exposure to PFOS resulted in higher levels of damage than PFOA in germ cells only in 0.001 mmol/L exposure group. RT-qPCR was used to further investigate the expression of genes associated with different stages of spermatogenesis, such as mitosis and meiosis, fibrous body-membranous organelles (FB-MOs), and sperm activation. The expression levels of wee-1.3, spe-4, spe-6, and spe-17 genes were increased, while those of puf-8, spe-10, fer-1, swm-1, try-5, and spe-15 genes were decreased. Our results suggesting that PFOS or PFOA may cause spermatogenesis damage by disrupting the mitotic proliferation, meiotic entry, formation of the MOs, fusion of the MOs and plasma membrane (PM), and pseudopods. Loss-of-function studies using puf-8 and spe-10 mutants revealed spe-10 gene was specifically involved in PFOS- or PFOA-induced reproductive toxicity via regulating one or more critical palmitoylation events, while puf-8 gene was not direct target of PFOS and PFOA, and PFOS and PFOA may act on the upstream gene of puf-8, thus affecting reproductive ability. Taken together, these results demonstrate the potential adverse impact of PFOS and PFOA exposure on spermatogenesis and provide valuable data for PFC risk assessment. Grapical abstract.

Exposure to per- and polyfluoroalkyl substances (PFASs) in serum versus semen and their association with male reproductive hormones

Given that per- and polyfluoroalkyl substances (PFASs) exhibit different distribution in the serum and semen of adult men, improving our understanding of the predictors of PFAS concentrations in paired serum and semen samples from an individual is essential. Here, we investigated and compared the effects of emerging and legacy PFAS concentrations in serum and semen on reproductive hormone levels in serum within a Chinese adult male population. We explored the relationships among perfluorooctanoate (PFOA), perfluorononanoate (PFNA), perfluorooctane sulfonate (PFOS), and chlorinated polyfluorinated ether sulfonate (6:2 Cl-PFESA) in serum and semen with reproductive hormones in serum among 651 adult men from Nanjing, China. Significant relationships among all analyzed serum and semen PFASs and decreased total testosterone (total T) were found. Serum and semen PFOA levels were associated with significant decreases in free T. Furthermore, the levels of sex hormone-binding globulin (SHBG) were significantly decreased in association with PFNA, PFOS, and 6:2 Cl-PFESA exposure. Negative relationships between the total T/luteinizing hormone (LH) ratio and semen concentrations of selected PFASs were also observed. After adjustment of PFAS concentrations (in both semen and serum), stronger associations of PFASs with total T, free T, estradiol (E2), SHBG, and total T/LH were observed in semen than in serum. We found that 84.8% of the associations between serum PFOA with total T were mediated by semen PFOA. Thus, elevated PFAS exposure may have negative effects on male reproductive health, and semen PFAS may be a better exposure indicator for the male reproductive system than serum PFAS.

Oxidative stress and mitochondrial membrane potential are involved in the cytotoxicity of perfluorododecanoic acid to neurons

Perfluorododecanoic acid (PFDoA), used in numerous commercial products, was recently demonstrated to accumulate in the brain more easily than other perfluorinated compounds and to cause cognitive deficits. In this study, pheochromocytoma 12 (PC12) cells were exposed to doses of PFDoA to explore the cytotoxicity of this compound to neurons. The results showed that treatment with PFDoA decreased PC12 cell viability dose-dependently. Treatment with 50 and 100 µM PFDoA significantly increased reactive oxygen species (p < 0.01) and malondialdehyde (p < 0.01) and decreased total antioxidant capacity (p < 0.05 and p < 0.01, respectively) in PC12 cells. The administration of 50 and 100 µM PFDoA led to a loss of mitochondrial membrane potential (MMP) (p < 0.05 and p < 0.01, respectively) in PC12 cells. The activity of caspase 3 was obviously increased (p < 0.05) in 100 µM PFDoA-treated PC12 cells. In general, the results demonstrated that PFDoA exposure could result in the disruption of MMP, which may contribute to the increase of oxidative stress and activation of the apoptotic signaling cascade in PC12 cells.

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.

Per- and polyfluoroalkyl substances exert strong inhibition towards human carboxylesterases

PFASs are highly persistent in both natural and living environment, and pose a significant risk for wildlife and human beings. The present study was carried out to determine the inhibitory behaviours of fourteen PFASs on metabolic activity of two major isoforms of carboxylesterases (CES). The probe substrates 2-(2-benzoyl-3-methoxyphenyl) benzothiazole (BMBT) for CES1 and fluorescein diacetate (FD) for CES2 were utilized to determine the inhibitory potentials of PFASs on CES in vitro. The results demonstrated that perfluorododecanoic acid (PFDoA), perfluorotetradecanoic acid (PFTA) and perfluorooctadecanoic acid (PFOcDA) strongly inhibited CES1 and CES2. The half inhibition concentration (IC₅₀) value of PFDoA, PFTA and PFOcDA for CES1 inhibition was 10.6 μM, 13.4 μM and 12.6 μM, respectively. The IC₅₀ for the inhibition of PFDoA, PFTA and PFOcDA towards CES2 were calculated to be 9.56 μM, 17.2 μM and 8.73 μM, respectively. PFDoA, PFTA and PFOcDA exhibited noncompetitive inhibition towards both CES1 and CES2. The inhibition kinetics parameters (K_i) were 27.7 μM, 26.9 μM, 11.9 μM, 4.04 μM, 29.1 μM, 27.4 μM for PFDoA-CES1, PFTA-CES1, PFOcDA-CES1, PFDoA-CES2, PFTA-CES2, PFOcDA-CES2, respectively. In vitro-in vivo extrapolation (IVIVE) predicted that when the plasma concentrations of PFDoA, PFTA and PFOcDA were greater than 2.77 μM, 2.69 μM and 1.19 μM, respectively, it might interfere with the metabolic reaction catalyzed by CES1 in vivo; when the plasma concentrations of PFDoA, PFTA and PFOcDA were greater than 0.40 μM, 2.91 μM, 2.74 μM, it might interfere with the metabolic reaction catalyzed by CES2 in vivo. Molecular docking was used to explore the interactions between PFASs and CES. In conclusion, PFASs were found to cause inhibitory effects on CES in vitro, and this finding would provide an important experimental basis for further in vivo testing of PFASs focused on CES inhibition endpoints.

Binding specificities of estrogen receptor with perfluorinated compounds: A cross species comparison

BACKGROUND

Perfluorinated compounds (PFCs) were reported to result in the endocrine disruption by activating the estrogen receptor (ER) and inducing ER-mediated transcriptions.

OBJECTIVE

The aim of the present work was to perform cross-species comparisons on the characteristics of eight PFCs binding to humans ERα and to rats ERα.

METHODS

In the present work, in vivo tests, including serum estradiol level assay and immunohistochemical staining, fluorescence assay and molecular models were applied.

RESULTS

Based on the in vivo experiments, the exposure of PFOA and PFOS to female rats was proved to increase the ERα expression in the terus, suggesting that PFCs may act as estrogenic compounds to activate ERα in vivo. The further fluorescence assay presented that these eight PFCs have stronger binding abilities to human ERα than to rat ERα. In addition, the differences in binding specificities between human ERα and rat ERα were identified in the process of molecular dynamics modeling with the term of helix position and the ability of coregulator recruitment. It can be found that more and stronger charge clamps could form between PFCs with human ERα than with rat ERα. Also, the eight PFCs presented lower binding energies in human ERα systems, which proved that eight PFCs presented much stronger binding abilities with human ERα.

DISCUSSION

In all, it can be concluded that PFCs might be more sensitive to human ERα than to that of rats, which also suggested the greater susceptibility to adverse effects on humans. The present work was a beginning assessment of a cross-species comparison, providing important information on health impacts of PFCs in humans.

Perfluoroalkyl substances exposure and risk of polycystic ovarian syndrome related infertility in Chinese women

Perfluoroalkyl substances (PFASs) are a family of synthetic, fluorinated organic compounds. They have been widely used in industrial applications and consumer products and widespread in the environment, wildlife and human. Experimental and epidemiologic evidence suggested that PFASs are capable of interfering with endocrine processes and have potential reproductive and developmental toxicities. Polycystic ovarian syndrome (PCOS), one of the main reasons of female infertility, is a common endocrine disorder in reproductive age women. We performed a case-control study to evaluate associations between PCOS-related infertility and PFASs concentrations in plasma. A total of 180 infertile PCOS-cases and 187 healthy controls were recruited from the Center for Reproductive Medicine of Shandong University. Blood specimens were collected at enrollment and analyzed for ten PFASs using liquid chromatography-tandem mass spectrometry. Multivariable logistic regression procedure was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for each PFAS. Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) were the dominant PFASs in the plasma of participants, with the median concentration of 5.07 ng/mL and 4.05 ng/mL, respectively. The median levels of individual PFAS were not significantly different between PCOS-cases and controls. While adjusted for the potential confounders (age, BMI, household income, education level, employment status, age at menarche, menstrual volume), the plasma concentration of perfluorododecanoic acid (PFDoA), a 12 carbons lengths of perfluorocarboxylic acids, was associated with a significantly increased risk of PCOS-related infertility (medium vs low tertile: OR = 2.36, 95% CI: 1.12, 4.99, P = 0.02; high vs low tertile: OR = 3.04, 95% CI: 1.19, 7.67, P = 0.02), with the P trend 0.01. No significant relationship was observed between PCOS-related infertility and other PFAS analytes in the adjusted model, despite perfluoroundecanoic acid showed a negative association (P trend 0.03). The potential reproductive health effects of PFASs and the underlying mechanisms merit further investigation in the future.

Perfluorododecanoic acid exposure induced developmental neurotoxicity in zebrafish embryos

Perfluorododecanoic acid (PFDoA), an artificial perfluorochemical, has been widely distributed in different ambient media and has been reported to have the potential to cause developmental neurotoxicity. However, the specific mechanism is largely unknown. In the current study, zebrafish embryos were treated with 0, 0.24, 1.2, and 6 mg/L PFDoA for 120 h. Exposure to PFDoA causes serious decreases in hatching delay, body length, as well as decreased locomotor speed in zebrafish larvae. Additionally, the acetylcholine (ACh) content as well as acetylcholinesterase (AChE) activity were determined to be significantly downregulated in PFDoA treatment groups. The level of dopamine was upregulated significantly after treating with 1.2 and 6 mg/L of PFDoA. Gene expressions related to the nervous system development were also analyzed, with the exception of the gene mesencephalic astrocyte-derived neurotrophic factor (manf), which is upregulated in the 6 mg/L treatment group. All other genes were significantly downregulated in larvae in the PFDoA group in different degrees. In general, the results demonstrated that PFDoA exposure could result in the disruption of the cholinergic system, dopaminergic signaling, and the central nervous system.

Per- and polyfluoroalkyl substances impact human spermatogenesis in a stem-cell-derived model

Per- and polyfluoroalkyl substances (PFASs) represent a highly ubiquitous group of synthetic chemicals used in products ranging from water and oil repellents and lubricants to firefighting foam. These substances can enter and accumulate in multiple tissue matrices in up to 100% of people assessed. Though animal models strongly identify these compounds as male reproductive toxicants, with exposed rodents experiencing declines in sperm count, alterations in hormones, and DNA damage in spermatids, among other adverse outcomes, human studies report conflicting conclusions as to the reproductive toxicity of these chemicals. Using an innovative, human stem-cell-based model of spermatogenesis, we assessed the effects of the PFASs perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), and a mixture of PFOS, PFOA, and PFNA for their impacts on human spermatogenesis in vitro under conditions relevant to the general and occupationally exposed populations. Here, we show that PFOS, PFOA, PFNA, and a mixture of PFOS, PFOA, and PFNA do not decrease in vitro germ cell viability, consistent with reports from human studies. These compounds do not affect mitochondrial membrane potential or increase reactive oxygen species generation, and they do not decrease cell viability of spermatogonia, primary spermatocytes, secondary spermatocytes, or spermatids in vitro under the conditions examined. However, exposure to PFOS, PFOA, and PFNA reduces expression of markers for spermatogonia and primary spermatocytes. While not having direct effects on germ cell viability, these effects suggest the potential for long-term impacts on male fertility through the exhaustion of the spermatogonial stem cell pool and abnormalities in primary spermatocytes.

ABBREVIATIONS

CDC: Centers for Disease Control; DMSO: dimethyl sulfoxide; GHR: growth hormone receptor; hESCs: human embryonic stem cells; PFASs: per- and polyfluoroalkyl substances; PFCs: perfluorinated compounds; PFNA: perfluorononanoic acid; PFOS: perfluorooctanesulfonic acid; PFOA: perfluorooctanoic acid; PLZF: promyelocytic leukemia zinc finger; ROS: reactive oxygen species; HILI: RNA-mediated gene silencing 2; SSC: spermatogonial stem cell.

Exposure to PFDoA causes disruption of the hypothalamus-pituitary-thyroid axis in zebrafish larvae

Perfluorododecanoic acid (PFDoA), a kind of perfluorinated carboxylic acid (PFCA) with 12 carbon atoms, has an extensive industrial utilization and is widespread in both wildlife and the water environment, and was reported to have the potential to cause a disruption in the thyroid hormone system homeostasis. In this study, zebrafish embryos/larvae were exposed to different concentrations of PFDoA (0, 0.24, 1.2, 6 mg/L) for 96 h post-fertilization (hpf). PFDoA exposure caused obvious growth restriction connected with the reduced thyroid hormones (THs) contents in zebrafish larvae, strengthening the interference effect on the growth of fish larvae. The transcriptional level of genes within the hypothalamic-pituitary-thyroid (HPT) axis was analyzed. The gene expression levels of thyrotropin-releasing hormone (trh) and corticotrophin-releasing hormone (crh) were upregulated upon exposure to 6 mg/L of PFDoA, and iodothyronine deiodinases (dio2) was upregulated in the 1.2 mg/L PFDoA group. The transcription of thyroglobulin (tg) and thyroid receptor (trβ) were significantly downregulated upon exposure to 1.2 mg/L and 6 mg/L of PFDoA. PFDoA could also decrease the levels of sodium/iodide symporter (nis) and transthyretin (ttr) gene expression in a concentration-dependent manner after exposure. A significant decrease in thyroid-stimulating hormoneβ (tshβ), uridinediphosphate-glucuronosyltransferase (ugt1ab) and thyroid receptor (trα) gene expression were observed at 6 mg/L PFDoA exposure. Upregulation and downregulation of iodothyronine deiodinases (dio1) gene expression were observed upon the treatment of 1.2 mg/L and 6 mg/L PFDoA, respectively. All the data demonstrated that gene expression in the HPT axis altered after different PFDoA treatment and the potential mechanisms of the disruption of thyroid status could occur at several steps in the process of synthesis, regulation, and action of thyroid hormones.

Endocrine and fitness correlates of long-chain perfluorinated carboxylates exposure in Arctic breeding black-legged kittiwakes

Increasing levels of poly- and perfluorinated alkyl substances (PFASs) have recently been described in Arctic biota. These emerging substances are of concern given their resistance to degradation and metabolization. Some studies have reported endocrine disrupting effects for some PFASs. However, there is a gap of knowledge on the potential relationships between PFASs and hormones mediating the life-history trade-off between reproduction and survival, such as glucocorticoids. The aims of this study were to (1) describe the concentrations of plasma perfluoroalkyl sulfonates and perfluoroalkyl carboxylates in Svalbard black-legged kittiwakes (Rissa tridactyla) in relation to gender and body-condition, (2) explore the relationships between PFASs and corticosterone (the major glucocorticoid in birds), and (3) assess the consequences of PFAS exposure for reproductive success. Perfluorononanoate was positively related to body-condition in male kittiwakes; perfluorotridecanoate and perfluorotetradecanoate to decreased baseline corticosterone in both sexes; and perfluorododecanoate was related to lower hatching success. These results underline the importance of considering each compound separately when investigating the hazardous effects of PFASs on wildlife.