Per- and polyfluoroalkyl substances alter innate immune function: evidence and data gaps

Per- and polyfluoroalkyl substances (PFASs) are a large class of compounds used in a variety of processes and consumer products. Their unique chemical properties make them ubiquitous and persistent environmental contaminants while also making them economically viable and socially convenient. To date, several reviews have been published to synthesize information regarding the immunotoxic effects of PFASs on the adaptive immune system. However, these reviews often do not include data on the impact of these compounds on innate immunity. Here, current literature is reviewed to identify and incorporate data regarding the effects of PFASs on innate immunity in humans, experimental models, and wildlife. Known mechanisms by which PFASs modulate innate immune function are also reviewed, including disruption of cell signaling, metabolism, and tissue-level effects. For PFASs where innate immune data are available, results are equivocal, raising additional questions about common mechanisms or pathways of toxicity, but highlighting that the innate immune system within several species can be perturbed by exposure to PFASs. Recommendations are provided for future research to inform hazard identification, risk assessment, and risk management practices for PFASs to protect the immune systems of exposed organisms as well as environmental health.

Public Health Risks of PFAS-Related Immunotoxicity Are Real

PURPOSE OF REVIEW

The discovery of per- and polyfluoroalkyl substances (PFAS) in the environment and humans worldwide has ignited scientific research, government inquiry, and public concern over numerous adverse health effects associated with PFAS exposure. In this review, we discuss the use of PFAS immunotoxicity data in regulatory and clinical decision-making contexts and question whether recent efforts adequately account for PFAS immunotoxicity in public health decision-making.

RECENT FINDINGS

Government and academic reviews confirm the strongest human evidence for PFAS immunotoxicity is reduced antibody production in response to vaccinations, particularly for tetanus and diphtheria. However, recent events, such as the economic analysis supporting the proposed national primary drinking water regulations and clinical monitoring recommendations, indicate a failure to adequately incorporate these data into regulatory and clinical decisions. To be more protective of public health, we recommend using all relevant immunotoxicity data to inform current and future PFAS-related chemical risk assessment and regulation. Biological measures of immune system effects, such as reduced antibody levels in response to vaccination, should be used as valid and informative markers of health outcomes and risks associated with PFAS exposure. Routine toxicity testing should be expanded to include immunotoxicity evaluations in adult and developing organisms. In addition, clinical recommendations for PFAS-exposed individuals and communities should be revisited and strengthened to provide guidance on incorporating immune system monitoring and other actions that can be taken to protect against adverse health outcomes.

Investigating mouse hepatic lipidome dysregulation following exposure to emerging per- and polyfluoroalkyl substances (PFAS)

Per- and polyfluoroalkyl substances (PFAS) are environmental pollutants that have been associated with adverse health effects including liver damage, decreased vaccine responses, cancer, developmental toxicity, thyroid dysfunction, and elevated cholesterol. The specific molecular mechanisms impacted by PFAS exposure to cause these health effects remain poorly understood, however there is some evidence of lipid dysregulation. Thus, lipidomic studies that go beyond clinical triglyceride and cholesterol tests are greatly needed to investigate these perturbations. Here, we have utilized a platform coupling liquid chromatography, ion mobility spectrometry, and mass spectrometry (LC-IMS-MS) separations to simultaneously evaluate PFAS bioaccumulation and lipid metabolism disruptions. For the study, liver samples collected from C57BL/6 mice exposed to either of the emerging PFAS hexafluoropropylene oxide dimer acid (HFPO-DA or "GenX") or Nafion byproduct 2 (NBP2) were assessed. Sex-specific differences in PFAS accumulation and liver size were observed for both PFAS, in addition to disturbed hepatic liver lipidomic profiles. Interestingly, GenX resulted in less hepatic bioaccumulation than NBP2 yet gave a higher number of significantly altered lipids when compared to the control group, implying that the accumulation of substances in the liver may not be a reliable measure of the substance's capacity to disrupt the liver's natural metabolic processes. Specifically, phosphatidylglycerols, phosphatidylinositols, and various specific fatty acyls were greatly impacted, indicating alteration of inflammation, oxidative stress, and cellular signaling processes due to emerging PFAS exposure. Overall, these results provide valuable insight into the liver bioaccumulation and molecular mechanisms of GenX- and NBP2-induced hepatotoxicity.

Legacy and emerging per- and polyfluoroalkyl substances suppress the neutrophil respiratory burst

Per- and polyfluoroalkyl substances (PFASs) are used in a multitude of processes and products, including nonstick coatings, food wrappers, and fire-fighting foams. These chemicals are environmentally-persistent, ubiquitous, and can be detected in the serum of 98% of Americans. Despite evidence that PFASs alter adaptive immunity, few studies have investigated their effects on innate immunity. The report here presents results of studies that investigated the impact of nine environmentally-relevant PFASs [e.g. perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid potassium salt (PFOS-K), perfluorononanoic acid (PFNA), perfluorohexanoic acid (PFHxA), perfluorohexane sulfonic acid (PFHxS), perfluorobutane sulfonic acid (PFBS), ammonium perfluoro(2-methyl-3-oxahexanoate) (GenX), 7H-perfluoro-4-methyl-3,6-dioxa-octane sulfonic acid (Nafion byproduct 2), and perfluoromethoxyacetic acid sodium salt (PFMOAA-Na)] on one component of the innate immune response, the neutrophil respiratory burst. The respiratory burst is a key innate immune process by which microbicidal reactive oxygen species (ROS) are rapidly induced by neutrophils in response to pathogens; defects in the respiratory burst can increase susceptibility to infection. The study here utilized larval zebrafish, a human neutrophil-like cell line, and primary human neutrophils to ascertain whether PFAS exposure inhibits ROS production in the respiratory burst. It was observed that exposure to PFHxA and GenX suppresses the respiratory burst in zebrafish larvae and a human neutrophil-like cell line. GenX also suppressed the respiratory burst in primary human neutrophils. This report is the first to demonstrate that these PFASs suppress neutrophil function and support the utility of employing zebrafish larvae and a human cell line as screening tools to identify chemicals that may suppress human immune function.

Estimation of the Half-Lives of Recently Detected Per- and Polyfluorinated Alkyl Ethers in an Exposed Community

To estimate half-lives for novel fluoroethers, the GenX Exposure Study obtained two serum measurements for per- and polyfluoroalkyl substances (PFAS) for 44 participants of age 12-86 years from North Carolina, collected 5 and 11 months after fluoroether discharges into the drinking water source were controlled. The estimated half-lives for these compounds were 127 days (95% confidence interval (95% CI) = 86, 243 days) for perfluorotetraoxadecanoic acid (PFO4DA), 296 days for Nafion byproduct 2 (95% CI = 176, 924 days), and 379 days (95% CI = 199, 3870 days) for perfluoro-3,5,7,9,11-pentaoxadodecanoic acid (PFO5DoA). Using these estimates and the literature values, a model was built that predicted PFAS half-lives using structural properties. Three chemical properties predicted 55% of the variance of PFAS half-lives based on 15 PFAS. A model with only molecular weight predicted 69% of the variance. Some properties can predict the half-lives of PFAS, but a deeper understanding is needed. These fluoroethers had biological half-lives longer than published half-lives for PFHxA and PFHpA (30-60 days) but shorter than those for PFOA and PFOS (800-1200 days). These are the first and possibly only estimates of human elimination half-lives of these fluoroethers.

Quantifying the impact of PFOA exposure on B-cell development and antibody production

Per- and polyfluoroalkyl substances (PFAS) are synthetic chemicals; the vast majority are environmentally and biologically persistent, and some have demonstrated toxicity, including cancer, effects on metabolism, endocrine disruption, and immune dysfunction. Suppression of T-cell-dependent antibody responses (TDAR) has been observed in numerous studies of PFAS but mechanisms remain elusive. Evidence from our work suggests that B cells and how they use energy are impacted by PFAS exposure. We hypothesize that a well-studied and immunotoxic PFAS, perfluorooctanoic acid (PFOA), alters B-cell subclasses and markers of their metabolism. Adult male and female C57BL/6 mice were given PFOA (0 or 7.5 mg/kg) via gavage for 15 days, a duration and dose sufficient to suppress the TDAR. After dosing and immunization of subgroups, spleens were prepared to quantify B-cell subsets. Flow cytometric analysis revealed decreased numbers of plasmablasts, follicular, naïve, and overall B-cell subclasses in female PFOA-exposed groups. Male PFOA-exposed groups had a significant increase in follicular B cells and other subsets had decreases, including in the overall number of B cells. Twenty-four hours after naïve B-cell isolation and ex vivo activation, metabolic measurements revealed a 5-fold increase in metabolic markers in response to stimulation in PFOA-exposed groups compared with controls. These findings suggest that B-cell development and survival may be hindered by PFOA exposure, but that activation of the remaining B cells was not. Based on these findings, PFOA-mediated suppression of the primary IgM antibody response results changes to specific subsets of B cells.

Widening the Lens on PFASs: Direct Human Exposure to Perfluoroalkyl Acid Precursors (pre-PFAAs)

Determining health risks associated with per-/polyfluoroalkyl substances (PFASs) is a highly complex problem requiring massive efforts for scientists, risk assessors, and regulators. Among the most poorly understood pressing questions is the relative importance of pre-PFAAs, which are PFASs that degrade to highly persistent perfluoroalkyl acids. How many of the vast number of existing pre-PFAAs are relevant for direct human exposure, and what are the predominant exposure pathways? What evidence of direct exposure to pre-PFAAs is provided by human biomonitoring studies? How important are pre-PFAAs and their biotransformation products for human health risk assessment? This article outlines recent progress and recommendations toward widening the lens on human PFAS exposure to include the pre-PFAA subclass.

Official health communications are failing PFAS-contaminated communities

BACKGROUND

Environmental health agencies are critical sources of information for communities affected by chemical contamination. Impacted residents and their healthcare providers often turn to federal and state agency webpages, fact sheets, and other documents to weigh exposure risks and interventions.

MAIN BODY

This commentary briefly reviews scientific evidence concerning per- and polyfluoroalkyl substances (PFAS) for health outcomes that concern members of affected communities and that have compelling or substantial yet differing degree of scientific evidence. It then features official documents in their own language to illustrate communication gaps, as well as divergence from scientific evidence and from best health communication practice. We found official health communications mostly do not distinguish between the needs of heavily contaminated communities characterized by high body burdens and the larger population with ubiquitous but substantially smaller exposures. Most health communications do not distinguish levels of evidence for health outcomes and overemphasize uncertainty, dismissing legitimate reasons for concern in affected communities. Critically, few emphasize helpful approaches to interventions. We also provide examples that can be templates for improvement.

CONCLUSIONS

Immediate action should be undertaken to review and improve official health communications intended to inform the public and health providers about the risks of PFAS exposure and guide community and medical decisions.

Cross-sectional associations between serum PFASs and inflammatory biomarkers in a population exposed to AFFF-contaminated drinking water

BACKGROUND

Per- and polyfluoroalkyl substances (PFASs) are widespread and persistent environmental contaminants. Exposure to several PFASs has been associated with altered immune function in humans, including autoimmune disease and impaired response to vaccination. However, changes to the profile of inflammatory biomarkers in adults exposed to PFASs has not been extensively described.

OBJECTIVE

To estimate cross-sectional associations between serum PFASs and markers of inflammation among adults in a population exposed to aqueous film forming foam (AFFF)-contaminated drinking water.

METHODS

We quantified concentrations of 48 PFASs in non-fasting serum samples from 212 non-smoking adults. In the same serum samples, we measured concentrations of ten pro- and anti-inflammatory cytokines. We restricted analysis to seven PFASs detected in >85% of participants and the following four cytokines detected in ≥30% of participants: interleukin [IL]-1β, IL-6, IL-10, and tumor necrosis factor [TNF]-α. We fit multiple linear regression or logistic regression models, adjusted for potential confounders, to estimate associations between concentrations of each PFAS and either continuous or categorical (above vs below limit of detection) concentrations of each cytokine. We additionally applied Bayesian kernel machine regression to describe the combined effect of the PFAS mixture on each cytokine outcome.

RESULTS

Certain PFAS concentrations in this sample were elevated compared to a US nationally representative sample; median levels of PFHxS, ΣPFOS and ΣPFOA in this sample were 13.8, 2.1 and 1.7 times higher, respectively, than medians observed in the U.S.

SAMPLE

Higher concentrations of multiple PFASs were significantly associated with lower odds of detectable IL-1β. Weaker associations were observed with other cytokines. In general, perfluoroalkyl carboxylic acids had inverse associations with TNF-α, whereas the perfluoroalkyl sulfonic acids showed positive associations.

CONCLUSIONS

We observed preliminary evidence of altered inflammatory profiles among adults with elevated serum concentrations of PFASs due to contaminated drinking water. Modifications to inflammatory pathways may be one mechanism by which PFAS exposures produce adverse health effects in humans, but this finding requires verification in longitudinal studies as well as phenotypic anchoring to immune function outcomes.

Addressing Urgent Questions for PFAS in the 21st Century

Despite decades of research on per- and polyfluoroalkyl substances (PFAS), fundamental obstacles remain to addressing worldwide contamination by these chemicals and their associated impacts on environmental quality and health. Here, we propose six urgent questions relevant to science, technology, and policy that must be tackled to address the "PFAS problem": (1) What are the global production volumes of PFAS, and where are PFAS used? (2) Where are the unknown PFAS hotspots in the environment? (3) How can we make measuring PFAS globally accessible? (4) How can we safely manage PFAS-containing waste? (5) How do we understand and describe the health effects of PFAS exposure? (6) Who pays the costs of PFAS contamination? The importance of each question and barriers to progress are briefly described, and several potential paths forward are proposed. Given the diversity of PFAS and their uses, the extreme persistence of most PFAS, the striking ongoing lack of fundamental information, and the inequity of the health and environmental impacts from PFAS contamination, there is a need for scientific and regulatory communities to work together, with cooperation from PFAS-related industries, to fill in critical data gaps and protect human health and the environment.

Immunotoxicity of an Electrochemically Fluorinated Aqueous Film-Forming Foam

Aqueous film-forming foams (AFFFs) are complex per- and polyfluoroalkyl substance (PFAS)-containing mixtures used extensively as fire suppressants. AFFF-impacted groundwater and surface water have contaminated drinking water with PFASs in many communities, raising concerns about health effects from drinking water exposures. As individual PFASs have been identified as immune hazards, the immunotoxicity of complex PFAS mixtures is also a concern. Adult female and male C57BL/6 mice were given a commercial AFFF formulation for 10 days via gavage; administered dose was based on combined content of perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS) measured in the formulation (0, 1.88, 3.75, 7.5, or 10 mg PFOS+PFOA/kg body weight). A PFOA positive control of 7.5 mg/kg body weight was also given. Compared with the 0 mg/kg group, the following changes were noted: Body weights of males exposed to 7.5 and 10 mg PFOS+PFOA/kg were reduced by 15%, on average; female body weights did not differ. Average relative liver weights were increased 50%-200% in males and 37.5%-193% in females and liver peroxisome proliferation was increased 2- to 12-fold in all doses of both sexes. Antigen-specific antibody production was suppressed, on average, by 13% in males and by 12.4% in females across all doses. Spleen cellularity and lymphocyte subpopulations did not differ by dose for either sex. Our data indicate that though this complex PFAS mixture contained fairly low PFOA content, it induced changes in C57BL/6 mice similar to changes induced by PFOA alone, likely due to the presence of PFOS and many other PFASs.

PFOS dominates PFAS composition in ambient fine particulate matter (PM2.5) collected across North Carolina nearly 20 years after the end of its US production

Contamination of drinking water by per- and polyfluoroalkyl substances (PFASs) emitted from manufacturing plants, fire-fighting foams, and urban waste streams has received considerable attention due to concerns over toxicity and environmental persistence; however, PFASs in ambient air remain poorly understood, especially in the United States (US). We measured PFAS concentrations in ambient fine particulate matter (PM_2.5) at 5 locations across North Carolina over a 1 year period in 2019. Thirty-four PFASs, including perfluoroalkyl carboxylic, perfluoroalkane sulfonic, perfluoroalkyl ether carboxylic and sulfonic acids were analyzed by UHPLC/ESI-MS/MS. Quarterly averaged concentrations ranged from <0.004-14.1 pg m^-3. Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) ranged from <0.18 to 14.1 pg m^-3, comparable to previous PM_2.5 measurements from Canada and Europe (<0.02-3.5 pg m^-3). Concentrations above 1 pg m^-3 were observed in July-September at Charlotte (14.1 pg m^-3, PFOA), Wilmington (4.75 pg m^-3, PFOS), and Research Triangle Park (1.37 pg m^-3, PFOS). Notably, PM_2.5 has a short atmospheric lifetime (<2 weeks), and thus, the presence of PFOS in these samples raises questions about their sources, since PFOS production was phased out in the US ∼20 years ago. This is the first US study to provide insights into ambient PFAS concentrations in PM_2.5.

Using Chicken Embryo as a Powerful Tool in Assessment of Developmental Cardiotoxicities

Chicken embryos are a classical model in developmental studies. During the development of chicken embryos, the time window of heart development is well-defined, and it is relatively easy to achieve precise and timely exposure via multiple methods. Moreover, the process of heart development in chicken embryos is similar to mammals, also resulting in a four-chambered heart, making it a valuable alternative model in the assessment of developmental cardiotoxicities. In our lab, the chicken embryo model is routinely used in the assessment of developmental cardiotoxicities following exposure to various environmental pollutants, including per- and polyfluoroalkyl substances (PFAS), particulate matter (PMs), diesel exhaust (DE) and nano materials. The exposure time can be freely selected based on the need, from the beginning of development (embryonic day 0, ED0) all the way to the day prior to hatch. The major exposure methods include air-cell injection, direct microinjection, and air-cell inhalation (originally developed in our lab), and the currently available endpoints include cardiac function (electrocardiography), morphology (histological assessments) and molecular biological assessments (immunohistochemistry, qRT-PCR, western blotting, etc.). Of course, the chicken embryo model has its own limitations, such as limited availability of antibodies. Nevertheless, with more laboratories starting to utilize this model, it can be used to make significant contributions to the study of developmental cardiotoxicities.

Per- and Polyfluoroalkyl Substance Toxicity and Human Health Review: Current State of Knowledge and Strategies for Informing Future Research

Reports of environmental and human health impacts of per- and polyfluoroalkyl substances (PFAS) have greatly increased in the peer-reviewed literature. The goals of the present review are to assess the state of the science regarding toxicological effects of PFAS and to develop strategies for advancing knowledge on the health effects of this large family of chemicals. Currently, much of the toxicity data available for PFAS are for a handful of chemicals, primarily legacy PFAS such as perfluorooctanoic acid and perfluorooctane sulfonate. Epidemiological studies have revealed associations between exposure to specific PFAS and a variety of health effects, including altered immune and thyroid function, liver disease, lipid and insulin dysregulation, kidney disease, adverse reproductive and developmental outcomes, and cancer. Concordance with experimental animal data exists for many of these effects. However, information on modes of action and adverse outcome pathways must be expanded, and profound differences in PFAS toxicokinetic properties must be considered in understanding differences in responses between the sexes and among species and life stages. With many health effects noted for a relatively few example compounds and hundreds of other PFAS in commerce lacking toxicity data, more contemporary and high-throughput approaches such as read-across, molecular dynamics, and protein modeling are proposed to accelerate the development of toxicity information on emerging and legacy PFAS, individually and as mixtures. In addition, an appropriate degree of precaution, given what is already known from the PFAS examples noted, may be needed to protect human health. Environ Toxicol Chem 2021;40:606-630. © 2020 SETAC.

The high persistence of PFAS is sufficient for their management as a chemical class

Per- and polyfluoroalkyl substances (PFAS) are a class of synthetic organic substances with diverse structures, properties, uses, bioaccumulation potentials and toxicities. Despite this high diversity, all PFAS are alike in that they contain perfluoroalkyl moieties that are extremely resistant to environmental and metabolic degradation. The vast majority of PFAS are therefore either non-degradable or transform ultimately into stable terminal transformation products (which are still PFAS). Under the European chemicals regulation this classifies PFAS as very persistent substances (vP). We argue that this high persistence is sufficient concern for their management as a chemical class, and for all "non-essential" uses of PFAS to be phased out. The continual release of highly persistent PFAS will result in increasing concentrations and increasing probabilities of the occurrence of known and unknown effects. Once adverse effects are identified, the exposure and associated effects will not be easily reversible. Reversing PFAS contamination will be technically challenging, energy intensive, and costly for society, as is evident in the efforts to remove PFAS from contaminated land and drinking water sources.

An overview of the uses of per- and polyfluoroalkyl substances (PFAS)

Per- and polyfluoroalkyl substances (PFAS) are of concern because of their high persistence (or that of their degradation products) and their impacts on human and environmental health that are known or can be deduced from some well-studied PFAS. Currently, many different PFAS (on the order of several thousands) are used in a wide range of applications, and there is no comprehensive source of information on the many individual substances and their functions in different applications. Here we provide a broad overview of many use categories where PFAS have been employed and for which function; we also specify which PFAS have been used and discuss the magnitude of the uses. Despite being non-exhaustive, our study clearly demonstrates that PFAS are used in almost all industry branches and many consumer products. In total, more than 200 use categories and subcategories are identified for more than 1400 individual PFAS. In addition to well-known categories such as textile impregnation, fire-fighting foam, and electroplating, the identified use categories also include many categories not described in the scientific literature, including PFAS in ammunition, climbing ropes, guitar strings, artificial turf, and soil remediation. We further discuss several use categories that may be prioritised for finding PFAS-free alternatives. Besides the detailed description of use categories, the present study also provides a list of the identified PFAS per use category, including their exact masses for future analytical studies aiming to identify additional PFAS.

An overview of the uses of per- and polyfluoroalkyl substances (PFAS)

Per- and polyfluoroalkyl substances (PFAS) are of concern because of their high persistence (or that of their degradation products) and their impacts on human and environmental health that are known or can be deduced from some well-studied PFAS. Currently, many different PFAS (on the order of several thousands) are used in a wide range of applications, and there is no comprehensive source of information on the many individual substances and their functions in different applications. Here we provide a broad overview of many use categories where PFAS have been employed and for which function; we also specify which PFAS have been used and discuss the magnitude of the uses. Despite being non-exhaustive, our study clearly demonstrates that PFAS are used in almost all industry branches and many consumer products. In total, more than 200 use categories and subcategories are identified for more than 1400 individual PFAS. In addition to well-known categories such as textile impregnation, fire-fighting foam, and electroplating, the identified use categories also include many categories not described in the scientific literature, including PFAS in ammunition, climbing ropes, guitar strings, artificial turf, and soil remediation. We further discuss several use categories that may be prioritised for finding PFAS-free alternatives. Besides the detailed description of use categories, the present study also provides a list of the identified PFAS per use category, including their exact masses for future analytical studies aiming to identify additional PFAS.

Are Fluoropolymers Really of Low Concern for Human and Environmental Health and Separate from Other PFAS?

Fluoropolymers are a group of polymers within the class of per- and polyfluoroalkyl substances (PFAS). The objective of this analysis is to evaluate the evidence regarding the environmental and human health impacts of fluoropolymers throughout their life cycle(s). Production of some fluoropolymers is intimately linked to the use and emissions of legacy and novel PFAS as polymer processing aids. There are serious concerns regarding the toxicity and adverse effects of fluorinated processing aids on humans and the environment. A variety of other PFAS, including monomers and oligomers, are emitted during the production, processing, use, and end-of-life treatment of fluoropolymers. There are further concerns regarding the safe disposal of fluoropolymers and their associated products and articles at the end of their life cycle. While recycling and reuse of fluoropolymers is performed on some industrial waste, there are only limited options for their recycling from consumer articles. The evidence reviewed in this analysis does not find a scientific rationale for concluding that fluoropolymers are of low concern for environmental and human health. Given fluoropolymers' extreme persistence; emissions associated with their production, use, and disposal; and a high likelihood for human exposure to PFAS, their production and uses should be curtailed except in cases of essential uses.

Scientific Basis for Managing PFAS as a Chemical Class

This commentary presents a scientific basis for managing as one chemical class the thousands of chemicals known as PFAS (per- and polyfluoroalkyl substances). The class includes perfluoroalkyl acids, perfluoroalkylether acids, and their precursors; fluoropolymers and perfluoropolyethers; and other PFAS. The basis for the class approach is presented in relation to their physicochemical, environmental, and toxicological properties. Specifically, the high persistence, accumulation potential, and/or hazards (known and potential) of PFAS studied to date warrant treating all PFAS as a single class. Examples are provided of how some PFAS are being regulated and how some businesses are avoiding all PFAS in their products and purchasing decisions. We conclude with options for how governments and industry can apply the class-based approach, emphasizing the importance of eliminating non-essential uses of PFAS, and further developing safer alternatives and methods to remove existing PFAS from the environment.

Strategies for grouping per- and polyfluoroalkyl substances (PFAS) to protect human and environmental health

Grouping strategies are needed for per- and polyfluoroalkyl substances (PFAS), in part, because it would be time and resource intensive to test and evaluate the more than 4700 PFAS on the global market on a chemical-by-chemical basis. In this paper we review various grouping strategies that could be used to inform actions on these chemicals and outline the motivations, advantages and disadvantages for each. Grouping strategies are subdivided into (1) those based on the intrinsic properties of the PFAS (e.g. persistence, bioaccumulation potential, toxicity, mobility, molecular size) and (2) those that inform risk assessment through estimation of cumulative exposure and/or effects. The most precautionary grouping approach of those reviewed within this article suggests phasing out PFAS based on their high persistence alone (the so-called "P-sufficient" approach). The least precautionary grouping approach reviewed advocates only grouping PFAS for risk assessment that have the same toxicological effects, modes and mechanisms of action, and elimination kinetics, which would need to be well documented across different PFAS. It is recognised that, given jurisdictional differences in chemical assessment philosophies and methodologies, no one strategy will be generally acceptable. The guiding question we apply to the reviewed grouping strategies is: grouping for what purpose? The motivation behind the grouping (e.g. determining use in products vs. setting guideline levels for contaminated environments) may lead to different grouping decisions. This assessment provides the necessary context for grouping strategies such that they can be adopted as they are, or built on further, to protect human and environmental health from potential PFAS-related effects.

Bioaccumulation of Novel Per- and Polyfluoroalkyl Substances in Mice Dosed with an Aqueous Film-Forming Foam

Per- and polyfluoroalkyl substances (PFASs) are widespread in the blood of the general human population, and their bioaccumulation is of considerable scientific and regulatory interest. PFAS exposure resulting from aqueous film-forming foam (AFFF) ingestion is poorly understood due to the complexity of AFFF mixtures and the presence of polyfluorinated substances that may undergo metabolic transformation. C57BL/6 mice were dosed with an AFFF primarily containing electrochemically fluorinated PFASs for 10 days, followed by a 6 day depuration. Urine was collected throughout the study and serum was collected post-depuration. Samples were analyzed via high-resolution mass spectrometry. Relative to the dosing solution, C6 and C7 perfluoroalkyl sulfonates (PFSAs) were enriched in dosed mouse serum, suggesting in vivo transformation of sulfonamide precursors. Some substituted C8 PFSAs [keto-perfluorooctane sulfonate (PFOS), hydrogen-PFOS, and unsaturated PFOS] appeared to be more bioaccumulative than linear PFOS, or were formed in vivo from unidentified precursors. A series of seven peaks in dosed mouse serum was tentatively identified as sulfonimide dimers that were either a minor component of the AFFF or were formed via metabolism of other AFFF components. This work highlights the importance of sulfonamide precursors in contributing to bioaccumulation of AFFF-associated PFSAs and identifies several classes of potentially bioaccumulative novel PFASs that warrant further investigation.

The concept of essential use for determining when uses of PFASs can be phased out

Because of the extreme persistence of per- and polyfluoroalkyl substances (PFASs) and their associated risks, the Madrid Statement argues for stopping their use where they are deemed not essential or when safer alternatives exist. To determine when uses of PFASs have an essential function in modern society, and when they do not, is not an easy task. Here, we: (1) develop the concept of "essential use" based on an existing approach described in the Montreal Protocol, (2) apply the concept to various uses of PFASs to determine the feasibility of elimination or substitution of PFASs in each use category, and (3) outline the challenges for phasing out uses of PFASs in society. In brief, we developed three distinct categories to describe the different levels of essentiality of individual uses. A phase-out of many uses of PFASs can be implemented because they are not necessary for the betterment of society in terms of health and safety, or because functional alternatives are currently available that can be substituted into these products or applications. Some specific uses of PFASs would be considered essential because they provide for vital functions and are currently without established alternatives. However, this essentiality should not be considered as permanent; rather, constant efforts are needed to search for alternatives. We provide a description of several ongoing uses of PFASs and discuss whether these uses are essential or non-essential according to the three essentiality categories. It is not possible to describe each use case of PFASs in detail in this single article. For follow-up work, we suggest further refining the assessment of the use cases of PFASs covered here, where necessary, and expanding the application of this concept to all other uses of PFASs. The concept of essential use can also be applied in the management of other chemicals, or groups of chemicals, of concern.

Dysfunctional microglia:neuron interactions with significant female bias in a developmental gene x environment rodent model of Alzheimer's disease

Signaling between microglia and neurons is poorly characterized in the pathophysiology of Alzheimer's disease (AD), particularly with regards to gene and environmental (GxE) interactions early in life. This study investigated the maladaptation of microglia:neuron signaling and subsequent susceptibility to neurodegeneration using a developmental origin of adult disease (DOAD) model of AD, characterized previously. Here, we report that postnatal exposure to lead (Pb) in a transgenic (Tg) rodent model of AD resulted in significant female bias consequent to GxE interactions. Atypical, non-neuroprotective microglial phenotypes were observed months after cessation of Pb exposure, as well as evidence for neuronal compensation, that was not observed in WT mice. Specifically, microglia from Pb-exposed Tg (GxE) females exhibited atypical polarization profiles for activation earlier and more severely than males and WT mice, that persisted over time to become contextually maladaptive. By postnatal day (PND) 240, microglia from GxE females also sequestered less neurotoxic iron in the hippocampus. In the same GxE female population, measures of neuronal parameters, such as hippocampal TrkB expression, revealed evidence of disharmonious and compensatory interactions with microglia within the pathological progression. Likewise, GxE interactions resulted in female-biased, late-life changes to key synaptic proteins crucial to synapse dynamics and microglial signaling. These incongruent microglia:neuronal dynamics were observed in GxE males at later ages compared to females, and not observed in either gene- or environment-only populations. Altogether, our results support a gene x environment model of female-biased microglial susceptibility to later-life development of AD, and highlight markers for maladaptive microglia:neuron signaling and compensation.

Exposure to per-fluoroalkyl and polyfluoroalkyl substances leads to immunotoxicity: epidemiological and toxicological evidence

In this perspective, we evaluate key and emerging epidemiological and toxicological data concerning immunotoxicity of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) and seek to reconcile conflicting conclusions from two reviews published in 2016. We summarize ways that immunosuppression and immunoenhancement are defined and explain how specific outcomes are used to evaluate immunotoxicity in humans and experimental animals. We observe that different approaches to defining immunotoxicological outcomes, particularly those that do not produce clinical disease, may lead to different conclusions from epidemiological and toxicological studies. The fundamental point that we make is that aspects of epidemiological studies considered as limitations can be minimized when data from toxicological studies support epidemiological findings. Taken together, we find that results of epidemiological studies, supported by findings from toxicological studies, provide strong evidence that humans exposed to PFOA and PFOS are at risk for immunosuppression.

Nevada desert dust with heavy metals suppresses IgM antibody production

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NDRA emits geogenic dusts that are comprised of a mineral-metal mixture.

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Exposure to NDRA geogenic dusts suppressed immune function in a mouse model.

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Similar desert surfaces emit dust in southern Nevada and elsewhere in the world.

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This study represents a desert environment; dust composition may vary by source.

Systemic health effects from exposure to a complex natural dust containing heavy metals from the Nellis Dunes Recreation Area (NDRA) near Las Vegas, NV, were evaluated. Several toxicological parameters were examined following lung exposure to emissive dust from three geologic sediment types heavily used for recreational off-road activities: yellow sand very rich in arsenic (termed CBN 5); a shallow cover of loose dune sand overlying a gravelly subsoil bordering dune fields (termed CBN 6); and brown claystone and siltstone (termed CBN 7). Adult female B6C3F1 mice were exposed by oropharyngeal administration to these three types of geogenic dusts at 0.01–100 mg of dust/kg of body weight, once per week for four weeks. The median grain sizes were 4.6, 3.1, and 4.4 μm, for CBN 5, 6, and 7, respectively. Each type of dust contained quantifiable amounts of aluminum, vanadium, chromium, manganese, iron, cobalt, copper, zinc, arsenic, strontium, cesium, lead, uranium, and others. Descriptive markers of immunotoxicity, neurotoxicity, hematology, and clinical chemistry parameters were assessed. Notable among all three CBN units was a systemic, dose-responsive decrease in antigen-specific IgM antibody responses. Geogenic dust from CBN 5 produced more than a 70% suppression in IgM responses, establishing a lowest adverse effect level (LOAEL) of 0.01 mg/kg. A suppression in IgM responses and a corresponding increase in serum creatinine determined a LOAEL of 0.01 mg/kg for CBN 6. The LOAEL for CBN 7 was 0.1 mg/kg and also was identified from suppression in IgM responses. These results are of concern given the frequent off-road vehicle traffic and high visitor rates at the NDRA, estimated at 300,000 each year.

A single dose of trichloroethylene given during development does not substantially alter markers of neuroinflammation in brains of adult mice

Trichloroethylene (TCE) is a widespread environmental contaminant associated with developmental immunotoxicity and neurotoxicity. Previous studies have shown that MRL^+/+ mice exposed to TCE from gestation through early-life demonstrate robust increases in inflammatory markers in peripheral CD4⁺ T-cells, as well as glutathione depletion and increased oxidative stress in cerebellum-associated with alterations in behavior. Since increased oxidative stress is associated with neuroinflammation, we hypothesized that neuroinflammatory markers could be altered relative to unexposed mice. MRL^+/+ mice were given 0.5 mg/ml of TCE in vehicle or vehicle (water with 1% Alkamuls EL-620) from conception through early adulthood via drinking water to dams and then directly to post-weaning offspring. Animals were euthanized at 49 days of age and levels of pro- and anti-inflammatory cytokines, density of T-cell staining, and micro-glial morphology were evaluated in brains to begin to ascertain a neuroinflammatory profile. Levels of IL-6 were decreased in female animals and while not statistically significant, and levels of IL-10 were higher in brains of exposed male and female animals. Supportive of this observation, although not statistically significant, the number of ameboid microglia was higher in exposed relative to unexposed animals. This overall profile suggests the emergence of an anti-inflammatory/neuroprotective phenotype in exposed animals, possibly as a compensatory response to neuroinflammation that is known to be induced by developmental exposure to TCE.

Health effects following subacute exposure to geogenic dust collected from active drainage surfaces (Nellis Dunes Recreation Area, Las Vegas, NV)

The specific health effects of direct inhalation of fine minerogenic dusts generated by natural soil surfaces remain poorly known and relatively little researched. To learn more about this exposure and its contribution to human health effects, we surveyed surface sediment and characterized dust from the Nellis Dunes Recreation Area (NDRA) in Clark County, Nevada, a popular off-road vehicle (ORV) recreational site. Dry drainage systems at NDRA are commonly used as natural trail systems for ORV recreation; these surfaces also are characterized by high concentrations of heavy metals. Geogenic dust with a median diameter of 4.05 μm, collected from drainage surfaces at NDRA contained a total elemental concentration of aluminum (79,651 μg/g), vanadium (100 μg/g), chromium (54 μg/g), manganese (753 μg/g), iron (33,266 μg/g), cobalt (14 μg/g), copper (37 μg/g) zinc (135 μg/g), arsenic (71 μg/g), strontium (666 μg/g), cesium (15 μg/g), lead (34 μg/g), and uranium (54.9 μg/g). Adult female B6C3F1 mice exposed via oropharyngeal aspiration to 0.01–100 mg dust/kg body weight, four times, a week apart, for 28-days, were evaluated for immuno- and neurotoxicological outcomes 24 h after the last exposure. Antigen-specific IgM responses were dose-responsively suppressed at 0.1, 1.0, 10 and 100 mg/kg. Splenic lymphocytic subpopulations, hematological and clinical chemistry parameters were affected. In brain tissue, antibodies against NF-68, and GFAP were not affected, whereas IgM antibodies against MBP were reduced by 26.6% only in the highest dose group. A lowest observed adverse effect level (LOAEL) of 0.1 mg/kg/day and a no observed adverse effect level (NOAEL) of 0.01 mg/kg/day were derived based on the antigen primary IgM responses after subacute exposure to this geogenic dust.

A Never-Ending Story of Per- and Polyfluoroalkyl Substances (PFASs)?

More than 3000 per- and polyfluoroalkyl substances (PFASs) are, or have been, on the global market, yet most research and regulation continues to focus on a limited selection of rather well-known long-chain PFASs, particularly perfluorooctanesulfonate (PFOS), perfluorooctanoic acid (PFOA) and their precursors. Continuing to overlook the vast majority of other PFASs is a major concern for society. We provide recommendations for how to proceed with research and cooperation to tackle the vast number of PFASs on the market and in the environment.

Evaluation of the immunomodulatory effects of 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)-propanoate in C57BL/6 mice

2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)-propanoate was designed to replace perfluorooctanoic acid (PFOA), which has been mostly phased out of U.S. production due to environmental persistence, detectable human and wildlife serum concentrations, and reports of systemic toxicity. In rodent models, PFOA exposure suppresses T cell-dependent antibody responses (TDAR) and vaccine responses in exposed humans. To determine replacement compound effects on TDAR and related parameters, male and female C57BL/6 mice were gavaged with 0, 1, 10, or 100 mg/kg/day for 28 days. Mice immunized with antigen on day 24 were evaluated for TDAR and splenic lymphocyte subpopulations five days later. Serum and urine were collected for test compound concentrations and liver peroxisome proliferation was measured. Relative liver weight at 10 and 100 mg/kg and peroxisome proliferation at 100 mg/kg were increased in both sexes. TDAR was suppressed in females at 100 mg/kg. T lymphocyte numbers were increased in males at 100 mg/kg; B lymphocyte numbers were unchanged in both sexes. Females had less serum accumulation and higher clearance than males, and males had higher urine concentrations than females at all times and doses. While this PFOA-replacement compound appears less potent at suppressing TDAR relative to PFOA, it produces detectable changes in parameters affected by PFOA; further studies are necessary to determine its full immunomodulatory profile and potential synergism with other per- and polyfluoroalkyl substances of environmental concern.

Perfluorooctanoic acid-induced toxicity in primary cultures of chicken embryo cardiomyocytes

Perfluorooctanoic acid (PFOA) is a widespread environmental contaminant that induces developmental cardiotoxicity. It is detectable in late stage chicken embryos and hatchling chickens. To investigate mechanism(s) of cardiotoxicity, primary cultures of cardiomyocytes were prepared from 10-day-old chicken embryos that were (A) pre-exposed to vehicle or 2 mg of PFOA/kg of egg weight in ovo or (B) incubated with PFOA in vitro at concentrations ranging from 0 to 100 µg/mL in medium for 1 or 36 h. When viability was assessed, survival of cardiomyocytes prepared from pre-exposed embryos did not differ from vehicle controls, even under conditions of serum starvation designed to challenge the cells. However, 1 h of exposure to 100 µg/mL of PFOA in vitro and 36 h of exposure to 75 and 100 µg/mL PFOA in vitro decreased viability. When contractility was evaluated, cardiomyocytes cultured from pre-exposed embryos exhibited decreases in time to maximum departure velocity and cell length at peak contraction, whereas cardiomyocytes exposed in vitro exhibited a reduction in the 50% relaxation time at a concentration of 1 µg/mL relative to vehicle controls. Morphological assessment revealed decreased cardiomyocytes axial length following in ovo PFOA exposure and 24 h in vitro PFOA 50 µg/mL exposure. Reactive oxygen species (ROS) generation, which was evaluated only in cardiomyocytes exposed to PFOA in vitro, was significantly elevated following incubation with 50 µg/mL of PFOA for 1 h. These data indicate that while in vitro exposure to relatively high concentrations of PFOA can induce cytotoxicity and ROS, developmental cardiotoxicity observed in ovo is not likely mediated via PFOA-induced overt cytotoxicity, but likely by altering early cardiac morphologic and function processes. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1580-1590, 2016.

Demographic, Reproductive, and Dietary Determinants of Perfluorooctane Sulfonic (PFOS) and Perfluorooctanoic Acid (PFOA) Concentrations in Human Colostrum

To determine demographic, reproductive, and maternal dietary factors that predict perfluoroalkyl substance (PFAS) concentrations in breast milk, we measured perfluorooctane sulfonic (PFOS) and perfluorooctanoic acid (PFOA) concentrations, using liquid chromatography-mass spectrometry, in 184 colostrum samples collected from women participating in a cohort study in Eastern Slovakia between 2002 and 2004. During their hospital delivery stay, mothers completed a food frequency questionnaire, and demographic and reproductive data were also collected. PFOS and PFOA predictors were identified by optimizing multiple linear regression models using Akaike's information criterion (AIC). The geometric mean concentration in colostrum was 35.3 pg/mL for PFOS and 32.8 pg/mL for PFOA. In multivariable models, parous women had 40% lower PFOS (95% CI: -56 to -17%) and 40% lower PFOA (95% CI: -54 to -23%) concentrations compared with nulliparous women. Moreover, fresh/frozen fish consumption, longer birth intervals, and Slovak ethnicity were associated with higher PFOS and PFOA concentrations in colostrum. These results will help guide the design of future epidemiologic studies examining milk PFAS concentrations in relation to health end points in children.

Associating Changes in the Immune System with Clinical Diseases for Interpretation in Risk Assessment

This overview is an update of the unit originally published in 2004. While the basic tenets of immunotoxicity have not changed in the past 10 years, several publications have explored the application of immunotoxicological data to the risk assessment process. Therefore, the goal of this unit is still to highlight relationships between xenobiotic-induced immunosuppression and risk of clinical diseases progression. In immunotoxicology, this may require development of models to equate moderate changes in markers of immune functions to potential changes in incidence or severity of infectious diseases. For most xenobiotics, exposure levels and disease incidence data are rarely available, and safe exposure levels must be estimated based on observations from experimental models or human biomarker studies. Thus, it is important to establish a scientifically sound framework that allows accurate and quantitative interpretation of experimental or biomarker data in the risk assessment process.

Association of Perfluoroalkyl Substances, Bone Mineral Density, and Osteoporosis in the U.S. Population in NHANES 2009-2010

BACKGROUND

Perfluoroalkyl substances (PFASs), including perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS), perfluorohexane sulfonic acid (PFHxS), and perfluorononanoic acid (PFNA), are detectable in the serum of 95% of the U.S.

OBJECTIVE

Considering the role of PFASs as endocrine disruptors, we examined their relationships with bone health.

METHODS

The association between serum PFAS concentration and bone mineral density at total femur (TFBMD), femoral neck (FNBMD), lumbar spine (LSBMD), and physician-diagnosed osteoporosis was assessed in 1,914 participants using data from the National Health and Nutritional Examination Survey 2009-2010.

RESULTS

The mean age of the participants was 43 years. Men had higher serum PFAS concentrations than women (p < 0.001) except for PFNA. In both sexes, serum PFOS concentrations were inversely associated with FNBMD (p < 0.05). In women, significant negative associations were observed for natural log (ln)-transformed PFOS exposure with TFBMD and FNBMD, and for ln-transformed PFOA exposure with TFBMD (p < 0.05). In postmenopausal women, serum PFOS was negatively associated with TFBMD and FNBMD, and PFNA was negatively associated with TFBMD, FNBMD, and LSBMD (all p < 0.05). With one log unit increase in serum PFOA, PFHxS, and PFNA, osteoporosis prevalence in women increased as follows: [adjusted odds ratios (aORs)] 1.84 (95% CI: 1.17, 2.905), 1.64 (95% CI: 1.14, 2.38), and 1.45 (95% CI: 1.02, 2.05), respectively. In women, the prevalence of osteoporosis was significantly higher in the highest versus the lowest quartiles of PFOA, PFHxS, and PFNA, with aORs of 2.59 (95% CI: 1.01, 6.67), 13.20 (95% CI: 2.72, 64.15), and 3.23 (95% CI: 1.44, 7.21), respectively, based on 77 cases in the study sample.

CONCLUSION

In a representative sample of the U.S. adult population, serum PFAS concentrations were associated with lower bone mineral density, which varied according to the specific PFAS and bone site assessed. Most associations were limited to women. Osteoporosis in women was also associated with PFAS exposure, based on a small number of cases.

CITATION

Khalil N, Chen A, Lee M, Czerwinski SA, Ebert JR, DeWitt JC, Kannan K. 2016. Association of perfluoroalkyl substances, bone mineral density, and osteoporosis in the U.S. population in NHANES 2009-2010. Environ Health Perspect 124:81-87; http://dx.doi.org/10.1289/ehp.1307909.

Suppression of antigen-specific antibody responses in mice exposed to perfluorooctanoic acid: Role of PPARα and T- and B-cell targeting

T-cell-dependent antibody responses (TDAR) are suppressed in female C57BL/6N mice exposed to ≥3.75 mg/kg of perfluorooctanoic acid (PFOA) for 15 days. To determine if suppression of humoral immunity by PFOA is peroxisome proliferator activated receptor alpha (PPARα)-dependent and if suppression is associated with specific targeting of T- or B-cells, three separate experiments were conducted: (1) female PPARα constitutive knockout (PPARα KO; B6.129S4-Ppar(tm1Gonz)N12) and wild-type controls (WT; C57BL/6-Tac) exposed to 0, 7.5, or 30 mg PFOA/kg for 15 days were immunized on Day 11 with a T-cell-dependent antigen and sera then collected for measures of antigen-specific IgM titers (TDAR) 5 days later; (2) female C57BL/6N WT mice exposed to 0, 0.94, 1.88, 3.75, or 7.5 mg PFOA/kg for 15 days were immunized with a T-cell-independent antigen on Day 11 and sera were then collected for analyses of antigen-specific IgM titers (TIAR) 7 days later; and (3) splenic lymphocyte phenotypes were assessed in unimmunized female C57BL/6N WT mice exposed to 0, 3.75, or 7.5 mg PFOA/kg for 10 days to investigate effects of PFOA in the absence of specific immunization. Separate groups of mice were immunized with a T-cell-dependent antigen after 11 days of exposure and splenic lymphocyte sub-populations were assessed after 13 or 15 days of exposure to assess numbers of stimulated cells. The results indicated that exposure to ≥1.88 mg PFOA/kg suppressed the TIAR; exposure to 30 mg PFOA/kg suppressed the TDAR in both PPARα KO and WT mice. The percentage of splenic B-cells was unchanged. Results obtained in the PPARα KO mice indicated that PPARα suppression of TDAR was independent of PPARα involvement. Suppression of the TIAR and the TDAR with minimal lymphocyte sub-population effects suggested that effects on humoral immunity are likely mediated by disruption of B-cell/plasma cell function.

Perfluorinated compounds: emerging POPs with potential immunotoxicity

Perfluorinated compounds (PFCs) have been recognized as an important class of environmental contaminants commonly detected in blood samples of both wildlife and humans. These compounds have been in use for more than 60 years as surface treatment chemicals, polymerization aids, and surfactants. They possess a strong carbon-fluorine bond, which leads to their environmental persistence. There is evidence from both epidemiology and laboratory studies that PFCs may be immunotoxic, affecting both cell-mediated and humoral immunity. Reported effects of PFCs include decreased spleen and thymus weights and cellularity, reduced specific antibody production, reduced survival after influenza infection, and altered cytokine production. Immunosuppression is a critical effect associated with exposure to PFCs, as it has been reported to reduce antibody responses to vaccination in children. Mounting evidence suggests that immunotoxicity in experimental animals can occur at serum concentrations below, within, or just above the reported range for highly exposed humans and wildlife. Considering bioaccumulation and exposure to multiple PFCs, the risk of immunotoxicity for humans and wildlife cannot be discounted. This review will discuss current and recently published work exploring the immunomodulatory effects of PFCs in experimental animals and humans.

Dosimetric anchoring of in vivo and in vitro studies for perfluorooctanoate and perfluorooctanesulfonate

In order to compare between in vivo toxicity studies, dosimetry is needed to translate study-specific dose regimens into dose metrics such as tissue concentration. These tissue concentrations may then be compared with in vitro bioactivity assays to perhaps identify mechanisms relevant to the lowest observed effect level (LOEL) dose group and the onset of the observed in vivo toxicity. Here, we examine the perfluorinated compounds (PFCs) perfluorooctanoate (PFOA) and perfluorooctanesulfonate (PFOS). We analyzed 9 in vivo toxicity studies for PFOA and 13 in vivo toxicity studies for PFOS. Both PFCs caused multiple effects in various test species, strains, and genders. We used a Bayesian pharmacokinetic (PK) modeling framework to incorporate data from 6 PFOA PK studies and 2 PFOS PK studies (conducted in 3 species) to predict dose metrics for the in vivo LOELs and no observed effect levels (NOELs). We estimated PK parameters for 11 combinations of chemical, species, strain, and gender. Despite divergent study designs and species-specific PK, for a given effect, we found that the predicted dose metrics corresponding to the LOELs (and NOELs where available) occur at similar concentrations. In vitro assay results for PFOA and PFOS from EPA's ToxCast project were then examined. We found that most in vitro bioactivity occurs at concentrations lower than the predicted concentrations for the in vivo LOELs and higher than the predicted concentrations for the in vivo NOELs (where available), for a variety of nonimmunological effects. These results indicate that given sufficient PK data, the in vivo LOELs dose regimens, but not necessarily the effects, could have been predicted from in vitro studies for these 2 PFCs.

Perfluorooctanoic acid induced-developmental cardiotoxicity: are peroxisome proliferator activated receptor α (PPARα) and bone morphorgenic protein 2 (BMP2) pathways involved?

Perfluorooctanoic acid (PFOA) is an environmental contaminant known to induce developmental toxicity in animal models through activation of the peroxisome proliferator-activated receptor α (PPARα). Previously, it was demonstrated that in ovo exposure to PFOA induced cardiotoxicity in chicken embryos and hatchlings. To investigate potential PPARα-mediated mechanisms, fertile chicken eggs were injected prior to incubation with WY 14,643, a PPARα agonist. Cardiac morphology and function were evaluated in late-stage embryos and hatchlings. Histologically, unlike PFOA, WY 14,643 did not induce thinning of the right ventricular wall. Via echocardiography, however, WY 14,643 induced effects similar to those of PFOA, including increased left ventricular wall thickness and mass, elevated heart rate, ejection fraction, fractional shortening, and decreased stroke volume. Additionally, to investigate mechanisms associated with early heart development, a separate group of fertile chicken eggs was injected prior to incubation with PFOA or WY 14,643 and in early-stage embryos, gene expression and protein concentration associated with the bone morphogenic protein (BMP2) pathway were determined. Although changes were not statistically consistent among doses, expression of BMP2, Nkx2.5, and GATA4 mRNA in early embryos was altered by PFOA exposure; however, protein concentrations of these targets were not markedly altered by either PFOA or WY 14,643. Protein levels of pSMAD1/5, a transcriptional regulator stimulated by BMPs, were altered by both PFOA and WY 14,643, but in different directions; PFOA reduced cytoplasmic pSMAD1/5, whereas WY 14,643 decreased nuclear pSMAD1/5. Taken together, these data suggest that developmental cardiotoxicity induced by PFOA likely involves both PPARα and BMP2 pathways.

Developmental immunotoxicity (DIT): assays for evaluating effects of exogenous agents on development of the immune system

Developmental immunotoxicity (DIT) occurs when exposure to environmental risk factors prior to adulthood, including chemical, biological, physical, or physiological factors, alters immune system development. DIT may elicit suppression, hyperactivation, or misregulation of immune responses and may present clinically as decreased resistance to pathogens, allergic and autoimmune diseases, and inflammatory diseases. Immunotoxicity testing guidelines established by the Environmental Protection Agency for adult animals (OPPTS 8703.7800) require functional tests and immunophenotyping that are suitable for detecting immunomodulation, especially immunosuppression. However, evaluating immune function in offspring that are not fully immunocompetent yields results that are challenging to interpret. Therefore, this unit will describe an optimum exposure scenario, reference two assays (immunophenotyping and histopathology) appropriate for detecting immunomodulation in weaning-age offspring, and reference four assays (immunophenotyping, histopathology, T cell-dependent antibody responses, and delayed-type hypersensitivity) appropriate for detecting immunomodulation in immunocompetent offspring. The protocol also will reference other assays (natural killer cell and cytotoxic T lymphocyte) with potential utility for assessing DIT.

Perflurooctanoic acid induces developmental cardiotoxicity in chicken embryos and hatchlings

Perfluorooctanoic acid (PFOA) is a widespread environmental contaminant that is detectable in serum of the general U.S. population. PFOA is a known developmental toxicant that induces mortality in mammalian embryos and is thought to induce toxicity via interaction with the peroxisome proliferator activated receptor alpha (PPARα). As the cardiovascular system is crucial for embryonic survival, PFOA-induced effects on the heart may partially explain embryonic mortality. To assess impacts of PFOA exposure on the developing heart in an avian model, we used histopathology and immunohistochemical staining for myosin to assess morphological alterations in 19-day-old chicken embryo hearts after PFOA exposure. Additionally, echocardiography and cardiac myofibril ATPase activity assays were used to assess functional alterations in 1-day-old hatchling chickens following developmental PFOA exposure. Overall thinning and thinning of a dense layer of myosin in the right ventricular wall were observed in PFOA-exposed chicken embryo hearts. Alteration of multiple cardiac structural and functional parameters, including left ventricular wall thickness, left ventricular volume, heart rate, stroke volume, and ejection fraction were detected with echocardiography in the exposed hatchling chickens. Assessment of ATPase activity indicated that the ratio of cardiac myofibril calcium-independent ATPase activity to calcium-dependent ATPase activity was not affected, which suggests that developmental PFOA exposure may not affect cardiac energetics. In summary, structural and functional characteristics of the heart appear to be developmental targets of PFOA, possibly at the level of cardiomyocytes. Additional studies will investigate mechanisms of PFOA-induced developmental cardiotoxicity.

Immune function in female B(6)C(3)F(1) mice is modulated by DE-71, a commercial polybrominated diphenyl ether mixture

Polybrominated diphenyl ethers (PBDEs) are an important class of flame-retardants that are environmentally persistent and bioaccumulative. Toxicity of these compounds has become a concern because detectable levels of PBDEs are present in humans and wildlife and they are structurally similar to polychlorinated biphenyls (PCBs). This study examined the effects of the commercial penta-BDE mixture, DE-71, in adult female B(6)C(3)F(1) mice on hematology, serum clinical chemistry, thyroid hormones, tissue histology, and several immunotoxicity end-points (lymphocyte proliferation, NK cell activity, splenic immunophenotypes, and SRBC-specific-IgM production). Mice were exposed via oral gavage for 28 days to achieve total administered doses (TAD) of 0, 0.5, 5, 50, or 100 mg/kg. No changes in histology, clinical chemistry, body or organ weights were observed. Serum total T3 and T4 levels were not altered by any of the DE-71 treatments. Peripheral blood monocyte numbers were decreased by the 0.5, 5, and 50 mg/kg treatments, but not by the 100 mg/kg TAD concentration. Compared to controls, mitogen-stimulated T- and B-cell proliferation was increased by the 100 mg/kg TAD concentration (ED(50) = 60 mg/kg TAD [2.14 mg/kg/day] and 58 mg/kg TAD [2.57 mg/kg/day], respectively). NK cell activity was decreased compared to controls by the 100 mg/kg TAD concentration (ED(50) = 20 mg/kg TAD [0.7 mg/kg/day]). No alterations were noted in thymic T-cell populations or in SRBC-specific-IgM production. Numbers of CD19(+)CD21(-), CD19(+)CD21(+), CD4(+)CD8(-), CD4(-)CD8(+), CD4(-)CD8(-), and MHC-II(+) cells in the spleen were not affected. However, the numbers of splenic CD4(+)CD8(+) cells were decreased compared to the controls by 0.5, 5, and 100 mg/kg TAD. This study provides an assessment of the systemic toxicity and immunotoxicity of DE-71, and indicates that immune parameters are modulated at exposure concentrations lower than previously reported.

Breaking patterns of environmentally influenced disease for health risk reduction: immune perspectives

BACKGROUND

Diseases rarely, if ever, occur in isolation. Instead, most represent part of a more complex web or "pattern" of conditions that are connected via underlying biological mechanisms and processes, emerge across a lifetime, and have been identified with the aid of large medical databases.

OBJECTIVE

We have described how an understanding of patterns of disease may be used to develop new strategies for reducing the prevalence and risk of major immune-based illnesses and diseases influenced by environmental stimuli.

FINDINGS

Examples of recently defined patterns of diseases that begin in childhood include not only metabolic syndrome, with its characteristics of inflammatory dysregulation, but also allergic, autoimmune, recurrent infection, and other inflammatory patterns of disease. The recent identification of major immune-based disease patterns beginning in childhood suggests that the immune system may play an even more important role in determining health status and health care needs across a lifetime than was previously understood.

CONCLUSIONS

Focusing on patterns of disease, as opposed to individual conditions, offers two important venues for environmental health risk reduction. First, prevention of developmental immunotoxicity and pediatric immune dysfunction can be used to act against multiple diseases. Second, pattern-based treatment of entryway diseases can be tailored with the aim of disrupting the entire disease pattern and reducing the risk of later-life illnesses connected to underlying immune dysfunction. Disease-pattern-based evaluation, prevention, and treatment will require a change from the current approach for both immune safety testing and pediatric disease management.