Phospholipid Levels Predict the Tissue Distribution of Poly- and Perfluoroalkyl Substances in a Marine Mammal

Deriving Membrane-Water and Protein-Water Partition Coefficients from In Vitro Experiments for Per- and Polyfluoroalkyl Substances (PFAS)

The phospholipid membrane-water partition coefficients (KMW) and equilibrium binding affinities for human serum albumin (HSA) of 60 structurally diverse perfluoroalkyl and polyfluoroalkyl substances (PFAS) were evaluated through laboratory measurements and modeling to enhance our understanding of PFAS distribution in organisms. Per- and polyfluoroalkyl carboxylic acids exhibited a 0.36 ± 0.01 log-unit increase in KMW as the fluorinated carbon chain length increased from C4 to C16, while per- and polyfluoroalkyl sulfonates showed a 0.37 ± 0.02 log-unit increase. The highest HSA affinity range was observed between C6 and C10, with the following structural subclass order: per- and polyfluoroalkyl sulfonates ≈ ether sulfonic acids > polyfluoroalkyl carboxylic acids > fluorotelomer unsaturated carboxylic acids > phosphate diesters ≈ per- and polyfluoroether carboxylic acids. A comparison between association rate constants (KA) and HSA-PFAS molecular docking predictions with AutoDock Vina indicated that modeling could effectively predict the affinity of PFAS to HSA, especially for PFAS carbon chain lengths from C4 to C10. Based on in vitro results, exposure-dependent PFAS partitioning in organisms was modeled by comparing distribution coefficients between PFAS in phospholipid membranes and HSA at different PFAS concentrations and demonstrated that at lower concentrations, PFAS had higher partitioning in HSA, while with increasing concentration, the proportion of binding relative to the aqueous phase shifted toward the phospholipid membrane. Few studies have compared the bioaccumulation of PFAS in phospholipid membranes and HSA. This research reports that protein-water distribution coefficients are higher than membrane-water partitioning coefficients at lower PFAS concentrations, which may have implications for interpreting exposure data and toxicity experiments.

An in vitro and machine learning framework for quantifying serum albumin binding of per- and polyfluoroalkyl substances

Per- and polyfluoroalkyl substances (PFAS) are a diverse class of anthropogenic chemicals; many are persistent, bioaccumulative, and mobile in the environment. Worldwide, PFAS bioaccumulation causes serious adverse health impacts, yet the physiochemical determinants of bioaccumulation and toxicity for most PFAS are not well understood, largely due to experimental data deficiencies. As most PFAS are proteinophilic, protein binding is a critical parameter for predicting PFAS bioaccumulation and toxicity. Among these proteins, human serum albumin (HSA) is the predominant blood transport protein for many PFAS. We previously demonstrated the utility of an in vitro differential scanning fluorimetry assay for determining relative HSA binding affinities for 24 PFAS. Here, we report HSA affinities for 65 structurally diverse PFAS from 20 chemical classes. We leverage these experimental data, and chemical/molecular descriptors of PFAS, to build 7 machine learning classifier algorithms and 9 regression algorithms, and evaluate their performance to identify the best predictive binding models. Evaluation of model accuracy revealed that the top-performing classifier model, logistic regression, had an AUROC (area under the receiver operating characteristic curve) statistic of 0.936. The top-performing regression model, support vector regression, had an R2 of 0.854. These top-performing models were then used to predict HSA-PFAS binding for chemicals in the EPAPFASINV list of 430 PFAS. These developed in vitro and in silico methodologies represent a high-throughput framework for predicting protein-PFAS binding based on empirical data, and generate directly comparable binding data of potential use in predictive modeling of PFAS bioaccumulation and other toxicokinetic endpoints.

Cleaner cuts: Farmed fish and skin-off fillets are lower in per- and polyfluoroalkyl substances (PFAS)

The ubiquitous occurrence and persistence of per- and polyfluoroalkyl substances (PFAS) in all environmental matrices and biota poses significant health risks to humans. Fish consumption is one of the main pathways humans are exposed to PFAS, yet general patterns in factors influencing PFAS content in fish fillets remain unknown. We assembled information on PFAS content (total quantified PFAS, PFOS, PFOA, and others) in fish fillets to assess the effect of fish origin (marine, freshwater, wild, or farmed), fillet type (skin-on or skin-off), and lipid content on PFAS variation across environments at a global scale. We found that these factors influenced PFAS contents in fish fillets, with concentrations reaching up to 2149 ng•g wet mass-1 (WM). Specifically, PFOS and PFOA in skin-off fillets were consistently lower in farmed than wild fish across freshwater and marine environments. In freshwater wild fish, PFOS was lower in skin-off fillets than skin-on fillets at group and species levels, and multiple PFAS showed an inverse relationship with the lipid content of skin-off fillets, though the slopes showed varying steepness depending on the carbon chain length and functional group of the PFAS. However, the high variability of PFAS content across sites in aquatic environments and the complexity of PFAS bioaccumulation mechanisms in fish tissues may lead to variable results at a fine scale (i.e., species level); this highlights general patterns of factors influencing PFAS bioaccumulation that may inform the management of human exposure to PFAS through dietary consumption.

Nanomolar PFOA Concentrations Affect Lipid Membrane Structure: Consequences for Bioconcentration Mechanisms

Independent methods show that sub-microMolar concentrations of perfluorooctanoic acid (PFOA), a member of the PFAS family of "forever chemicals", change the properties of DPPC vesicle bilayers. Specifically, calorimetry measurements show that PFOA at concentrations as low as 0.1 nM lowers DPPC's gel-liquid crystalline transition enthalpy by several J/g without changing the transition temperature (Tgel-LC), and dynamic light scattering (DLS) data illustrate that PFOA markedly broadens the size distribution of DPPC vesicles. Furthermore, DLS results from PFOA-containing, DPPC vesicle solutions also contain smaller objects having diameters of 30-50 nm. Close inspection of cryo-EM images reveals that DPPC vesicles formed in the presence of PFOA are multilamellar and the smaller objects have a clear bilayer structure similar to niosomes. A consequence of these PFOA-induced changes to DPPC bilayer structure is that the bilayers themselves are more susceptible to secondary solute accumulation. Time resolved emission measurements of Coumarin 152 (C152) report that C152 is 3-fold more likely to partition into the bilayer's acyl chain, hydrophobic interior when PFOA is present, and fluorescence lifetimes from C152 partitioned into the polar region of the lipid bilayer show evidence of PFOA-induced membrane hydration below Tgel-LC.

Construction of interpretable ensemble learning models for predicting bioaccumulation parameters of organic chemicals in fish

Accurate prediction of bioaccumulation parameters is essential for assessing exposure, hazards, and risks of chemicals. However, the majority of prediction models on bioaccumulation parameters are individual models based on a single algorithm and lack model interpretation, resulting in unsatisfactory prediction accuracy due to inherent constraints of the algorithm and weak interpretability. Ensemble learning (EL) that combine multiple algorithms, coupled with SHapley Additive exPlanation (SHAP) method, may overcome the limitations. Herein, EL models were constructed for three bioaccumulation parameters using datasets covering 2496 chemicals. The EL models demonstrated superior prediction accuracy compared to both individual models developed in this study and those from previous research, achieving a coefficient of determination of up to 0.861 on the validation sets. Applicability domains were characterized using a structure-activity landscape-based (abbreviated as ADSAL) methodology. The optimal EL models, together with the ADSAL, were successfully used to predict bioaccumulation parameters for 4374 chemicals included in the Inventory of Existing Chemical Substances of China. Model interpretation using the SHAP method offered insight into key features influencing bioaccumulation potential, including hydrophobicity, water solubility, polarizability, ionization potential, weight, and volume of molecules. Overall, the study provides data and models to support the sound management and risk assessment of chemicals.

Development and Evaluation of Aquatic and Terrestrial Food Web Bioaccumulation Models for Per- and Polyfluoroalkyl Substances

There is a need for reliable models to predict the food web bioaccumulation and assess ecological and human health risks of per- and polyfluoroalkyl substances (PFAS). This present study presents (i) the development of novel mechanistic aquatic and terrestrial food web bioaccumulation models for PFAS and (ii) an evaluation of model performance using available laboratory and field data. Model predictions of laboratory-measured bioconcentration factors and field-based bioaccumulation factors of PFAS in fish were in good agreement with observed data as measured by the mean model bias (MB), representing systematic over- or under-estimation and the standard deviation of the MB, representing general uncertainty. The models provide a mechanistic framework for evaluating the combined effect of simultaneously occurring uptake and elimination processes and indicate food web-specific magnification of PFAS, with the highest degree of biomagnification occurring in food webs composed of air-breathing wildlife. Albumin-water, structural protein-water, membrane-water distribution coefficients, and renal clearance rate are among the most important model parameters. With further development and testing, these models may be useful for future PFAS screening and risk assessment initiatives and advance bioaccumulation studies of PFAS by providing a mechanistic framework for PFAS bioaccumulation.

Unbound Fractions of PFAS in Human and Rodent Tissues: Rat Liver a Suitable Proxy for Evaluating Emerging PFAS?

Adverse health effects associated with exposures to perfluoroalkyl and polyfluoroalkyl substances (PFAS) are a concern for public health and are driven by their elimination half-lives and accumulation in specific tissues. However, data on PFAS binding in human tissues are limited. Accumulation of PFAS in human tissues has been linked to interactions with specific proteins and lipids in target organs. Additional data on PFAS binding and unbound fractions (funbound) in whole human tissues are urgently needed. Here, we address this gap by using rapid equilibrium dialysis to measure the binding and funbound of 16 PFAS with 3 to 13 perfluorinated carbon atoms (ηpfc = 3-13) and several functional headgroups in human liver, lung, kidney, heart, and brain tissue. We compare results to mouse (C57BL/6 and CD-1) and rat tissues. Results show that funbound decreases with increasing fluorinated carbon chain length and hydrophobicity. Among human tissues, PFAS binding was generally greatest in brain > liver ≈ kidneys ≈ heart > lungs. A correlation analysis among human and rodent tissues identified rat liver as a suitable surrogate for predicting funbound for PFAS in human tissues (R2 ≥ 0.98). The funbound data resulting from this work and the rat liver prediction method offer input parameters and tools for toxicokinetic models for legacy and emerging PFAS.

Dioxins vs. PFAS: Science and Policy Challenges

BACKGROUND

Dioxin-like chemicals are a group of ubiquitous environmental toxicants that received intense attention in the last two decades of the 20th century. Through extensive mechanistic research and validation, the global community has agreed upon a regulatory strategy for these chemicals that centers on their common additive activation of a single receptor. Applying these regulations has led to decreased exposure in most populations studied. As dioxin-like chemicals moved out of the limelight, research and media attention has turned to other concerning contaminants, including per- and polyfluoroalkyl substances (PFAS). During the 20th century, PFAS were also being quietly emitted into the environment, but only in the last 20 years have we realized the serious threat they pose to health. There is active debate about how to appropriately classify and regulate the thousands of known PFAS and finding a solution for these "forever chemicals" is of the utmost urgency.

OBJECTIVES

Here, we compare important features of dioxin-like chemicals and PFAS, including the history, mechanism of action, and effective upstream regulatory strategies, with the objective of gleaning insight from the past to improve strategies for addressing PFAS.

DISCUSSION

The differences between these two chemical classes means that regulatory strategies for dioxin-like chemicals will not be appropriate for PFAS. PFAS exert toxicity by both receptor-based and nonreceptor-based mechanisms, which complicates mixtures evaluation and stymies efforts to develop inexpensive assays that accurately capture toxicity. Furthermore, dioxin-like chemicals were unwanted byproducts, but PFAS are useful and valuable, which has led to intense resistance against efforts to restrict their production. Nonetheless, useful lessons can be drawn from dioxin-like chemicals and applied to PFAS, including eliminating nonessential production of new PFAS and proactive investment in environmental remediation to address their extraordinarily long environmental persistence. https://doi.org/10.1289/EHP14449.

Unique hepatic maternal transfer pattern of trace metals and perfluoroalkyl substances (PFAS) in a bluntnose sixgill shark (Hexanchus griseus)

The fate and distribution of environmental contaminants includes bioaccumulation within marine organisms. A deceased 4-m long adult female bluntnose sixgill shark, pregnant with 72 pups, was recovered from Coles Bay on Vancouver Island, BC, Canada in 2019. This specimen provided a unique opportunity to examine maternal transfer of contaminants in a yolk-sac viviparous shark species. Liver subsamples of the adult and offspring were analyzed for 18 targeted inorganic elements by inductively coupled plasma optical emission spectroscopy (ICP-OES) and 21 targeted perfluoroalkyl substances (PFAS) by liquid chromatography-electrospray ionization-high resolution mass spectrometry (LC-ESI-Orbitrap MS). The maternal-offspring transfer efficiencies in liver tissue were subsequently examined for both contaminant classes. Concentrations of all detectable metals apart from calcium and magnesium were found to be higher in the mother compared to the offspring, including substantial levels of toxic cadmium (6 ± 2 mg kg-1 dw) and lead (7 ± 3 mg kg-1 dw). Conversely, high maternal transfer efficiencies were observed for PFAS (i.e., ΣPFAS = 71 ± 9 ng g-1 ww in offspring compared to 13 ± 9 ng g-1 ww in the mother). This study highlighted the unique maternal transfer characteristics of PFAS in bluntnose sixgill sharks depending on the structure of the polar head group, with greater liver-to-liver transfer efficiencies observed for perfluorocarboxylic acids (PFCAs) than perfluorosulfonic acids (PFSAs) of the same fluorocarbon chain length.

Species Difference? Bovine, Trout, and Human Plasma Protein Binding of Per- and Polyfluoroalkyl Substances

Per- and polyfluoroalkyl substances (PFAS) strongly bind to proteins and lipids in blood, which govern their accumulation and distribution in organisms. Understanding the plasma binding mechanism and species differences will facilitate the quantitative in vitro-to-in vivo extrapolation and improve risk assessment of PFAS. We studied the binding mechanism of 16 PFAS to bovine serum albumin (BSA), trout, and human plasma using solid-phase microextraction. Binding of anionic PFAS to BSA and human plasma was found to be highly concentration-dependent, while trout plasma binding was linear for the majority of the tested PFAS. At a molar ratio of PFAS to protein ν < 0.1 molPFAS/molprotein, the specific protein binding of anionic PFAS dominated their human plasma binding. This would be the scenario for physiological conditions (ν < 0.01), whereas in in vitro assays, PFAS are often dosed in excess (ν > 1) and nonspecific binding becomes dominant. BSA was shown to serve as a good surrogate for human plasma. As trout plasma contains more lipids, the nonspecific binding to lipids affected the affinities of PFAS for trout plasma. Mass balance models that are parameterized with the protein-water and lipid-water partitioning constants (chemical characteristics), as well as the protein and lipid contents of the plasma (species characteristics), were successfully used to predict the binding to human and trout plasma.

Bioaccumulation and trophic transfer of per- and polyfluoroalkyl substances in a subtropical mangrove estuary food web

Mangrove estuaries are an important land-sea transitional ecosystem that is currently under various pollution pressures, while there is a lack of research on per- and polyfluoroalkyl substances (PFAS) in the organisms of mangrove estuaries. In this study, we investigated the distribution and seasonal variation of PFAS in the tissues of organisms from a mangrove estuary. The PFAS concentrations in fish tissues varied from 0.45 ng/g ww to 17.67 ng/g ww and followed the order of viscera > head > carcass > muscle, with the highest tissue burden found in the fish carcass (39.59 ng). The log BAF values of PFDoDA, PFUnDA, and PFDA in the whole fish exceeded 3.70, indicating significant bioaccumulation. The trophic transfer of PFAS in the mangrove estuary food web showed a dilution effect, which was mainly influenced by the spatial heterogeneity of PFAS distribution in the estuarine environment, and demonstrated that the gradient dilution of PFAS in the estuary habitat environment can disguise the PFAS bio-magnification in estuarine organisms, and the larger the swimming ranges of organisms, the more pronounced the bio-dilution effect. The PFOA-equivalent HRs of category A and B fish were 3.48-5.17 and 2.59-4.01, respectively, indicating that mangrove estuarine residents had a high PFAS exposure risk through the intake of estuarine fish.

Unraveling the link between heavy metals, perfluoroalkyl substances and depression: Insights from epidemiological and bioinformatics strategies

Heavy metals and per- and polyfluoroalkyl substances (PFASs) have become particularly important when studying the development of depression, a common illness that severely restricts psychosocial functioning and diminishes quality of life. Therefore, the potential joint effects of heavy metal and PFAS exposure on depression, as well as the underlying mechanisms involved, were investigated by using integrated epidemiological and bioinformatic approaches in the present study. A thorough analysis of 7301 samples from the National Health and Nutrition Examination Survey (NHANES) cycles that occurred between 2005 and 2018 was performed. Single-exposure studies have shown that cadmium exposure is positively associated with depression, whereas perfluorooctanesulfonic acid (PFOS) exposure and perfluorodecanoic acid (PFDE) exposure are negatively associated with depression. Furthermore, the Bayesian kernel machine regression (BKMR) and quantile g-computation (QGcomp) models were employed to investigate the collective impact of exposure to mixed metals on depression. Cadmium emerged as the principal contributor to depression. Moreover, the addition of PFAS to the metal mixture had an antagonistic effect on depression, with PFOS having the most prominent influence. Analysis of the effects of co-exposure to cadmium and PFOS confirmed the presence of an antagonistic effect. The inflection points of cadmium and PFOS were determined to be -1.11 and 2.27, respectively. Additionally, exposure to cadmium and PFOS had the opposite effects on two crucial pathways, namely, the rap1 and calcium signaling pathways, which involve core genes related to depression such as ADORA2A, FGF2, and FGFR1. These findings have significant implications for future studies and provide new strategies for exploring the mechanisms underlying co-exposure effects.

Per/Polyfluoroalkyl Substances (PFASs) in a Marine Apex Predator (White Shark, Carcharodon carcharias) in the Northwest Atlantic Ocean

Per/polyfluoroalkyl substances (PFASs) are ubiquitous, highly persistent anthropogenic chemicals that bioaccumulate and biomagnify in aquatic food webs and are associated with adverse health effects, including liver and kidney diseases, cancers, and immunosuppression. We investigated the accumulation of PFASs in a marine apex predator, the white shark (Carcharodon carcharias). Muscle (N = 12) and blood plasma (N = 27) samples were collected from 27 sharks during 2018-2021 OCEARCH expeditions along the eastern coast of North America from Nova Scotia to Florida. Samples were analyzed for 47 (plasma) and 43 (muscle) targeted PFASs and screened for >2600 known and novel PFASs using liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS). Perfluoroalkyl carboxylates with carbon chain-length C11 to C14 were frequently detected above the method reporting limits in plasma samples, along with perfluorooctanesulfonate and perfluorodecanesulfonate. Perfluoropentadecanoate was also detected in 100% of plasma samples and concentrations were estimated semiquantitatively as no analytical standard was available. Total concentrations of frequently detected PFASs in plasma ranged from 0.56 to 2.9 ng mL-1 (median of 1.4 ng mL-1). In muscle tissue, nine targeted PFASs were frequently detected, with total concentration ranging from 0.20 to 0.84 ng g-1 ww. For all frequently detected PFASs, concentrations were greater in plasma than in muscle collected from the same organism. In both matrices, perfluorotridecanoic acid was the most abundant PFAS, consistent with several other studies. PFASs with similar chain-lengths correlated significantly among the plasma samples, suggesting similar sources. Total concentrations of PFASs in plasma were significantly greater in sharks sampled off of Nova Scotia than all sharks from other locations, potentially due to differences in diet. HRMS suspect screening tentatively identified 13 additional PFASs in plasma, though identification confidence was low, as no MS/MS fragmentation was collected due to low intensities. The widespread detection of long-chain PFASs in plasma and muscle of white sharks highlights the prevalence and potential biomagnification of these compounds in marine apex predators.

Per- and polyfluoroalkyl substances (PFAS) exposure in plasma and their blood-brain barrier transmission efficiency-A pilot study

Per- and polyfluoroalkyl substances (PFAS) have been shown to penetrate the blood-brain barrier (BBB) and accumulate in human brain. The BBB transmission and accumulation efficiency of PFAS, as well as the potential health risks from human co-exposure to legacy and emerging PFAS due to differences in transport efficiency, need to be further elucidated. In the present pilot study, 23 plasma samples from glioma patients were analyzed for 17 PFAS. The concentrations of PFAS in six paired brain tissue and plasma samples were used to calculate the BBB transmission efficiency of PFAS (RPFAS). This RPFAS analysis was conducted with utmost care and consideration amid the limited availability of valuable paired samples. The results indicated that low molecular weight PFAS, including short-chain and emerging PFAS, may have a greater potential for accumulation in brain tissue than long-chain PFAS. As an alternative to perfluorooctane sulfonic acid (PFOS), 6:2 chlorinated polyfluorinated ether sulfonate (6:2 Cl-PFESA) exhibited brain accumulation potential similar to that of PFOS, suggesting it may not be a suitable substitute concerning health risk in brain. The BBB transmission efficiencies of perfluorooctanoic acid, PFOS, and 6:2 Cl-PFESA showed similar trends with age, which may be an important factor influencing the entry of exogenous compounds into the brain. A favorable link between perfluorooctane sulfonamide (FOSA) and the development and/or progression of glioma may be implicated by a strong positive correlation (r2 = 0.94; p < 0.01) between RFOSA and Ki-67 (a molecular marker of glioma). However, a causal relationship between RFOSA and glioma incidence were not established in the present study. The present pilot study conducted the first examination of BBB transmission efficiency of PFAS from plasma to brain tissue and highlighted the importance of reducing and/or controlling exposure to PFAS.

Investigating the effects of PFOA accumulation and depuration on specific phospholipids in zebrafish through imaging mass spectrometry

Perfluorooctanoic acid (PFOA) is an emerging persistent organic pollutant. Exposure to PFOA was observed to have a correlation with the expression levels of phospholipids. However, there are currently no studies that directly visualize the effects of PFOA on phospholipids. To this end, matrix-assisted laser desorption/ionization time of flight imaging mass spectrometry (MALDI-TOF-IMS) was used to visualize changes in phospholipids in the different tissues of zebrafish following exposure to PFOA. This study found that the major perturbed phospholipids were phosphatidylcholine (PC), diacylglycerol (DG), phosphatidic acid (PA), phosphatidylglycerol (PG), sphingomyelin (SM), and triacylglycerol (TG). These perturbed phospholipids caused by PFOA were reversible in some tissues (liver, gill, and brain) and irreversible in others (such as the highly exposed intestine). Moreover, the spatial distribution of perturbed phospholipids was mainly located around the edge or center of the tissues, implying that these tissue regions need special attention. This study provides novel insight into the biological toxicity and toxicity mechanisms induced by emerging environmental pollutants.

Structural dependence of PFAS oxidation in a boron doped diamond-electrochemical system

Driven by long-term persistence and adverse health impacts of legacy perfluorooctanoic acid (PFOA), production has shifted towards shorter chain analogs (C4, perfluorobutanoic acid (PFBA)) or fluorinated alternatives such as hexafluoropropylene oxide dimer acid (HFPO-DA, known as GenX) and 6:2 fluorotelomer carboxylic acid (6:2 FTCA). Yet, a thorough understanding of treatment processes for these alternatives is limited. Herein, we conducted a comprehensive study using an electrochemical approach with a boron doped diamond anode in Na2SO4 electrolyte for the remediation of PFOA common alternatives, i.e., PFBA, GenX, and 6:2 FTCA. The degradability, fluorine recovery, transformation pathway, and contributions from electro-synthesized radicals were investigated. The results indicated the significance of chain length and structure, with shorter chains being harder to break down (PFBA (65.6 ± 5.0%) < GenX (84.9 ± 3.3%) < PFOA (97.9 ± 0.1%) < 6:2 FTCA (99.4 ± 0.0%) within 120 min of electrolysis). The same by-products were observed during the oxidation of both low and high concentrations of parent PFAS (2 and 20 mg L-1), indicating that the fundamental mechanism of PFAS degradation remained consistent. Nevertheless, the ratio of these by-products to the parent PFAS concentration varied which primarily arises from the more rapid PFAS decomposition at lower dosages. For all experiments, the main mechanism of PFAS oxidation was initiated by direct electron transfer at the anode surface. Sulfate radical (SO4•-) also contributed to the oxidation of all PFAS, while hydroxyl radical (•OH) only played a role in the decomposition of 6:2 FTCA. Total fluorine recovery of PFBA, GenX, and 6:2 FTCA were 96.5%, 94.0%, and 76.4% within 240 min. The more complex transformation pathway of 6:2 FTCA could explain its lower fluorine recovery. Detailed decomposition pathways for each PFAS were also proposed through identifying the generated intermediates and fluorine recovery. The proposed pathways were also assessed using 19F Nuclear Magnetic Resonance (NMR) spectroscopy.

Species-Specific Unbound Fraction Differences in Highly Bound PFAS: A Comparative Study across Human, Rat, and Mouse Plasma and Albumin

Per- and polyfluoroalkyl substances (PFAS) are a diverse group of fluorinated compounds which have yet to undergo comprehensive investigation regarding potential adverse health effects and bioaccumulative properties. With long half-lives and accumulative properties, PFAS have been linked to several toxic effects in both non-clinical species such as rat and mouse as well as human. Although biological impacts and specific protein binding of PFAS have been examined, there is no study focusing on the species-specific fraction unbound (fu) in plasma and related toxicokinetics. Herein, a presaturation equilibrium dialysis method was used to measure and validate the binding of 14 individual PFAS with carbon chains containing 4 to 12 perfluorinated carbon atoms and several functional head-groups to albumin and plasma of mouse (C57BL/6 and CD-1), rat, and human. Equivalence testing between each species-matrix combination showed positive correlation between rat and human when comparing fu in plasma and binding to albumin. Similar trends in binding were also observed for mouse plasma and albumin. Relatively high Spearman correlations for all combinations indicate high concordance of PFAS binding regardless of matrix. Physiochemical properties of PFAS such as molecular weight, chain length, and lipophilicity were found to have important roles in plasma protein binding of PFAS.

Integrated evidence of transcriptional, metabolic, and intestinal microbiota changes in Ruditapes philippinarum due to perfluorooctanoic acid-induced immunotoxicity

Perfluorooctanoic acid (PFOA) is a toxic pollutant that bioaccumulates and is a significant public health concern due to its ubiquitous and persistent occurrence in global environments. Few studies have evaluated the adverse effects of PFOA on immune system, and this is particularly true for mollusks. Here, the PFOA-associated effects on immune system were evaluated in Ruditapes philippinarum using integrated analysis of metabolomes, microbiomes, and transcriptomes, providing evidence for possible mechanisms related to immunotoxicity. PFOA exposure caused clear variation in several important metabolites related to immune regulatory function within the haemolyph from R. philippinarum, while also altering key metabolic pathways, including those of lipids, unsaturated fatty acids (UFAs), and bile acids (BAs). After exposure to PFOAs, intestinal bacterial communities also clearly changed, with the predominant microflora becoming Mycoplasma and Bacteroidetes that are related to intestinal inflammation. Molecular analyses provided consistent results, wherein the expression of immune-related genes was significantly altered. Integration of the multi-'omics' analyses suggested that the TLR/MyD88/NF-kB pathway, along with PI3K-Akt-mTOR pathway, PPAR-mediated lipid metabolism and the autophagy signaling pathway, likely play important roles in initiating immunotoxic effects in R. philippinarum after PFOA exposure. These results provide further evidence that PFOA exposure can lead to immunologic dysfunction and also provide new insights into the mechanisms of PFAS alteration of bivalve immune function.

Visualization of PFOA accumulation and its effects on phospholipid in zebrafish liver by MALDI Imaging

Exposure to poly- and perfluoroalkyl substances (PFASs) can result in bioaccumulation. Initial findings suggested that PFASs could accumulate in tissues rich in both phospholipids and proteins. However, our current understanding is limited to the average concentration of PFASs or phospholipid content across entire tissue matrices, leaving unresolved the spatial variations of lipid metabolism associated with PFOA in zebrafish tissue. To address gap, we developed a novel methodology for concurrent spatial profiling of perfluorooctanoic acid (PFOA) and individual phospholipids within zebrafish hepatic tissue sections, utilizing matrix-assisted laser desorption/ionization time of flight imaging mass spectrometry (MALDI-TOF-MSI). 5-diaminonapthalene (DAN) matrix and laser sensitivity of 50.0 were optimized for PFOA detection in MALDI-TOF-MSI analysis with high spatial resolution (25 μm). PFOA was observed to accumulate within zebrafish liver tissue. H&E staining results corroborating the damage inflicted by PFOA accumulation, consistent with MALDI MSI results. Significant up-regulation of 15 phospholipid species was observed in zebrafish groups exposed to PFOA, with these phospholipid demonstrating varied spatial distribution within the same tissue. Furthermore, co-localized imaging of distinct phospholipids and PFOA within identical tissue sections suggested there could be two distinct potential interactions between PFOA and phospholipids, which required further investigation. The MALDI-TOF-IMS provides a new tool to explore in situ spatial distributions and variations of the endogenous metabolites for the health risk assessment and ecotoxicology of emerging environmental pollutants.

Occurrence and pattern of legacy and emerging per- and Poly-FluoroAlkyl substances (PFAS) in eggs of loggerhead turtle Caretta caretta from western Mediterranean

Per-and Poly-FluoroAlkyl Substances (PFAS) are a class of persistent, toxic, and mobile and chemicals both from industrial sources and from the use and disposal of Consumers products containing PFAS, whose concentration in marine food webs could pose a toxicological risk for biota and humans. In 2021, unhatched eggs were sampled from 41 loggerhead turtle Caretta caretta nests from the Italian shores of the Campania Region (Southern Italy). Whole eggs were analysed for the presence of 66 legacy and emerging PFAS with Liquid Chromatography coupled to Hybrid High Resolution Mass Spectrometry. A median Σ66 Per- and Poly-FluoroAlkyl Substances value of 3.34 ng/g egg fresh weight was found; perfluoroctane sulfonate (PFOS) represented the most contributing congener (47%), followed by perfluoro-n-undecanoic acid, perfluoro-n-tridecanoic acid, perfluoro-n-decanoic acid, perfluoro-n-decanoic acid, and perfluoro-n-tetradecanoic acid, respectively. Such compounds showed a log-norm distribution, suggesting found concentrations could represent the baseline levels in the considered sampling area. Emerging ChloroPolyFluoroPolyEthers Carboxylic Acids (ClPFECAs) were found in 20 out of 41 samples in the range 0.01-1.59 ng/g. Four samples had 20-100 fold higher concentration compared to that of other samples, suggesting the presence of hot spot areas possibly related to presence of fluoropolymer-based marine litter turtles may ingest. The analysis of two paired eggs/liver samples recovered from stranded animals revealed PFAS concentration in the same order of magnitude, supporting the role of vitellogenin in their selective transfer to yolk. Significant (P = 0.0155) Kendall negative correlation coefficient of -0.2705 among PFOS content in eggs and the recorded hatching success prompts for further investigation on associated exposure assessment and related eco-toxicity risk. This work reports for the first time PFAS presence in georeferenced loggerhead turtle eggs of the Mediterranean Sea and results represent a starting point to study PFAS time-trends in this vulnerable species.

Binding of Per- and Polyfluoroalkyl Substances (PFAS) to Serum Proteins: Implications for Toxicokinetics in Humans

Per- and polyfluoroalkyl substances (PFAS) are a diverse class of highly persistent anthropogenic chemicals that are detectable in the serum of most humans. PFAS exposure has been associated with many adverse effects on human health including immunotoxicity, increased risk of certain cancers, and metabolic disruption. PFAS binding to the most abundant blood serum proteins (human serum albumin [HSA] and globulins) is thought to affect transport to active sites, toxicity, and elimination half-lives. However, few studies have investigated the competitive binding of PFAS to these proteins in human serum. Here, we use C18 solid-phase microextraction fibers to measure HSA-water and globulin-water distribution coefficients (DHSA/w, Dglob/w) for PFAS with carbon chains containing 4 to 13 perfluorinated carbons (ηpfc = 4-13) and several functional head-groups. PFAS with ηpfc < 7 were highly bound to HSA relative to globulins, whereas PFAS with ηpfc ≥ 7 showed a greater propensity for binding to globulins. Experimentally measured DHSA/w and Dglob/w and concentrations of serum proteins successfully predicted the variability in PFAS binding in human serum. We estimated that the unbound fraction of serum PFAS varied by up to a factor of 2.5 among individuals participating in the 2017-2018 U.S. National Health and Nutrition Examination Survey. These results suggest that serum HSA and globulins are important covariates for epidemiological studies aimed at understanding the effects of PFAS exposure.

Correlation analysis between per-fluoroalkyl and poly-fluoroalkyl substances exposure and depressive symptoms in adults: NHANES 2005-2018

BACKGROUND

Excessive exposure to per and poly-fluoroalkyl compounds (PFAS) can lead to various negative health effects. However, there's a lack of research studying the link between PFAS exposure and depression in adults, and the existing findings are inconsistent.

OBJECTIVES

Utilizing data collected from the National Health and Nutrition Examination Survey (NHANES) database spanning 2005 to 2018, this study aimed to examine the potential connection between PFAS exposure and depressive symptoms in adults.

METHODS

The correlation between individual PFAS exposure and depressive symptoms was examined through the establishment of weighted logistic regression models (crude model, model 1, model 2) and restricted cubic spline models. To verify the stability of the model, receiver operating characteristic (ROC) curves of the logistic regression model were generated, and a ten-fold cross-validation model was employed. Additionally, the relationship between adult depressive symptoms and mixed PFAS exposure was tested through the utilization of quantile g-computation (qgcomp).

RESULTS

The findings revealed that heightened exposure levels to PFOA, PFHxS, and PFUnDA, were connected with a diminished risk of depressive symptoms in adults (ORPFOA: 0.67, 95 % confidence interval (CI): 0.47, 0.95; ORPFHxS: 0.66, 95 %CI: 0.49, 0.89; ORPFUnDA: 0.65, 95 %CI: 0.45, 0.96). PFOS, PFHxS, and PFDA demonstrated a dose-response relationship with the risk of depressive symptoms. The ROC curve indicated model stability, with recognition accuracy exceeding 90 % in the cross-validation model. The outcomes of qgcomp demonstrated that an increase in serum PFAS concentration was linked to a decreased risk of depressive symptoms in adults (OR: 0.85, 95 %CI: 0.75, 0.96).

DISCUSSION

Due to the cross-sectional design of this study, it's important to acknowledge the potential for reverse causality between PFAS exposure and depressive symptoms. As a result, the outcomes should not be oversimplified to interpret PFAS exposure as a protective factor against adult depressive symptoms.

Bioaccumulation, tissue distributions, and maternal transfer of perfluoroalkyl carboxylates (PFCAs) in laying hens

Laying hens were exposed to feeds spiked with a series of perfluoroalkyl carboxylates (PFCAs) ranging from perfluorobutanoic acid (C4) to perfluorooctadecanoic acid (C18) to investigate their bioaccumulation, tissue distribution, and maternal transfer. We found that PFCAs with longer carbon chains (>8) were more efficiently absorbed in the gastrointestinal tract than those with shorter chains (≤8), and that the rate of depuration varied inversely with the carbon chain length in a U-shaped pattern. Moreover, bioaccumulation potential increased with increasing carbon-chain length, except for C4. Distinct affinities were observed for specific carbon-chain PFCAs across various tissues, evident from their differential accumulation during both uptake and depuration phases. Specifically, C9 showed a higher affinity for serum and liver, C12 was more prevalent in yolk, C14 was notably abundant in the brain, and C18 was predominant in other tissues. Furthermore, the egg-maternal ratio (EMR) increased with increasing carbon-chain length from C7 to C11 and reached a plateau phase for C12 to C18. Our study also confirmed the key role of phospholipids in the tissue distribution and maternal transfer of long-chain PFCAs. This study sheds light on the interaction between PFCAs and biological tissues and reveals the toxicokinetic factors that influence the bioaccumulation of PFCAs. Further research is needed to identify the specific proteins or components that mediate the tissue-specific affinity for different carbon-chain lengths of PFCAs.

Building Chemical Intuition about Physicochemical Properties of C8-Per-/Polyfluoroalkyl Carboxylic Acids through Computational Means

We have predicted acid dissociation constants (pK a), octanol-water partition coefficients (K OW), and DMPC lipid membrane-water partition coefficients (K lipid-w) of 150 different eight-carbon-containing poly-/perfluoroalkyl carboxylic acids (C8-PFCAs) utilizing the COnductor-like Screening MOdel for Realistic Solvents (COSMO-RS) theory. Different trends associated with functionalization, degree of fluorination, degree of saturation, degree of chlorination, and branching are discussed on the basis of the predicted values for the partition coefficients. In general, functionalization closest to the carboxylic headgroup had the greatest impact on the value of the predicted physicochemical properties.

Research Priorities for the Environmental Risk Assessment of Per- and Polyfluorinated Substances

Per- and polyfluorinated substances (PFAS) are a group of thousands of ubiquitously applied persistent industrial chemicals. The field of PFAS environmental research is developing rapidly, but suffers from substantial biases toward specific compounds, environmental compartments, and organisms. The aim of our study was therefore to highlight current developments and to identify knowledge gaps and subsequent research needs that would contribute to a comprehensive environmental risk assessment for PFAS. To this end, we consulted the open literature and databases and found that knowledge of the environmental fate of PFAS is based on the analysis of <1% of the compounds categorized as PFAS. Moreover, soils and suspended particulate matter remain largely understudied. The bioavailability, bioaccumulation, and food web transfer studies of PFAS also focus on a very limited number of compounds and are biased toward aquatic biota, predominantly fish, and less frequently aquatic invertebrates and macrophytes. The available ecotoxicity data revealed that only a few PFAS have been well studied for their environmental hazards, and that PFAS ecotoxicity data are also strongly biased toward aquatic organisms. Ecotoxicity studies in the terrestrial environment are needed, as well as chronic, multigenerational, and community ecotoxicity research, in light of the persistency and bioaccumulation of PFAS. Finally, we identified an urgent need to unravel the relationships among sorption, bioaccumulation, and ecotoxicity on the one hand and molecular descriptors of PFAS chemical structures and physicochemical properties on the other, to allow predictions of exposure, bioaccumulation, and toxicity. Environ Toxicol Chem 2023;42:2302-2316. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Paired Liver:Plasma PFAS Concentration Ratios from Adolescents in the Teen-LABS Study and Derivation of Empirical and Mass Balance Models to Predict and Explain Liver PFAS Accumulation

Animal studies have pointed at the liver as a hotspot for per- and polyfluoroalkyl substances (PFAS) accumulation and toxicity; however, these findings have not been replicated in human populations. We measured concentrations of seven PFAS in matched liver and plasma samples collected at the time of bariatric surgery from 64 adolescents in the Teen-Longitudinal Assessment of Bariatric Surgery (Teen-LABS) study. Liver:plasma concentration ratios were perfectly explained (r2 > 0.99) in a multilinear regression (MLR) model based on toxicokinetic (TK) descriptors consisting of binding to tissue constituents and membrane permeabilities. Of the seven matched plasma and liver PFAS concentrations compared in this study, the liver:plasma concentration ratio of perfluoroheptanoic acid (PFHpA) was considerably higher than the liver:plasma concentration ratio of other PFAS congeners. Comparing the MLR model with an equilibrium mass balance model (MBM) suggested that complex kinetic transport processes are driving the unexpectedly high liver:plasma concentration ratio of PFHpA. Intratissue MBM modeling pointed to membrane lipids as the tissue constituents that drive the liver accumulation of long-chain, hydrophobic PFAS, whereas albumin binding of hydrophobic PFAS dominated PFAS distribution in plasma. The liver:plasma concentration data set, empirical MLR model, and mechanistic MBM modeling allow the prediction of liver from plasma concentrations measured in human cohort studies. Our study demonstrates that combining biomonitoring data with mechanistic modeling can identify underlying mechanisms of internal distribution and specific target organ toxicity of PFAS in humans.

Legacy and Emerging Per- and Polyfluoroalkyl Substances Surveillance in Bufo gargarizans from Inlet Watersheds of Chaohu Lake, China: Tissue Distribution and Bioaccumulation Potential

Amphibians are sensitive biomonitors of environmental pollutants but reports regarding per- and polyfluoroalkyl substances (PFAS), a class of synthetic organofluorine substances, are limited. In this study, samples of water and Chinese toads (Bufo gargarizans) were collected in Chaohu Lake, China. Tissue-specific bioaccumulation characteristics of 39 PFAS, including 19 perfluoroalkyl acids (PFAAs), 8 emerging PFAS, and 12 PFAA precursors, were investigated, and the levels of some biochemical indicators were determined. The highest PFAS concentrations were found in the liver [215.97 ng/g dry weight (dw)] of Chinese toads, followed by gonads (135.42 ng/g dw) and intestine (114.08 ng/g dw). A similar tissue distribution profile was found between legacy and emerging PFAS in the toads, and the occurrence of two emerging PFAS, 2,3,3,3-tetrafluoro-2-propanoate (HFPO-DA) and 6:2 hydrogen-substituted polyfluorooctane ether sulfonate (6:2 H-PFESA) in the amphibians were for the first time reported. Field-based bioaccumulation factors of HFPO-DA were higher than perfluorooctanoic acid, indicating the higher bioaccumulation potential of this emerging PFAS than the legacy C8 compound. Males had significantly higher gonad PFAS levels than females while estradiol levels in gonads increased with increasing concentrations of certain PFAS (e.g., 6:2 H-PFESA), implying that PFAS may trigger estrogenic effects in the toads, especially for male toads.

Impact of per- and polyfluorinated alkyl substances (PFAS) on the marine environment: Raising awareness, challenges, legislation, and mitigation approaches under the One Health concept

Per- and polyfluorinated alkyl substances (PFAS) have long been known for their detrimental effects on the ecosystems and living organisms; however the long-term impact on the marine environment is still insufficiently recognized. Based on PFAS persistence and bioaccumulation in the complex marine food network, adverse effects will be exacerbated by global processes such as climate change and synergies with other pollutants, like microplastics. The range of fluorochemicals currently included in the PFAS umbrella has significantly expanded due to the updated OECD definition, raising new concerns about their poorly understood dynamics and negative effects on the ocean wildlife and human health. Mitigation challenges and approaches, including biodegradation and currently studied materials for PFAS environmental removal are proposed here, highlighting the importance of ongoing monitoring and bridging research gaps. The PFAS EU regulations, good practices and legal frameworks are discussed, with emphasis on recommendations for improving marine ecosystem management.

Associations of perfluoroalkyl substances (PFAS) with lipid and lipoprotein profiles

BACKGROUND

Perfluoroalkyl substances (PFAS) are man-made chemicals with unique properties that are widely distributed in humans and the environment. Recent studies suggest that PFAS are involved in cholesterol metabolism, however, the mechanisms underlying the associations are poorly understood.

OBJECTIVE

We aimed to evaluate associations of plasma PFAS with detailed lipid and lipoprotein subfractions in an adult population of men and women.

METHODS

We measured concentrations of cholesterol and triglycerides in lipoprotein subfractions, apolipoprotein subclasses, as well as fatty acid and different phospholipid measures, using serum proton nuclear magnetic resonance (1H-NMR), and four plasma PFAS using liquid chromatography-mass spectrometry (UHPLC-MS/MS). Measurements were available for 493 participants (all aged 50 years, 50% female). Multivariable linear regression was used to estimate the association of four PFAS with 43 different 1H-NMR measures, with adjustment for body mass index (BMI), smoking, education, and physical activity.

RESULTS

We found that perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorodecanoic acid (PFDA), but not perfluorohexanesulfonate (PFHxS), concentrations were consistently positively associated with concentrations of cholesterol in lipoprotein subfractions, apolipoproteins, as well as composite fatty acid- and phospholipid profiles. The most consistent associations were found for the relationship of PFAS with total cholesterol in intermediate-density lipoprotein (IDL), across all low-density lipoprotein (LDL) subfractions and small high-density lipoprotein (HDL). Moreover, we found weak to null evidence for an association of any of the measured 13 triglyceride lipoprotein subfractions with PFAS.

CONCLUSIONS

Our results suggest that plasma PFAS concentrations are associated with cholesterol in small HDL, IDL and all LDL subfractions, as well as apolipoproteins and composite fatty acid and phospholipid profiles but to a lesser extent with triglycerides in lipoproteins. Our findings draw attention to the need for more detailed measurements of lipids across various lipoprotein subfractions and subclasses in assessing the role of PFAS in lipid metabolism.

IMPACT

By performing an in-depth characterization of circulating cholesterol and triglycerides in lipoprotein subfractions, apolipoprotein, fatty acid, and phospholipid concentrations, this study has expanded upon the limited literature available on the associations of plasma PFAS concentrations beyond clinical routine laboratory testing for lipids.

Developing Methods for Assessing Trophic Magnification of Perfluoroalkyl Substances within an Urban Terrestrial Avian Food Web

We investigated the trophic magnification potential of perfluoroalkyl substances (PFAS) in a terrestrial food web by using a chemical activity-based approach, which involved normalizing concentrations of PFAS in biota to their relative biochemical composition in order to provide a thermodynamically accurate basis for comparing concentrations of PFAS in biota. Samples of hawk eggs, songbird tissues, and invertebrates were collected and analyzed for concentrations of 18 perfluoroalkyl acids (PFAAs) and for polar lipid, neutral lipid, total protein, albumin, and water content. Estimated mass fractions of PFCA C8-C11 and PFSA C4-C8 predominantly occurred in albumin within biota samples from the food web with smaller estimated fractions in polar lipids > structural proteins > neutral lipids and insignificant amounts in water. Estimated mass fractions of longer-chained PFAS (i.e., C12-C16) mainly occurred in polar lipids with smaller estimated fractions in albumin > structural proteins > neutral lipids > and water. Chemical activity-based TMFs indicated that PFNA, PFDA, PFUdA, PFDoA, PFTrDA, PFTeDA, PFOS, and PFDS biomagnified in the food web; PFOA, PFHxDA, and PFHxS did not appear to biomagnify; and PFBS biodiluted. Chemical activity-based TMFs for PFCA C8-C11 and PFSA C4-C8 were in good agreement with corresponding TMFs derived with concentrations normalized to only total protein in biota, suggesting that concentrations normalized to total protein may be appropriate proxies of chemical activity-based TMFs for PFAS, which predominantly partition to albumin. Similarly, TMFs derived with concentrations normalized to albumin may be suitable proxies of chemical activity-based TMFs for longer-chained PFAS, which predominantly partition to polar lipids.

PPARα/ACOX1 as a novel target for hepatic lipid metabolism disorders induced by per- and polyfluoroalkyl substances: An integrated approach

BACKGROUND

Per- and polyfluoroalkyl substances (PFAS) are persistent and ubiquitous environmental contaminants with well-documented hepatotoxicity. However, the mechanistic linkage between PFAS exposure and non-alcoholic fatty liver disease (NAFLD) remains largely elusive.

OBJECTIVES

This study aimed to explore PFAS-to-NAFLD link and the relevant molecular mechanisms.

METHODS

The cross-sectional analyses using National Health and Nutrition Examination Survey (NHANES) data were conducted to investigate the association between PFAS exposure and NAFLD. A combination of in silico toxicological analyses, bioinformatics approaches, animal experiments, and in vitro assays was used to explore the molecular initiating events (MIEs) and key events (KEs) in PFAS-induced hepatic lipid metabolism disorders.

RESULTS

The cross-sectional analyses with NHANES data revealed the significant association between PFAS exposure and hepatic steatosis/NAFLD. The in silico toxicological analyses showed that PPARα activation induced by perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), prototypical representatives of PFAS, is the critical MIE associated with NAFLD-predominant liver diseases. Transcriptome-based bioinformatic annotation and analyses identified that transcriptional upregulation of hepatic acyl-CoA oxidase 1 (ACOX1) in PPARα-regulated peroxisomal β-oxidation pathway was the KE involved with PFOA/PFOS-perturbed hepatic lipid metabolic pathways in humans, mice and rats. The in vivo and in vitro assays further verified that ACOX1-mediated oxidative stress contributed to mitochondrial compromise and lipid accumulation in PFOA/PFOS-exposed mouse hepatocytes, which could be mitigated by co-treatment with ACOX1 inhibitor and mitochondria ROS scavenger. Additionally, we observed that besides PFOA and PFOS, hepatic ACOX1 exhibited good-fit response to short-term exposures of long-chain (C7-C10) perfluoroalkyl carboxylic acids (PFHpA, PFNA, PFDA) and perfluoroalkyl sulfonic acids (PFHpS, PFDS) in human hepatocyte spheroids through benchmark dose (BMD) modeling.

CONCLUSION

Our study unveils a novel molecular target for PFAS-induced hepatic lipid metabolic disorders, shedding new light on prediction, assessment, and mitigation of PFAS hepatotoxicity.

A State-of-the-Science Review of Interactions of Per- and Polyfluoroalkyl Substances (PFAS) with Renal Transporters in Health and Disease: Implications for Population Variability in PFAS Toxicokinetics

BACKGROUND

Per- and polyfluoroalkyl substances (PFAS) are ubiquitous in the environment and have been shown to cause various adverse health impacts. In animals, sex- and species-specific differences in PFAS elimination half-lives have been linked to the activity of kidney transporters. However, PFAS molecular interactions with kidney transporters are still not fully understood. Moreover, the impact of kidney disease on PFAS elimination remains unclear.

OBJECTIVES

This state-of-the-science review integrated current knowledge to assess how changes in kidney function and transporter expression from health to disease could affect PFAS toxicokinetics and identified priority research gaps that should be addressed to advance knowledge.

METHODS

We searched for studies that measured PFAS uptake by kidney transporters, quantified transporter-level changes associated with kidney disease status, and developed PFAS pharmacokinetic models. We then used two databases to identify untested kidney transporters that have the potential for PFAS transport based on their endogenous substrates. Finally, we used an existing pharmacokinetic model for perfluorooctanoic acid (PFOA) in male rats to explore the influence of transporter expression levels, glomerular filtration rate (GFR), and serum albumin on serum half-lives.

RESULTS

The literature search identified nine human and eight rat kidney transporters that were previously investigated for their ability to transport PFAS, as well as seven human and three rat transporters that were confirmed to transport specific PFAS. We proposed a candidate list of seven untested kidney transporters with the potential for PFAS transport. Model results indicated PFOA toxicokinetics were more influenced by changes in GFR than in transporter expression.

DISCUSSION

Studies on additional transporters, particularly efflux transporters, and on more PFAS, especially current-use PFAS, are needed to better cover the role of transporters across the PFAS class. Remaining research gaps in transporter expression changes in specific kidney disease states could limit the effectiveness of risk assessment and prevent identification of vulnerable populations. https://doi.org/10.1289/EHP11885.

Can blood proteome diversity among fish species help explain perfluoroalkyl acid trophodynamics in aquatic food webs?

Per- and polyfluoroalkyl substances (PFAS) are a diverse family of industrially significant synthetic chemicals infamous for extreme environmental persistence and global environmental distribution. Many PFAS are bioaccumulative and biologically active mainly due to their tendency to bind with various proteins. These protein interactions are important in determining the accumulation potential and tissue distribution of individual PFAS. Trophodynamics studies including aquatic food webs present inconsistent evidence for PFAS biomagnification. This study strives to identify whether the observed variability in PFAS bioaccumulation potential among species could correspond with interspecies protein composition differences. Specifically, this work compares the perfluorooctane sulfonate (PFOS) serum protein binding potential and the tissue distribution of ten perfluoroalkyl acids (PFAAs) detected in alewife (Alosa pseudoharengus), deepwater sculpin (Myoxocephalus thompsonii), and lake trout (Salvelinus namaycush) of the Lake Ontario aquatic piscivorous food web. These three fish sera and fetal bovine reference serum all had unique total serum protein concentrations. Serum protein-PFOS binding experiments showed divergent patterns between fetal bovine serum and fish sera, suggesting potentially two different PFOS binding mechanisms. To identify interspecies differences in PFAS-binding serum proteins, fish sera were pre-equilibrated with PFOS, fractionated by serial molecular weight cut-off filter fractionation, followed by liquid chromatography-tandem mass spectrometry analysis of the tryptic protein digests and the PFOS extracts of each fraction. This workflow identified similar serum proteins for all fish species. However, serum albumin was only identified in lake trout, suggesting apolipoproteins are likely the primary PFAA transporters in alewife and deepwater sculpin sera. PFAA tissue distribution analysis provided supporting evidence for interspecies variations in lipid transport and storage, which may also contribute to the varied PFAA accumulation in these species. Proteomics data are available via ProteomeXchange with identifier PXD039145.

Occurrence and Bioaccumulation Patterns of Per- and Polyfluoroalkyl Substances (PFAS) in the Marine Environment

Per- and polyfluoroalkyl substances (PFAS) are a group of synthetic compounds used in commercial applications, household products, and industrial processes. The concern around the environmental persistence, bioaccumulation and toxicity of this vast contaminant class continues to rise. We conducted a review of the scientific literature to compare patterns of PFAS bioaccumulation in marine organisms and identify compounds of potential concern. PFAS occurrence data in seawater, sediments, and several marine taxa was analyzed from studies published between the years 2000 and 2020. Taxonomic and tissue-specific differences indicated elevated levels in protein-rich tissues and in air-breathing organisms compared to those that respire in water. Long-chain perfluoroalkyl carboxylic acids, particularly perfluoroundecanoic acid, were detected at high concentrations across several taxa and across temporal studies indicating their persistence and bioaccumulative potential. Perfluorooctanesulfonic acid was elevated in various tissue types across taxa. Precursors and replacement PFAS were detected in several marine organisms. Identification of these trends across habitats and taxa can be applied towards biomonitoring efforts, determination of high-risk taxa, and criteria development. This review also highlights challenges related to PFAS biomonitoring including (i) effects of environmental and biological variables, (ii) evaluation of protein binding sites and affinities, and (iii) biotransformation of precursors.

Sex-Specific Bioaccumulation, Maternal Transfer, and Tissue Distribution of Legacy and Emerging Per- and Polyfluoroalkyl Substances in Snakes (Enhydris chinensis) and the Impact of Pregnancy

The effects of sex and pregnancy on the bioaccumulation and tissue distribution of legacy and emerging per- and polyfluoroalkyl substances (PFASs) in Chinese water snakes were investigated. The bioaccumulation factor of PFASs showed a positive correlation with their protein-water partition coefficients (log K_PW), and steric hindrance effects were observed when the molecular volume was > 357 ų. PFAS levels in females were significantly lower than those in males. The chemical composition of pregnant females was significantly different from that of non-pregnant females and males. The maternal transfer efficiencies of perfluorooctane sulfonic acid were higher than those of other PFASs, and a positive correlation between the maternal transfer potential and log K_PW was observed for other PFASs. Tissues with high phospholipid content exhibited higher concentrations of ∑PFASs. Numerous physiological changes occurred in maternal organ systems during pregnancy, leading to the re-distribution of chemicals among different tissues. The change in tissue distribution of PFASs that are easily and not-so-easily maternally transferred was in the opposite direction. The extent of compound transfer from the liver to the egg determined tissue re-distribution during pregnancy.

Evaluation of Per- and Polyfluoroalkyl Substances (PFAS) In Vitro Toxicity Testing for Developmental Neurotoxicity

Per- and polyfluoroalkyl substances (PFAS) are a diverse set of commercial chemicals widely detected in humans and the environment. However, only a limited number of PFAS are associated with epidemiological or experimental data for hazard identification. To provide developmental neurotoxicity (DNT) hazard information, the work herein employed DNT new approach methods (NAMs) to generate in vitro screening data for a set of 160 PFAS. The DNT NAMs battery was comprised of the microelectrode array neuronal network formation assay (NFA) and high-content imaging (HCI) assays to evaluate proliferation, apoptosis, and neurite outgrowth. The majority of PFAS (118/160) were inactive or equivocal in the DNT NAMs, leaving 42 active PFAS that decreased measures of neural network connectivity and neurite length. Analytical quality control indicated 43/118 inactive PFAS samples and 10/42 active PFAS samples were degraded; as such, careful interpretation is required as some negatives may have been due to loss of the parent PFAS, and some actives may have resulted from a mixture of parent and/or degradants of PFAS. PFAS containing a perfluorinated carbon (C) chain length ≥8, a high C:fluorine ratio, or a carboxylic acid moiety were more likely to be bioactive in the DNT NAMs. Of the PFAS positives in DNT NAMs, 85% were also active in other EPA ToxCast assays, whereas 79% of PFAS inactives in the DNT NAMs were active in other assays. These data demonstrate that a subset of PFAS perturb neurodevelopmental processes in vitro and suggest focusing future studies of DNT on PFAS with certain structural feature descriptors.

Prenatal Exposure to Legacy and Alternative Per- and Polyfluoroalkyl Substances and Neuropsychological Development Trajectories over the First 3 Years of Life

The neurotoxic effects of prenatal exposure to per- and polyfluoroalkyl substances (PFAS) on offspring animals are well-documented. However, epidemiological evidence for legacy PFAS is inconclusive, and for alternative PFAS, it is little known. In this investigation, we selected 718 mother-child pairs from the Chinese Maoming Birth Cohort Study and measured 17 legacy and alternative PFAS in the third-trimester serum. Neuropsychological developments (communication, gross motor function, fine motor function, problem solving ability, and personal-social skills) were assessed at 3, 6, 12, 18, 24, and 36 months using the Ages and Stages Questionnaires 3rd edition. Trajectories of each subscale were classified into persistently low and persistently high groups via group-based trajectory modeling. Logistic regression and grouped weighted quantile sum were fitted to assess the potential effects of individual PFAS and their mixtures, respectively. Higher linear PFHxS levels were associated with elevated odds for the persistently low trajectories of communication (OR = 1.73; 95% CI: 1.12, 2.66) and problem solving ability (OR = 2.11; 95% CI: 1.14, 3.90). Similar findings were observed for linear PFOS, 1m-PFOS, PFDA, PFDoDA, PFUnDA, and legacy PFAS mixture. However, no association was observed for alternative PFAS and their mixture. We provided insights into the longitudinal links between prenatal legacy/alternative PFAS exposure and neuropsychological development trajectories over the first 3 years of life.

Maternal per- and poly-fluoroalkyl substances exposures associated with higher depressive symptom scores among immigrant women in the Chemicals in Our Bodies cohort in San Francisco

BACKGROUND

Exposure to per- and poly-fluoroalkyl substances (PFAS) remains an important public health issue due to widespread detection and persistence in environmental media, slow metabolism in humans, and influences on physiological processes such as neurological signaling. Maternal depression is highly prevalent during pregnancy and postpartum and is potentially sensitive to PFAS. The health risks associated with PFAS may be further amplified in historically marginalized communities, including immigrants.

OBJECTIVE

Evaluate maternal concentrations of PFAS in association with depression scores during pregnancy and whether effects differ between US born and immigrant women.

METHODS

Our study sample included 282 US born and 235 immigrant pregnant women enrolled in the Chemicals in Our Bodies prospective birth cohort based in San Francisco, CA. We measured 12 PFAS in serum samples collected in the second trimester and depressive symptom scores were assessed using the Center for Epidemiologic Studies Depression Scale. Associations were estimated using linear regression, adjusting for maternal age, education, pre-pregnancy body mass index, and parity. Associations with a PFAS mixture were estimated using quantile g-computation.

RESULTS

In adjusted linear regression models, a twofold increase in two PFAS was associated with higher depression scores in the overall sample, and this association persisted only among immigrant women (β [95 % confidence interval]: perfluorooctane sulfonic acid (2.7 [0.7-4.7]) and methyl-perfluorooctane sulfonamide acetic acid (2.9 [1.2-4.7]). Quantile g-computation indicated that simultaneously increasing all PFAS in the mixture by one quartile was associated with increased depressive symptoms among immigrant women (mean change per quartile increase = 1.12 [0.002, 2.3]), and associations were stronger compared to US born women (mean change per quartile increase = 0.09 [-1.0, 0.8]).

CONCLUSIONS

Findings provide new evidence that PFAS are associated with higher depression symptoms among immigrant women during pregnancy. Results can inform efforts to address environmental factors that may affect depression among US immigrants.

Fish tissue conversion factors for mercury, cadmium, lead and nine per- and polyfluoroalkyl substances for use within contaminant monitoring

Fish tissue levels have to comply with environmental quality standards (EQSs) within the European Water Framework Directive. However, within monitoring, contaminants are sometimes measured in a different tissue than the tissue for which the environmental (whole fish) or human (fillet (equivalent to muscle tissue)) quality standard is set. Tissue conversion factors (k), describing the relationship between concentrations in different tissues, can be used to obtain a quality standard for the appropriate tissue. Several different approaches have been suggested for the calculation of k. For monitoring purposes, we propose the use of a simple, easy reproducible approach that assumes proportionality between two tissue, or tissue and whole fish, concentrations. This allows for an easy comparison of studies and adoption of ks into independent monitoring programs. Here, we determined ks for three metals (mercury (Hg), lead (Pb), cadmium (Cd)) and nine per- and polyfluoroalkyl substances (PFAS) including perfluorooctanesulfonic acid (PFOS) across six marine and freshwater fish species from Northern European lakes and the Baltic Sea. We found significant species differences for Hg for k_{muscle/whole fish}, for Cd and Pb for k_{liver/whole fish} and for Cd for k_liver/muscle. For perfluoroalkyl carboxylic acids (PFCA), we found a chain length dependence with lowest k_liver/muscle at low and high chain lengths (C₈, C₁₃) and highest for median chain lengths (C₉-C₁₂). Further, there were differences between fish species with k_liver/muscle for PFOS almost doubling from eelpout (10.3) to herring (19.2) and increasing up to a factor 4 between eelpout and herring for other PFASs. FOSA had two distinctive groups, herring with a k_liver/muscle of 48.7 and a second group with ks of 2.3 to 5.9 for all other fish species. Our results suggest that differences in the tissue somatic index, and contaminant uptake, tissue transfer and metabolism result in the need for species-specific ks within monitoring.

Novel insights into the mediating roles of cluster of differentiation 36 in transmembrane transport and tissue partition of per- and polyfluoroalkyl substances in mice

Transmembrane transport is important for bioaccumulation of per- and polyfluoroalkyl substances (PFASs) in organisms, but has not yet been well understood. Here, the roles of cluster of differentiation 36 (CD36) in accumulation of PFASs were investigated. CD36 was overexpressed in Escherichia coli to get CD36-BL21 strain, and the binding affinities of 20 PFASs with CD36 were determined by microscale thermophoresis, which grew up to 17.5 μM with increasing carbon chain length. Consequently, the accumulation of most PFASs was remarkably promoted in CD36-BL21 in comparison to the wild strain, and the enhancement was proportional to their binding affinities with CD36 (r = -0.96). However, this effect was depressed greatly as CD36 was inhibited by sulfo-N-succinimidyl oleate (SSO). Additionally, as the mice received SSO pretreatment before they were exposed to perfluorododecanoic acid, its accumulation in the tissues rich in CD36, such as liver, was suppressed, but increased by 1.1 times in the serum. These indicated that CD36 played critical roles in the transmembrane transport and tissue partition of PFASs in organisms. The developed relationship between liver-blood partition of PFASs and their binding affinities with intracellular proteins was distinctly improved by incorporating that with CD36 (r = -0.97).

The Relationship between Typical Environmental Endocrine Disruptors and Kidney Disease

Endocrine disrupting chemicals (EDCs) are exogenous substances that alter the endocrine function of an organism, to result in adverse effects on growth and development, metabolism, and reproductive function. The kidney is one of the most important organs in the urinary system and an accumulation point. Studies have shown that EDCs can cause proteinuria, affect glomeruli and renal tubules, and even lead to diabetes and renal fibrosis in animal and human studies. In this review, we discuss renal accumulation of select EDCs such as dioxins, per- and polyfluoroalkyl substances (PFAS), bisphenol A (BPA), and phthalates, and delineate how exposures to such EDCs cause renal lesions and diseases, including cancer. The regulation of typical EDCs with specific target genes and the activation of related pathways are summarized.

PFAS and Precursor Bioaccumulation in Freshwater Recreational Fish: Implications for Fish Advisories

Per- and polyfluoroalkyl substances (PFAS) are a diverse class of fluorinated anthropogenic chemicals that include perfluoroalkyl acids (PFAA), which are widely used in modern commerce. Many products and environmental samples contain abundant precursors that can degrade into terminal PFAA associated with adverse health effects. Fish consumption is an important dietary exposure source for PFAS that bioaccumulate in food webs. However, little is known about bioaccumulation of PFAA precursors. Here, we identify and quantify PFAS in recreational fish species collected from surface waters across New Hampshire, US, using a toolbox of analytical methods. Targeted analysis of paired water and tissue samples suggests that many precursors below detection in water have a higher bioaccumulation potential than their terminal PFAA. Perfluorobutane sulfonamide (FBSA), a short-chain precursor produced by electrochemical fluorination, was detected in all fish samples analyzed for this compound. The total oxidizable precursor assay interpreted using Bayesian inference revealed fish muscle tissue contained additional, short-chain precursors in high concentration samples. Suspect screening analysis indicated these were perfluoroalkyl sulfonamide precursors with three and five perfluorinated carbons. Fish consumption advisories are primarily being developed for perfluorooctane sulfonate (PFOS), but this work reinforces the need for risk evaluations to consider additional bioaccumulative PFAS, including perfluoroalkyl sulfonamide precursors.

PFOA exposure causes variations of Acot1 among tissues in rats, and Acot1 in serum can be potentially used as a sensitive marker for health monitoring

Perfluorooctanoic acid (PFOA) is a type of 8-carbon perfluoroalkyl substances (PFASs) widely used in industrial and domestic products, which now is a persistent organic pollutant (POP) found in the environment. Its structure is similar to fatty acids, which enables it to induce the expression of ACOT genes. To investigate the expression levels of Acot1 in various tissues and organs after exposure to PFOA for 28 days in rats, and to compare the variations of Acot1 expression in different tissues, we sectioned samples and incubated with Acot1 antibody. The results show that the transcription and protein expression levels of Acot1 in the liver and kidney of rats increased significantly. Meanwhile, the transcription and protein expression of Acot1 gene were also detected in testis, muscle, and adipose. The results of immunohistochemistry were also verified by western blot detection, and we detected the transcription of Acot1 gene in these tissues and found that they all increased in varying degrees. In this study, the expression of Acot1 protein in rat serum was detected for the first time, and the expression of Acot1 in rat serum was found to be significantly increased after PFOA exposure. In addition, the expression level of Acot1 in rat organism was found to be higher than that in the control group after 4 days of depuration for 7 days of acute PFOA exposure, and Acot1 protein expression also showed an increase with increasing exposure time, indicating that Acot1 can be used as a sensitive biomarker for health monitoring of PFOA occupational workers or exposed persons.

Health-related toxicity of emerging per- and polyfluoroalkyl substances: Comparison to legacy PFOS and PFOA

Per- and polyfluoroalkyl substances (PFAS) are highly persistent, manufactured chemicals used in various manufacturing processes and found in numerous commercial products. With over 9000 compounds belonging to this chemical class, there is increasing concern regarding human exposure to these compounds due to their persistent, bioaccumulative, and toxic nature. Human exposure to PFAS may occur from a variety of exposure sources, including, air, food, indoor dust, soil, water, from the transfer of PFAS from non-stick wrappers to food, use of cosmetics, and other personal care products. This critical review presents recent research on the health-related impacts of PFAS exposure, highlighting compounds other than Perfluorooctanoic acid (PFOA) and Perfluoroctane sulfonate (PFOS) that cause adverse health effects, updates the current state of knowledge on PFAS toxicity, and, where possible, elucidates cause-and-effect relationships. Recent reviews identified that exposure to PFAS was associated with adverse health impacts on female and male fertility, metabolism in pregnancy, endocrine function including pancreatic dysfunction and risk of developing Type 2 diabetes, lipid metabolism and risk of childhood adiposity, hepatic and renal function, immune function, cardiovascular health (atherosclerosis), bone health including risk for dental cavities, osteoporosis, and vitamin D deficiency, neurological function, and risk of developing breast cancer. However, while cause-and-effect relationships for many of these outcomes were not able to be clearly elucidated, it was identified that 1) the evidence derived from both animal models and humans suggested that PFAS may exert harmful impacts on both animals and humans, however extrapolating data from animal to human studies was complicated due to differences in exposure/elimination kinetics, 2) PFAS precursor kinetics and toxicity mechanism data are still limited despite ongoing exposures, and 3) studies in humans, which provide contrasting results require further investigation of the long-term-exposed population to better evaluate the biological toxicity of chronic exposure to PFAS.

A food web bioaccumulation model for the accumulation of per- and polyfluoroalkyl substances (PFAS) in fish: how important is renal elimination?

Per- and polyfluoroalkyl substances (PFAS) are a large class of highly fluorinated anthropogenic chemicals. Some PFAS bioaccumulate in aquatic food webs, thereby posing risks for seafood consumers. Existing models for persistent organic pollutants (POPs) perform poorly for ionizable PFAS. Here we adapt a well-established food web bioaccumulation model for neutral POPs to predict the bioaccumulation behavior of six perfluoroalkyl acids (PFAAs) and two perfluoroalkyl ether acids (HFPO-DA, 9-Cl-PF3ONS) produced as PFAA replacements. The new model includes sorption to blood plasma proteins and phospholipids, empirically parameterized membrane transport, and renal elimination for PFAAs. Improved performance relative to prior models without these updates is shown by comparing simulations to field and lab measurements. PFAS with eight or more perfluorinated carbons (η_pfc ≥ 8, i.e., C8 perfluorosulfonic acid, C10-C11 perfluorocarboxylic acid, 9-Cl-PF3ONS) are often the most abundant in aquatic food webs. The new model reproduces their observed bioaccumulation potential within a factor of two for >80% of fish species, indicating its readiness to support development of fish consumption advisories for these compounds. Results suggest bioaccumulation of η_pfc ≥ 8 PFAS is primarily driven by phospholipid partitioning, and that renal elimination is negligible for these compounds. However, specific protein binding mechanisms are important for reproducing the observed tissue concentrations of many shorter-chain PFAAs, including protein transporter-mediated renal elimination. Additional data on protein-binding and membrane transport mechanisms for PFAS are needed to better understand the biological behavior of shorter-chain PFAAs and their alternatives.

Pseudomonas sp. Strain 273 Incorporates Organofluorine into the Lipid Bilayer during Growth with Fluorinated Alkanes

Anthropogenic organofluorine compounds are recalcitrant, globally distributed, and a human health concern. Although rare, natural processes synthesize fluorinated compounds, and some bacteria have evolved mechanisms to metabolize organofluorine compounds. Pseudomonas sp. strain 273 grows with 1-fluorodecane (FD) and 1,10-difluorodecane (DFD) as carbon sources, but inorganic fluoride release was not stoichiometric. Metabolome studies revealed that this bacterium produces fluorinated anabolites and phospholipids. Mass spectrometric fatty acid profiling detected fluorinated long-chain (i.e., C₁₂-C₁₉) fatty acids in strain 273 cells grown with FD or DFD, and lipidomic profiling determined that 7.5 ± 0.2 and 82.0 ± 1.0% of the total phospholipids in strain 273 grown with FD or DFD, respectively, were fluorinated. The detection of the fluorinated metabolites and macromolecules represents a heretofore unrecognized sink for organofluorine, an observation with consequences for the environmental fate and transport of fluorinated aliphatic compounds.

Emissions, Isomer-Specific Environmental Behavior, and Transformation of OBS from One Major Fluorochemical Manufacturing Facility in China

Sodium p-perfluorous nonenoxybenzenesulfonate (OBS), a novel alternative to perfluorooctane sulfonic acid (PFOS), has been widely used in various fields in China and has certain toxic effects similar to PFOS. This study monitored OBS and 15 legacy PFASs in surface water, sediment, soil, and crucian carp near a fluorochemical manufacturing factory (FMF) in Suqian, China, focusing on the emission, isomer-specific environmental fate, and transformation of OBS. One to four orders of magnitude higher concentrations of OBS than other polyfluoroalkyl substances (PFASs) in all samples indicate that industrial emission is an important point source of OBS in the surrounding environment. The concentrations of OBS in surface water, sediment, and soil decreased exponentially as the distance from the FMF increases. The proportions of OBS-c, the dominant isomer, increased in the order: water (75.5 ± 6.4%), sediment (85.7 ± 10%), fish (muscle: 94.1 ± 0.99%; blood: 93.5 ± 1.4%), suggesting its preferential accumulation in sediment and fish than other isomers. Mono-hydroxylated transformation products of OBS were first identified in water, sediment, and fish, suggesting its hydroxylation may exist in the real environment. The transformation of OBS may explain its significantly lower bioaccumulation than PFOS in fish. However, considering the higher BAF of OBS than the regulatory bioaccumulation criterion and the possible stronger toxicity of its transformation products, further studies on its bioaccumulation and transformation are warranted.

Insights into the Competitive Mechanisms of Per- and Polyfluoroalkyl Substances Partition in Liver and Blood

Some per- and polyfluoroalkyl substances (PFASs) tend to be accumulated in liver and cause hepatotoxicity. However, the difficulty to directly measure liver concentrations of PFASs in humans hampers our understanding of their hepatotoxicity and mechanisms of action. We investigated the partitioning of 11 PFASs between liver and blood in male CD-1 mice. Although accumulation of the perfluoroalkanesulfonic acids (PFSAs) in mice serum was higher than their carboxylic acids (PFCAs) counterparts as expected, the liver-blood partition coefficients (R_L/S) of PFSAs were lower than the PFCAs R_L/S, implying a competition between liver and blood. The in vitro experiments further indicated that the partitioning was dominantly determined by their competitive binding between human liver fatty acid binding protein (hL-FABP) and serum albumin (HSA). The binding affinities (K_d) of PFASs to both proteins were measured. The correlations between the R_L/S and log K_d (hL-FABP)/log K_d (HSA) were stronger than those with log K_d (hL-FABP) alone, magnifying that the partitioning was dominantly controlled by competitive binding between hL-FABP and HSA. Therefore, the liver concentrations of the selected PFASs in humans could be predicted from the available serum concentrations, which is important for assessing their hepatotoxicity.

Tissue-Specific Uptake, Depuration Kinetics, and Suspected Metabolites of Three Emerging Per- and Polyfluoroalkyl Substances (PFASs) in Marine Medaka

Restrictions on legacy per- and polyfluoroalkyl substances (PFASs) have led to the widespread use of emerging PFASs. However, their toxicokinetics have rarely been reported. Here, tissue-specific uptake and depuration kinetics of perfluoroethylcyclohexanesulfonate (PFECHS) and 6:2 and 8:2 chlorinated polyfluoroalkyl ether sulfonates (Cl-PFESAs) were studied in marine medaka (Oryzias melastigma). The fish were exposed to these substances for 28 days (0.2 μg/L), followed by a clearance period of 14 days. The depuration constant (k_d) of PFECHS [0.103 ± 0.009 day^-1 (mean ± standard deviation)] was reported for the first time. Among the six studied tissues, the highest concentrations of 6:2 Cl-PFESA, 8:2 Cl-PFESA, and PFECHS were found in the liver [1540, 1230, and 188 ng (g of wet weight)^-1, respectively] on day 28 while the longest residence times were found in the eyes (t_1/2 values of 21.7 ± 4.3, 23.9 ± 1.5, and 17.3 ± 0.8 days, respectively). No significant positive correlation was found between the bioconcentration factors of the studied PFASs and the phospholipid or protein contents in different tissues of the studied fish. Potential metabolites of Cl-PFESAs, i.e., their hydrogen-substituted analogues (H-PFESAs), were identified by time-of-flight mass spectrometry. However, the biotransformation rates were low (<0.19%), indicating the poor capacity of marine medaka to metabolize Cl-PFESAs to H-PFESAs.

Bioaccumulation of polyfluoroalkyl substances in the Lake Huron aquatic food web

Polyfluoroalkyl substances (PFAS) are a group of fluorinated organic chemicals that have been produced for industrial and commercial application since the 1950s. PFAS are highly persistent and ubiquitous in water, sediment, and biota. Toxic effects of PFAS on humans and the ecosystem have increased scientific and public concern. To better understand the distribution of PFAS in the Laurentian Great Lakes, carbon (¹²C and ¹³C) and nitrogen (¹⁴N and ¹⁵N) stable isotope enrichment, fatty acid profiles, and PFAS were measured in the Lake Huron (LH) aquatic food web. The trophic level of the organisms was estimated using δ¹⁵N and found to be a determinant of PFAS biomagnification. The δ¹³C and fatty acid profiles were used to assess the carbon/energy flow pathway and predator-prey relationships, respectively. The δ¹³C, δ¹⁵N, and fatty acids were used to elucidate the trophodynamics and understand the PFAS trophic transfer in the LH aquatic food web. Perfluorooctanesulfonic acid (PFOS) was the dominant PFAS observed, followed by C9 - C11 perfluorinated carboxylic acids (PFCA). The highest PFOS concentrations (45 ± 11 ng/g, wet weight (wwt)) were detected in lake trout (Salvelinus namaycush), while the highest total PFCA concentrations (sum of C4 - C16 PFCAs) were detected in deepwater sculpin (Myoxocephalus thompsonii). With the exception of perfluorooctanoic acid (PFOA), C8-C14 PFAS biomagnification factors (BMFs) were found to be generally greater than 1, suggesting PFAS biomagnification from prey to predator. Trophic magnification factors (TMFs) of C8-C14 PFCA were found to be independent of compound hydrophobicity.