Hepatotoxic Effects of Hexafluoropropylene Oxide Trimer Acid (HFPO-TA), A Novel Perfluorooctanoic Acid (PFOA) Alternative, on Mice

Thyroid disrupting effects and the developmental toxicity of hexafluoropropylene oxide oligomer acids in zebrafish during early development

As perfluorooctanoic acid (PFOA) alternatives, hexafluoropropylene oxide dimeric acid (HFPO-DA) and hexafluoropropylene oxide trimeric acid (HFPO-TA) have been increasingly used and caused considerable water pollution. However, their toxicities to aquatic organisms are still not well known. Therefore, in this study, zebrafish embryos were exposed to PFOA (0, 1.5, 3 and 6 mg/L), HFPO-DA (0, 3, 6 and 12 mg/L) and HFPO-TA (0, 1, 2 and 4 mg/L) to comparatively investigate their thyroid disrupting effects and the developmental toxicity. Results demonstrated that waterborne exposure to PFOA and its two alternatives decreased T4 contents, the heart rate and swirl-escape rate of zebrafish embryos/larvae. The transcription levels of genes related to thyroid hormone regulation (crh), biosynthesis (tpo and tg), function (trα and trβ), transport (transthyretin, ttr), and metabolism (dio1, dio2 and ugt1ab), were differently altered after the exposures, which induced the thyroid disrupting effects and decreased the heart rate. In addition, the transcription levels of some genes related to the nervous system development were also significantly affected, which was associated with the thyroid disrupting effects and consequently affected the locomotor activity of zebrafish. Therefore, HFPO-DA and HFPO-TA could not be safe alternatives to PFOA. Further studies to uncover the underlying mechanisms of these adverse effects are warranted.

Regulating the absorption and excretion of perfluorooctane sulfonate and its alternatives through influencing enterohepatic circulation

Enterohepatic circulation has been reported to play a significant role in the bioaccumulation of PFASs. In this study, the tissue distribution and excretion of PFOS and its alternatives, namely 6:2 and 8:2 fluorotelomer sulfonic acid (FTSA) was investigated using a mouse assay with a focus on role of enterohepatic circulation. Liver was the primarily accumulating organ for PFOS and 8:2 FTSA (33.4 % and 25.8 % of total doses absorbed after 14 days), whereas 65 % of 6:2 FTSA was excreted via urine within 24 h. Peak levels of 8:2 FTSA and PFOS were found in the gallbladder, implying the important role of enterohepatic circulation in PFASs reabsorption. The role of enterohepatic circulation was further evaluated through co-exposure of 8:2 FTSA and PFOS with medicines (namely metformin (MET) and ursodeoxycholic acid (UDCA)). MET reduced accumulation of 8:2 FTSA and PFOS in the liver by 68.6 % and 65.8 %, through down-regulation of bile acid transporter (Asbt) and enhancement of fecal excretion. Conversely, UDCA raised their concentrations by 21.9 % and 34.6 % compared to that exposed solely to PFASs. A strong positive correlation was identified between PFASs serum levels and Asbt expression. This study illuminated PFAS bioaccumulation mechanisms and suggested potential strategies to mitigate the exposure risks.

Disruption of zebrafish sex differentiation by emerging contaminants hexafluoropropylene oxides at environmental concentrations via antagonizing androgen receptor pathways

As alternatives of perfluorooctanoic acid (PFOA), hexafluoropropylene oxide dimeric acid (HFPO-DA) and trimeric acid (HFPO-TA) have been detected increasingly in environmental media and even humans. They have been shown to exhibit reproductive toxicity to model species, but their effects on human remain unclear due to the knowledge gap in their mode of action. Herein, (anti-)androgenic effects of the two HFPOs and PFOA were investigated and underlying toxicological mechanism was explored by combining zebrafish test, cell assay and molecular docking simulation. Exposure of juvenile zebrafish to the chemicals during sex differentiation promoted feminization, with HFPO-TA acting at an environmental concentration of 1 μg/L. The chemicals inhibited proliferation of human prostate cells and transcriptional activity of human and zebrafish androgen receptors (AR), with HFPO-TA displaying the strongest potency. Molecular docking revealed that the chemicals bind to AR in a conformation similar to a known AR antagonist. Combined in vivo, in vitro and in silico results demonstrated that the chemicals disrupted sex differentiation likely by antagonizing AR-mediated pathways, and provided more evidence that HFPO-TA is not a safe alternative to PFOA.

Rethinking alternatives to fluorinated pops in aqueous environment and corresponding destructive treatment strategies

Alternatives are being developed to replace fluorinated persistent organic pollutants (POPs) listed in the Stockholm Convention, bypass environmental regulations, and overcome environmental risks. However, the extensive usage of fluorinated POPs alternatives has revealed potential risks such as high exposure levels, long-range transport properties, and physiological toxicity. Therefore, it is imperative to rethink the alternatives and their treatment technologies. This review aims to consider the existing destructive technologies for completely eliminating fluorinated POPs alternatives from the earth based on the updated classification and risks overview. Herein, the types of common alternatives were renewed and categorized, and their risks to the environment and organisms were concluded. The efficiency, effectiveness, energy utilization, sustainability, and cost of various degradation technologies in the treatment of fluorinated POPs alternatives were reviewed and evaluated. Meanwhile, the reaction mechanisms of different fluorinated POPs alternatives are systematically generalized, and the correlation between the structure of alternatives and the degradation characteristics was discussed, providing mechanistic insights for their removal from the environment. Overall, the review supplies a theoretical foundation and reference for the control and treatment of fluorinated POPs alternatives pollution.

A review on the advancement in photocatalytic degradation of poly/perfluoroalkyl substances in water: Insights into the mechanisms and structure-function relationship

Poly/perfluoroalkyl substances (PFAS) are persistent organic pollutants and ubiquitous in aquatic environment, which are hazardous to organisms and human health. Several countries and regions have taken actions to regulate or limit the production and emission of some PFAS. Even though a series of water treatment technologies have been developed for removal of PFAS to eliminate their potential adverse effects, the removal and degradation performance are usually unsatisfactory. Photocatalytic degradation of PFAS is considered as one of the most effective approaches due to the mild operation conditions and environmental friendliness. This review systematically summarized the recent advances in photocatalytic degradation of PFAS based on heterogeneous photocatalysts, including TiO2-, Ga2O3-, In2O3-, ZnO-, Bi-based, and others. Overall, two mainly degradation mechanisms were involved, including photo-oxidation (involving the holes and oxidative radicals) and photo-reduction types (by e- and reductive radicals). The band structures of the photocatalysts, degradation pathways, structure-function relationship, and impacting factors were further discussed to elucidate the essential reasons for the enhanced degradation of PFAS. Furthermore, the review identified the major knowledge gaps to solve the issues of photocatalysis in real application. This paper also propounded several strategies to promote the design and optimization of high-efficient photocatalysts, and meet the challenges to remove PFAS through photodegradation technologies.

Persistent metabolic toxicities following developmental exposure to hexafluoropropylene oxide trimer acid (HFPO-TA): Roles of peroxisome proliferator activated receptor gamma

BACKGROUND

Hexafluoropropylene oxide trimer acid (HFPO-TA), a perfluorooctanoic acid (PFOA) substitute, exhibited strong affinity and capability to activate peroxisome proliferator activated receptor gamma (PPARγ), a lipid metabolism regulator, suggesting potential to induce metabolic toxicities.

METHODS

Fertile chicken eggs were exposed to 0, 0.5, 1 or 2 mg/kg (egg weight) HFPO-TA and incubated until hatch. Serum from 0- and 3- month-old chickens were subjected to liquid chromatography ultra-high resolution mass spectrometry for HFPO-TA concentration, while liver, pancreas and adipose tissue samples were collected for histopathological assessments. In ovo PPARγ reporter and silencing system were established with lentivirus microinjection. qRT-PCR and immunohistochemistry were utilized to evaluate the expression levels of PPARγ downstream genes.

RESULTS

In 3-month-old animals developmentally exposed to HFPO-TA, adipose tissue hyperplasia, hepatic steatosis, pancreas islet hypertrophy and elevated serum free fatty acid / insulin levels were observed. Results of reporter assay and qRT-PCR indicated HFPO-TA-mediated PPARγ transactivation in chicken embryo. Silencing of PPARγ alleviated HFPO-TA-induced changes, while PPARγ agonist rosiglitazone mimicked HFPO-TA-induced effects. qRT-PCR and immunohistochemistry revealed that FASN and GPD1 were upregulated following developmental exposure to HFPO-TA in 3-month-old animals.

CONCLUSIONS

Developmental exposure to HFPO-TA induced persistent metabolic toxicities in chickens, in which PPARγ played a central role.

Comparative steroidogenic effects of hexafluoropropylene oxide trimer acid (HFPO-TA) and perfluorooctanoic acid (PFOA): Regulation of histone modifications

As a widely used alternative to perfluorooctanoic acid (PFOA), hexafluoropropylene oxide trimer acid (HFPO-TA) has been detected in the environment and humans; however, little is known regarding its male reproductive toxicity. To compare the effects of HFPO-TA on steroid hormone synthesis with PFOA, we exposed Leydig cells (MLTC-1) to non-lethal doses (0.1, 1, and 10 μM) of PFOA and HFPO-TA for 48 h. It was found that the levels of steroid hormones, 17α-hydroxyprogesterone (OHP), androstenedione (ASD), and testosterone (T) were significantly increased in 1 and 10 μM of PFOA and HFPO-TA groups, with greater elevation being observed in the HFPO-TA groups than in the PFOA groups at 10 μM. We further showed that the two rate-limiting steroidogenic genes (Star and Cyp11a1) were up-regulated, while Hsd3b, Cyp17a1, and Hsd17b were down-regulated or unchanged after PFOA/HFPO-TA exposure. Moreover, PFOA exposure significantly up-regulated histone H3K4me1/3 and H3K9me1, while down-regulated H3K4me2 and H3K9me2/3 levels. By contrast, H3K4me2/3 and H3K9me2/3 were enhanced, while H3K4me1 and H3K9me1 were repressed after HFPO-TA treatment. It was further confirmed that H3K4me1/3 were increased and H3K9me2 was decreased in Star and Cyp11a1 promoters by PFOA, while HFPO-TA increased H3K4me2/3 and decreased H3K9me1 in the two gene promoters. Therefore, we propose that low levels of PFOA/HFPO-TA enhance the expression of Star and Cyp11a1 by regulating H3K4 and H3K9 methylation, thus stimulating the production of steroid hormones in MLTC-1 cells. Collectively, HFPO-TA exhibits stronger effects on steroidogenesis compared to PFOA, which may be ascribed to the distinct regulation of histone modifications. These data suggest that HFPO-TA does not appear to be a safer alternative to PFOA on the aspect of male reproductive toxicity.

Transcriptome and Metabolome analysis reveal HFPO-TA induced disorders of hepatic glucose and lipid metabolism in rat by interfering with PPAR signaling pathway

PFOA is one of the most representative compounds in the family of perfluorinated organic compounds. Due to its varying toxicity, alternatives to PFOA are beginning to emerge. HFPO-TA is an alternative for PFOA. It is currently unclear whether HFPO-TA affects glucose and lipid metabolism. In this study, rats were used as an animal model to investigate the effects of HFPO-TA on liver glucose and lipid metabolism. We found that HFPO-TA can affect glucose tolerance. Through omics analysis and molecular detection, it was found that HFPO-TA mainly affects the PPAR signaling pathway in the liver of rats, inhibiting liver glycolysis while promoting glucose production. HFPO-TA not only promotes the synthesis of fatty acids in the liver, but also promotes the breakdown of fatty acids, which ultimately leads to the disruption of hepatic glucose and lipid metabolism. The effects of HFPO-TA on metabolism are discussed in this paper to provide a reference for the risk assessment of this PFOA substitute.

Accumulation features and temporal trends (2002-2015) for legacy and emerging per- and polyfluoroalkyl substances (PFASs) in finless porpoises bycaught off Korean coasts

Legacy and emerging per- and polyfluoroalkyl substances (PFASs) were measured in livers of finless porpoises (Neophocaena asiaeorientalis; n = 167) collected in Korean waters from 2002 to 2015 to investigate their occurrence, bioaccumulation feature, temporal trends, and ecotoxicological implications. Perfulorooctane sulfonate (PFOS), perfluoroundecanoate (PFUnDA), and perfluorotridecanoate (PFTrDA) were the predominant PFASs found in the porpoises. The concentration of 6:2 chlorinated polyfluoroalkyl ether sulfonate (F-53B), an alternative to PFOS, was comparable to that of PFTrDA. Perfluorooctane sulfonamide (FOSA), a precursor of PFOS, was also detected in all the porpoises examined. All PFASs, including F-53B, accumulated to higher concentrations in immature porpoises compared with mature specimens, implying substantial maternal transfer and limited metabolizing capacity for PFASs. A significant correlation was observed between PFOS and F-53B concentrations, indicating similar bioaccumulation processes. Based on prenatal exposure and toxicity, F-53B is an emerging contaminant in marine ecosystems. Significantly increasing trends were observed in the concentrations of sulfonates, carboxylates, and F-53B between 2002/2003 and 2010, whereas the FOSA concentration significantly decreased. During 2010-2015, decreasing trends were observed in the concentrations of FOSA and sulfonates, whereas concentrations of carboxylate and F-53B increased without statistical significance, likely due to a gap for the implementation of regulatory actions between sulfonates and carboxylates. Although PFOS and PFOA were found to pose little health risk to porpoises, the combined toxicological effects of other contaminants should be considered to protect populations and to mitigate PFAS contamination in marine ecosystems.

Hexafluoropropylene oxide trimer acid, a perfluorooctanoic acid alternative, induces cardiovascular toxicity in zebrafish embryos

As an increasingly used alternative to perfluorooctanoic acid (PFOA), hexafluoropropylene oxide trimer acid (HFPO-TA) has been widely detected in global water environments. However, little is known regarding its toxic effects on cardiovascular development. Here, zebrafish embryos were treated with egg water containing 0, 60, 120, or 240 mg/L HFPO-TA. Results showed that HFPO-TA treatment led to a significant reduction in both larval survival percentage and heart rate. Furthermore, HFPO-TA exposure caused severe pericardial edema and elongation of the sinus venous to bulbus arteriosus distance (SV-BA) in Tg (myl7: GFP) transgenic larvae, disrupting the expression of genes involved in heart development and thus causing abnormal heart looping. Obvious sprouting angiogenesis was observed in the 120 and 240 mg/L exposed Tg (fli: GFP) transgenic larvae. HFPO-TA treatment also impacted the mRNA levels of genes involved in the vascular endothelial growth factor (VEGF) pathway and embryonic vascular development. HFPO-TA exposure significantly decreased erythrocyte number in Tg (gata1: DsRed) transgenic embryos and influenced gene expression associated with the heme metabolism pathway. HFPO-TA also induced oxidative stress and altered the transcriptional levels of genes related to cell cycle and apoptosis, inhibiting cell proliferation while promoting apoptosis. Therefore, HFPO-TA exposure may induce abnormal development of the cardiovascular and hematopoietic systems in zebrafish embryos, suggesting it may not be a suitable or safe alternative for PFOA.

The hepatotoxicity of hexafluoropropylene oxide trimer acid caused by apoptosis via endoplasmic reticulum-mitochondrial crosstalk

As a ubiquitous pollutant in the environment, hexafluoropropylene oxide trimer acid (HFPO-TA) has been proven to have strong hepatotoxicity. However, the underlying mechanism is still unclear. Consequently, in vivo and in vitro models of HFPO-TA exposure were established to investigate the detrimental effects of HFPO-TA on the liver. In vivo, we discovered that HFPO-TA enhanced endoplasmic reticulum (ER)-mitochondrial association, caused mitochondrial oxidative damage, activated ER stress, and induced apoptosis in mouse livers. In vitro experiments confirmed that IP3R overexpression on ER structure increased mitochondrial calcium levels, which led to mitochondrial damage and mitochondria-dependent apoptosis in HepG2 cells exposed to HFPO-TA. Subsequently, damaged mitochondria released a large amount of mitochondrial ROS, which activated ER stress and ER stress-dependent apoptosis. In conclusion, this study demonstrates that HFPO-TA can induce apoptosis by regulating the crosstalk between ER and mitochondria, ultimately leading to liver damage. These findings reveal the significant hepatotoxicity of HFPO-TA and its potential mechanisms.

Nationwide distribution of perfluoroalkyl ether carboxylic acids in Chinese diets: An emerging concern

With the phase-out of perfluorooctanoic acid (PFOA) and its replacement by perfluoroalkyl ether carboxylic acids (PFECAs), there is a potential for increased exposure to various new PFECAs among the general population in China. While there are existing studies on dietary exposure to legacy perfluoroalkyl and polyfluoroalkyl substances (PFASs), research on dietary exposure to PFECAs, especially among the general Chinese populace, remains scarce. In the present study, we investigated the distribution of PFECAs in dietary sources from 33 cities across five major regions in China, along with the associated dietary intake. Analysis indicated that aquatic animal samples contained higher concentrations of legacy PFASs compared to those from terrestrial animals and plants. In contrast, PFECAs were found in higher concentrations in plant and terrestrial animal samples. Notably, hexafluoropropylene oxide dimer (HFPO-DA) was identified as the dominant compound in vegetables, cereals, pork, and mutton across the five regions, suggesting widespread dietary exposure. PFECAs constituted the majority of PFAS intake (57 %), with the estimated daily intake (EDI) of HFPO-DA ranging from 2.33 to 3.96 ng/kg bw/day, which corresponds to 0.78-1.32 times the reference dose (RfD) (3.0 ng/kg bw/day) set by the United States Environmental Protection Agency. Given the ubiquity of HFPO-DA and many other PFECAs in the nationwide diet of China, there is an urgent need for further research into these chemicals to establish relevant safety benchmarks or consumption advisory values for the diet.

Suspect, Nontarget Screening, and Toxicity Prediction of Per- and Polyfluoroalkyl Substances in the Landfill Leachate

Landfills are the final stage of urban wastes containing perfluoroalkyl and polyfluoroalkyl substances (PFASs). PFASs in the landfill leachate may contaminate the surrounding groundwater. As major environmental pollutants, emerging PFASs have raised global concern. Besides the widely reported legacy PFASs, the distribution and potential toxic effects of numerous emerging PFASs remain unclear, and unknown PFASs still need discovery and characterization. This study proposed a comprehensive method for PFAS screening in leachate samples using suspect and nontarget analysis. A total of 48 PFASs from 10 classes were identified; nine novel PFASs including eight chloroperfluoropolyether carboxylates (Cl-PFPECAs) and bistriflimide (HNTf2) were reported for the first time in the leachate, where Cl-PFPECA-3,1 and Cl-PFPECA-2,2 were first reported in environmental media. Optimized molecular docking models were established for prioritizing the PFASs with potential activity against peroxisome proliferator-activated receptor α and estrogen receptor α. Our results indicated that several emerging PFASs of N-methyl perfluoroalkyl sulfonamido acetic acids (N-MeFASAAs), n:3 fluorotelomer carboxylic acid (n:3 FTCA), and n:2 fluorotelomer sulfonate (n:2 FTSA) have potential health risks that cannot be ignored.

Emerging and legacy per- and polyfluoroalkyl substances (PFAS) in fluorochemical wastewater along full-scale treatment processes: Source, fate, and ecological risk

The increasing applications of emerging per- and polyfluoroalkyl substances (PFAS) have raised global concern. However, the release of emerging PFAS from the fluorochemical industry remains unclear. Herein, the occurrence of 48 emerging and legacy PFAS in wastewater from 10 fluorochemical manufacturers and mass flows of PFAS in a centralized wastewater treatment plant were investigated. Their distribution and ecological risk in neighboring riverine water were also evaluated. In wastewater from fluorochemical manufacturers, PFAS concentrations were in the range of 14,700-5200,000 ng/L and 2 H,2 H-perfluorooctanoic acid (6:2 FTCA), perfluorooctanoic acid (PFOA), N-ethyl perfluorooctane sulfonamide (N-EtFOSA), and 1 H,1 H,2 H,2 H-perfluorodecanesulfonate (8:2 FTS) were the major PFAS detected. Several PFAS displayed increased mass flows after wastewater treatment, especially PFOA and 6:2 FTCA. The mass flows of PFAS increased from - 20% to 233% after the activated sludge system but decreased by only 0-13% after the activated carbon filtration. In riverine water, PFAS concentrations were in the range of 5900-39,100 ng/L and 6:2 FTCA, 1 H,1 H,2 H,2 H-perfluorodecyl phosphate monoester (8:2 monoPAP), 1 H,1 H,2 H,2 H-perfluorooctyl phosphate monoester (6:2 monoPAP), PFOA, and perfluorohexanoic acid (PFHxA) were the major PFAS detected. PFOA and 6:2 FTCA exhibited comparable hazard quotients for ecological risk. Current wastewater treatment processes cannot fully remove various PFAS discharged by fluorochemical manufacturers, and further investigations on their risk are needed for better chemical management.

GenX analogs exposure induced greater hepatotoxicity than GenX mainly via activation of PPARα pathway while caused hepatomegaly in the absence of PPARα in female mice

Despite their use as substitutes for perfluorooctanoic acid, the potential toxicities of hexafluoropropylene oxide dimer acid (HFPO-DA, commercial name: GenX) and its analogs (PFDMOHxA, PFDMO2HpA, and PFDMO2OA) remain poorly understood. To assess the hepatotoxicity of these chemicals on females, each chemical was orally administered to female C57BL/6 mice at the dosage of 0.5 mg/kg/d for 28 d. The contribution of peroxisome proliferator-activated receptors (PPARα and γ) and other nuclear receptors involving in these toxic effects of GenX and its analogs were identified by employing two PPAR knockout mice (PPARα-/- and PPARγΔHep) in this study. Results showed that the hepatotoxicity of these chemicals increased in the order of GenX < PFDMOHxA < PFDMO2HpA < PFDMO2OA. The increases of relative liver weight and liver injury markers were significantly much lower in PPARα-/- mice than in PPARα+/+ mice after GenX analog exposure, while no significant differences were observed between PPARγΔHep and its corresponding wildtype groups (PPARγF/F mice), indicating that GenX analog induce hepatotoxicity mainly via PPARα instead of PPARγ. The PPARα-dependent complement pathways were inhibited in PFDMO2HpA and PFDMO2OA exposed PPARα+/+ mice, which might be responsible for the observed liver inflammation. In PPARα-/- mice, hepatomegaly and increased liver lipid content were observed in PFDMO2HpA and PFDMO2OA treated groups. The activated pregnane X receptor (PXR) and constitutive activated receptor (CAR) pathways in the liver of PPARα-/- mice, which were highlighted by bioinformatics analysis, provided a reasonable explanation for hepatomegaly in the absence of PPARα. Our results indicate that GenX analogs could induce more serious hepatotoxicity than GenX whether there is a PPARα receptor or not. These chemicals, especially PFDMO2HpA and PFDMO2OA, may not be appropriate PFOA alternatives.

Per- and polyfluoroalkyl substance (PFAS) mixtures induce gut microbiota dysbiosis and metabolic disruption in silkworm (Bombyx mori L.)

Mixed legacy and emerging per- and polyfluoroalkyl substances (PFASs) are commonly found in soil and dust; however, the potential toxicity of PFAS mixtures (mPFASs) in insects is unknown. Using 16S rRNA gene sequencing and transcriptome sequencing (RNA-Seq), we evaluated the adverse effects of mPFASs on silkworms, a typical lepidopteran insect. After exposure to mPFASs, the silkworm midgut was enriched with high levels of PFASs, which induced histopathological changes. The composition of the midgut microbiota was significantly affected by mPFAS exposure, and functional predictions revealed significant disruption of some metabolic pathways. RNA-seq analysis revealed that mPFASs significantly changed the transcription profiles. Functional enrichment analysis of the differentially expressed genes also revealed that biological processes related to metabolic pathways and the digestive system were significantly affected, similar to the results of the gut microbiota analysis, suggesting that mPFAS exposure had an adverse effect on the metabolic function of silkworms and may further affect their normal growth. Finally, the significant correlation between abundance changes in the gut microbiota and metabolism/digestion-related genes further highlighted the role of the gut microbiota in mPFAS-related processes affecting the metabolic functions of silkworms. To our knowledge, this study is the first to evaluate the toxic effects of mPFASs in insects and provide basic data for further PFAS toxicity investigations in insects and comprehensive ecological risk assessments of mPFASs.

Adverse effects of gestational exposure to hexafluoropropylene oxide trimer acid (HFPO-TA) homologs on maternal, fetal, and placental health in mice

In an effort to identify and develop potential alternatives for perfluorooctanoic acid (PFOA), PFDMO2HpA and PFDMO2OA have been engineered by reducing the -CF2 content in the molecular structure of hexafluoropropylene oxide trimer acid (HFPO-TA). Yet, despite their subsequent presence in environmental samples, there is a paucity of information regarding their toxicity, particularly on pregnancy. Here, pregnant CD-1 mice were exposed to PFDMO2HpA (0, 0.04, 0.16, 0.63, 2.5, or 10 mg/kg/day) or PFDMO2OA (0, 0.01, 0.04, 0.16, 0.63, or 2.5 mg/kg/day) via oral gavage from gestational days 2 (GD2) to 12 or 18 to evaluate the detrimental effects on dams and embryo-placenta units. Both two chemicals can transfer across the placenta, with a higher transfer ratio in late-pregnancy (GD18) than in mid-pregnancy (GD12), and PFDMO2OA being transferred at a higher rate than PFDMO2HpA. PFDMO2HpA/PFDMO2OA exposure caused maternal hepatotoxicity and fetal hepatomegaly, showing the lowest no-observed-adverse-effect level among all observed endpoints, which were used for calculating their reference dose (13.33 ng/kg/day). In the 2.5 and 10 mg/kg/day PFDMO2HpA groups as well as 2.5 mg/kg/day PFDMO2OA group at GD18, besides the abnormally high abortion rates exceeding 5 %, survival fetal weight was notably reduced (2.33 %, 6.44 %, and 5.59 % decrease relative to corresponding controls, respectively). Concurrently, placentas exhibited significant enlargement following PFDMO2HpA or PFDMO2OA exposure at doses of 0.63 mg/kg/day or higher, resulting in diminished placental efficiency. The deleterious effects of two chemicals on dams, fetuses, and placentas were stronger than that of PFOA or HFPO-DA, suggesting that neither PFDMO2HpA nor PFDMO2OA is suitable PFOA alternative. Bioinformatics analyses revealed significant alterations in the expression of genes involved in inflammation and immunity in the placenta upon exposure to 10 mg/kg/day PFDMO2HpA and 2.5 mg/kg/day PFDMO2OA at GD18, potentially elucidating mechanism behind the observed decrease in placental efficiency and increase in abortion rates after exposure.

Prenatal exposure to hexafluoropropylene oxide trimer acid (HFPO-TA) disrupts the maternal gut microbiome and fecal metabolome homeostasis

Initially considered a "safe" substitute for perfluorooctanoic acid (PFOA), hexafluoropropylene oxide trimer acid (HFPO-TA) has been extensively used in the production of fluoropolymers for several years, leading to its environmental ubiquity and subsequent discovery of its significant bio-accumulative properties and toxicological effects. However, the specific impact of HFPO-TA on females, particularly those who are pregnant, remains unclear. In the present study, pregnant mice were exposed to 0.63 mg/kg/day HFPO-TA from gestational day (GD) 2 to GD 18. We then determined the potential effects of exposure on gut microbiota and fecal metabolites at GD 12 (mid-pregnancy) and GD 18 (late pregnancy). Our results revealed that, in addition to liver damage, HFPO-TA exposure during the specified window altered the structure and function of cecal gut microbiota. Notably, these changes showed the opposite trends at GD 12 and GD 18. Specifically, at GD 12, HFPO-TA exposure primarily resulted in the down-regulation of relative abundances within genera from the Bacteroidetes and Proteobacteria phyla, as well as associated Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. With extended exposure time, the down-regulated genera within Proteobacteria became significantly up-regulated, accompanied by corresponding up-regulation of human disease- and inflammation-associated pathways, suggesting that HFPO-TA exposure can induce intestinal inflammation and elevate the risk of infection during late pregnancy. Pearson correlation analysis revealed that disturbances in the gut microbiota were accompanied by abnormal fecal metabolite. Additionally, alterations in hormones related to the steroid hormone biosynthesis pathway at both sacrifice time indicated that HFPO-TA exposure might change the steroid hormone level of pregnant mice, but need further study. In conclusion, this study provides new insights into the mechanisms underlying HFPO-TA-induced adverse effects and increases awareness of potential persistent health risks to pregnant females.

Kynurenic Acid Plays a Protective Role in Hepatotoxicity Induced by HFPO-DA in Male Mice

Following its introduction as an alternative to perfluorooctanoic acid, hexafluoropropylene oxide dimer acid (HFPO-DA) has been extensively detected in various environmental matrices. Despite this prevalence, limited information is available regarding its hepatotoxicity biomarkers. In this study, toxicokinetic simulations indicated that under repeated treatment, HFPO-DA in mice serum reached a steady state by the 4th day. To assess its subacute hepatic effects and identify potential biomarkers, mice were administered HFPO-DA orally at doses of 0, 0.1, 0.5, 2.5, 12.5, or 62.5 mg/kg/d for 7 d. Results revealed that the lowest observed adverse effect levels were 0.5 mg/kg/d for hepatomegaly and 2.5 mg/kg/d for hepatic injury. Serum metabolomics analysis identified 34, 58, and 118 differential metabolites in the 0.1, 0.5, and 2.5 mg/kg/d groups, respectively, compared to the control group. Based on weighted gene coexpression network analysis, eight potential hepatotoxicity-related metabolites were identified; among them, kynurenic acid (KA) in mouse serum exhibited the highest correlation with liver injury. Furthermore, liver-targeted metabolomics analysis demonstrated that HFPO-DA exposure induced metabolic migration of the kynurenine pathway from KA to nicotinamide adenine dinucleotide, resulting in the activation of endoplasmic reticulum stress and the nuclear factor kappa-B signaling pathway. Notably, pretreatment with KA significantly attenuated liver injury induced by HFPO-DA exposure in mice, highlighting the pivotal roles of KA in the hepatotoxicity of HFPO-DA.

Dietary exposure to per- and polyfluoroalkyl substances: Potential health impacts on human liver

Per- and polyfluoroalkyl substances (PFAS), dubbed "forever chemicals", are widely present in the environment. Environmental contamination and food contact substances are the main sources of PFAS in food, increasing the risk of human dietary exposure. Numerous epidemiological studies have established the link between dietary exposure to PFAS and liver disease. Correspondingly, PFAS induced-hepatotoxicity (e.g., hepatomegaly, cell viability, inflammation, oxidative stress, bile acid metabolism dysregulation and glycolipid metabolism disorder) observed from in vitro models and in vivo rodent studies have been extensively reported. In this review, the pertinent literature of the last 5 years from the Web of Science database was researched. This study summarized the source and fate of PFAS, and reviewed the occurrence of PFAS in food system (natural and processed food). Subsequently, the characteristics of human dietary exposure PFAS (population characteristics, distribution trend, absorption and distribution) were mentioned. Additionally, epidemiologic evidence linking PFAS exposure and liver disease was alluded, and the PFAS-induced hepatotoxicity observed from in vitro models and in vivo rodent studies was comprehensively reviewed. Lastly, we highlighted several critical knowledge gaps and proposed future research directions. This review aims to raise public awareness about food PFAS contamination and its potential risks to human liver health.

Binding interaction of environmental DNA with typical emerging perfluoroalkyl acids and its impact on bioavailability

As the replacement compounds of perfluoroalkyl acids (PFAAs), emerging PFAAs generally exhibit equal or more hazardous toxicity than legacy PFAAs. Numerous DNA as environmental organic matters coexists with emerging PFAAs, but their interactions and the resulting interaction impacts on the bioavailability of emerging PFAAs remain insufficiently understood. Here, we studied the binding strength and mechanism between DNA and emerging PFAAs (perfluorobutyric acid, perfluorobutylsulfonic acid, and hexafluoropropylene oxide dimer acid) using perfluorooctanoic acid as the control, and further investigated the impacts of DNA binding on the bioavailability of the emerging PFAAs. Isothermal titration calorimetry and quantum chemical calculation found that the emerging PFAAs could bind with DNA bases (main thymine) by van der Waals force and halogen-bond, showing the binding affinities in the range of 7.87 × 104 to L/mol to 6.54 × 106 L/mol. The PFAAs-DNA binding significantly decreased the bioavailability of the PFAAs in both seedlings and plants of pakchoi (Brassica chinensis L.), with little differences in bioavailability change extent among PFAAs. The findings highlight the universality and similarity of the DNA binding effects on PFAAs bioavailability, which can be the natural detoxification mechanism for response to the PFAAs pollution.

Adipogenic and osteogenic effects of OBS and synergistic action with PFOS via PPARγ-RXRα heterodimers

Sodium p-perfluorous nonenoxybenzenesulfonate (OBS) is a novel alternative to perfluorooctane sulfonate (PFOS), with environmental health risks largely unknown. The present study aims to unravel the adipogenesis effects and underlying molecular initiating events of OBS, which are crucial for understanding and predicting its adverse outcome. In undifferentiated human mesenchymal stem cells (hMSCs), exposure to 1-100 nM of OBS for 7 days stimulated reactive oxygen species production. In the subsequent multipotent differentiation, hMSCs favored adipogenesis and repressed osteogenesis. The point of departure (PoD) for cellular responses of OBS was 38.85 nM, higher than PFOS (0.39 nM). Notably, OBS/PFOS co-exposure inhibited osteogenesis and synergistically promoted adipogenesis. Consistently, the expression of adipogenic marker genes was up-regulated, while that of osteogenic marker genes was down-regulated. The decreased adiponectin and elevated tumor necrosis factor α (TNFα) secretion were observed in differentiated cells exposed to the mixture of OBS and PFOS. The co-treatment of a peroxisome proliferator-activated receptor γ (PPARγ) antagonist alleviated the adipogenic effects of PFOS and its combination with OBS. Moreover, OBS/PFOS co-exposure induced peroxisome PPARγ activation in reporter gene assays, and increased formation of PPARγ - retinoid X receptor α (RXRα) heterodimers measured by co-immunoprecipitation assays. Molecular docking showed interaction energy of OBS (-20.7 kcal/mol) with intact PPARγ-RXRα complex was lower than that of PFOS (-25.9 kcal/mol). Overall, single OBS exhibited lower potency in inducing adipogenesis but is comparable to PFOS in repressing osteogenesis, whereas OBS/PFOS co-exposure increases interaction with PPARγ-RXRα heterodimers, resulting in the synergistic activation of PPARγ, ultimately enhancing adipogenesis at the expense of osteogenic differentiation. The results indicate the potential health risks of increased obesity and decreased bone density caused by OBS and its co-exposure with PFOS, as well as other perfluorinated alkylated substances mixtures.

Hexafluoropropylene oxide trimer acid exposure triggers necroptosis and inflammation through the Wnt/β-catenin/NF-κB axis in the liver

Hexafluoropropylene oxide trimer acid (HFPO-TA), an emerging alternative to perfluorooctanoic acid (PFOA), has recently been identified as a significant environmental pollutant. Nevertheless, there is a scarcity of studies regarding the hepatotoxic effects of HFPO-TA. Here, we investigated the types and potential mechanisms of liver damage caused by HFPO-TA. Initially, we validated that the introduction of HFPO-TA resulted in the Wnt/β-catenin signaling (W/β signaling) activation, as well as the induction of necroptosis and inflammation, both in the liver of mice and in HepG2 cells. Subsequently, we established that the W/β signaling mediated the necroptosis and inflammation observed in the liver and HepG2 cells exposed to HFPO-TA. Finally, we demonstrated that the phosphorylated form of NF-κB p65 (p-NF-κB p65) played a role in mediating the necroptosis and inflammation, and its activity could be regulated by the W/β signaling pathway in the liver of mice and HepG2 cells exposed to HFPO-TA. In conclusion, our investigation elucidates the role of HFPO-TA in inducing necroptosis and inflammation in the liver, which is facilitated through the activation of the W/β/NF-κB axis.

Comprehensive Assessment of Exposure Pathways for Perfluoroalkyl Ether Carboxylic Acids (PFECAs) in Residents Near a Fluorochemical Industrial Park: The Unanticipated Role of Cereal Consumption

With the replacement of perfluorooctanoic acid (PFOA) with perfluorinated ether carboxylic acids (PFECAs), residents living near fluorochemical industrial parks (FIPs) are exposed to various novel PFECAs. Despite expectations of low accumulation, short-chain PFECAs, such as perfluoro-2-methoxyacetic acid (PFMOAA), previously displayed a considerably high body burden, although the main exposure routes and health risks remain uncertain. Here, we explored the distribution of perfluoroalkyl and polyfluoroalkyl substances (PFASs) in diverse environmental media surrounding a FIP in Shandong Province, China. PFECAs were found at elevated concentrations in all tested matrices, including vegetables, cereals, air, and dust. Among residents, 99.3% of the ∑36PFAS exposure, with a 43.9% contribution from PFECAs, was due to gastrointestinal uptake. Dermal and respiratory exposures were negligible at 0.1 and 0.6%, respectively. The estimated daily intake (EDI) of PFMOAA reached 114.0 ng/kg body weight (bw)/day, ranking first among all detected PFECAs. Cereals emerged as the dominant contributor to PFMOAA body burden, representing over 80% of the overall EDI. The median EDI of hexafluoropropylene oxide dimer acid (HFPO-DA) was 17.9 ng/kg bw/day, markedly higher than the USEPA reference doses (3.0 ng/kg bw/day). The absence of established threshold values for other PFECAs constrains a comprehensive risk assessment.

Toxicity of decabromodiphenyl ethane on lettuce: Evaluation through growth, oxidative defense, microstructure, and metabolism

Decabromodiphenyl ethane (DBDPE) as the most widely used novel brominated flame retardants (NBFRs), has become a ubiquitous emerging pollutant in the environment. However, its toxic effects on vegetable growth during agricultural production have not been reported. In this study, we investigated the response mechanisms of hydroponic lettuce to DBDPE accumulation, antioxidant stress, cell structure damage, and metabolic pathways after exposure to DBDPE. The concentration of DBDPE in the root of lettuce was significantly higher than that in the aboveground part. DBDPE induced oxidative stress on lettuce, which stimulated the defense of the antioxidative system of lettuce cells, and the cell structure produced slight plasma-wall separation. In terms of metabolism, metabolic pathway disorders were caused, which are mainly manifested as inhibiting amino acid biosynthesis and metabolism-related pathways, interfering with the biosyntheses of amino acids, organic acids, fatty acids, carbohydrates, and other substances, and ultimately manifested as decreased total chlorophyll content and root activity. In turn, metabolic regulation alleviated antioxidant stress. The mechanisms of the antioxidative reaction of lettuce to DBDPE were elucidated by IBR, PLS-PM analysis, and molecular docking. Our results provide a theoretical basis and research necessity for the evaluation of emerging pollutants in agricultural production and the safety of vegetables.

Hepatic Transcriptome Comparative In Silico Analysis Reveals Similar Pathways and Targets Altered by Legacy and Alternative Per- and Polyfluoroalkyl Substances in Mice

Per- and poly-fluoroalkyl substances (PFAS) are a large class of fluorinated carbon chains that include legacy PFAS, such as perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), and perfluorohexane sulfonate (PFHxS). These compounds induce adverse health effects, including hepatotoxicity. Potential alternatives to the legacy PFAS (HFPO-DA (GenX), HFPO4, HFPO-TA, F-53B, 6:2 FTSA, and 6:2 FTCA), as well as a byproduct of PFAS manufacturing (Nafion BP2), are increasingly being found in the environment. The potential hazards of these new alternatives are less well known. To better understand the diversity of molecular targets of the PFAS, we performed a comparative toxicogenomics analysis of the gene expression changes in the livers of mice exposed to these PFAS, and compared these to five activators of PPARα, a common target of many PFAS. Using hierarchical clustering, pathway analysis, and predictive biomarkers, we found that most of the alternative PFAS modulate molecular targets that overlap with legacy PFAS. Only three of the 11 PFAS tested did not appreciably activate PPARα (Nafion BP2, 6:2 FTSA, and 6:2 FTCA). Predictive biomarkers showed that most PFAS (PFHxS, PFOA, PFOS, PFNA, HFPO-TA, F-53B, HFPO4, Nafion BP2) activated CAR. PFNA, PFHxS, PFOA, PFOS, HFPO4, HFPO-TA, F-53B, Nafion BP2, and 6:2 FTSA suppressed STAT5b, activated NRF2, and activated SREBP. There was no apparent relationship between the length of the carbon chain, type of head group, or number of ether linkages and the transcriptomic changes. This work highlights the similarities in molecular targets between the legacy and alternative PFAS.

Dose Response, Dosimetric, and Metabolic Evaluations of Replacement PFAS Perfluoro-(2,5,8-trimethyl-3,6,9-trioxadodecanoic) Acid (HFPO-TeA)

Few studies are available on the environmental and toxicological effects of perfluoroalkyl ether carboxylic acids (PFECAs), such as GenX, which are replacing legacy PFAS in manufacturing processes. To collect initial data on the toxicity and toxicokinetics of a longer-chain PFECA, male and female Sprague Dawley rats were exposed to perfluoro-(2,5,8-trimethyl-3,6,9-trioxadodecanoic) acid (HFPO-TeA) by oral gavage for five days over multiple dose levels (0.3-335.2 mg/kg/day). Clinically, we observed mortality at doses >17 mg/kg/day and body weight changes at doses ≤17 mg/kg/day. For the 17 mg/kg/day dose level, T3 and T4 thyroid hormone concentrations were significantly decreased (p < 0.05) from controls and HFPO-TeA plasma concentrations were significantly different between sexes. Non-targeted analysis of plasma and in vitro hepatocyte assay extractions revealed the presence of another GenX oligomer, perfluoro-(2,5-dimethyl-3,6-dioxanonanoic) acid (HFPO-TA). In vitro to in vivo extrapolation (IVIVE) parameterized with in vitro toxicokinetic data predicted steady-state blood concentrations that were within seven-fold of those observed in the in vivo study, demonstrating reasonable predictivity. The evidence of thyroid hormone dysregulation, sex-based differences in clinical results and dosimetry, and IVIVE predictions presented here suggest that the replacement PFECA HFPO-TeA induces a complex and toxic exposure response in rodents.

Synthesis, Surface Activity, and Foamability of Two Short-Chain Fluorinated Sulfonate Surfactants with Ether Bonds

Fluorinated surfactants are widely used in many fields because of their excellent surface active properties, but their high stability has caused many environmental problems. With the ban and restriction of classical long-chain fluorinated surfactants such as perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) worldwide, the development and replacement of their alternatives is now a major challenge. How to reduce environmental persistence, bioaccumulation, and biotoxicity while maintaining high surface activity has become an important issue in the development of fluorinated surfactants. Using short-chain fluorinated surfactants is one of the important solutions to resolve the pollution of organic fluorinated compounds. In this article, we synthesized two short-chain fluorinated surfactants with ether bonds. One of them 6:2 FTESNa (2) used the perfluoroalkyl chain (n-C6F13-) and the other C72 FEESNa (4) used the fluoroether segment with six fluorinated carbons and two oxygens (CF3OCF(CF3)CF2OCF(CF3)). The surface activity, foam performance, and wettability of the two molecules were measured. The surface tensions at critical micelle concentration (γcmc) and the critical micelle concentration (cmc) of 2 and 4 were 17.6 mN/m (2.2 g/L) and 20.2 mN/m (4.6 g/L), respectively. Both of them were significantly superior to the surface activity of 6:2 FTSNa (7) which is one of the current alternatives for PFOS. Additionally, the foamability and foam stability of both 2 and 4 were better than that of 7. In the aspect of wettability on PTFE, that of 4 was greater than those of 2 and 7. In summary, this work provided a new choice for alternatives of PFOS and PFOA.

Underlying Mechanisms for the Sex- and Chemical-Specific Hepatotoxicity of Perfluoroalkyl Phosphinic Acids in Common Carp (Cyprinus carpio)

The hepatotoxicities of perfluoroalkyl and polyfluoroalkyl substances (PFASs) have been extensively investigated, while little is known about the sex-specific differences. In this study, common carp were exposed to the emerging perfluoroalkyl phosphinic acids (6:6 and 8:8 PFPiAs) for 14 days to disclose sex-specific hepatotoxicity. Apparent hepatotoxicity, including cell necrosis, apoptosis, and steatosis, was observed in both male and female carp liver. The observed hepatocyte steatosis was predominantly attributed to the dysregulation of hepatic lipid metabolism but was based on sex-specific mechanisms. It was manifested as inhibited oxidative decomposition of fatty acids (FAs) in the female liver, whereas it enhanced the uptake of FAs into the male liver, both of which led to excessive lipid accumulation. Untargeted lipidomics validated that the metabolism pathways of FA, sphingolipid, glycerolipid, and glycerophospholipid were disrupted by both compounds, leading to the generation of reactive oxygen species and oxidative stress. The oxidative stress further evolved into inflammation, manifested as promoted expression of proinflammatory cytokines and repressed expression of anti-inflammatory cytokines. Consistently, all of the changes were more noticeable in male carp, suggesting that male fish were more susceptible to PFPiA disruption. 8:8 PFPiA was less accumulated but caused stronger hepatotoxicity than 6:6 PFPiA, possibly because of the stronger binding capacity of 8:8 PFPiA to nuclear transcription factors mediating lipid metabolism and inflammation. The findings of this study highlight the significance of sex- and chemical-dependent bioaccumulation and the toxicity of PFASs in organisms.

Toxicity comparison of perfluorooctanoic acid (PFOA), hexafluoropropylene oxide dimer acid (HFPO-DA), and hexafluoropropylene oxide trimer acid (HFPO-TA) in zebrafish gut

Hexafluoropropylene oxide dimer acid (HFPO-DA) and hexafluoropropylene oxide trimer acid (HFPO-TA) are considered as alternatives to perfluorooctanoic acid (PFOA). In this study, zebrafish were exposed to different concentrations of PFOA, HFPO-DA, and HFPO-TA (5 μg/L and 500 μg/L), and the toxic effects on oxidative damage, inflammation, and cell apoptosis in the gut were compared. Additionally, changes in gut metabolome profiles and microbial community structure were analyzed. The results revealed that exposures to HFPO-DA and HFPO-TA led to lower levels of oxidative damage compared to PFOA exposure. However, all three treatments had comparable effects on inflammation and apoptosis. The main biological pathways affected by all three exposures were lipid metabolism, nucleotide metabolism, amino acid metabolism, and environmental information processing. The effects on metabolome profiles were much higher for HFPO-DA and HFPO-TA compared to PFOA at a concentration of 5 μg/L. At a concentration of 500 μg/L, HFPO-DA and HFPO-TA showed similar effects to PFOA. This study also examined the Pearson correlations between gut microbiota and the toxic effects mentioned above. The abundance of specific apoptosis-related genera differed among the three target chemicals, suggesting they may act differently in inducing apoptosis. The correlations between HFPO-DA and HFPO-TA were mostly similar, which helps explain the similar effects observed in their respective treatment groups on metabolic profiles. Overall, this study indicates that HFPO-DA and HFPO-TA may not be safe alternatives to PFOA and provides valuable insights into their toxic effects and risk assessment in water environments.

Accumulation and glucocorticoid signaling suppression by four emerging perfluoroethercarboxylic acids based on animal exposure and cell testing

Various perfluoroethercarboxylic acids (PFECA) have emerged as next-generation replacements of legacy per- and polyfluoroalkyl substances (PFAS). However, there is a paucity of information regarding their bioaccumulation ability and hazard characterization. Here, we explored the accumulation and hepatotoxicity of four PFECA compounds (HFPO-DA, HFPO-TA, PFO4DA, and PFO5DoDA) in comparison to perfluorooctanoic acid (PFOA) after chronic low-dose exposure in mice. Except for HFPO-DA, the levels of all tested PFAS in the liver exceeded that in serum. High molecular weight PFECA compounds (PFO5DoDA and HFPO-TA) showed stronger accumulation capacity and longer half-lives (t1/2) than low molecular weight PFECA compounds (HFPO-DA and PFO4DA) and even legacy PFOA. Although hepatomegaly is a common apical end point of PFAS exposure, the differentially expressed gene (DEG) profiles in the liver suggested significant differences between PFOA and the four PFECA compounds. Gene enrichment analysis supported a considerable inhibitory effect of PFECA, but not PFOA, on the glucocorticoid receptor (GR) signaling pathway. Both HFPO-TA and PFO5DoDA demonstrated a more pronounced ability to perturb RNA expression profiles in vivo and to suppress GR signaling in vitro compared to HFPO-DA and PFO4DA. Calculated reference doses (RfDs) emphasized the potential hazard of PFECA to human health. Overall, our findings indicate that PFECA alternatives do not ease the concerns raised from legacy PFAS pollution.

Transcriptome and Metabolome Analyses Reveal Perfluorooctanoic Acid-Induced Kidney Injury by Interfering with PPAR Signaling Pathway

Perfluorooctanoic acid (PFOA) is widely used in aviation science and technology, transportation, electronics, kitchenware, and other household products. It is stable in the environment and has potential nephrotoxicity. To investigate the effect of PFOA exposure during pregnancy on the kidneys of offspring mice, a total of 20 mice at day 0 of gestation were randomly divided into two groups (10 mice in each group), and each group was administered 0.2 mL of PFOA at a dose of 3.5 mg/kg or deionized water by gavage during gestation. The kidney weight, kidney index, histopathological observation, serum biochemistry, transcriptomics, and metabolomics of the kidneys of the 35-day offspring mice were analyzed. In addition, malondialdehyde (MDA), superoxide dismutase (SOD), and catalase (CAT) levels in the kidney were measured. Transcriptome analysis results showed that 387 genes were up-regulated and 283 genes were down-regulated compared with the control group. These differentially expressed genes (DEGs) were mainly concentrated in the peroxisome-proliferator-activated receptor (PPAR) signaling pathway and circadian rhythm. Compared with the control group, 64 and 73 metabolites were up- and down-regulated, respectively, in the PFOA group. The altered metabolites were mainly enriched in the biosynthesis of unsaturated fatty acids. PFOA can affect the expression levels of circadian rhythm-related genes in the kidneys of offspring mice, and this change is influenced by the PPAR signaling pathway. PFOA causes oxidative stress in the kidneys, which is responsible for significant changes in metabolites associated with the biosynthesis of unsaturated fatty acids.

New Insights into the Accumulation, Transport, and Distribution Mechanisms of Hexafluoropropylene Oxide Homologues, Important Alternatives to Perfluorooctanoic Acid, in Lettuce (Lactuca sativa L.)

Hexafluoropropylene oxide (HFPO) homologues, which are important alternatives to perfluorooctanoic acid, have been frequently identified in crops. Although exposure to HFPO homologues via crops may pose non-negligible threats to humans, their impact on crops is still unknown. In this study, the accumulation, transport, and distribution mechanisms of three HFPO homologues in lettuce were investigated at the plant, tissue, and cell levels. More specifically, HFPO trimer acid and HFPO tetramer acid were primarily fixed in roots and hardly transported to shoots (TF, 0.06-0.63). Conversely, HFPO dimer acid (HFPO-DA) tended to accumulate in lettuce shoots 2-264 times more than the other two homologues, thus resulting in higher estimated daily intake values. Furthermore, the dissolved organic matter derived from root exudate enhanced HFPO-DA uptake by increasing its desorption fractions in the rhizosphere. The transmembrane uptake of HFPO homologues was controlled by means of a transporter-mediated active process involving anion channels, with the uptake of HFPO-DA being additionally facilitated by aquaporins. The higher accumulation of HFPO-DA in shoots was attributed to the larger proportions of HFPO-DA in the soluble fraction (55-74%) and its higher abundance in both vascular tissues and xylem sap. Our findings expand the understanding of the fate of HFPO homologues in soil-crop systems and reveal the underlying mechanisms of the potential exposure risk to HFPO-DA.

Trophic behaviors of PFOA and its alternatives perfluoroalkyl ether carboxylic acids (PFECAs) in a coastal food web

With the increasing restrictions and concerns about legacy poly- and perfluoroalkyl substances (PFAS), the production and usage of alternatives, i.e., perfluoroalkyl ether carboxylic acids (PFECAs), have risen recently. However, there is a knowledge gap regarding the bioaccumulation and trophic behaviors of emerging PFECAs in coastal ecosystems. The bioaccumulation and trophodynamics of perfluorooctanoic acid (PFOA) and its substitutes (PFECAs) were investigated in Laizhou Bay, which is located downstream of a fluorochemical industrial park in China. Hexafluoropropylene oxide trimer acid (HFPO-TrA), perfluoro-2-methoxyacetic acid (PFMOAA) and PFOA constituted the dominant compounds in the ecosystem of Laizhou Bay. PFMOAA was dominant in invertebrates, whereas the long-chain PFECAs preferred to accumulate in fishes. The PFAS concentrations in carnivorous invertebrates were higher than those in filter-feeding species. Considering migration behaviors, the ∑PFAS concentrations followed the order oceanodromous fish < diadromous fish < non-migratory fish. The trophic magnification factors (TMFs) of long-chain PFECAs (HFPO-TrA, HFPO-TeA and PFO5DoA) were >1, suggesting trophic magnification potential, while biodilution for short-chain PFECAs (PFMOAA) was observed. The intake of PFOA in seafood may constitute a great threat to human health. More attention should be given to the impact of emerging hazardous PFAS on organisms for the health of ecosystems and human beings.

Mechanistic Investigations of Thermal Decomposition of Perfluoroalkyl Ether Carboxylic Acids and Short-Chain Perfluoroalkyl Carboxylic Acids

In this study, we investigated the thermal decomposition mechanisms of perfluoroalkyl ether carboxylic acids (PFECAs) and short-chain perfluoroalkyl carboxylic acids (PFCAs) that have been manufactured as replacements for phased-out per- and polyfluoroalkyl substances (PFAS). C-C, C-F, C-O, O-H, and C═C bond dissociation energies were calculated at the M06-2X/Def2-TZVP level of theory. The α-C and carboxyl-C bond dissociation energy of PFECAs declines with increasing chain length and the attachment of an electron-withdrawing trifluoromethyl (-CF3) group to the α-C. Experimental and computational results show that the thermal transformation of hexafluoropropylene oxide dimer acid to trifluoroacetic acid (TFA) occurs due to the preferential cleavage of the C-O ether bond close to the carboxyl group. This pathway produces precursors of perfluoropropionic acid (PFPeA) and TFA and is supplemented by a minor pathway (CF3CF2CF2OCFCF3COOH → CF3CF2CF2· + ·OCFCF3COOH) through which perfluorobutanoic acid (PFBA) is formed. The weakest C-C bond in PFPeA and PFBA is the one connecting the α-C and the β-C. The results support (1) the C-C scission in the perfluorinated backbone as an effective PFCA thermal decomposition mechanism and (2) the thermal recombination of radicals through which intermediates are formed. Additionally, we detected a few novel thermal decomposition products of studied PFAS.

Bile acid metabolism disorder mediates hepatotoxicity of Nafion by-product 2 and perfluorooctane sulfonate in male PPARα-KO mice

Perfluorooctane sulfonate (PFOS) and Nafion by-product 2 (H-PFMO2OSA) induce hepatotoxicity in male mice via activation of the peroxisome proliferator-activated receptor α (PPARα) pathway; however, accumulating evidence suggests that PPARα-independent pathways also play a vital role in hepatotoxicity after exposure to per- and polyfluoroalkyl substances (PFASs). Thus, to assess the hepatotoxicity of PFOS and H-PFMO2OSA more comprehensively, adult male wild-type (WT) and PPARα knockout (PPARα-KO) mice were exposed to PFOS and H-PFMO2OSA (1 or 5 mg/kg/d) for 28 d via oral gavage. Results showed that although elevations in alanine transaminase (ALT) and aspartate aminotransferase (AST) were alleviated in PPARα-KO mice, liver injury, including liver enlargement and necrosis, was still observed after PFOS and H-PFMO2OSA exposure. Liver transcriptome analysis identified fewer differentially expressed genes (DEGs) in the PPARα-KO mice than in the WT mice, but more DEGs associated with the bile acid secretion pathway after PFOS and H-PFMO2OSA treatment. Total bile acid content in the liver was increased in the 1 and 5 mg/kg/d PFOS-exposed and 5 mg/kg/d H-PFMO2OSA-exposed PPARα-KO mice. Furthermore, in PPARα-KO mice, proteins showing changes in transcription and translation levels after PFOS and H-PFMO2OSA exposure were involved in the synthesis, transportation, reabsorption, and excretion of bile acids. Thus, exposure to PFOS and H-PFMO2OSA in male PPARα-KO mice may disturb bile acid metabolism, which is not under the control of PPARα.

Toxicological Mechanisms of Emerging Per-/poly-fluoroalkyl Substances: Focusing on Transcriptional Activity and Gene Expression Disruption

Environmental and human monitoring studies have witnessed increasing occurrence of emerging per-/poly-fluoroalkyl substances (ePFASs) worldwide. Three classes of ePFASs, namely chlorinated polyfluoroalkylether sulfonic acids, hexafluoropropylene oxide homologues and short-chain perfluoroalkyl acids attracted the most attention. It is, therefore, the goal of this review to systematically and critically analyse the toxicity and toxicological mechanisms of these ePFASs based on the papers published between 2017 and 2022. The review summarized the main findings from both in vivo and in vitro studies, covering the hepatotoxicity of ePFASs and their interference with the endocrine system, including reproductive, developmental and thyroid toxicity. It also summarized the changes in gene expression in the hypothalamic-pituitary-thyroid axis and hypothalamic-pituitary-gonad axis of the model organisms after ePFASs exposure. The changes in gene expression in vitro and in vivo provide a clearer understanding of the toxicological mechanisms of ePFASs interference on hormonal levels (i.e., estradiol, testosterone, and thyroid hormones), developmental disturbance (e.g., swim bladder dysfunction) and lipid metabolism disruption (e.g., lipid droplet accumulation and hepatomegaly). In the end, future research directions on the toxicological mechanisms of ePFASs are suggested.

Per/polyfluoroalkyl substances modulate plasmid transfer of antibiotic resistance genes: A balance between oxidative stress and energy support

Emerging contaminants can accelerate the transmission of antibiotic resistance genes (ARGs) from environmental bacteria to human pathogens via plasmid conjugation, posing a great challenge to the public health. Although the toxic effects of per/polyfluoroalkyl substances (PFAS) as persistent organic pollutants have been understood, it is still unclear whether and how PFAS modulate the transmission of ARGs. In this study, we for the first time reported that perfluorooctanoic acid (PFOA), perfluorododecanoic acid (PFDoA) and ammonium perfluoro (2-methyl-3-oxahexanoate) (GenX) at relatively low concentrations (0.01, 0.1 mg/L) promoted the conjugative transfer of plasmid RP4 within Escherichia coli, while the plasmid conjugation was inhibited by PFOA, PFDoA and GenX at relatively high concentrations (1, 10 mg/L). The non-unidirectional conjugation result was ascribed to the co-regulation of ROS overproduction, enhanced cell membrane permeability, shortage of energy support as well as l-arginine pool depletion. Taking the well-known PFOA as an example, it significantly enhanced the conjugation frequency by 1.4 and 3.4 times at relatively low concentrations (0.01, 0.1 mg/L), respectively. Exposure to PFOA resulted in enhanced cell membrane permeability and ROS overproduction in donor cells. At high concentrations of PFOA (1, 10 mg/L), although enhanced oxidative stress and cell membrane permeability still occurred, the ATP contents in E. coli decreased, which contributed to the inhibited conjugation. Transcriptome analysis further showed that the expression levels of genes related to arginine biosynthesis (argA, argC, argF, argG, argI) and transport (artJ, artM, artQ) pathways were significantly increased. Intracellular l-arginine concentration deficiency were observed at high concentrations of PFOA. With the supplementary exogenous arginine, it was demonstrated that arginine upregulated conjugation transfer- related genes (trfAp, trbBp) and restores the cell number of transconjugants in PFOA-treated group. Therefore, the inhibited conjugation at high concentrations PFOA were attributed to the shortage of ATP and the depletion of L-arginine pool. These findings provide important insights into the effect environmental concentrations of PFAS on the conjugative transfer of ARGs, and update the regulation mechanism of plasmid conjugation, which is critical for the management of antibiotic resistance in aquatic environments.

Exposure to PFOA and its novel analogs disrupts lipid metabolism in zebrafish

Perfluorooctanoic acid (PFOA), a typical perfluoroalkyl group compound, has received worldwide attention due to its significant environmental toxicity. Following regulatory bans on the production and emission of PFOA, concerns have been raised about the potential health risks and the safety of novel perfluoroalkyl analogues. HFPO-DA (trade name Gen-X) and HFPO-TA are two perfluoroalkyl analogues known to be bioaccumulative, whose level of toxicity and whether they are safe alternatives to PFOA remain unclear. In the following study, the physiological and metabolic effects of exposure to PFOA and its novel analogues were explored in zebrafish using 1/3 LC₅₀ (PFOA 100 μM, Gen-X 200 μM, HFPO-TA 30 μM). At the same LC₅₀ toxicological effect, exposure to PFOA and HFPO-TA resulted in abnormal phenotypes such as spinal curvature, pericardial edema and aberrant body length, while Gen-X was little changed. Metabolically, PFOA, HFPO-TA and Gen-X all significantly increased total cholesterol in exposed zebrafish with PFOA and HFPO-TA also increasing total triglyceride levels. Transcriptome analysis showed that the number of differentially expressed genes in PFOA, Gen-X, and HFPO-TA treated conditions compared to control groups were 527, 572, and 3, 933, respectively. KEGG and GO analysis of differentially expressed genes revealed pathways and functions related to lipid metabolism as well as significant activation of the peroxisome proliferators-activated receptor (PPARs) pathway. Furthermore, RT-qPCR analysis identified significant dysregulation in the downstream target genes of PPARα, which is responsible for lipid oxidative catabolism, and the SREBP pathway, which is responsible for lipid synthesis. In conclusion, both perfluoroalkyl analogues HFPO-TA and Gen-X exhibit significant physiological and metabolic toxicity to aquatic organisms and their environmental accumulation should be closely regulated.

Fabrication and characterizations of Zn-doped SnO2-Ti4O7 anode for electrochemical degradation of hexafluoropropylene oxide dimer acid and its homologues

Hexafluoropropylene oxide dimer acid (HFPO-DA) and its homologues, as perfluorinated ether alkyl substances with strong antioxidant properties, have rarely been reported by electrooxidation processes to achieve good results. Herein, we report the use of an oxygen defect stacking strategy to construct Zn-doped SnO₂-Ti₄O₇ for the first time and enhance the electrochemical activity of Ti₄O₇. Compared with the original Ti₄O₇, the Zn-doped SnO₂-Ti₄O₇ showed a 64.4% reduction in interfacial charge transfer resistance, a 17.5% increase in the cumulative rate of •OH generation, and an enhanced oxygen vacancy concentration. The Zn-doped SnO₂-Ti₄O₇ anode exhibited high catalytic efficiency of 96.4% for HFPO-DA within 3.5 h at 40 mA/cm². Hexafluoropropylene oxide trimer and tetramer acid exhibit more difficult degradation due to the protective effect of the -CF₃ branched chain and the addition of the ether oxygen atom leading to a significant increase in the C-F bond dissociation energy. The degradation rates of 10 cyclic degradation experiments and the leaching concentrations of Zn and Sn after 22 electrolysis experiments demonstrated the good stability of the electrodes. In addition, the aqueous toxicity of HFPO-DA and its degradation products was evaluated. This study analyzed the electrooxidation process of HFPO-DA and its homologues for the first time, and provided some new insights.

Hexafluoropropylene oxide trimer acid causes fibrosis in mice liver via mitochondrial ROS/cGAS-STING/NLRP3-mediated pyroptosis

Hexafluoropropylene oxide trimer acid (HFPO-TA) causes hepatotoxicity, however, its underlying mechanisms have not been conclusively determined. We investigated the effects of HFPO-TA on mice liver after 28 days of orally administered 0 or 0.5 mg/kg/d HFPO-TA. Administration of HFPO-TA induced mitochondrial ROS (mtROS) overexpression, cGAS-STING signaling activation, pyroptosis and fibrosis in mice liver. To determine the HFPO-TA-associated hepatotoxic mechanisms, mtROS, cGAS-STING signaling and pyroptosis intervention assays were performed in HFPO-TA-exposed mice liver. First, mtROS was found to be an upstream regulatory target of cGAS-STING signaling, pyroptosis and fibrosis. Second, cGAS-STING signaling was established to be an upstream regulatory mechanism of pyroptosis and fibrosis. Finally, pyroptosis was shown to regulate fibrosis. The above results confirm that HFPO-TA causes mice liver fibrosis via mtROS/cGAS-STING/NLRP3-mediated pyroptosis.

Determination of in vitro hepatotoxic potencies of a series of perfluoroalkyl substances (PFASs) based on gene expression changes in HepaRG liver cells

Per- and polyfluoroalkyl substances (PFASs) are omnipresent and have been shown to induce a wide range of adverse health effects, including hepatotoxicity, developmental toxicity, and immunotoxicity. The aim of the present work was to assess whether human HepaRG liver cells can be used to obtain insight into differences in hepatotoxic potencies of a series of PFASs. Therefore, the effects of 18 PFASs on cellular triglyceride accumulation (AdipoRed assay) and gene expression (DNA microarray for PFOS and RT-qPCR for all 18 PFASs) were studied in HepaRG cells. BMDExpress analysis of the PFOS microarray data indicated that various cellular processes were affected at the gene expression level. From these data, ten genes were selected to assess the concentration-effect relationship of all 18 PFASs using RT-qPCR analysis. The AdipoRed data and the RT-qPCR data were used for the derivation of in vitro relative potencies using PROAST analysis. In vitro relative potency factors (RPFs) could be obtained for 8 PFASs (including index chemical PFOA) based on the AdipoRed data, whereas for the selected genes, in vitro RPFs could be obtained for 11-18 PFASs (including index chemical PFOA). For the readout OAT5 expression, in vitro RPFs were obtained for all PFASs. In vitro RPFs were found to correlate in general well with each other (Spearman correlation) except for the PPAR target genes ANGPTL4 and PDK4. Comparison of in vitro RPFs with RPFs obtained from in vivo studies in rats indicate that best correlations (Spearman correlation) were obtained for in vitro RPFs based on OAT5 and CXCL10 expression changes and external in vivo RPFs. HFPO-TA was found to be the most potent PFAS tested, being around tenfold more potent than PFOA. Altogether, it may be concluded that the HepaRG model may provide relevant data to provide insight into which PFASs are relevant regarding their hepatotoxic effects and that it can be applied as a screening tool to prioritize other PFASs for further hazard and risk assessment.

Hexafluoropropylene oxide tetramer acid (HFPO-TeA)-induced developmental toxicities in chicken embryo: Peroxisome proliferator-activated receptor Alpha (PPARα) is involved

Hexafluoropropylene oxide tetramer acid (HFPO-TeA) is an emerging environmental contaminant, with environmental presence but limited toxicological information. To investigate its potential developmental toxicities, various doses of HFPO-TeA exposure were achieved in chicken embryos via air cell injection, and the exposed embryos were incubated until hatch. Within 24 h of hatch, the hatchling chickens were assessed with electrocardiography and histopathology for toxicological evaluation. For mechanistic investigation, in ovo silencing of PPARα was achieved via lentivirus microinjection, then the morphological/functional endpoints along with protein expression levels of PPARα-regulated genes were assessed. HFPO-TeA exposure in chicken embryo resulted in developmental cardiotoxicity and hepatotoxicity. Specifically, decreased right ventricular wall thickness, increased heart rate and hepatic steatosis were observed, whereas silencing of PPARα resulted in alleviation of observed toxicities. Western blotting for EHHADH and FABPs suggested that developmental exposure to HFPO-TeA effectively increased the expression levels of both targets in hatchling chicken heart and liver tissue samples, while PPARα silencing prevented such changes, suggesting that PPARα and its downstream genes are playing critical roles in HFPO-TeA induced developmental toxicities.

Uptake and translocation of both legacy and emerging per- and polyfluorinated alkyl substances in hydroponic vegetables

The extensive use of per- and polyfluorinated alkyl substances (PFASs) and their substitutes has resulted in their frequent detections in environmental matrices. However, limited information is known about their uptake into vegetables and health risk through diet, particularly for those emerging alternatives. In this study, a total of 17 PFASs (namely 12 legacy PFASs and 5 of their alternatives) were compared for their accumulation into four staple vegetables (lettuce, Chinese cabbage, chrysanthemum coronarium, and cucumber) in hydroponic system with single PFAS concentration being 10 μg/L, except for 8:2 chlorinated polyfluoroalkyl ether sulfonate (Cl-PFESA) as 0.5 μg/L. The sum concentrations of 17 PFASs in edible parts were in the order of Chinese cabbage leaf (13,456 ng/g) > lettuce leaf (5996 ng/g) > cucumber fruit (4115 ng/g) >chrysanthemum coronarium stem (3999 ng/g). For perfluorooctanoate acid (PFOA) and its alternatives, hexafluoropropylene oxide trimer acid (HFPO-TA) preferentially accumulated in roots than PFOA with root concentration factors being 35.7-99.9. Translocation to edible parts was more remarkable for hexafluoropropylene oxide dimer acid (HFPO-DA) compared with PFOA in lettuce and cucumber. For perfluorooctanesulfonate acid (PFOS) and its alternatives, roots of all the four vegetables were found to more readily accumulate 8:2 Cl-PFESA than PFOS, but 8:2 Cl-PFESA was hardly translocated to the aerial parts. Significantly (p < 0.05) higher edible concentrations of 8:2 and 6:2 fluorotelomer sulfonic acids (FTSA) than that of PFOS were observed for cucumber.

Emerging and Legacy Perfluoroalkyl Substances in Breastfed Chinese Infants: Renal Clearance, Body Burden, and Implications

BACKGROUND

Human breast milk is a primary route of exposure to perfluoroalkyl substances (PFAS) in infants. To understand the associated risks, the occurrence of PFAS in human milk and the toxicokinetics of PFAS in infants need to be addressed.

OBJECTIVES

We determined levels of emerging and legacy PFAS in human milk and urine samples from Chinese breastfed infants, estimated renal clearance, and predicted infant serum PFAS levels.

METHODS

In total, human milk samples were collected from 1,151 lactating mothers in 21 cities in China. In addition, 80 paired infant cord blood and urine samples were obtained from two cities. Nine emerging PFAS and 13 legacy PFAS were analyzed in the samples using ultra high-performance liquid chromatography tandem mass spectrometry. Renal clearance rates (CLrenals) of PFAS were estimated in the paired samples. PFAS serum concentrations in infants (<1 year of age) were predicted using a first-order pharmacokinetic model.

RESULTS

All nine emerging PFAS were detected in human milk, with the detection rates of 6:2 Cl-PFESA, PFMOAA, and PFO5DoDA all exceeding 70%. The level of 6:2 Cl-PFESA in human milk (median concentration=13.6 ng/L) ranked third after PFOA (336 ng/L) and PFOS (49.7 ng/L). The estimated daily intake (EDI) values of PFOA and PFOS exceeded the reference dose (RfD) of 20 ng/kg BW per day recommended by the U.S. Environmental Protection Agency in 78% and 17% of breastfed infant samples, respectively. 6:2 Cl-PFESA had the lowest infant CLrenal (0.009mL/kg BW per day), corresponding to the longest estimated half-life of 49 y. The average half-lives of PFMOAA, PFO2HxA, and PFO3OA were 0.221, 0.075, and 0.304 y, respectively. The CLrenals of PFOA, PFNA, and PFDA were slower in infants than in adults.

CONCLUSIONS

Our results demonstrate the widespread occurrence of emerging PFAS in human milk in China. The relatively high EDIs and half-lives of emerging PFAS suggest potential health risks of postnatal exposure in newborns. https://doi.org/10.1289/EHP11403.

Hexafluoropropylene oxide trimer acid (HFPO-TA) disturbs embryonic liver and biliary system development in zebrafish

Hexafluoropropylene oxide trimer acid (HFPO-TA), a novel alternative to perfluorooctanoic acid (PFOA), has emerged as a potential environmental pollutant. Here, to investigate the toxic effects of HFPO-TA on liver and biliary system development, zebrafish embryos were exposed to 0, 50, 100, or 200 mg/L HFPO-TA from 6 to 120 h post-fertilization (hpf). Results showed that the 50 % lethal concentration (LC₅₀) of HFPO-TA was 231 mg/L at 120 hpf, lower than that of PFOA. HFPO-TA exposure decreased embryonic hatching, survival, and body length. Furthermore, HFPO-TA exerted higher toxicity at the specification stage than during the differentiation and maturation stages, leading to small-sized livers in Tg(fabp10a: DsRed) transgenic larvae and histopathological changes. Significant decreases in the mRNA expression of genes related to liver formation were observed. Alanine transaminase (ALT), aspartate aminotransferase (AST), total bilirubin (TBIL), and direct bilirubin (DBIL) levels were significantly increased. HFPO-TA decreased total cholesterol (TCHO) and triglyceride (TG) activities, disturbed lipid metabolism through the peroxisome proliferator-activated receptor (PPAR) pathway, and induced an inflammatory response. Furthermore, HFPO-TA inhibited intrahepatic biliary development in Tg(Tp1:eGFP) transgenic larvae and interfered with transcription of genes associated with biliary duct development. HFPO-TA reduced bile acid synthesis but increased bile acid transport, resulting in disruption of bile acid metabolism. Therefore, HFPO-TA influenced embryonic liver and biliary system morphogenesis, caused liver injury, and may be an unsafe alternative for PFOA.

Recent trends in degradation strategies of PFOA/PFOS substitutes

The global elimination and restriction of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), respectively, have urged manufacturers to shift production to their substitutes which still pose threat to the environment with their bioaccumulation, toxicity and migration issues. In this context, efficient technologies and systematic mechanistic studies on the degradation of PFOA/PFOS substitutes are highly desirable. In this review, we summarize the progress in degrading PFOA/PFOS substitutes, including four kinds of mainstream methods. The pros and cons of the present technologies are analyzed, which renders the discussion of future prospects on rational optimizations. Additional discussion is made on the differences in the degradation of various kinds of substitutes, which is compared to the PFOA/PFOS and derives designing principles for more degradable F-containing compounds.

Research Progress on Up-Conversion Fluorescence Probe for Detection of Perfluorooctanoic Acid in Water Treatment

Perfluorooctanoic acid (PFOA) is a new type of organic pollutant in wastewater that is persistent, toxic, and accumulates in living organisms. The development of rapid and sensitive analytical methods to detect PFOA in environmental media is of great importance. Fluorescence detection has the advantages of high efficiency and low cost, in which fluorescent probes have excellent fluorescence properties, excellent bio-solubility, and remarkable photostability. It is necessary to review the fluorescence detection routes for PFOA. In addition, the up-conversion of fluorescent materials (UCNPs), as fluorescent materials to prepare fluorescent probes with, has significant advantages and also attracts the attention of researchers, however, reviews related to their application in detecting PFOA and comparing them with other routes are rare. Furthermore, there are many strategies to improve the performance of up-conversion fluorescent probes including SiO₂ modification and amino modification. These strategies can enhance the detection effect of PFOA. Thus, this work reviews the types of fluorescence detection, the design, and synthesis of UCNPs, their recognition mechanism, properties, and their application progress. Moreover, the development trend and prospects of these detection probes are given.

Comprehensive profiles of per- and polyfluoroalkyl substances in Chinese and African municipal wastewater treatment plants: New implications for removal efficiency

Municipal wastewater treatment plants (WWTPs) can reflect the pollution status of per- and polyfluoroalkyl substances (PFASs) pollution. Here, matched influent, effluent, and sludge samples were collected from 58 municipal WWTPs in China, South Sudan, Tanzania, and Kenya. Target and suspect screening of PFASs was performed to explore their profiles in WWTPs and assess removal efficiency and environmental emissions. In total, 155 and 58 PFASs were identified in WWTPs in China and Africa, respectively; 146 and 126 PFASs were identified in wastewater and sludge, respectively. Novel compounds belonging to per- and polyfluoroalkyl ether carboxylic acids (PFECAs) and sulfonic acids (PFESAs), hydrogen-substituted polyfluorocarboxylic acids (H-PFCAs), and perfluoroalkyl sulfonamides (PFSMs) accounted for a considerable proportion of total PFASs (ΣPFASs) in Chinese WWTPs and were also widely detected in African samples. In China, estimated national emissions of ΣPFASs in WWTPs exceeded 16.8 t in 2015, with >60 % originating from emerging PFASs. Notably, current treatment processes are not effective at removing PFASs, with 35 of the 54 WWTPs showing emissions higher than mass loads. PFAS removal was also structure dependent. Based on machine learning models, we found that molecular descriptors (e.g., LogP and molecular weight) may affect adsorption behavior by increasing hydrophobicity, while other factors (e.g., polar surface area and molar refractivity) may play critical roles in PFAS removal and provide novel insights into PFAS pollution control. In conclusion, this study comprehensively screened PFASs in municipal WWTPs and determined the drivers affecting PFAS behavior in WWTPs based on machine learning models.

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).