Parental exposure to 6:2 chlorinated polyfluorinated ether sulfonate (F-53B) induced transgenerational thyroid hormone disruption in zebrafish

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.

Per-polyfluoroalkyl substances (PFAS) as thyroid disruptors: is there evidence for multi-transgenerational effects?

INTRODUCTION

The environmental spread of pollutants has led to a persistent exposure of living beings to multiple chemicals, by now become ubiquitous in the surrounding environment. Environmental exposure to these substances has been reported to cause multi- and/or transgenerational health effects. Per- and Polyfluorinated Substances (PFAS) raise great concern, given their known effects both as endocrine disruptors and potential carcinogens. The multi/trans-generational effects of different endocrine disruptors have been investigated by several studies, and harmful effects observed also for PFAS.

AREAS COVERED

This review examines the current data on the multi-trans-generational effects of PFAS, with a focus on their impact on the thyroid axis. The aim is to determine if there is evidence of potential multi-trans-generational effects of PFAS on the thyroid and/or if more research is needed.

EXPERT OPINION

PFAS exposure impacts thyroid homeostasis and can cross the placental barrier. In addition PFAS have shown multi-transgenerational effects in laboratory experiences and animal models, but thyroid disruptive effects of PFAS were also investigated only in a small number of these studies. Efforts are needed to study the adverse effects of PFAS, as not all PFAS are regulated and removal strategies are still being developed.

Paternal exposures to endocrine-disrupting chemicals induce intergenerational epigenetic influences on offspring: A review

Endocrine-disrupting chemicals (EDCs) are ubiquitous in ecological environments and have become a great issue of public health concern since the 1990 s. There is a deep scientific understanding of the toxicity of EDCs. However, recent studies have found that the abnormal physiological functions of the parents caused by EDCs could be transmitted to their unexposed offspring, leading to intergenerational toxicity. We questioned whether sustained epigenetic changes occur through the male germline. In this review, we (1) systematically searched the available research on the intergenerational impacts of EDCs in aquatic and mammal organisms, including 42 articles, (2) summarized the intergenerational genetic effects, such as decreased offspring survival, abnormal reproductive dysfunction, metabolic disorders, and behavioral abnormalities, (3) summarized the mechanisms of intergenerational toxicity through paternal interactions, and (4) propose suggestions on future research directions to develop a deeper understanding of the ecological risk of EDCs.

Long-term tralopyril exposure results in endocrinological and transgenerational toxicity: A two-generation study of marine medaka (Oryzias melastigma)

This study aims to investigate the impact of tralopyril, a newly developed marine antifouling agent, on the reproductive endocrine system and developmental toxicity of offspring in marine medaka. The results revealed that exposure to tralopyril (0, 1, 20 μg/L) for 42 days resulted in decreased reproductive capacity in marine medaka. Moreover, it disrupted the levels of sex hormones E2 and T, as well as the transcription levels of genes related to the HPG axis, such as cyp19b and star. Sex-dependent differences were observed, with females experiencing more pronounced effects. Furthermore, intergenerational toxicity was observed in F1 offspring, including increased heart rate, changes in retinal morphology and cartilage structure, decreased swimming activity, and downregulation of transcription levels of relevant genes (HPT axis, GH/IGF axis, cox, bmp4, bmp2, runx2, etc.). Notably, the disruption of the F1 endocrine system by tralopyril persisted into adulthood, indicating a transgenerational effect. Molecular docking analysis suggested that tralopyril's RA receptor activity might be one of the key factors contributing to the developmental toxicity observed in offspring. Overall, our study highlights the potential threat posed by tralopyril to the sustainability of fish populations, as it can disrupt the endocrine system and negatively impact aquatic organisms for multiple generations.

PFOS and F-53B disrupted inner cell mass development in mouse preimplantation embryo

Perfluorooctane sulfonic acid (PFOS) is a perfluoroalkyl and polyfluoroalkyl substance (PFAS) widely used in daily life. As its toxicity was confirmed, it has been gradually substituted by F-53B (chlorinated polyfluoroalkyl sulfonates, Cl-PFESAs) in China. PFOS exposure during prenatal development may hinder the development of preimplantation embryos, as indicated by recent epidemiological research and in vivo assays. However, the embryotoxicity data for F-53B are scarce. Furthermore, knowledge about the toxicity of F-53B and PFOS exposure to internal follicular fluid concentrations on early preimplantation embryo development remains limited. In this study, internal exposure concentrations of PFOS (10 nM) and F-53B (2 nM) in human follicular fluid were chosen to study the effects of PFAS on early mouse preimplantation embryo development. We found that both PFOS and F-53B treated zygotes exhibited higher ROS activity in 8-cell embryos but not in 2-cell stage embryos. PFOS and F-53B significantly affected the proportion and aggregation of the inner cell mass (ICM) in the blastocyst, but not the total cell number. Mouse embryonic stem cells (mESCs, isolated from the ICM) and embryoid body (EB) assays were employed to assess the toxicity of PFOS and F-53B on the development and differentiation of embryonic pluripotent cells. These results suggested that mESCs exhibited more DNA damage and abnormal germ layer differentiation after brief exposure to PFOS or F-53B. Finally, RNA-sequencing revealed that PFOS and F-53B exposure affected mESCs biosynthetic processes and chromatin-nucleosome assembly. Our results indicate that F-53B has potential risks as an alternative to PFOS, which disrupts ICM development and differentiation.

Comparative Toxicological Effects of Perfluorooctane Sulfonate and Its Alternative 6:2 Chlorinated Polyfluorinated Ether Sulfonate on Earthworms

High levels of 6:2 chlorinated polyfluorinated ether sulfonate (F-53B), which is a substitute for perfluorooctane sulfonate (PFOS), are detected in various environmental matrices, wildlife, and humans. Chlorinated polyfluorinated ether sulfonate has received increased attention due to its potential risk to ecosystems. However, its toxicity in the soil organisms remains unclear. In the present study, a comparative investigation was conducted on the toxicities of 6:2 Chlorinated polyfluorinated ether sulfonate (F-53B) and PFOS to the earthworm Eisenia. fetida. F-53B was significantly more acutely toxic to earthworms than PFOS, with median lethal concentrations of 1.43 and 1.83 mmol/kg dry soil (~816 and 984 mg/kg dry soil), respectively. Although both F-53B and PFOS, at 0.4 mmol/kg dry soil (=228 and 215 mg/kg dry soil) caused oxidative stress in earthworms, as evidenced by increased superoxide dismutase, peroxidase, and catalase activities as well as malondialdehyde level, the stress caused by F-53B was higher than that caused by PFOS. In transcriptomic and metabolomic studies, negative effects of PFOS and F-53B were observed on several metabolic processes in earthworms, including protein digestion and amino acid absorption, lipid metabolism, and the immune response. Compared with PFOS, F-53B exhibited a weaker disruption of lipid metabolism, comparable potency for toxicity to the immune response, and a stronger potency in extracellular matrix destruction along with apoptosis and ferroptosis induction. Hence, our data suggest that F-53B is more toxic than PFOS to earthworms. The findings provide some new insights into the potential toxicity of F-53B to soil organisms. Environ Toxicol Chem 2024;43:170-181. © 2023 SETAC.

Degradation of emerging per- and polyfluoroalkyl substances (PFAS) using an electrochemical plug flow reactor

In recent years, shorter-chain fluorinated compounds have been manufactured as alternatives to legacy per- and polyfluoroalkyl substances (PFAS) after a global ban on some long-chain PFAS. This study is the first to investigate the degradability of emerging PFAS by an electrochemical plug flow reactor (EPFR). Ten different emerging PFAS, representing classes of fluorotelomer alcohol, perfluoroalkyl ether carboxylate, polyfluoroalkyl ethersulfonic acids, perfluoroalkyl ether/polyether carboxylates, perfluoroether sulfonate, N-alkyl perfluoroalkylsulfonamido carboxylate, fluoroalkyl phosphonic acid, and perfluoro alkane sulfonamide were investigated. The process kinetics was performed. The degradation of parent compounds increased with increasing retention time (RT). At 45.2 min of RT, the degradation of parent compounds ranged between 68%-100% with a current density of 17.2 mA/cm2. A linear increase in pseudo-first order rate constants was observed for all PFAS with increasing current density from 5.7 to 28.7 mA/cm2 (R2 > 0.91). The effect of pH, natural organic matter, and bicarbonate on the degradation, defluorination, and fluorine mass balance are reported. Alkaline pH (11) caused a decrease in degradation for all PFAS. While the presence of natural organic matter (NOM) significantly decreased the degradation and defluorination processes, the presence of bicarbonate at all studied concentrations (25, 50, and 100 mg/L) did not affect the process efficiency. The defluorination reduced to 34% from 81% with 15 mg/L NOM. The unknown/undetected fluorine fraction also increased in the presence of 15 mg/L NOM indicating the formation of NOM-PFAS complexes. Additionally, C2-C8 perfluoro carboxylic acids (PFCAs), one perfluoro sulfonic acid (PFSA), two H-PFCAs, and 4:2 fluorotelomer sulfonate (FTS) were identified as degradation byproducts in suspect screening. The electrical energy per order for PFAS ranged between 1.8 and 19.4 kWh/m3. This study demonstrates that emerging types of PFAS can potentially be degraded using an EPFR with relatively low electrical energy requirements.

Maternal transfer of F-53B inhibited neurobehavior in zebrafish offspring larvae and potential mechanisms: Dopaminergic dysfunction, eye development defects and disrupted calcium homeostasis

Maternal exposure to environment toxicants is an important risk factor for neurobehavioral health in their offspring. In our study, we investigated the impact of maternal exposure to chlorinated polyfluoroalkyl ether sulfonic acids (Cl-PFESAs, commercial name: F-53B) on behavioral changes and the potential mechanism in the offspring larvae of zebrafish. Adult zebrafish exposed to Cl-PFESAs (0, 0.2, 2, 20 and 200 μg/L) for 21 days were subsequently mated their embryos were cultured for 5 days. Higher concentrations of Cl-PFESAs in zebrafish embryos were observed, along with, reduced swimming speed and distance travelled in the offspring larvae. Molecular docking analysis revealed that Cl-PFESAs can form hydrogen bonds with brain-derived neurotropic factor (BDNF), protein kinase C, alpha, (PKCα), Ca2+-ATPase and Na, K - ATPase. Molecular and biochemical studies evidenced Cl-PFESAs induce dopaminergic dysfunction, eye developmental defects and disrupted Ca2+ homeostasis. Together, our results showed that maternal exposure to Cl-PFESAs lead to behavioral alteration in offspring mediated by disruption in Ca2+ homeostasis, dopaminergic dysfunction and eye developmental defects.

Interactive effects of polystyrene nanoplastics and 6:2 chlorinated polyfluorinated ether sulfonates on the histomorphology, oxidative stress and gut microbiota in Hainan Medaka (Oryzias curvinotus)

Nanoplastics adsorb surrounding organic contaminants in the environment, which alters the physicochemical properties of contaminants and affects associated ecotoxicological effects on aquatic life. The current work aims to explore the individual and combined toxicological implications of polystyrene nanoplastics (80 nm) and 6:2 chlorinated polyfluorinated ether sulfonate (Cl-PFAES, trade name: F-53B) in an emerging freshwater fish model Hainan Medaka (Oryzias curvinotus). Therefore, O. curvinotus were exposed to 200 μg/L of PS-NPs or 500 μg/L of F-53B in the single or mixture exposure for 7 days to investigate the effects on fluorescence accumulation, tissue damage, antioxidant capacity and intestinal flora. The PS-NPs fluorescence intensity was significantly higher in the single exposure treatment than it in combined exposure treatment (p < 0.01). Histopathological results showed that exposure to PS-NPs or F-53B inflicted varying degree of damages to the gill, liver, and intestine, and these damage were also present in the corresponding tissues of the combined treatment group, illustrating a stronger extent of destruction of these tissues by the combined treatment. Compared to the control group, combined exposure group elevated the malondialdehyde (MDA) content, superoxide dismutase (SOD) and catalase (CAT) activities except in the gill. In addition, the adverse contribution of PS-NPs and F-53B on the enteric flora in the single and combined exposure groups was mainly characterised in the form of reductions in the number of probiotic bacteria (Firmicutes) and this reduction was aggravated by the combined exposure group. Collectively, our results indicated that the toxicological effects of PS-NPs and F-53B on pathology, antioxidant capacity and microbiomics of medaka may be modulated by the interaction of two contaminants with mutually interactive effects. And our work offers fresh information on the combined toxicity of PS-NPs and F-53B to aquatic creatures along with a molecular foundation for the environmental toxicological mechanism.

Effects of PFOS, F-53B and OBS on locomotor behaviour, the dopaminergic system and mitochondrial function in developing zebrafish (Danio rerio)

Perfluorooctanesulfonic acid (PFOS) has widely been reported to persist in the environment and to elicit neurotoxicological effects in wildlife and humans. Following the restriction of PFOS use, 6:2 chlorinated polyfluorinated ether sulfonate (F-53B) and sodium p-perfluorous nonenoxybenzene sulfonate (OBS) have emerged as novel PFOS alternatives and have been detected in the environment. However, knowledge on the toxicological effects of these alternatives remains scarce. Using developing transgenic Tg(dat:eGFP) zebrafish, we evaluated the consequences of exposure to 0, 0.1 and 1 mg/l PFOS, F-53B and OBS on the dopaminergic system, locomotor behaviour and mitochondrial function. All compounds generally reduced locomotor activity under light conditions irrespective of exposure concentration. Exposure to OBS (at all concentrations), as well as PFOS and F-53B (at 1 mg/l), significantly reduced subpallial dopaminergic neuron abundance. PFOS also significantly reduced dat and pink1 expression irrespective of exposure concentration, while F-53B and OBS tended to reduce mitochondrial pink1 and fis1 expression across concentrations without reaching statistical significance. Mitochondrial function, in the form of reduced oxygen consumption rate and marginally inhibited ATP-linked oxygen consumption rate, was affected only in response to 1 mg/l PFOS. Together, PFOS and the emerging contaminants F-53B and OBS inhibit locomotion at similar concentrations, a finding correlated with decreased dopaminergic neuron numbers in the subpallium and decreased expression of pink1. These findings are relevant to wildlife and human health, as they suggest that PFOS as well as replacement compounds affect locomotion likely in part by negatively impacting the dopamine system.

Reversibility of Thyroid Hormone System-Disrupting Effects on Eye and Thyroid Follicle Development in Zebrafish (Danio rerio) Embryos

Early vertebrate development is partially regulated by thyroid hormones (THs). Environmental pollutants that interact with the TH system (TH system-disrupting chemicals [THSDCs]) can have massively disrupting effects on this essential phase. Eye development of fish is directly regulated by THs and can, therefore, be used as a thyroid-related endpoint in endocrine disruptor testing. To evaluate the effects of THSDC-induced eye malformations during early development, zebrafish (Danio rerio) embryos were exposed for 5 days postfertilization (dpf) to either propylthiouracil, a TH synthesis inhibitor, or tetrabromobisphenol A, which interacts with TH receptors. Subsequently, one half of the embryos were exposed further to the THSDCs until 8 dpf, while the other half of the embryos were raised in clean water for 3 days to check for reversibility of effects. Continued THSDC exposure altered eye size and pigmentation and induced changes in the cellular structure of the retina. This correlated with morphological alterations of thyroid follicles as revealed by use of a transgenic zebrafish line. Interestingly, effects were partly reversible after a recovery period as short as 3 days. Results are consistent with changes in TH levels measured in different tissues of the embryos, for example, in the eyes. The results show that eye development in zebrafish embryos is very sensitive to THSDC treatment but able to recover quickly from early exposure by effective repair mechanisms. Environ Toxicol Chem 2023;42:1276-1292. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Exposure to per- and polyfluoroalkyl substances in early pregnancy, risk of gestational diabetes mellitus, potential pathways, and influencing factors in pregnant women: A nested case-control study

Although previous studies have reported an association between maternal serum perfluoroalkyl substance (PFAS) exposure and gestational diabetes mellitus (GDM) risk, results have been inconsistent. Few studies have focused on the combined effects of emerging and legacy PFASs on glucose homeostasis while humans are always exposed to multiple PFASs simultaneously. Moreover, the potential pathways by which PFAS exposure induces GDM are unclear. A total of 295 GDM cases and 295 controls were enrolled from a prospective cohort of 2700 pregnant women in Shanghai, China. In total, 16 PFASs were determined in maternal spot serum samples in early pregnancy. We used conditional logistic regression, multiple linear regression, and Bayesian kernel machine regression (BKMR) to examine individual and joint effects of PFAS exposure on GDM risk and oral glucose tolerance test outcomes. The mediating effects of maternal serum biochemical parameters, including thyroid and liver function were further assessed. Maternal perfluorooctanoic acid (PFOA) exposure was associated with an increased risk of GDM (odds ratio (OR) = 1.68; 95% confidence interval (95% CI): 1.10, 2.57), consistent with higher concentrations in GDM cases than controls. Based on mediation analysis, an increase in the free triiodothyronine to free thyroxine ratio partially explained the effect of this association. For continuous glycemic outcomes, positive associations were observed between several PFASs and 1-h and 2-h glucose levels. In BKMR, PFAS mixture exposure showed a positive trend with GDM incidence, although the CIs were wide. These associations were more pronounced among women with normal pre-pregnancy body mass index (BMI). Mixed PFAS congeners may affect glucose homeostasis by increasing 1-h glucose levels, with perfluorononanoic acid found to be a main contributor. Exposure to PFASs was associated with increased risk of GDM and disturbance in glucose homeostasis, especially in normal weight women. The PFAS-associated disruption of maternal thyroid function may alter glucose homeostasis.

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.

Associations of prenatal PFAS exposure and early childhood neurodevelopment: Evidence from the Shanghai Maternal-Child Pairs Cohort

Epidemiological data on the effects of perfluoroalkyl and polyfluoroalkyl substances (PFAS) on infant neurodevelopment trajectories are far from being sufficiently addressed. In this study, 1285 mother-child pairs were recruited during 2016-2017. A high-performance liquid chromatography-triple quadrupole mass spectrometer was used to measure 16 PFAS levels in cord serum. Ages and Stages Questionnaires were used to examine children's neurodevelopment at 2, 6, 12, and 24 months of age. Group-based trajectory models were applied to derive the neurodevelopmental trajectories. Children with relatively low scores from 2 to 24 months were classified into a low-score group and were used as a risk group in each domain. Multiple linear regression, logistic regression, and quantile-based g-computation were performed to assess associations of single or mixture PFAS exposures with neurodevelopment and trajectories. Perfluorooctane sulphonate (PFOS), perfluorooctanoic acid (PFOA), perfluorohexanesulfonic acid (PFHxS), and 6:2 chlorinated polyfluorooctane ether sulfonate (6:2Cl-PFESA) were detected in over 90 % samples. PFOA had the highest concentration (median: 4.61 μg/L). Each ln-unit (μg/L) increase of PFAS (e.g., PFOA, PFOS, PFHxS, 6:2Cl-PFESA) was associated with poor scores of communication domain at 6 months, with the effect size ranging from -0.69 to -0.44. PFOS (OR: 1.14, (1.03, 1.26), PFDA (OR:1.08, (1.02, 1.15)), PFHxS (OR:1.31, (1.12, 1.56)), and 6:2Cl-PFESA (OR:1.08, (1.00, 1.16)) were associated with an increased risk of being in the low-score group in the early childhood communication domain's trajectory. Each mixture quartile increment was associated with a 1.60 (-2.76, -0.45) decrease in communication domain scores of 6-month-old infants, and the mixture effect was mainly attributed to PFOS. Each mixture quartile increase was associated with a 1.23-fold (1.03, 1.46) risk of being in the low-score group of the communication domain, and the mixture effect was mainly attributed to PFOS. In conclusion, PFAS and their mixtures might adversely affect childhood neurodevelopment. The gender-specific associations existed in the above associations.

Sex-specific thyroid disruption caused by phenanthrene in adult zebrafish (Danio rerio)

Polycyclic aromatic hydrocarbons (PAHs) are well-known contaminants with widespread distribution in environment and food. Phenanthrene is one of the most abundant PAHs in food and aquatic environment and generates reproductive and developmental toxicity in zebrafish. Nonetheless, whether phenanthrene caused sex-specific thyroid disruption in adult zebrafish is unclear. To determine this, adult zebrafish (male and female) were treated with phenanthrene (0, 0.85, 8.5, and 85 μg/L) for 60 days. After the treatment period, we assessed the concentrations of thyroid hormones (THs) and expression levels of genes in the hypothalamic-pituitary-thyroid (HPT) axis. The results showed that phenanthrene exposure can lead to thyroid disruption in both male and female zebrafish. Exposure to phenanthrene dramatically reduced the levels of L-thyroxine (T4) and L-triiodothyronine (T3) in both male and female zebrafish, with a similar trend in both. However, the genes expression profiles of hypothalamic-pituitary-thyroid (HPT) axis were sex-specific. In all, the present study demonstrated that phenanthrene exposure could result in sex-specific thyroid disruption in adult zebrafish.

Prenatal exposure to perfluorooctane sulfonate alternatives and associations with neonatal thyroid stimulating hormone concentration: A birth cohort study

BACKGROUND

Chlorinated polyfluorinated ether sulfonic acids (Cl-PFESA) and perfluorobutane sulfonate (PFBS), used as perfluorooctanesulfonate (PFOS) alternatives, were indicated as thyroid hormone disruptive toxicants in experimental studies. However, it is unclear whether prenatal exposure to Cl-PFESA and PFBS affects neonatal thyroid stimulating hormone (TSH) in human.

OBJECTIVE

To disclose the relationships between prenatal Cl-PFESAs and PFBS exposure and neonatal thyroid-stimulating hormone (TSH) levels based on a perspective cohort study.

METHODS

A total of 1015 pairs of mother and newborn were included from an ongoing birth cohort study in Wuhan, China, between 2013 and 2014. Six PFASs in cord blood sera and TSH concentration in neonatal postpartum heel sticks blood were quantified. Mixed linear and weighted quantile sum (WQS) regression models were applied to assess the individual and combination effects of PFASs exposure on neonatal TSH levels with multiple covariates adjustments.

RESULTS

After adjusting for potential confounders and other five PFASs, for each 1-ng/mL increase of PFBS or 8:2 Cl-PFESA, was negatively associated with 25.90% (95%CI: 37.37%, -12.32%; P < 0.001) and 27.19% (95%CI: 46.15%, -1.55%; P = 0.033) change in TSH in male but not female infants, respectively. No significant association was found between other PFASs exposure and neonatal TSH. Higher PFAS mixture in cord blood was significantly associated with decrease TSH concentration in all newborns (β = -0.36; 95%CI: 0.58, -0.13; P = 0.001) identified by WQS regression model. PFBS, PFOS and 6:2 Cl-PFESA were the major contributors to the neonatal TSH decrement with the weights of 56.50%, 18.71%, 12.81% among PFAS mixture, respectively.

CONCLUSIONS

our prospective cohort study suggested a negative association of cord serum PFBS and 8:2 CI-PFESA with TSH concentration in newborns, especially for boys. Additional studies are required to elaborate on the underlying biological mechanisms, especially for PFBS.

Comparison of developmental toxicity induced by PFOA, HFPO-DA, and HFPO-TA in zebrafish embryos

Hexafluoropropylene oxide dimer acids (HFPO-DA) and hexafluoropropylene oxide trimer acids (HFPO-TA) are alternatives to perfluorooctanoic acid (PFOA). However, little information on the comparison of their toxicities is available. Here, zebrafish embryos were exposed to PFOA, HFPO-DA, and HFPO-TA with exposure concentrations of 5 and 500 μg/L. Behavioral abnormal, enzyme activities and gene expression profiles in zebrafish embryos were determined. Results showed that exposure to PFOA and its alternatives increased heart rates and inhibited locomotor activity of zebrafish embryos. Further, their exposures changed the enzyme activities (acetylcholinesterase and oxidative stress-related enzymes), ATP content, and expressions of genes related to hypothalamic-pituitary-thyroid (HPT) axis, apoptosis, and lipid metabolism. Comparison analyses found that PFOA, HFPO-TA, and HFPO-DA exposures induced different effects on the embryonic development of zebrafish, which indicates the different modes of action. The HFPO-DA exposure induced specific effects on the disorder of lipid metabolism, HPT axis, and neurodevelopment. The HFPO-TA exposure also induced different effects from the PFOA exposure, which focused on lipid metabolism. The current data shows that the HFPO-DA and HFPO-TA might not be safe alternatives to PFOA. This study provides a new understanding of the biological hazards of PFOA alternatives in aquatic organisms, which can guide their usage.

A sensitive and robust method for the simultaneous determination of thirty-three legacy and emerging per- and polyfluoroalkyl substances in human plasma and serum

Legacy and emerging per- and polyfluoroalkyl substances (PFAS) have attracted growing attention due to their potential adverse effects on humans. We developed a method to simultaneously determine thirty-three PFAS (legacy PFAS, precursors, and alternatives) in human plasma and serum using solid phase extraction coupled to ultra-performance liquid chromatography-tandem mass spectrometry (SPE-UPLC-MS/MS). The method yielded good linearity (>0.995) and excellent limits of detection (LODs) (0.0005~0.012 ng mL^-1 in plasma and 0.002~0.016 ng mL^-1 in serum). The relative recoveries ranged from 80.1 to 116%, with intra- and inter-day precision less than 14.3%. The robustness of this method has been tested continuously for 10 months (coefficients of variation <14.9%). Our method was successfully applied to the PFAS analysis of 42 real human plasma and serum samples collected from women. The proposed method is attractive for the biomonitoring of multi-class PFAS in human health risk assessment and epidemiological studies.

Parental whole life-cycle exposure to tris (2-chloroethyl) phosphate (TCEP) disrupts embryonic development and thyroid system in zebrafish offspring

Tris (2-chloroethyl) phosphate (TCEP), an emerging environmental pollutant, has been frequently detected in natural waters. The objective of this study was to investigate possible parental transfer of TCEP and transgenerational effects on the early development and thyroid hormone homeostasis in F1 larvae following parental whole life-cycle exposure to TCEP. To this end, zebrafish (Danio rerio) embryos were exposed to environmentally relevant concentrations (0.8, 4, 20 and 100 μg/L) of TCEP for 120 days until sexual maturation. Parental exposure to TCEP resulted in significant levels of TCEP, developmental toxicity including decreased survival and final hatching rates, accelerated heart rate and elevated malformation rate, as well as induction of oxidative stress and cell apoptosis in F1 offspring. In F1 eggs, declined thyroxin (T4) levels were observed, consistent with those in plasma of F0 adult females, indicating the maternal transfer of thyroid endocrine disruption to the offspring. In addition, mRNA levels of several genes along the hypothalamic-pituitary-thyroid (HPT) axis were significantly modified in F1 larvae, which could be linked to transgenerational developmental toxicity and thyroid hormone disruption. For the first time, we revealed that the parental exposure to environmentally relevant levels of TCEP could cause developmental toxicity and thyroid endocrine disruption in subsequent unexposed generation.

Environmentally relevant concentrations of F-53B induce eye development disorders-mediated locomotor behavior in zebrafish larvae

The perfluorooctane sulfonate alternative, F-53B, induces multiple physiological defects but whether it can disrupt eye development is unknown. We exposed zebrafish to F-53B at four different concentrations (0, 0.15, 1.5, and 15 μg/L) for 120 h post-fertilization (hpf). Locomotor behavior, neurotransmitters content, histopathological alterations, morphological changes, cell apoptosis, and retinoic acid signaling were studied. Histology and morphological analyses showed that F-53B induced pathological changes in lens and retina of larvae and eye size were significantly reduced as compared to control. Acridine orange (AO) staining revealed a dose-dependent increase in early apoptosis, accompanied by upregulation of p53, casp-9 and casp-3 genes. Genes related to retinoic acid signaling (aldh1a2), lens developmental (cryaa, crybb, crygn, and mipa) and retinal development (pax6, rx1, gant1, rho, opn1sw and opn1lw) were significantly downregulated. In addition, behavioral responses (swimming speed) were significantly increased, while no significant changes in the neurotransmitters (dopamine and acetylcholine) level were observed. Therefore, in this study we observed that exposure to F-53B inflicted histological and morphological changes in zebrafish larvae eye, induced visual motor dysfunctions, perturbed retinoid signaling and retinal development and ultimately triggering apoptosis.

Exposure to enrofloxacin and depuration: Endocrine disrupting effect in juvenile grass carp (Ctenopharyngodon idella)

This study aimed to determine the effects of Enrofloxacin (ENR) exposure and depuration on the disruption of thyroid function and growth of juvenile grass carp (Ctenopharyngodon idella) as well as to assess the risk of ENR exposure to human health. Juvenile grass carp were treated with ENR solutions at different concentration gradients for 21 days and then depurated for 14 days. The results indicated ENR accumulation in the juvenile grass carp muscles, which persisted after depuration. In addition, exposure to ENR could alter growth by regulating the expression of genes associated with growth hormone/insulin-like growth factor (GH)/IGF) axis and the hypothalamic-pituitary-thyroid (HPT) axis. During ENR exposure, no significant changes in growth hormone levels were observed; however, a significant increase in the growth hormone level was noted. GH/IGF axis-related genes were upregulated after ENR exposure, and their expression levels remained high after depuration. Notably, a significant increase in the serum triiodothyronine (T3) and thyroxine (T4) levels coincided with the upregulation of HPT axis-related genes in both exposure and depuration treatments, and their expression levels remained high after depuration. Therefore, juvenile grass carp exposure to ENR induces physiological stress through HPT and GH/IGF axes that cannot be recovered after depuration. ENR accumulates in the muscles of juvenile grass carp and may pose a threat to human health. Therefore, exposure of juvenile grass carp to ENR results in impaired thyroid function and impaired growth. In addition, consumption of ENR-exposed fish poses human health risks.

Next generation per- and poly-fluoroalkyl substances: Status and trends, aquatic toxicity, and risk assessment

Widespread application of poly- and per-fluoroalkyl substances (PFAS) has resulted in some substances being ubiquitous in environmental matrices. That and their resistance to degradation have allowed them to accumulate in wildlife and humans with potential for toxic effects. While specific substances of concern have been phased-out or banned, other PFAS that are emerging as alternative substances are still produced and are being released into the environment. This review focuses on describing three emerging, replacement PFAS: perfluoroethylcyclohexane sulphonate (PFECHS), 6:2 chlorinated polyfluoroalkyl ether sulfonate (6:2 Cl-PFAES), and hexafluoropropylene oxide dimer acid (HFPO-DA). By summarizing their physicochemical properties, environmental fate and transport, and toxic potencies in comparison to other PFAS compounds, this review offers insight into the viabilities of these chemicals as replacement substances. Using the chemical scoring and ranking assessment model, the relative hazards, uncertainties, and data gaps for each chemical were quantified and related to perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) based on their chemical and uncertainty scores. The substances were ranked PFOS > 6:2 Cl-PFAES > PFOA > HFPO-DA > PFECHS according to their potential toxicity and PFECHS > HFPO-DA > 6:2 Cl-PFAES > PFOS > PFOA according to their need for future research. Since future uses of PFAS remain uncertain in the face of governmental regulations and production bans, replacement PFAS will continue to emerge on the world market and in the environment, raising concerns about their general lack of information on mechanisms and toxic potencies.

Chlorinated Polyfluorinated Ether Sulfonates and Thyroid Hormone Levels in Adults: Isomers of C8 Health Project in China

Chlorinated polyfluorinated ether sulfonates (Cl-PFESAs) are one kind of replacement chemistry for perfluorooctanesulfonate (PFOS). Recent studies have shown that Cl-PFESAs could interfere with thyroid function in animal models. However, epidemiological evidence on the link between Cl-PFESAs and thyroid function remains scarce. In this study, we focused on two representative legacy perfluoroalkyl substances (PFAS), including PFOS and perfluorooctanoic acid (PFOA), and two PFOS alternatives (6:2 and 8:2 Cl-PFESAs) in the general adult population from a cross-sectional study, the "Isomers of C8 Health Project in China". Three serum thyroid hormones (THs), thyroid stimulating hormone (TSH), free triiodothyronine (FT3), and free thyroxine (FT4), were measured. We fitted generalized linear regression, restricted cubic spline regression, and Bayesian kernel machine regression models to assess associations of individual Cl-PFESAs, legacy PFAS, and PFAS mixtures with THs, respectively. We found individual PFAS and their mixtures were nonlinearly associated with THs. The estimated changes of the TSH level (μIU/mL) at the 95th percentile of 6:2 Cl-PFESA and PFOS against the 5th percentile were -0.74 (95% CI: -0.94, -0.54) and -1.18 (95% CI: -1.37, -0.98), respectively. The present study provided epidemiological evidence for the association of 6:2 Cl-PFESA with thyroid hormone levels in the general adult population.

Environmental Co-Exposure to Potassium Perchlorate and Cd Caused Toxicity and Thyroid Endocrine Disruption in Zebrafish Embryos and Larvae (Danio rerio)

The increasing pollution of aquatic habitats with anthropogenic compounds has led to various test strategies to detect hazardous chemicals. However, information on the effects of pollutants on the thyroid system in fish, which is essential for growth, development, and parts of reproduction, is still scarce. Modified early life-stage tests were carried out with zebrafish exposed to the known thyroid inhibitor potassium perchlorate (0.1, 1, 1.5, 2, 2.5, and 5 mM) to identify adverse effects on embryo development. The endogenous antioxidant defense mechanism is one of the key functions of the thyroid gland; in this regard, we examined the co-exposure to potassium perchlorate (KClO₄), which could disrupt thyroid function, with cadmium (Cd), a known pro-oxidant compound. Zebrafish embryos were exposed to control KClO₄ 1 mM and Cd 0.5 μM for 96 h after fertilization (hpf) individually and in combination. The morphological alteration, body length, and messenger RNA (mRNA) expression related to thyroid function and oxidative stress, thyroid hormone levels, and malondialdehyde were measured. Significant down-regulation of mRNAs related to thyroid function (thyroid hormone receptor-alpha (THRα), thyroid hormone receptor-beta (THRβ), haematopoietically expressed homeobox (hhex)) and decreased thyroxin (T4) levels were observed after co-exposure to KClO₄ and Cd, but this was not observed in the individually treated groups. These results suggest that co-exposure to KClO₄ and Cd could affect antioxidant defense mechanisms and potentially normally increase Cd toxicity on mRNA expression, altering the thyroid functions important in zebrafish embryonic developmental stages.

Photodegradation of F-53B in aqueous solutions through an UV/Iodide system

Advanced reduction by strong reducing hydrated electrons is a promising approach to degrade per- and polyfluoroalkyl substances (PFAS). This research aimed to investigate the effectiveness of UV/Iodide system for 6:2 chlorinated polyfluorinated ether sulfonate (6:2 Cl-PFESA, F-53B) degradation in aqueous solutions. Results from this work demonstrated that UV irradiation with an addition of 0.3 mM KI resulted in 55.99% degradation of F-53B within 15 min and almost 100% within 2 h. The defluorination efficiency of F-53B in the UV/Iodide system was 2.6 times higher than that in the sole UV system after 2 h of irradiation. The degradation efficiency of F-53B was not significantly affected by air purging. The defluorination efficiency with air bubbling, however, was 14.57% lower than that with nitrogen purging. The photodegradation of F-53B in the UV/Iodide system could be well described by a pseudo-first-order kinetic model. Degradation rate constant of F-53B correlated positively with the initial concentration. At 20 μg/L, the pseudo-first-order rate constant was 5.641 × 10^-2 min^-1 and the half-life was 12.29 min. Higher initial concentration also required less energy input to achieve the same degradation efficiency. The detection and identification of degradation intermediates implied that destruction of F-53B started from dechlorination and followed by continuously "flaking off" CF₂ units.

Human exposure to F-53B in China and the evaluation of its potential toxicity: An overview

Chlorinated polyfluoroalkyl ether sulfonic acid (Cl-PFESAs, trade name F-53B), an alternative to perfluorooctane sulfonate (PFOS), has been widely used as a mist suppressant in the Chinese electroplating industry since the 1970 s. Due to greater restrictions on PFOS globally in recent years, the production and use of F-53B correspondingly increased, consequently causing more emissions into the environment. In China, an increasing number of studies report frequent detection and broad exposure to F-53B in the natural environment, various wildlife and the human body. In human blood, the detection rate of F-53B is almost 80%, accounting for 8.69 to 28% of ∑per- and polyfluoroalkyl substances (PFASs). F-53B is the most biopersistent PFAS in humans to date, with a half-life of 15.3 years. In addition, F-53B displays protein binding affinity and high human placental permeability. Recently, some epidemiological studies have reported the health risks associated with F-53B in humans, including abnormal serum lipid metabolism, vascular dysfunction, endocrine disorders and even adverse birth outcomes. Various in vivo and in vitro studies have demonstrated the toxicity of F-53B, such as hepatotoxicity, interference effects on the endocrine system, as well as reproductive and developmental toxicity. Our aims are to review studies on human F-53B exposure levels, trends and associated health effects; evaluate the potential toxicity; and predict directions for future research.

Developmental toxicant exposures and sex-specific effects on epigenetic programming and cardiovascular health across generations

Despite substantial strides in diagnosis and treatment, cardiovascular diseases (CVDs) continue to represent the leading cause of death in the USA and around the world, resulting in significant morbidity and loss of productive years of life. It is increasingly evident that environmental exposures during early development can influence CVD risk across the life course. CVDs exhibit marked sexual dimorphism, but how sex interacts with environmental exposures to affect cardiovascular health is a critical and understudied area of environmental health. Emerging evidence suggests that developmental exposures may have multi- and transgenerational effects on cardiovascular health, with potential sex differences; however, further research in this important area is urgently needed. Lead (Pb), phthalate plasticizers, and perfluoroalkyl substances (PFAS) are ubiquitous environmental contaminants with numerous adverse human health effects. Notably, recent evidence suggests that developmental exposure to each of these toxicants has sex-specific effects on cardiovascular outcomes, but the underlying mechanisms, and their effects on future generations, require further investigation. This review article will highlight the role for the developmental environment in influencing cardiovascular health across generations, with a particular emphasis on sex differences and epigenetic mechanisms. In particular, we will focus on the current evidence for adverse multi and transgenerational effects of developmental exposures to Pb, phthalates, and PFAS and highlight areas where further research is needed.

Adverse effects of bisphenol B exposure on the thyroid and nervous system in early life stages of zebrafish

Bisphenol B (BPB), a widely used alternative of bisphenol A (BPA), has been detected in various environmental media and foodstuffs. However, the knowledge of the health risks about BPB is still limited. In this study, the effects of BPB on thyroid hormone homeostasis and neuronal development were evaluated by exposure of embryos 2 h post-fertilization (hpf) to BPB (0, 1, 10, 100 and 1000 μg/L) until 144 hpf. The results showed that 100 and 1000 μg/L BPB exposed larvae exhibited abnormal morphologies in phenotype and brain histological patterns. Significant decline of thyroid hormone thyroxine (T4) content and elevation of 3,5,3'-triiodothyronine (T3) content, along with the up-regulated expression of tg, trhr1, dio1, dio2, thrα, thrβ genes and down-regulated expression of tsh, ttr and trh genes in BPB exposed zebrafish larvae were observed. Moreover, locomotor activity of larvae was decreased, and the transcription of genes (e.g., elavl3, gap43, zn5, α-tubulin, syn2a and mbp) related to neuronal development were inhibited after exposure to BPB. The mechanism of neurotoxicity and thyroid disruption in zebrafish larvae induced by BPB were discussed.

A Review of Per- and Polyfluorinated Alkyl Substance Impairment of Reproduction

In this review article, we compiled peer-reviewed literature describing PFAS exposure and reproductive effects in animals and humans. The aim was to compare environmental occurrence and effects of the most prominent long-chain PFAS compounds and their short-chain replacements. Long-chain PFAS compounds are known to persist in the environment due to their chemical stability, and also known to bioaccumulate; hence, these compounds are being replaced globally. Indeed, PFOA and PFOS are considered long-chain "forever pollutants," and thus the potential reproductive risk may continue for decades. Much less is known about their short-chain replacements despite the fact that they becoming more widespread in the environment. Short-chain PFAS are generally less bioaccumulative than long-chain, but they are more mobile and persistent in aquatic ecosystems. The three most prominent of these are commonly referred to as GenX, ADONA and F53B. The short-chain PFAS have similar physical and chemical properties as their predecessors; however, because they are relatively new, much less is known about the potential to disrupt reproduction. Indeed, high-quality epidemiological studies are needed to determine associations between short-chain PFAS exposure and effects on reproductive health. However, epidemiological evidence is mounting that long-chain PFAS exposure is associated with reproductive effects (i.e., decrease in fertility, reduced fetal growth and birth weight, pregnancy-induced hypertension and preeclampsia, thyroid hormone disruption during pregnancy, and preterm birth). Evidence from animal models and human cell lines indicates that short-chain PFAS similarly affect reproductive endpoints; however, epidemiological studies are scarce and inconsistent. Although short-chain PFAS have been quantified in drinking water and sediment worldwide, most of these studies did not focus on quantitation of GenX, ADONA, and F53B. There are also many other short-chain PFAS byproducts of manufacturing that have yet to be identified and studied. When sum total concentration of long- and short-chain PFAS are considered, the concentration rises by an order or magnitude or greater, as will the risk of exposure and subsequent reproductive effects.

6:2 Cl-PFESA has the potential to cause liver damage and induce lipid metabolism disorders in female mice through the action of PPAR-γ

6:2 Cl-PFESA is a polyfluoroalkyl ether with high environmental persistence that has been confirmed to have significant adverse effects on animals. In this study, 6-week-old female C57BL/6 mice were exposed to 0, 1, 3 and 10 μg/L 6:2 Cl-PFESA for 10 weeks to estimate the hepatotoxicity of 6:2 Cl-PFESA and explore its underlying molecular mechanism. The results indicated that 6:2 Cl-PFESA preferentially bioaccumulated in the liver and induced hepatic cytoplasmic vacuolation and hepatomegaly in mice. In addition, serum metabolic profiling showed that 6:2 Cl-PFESA exposure caused an abnormal increase in amino acids and an abnormal decrease in acyl-carnitine, which interfered with fatty acid transport and increased the risk of metabolic diseases. Further experiments showed that 6:2 Cl-PFESA formed more hydrogen bonds with PPAR-γ than PFOS, Rosi and GW9662, and the binding affinity of 6:2 Cl-PFESA toward PPAR-γ was the highest among the ligands. 6:2 Cl-PFESA promoted the differentiation of 3T3-L1 cells by increasing PPAR-γ expression. Therefore, our results showed that 6:2 Cl-PFESA has the potential to induce liver damage and dysfunction in female mice, and this effect was achieved through PPAR-γ. This study is the first to reveal the hepatic toxicity of 6:2 Cl-PFESA in female mammals and provides new insights for subsequent in-depth research.

Immunotoxicity of F53B, an alternative to PFOS, on zebrafish (Danio rerio) at different early life stages

As an alternative to perfluorooctane sulfonate (PFOS), 6:2 chlorinated polyfluorinated ether sulfonate (F53B) has emerged in the Chinese market in recent years and has been frequently detected in the aquatic environment, but its ecological risk assessment is limited. In this study, zebrafish embryos and larvae were separately exposed to F53B, and their 96-h LC₅₀ values were estimated to be 15.1 mg/L and 2.4 mg/L, respectively, suggesting that embryos were more resistant to F53B than larvae. The bioconcentration factor in larvae was basically higher than that of embryos, and the body growth of larvae was significantly affected by F53B rather than embryos, indicating that F53B may cause more severe toxicity to larvae. In addition to the excessive production of ROS and NO, the expression of many immune-related genes was increased in both embryos and larvae, but the number of dysregulated genes in larvae was more than that in embryos. Finally, the results of Point of Departure (PoD) indicated that the immunotoxicity of F53B was more sensitive to larvae than embryos at the molecular level. Our findings revealed the ecological risk of F53B by exploring the adverse effects of immunoregulation at different early life stages of zebrafish and indicated that the zebrafish larvae were more sensitive than embryos.

Parental transfer of nanopolystyrene-enhanced tris(1,3-dichloro-2-propyl) phosphate induces transgenerational thyroid disruption in zebrafish

Plastic is a globally recognized superwaste that can affect human health and wildlife when it accumulates and is amplified in the food chain. Microplastics (plastic particles < 5 mm) and nanoplastics (plastic particles < 100 nm) can interact with organic pollutants already present in the aquatic environment, potentially acting as carriers for pollutants entering organisms and thus influencing the bioavailability and toxicity of those pollutants. In this study, we investigated the transfer kinetics and transgenerational effects of exposure to tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) and polystyrene nanoplastics (PS-NPs) in F1 offspring. At 90 days postfertilization, zebrafish (Danio rerio) strain AB was exposed to either TDCIPP (0, 0.47, 2.64, or 12.78 μg/L) or PS-NPs (10 mg/L) or their combination for 120 days. The results showed that TDCIPP and PS-NPs accumulated in the gut, gill, head, and liver of the zebrafish in a sex-dependent manner. The presence of PS-NPs promoted the bioaccumulation of TDCIPP in the adult fish and increased the parental transfer of TDCIPP to their offspring. We demonstrate that parental exposure to TDCIPP alone or in combination with PS-NPs induces thyroid disruption in adults, and then leads to thyroid endocrine disruption in their larval offspring. Reduced thyroxine (T4) and 3,5,3'-triiodothyronine (T3) levels contributed to the observed transgenerational thyroid dysfunction, which inhibited developmental growth and disturbed the transcription of genes and expression of proteins involved in the hypothalamic-pituitary-thyroid (HPT) axis in the F1 larvae. The increased transfer of TDCIPP to the offspring in the presence of PS-NPs also enhanced transgenerational thyroid endocrine disruption, demonstrated by a further reduction in T4 and the upregulation of thyroglobulin (tg), uridine diphosphate-glucuronosyltransferase (ugt1ab), thyroid-stimulating hormone (tshβ), and thyroid hormone receptor (trα) expression in the F1 larvae compared with the effects of parental TDCIPP exposure alone. Overall, our results indicate that the presence of PS-NPs modifies the bioavailability of TDCIPP and aggravates transgenerational thyroid disruption in zebrafish.

The joint effect of parental exposure to microcystin-LR and polystyrene nanoplastics on the growth of zebrafish offspring

The coexistence of nanoplastics (NPs) and various pollutants in the environment has become a problem that cannot be ignored. In order to identify the microcystin-LR (MCLR) bioaccumulation and the potential impacts on the early growth of F1 zebrafish (Danio rerio) offspring in the presence of polystyrene nanoplastics (PSNPs), PSNPs and MCLR were used to expose adult zebrafish for 21days. The exposure groups divided into MCLR (0, 0.9, 4.5 and 22.5μgL^-1) alone groups and PSNP (100μgL^-1) and MCLR co-exposure groups. F1 embryos were collected and developed to 120 h post-fertilization (hpf) in clear water. Compared with the exposure to MCLR only, the combined exposure increased the parental transfer of MCLR to the offspring and subsequently exacerbated the growth inhibition of F1 larvae. Further research clarified that combined exposure of PSNPs and MCLR could reduce the levels of thyroxine (T4) and 3, 5, 3'-triiodothyronine (T3) by altering the expression of hypothalamus-pituitary-thyroid (HPT) axis-related genes, eventually leading to growth inhibition of F1 larvae. Our results also exhibited combined exposure of PSNPs and MCLR could change the transcription of key genes of the GH/IGF axis compared with MCLR single exposure, suggesting the GH/IGF axis was a potential target for the growth inhibition of F1 larvae in PSNPs and MCLR co-exposure groups. The present study highlights the potential risks of coexistence of MCLR and PSNPs on development of fish offspring, and the environmental risks to aquatic ecosystems.

First insights into the formation and long-term dynamic behaviors of nonextractable perfluorooctanesulfonate and its alternative 6:2 chlorinated polyfluorinated ether sulfonate residues in a silty clay soil

Per- and polyfluoroalkyl substances (PFAS) are persistent and toxic contaminants that are ubiquitous in the environment. They can incorporate into soil as nonextractable residues (NER) which are not detectable with conventional analytical protocols but are still possible to remobilize with changes of surrounding conditions, and thus will be bioavailable again. Therefore, there is a need to investigate thoroughly the long-term fate of NER-PFAS. In this study, a 240-day incubation of perfluorooctanesulfonate (PFOS) and its alternative 6:2 chlorinated polyfluorinated ether sulfonate (F-53B) in a silty clay topsoil was carried out. Solvent extraction, alkaline hydrolysis and sequential chemical degradation were applied on periodically sampled soil to obtain extractable, moderately bound and deeply bound PFAS, respectively. The results confirmed the formation of NER of both compounds but with different preferences of incorporating mechanisms. NER-PFOS was formed predominantly by covalent binding (via head group) and strong adsorption (via tail group). The formation of NER-F-53B was mainly driven by physical entrapment. Both bound compounds within the incubation period showed three-stage behaviors including an initial period with slight release followed by a (re) incorporating stage and a subsequent remobilizing stage. This work provides some first insights on the long-term dynamic behaviors of nonextractable PFAS and will be conducive to their risk assessment and remediation (e.g. estimating potential NER-PFAS level based on their free extractable level, and selecting remediation methods according to their prevailing binding mechanisms).

Effects of the tributyltin on the blood parameters, immune responses and thyroid hormone system in zebrafish

Tributyltin (TBT) is a widely used organotin compound around the world and was frequently detected in surface waters, which would pose risk to aquatic organisms. However, the mechanisms of TBT-induced toxicity is not full clear. The present study investigated the effects of the tributyltin (TBT) on the blood parameters, immune responses and thyroid hormone system in zebrafish. Fish were exposed to sublethal concentrations of TBT (10 ng/L, 100 ng/L and 300 ng/L) for 6 weeks. The effects of long-term exposure to TBT on blood parameters (NH3, ammonia; GLU, glucose; TP, total proteins; CK, creatine kinase; ALT, alanine aminotransferase; AST, aspartate aminotransferase), immune responses (Lys, lysozyme; IgM, immunoglobulin M) and some indexes related thyroid hormone system (T3, 3,5,3'-triiodothyronine; T4, thyroxine) were measured in zebrafish, as well as the expression of genes related to immune responses and thyroid hormone system. Based on the results, the physiological-biochemical responses was significantly enhanced with an increase in TBT concentration, reflected by the abnormal blood indices, dysregulation of endocrine system and immunotoxicity in zebrafish under TBT stress. The present study greatly extends our understanding of adverse effects of TBT on aquatic organisms.

Temporal Trends in Prenatal Exposure (1998-2018) to Emerging and Legacy Per- and Polyfluoroalkyl Substances (PFASs) in Cord Plasma from the Beijing Cord Blood Bank, China

Due to developmental toxicity, prenatal exposure to per- and polyfluoroalkyl substances (PFASs) in animals may result in adverse effects on the fetus. However, little information is available on PFASs presence in the human cord plasma. Here, we measured the levels of 37 emerging and legacy PFASs in 650 cord plasma samples collected every 5 years spanning 1998 to 2018 by the Beijing Cord Blood Bank and evaluated changes in PFASs concentrations using generalized additive models. We observed an increase in the concentrations of 24 PFASs (Σ₂₄PFASs) from 1998 to 2003 followed by a decrease every 5 years from 2003 to 2018. For legacy PFASs, similar trends were observed for PFOS, whereas PFOA levels did not decline until 2013. For emerging chemicals, 6:2 Cl-PFESA showed a similar trend as PFOS, and prenatal exposure to 6:2 Cl-PFESA could be traced back to 1998, with a median concentration of 0.411 ng/mL in plasma. Our data showed that prenatal exposure to legacy PFASs has gradually decreased in cord plasma from the Beijing Cord Blood Bank in recent years, and the discovery of the presence of emerging chemicals in 1998 suggested that further evaluation is needed to assess possible health risks to pregnant women and fetuses.

Orally Administered 6:2 Chlorinated Polyfluorinated Ether Sulfonate (F-53B) Causes Thyroid Dysfunction in Rats

The compound 6:2 chlorinated polyfluorinated ether sulfonate (F-53B), a replacement for perfluorooctanesulfonate (PFOS) in the electroplating industry, has been widely detected in numerous environmental matrices, human sera, and organisms. Due to regulations that limit PFOS use, F-53B use is expected to increase. Therefore, in this study, we performed a subchronic oral toxicity study of F-53B in Sprague Dawley (SD) rats. F-53B was administered orally once daily to male and female rats for 28 days at doses of 5, 20, and 100 mg/kg/day. There were no toxicologically significant changes in F-53B-treated rats, except in the thyroid gland. However, F-53B slightly reduced the serum concentrations of thyroid hormones, including triiodothyronine and thyroxine, compared with their concentrations in the vehicle group. F-53B also induced follicular hyperplasia and was associated with increased thyroid hormone biosynthesis-associated protein expression. These results demonstrate that F-53B is a strong regulator of thyroid hormones in SD rats as it disrupts thyroid function. Thus, caution should be exercised in the industrial application of F-53B as an alternative for PFOS.

Parental exposure to cadmium chloride causes developmental toxicity and thyroid endocrine disruption in zebrafish offspring

Cadmium is a common heavy metal pollutant. Previous studies have found that long-term cadmium exposure can cause damage to multiple organs/systems in humans and experimental animals; however, there are few studies that elucidate its effects on offspring development, discuss whether it can be transmitted to offspring from the parent, and debate whether it affects the functional development of the thyroid hormone system in offsprings. In this study, sexually mature zebrafish were exposed to different concentrations of cadmium chloride (0.01 μmol/L, 0.1 μmol/L, and 1 μmol/L) to study reproductive toxicity. It was found that parental zebrafish exposed to 1 μmol/L of cadmium chloride produced offsprings with different degrees of malformation. At 5 days post-fertilization (dpf), the levels of 3,5,3'-triiododenosine (T3) and thyroxine (T4) in the zebrafish were decreased. At 10 dpf, the T4 and T3 levels in the zebrafish of the offspring were significantly reduced. At the same time, the expression of thyroid receptor (trα and trβ) genes in five dpf larvae was significantly up-regulated in the 1 μmol/L treatment group relative to the control group. The mRNAs of thyroid hormone synthesis and metabolism-related genes (tshβ, dio1, dio2, ugt1ab, and ttr) were significantly up-regulated in the 0.1 μmol/L and 1 μmol/L treatment groups. This study demonstrates that parental cadmium chloride exposure produces reproductive toxicity in zebrafish and that the effects can be transferred from the parent to the offspring, resulting in developmental toxicity in the thyroid endocrine system.

Toxicokinetics and persistent thyroid hormone disrupting effects of chronic developmental exposure to chlorinated polyfluorinated ether sulfonate in Chinese rare minnow

The abnormality in thyroid hormone modulation in developmental fish, vulnerable to per- and polyfluorinated substances, is of particular concerns for the alternative substances. Juvenile rare minnows, were exposed to chlorinated polyfluoroalkyl ether sulfonates (Cl-PFESAs), the novel alternatives to perfluorooctane sulfonate (PFOS), for 4 weeks followed by 12 weeks of depuration. Half lives were determined to be 33 d, 29 d, and 47 d for total Cl-PFESAs, C8 Cl-PFESA and C10 Cl-PFESA, respectively. Preliminary toxicity test suggested that Cl-PFESAs are moderately toxic to Rare minnow with a LC50 of 20.8 mg/L (nominal concentration） after 96 h of exposure. In the chronic toxicity test, fishes were exposed to Cl-PFESAs at geometric mean measured concentrations of 86.5 μg/L, 162 μg/L and 329 μg/L. In juvenile fishes exposed to Cl-PFESAs for 4 weeks, gene profile sequencing analysis identified 3313 differentially expressed genes, based on which pathways regulating thyroid hormone synthesis and steroid synthesis were enriched. Both whole body total and free 3,5,3'-triiodothyronine (T3) levels were significantly increased. mRNA expression of genes regulating thyroid hormone synthesis (corticotropin-releasing hormone (CRH), thyroid-stimulating hormone (THS), sodium/iodide symporter (NIS), thyroglobulin (TG), and thyroid peroxidase (TPO), transport (transthyretin,TTR), deiodinase (Dio1, Dio2) and receptor (TRα and TRβ) were decreased. Uridinediphosphate glucoronosyl-transferases (UGT1A) gene, regulating THs metabolism, was also decreased. In adult fish, thyroid hormone and genes expression in hypothalamic-pituitary-thyroid axis remained at disturbed levels after 12 weeks of depuration without exposure. Chronic developmental exposure to Cl-PFESAs caused persistent thyroid hormone disrupting effects in fish, highlighting a necessity of comprehensive ecological risk assessment.

F-53B and PFOS treatments skew human embryonic stem cell in vitro cardiac differentiation towards epicardial cells by partly disrupting the WNT signaling pathway

F-53B and PFOS are two per- and polyfluoroalkyl substances (PFASs) widely utilized in the metal plating industry as mist suppressants. Recent epidemiological studies have linked PFASs to cardiovascular diseases and alterations in heart geometry. However, we still have limited understanding of the effects of F-53B and PFOS on the developing heart. In this study, we employed a human embryonic stem cell (hESC)-based cardiac differentiation system and whole transcriptomics analyses to evaluate the potential developmental cardiac toxicity of F-53B and PFOS. We utilized F-53B and PFOS concentrations of 0.1-60 μM, covering the levels detected in human blood samples. We demonstrated that both F-53B and PFOS inhibited cardiac differentiation and promoted epicardial specification via upregulation of the WNT signaling pathway. Most importantly, the effects of F-53B were more robust than those of PFOS. This was because F-53B treatment disrupted the expression of more genes and led to lower cardiac differentiation efficiency. These findings imply that F-53B may not be a safe replacement for PFOS.

Environmental co-exposure to TBT and Cd caused neurotoxicity and thyroid endocrine disruption in zebrafish, a three-generation study in a simulated environment

Although the coexistence of heavy metals and environmental hormones always occur in aquatic environment, the information of the combined impacts remains unclear. To explore the multi-generational toxicity of cadmium (Cd) and tributyltin (TBT), adult zebrafish (Danio rerio) (F0) were exposed to different treated groups (100 ng/l Cd, 100 ng/l TBT and their mixture) for 90 d, with their offspring (F1 and F2) subsequently reared in the same exposure solutions corresponding to their parents. Both developmental neurotoxicity and thyroid disturbances were examined in the three (F0, F1, and F2) generations. Our results showed that co-exposure to Cd and TBT induced the developmental neurotoxicity in F1 and F2 generations, reflected by the significant lower levels of neurotransmitters (dopamine and serotonin) and the inhibited acetylcholinesterase (AChE) activities. And the thyroid endocrine disruption were observed in the two-generations larval offspring by parental exposure to Cd and/or TBT, including the significantly decreasing levels of thyroid hormones and the down-regulated the expression of genes involved in the hypothalamus-pituitary-thyroid axis, compared to the control. Additional, the embryonic toxicity and growth inhibition were also determined in the fish larvae. Overall, this study examined the impacts of parental co-exposure to Cd and TBT, with regard to developmental inhibition, nervous system damage and endocrine disruption, which highlighted that co-exposure influences are complicated and need to be considered for accurate environmental risk assessment.

Parental exposure to triphenyltin inhibits growth and disrupts thyroid function in zebrafish larvae

Triphenyltin (TPT) is widely used and commonly found in a water environment, so its effects on aquatic systems are of great concern. This study aimed to reveal the effects of chronic parental exposure of TPT on thyroid disruption and growth inhibition in zebrafish. Adult zebrafish (F0 generation) were exposed to environmentally relevant concentrations (1, 10, and 100 ng/L) of TPT for 60 days, and the larvae (F1 generation) were tested without TPT treatment. Results demonstrated that parental exposure to TPT disrupts thyroid function in zebrafish offspring: serum thyroxine (T4) significantly decreased, while serum 3,5,3'-triiodothyronine (T3) increased, and several genes involved in the hypothalamic-pituitary-thyroid (HPT) axis were down-regulated. In addition, we observed developmental abnormalities in the larvae, demonstrated by a significantly altered hatching rate, malformation rate, body length, heart rate, and survival rate, as well as down-regulation of genes involved in the growth hormone/insulin-like growth factor (GH/IGF) axis. Therefore, parental exposure to TPT induces toxicity in fish offspring through perturbation of the HPT and GH/IGF axes.

Perfluoropolyether carboxylic acids (novel alternatives to PFOA) impair zebrafish posterior swim bladder development via thyroid hormone disruption

Perfluoropolyether carboxylic acids (PFECAs, CF₃(OCF₂)_nCOO^-, n = 2-5) are novel alternatives to perfluorooctanoic acid (PFOA) and are widely used in industrial production. However, although they have been detected in surface water and human blood, their toxicities on aquatic organisms remain unknown. We used zebrafish embryos to compare the developmental toxicities of various PFECAs (e.g., perfluoro (3,5,7-trioxaoctanoic) acid (PFO3OA), perfluoro (3,5,7,9-tetraoxadecanoic) acid (PFO4DA), and perfluoro (3,5,7,9,11-pentaoxadodecanoic) acid (PFO5DoDA)) with that of PFOA and to further reveal the key events related to toxicity caused by these chemicals. Results showed that, based on half maximal effective concentrations (EC₅₀), toxicity increased in the order: PFO5DoDA > PFO4DA > PFOA > PFO3OA, with uninflated posterior swim bladders the most frequently observed malformation. Similar to PFOA, PFECA exposure significantly lowered thyroid hormone (TH) levels (e.g., T3 (3,5,3'-L-triiodothyronine) and T4 (L-thyroxine)) in the whole body of larvae at 5 d post-fertilization following disrupted TH metabolism. In addition, the transcription of UDP glucuronosyltransferase 1 family a, b (ugt1ab), a gene related to TH metabolism, increased dose-dependently. Exogeneous T3 or T4 supplementation partly rescued PFECA-induced posterior swim bladder malformation. Our results further suggested that PFECAs primarily damaged the swim bladder mesothelium during early development. This study is the first to report on novel emerging PFECAs as thyroid disruptors causing swim bladder malformation. Furthermore, given that PFECA toxicity increased with backbone OCF₂ moieties, they may not be safer alternatives to PFOA.

Effects of low concentrations of triphenyltin on neurobehavior and the thyroid endocrine system in zebrafish

In the present study, to evaluate neurobehavioral toxicity and the thyroid-disrupting effects of environmental levels of triphenyltin (TPT), the zebrafish larvae were exposed to 1, 10 and 100 ng/l TPT. In the neurobehavioral assay, increased levels of dopamine and serotonin, decreased content of nitric oxide, inhibited activities of acetylcholinesterase and monoamine oxidase were observed in the whole body of zebrafish larvae after TPT treatment, as well as the serious abnormal non-reproductive behavior. Moreover, the whole-body the T4 levels were markedly decreased significantly, whereas T3 levels were not significantly changed under TPT stress. In addition, TPT exposure significantly changed the expression levels of genes related to thyroid system, including corticotropin-releasing hormone gene crh, thyroid-stimulating hormone gene tshβ, thyroglobulin gene tg, sodium/iodide symporter gene nis, thyroid hormone nuclear receptor trα, isoform trβ, types I deiodinase gene dio1and types II deiodinase gene dio2. The regulated responsiveness of thyroid hormone and related genes expression levels suggested that TPT could induce the thyroid disrupting effects in zebrafish larvae. Therefore, our results provide new aspects of TPT as an endocrine disrupting chemical.

Comparative thyroid disruption by o,p'-DDT and p,p'-DDE in zebrafish embryos/larvae

1,1-Trichloro-2-(p-chlorophenyl)-2-(o-chlorophenyl) ethane (o,p'-DDT) and 1,1-dichloro-2,2-bis (p-chlorophenyl)-ethylene (p,p'-DDE) cause thyroid disruption, but the underlying mechanisms of these disturbances in fish remain unclear. To explore the potential mechanisms of thyroid dysfunction caused by o,p'-DDT and p,p'-DDE, thyroid hormone and gene expression levels in the hypothalamic-pituitary-thyroid (HPT) axis were measured, and the developmental toxicity were recorded in zebrafish larvae. Zebrafish embryos/larvae were exposed to o,p'-DDT (0, 0.28, 2.8, and 28 nM; or 0, 0.1, 1, and 10 μg/L) and p,p'-DDE (0, 1.57, 15.7, and 157 nM; or 0, 0.5, 5, and 50 μg/L) for 7 days. The genes related to thyroid hormone synthesis (crh, tshβ, tg, nis and tpo) and thyroid development (nkx2.1 and pax8) were up-regulated in both the o,p'-DDT and p,p'-DDE exposure groups. Zebrafish embryos/larvae exposed to o,p'-DDT showed significantly increased total whole-body T4 and T3 levels, with the expression of ugt1ab and dio3 being significantly down-regulated. However, the p,p'-DDE exposure groups showed significantly lowered whole-body total T4 and T3 levels, which were associated with up-regulation and down-regulation expression of the expression of dio2 and ugt1ab, respectively. Interestingly, the ratio of T3 to T4 was significantly decreased in the o,p'-DDT (28 nM) and p,p'-DDE (157 nM) exposure groups, suggesting an impairment of thyroid function. In addition, reduced survival rates and body lengths and increased malformation rates were recorded after treatment with either o,p'-DDT or p,p'-DDE. In summary, our study indicates that the disruption of thyroid states was different in response to o,p'-DDT and p,p'-DDE exposure in zebrafish larvae.

Cationic polymer for selective removal of GenX and short-chain PFAS from surface waters and wastewaters at ng/L levels

The emerging classes of perfluorinated alkyl substances (PFAS) (e.g., Perfluorobutanoic acid (PFBA), perfluorobutane sulfonic acid (PFBS), GenX, ADONA, and F-53B) are persistent and recalcitrant to removal by conventional treatment techniques. Herein, we report on poly (N-[3-(dimethylamino)propyl]acrylamide, methyl chloride quaternary, DMAPAA-Q) hydrogel matrix as an effective sorbent for sequestering PFAS from different water matrices. The selective removal of 16 PFAS from different classes using DMAPAA-Q polymer was confirmed in surface waters and treated wastewater at environmentally relevant concentration (i.e., <1000 ng/L). The results showed fast removal kinetics with equilibrium time of 60-120 min and a higher removal of sulfonated than carboxylic PFAS, regardless of their chain lengths. These observations were in agreement with adsorption energy calculations of short- and long-chain PFAS on poly DMAPAA-Q hydrogel using density functional theory (DFT). No desorption was observed when the experimental time was extended to 24 h, which gives an added advantage of poly DMAPAA-Q hydrogel over previously reported adsorbents in the literature. In addition, the removal efficiency was not affected under a varying pH range of 4-10. The impact of background anions on PFAS removal by poly DMAPAA-Q hydrogel was tested and found to follow an order of SO₄^2- > Cl^- > NO₃^-. The performance of poly DMAPAA-Q hydrogel was maintained in six consecutive adsorption/regeneration cycles to remove PFAS. The unique fast kinetics and high adsorption activity of poly DMAPAA-Q hydrogel towards PFAS exhibits a great potential for being a promising material for PFAS control.