Chronic exposure to 6:2 chlorinated polyfluorinated ether sulfonate acid (F-53B) induced hepatotoxic effects in adult zebrafish and disrupted the PPAR signaling pathway in their offspring

Biochemical and transcriptomic analyses reveal the toxicological response and potential mechanism of butyl benzyl phthalate in zebrafish gills

Butyl benzyl phthalate (BBP), a common phthalate plasticizer, is frequently detected in aquatic environments. However, there has been relatively little research on its effects on gill-related responses. This study exposed adult zebrafish to BBP concentrations ranging from 5 to 500 μg/L for 28 days, specifically investigating its toxicity in the gills. Assessment of oxidative stress biomarkers and gene expression related to apoptosis and mitochondria was conducted. Results demonstrated that exposure to 500 μg/L of BBP disrupted the antioxidant defense system, leading to lipid peroxidation and DNA damage. Moreover, the expression level of the caspase-3 gene exhibited an approximate two-fold increase, whereas the expression of 18rs-rrn decreased by 50 % on day 28. Gene Ontology enrichment analysis indicated suppressed expression of antioxidant and metabolic process terms, alongside inhibition of metabolism, immune, and signal transduction-related pathways. This study offers novel insights into the toxic effects and mechanisms of BBP on fish, providing valuable data for assessing environmental risks linked to BBP contamination and advocating for its management in aquatic ecosystems.

Histology and transcriptomic analysis reveal the inflammation and affected pathways under 2-methylisoborneol (2-MIB) exposure on grass carp

2-Methylisoborneol (2-MIB) is a common and widely distributed off-flavor compound in water. However, the toxic mechanisms of 2-MIB on aquatic organisms remain largely unexplored. In this study, grass carp larvae were exposed to different concentrations (0, 5, and 20 μg L-1) of 2-MIB for 96 h. The accumulation of 2-MIB in the dorsal muscle was measured. Histological analysis, ultrastructure observations, and transcriptomic sequencing were conducted on the liver tissues. The results showed that 2-MIB accumulated significantly in the fish muscle, with the accumulation increasing as the exposure concentration increased through gas chromatography-mass spectrometry (GC-MS) detection. Histological and ultrastructure observations indicated that 2-MIB caused concentration-dependent inflammatory infiltration and mitochondrial damage in the liver. Transcriptomic analysis revealed lipid metabolism disorders induced by exposure to 2-MIB in grass carp. Additionally, 5 μg L-1 2-MIB affected the neurodevelopment and cardiovascular system of grass carp larvae through extracellular matrix (ECM)-receptor interaction and focal adhesion pathway. Furthermore, several pathways related to the digestive system were significantly enriched, implying that 2-MIB may impact pancreatic secretion function, protein digestion and absorption processes. These findings provide new insights into the potential toxicological mechanisms of 2-MIB.

Changing the structure of PFOA and PFOS: a chemical industry strategy or a solution to avoid thyroid-disrupting effects?

BACKGROUND

The family of perfluoroalkyl and polyfluoroalkyl substances (PFAS) raised concern for their proven bioaccumulation and persistence in the environment and animals as well as for their hazardous health effects. As a result, new congeners of PFAS have rapidly replaced the so-called "old long-chain PFAS" (mainly PFOA and PFOS), currently out-of-law and banned by most countries. These compounds derive from the original structure of "old long-chain PFAS", by cutting or making little conformational changes to their structure, thus obtaining new molecules with similar industrial applications. The new congeners were designed to obtain "safer" compounds. Indeed, old-long-chain PFAS were reported to exert thyroid disruptive effects in vitro, and in vivo in animals and humans. However, shreds of evidence accumulated so far indicate that the "restyling" of the old PFAS leads to the production of compounds, not only functionally similar to the previous ones but also potentially not free of adverse health effects and bioaccumulation. Studies aimed at characterizing the effects of new-PFAS congeners on thyroid function indicate that some of these new-PFAS congeners showed similar effects.

PURPOSE

The present review is aimed at providing an overview of recent data regarding the effects of novel PFAS alternatives on thyroid function.

RESULTS AND CONCLUSIONS

An extensive review of current legislation and of the shreds of evidence obtained from in vitro and in vivo studies evaluating the effects of the exposure to novel PFOA and PFOS alternatives, as well as of PFAS mixture on thyroid function will be provided.

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.

Per- and polyfluoroalkyl substances in Chinese commercially available red swamp crayfish (Procambarus clarkii): Implications for human exposure and health risk assessment

The extensive utilization of per- and polyfluoroalkyl substances (PFASs) has led to their pervasive presence in the environment, resulting in contamination of aquatic products. Prolonged exposure to PFASs has been linked to direct hepatic and renal damage, along with the induction of oxidative stress, contributing to a spectrum of chronic ailments. Despite the recent surge in popularity of red swamp crayfish as a culinary delicacy in China, studies addressing PFASs' exposure and associated health risks from their consumption remain scarce. To address this gap, our study investigated the PFASs' content in 85 paired edible tissue samples sourced from the five primary red swamp crayfish breeding provinces in China. The health risks associated with dietary exposure were also assessed. Our findings revealed widespread detection of PFASs in crayfish samples, with short-chain perfluoroalkyl carboxylic acids (PFCAs) exhibiting the highest concentrations. Notably, the total PFAS concentration in the hepatopancreas (median: 160 ng/g) significantly exceeded that in muscle tissue (5.95 ng/g), as did the concentration of every single substance. The hazard quotient of perfluorohexanesulfonic acid (PFHxS) via consuming crayfish during peak season exceeded 1. In this case, a potential total non-cancer health risk of PFASs, which is mainly from the hepatopancreas and associated with PFHxS, is also observed (hazard index>1). Thus, it is recommended to avoid consuming the hepatopancreas of red swamp crayfish. Greater attention should be paid to governance technology innovation and regulatory measure strengthening for short-chain PFASs.

Hepatic injury and ileitis associated with gut microbiota dysbiosis in mice upon F-53B exposure

Chlorinated polyfluorinated ether sulfonate (F-53B), a substitute of perfluorooctane sulfonic acid (PFOS), has attracted significant attention for its link to hepatotoxicity and enterotoxicity. Nevertheless, the underlying mechanisms of F-53B-induced enterohepatic toxicity remain incompletely understood. This study aimed to explore the role of F-53B exposure on enterohepatic injury based on the gut microbiota, pathological and molecular analysis in mice. Here, we exposed C57BL/6 mice to F-53B (0, 4, 40, and 400 μg/L) for 28 days. Our findings revealed a significant accumulation of F-53B in the liver, followed by small intestines, and feces. In addition, F-53B induced pathological collagen fiber deposition and lipoid degeneration, up-regulated the expression of fatty acid β-oxidation-related genes (PPARα and PPARγ, etc), while simultaneously down-regulating pro-inflammatory genes (Nlrp3, IL-1β, and Mcp1) in the liver. Meanwhile, F-53B induced ileal mucosal barrier damage, and an up-regulation of pro-inflammatory genes and mucosal barrier-related genes (Muc1, Muc2, Claudin1, Occludin, Mct1, and ZO-1) in the ileum. Importantly, F-53B distinctly altered gut microbiota compositions by increasing the abundance of Akkermansia and decreasing the abundance of Prevotellaceae_NK3B31_group in the feces. F-53B-altered microbiota compositions were significantly associated with genes related to fatty acid β-oxidation, inflammation, and mucosal barrier. In summary, our results demonstrate that F-53B is capable of inducing hepatic injury, ileitis, and gut microbiota dysbiosis in mice, and the gut microbiota dysbiosis may play an important role in the F-53B-induced enterohepatic toxicity.

Per- and polyfluoroalkyl substances induce lipid metabolic impairment in fish: Integration on field investigation and laboratory study

The biotoxicity of perfluoroalkyl and polyfluoroalkyl substances (PFASs) to aquatic organisms has been widely concerned. However, studies on toxic effects of PFASs are usually evaluated directly by using laboratory exposure rather than laboratory validation based on data obtained in the field. In this study, wild catfish (Silurus meridinalis) was explored on the relationship between PFASs bioaccumulation and lipid disorders. Nine and thirteen lipid metabolites were significantly associated with perfluorooctane sulfonate (PFOS) and 6:2/8:2Cl-PFESA (trade name F-53B) exposures, respectively; and the correlated lipid metabolites were the fatty acid (FA) and conjugates, FA esters, steroids, and glycerophosphate subclasses. The effects of PFASs on lipid metabolism of fish and its mechanism were further analyzed through exposure experiments. Zebrafish (Danio rerio) of different sexes underwent PFOS and F-53B exposures for 21 days at 100 ng/L and 100 μg/L. By determining gene expression levels, hepatic lipid contents, and histopathological change, the adverse effects order on lipid metabolism in male or female was 100 μg/L F-53B > 100 μg/L PFOS > 100 ng/L F-53B > 100 ng/L PFOS; the stress response in male was more intensive than that in female. PFOS and F-53B activated the peroxisome proliferator-activated receptor pathway, promoting the processes of FA and total cholesterol (T-CHO) transport, FA β-oxidation, FA synthesis, and finally induced FA and T-CHO transportation from blood into liver, then accelerated FA to FA ester transformation, and CHO into steroids. Laboratory experiments confirmed the field analysis. This study innovatively explored the adverse effects of PFOS and F-53B on lipid metabolism and their mechanisms at field and laboratory levels, highlighting concerns regarding PFASs health risks.

Potential effects of individual and combined exposure to tetraconazole and cadmium on zebrafish from the perspective of enantioselectivity and intestinal microbiota

As the wide use of pesticides, they could form combined pollution with heavy metals, which would affect their environmental behaviors and toxic effects. Particularly, the effects would be more intricate for chiral pesticides. In this study, the accumulation and dissipation trends of tetraconazole enantiomers in zebrafish were investigated by individual and combined exposure of cadmium (Cd) and tetraconazole (including racemate and enantiomers) after confirming the absolute configuration of tetraconazole enantiomer. For the enantiomer treatments, Cd enhanced the accumulation of S-(+)-tetraconazole, but declined the concentrations of R-(-)-tetraconazole in zebrafish. The dissipation half-lives of tetraconazole enantiomers were extended by 1.65-1.44 times after the combined exposure of Cd and enantiomers. The community richness and diversity of intestinal microbiota were reduced in all treatments, and there were significant differences in R + Cd treatment. There was synergistic effect between Cd and S-(+)-tetraconazole for the effects on the relative abundances of Fusobacteria, Firmicutes, Proteobacteria, Actinobacteria, and Bacteroidetes. For R-(-)-tetraconazole, Cd mainly exhibited antagonistic effects. In the combined exposure of Cd and S-(+)-tetraconazole, the relative abundance changes of Cetobacterium (Fusobacteria, increase) and Edwardsiella (Proteobacteria, decrease) might affect the carbohydrate metabolism and energy metabolism, and led to the increase of S-(+)-tetraconazole bioaccumulation concentration. In the combined exposure of Cd and R-(-)-tetraconazole, Cd could increase the relative abundance of Edwardsiella (Proteobacteria), and affect the amino acid metabolism, which might reduce the bioaccumulation concentration of R-(-)-tetraconazole. This study reported for the first time that the abundance of intestinal microbiota in zebrafish might affect the bioaccumulation and dissipation of tetraconazole enantiomers, and would provide new insight for the study of combined pollutions.

Hepatotoxicity induced in rats by chronic exposure to F-53B, an emerging replacement of perfluorooctane sulfonate (PFOS)

A plethora of studies have shown the prominent hepatotoxicity caused by perfluorooctane sulfonate (PFOS), yet the research on the causality of F-53 B (an alternative for PFOS) exposure and liver toxicity, especially in mammals, is largely limited. To investigate the effects that chronic exposure to F-53 B exert on livers, in the present study, male SD rats were administrated with F-53 B in a certain dose range (0, 1, 10, 100, 1000 μg/L, eight rats per group) for 6 months via drinking water and the hepatotoxicity resulted in was explored. We reported that chronic exposure to 100 and 1000 μg/L F-53 B induced remarkable histopathological changes in liver tissues such as distinct swollen cells and portal vein congestion. In addition, the increase of cytokines IL-6, IL-2, and IL-8 upon long-term administration of F-53 B demonstrated the high level of inflammation. Moreover, F-53 B exposure was revealed to disrupt the lipid metabolism in the rat livers, mainly manifesting as the upregulation of some proteins involved in lipid synthesis and degradation, including ACC, FASN, SREBP-1c as well as ACOX1. These findings provided new evidence for the adverse effects caused by chronic exposure to F-53 B in rodents. It is crucial for industries, regulatory agencies as well as the public to remain vigilant about the adverse health effects associated with the emerging PFOS substitutes such as F-53 B. Implementation of regular monitoring and risk assessments is of great importance to alleviate environmental concerns towards PFOS alternatives exposure, and furthermore, to minimize the latent health risks to the public health.

Evidence of promoting effects of 6:2 Cl-PFESA on hepatocellular carcinoma proliferation in humans: An ideal alternative for PFOS in terms of environmental health?

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are synthetic chemicals, encompassing compounds like perfluorooctane sulfonate (PFOS), which have widespread applications across various industries, including food packaging and firefighting. In recent years, China has increasingly employed 6:2 Cl-PFESA as an alternative to PFOS. Although the association between PFAS exposure and hepatocellular carcinoma (HCC) has been demonstrated, the underlying mechanisms that promote HCC proliferation are uncleared. Therefore, we aimed to investigate the effects and differences of PFOS and 6:2 Cl-PFESA on HCC proliferation through in vivo and in vitro tumor models. Our results reveal that both PFOS and 6:2 Cl-PFESA significantly contribute to HCC proliferation in vitro and in vivo. Exposure led to reduced population doubling times, enlarged cell colony sizes, enhanced DNA synthesis efficiency, and a higher proportion of cells undergoing mitosis. Furthermore, both PFOS and 6:2 Cl-PFES) have been shown to activate the PI3K/AKT/mTOR signaling pathway and inhibit necroptosis. This action consequently enhances the proliferation of HCC cells. Our phenotypic assay findings suggest that the tumorigenic potential of 6:2 Cl-PFESA surpasses that of PFOS; in a subcutaneous tumor model using nude mice, the mean tumor weight for the 6:2 Cl-PFESA-treated cohort was 2.33 times that observed in the PFOS cohort (p < 0.01). Despite 6:2 Cl-PFESA being considered a safer substitute for PFOS, the pronounced effects of this chemical on HCC cell growth warrant a thorough assessment of hepatotoxicity risks linked to its usage.

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.

The untold story of PFAS alternatives: Insights into the occurrence, ecotoxicological impacts, and removal strategies in the aquatic environment

Due to increasing regulations on the production and consumption of legacy per- and polyfluoroalkyl substances (PFAS), the global use of PFAS substitutes increased tremendously, posing serious environmental risks owing to their bioaccumulation, toxicity, and lack of removal strategies. This review summarized the spatial distribution of alternative PFAS and their ecological risks in global freshwater and marine ecosystems. Further, toxicological effects of novel PFAS in various freshwater and marine species were highlighted. Moreover, degradation mechanisms for alternative PFAS removal from aquatic environments were compared and discussed. The spatial distribution showed that 6:2 chlorinated polyfluorinated ether sulfonate (6:2 CI-PFAES, also known as F-53B) was the most dominant emerging PFAS found in freshwater. Additionally, the highest levels of PFBS and PFBA were observed in marine waters (West Pacific Ocean). Moreover, short-chain PFAS exhibited higher concentrations than long-chain congeners. The ecological risk quotients (RQs) for phytoplankton were relatively higher >1 than invertebrates, indicating a higher risk for freshwater phytoplankton species. Similarly, in marine water, the majority of PFAS substitutes exhibited negligible risk for invertebrates and fish, and posed elevated risks for phytoplanktons. Reviewed studies showed that alternative PFAS undergo bioaccumulation and cause deleterious effects such as oxidative stress, hepatoxicity, neurotoxicity, histopathological alterations, behavioral and growth abnormalities, reproductive toxicity and metabolism defects in freshwater and marine species. Regarding PFAS treatment methods, photodegradation, photocatalysis, and adsorption showed promising degradation approaches with efficiencies as high as 90%. Finally, research gaps and future perspectives for alternative PFAS toxicological implications and their removal were offered.

Migration mechanism and risk assessment of per- and polyfluoroalkyl substances in the Ya'Er Lake oxidation pond area, China

The migration mechanisms, sources, and environmental risks of 29 legacy and emerging perfluorinated and polyfluoroalkyl species present in an oxidation pond (Ya'Er Lake) were investigated for treating sewage based on the analysis of their occurrence and distribution. The concentration of per- and polyfluoroalkyl substances (PFAS) in pond area was between 0.30 and 63.2 ng/g dw (dry weight), with the overall average concentration of 8.00 ng/g dw. Notably, the PFAS concentrations in the surface sediments near the sewage outlet in Pond-1 (50.2 ng/g dw) and Pond-5 (average 15.1 ng/g dw) were 1-2 orders of magnitude higher than those in other areas. In general, the legacy PFAS, i.e., perfluorooctane sulfonic acid was considered to be the major pollutant in the polluted area, on average, accounting for 73.0% of the total concentration of PFAS pollutants. By evaluating the regional distribution of different PFAS homologs, the short-chain PFAS pollutants with lower Kow were found to migrate farther in both horizontal and vertical directions. The sewage outlets in Pond-1 and Pond-5 are the main pollution sources in polluted area and the emerging PFAS pollutants in Pond-5 have replaced the legacy PFAS pollutants as the main pollutants. Based on positive matrix factorization analysis, three main industrial sources of PFAS pollutants in the study area were identified: protective coating, fire-fighting, and food packaging sources. Moreover, the environmental risk assessment results showed that most study areas exhibited medium environmental risk (0.01 ≤ Risk quotient (RQ) < 1), indicating that the ecological environment risks in this area need further attention.

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.

Overall and individual associations between per- and polyfluoroalkyl substances and liver function indices and the metabolic mechanism

Per- and polyfluoroalkyl substances (PFAS) can disrupt liver homeostasis. Studies have shown that a single exposure to PFAS may provoke abnormal liver function; however, few studies have investigated the overall effect of PFAS mixtures. We aimed to investigate associations between exposure to PFAS mixtures and liver function indices and explore the relevant mechanisms. This study included 278 adult males from Guangzhou, China. Serum metabolite profiles were analyzed using untargeted metabolomics. We applied weighted quantile sum (WQS) regression as well as Bayesian kernel machine regression (BKMR) to analyze the association of nine PFAS mixtures with 14 liver function indices. PFAS mixtures were positively associated with apolipoprotein B (APOB) and gamma-glutamyltransferase (GGT) and negatively associated with direct bilirubin (DBIL) and total bilirubin (TBIL) in both the WQS and BKMR analyses. In addition, Spearman's correlation test showed individual PFAS correlated with APOB, GGT, TBIL, and DBIL, while there's little correlation between individual PFAS and other liver function indices. In linear regression analysis, PFHxS, PFOS, PFHpS, PFNA, PFDA, and PFUdA were associated with APOB; PFOA, PFDA, PFOS, PFNA, and PFUdA were associated with GGT. Subsequently, a metabolome-wide association study and mediation analysis were combined to explore metabolites that mediate these associations. The mechanisms linking PFAS to APOB and GGT are mainly related with amino acid and glycerophospholipid metabolism. High-dimensional mediation analysis showed that glycerophospholipids are the main markers of the association between PFAS and APOB, and that (R)-dihydromaleimide, Ile Leu, (R)-(+)-2-pyrrolidone-5-carboxylic acid, and L-glutamate are the main markers of the association between PFAS and GGT. In summary, overall associations between PFAS and specific indices of liver function were found using two statistical methods; the metabolic pathways and markers identified here may serve to prompt more detailed study in animal-based systems, as well as a similar detailed analysis in other populations.

The toxic mechanism of 6:2 Cl-PFESA in adolescent male rats: Endocrine disorders and liver inflammation regulated by the gut microbiota-gut-testis/liver axis

In previous studies, 6:2 chlorinated polyfluorinated ether sulfonic acid (6:2 Cl-PFESA), a perfluorooctanesulfonate alternative, has been demonstrated to be toxic to mammals. However, the toxic mechanism of 6:2 Cl-PFESA in mammals is unknown. Herein, adolescent male rats were administered 50 μg/kg/Day 6:2 Cl-PFESA for 28 days (oral gavage) to estimate the toxicity of 6:2 Cl-PFESA and investigate its toxic mechanism. Significant changes in some hematological indicators (e.g., aspartate transaminase and neutrophils) and liver sections (inflammatory cell infiltration) indicated that 6:2 Cl-PFESA exposure caused rat hepatotoxicity. Six steroid hormones (e.g., testosterone, progesterone, and cortisol) in serum and thirteen genes in testicles (related to the pathway of steroid hormone biosynthesis) were significantly regulated in 6:2 Cl-PFESA-treated rats. This suggested that 6:2 Cl-PFESA induced rat endocrine disorders. Compared to the controls, the mean relative abundance of Ruminococcaceae, Pasteurellaceae, Micrococcaceae, and Desulfovibrionaceae was significantly regulated by 1.3-, 0.40-, 0.32-, and 3.2-fold in the 6:2 Cl-PFESA rats, respectively. The 6:2 Cl-PFESA treatment also significantly disturbed 47 gut metabolites (29 upregulated and 18 downregulated), mainly bile acids, short-chain fatty acids, and amino acids. In summary, 6:2 Cl-PFESA induced endocrine disorders and liver inflammation in rats by altering the gut microbiota-gut-testis/liver axis. This study first reveals the toxic mechanism of 6:2 Cl-PFESA in mammals through a multiomics approach and provides comprehensive insight into the toxic mechanism of 6:2 Cl-PFESA.

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.

Bioaccumulation, tissue distribution, and maternal transfer of novel PFOS alternatives (6:2 Cl-PFESA and OBS) in wild freshwater fish from Poyang Lake, China

As emerging alternatives to perfluorooctane sulfonate (PFOS), 6:2 chlorinated polyfluoroalkyl ether sulfonic acid (6:2 Cl-PFESA) and sodium p-perfluorous nonenox-benzenesulfonate (OBS) were frequently detected in the four freshwater fish species collected from Poyang Lake. Median concentrations of 6:2 Cl-PFESA and OBS in fish tissues were 0.046-6.0 and 0.46-5.1 ng/g wet weight, respectively. The highest concentrations of 6:2 Cl-PFESA was found in fish livers, whereas OBS was found in the pancreas, brain, gonads, and skin. The tissue distribution pattern of 6:2 Cl-PFESA is similar to that of PFOS. The tissue/liver ratios of OBS were higher than those of PFOS, suggesting that OBS has a greater tendency to transfer from the liver to other tissues. The logarithmic bioaccumulation factors (log BAFs) of 6:2 Cl-PFESA in three carnivorous fish species were greater than 3.7, whereas those of OBS were less than 3.7, indicating that 6:2 Cl-PFESA had a strong bioaccumulation potential. Notably, sex- and tissue-specific bioaccumulation of OBS has also been observed in catfish. Most tissues (except the gonads) exhibited higher OBS concentrations in males than in females. However, no differences were found for 6:2 Cl-PFESA and PFOS. Maternal transfer efficiency of OBS was higher than that of 6:2 Cl-PFESA and PFOS in catfish (p < 0.05), indicating that OBS presents a higher risk of exposure to males and offspring through maternal offloading.

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.

Transcriptome sequencing and metabolite analysis reveal the single and combined effects of microplastics and di-(2-ethylhexyl) phthalate on Peneaus vannamei

Due to the rising usage of plastics, plastic debris are present throughout marine ecosystems and detrimentally affects marine biota. Additionally, plastics likely result in elusive toxicity effects due to addition of plasticizers. The aim of the present study was to reveal the potential effects and mechanism of microplastics (MPs), di-(2-ethylhexyl) phthalate (DEHP) and copollution of MPs and DEHP (MPs-DEHP) on Peneaus vannamei (P. vannamei) juveniles regarding oxidative stress, transcriptomics and metabolomics. MPs, DEHP and MPs-DEHP significantly induced the activities of superoxide dismutase (SOD) and catalase (CAT); MPs and DEHP have an antagonistic effect for malondialdehyde (MDA); suggesting that disorders of the antioxidant defence systems. 13, 133 and 58 differentially expressed genes and 21, 82 and 39 differentially expressed metabolites were responsible for the distinction of MPs, DEHP and MPs-DEHP groups, respectively. The combination of transcriptomic and metabolomic analyses showed that MPs, DEHP and MPs-DEHP exposure disturbed amino acid and lipid metabolism, and further induced inflammatory responses and dysfunction of purine metabolism. Furthermore, the presence of MPs might alleviate the biotoxicity of DEHP in P. vannamei. These findings provide new insights into the single and combined toxicological effects of MPs and additives for marine biota.

Platymonas helgolandica-driven nitrogen removal from mariculture wastewater under different photoperiods: Performance evaluation, enzyme activity and transcriptional response

The nitrogen removal performance and biological mechanism of Platymonas helgolandica var. Tsingtaoensis (P. helgolandica) were investigated in treating mariculture wastewater under different light: dark (L:D) photoperiods. The growth of P. helgolandica was positively correlated with the photoperiods from 6L:18D to 15L:9D, and the highest photosynthetic activity appeared under 6L:18D photoperiod on day 3. P. helgolandica exhibited the highest removal efficiencies of total nitrogen and COD at 89 % and 93 % under 15L:9D photoperiod, respectively. NH₄⁺-N assimilation was proportional to the photoperiods from 6L:18D to 15L:9D and longer illumination promoted NO₂^--N removal. However, the highest NO₃^--N reduction rate was achieved under 12L:12D photoperiod. The different nitrogen-transformed enzymatic activities were affected by photoperiod. Transcriptome revealed that unigenes were enriched in nitrogen metabolism and photosynthesis pathways, of which the functional gene expression was up-regulated significantly. This study provides insights into the optimization of photoperiod for mariculture wastewater treatment by P. helgolandica.

Toxicity assessment of hexafluoropropylene oxide-dimer acid on morphology, heart physiology, and gene expression during zebrafish (Danio rerio) development

Hexafluoropropylene oxide-dimer acid (HFPO-DA) is one of the emerging replacements for the "forever" carcinogenic and toxic long-chain PFAS. HFPO-DA is a polymerization aid used for manufacturing fluoropolymers, whose global distribution and undetermined toxic properties are a concern regarding human and ecological health. To assess embryotoxic potential, zebrafish embryos were exposed to HFPO-DA at concentrations of 0.5-20,000 mg/L at 24-, 48-, and 72-h post-fertilization (hpf). Heart rate increased significantly in embryos exposed to 2 mg/L and 10 mg/L HFPO-DA across all time points. Spinal deformities and edema phenotypes were evident among embryos exposed to 1000-16,000 mg/L HFPO-DA at 72 hpf. A median lethal concentration (LC₅₀) was derived as 7651 mg/L at 72 hpf. Shallow RNA sequencing analysis of 9465 transcripts identified 38 consistently differentially expressed genes at 0.5 mg/L, 1 mg/L, 2 mg/L, and 10 mg/L HFPO-DA exposures. Notably, seven downregulated genes were associated with visual response, and seven upregulated genes were expressed in or regulated the cardiovascular system. This study identifies biological targets and molecular pathways affected during animal development by an emerging, potentially problematic, and ubiquitous industrial chemical.

Fractionation of perfluoroalkyl acids (PFAAs) along the aquatic food chain promoted by competitive effects between longer and shorter chain PFAAs

Perfluoroalkyl acids (PFAAs) are proteinophilic pollutants. We hypothesized that fractionation of PFAAs may occur along a food chain. To testify this hypothesis, we investigated the bioconcentration, bioaccumulation, and fractionation of 11 kinds of PFAAs (C-F = 3-11) along an aquatic food chain consisting of D. magna, zebrafish, and cichlid. The results showed that the proportions of PFNA, PFOA, and all shorter chain PFAAs in the D. magna and fish tissues were lower than the ones in exposure water, opposing to the other longer chain PFAAs. Predation promoted such fractionation differences, and the proportions of PFNA, PFOA, and all shorter chain PFAAs in organisms decreased while those of the other longer chain PFAAs increased along the food chain. The results of isothermal titration calorimetry and molecular docking experiments showed that binding affinities of PFAAs and fish proteins increased with the number of perfluorinated carbons, resulting in a substitution of shorter chain PFAAs by their longer chain analogues. It also triggered the differences in the uptake and elimination of PFFAs and competitive bioaccumulation between longer and shorter chain PFAAs. This study suggests that fractionation should be considered in studying environmental behaviors and evaluating ecological risks of multiple PFAAs.

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.

PFAS-induced lipidomic dysregulations and their associations with developmental toxicity in zebrafish embryos

Per- and polyfluoroalkyl substances (PFASs) are persistent environmental contaminants, posing developmental toxicity to fish and human. PFAS-induced lipid metabolism disorders were demonstrated using the zebrafish (Danio rerio) embryo model, but the detailed changes of lipid compositions and the influence of these changes on the biological development are still unclear. Herein, lipidomics analysis was performed to reveal the dysregulations of lipid metabolism in zebrafish embryos exposed to perfluorooctanoic acid (PFOA) or perfluorooctane sulfonate (PFOS) through microinjection. Various abnormal phenotypes were observed, including heart bleeding, pericardium edema, spinal curvature and increased heart rate at 72 h after fertilization, especially in the PFOS exposure groups. Lipidomic profiling found downregulated phosphatidylethanolamines in the PFAS-exposed embryos, especially those containing a docosahexaenoyl (DHA) chain, indicating an excessive oxidative damage to the embryos. Glycerolipids were mainly upregulated in the PFOA groups but downregulated in the PFOS groups. These aberrations may reflect oxidative stress, energy metabolism malfunction and proinflammatory signals induced by PFASs. However, supplement of DHA may not be effective in recovering the lipidomic dysregulations and protecting from the developmental toxicity induced by PFASs, showing the complexity of the toxicological mechanisms. This work has revealed the associations between the abnormal phenotypes and dysregulations of lipid metabolism in zebrafish embryos induced by PFASs from the aspect of lipidomics, and discovered the underlying molecular mechanisms of the developmental toxicity of PFASs.

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.

F-53B induces hepatotoxic effects and slows self-healing in ulcerative colitis in mice

Chlorinated polyfluorinated ether sulfonate (F-53 B) is a distinct substitute for perfluorooctane sulphonate. It has been reported to be biologically toxic to mammals, causing enteric toxicity, liver toxicity and neurotoxicity. However, studies about the effects of F-53 B on patients with gastrointestinal diseases such as inflammatory bowel disease are very limited. In this study, whether the toxic impacts of F-53 B on the gut and liver can be exacerbated in mice with colitis was explored. The sensitivity of mice with acute colitis caused by dextran sulfate sodium salt (DSS) to F-53 B was compared with that of healthy mice. The mice were administered water containing F-53 B at doses of 10 and 100 μg/L sequentially for two weeks, respectively. F-53 B exposure exacerbated DSS-induced colonic inflammation, including inducing shortening of colon length, inflammatory cell infiltration and more severe histopathological symptoms. In addition, F-53 B administration significantly increased the levels of inflammatory cytokines, including interleukin (IL)-1, IL-6 and tumour necrosis factor-α, in the plasma of mice with enteritis compared with control group. F-53 B impaired intestinal integrity of mice with colitis by downregulating Claudin-1 and antimicrobial peptide-related genes while elevating serum lipopolysaccharide levels. In addition, in mice with colitis, F-53 B increased the levels of serum total cholesterol, triglyceride, low-density lipoprotein cholesterol, aspartate aminotransferase, and alanine aminotransferase, resulted in more severe liver inflammation and increased the level of genes related to the Gasdermin D-mediated pyrolysis. Conclusively, our results indicated that F-53 B delayed the self-healing of ulcerative colitis (UC) and caused liver inflammation in mice. This study provided some new insights into the health risks of F-53 B and raises concerns about the health of individuals with UC.

Integration of metabolomics and proteomics reveals the underlying hepatotoxic mechanism of perfluorooctane sulfonate (PFOS) and 6:2 chlorinated polyfluoroalkyl ether sulfonic acid (6:2 Cl-PFESA) in primary human hepatocytes

Perfluorooctane sulfonate (PFOS) and its alternative 6:2 chlorinated polyfluorinated ether sulfonate (6:2 Cl-PFESA) are ubiquitous in various environmental and human samples. They have been reported to have hepatotoxicity effects, but the potential mechanisms remain unclear. Herein, we integrated metabolomics and proteomics analysis to investigate the altered profiles in metabolite and protein levels in primary human hepatocytes (PHH) exposed to 6:2 Cl-PFESA and PFOS at human exposure relevant concentrations. Our results showed that 6:2 Cl-PFESA exhibited higher perturbation effects on cell viability, metabolome and proteome than PFOS. Integration of metabolomics and proteomics revealed that the alteration of glycerophospholipid metabolism was the critical pathway of 6:2 Cl-PFESA and PFOS-induced lipid metabolism disorder in primary human hepatocytes. Interestingly, 6:2 Cl-PFESA-induced cellular metabolic process disorder was associated with the cellular membrane-bounded signaling pathway, while PFOS was associated with the intracellular transport process. Moreover, the disruption effects of 6:2 Cl-PFESA were also involved in inositol phosphate metabolism and phosphatidylinositol signaling system. Overall, this study provided comprehensive insights into the hepatic lipid toxicity mechanisms of 6:2 Cl-PFESA and PFOS in human primary hepatocytes.

The effects of exposure to environmentally relevant PFAS concentrations for aquatic organisms at different consumer trophic levels: Systematic review and meta-analyses

Per-and polyfluoroalkyl substances (PFAS) is a collective name for approximately 4700 synthetic chemicals ubiquitous in the aquatic environment worldwide. They are used in a wide array of products and are found in living organisms around the world. Some PFAS have been associated with cancer, developmental toxicity, endocrine disruption, and other health effects. Only a fraction of PFAS are currently monitored and regulated and the presence and effects on aquatic organisms of many PFAS are largely unknown. The aim of this study is to investigate the health effects of environmentally relevant concentrations of PFAS on aquatic organisms at different consumer trophic levels through a systematic review and meta-analysis. The main result shows that PFAS in concentrations up to 13.5 μg/L have adverse effects on body size variables for secondary consumers. However, no significant effects on liver or gonad somatic indices and neither on fecundity were found. In addition, the results show that there are large research gaps for PFAS effects on different organisms in aquatic environments at environmentally relevant concentrations. Most studies have been performed on secondary consumers and there is a substantial lack of studies on other consumers in aquatic ecosystems.

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.

Toxic effects and transcriptional responses in zebrafish liver cells following perfluorooctanoic acid exposure

As a typical type of persistent organic pollutant, perfluorooctanoic acid (PFOA) is pervasive in the environment. Multiple studies have found that PFOA has hepatotoxicity, but the mechanism remains poorly understood. In this study, the toxic effects of different concentrations of PFOA on zebrafish liver cells were systematically assessed by recording cell survival, ultrastructural observations, and transcriptome analyses. The results showed that the inhibition of cell viability and the massive accumulation of autophagic vacuoles were observed at 400 µM PFOA, while transcriptomic changes occurred with treatments of 1 and 400 µM PFOA. The transcription levels of 1055 (977 up- and 78 down-regulated genes) and 520 (446 up- and 74 down-regulated genes) genes were significantly changed after treatment with 1 and 400 µM PFOA, respectively. Based on Kyoto encyclopedia of genes and genomes (KEGG) enrichment analysis, significant expression changes were observed in autophagy, tight junction, signal transduction, immune system, endocrine system, and metabolism-related pathways, indicating that such processes were greatly affected by PFOA exposure. The findings of this study will provide a scientific basis for the toxic effects and potential toxic mechanisms of PFOA on zebrafish, and provide information for ecological risk assessments.

Persistent impairment of gonadal development in rare minnow (Gobiocypris rarus) after chronic exposure to chlorinated polyfluorinated ether sulfonate

The delayed and persistent adverse effects caused by developmental exposure to per- and poly-fluorinated substances are of significant concern. Juvenile rare minnows (Gobiocypris rarus), were exposed to chlorinated polyfluoroalkyl ether sulfonate (Cl-PFESA) at measured medium concentrations of 86.5 μg/L, 162 μg/L and 329 μg/L, for 4 weeks followed by 12 weeks of depuration. After 4 weeks of exposure, the body weight and length of the juvenile fish were increased compared to controls. Gene expression of gnrh3, lhβ, and cyp19a was decreased, and ar and erα were upregulated. Transcriptomic analysis revealed enrichment of multiple pathways related to gonadal development. After 12 weeks of depuration, the gonadosomatic indices were decreased in female fish in a concentration-dependent manner, with a significant decrease to 59% of control in 329 μg/L group. Histological analysis found increasing numbers of degenerating oocytes and perinucleolar oocytes, and decreasing numbers of mature vitellogenic oocytes in female fish treated by Cl-PFESA. Enlarged interstitial space of the testis was observed in the exposed male fish. Gene expression levels of gnrh3, lhβ, ar, erα, and vtg were upregulated in the adult fish. Chronic developmental exposure to Cl-PFESA caused persistent effects on gonadal development of fish, highlighting the necessity of a comprehensive ecological risk assessment.

Aberrant hepatic lipid metabolism associated with gut microbiota dysbiosis triggers hepatotoxicity of novel PFOS alternatives in adult zebrafish

Perfluorooctane sulfonate (PFOS) has been reported to induce hepatotoxicity in wildlife and humans. Novel PFOS alternatives have been widely used following restrictions on PFOS, but little is known about their potential toxicity. Here, the first comprehensive investigation on the chronic hepatotoxicity and underlying molecular mechanisms of PFOS, 6:2Cl-PFESA (F-53B), and sodium p-perfluorous nonenoxybenzene sulfonate (OBS) was carried out on adult zebrafish through a histopathological examination, biochemical measurement, and multi-omics analysis. PFOS and its alternatives caused changes in liver histopathology and liver function indices in the order of F-53B > PFOS > OBS, which was consistent with their concentration in the liver. In silico modeling and transcriptional profiles suggested that the aberrant hepatic lipid metabolism induced by F-53B and PFOS was initiated by the action on peroxisome proliferator-activated receptor γ (PPARγ), which triggered changes in downstream genes transcription and led to an imbalance between lipid synthesis and expenditure. Gut microbiome analysis provided another novel mechanistic perspective that changes in the abundance of Legionella, Ralstonia, Brevundimonas, Alphaproteobacteria, Plesiomonas, and Hyphomicrobium might link to alterations in the PPAR pathway based on their significant correlation. This study provides insight into the molecular mechanisms of hepatotoxicity induced by PFOS and its novel alternatives and highlights the need for concern about their environmental exposure risks.

Antioxidant Responses Induced by PFAS Exposure in Freshwater Fish in the Veneto Region

In recent decades, the interest in PFAS has grown exponentially around the world, due to the toxic effects induced by these chemical compounds in humans, as well as in other animals and plants. However, current knowledge related to the antistress responses that organisms can express when exposed to these substances is still insufficient and, therefore, requires further investigation. The present study focuses on antioxidant responses in Squalius cephalus and Padogobius bonelli, exposed to significant levels of PFAS in an area of the Veneto Region subjected to a recent relevant pollution case. These two ubiquitous freshwater species were sampled in three rivers characterised by different concentrations of PFAS. Several biomarkers of oxidative stress were evaluated, and the results suggest that PFAS chronic exposure induces some physiological responses in the target species, at both cellular and tissue scales. The risk of oxidative stress seems to be kept under control by the antioxidant system by means of gene activation at the mitochondrial level. Moreover, the histological analysis suggests an interesting protective mechanism against damage to the protein component based on lipid vacuolisation.

Perfluorooctane sulfonates induces neurobehavioral changes and increases dopamine neurotransmitter levels in zebrafish larvae

It has been reported that exposure to perfluorooctane sulfonates (PFOS) causes behavioral abnormalities in zebrafish larvae, but the possible mechanisms underlying these changes remain unexplored. In this study, zebrafish embryos (2 h postfertilization, 2-hpf) were exposed to PFOS at different concentrations (0, 0.032, 0.32 and 3.2 mg/L) for 120 h. Developmental endpoints and the locomotion behavior of larvae were evaluated. Reactive oxygen species (ROS) levels, dopamine contents, several genes and proteins related to neurodevelopment and dopamine signaling were examined. Our results indicate that increased ROS levels in the zebrafish larvae heads may be causally associated with neurodevelopment damage. Meanwhile, brain-derived neurotrophic factor (BDNF) and alpha1-Tubulin (α1-Tubulin) protein contents were significantly increased, which may be a compensatory mechanism for the impaired central nervous system. PFOS-induced locomotor hyperactivity was observed in the first light phase and dark phase at the 0.32 and 3.2 mg/L of PFOS. Upregulation of dopamine-related genes tyrosine hydroxylase (th) and dopamine transporter (dat) associated with increased dopamine contents in the 3.2 mg/L of PFOS. In addition, protein expression of TH and DAT were noted at the 0.32 and 3.2 mg/L of PFOS concentrations. Our results suggested that PFOS induces neurobehavioral changes in zebrafish larvae, possibly by perturbing a dopamine signaling pathway. In addition, PFOS induced development damage, such as increased malformation rate and shorter body length.

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.

Per- and perfluoroalkyl substances alternatives, mixtures and liver function in adults: A community-based population study in China

Experimental evidence has shown that per- and polyfluoroalkyl substances (PFAS) alternatives and mixtures may exert hepatotoxic effects in animals. However, epidemiological evidence is limited. This research aimed to explore associations of PFAS and the alternatives with liver function in a general adult population. The study participants consisted of 1,303 adults from a community-based cross-sectional investigation in Guangzhou, China, from November 2018 to August 2019. We selected 13 PFAS with detection rates > 85% in serum samples and focused on perfluorooctane-sulfonic acid (PFOS), perfluorooctanoic acid (PFOA) and their alternatives [6:2 chlorinated polyfluorinated ether sulfonate (6:2 Cl-PFESA), 8:2 Cl-PFESA, and perfluorohexanoic acid (PFHxA)] as predictors of outcome. Six liver function biomarkers (ALB, ALT, AST, GGT, ALP, and DBIL) were chosen as outcomes. We applied regression models with restricted cubic spline function to explore correlations between single PFAS and liver function and inspected the combined effect of PFAS mixtures on liver by applying Bayesian kernel machine regression (BKMR). We discovered positive associations among PFAS and liver function biomarkers except for ALP. For example, compared with the 25th percentile of PFAS concentration, the level of ALT increased by 12.36% (95% CI: 7.91%, 16.98%) for ln-6:2 Cl-PFESA, 5.59% (95% CI: 2.35%, 8.92%) for ln-8:2 Cl-PFESA, 3.56% (95% CI: -0.39%, 7.68%) for ln-PFHxA, 13.91% (95% CI: 8.93%, 19.13%) for ln-PFOA, and 14.25% (95% CI: 9.91%, 18.77%) for ln-PFOS at their 75th percentile. In addition, higher exposed serum PFAS was found to be correlated with greater odds of abnormal liver function. Analysis from BKMR models also showed an adverse association between PFAS mixtures and liver function. The combined effect of the PFAS mixture appeared to be non-interactive, in which PFOS was the main contributor to the overall effect. Our findings provide evidence of associations between PFAS alternatives, PFAS mixtures, and liver function in the general adult population.

Metabolic Consequences of Developmental Exposure to Polystyrene Nanoplastics, the Flame Retardant BDE-47 and Their Combination in Zebrafish

Single-use plastic production is higher now than ever before. Much of this plastic is released into aquatic environments, where it is eventually weathered into smaller nanoscale plastics. In addition to potential direct biological effects, nanoplastics may also modulate the biological effects of hydrophobic persistent organic legacy contaminants (POPs) that absorb to their surfaces. In this study, we test the hypothesis that developmental exposure (0–7 dpf) of zebrafish to the emerging contaminant polystyrene (PS) nanoplastics (⌀100 nm; 2.5 or 25 ppb), or to environmental levels of the legacy contaminant and flame retardant 2,2′,4,4′-Tetrabromodiphenyl ether (BDE-47; 10 ppt), disrupt organismal energy metabolism. We also test the hypothesis that co-exposure leads to increased metabolic disruption. The uptake of nanoplastics in developing zebrafish was validated using fluorescence microscopy. To address metabolic consequences at the organismal and molecular level, metabolic phenotyping assays and metabolic gene expression analysis were used. Both PS and BDE-47 affected organismal metabolism alone and in combination. Individually, PS and BDE-47 exposure increased feeding and oxygen consumption rates. PS exposure also elicited complex effects on locomotor behaviour with increased long-distance and decreased short-distance movements. Co-exposure of PS and BDE-47 significantly increased feeding and oxygen consumption rates compared to control and individual compounds alone, suggesting additive or synergistic effects on energy balance, which was further supported by reduced neutral lipid reserves. Conversely, molecular gene expression data pointed to a negative interaction, as co-exposure of high PS generally abolished the induction of gene expression in response to BDE-47. Our results demonstrate that co-exposure to emerging nanoplastic contaminants and legacy contaminants results in cumulative metabolic disruption in early development in a fish model relevant to eco- and human toxicology.

Comparative chronic toxicities of PFOS and its novel alternatives on the immune system associated with intestinal microbiota dysbiosis in adult zebrafish

6:2 Chlorinated polyfluorinated ether sulfonate (F-53B) and sodium p-perfluorous nonenoxybenzene sulfonate (OBS) are widely used as perfluorooctane sulfonate (PFOS) alternatives in the Chinese market. Here, adult zebrafish were chronically exposed to 1 μM PFOS, F-53B, and OBS for 21 days to investigate the comparative immunotoxicity of these three per- and polyfluoroalkyl substances (PFAS). PFOS induced more severe oxidative stress in the liver than F-53B and OBS, and these three PFAS induced similar anti-inflammatory effects by repressing the expression of pro-inflammatory cytokines. The intestinal microbiota analysis showed that the relative abundance of Plesiomonas, Aeromonas, Cetobacterium, Shewanella, and Vibrio changed with the same trend in the three PFAS treatment groups. Furthermore, the PFAS increased the expression of hepcidin, muc, the immune-related genes mpo and saa, and decreased the expression of the tight junction-related gene occ in the intestine; moreover, villus height of the intestine was reduced after PFAS exposure, which indicated the functional disruption of the intestine. In particular, the significant correlation between the changed intestinal microbiota and liver and intestinal indicators also suggested the interaction between the immune system and intestinal microbiota. Taken together, our results indicate that exposure to PFOS and its alternatives F-53B and OBS can induce hepatic immunotoxicity associated with intestinal microbiota dysbiosis in adult zebrafish.

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.

Associations between both legacy and alternative per- and polyfluoroalkyl substances and glucose-homeostasis: The Isomers of C8 health project in China

BACKGROUND

Epidemiological studies on the associations of legacy per- and polyfluoroalkyl substances (PFASs) and glucose homeostasis remain discordant. Understanding of PFAS alternatives is limited, and few studies have reported joint associations of PFASs and PFAS alternatives.

OBJECTIVES

To investigate associations of novel PFAS alternatives (chlorinated perfluoroalkyl ether sulfonic acids, Cl-PFESAs and perfluorobutanoic acid, PFBA) and two legacy PFASs (Perfluorooctanoic acid, PFOA and perfluorooctane sulfonate, PFOS) with glucose-homeostasis markers and explore joint associations of 13 legacy and alternative PFASs with the selected outcomes.

METHODS

We used cross-sectional data of 1,038 adults from the Isomers of C8 Health Project in China. Associations of PFASs and PFAS alternatives with glucose-homeostasis were explored in single-pollutant models using generalized linear models with natural cubic splines for PFASs. Bayesian Kernel Machine Regression (BKMR) models were applied to assess joint associations of exposures and outcomes. Sex-specific analyses were also conducted to evaluate effect modification.

RESULTS

After adjusting for confounders, both legacy (PFOA, PFOS) and alternative (Cl-PFESAs and PFBA) PFASs were positively associated with glucose-homeostasis markers in single-pollutant models. For example, in the total study population, estimated changes with 95% confidence intervals (CI) of fasting glucose at the 95th percentile of 6:2Cl-PFESA and PFOS against the thresholds were 0.90 (95% CI: 0.59, 1.21) and 0.44 (95% CI: 0.26, 0.62). Positive joint associations were found in BKMR models with 6:2Cl-PFESA contributing most. Sex-specific associations existed in both single- and multi-pollutant models.

CONCLUSIONS

Legacy and alternative PFASs were positively associated with glucose-homeostasis markers. 6:2Cl-PFESA was the primary contributor. Sex-specific associations were also identified. These results indicate that joint associations and effect modification should be considered in risk assessment. However, further studies are recommended to strengthen our findings and to elucidate the mechanisms of action of legacy and alternative PFASs.

Lipid metabolism disorders effects of 6:2 chlorinated polyfluorinated ether sulfonate through Hsa-miRNA-532-3p/Acyl-CoA oxidase 1(ACOX1) pathway

6:2 Chlorinated polyfluorinated ether sulfonate (6:2 Cl-PFESA), an alternative product of perfluorooctane sulfonate (PFOS), has been frequently detected in various environmental, wildlife, and human samples. A few studies revealed the hepatotoxicity of 6:2 Cl-PFESA in animals, but the underlying toxicity mechanisms remain largely unknown. In this study, we investigated the lipid metabolism disorders of 6:2 Cl-PFESA through miRNA-gene interaction mode in Huh-7 cells. Our results showed that 6:2 Cl-PFESA significantly promoted cellular lipid accumulation and increased the expression of Acyl-CoA oxidase 1 (ACOX1), with the lowest effective concentrations (LOECs) of 3 μM. In silico analysis showed that hsa-miR-532-3p is a potential miRNA molecule targeting ACOX1. Fluorescent-based RNA electrophoretic mobility shift assay (FREMSA) and ACOX1-mediated luciferase reporter gene assays showed that hsa-miR-532-3p could directly bind to ACOX1 and inhibit its transcription activity. Besides, 6:2 Cl-PFESA decreased the expression of hsa-miR-532-3p in the PPARα-independent manner. Overexpression of hsa-miR-532-3p promoted 6:2 Cl-PFESA-induced cellular lipid accumulation and decreased the ACOX1 production in Huh-7 cells. Taken together, at human exposure relevant concentrations, 6:2 Cl-PFESA might upregulate the expression levels of ACOX1 through downregulating hsa-miR-532-3p, and disturbed lipid homeostasis in Huh-7 cells, which revealed a novel epigenetic mechanism of 6:2 Cl-PFESA-induced hepatic lipid toxic effects.

Exposure to novel and legacy per- and polyfluoroalkyl substances (PFASs) and associations with type 2 diabetes: A case-control study in East China

Associations between per- and polyfluoroalkyl substances (PFASs) and the incidence of type 2 diabetes are controversial in epidemiological studies. In addition, limited data are available for assessing the health effects of novel PFAS alternatives. Our study evaluated the effects of PFAS exposure on type 2 diabetes by estimating the associations of PFASs in human serum with the risk of type 2 diabetes and levels of glycemic biomarkers and lipid fractions. The case-control study consisted of 304 participants from Shandong Province, East China, half of which were diagnosed with type 2 diabetes. Logistic regression showed that most PFASs were inversely associated with the risk of type 2 diabetes after adjusting for age, sex, and body mass index. However, concentrations of perfluorooctanoic acid (PFOA) in the control group were positively associated with fasting plasma glucose levels (β = 0.04, 95% confidence interval (CI): 0.0003, 0.08), which may promote the development of type 2 diabetes. Furthermore, each log-unit increase in the concentrations of perfluorononanoic acid (PFNA), perfluoroundecanoic acid (PFUnDA), and 6:2 chlorinated polyfluoroalkyl ether sulfonic acid (Cl-PFESA) were associated with a total cholesterol increase (i.e., 17.49% (95% CI: 0.93%, 34.90%), 17.49% (95% CI: 4.71%, 31.83%), and 17.49% (95% CI: 4.71%, 31.83%), respectively). Positive associations were also observed between PFNA, PFUnDA, perfluorooctane sulfonate (PFOS), and 6:2 Cl-PFESA and low-density lipoprotein cholesterol. However, no associations between PFASs and hemoglobin A1c, triglycerides, or high-density lipoprotein cholesterol reached statistical significance, nor associations between PFAS mixtures and outcomes of interest. In conclusion, the significant correlations between serum PFASs and glycemic biomarkers and lipid fractions indicated that PFAS exposure may be a potential diabetogenic factor. To the best of our knowledge, this is the first study to assess the associations between novel Cl-PFESAs and type 2 diabetes, although the inverse associations observed require clarification in future studies.

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.

Perfluorooctane sulfonate alternatives and metabolic syndrome in adults: New evidence from the Isomers of C8 Health Project in China

Chlorinated polyfluoroalkyl ether sulfonates (Cl-PFESAs), are ubiquitous alternatives to perfluorooctane sulfonate (PFOS), a widely used poly- and perfluoroalkyl substance (PFAS). Despite in vivo and in vitro evidence of metabolic toxicity, no study has explored associations of Cl-PFESAs concentrations with metabolic syndrome (MetS) in a human population. To help address this data gap, we quantified 32 PFAS, including 2 PFOS alternative Cl-PFESAs (6:2 and 8:2 Cl-PFESAs) in serum from 1228 adults participating in the cross-sectional Isomers of C8 Health Project in China study. The odds ratios (ORs) and 95% confidence intervals (CIs) of MetS and its various components were estimated using individual PFAS as a continuous or categorical predictor in multivariate regression models. The association between the overall mixture of PFAS and MetS was examined using probit Bayesian Kernel Machine Regression (BKMR-P). Greater serum PFAS concentrations were associated with higher odds of MetS and demonstrated a statistically significant dose-response trend (P for trend < 0.001). For example, each ln-unit (ng/mL) increase in serum 6:2 Cl-PFESA was associated with a higher prevalence of MetS (OR = 1.52, 95% CI: 1.25, 1.85). MetS was also 2.26 (95% CI: 1.59, 3.23) times more common in the highest quartile of serum 6:2 Cl-PFESA concentration than the lowest, and particularly high among women (OR = 6.41, 95% CI: 3.65, 11.24). The BKMR-P analysis showed a positive association between the overall mixture of measured PFAS and the odds of MetS, but was only limited to women. While our results suggest that exposure to Cl-PFESAs was associated with MetS, additional longitudinal studies are needed to more definitively address the potential health concerns of these PFOS alternatives.

Effects of penconazole enantiomers exposure on hormonal disruption in zebrafish Danio rerio (Hamilton, 1822)

PEN is a widely used triazole fungicide, usually used to control grape white rot. In the process of agricultural use, PEN will be scattered to the soil and water environment, which brings certain environmental safety risks. In this study, we used a 200-μg/L solution of Rac-PEN, (+)-PEN, and (-)-PEN to perform a 28-day exposure test on zebrafish. The results showed that long-term low-dose PEN exposure did not significantly change the growth factor K and the number of spawning of zebrafish. However, the content of four important hormones vitellogenin, 17β-estradiol, testosterone, and 11-ketotestosterone in zebrafish has changed significantly. Furthermore, we measured the expression of hypothalamus-pituitary-gonads-liver (HPGL) axis-related genes, and the results showed that the expressions of related genes in the brain, gonads, and liver all changed significantly. Combining the above results, we can conclude that PEN has obvious endocrine disrupting effect on zebrafish, and has gender-specific endocrine effects. Meanwhile, Rac-PEN and (+)-PEN had stronger effects on the endocrine system of zebrafish than (-)-PEN.

Zebrafish as the toxicant screening model: Transgenic and omics approaches

The production of large amounts of synthetic industrial and biomedical compounds, together with environmental pollutants, poses a risk to our ecosystem and induces negative effects on the health of wildlife and human beings. With the emergence of the global problem of chemical contamination, the adverse biological effects of these chemicals are gaining attention among the scientific communities, industry, governments, and the public. Among these chemicals, endocrine disrupting chemicals (EDCs) are regarded as one of the major global issues that potentially affecting our health. There is an urgent need of understanding the potential hazards of such chemicals. Zebrafish have been widely used in the aquatic toxicology. In this review, we first discuss the strategy of transgenic lines that used in the toxicological studies, followed by summarizing the current omics approaches (transcriptomics, proteomics, metabolomics, and epigenomics) on toxicities of EDCs in this model. We will also discuss the possible transgenerational effects in zebrafish and future prospective of the integrated omics approaches with customized transgenic organism. To conclude, we summarize the current findings in the field, and provide our opinions on future environmental toxicity research in the zebrafish model.

NOD-like receptor signaling pathway activation: A potential mechanism underlying negative effects of benzo(α)pyrene on zebrafish

Benzo(α)pyrene (BaP) is one of typical polycyclic aromatic hydrocarbons (PAHs) in aquatic environments and has been shown to cause toxic effects to aquatic animals. Although the negative effects of BaP have been investigated, the potential toxic mechanisms remain uncharacterized. To explore the potential mechanisms mediating the toxic effects of BaP, zebrafish (Danio rerio) were exposed to BaP for 15 days and the toxic effects of BaP in zebrafish liver were investigated using physiological and transcriptomic analyses. After 15-day BaP exposure, zebrafish liver exhibited abnormalities including increased cytoplasmic vacuolation, inflammatory cell infiltration, swelled nuclei and irregular pigmentation. BaP exposure also induced oxidative stress to the liver of zebrafish. Transcriptomic profiles revealed 5129 differentially expressed genes (DEGs) after 15-days of BaP exposure, and the vast majority of DEGs were up-regulated under BaP treatment. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses suggest that genes related to immune response were significantly dysregulated. Furthermore, the nucleotide-binding, oligomerization domain (NOD)-like receptor signaling pathway was significantly enriched and most of the genes in this pathway exhibited enhanced expression after BaP exposure. These results partially explained the mechanisms underlying the toxic effects of BaP on zebrafish liver. In conclusion, BaP has the potential to induce physiological responses in zebrafish liver through altering associated genes.