An environmentally relevant mixture of polychlorinated biphenyls (PCBs) and polybrominated diphenylethers (PBDEs) disrupts mitochondrial function, lipid metabolism and neurotransmission in the brain of exposed zebrafish and their unexposed F2 offspring

Exposure to the Polychlorinated biphenyl mixture Aroclor 1254 elicits neurological and cardiac developmental effects in early life stage zebrafish (Danio rerio)

The goal of this study was to compare the bioaccumulation of the PCB mixture Aroclor 1254 in zebrafish to cardiac and neurologic outcomes. The establishment of effect concentrations (ECs) for cardiac and neurotoxic effects of PCBs in early life stage fish is challenging due to a lack of measured PCB concentrations in test media (e.g., fish tissue), the lack of standard exposure methods, and the propensity of PCBs to adsorb to test glassware and materials resulting in discrepancies in ECs from different studies with similar endpoints. Reporting tissue concentrations in test organisms will allow for standardization across different tests and thus may improve estimations of effect thresholds. Early life stage zebrafish (Danio rerio) are a common environmental toxicological model well represented within the literature, making them ideal for comparisons across multiple studies. Embryos were exposed at 6 h post fertilization (hpf) to aqueous Aroclor 1254 for 96 h with or without renewal in addition to a PCB 126 positive control for cardiotoxicity. PCB concentrations were measured in both exposure solutions and tissue samples. Measured concentrations of Aroclor 1254 in test solutions ranged from 8.7% to 870% of nominal concentrations. Heart rate, pericardial edema, and neurological endpoints (eye tremors) were measured in 102 hpf larvae. Pericardial edema was not present in Aroclor 1254-treated zebrafish but was observed in those exposed to PCB-126. Concentration-dependent bradycardia was observed in zebrafish exposed to Aroclor 1254 and PCB-126. Similarly, a concentration-dependent increase in eye tremor behavior was observed in embryos exposed to Aroclor 1254. Data produced by this study demonstrate novel toxicological effects of Aroclor 1254 and highlight the importance of measuring PCBs in both exposure and receptor media.

Enhanced competitiveness of Spirodela polyrhiza in co-culture with Salvinia natans under combined exposure to polystyrene nanoplastics and polychlorinated biphenyls

Micro- and nanoplastics (MNPs) and polychlorinated biphenyls (PCBs) are prevalent in the environment and pose potential threats to ecosystems. However, studies on the phytotoxicity of MNPs and PCBs on primary producers are limited. This study investigated the effects of polystyrene nanoplastics (PS-NPs, 10 mg/L) and 2,2',5,5'-tetrachlorobiphenyl (PCB-52, 0.1 mg/L), on the growth of Spirodela polyrhiza and Salvinia natans, and their impact on plant competitive ability under co-culture conditions. Laser confocal microscopy images revealed that PS-NPs accumulated on the leaf and root surfaces of both species. Combined exposure to PS-NPs and PCB-52 significantly inhibited the average specific and relative growth rates (RGR) of both species, reduced chlorophyll a and b levels, and slightly increased carotenoid content, disrupting the photosynthetic system. PCB-52 exacerbated PS-NPs accumulation on plants, leading to increased hydrogen peroxide (H2O2) and superoxide anion (O2-) production in both roots and leaves. This affects the activity of superoxide dismutase (SOD), peroxidase (POD), malondialdehyde (MDA), and the soluble protein content. The combined treatment with PS-NPs and PCB-52 induced greater ecological stress in both species than the treatment with PS-NPs alone. In addition, the combined treatment with PS-NPs and PCB-52 significantly improved the relative yield and competition balance index of S. polyrhiza, indicating that PS-NPs + PCB-52 enhanced the competitive ability of S. polyrhiza when co-cultured with S. natans. This study confirmed the effects of co-exposure to PS-NPs and PCB-52 on aquatic plant growth and species competition, contributing to better insight into the ecological impacts of MNPs and organic pollutants.

Early-life exposure to PCBs and PFAS exerts negative effects on the developing central nervous system

Persistent organic pollutants (POPs) are ubiquitous in the environment and display the capacity to bioaccumulate in living organisms, constituting a hazard to both wildlife and humans. Although restrictions have been applied to prohibit the production of several POPs since the 1960s, high levels of these compounds can still be detected in many environmental and biological matrices, due to their chemical properties and significantly long half-lives. Some POPs can be passed from mother to the fetus and can gain entry to the central nervous system (CNS), by crossing the blood-brain barrier (BBB), resulting in significant deleterious effects, including neurocognitive and psychiatric abnormalities, which may lead to long-term socio-economic burdens. A growing body of evidence obtained from clinical and experimental studies has increasingly indicated that these POPs may influence neurodevelopment through several cellular and molecular mechanisms. However, studies assessing their mechanisms of action are still incipient, requiring further research. Polychlorinated biphenyls (PCBs) and per- and polyfluoroalkyl substances (PFAS) are two of the main classes of POPs associated with disturbances in different human systems, mainly the nervous and endocrine systems. This narrative review discusses the main PCB and PFAS effects on the CNS, focusing on neuroinflammation and oxidative stress and their consequences for neural development and BBB integrity. Moreover, we propose which mechanisms could be involved in POP-induced neurodevelopmental defects. In this sense, we highlight potential cellular and molecular pathways by which these POPs can affect neurodevelopment and could be further explored to propose preventive therapies and formulate public health policies.

Advanced understanding of the polybrominated diphenyl ethers (PBDEs): Insights from total environment to intoxication

Polybrominated diphenyl ethers (PBDEs) are brominated compounds connected by ester bonds between two benzene rings. There are 209 congeners of PBDEs, classified according to the number and position of the bromine atoms. Due to their low cost and superior flame retardant properties, PBDEs have been extensively used as flame retardants in electronic products, plastics, textiles, and other materials since the 1970s. PBDEs are classified as persistent organic pollutants (POPs) under the Stockholm Convention because of their environmental persistence, bioaccumulation, and toxicity to both humans and wildlife. Due to their extensive use and significant quantities, PBDEs have been detected across a range of environments and biological organisms. These compounds are known to cause damage to the metabolic system, exhibit neurotoxicity, and pose reproductive hazards. This review investigates the environmental distribution and human exposure pathways of PBDEs. Using China-a country with significant PBDE use-as an example, it highlights substantial regional and temporal variations in PBDE concentrations and notes that certain environmental levels may pose risks to human health. The article then examines the toxic effects and mechanisms of PBDEs on several major target organs, summarizing recent research and the specific mechanisms underlying these toxic effects from multiple toxicological perspectives. This review enhances our understanding of PBDEs' environmental distribution, exposure pathways, and toxic mechanisms, offering valuable insights for further research and management strategies.

Two Hits of EDCs Three Generations Apart: Evaluating Multigenerational Anxiety-Like Behavioral Phenotypes in Male Rats Exposed to Aroclor 1221 and Vinclozolin

BACKGROUND

Increasing evidence supports an association of endocrine-disrupting chemical (EDC) exposures with adverse biological effects in humans and wildlife. Recent studies reveal that health consequences of environmental exposures may persist or emerge across generations. This creates a dual conundrum: that we are exposed to contemporary environmental chemicals overlaid upon the inheritance of our ancestors' exposure profiles. Even when legacy EDCs are phased out, they may remain relevant due to persistence in the environment together with intergenerational inheritance of their adverse biological effects. Thus, we all possess a body burden of legacy contaminants, and we are also increasingly exposed to new generations of EDCs.

OBJECTIVES

We assessed the effects of direct and ancestral exposures to EDCs across six generations on anxiety-like behaviors in male rats using our "two hits, three generations apart" multigenerational EDC exposure experimental model. We investigated two classes of EDCs with distinct hormonal actions and historical use-the weakly estrogenic polychlorinated biphenyl (PCB) mixture Aroclor 1221 (A1221) and the anti-androgenic fungicide vinclozolin (VIN)-in both the maternal and paternal line. We also determined if a hormonal mechanism drives these effects across generations.

METHODS

Rats were gestationally exposed to A1221, VIN, or vehicle [dimethyl sulfoxide (DMSO)] in the F1 generation. Three generations later, the F4 generation was given the same or a different exposure. Anxiety-like behavior was measured in the open field test, light:dark box, and elevated plus maze across generations. Serum was collected at the end of the experiment, and concentrations of estradiol and corticosterone were analyzed.

RESULTS

Although direct exposure did not affect behavior in F1 males, ancestral exposure to VIN decreased anxiety-like behavior in the F3 paternal line compared to vehicle. In the F4 paternal line, ancestral A1221 followed by direct exposure to VIN increased anxiety-like behavior compared to controls. In the F6 maternal line, relative to vehicle, the double ancestral hits of A1221/VIN decreased anxiety-like behavior. Serum hormones weakly predicted behavioral changes in the F4 paternal line and were modestly affected in the F4 and F6 maternal lines.

DISCUSSION

Our data suggest that anxiety-like behavioral phenotypes emerge transgenerationally in male rats in response to EDC exposure and that multiple hits of either the same or a different EDC can increase the impact in a lineage-specific manner. https://doi.org/10.1289/EHP15684.

Interactions of Polychlorinated Biphenyls and Their Metabolites with the Brain and Liver Transcriptome of Female Mice

Exposure to polychlorinated biphenyls (PCBs) is linked to neurotoxic effects. This study aims to close knowledge gaps regarding the specific modes of action of PCBs in female C57BL/6J mice (>6 weeks) orally exposed for 7 weeks to a human-relevant PCB mixture (MARBLES mix) at 0, 0.1, 1, and 6 mg/kg body weight/day. PCB and hydroxylated PCB (OH-PCBs) levels were quantified in the brain, liver, and serum; RNA sequencing was performed in the striatum, prefrontal cortex, and liver, and metabolomic analyses were performed in the striatum. Profiles of PCBs but not their hydroxylated metabolites were similar in all tissues. In the prefrontal cortex, PCB exposure activated the oxidative phosphorylation respiration pathways, while suppressing the axon guidance pathway. PCB exposure significantly changed the expression of genes associated with neurodevelopmental and neurodegenerative diseases in the striatum, impacting pathways like growth hormone synthesis and dendrite development. PCBs did not affect the striatal metabolome. In contrast to the liver, which showed activation of metabolic processes following PCB exposure and the induction of cytochrome P450 enzymes, the expression of xenobiotic processing genes was not altered by PCB exposure in either brain region. Network analysis revealed complex interactions between individual PCBs (e.g., PCB28 [2,4,4'-trichlorobiphenyl]) and their hydroxylated metabolites and specific differentially expressed genes (DEGs), underscoring the need to characterize the association between specific PCBs and DEGs. These findings enhance the understanding of PCB neurotoxic mechanisms and their potential implications for human health.

Placental-brain axis in females detected within broadly impacted metabolic gene networks protects against prenatal PCB exposure

Background

Neurodevelopmental disorders have a strong male bias that is poorly understood. Placenta is a rich source of molecular information about environmental interactions with genetics (including biological sex), that affect the developing brain. We investigated placental-brain transcriptional responses in an established mouse model of prenatal exposure to a human-relevant mixture of polychlorinated biphenyls (PCBs).

Results

To understand sex, tissue, and dosage effects in embryonic (E18) brain and placenta by RNAseq, we used weighted gene correlation network analysis (WGCNA) to create correlated gene networks that could be compared across sex or tissue. WGCNA revealed that expression within most correlated gene networks was significantly and strongly associated with PCB exposures, but frequently in opposite directions between male-female and placenta-brain comparisons. In both WGCNA and differentially expressed gene analyses, male brain showed more PCB-induced transcriptional changes than male placenta, but the reverse pattern was seen in females. Furthermore, non-monotonic dose responses to PCBs were observed in most gene networks but were most prominent in male brain. The transcriptomic effects of low dose PCB exposure were significantly reversed by dietary folic acid supplementation across both sexes, but these effects were strongest in female placenta. PCB-dysregulated and folic acid-reversed gene networks were commonly enriched in functions in metabolic pathways involved in energy usage and translation, with female-specific protective effects enriched in PPAR, thermogenesis, glycerolipids, and O-glycan biosynthesis, as opposed to toxicant responses in male brain.

Conclusions

The female protective effect in prenatal PCB exposures appears to be mediated by dose-dependent sex differences in transcriptional modulation of metabolism in placenta.

Long-term dietary exposure to 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) reduced feeding in common carp (Cyprinus carpio): Via the JAK-STAT signaling pathway

Polybrominated diphenyl ethers (PBDEs) are widely present in water ecosystems where they pose a significant threat to aquatic life, but our knowledge about how PBDEs affect feeding is limited. Therefore, this study explored the effects of continuous dietary exposure to 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) (40 and 4000 ng/g) on the feeding in common carp (Cyprinus carpio) and the underlying mechanism. BDE-47 significantly decreased the food intake of carp. Transcriptome analysis of brain tissue showed that BDE-47 mainly affected the nervous, immune, and endocrine systems. Further examination of the expression levels of appetite factors in the brain revealed that BDE-47 caused dysregulation of appetite factors expressions such as agrp, pomc, cart, etc. In addition, the JAK-STAT signaling pathway was activated under BDE-47 exposure. It can be concluded from these findings that BDE-47 activated the JAK-STAT signaling pathway, causing imbalanced expression of appetite factors, leading to disordered feeding behavior and decreased food intake in carp. These results provide an important reference for a more comprehensive understanding of the hazards posed by BDE-47 on animal feeding and the associated mechanisms.

Per- and Polyfluoroalkyl Substances: Impacts on Morphology, Behavior and Lipid Levels in Zebrafish Embryos

The presence of per- and polyfluoroalkyl substances (PFASs) in aquatic environments is often persistent and widespread. Understanding the potential adverse effects from this group of chemicals on aquatic communities allows for better hazard characterization. This study examines impacts on zebrafish (Danio rerio) embryo physiology, behavior, and lipid levels from exposure to perfluorooctanoic acid (PFOA), perfluorohexane sulfonate (PFHxS), and heptadecafluorooctanesulfonic acid (PFOS). Embryos were exposed to lethal and sublethal levels of each chemical and monitored for alterations in physiological malformations, mortality, lipid levels, and behavior (only PFOA and PFHxS). The predicted 50% lethal concentrations for 120 hpf embryos were 528.6 ppm PFOA, 14.28 ppm PFHxS, and 2.14 ppm PFOS. Spine curvature and the inability of the 120 hpf embryos to maintain a dorsal-up orientation was significantly increased at 10.2 ppm PFHxS and 1.9 ppm PFOS exposure. All measured 120 hpf embryo behaviors were significantly altered starting at the lowest levels tested, 188 ppm PFOA and 6.4 ppm PFHxS. Lipid levels decreased at the highest PFAS levels tested (375 PFOA ppm, 14.4 PFHxS ppm, 2.42 ppm PFOS). In general, the PFAS chemicals, at the levels examined in this study, increased morphological deformities, embryo activity, and startle response time, as well as decreased lipid levels in 120 hpf zebrafish embryos.

Effects of exposure to 3,6-DBCZ on neurotoxicity and AhR pathway during early life stages of zebrafish (Danio rerio)

Polyhalogenated carbazoles (PHCZs) are emerging environmental pollutants, yet limited information is available on their embryotoxicity and neurotoxicity. Therefore, the current work was performed to investigate the adverse effects of 3,6-dibromocarbazole (3,6-DBCZ), a typical PHCZs homolog, on the early life stages of zebrafish larvae. It revealed that the 96-hour post-fertilization (hpf) median lethal concentration (LC50) value of 3,6-DBCZ in zebrafish larvae was determined to be 0.7988 mg/L. Besides, 3,6-DBCZ reduced survival rates at concentrations ≥ 1 mg/L and decreased hatching rates at ≥ 0.25 mg/L at 48 hpf. In behavior tests, it inhibited locomotor activities and reduced the frequency of recorded acceleration states in response to optesthesia (a sudden bright light stimulus) at concentrations ≥ 160 μg/L. Meanwhile, 3,6-DBCZ exposure decreased the frequency of recorded acceleration states in the startle response (tapping mode) at concentrations ≥ 6.4 μg/L. Pathologically, with the transgenic zebrafish model (hb9-eGFP), we observed a strikingly decreased axon length and number in motor neurons after 3,6-DBCZ treatment, which may be ascribed to the activation of the AhR signaling pathway, as evidenced by the molecular docking analysis and Microscale thermophoresis (MST) assay suggested that 3,6-DBCZ binding to AhR-ARNT2 compound proteins. Through interaction with AhR-ARNT, a striking reduction of the anti-oxidative stress (sod1/2, nqo1, nrf2) and neurodevelopment-related genes (elavl3, gfap, mbp, syn2a) were observed after 3,6-DBCZ challenge, accompanied by a marked increased inflammatory genes (TNFβ, IL1β, IL6). Collectively, our findings reveal a previously unrecognized adverse effect of 3,6-DBCZ on zebrafish neurodevelopment and locomotor behaviors, potentially mediated through the activation of the AhR pathway. Furthermore, it provides direct evidence for the toxic concentrations of 3,6-DBCZ and the potential target signaling in zebrafish larvae, which may be beneficial for the risk assessment of the aquatic ecosystems.

A complex mixture of polycyclic aromatic compounds causes embryotoxic, behavioral, and molecular effects in zebrafish larvae (Danio rerio), and in vitro bioassays

Polycyclic aromatic compounds (PACs) are prevalent in the environment, typically found in complex mixtures and high concentrations. Our understanding of the effects of PACs, excluding the 16 priority polycyclic aromatic hydrocarbons (16 PAHs), remains limited. Zebrafish embryos and in vitro bioassays were utilized to investigate the embryotoxic, behavioral, and molecular effects of a soil sample from a former gasworks site in Sweden. Additionally, targeted chemical analysis was conducted to analyze 87 PACs in the soil, fish, water, and plate material. CALUX® assays were used to assess the activation of aryl hydrocarbon and estrogen receptors, as well as the inhibition of the androgen receptor. Larval behavior was measured by analyzing activity during light and darkness and in response to mechanical stimulation. Furthermore, qPCR analyses were performed on a subset of 36 genes associated with specific adverse outcomes, and the total lipid content in the larvae was measured. Exposure to the sample resulted in embryotoxic effects (LC50 = 0.480 mg dry matter soil/mL water). The mixture also induced hyperactivity in darkness and hypoactivity in light and in response to the mechanical stimulus. qPCR analysis revealed differential regulation of 15 genes, including downregulation of opn1sw1 (eye pigmentation) and upregulation of fpgs (heart failure). The sample caused significant responses in three bioassays (ERα-, DR-, and PAH-CALUX), and the exposed larvae exhibited elevated lipid levels. Chemical analysis identified benzo[a]pyrene as the predominant compound in the soil and approximately half of the total PAC concentration was attributed to the 16 PAHs. This study highlights the value of combining in vitro and in vivo methods with chemical analysis to assess toxic mechanisms at specific targets and to elucidate the possible interactions between various pathways in an organism. It also enhances our understanding of the risks associated with environmental mixtures of PACs and their distribution during toxicity testing.

Toxic Effects and Mechanisms of Polybrominated Diphenyl Ethers

Polybrominated diphenyl ethers (PBDEs) are a group of flame retardants used in plastics, textiles, polyurethane foam, and other materials. They contain two halogenated aromatic rings bonded by an ester bond and are classified according to the number and position of bromine atoms. Due to their widespread use, PBDEs have been detected in soil, air, water, dust, and animal tissues. Besides, PBDEs have been found in various tissues, including liver, kidney, adipose, brain, breast milk and plasma. The continued accumulation of PBDEs has raised concerns about their potential toxicity, including hepatotoxicity, kidney toxicity, gut toxicity, thyroid toxicity, embryotoxicity, reproductive toxicity, neurotoxicity, and immunotoxicity. Previous studies have suggested that there may be various mechanisms contributing to PBDEs toxicity. The present study aimed to outline PBDEs' toxic effects and mechanisms on different organ systems. Given PBDEs' bioaccumulation and adverse impacts on human health and other living organisms, we summarize PBDEs' effects and potential toxicity mechanisms and tend to broaden the horizons to facilitate the design of new prevention strategies for PBDEs-induced toxicity.

Evaluation of BDE-47-induced neurodevelopmental toxicity in zebrafish embryos

There are growing concerns about the neurodevelopmental toxicity of polybrominated diphenyl ethers (PBDEs), but the toxicological phenotypes and mechanisms are not well elucidated. Here, zebrafish (Danio rerio) were exposed to 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) from 4 to 72 h post-fertilization (hpf). The results showed that BDE-47 stimulated the production of dopamine and 5-hydroxytryptamine, but inhibited expression of Nestin, GFAP, Gap43, and PSD95 in 24 hpf embryos. Importantly, we unraveled the inhibitory effects of BDE-47 on neural crest-derived melanocyte differentiation and melanin syntheses process, evidenced by disrupted expression of wnt1, wnt3, sox10, mitfa, tyrp1a, tyrp1b, tryp2, and oca2 gene in 72 hpf embryos and decreased tyrosinase activities in embryos at 48 and 72 hpf. The transcriptional activities of myosin VAa, kif5ba, rab27a, mlpha, and cdc42 genes, which are associated with intracellular transport process, were also disturbed during zebrafish development. Ultimately, these alterations led to fast spontaneous movement and melanin accumulation deficit in zebrafish embryos upon BDE-47 exposure. Our results provide an important extension for understanding the neurodevelopmental effects of PBDEs and facilitate the comprehensive evaluation of neurotoxicity in embryos.

Multi- and Transgenerational Developmental Impairments Are Induced by Decabromodiphenyl Ethane (DBDPE) in Zebrafish Larvae

A novel brominated flame retardant decabromodiphenyl ethane (DBDPE) has become a ubiquitous emerging pollutant; hence, the knowledge of its long-term toxic effects and underlying mechanism would be critical for further health risk assessment. In the present study, the multi- and transgenerational toxicity of DBDPE was investigated in zebrafish upon a life cycle exposure at environmentally relevant concentrations. The significantly increased malformation rate and declined survival rate specifically occurred in unexposed F2 larvae suggested transgenerational development toxicity by DBDPE. The changing profiles revealed by transcriptome and DNA methylome confirmed an increased susceptibility in F2 larvae and figured out potential disruptions of glycolipid metabolism, mitochondrial energy metabolism, and neurodevelopment. The changes of biochemical indicators such as ATP production confirmed a disturbance in the energy metabolism, whereas the alterations of neurotransmitter contents and light-dark stimulated behavior provided further evidence for multi- and transgenerational neurotoxicity in zebrafish. Our findings also highlighted the necessity for considering the long-term impacts when evaluating the health of wild animals as well as human beings by emerging pollutants.

Exposure of zebrafish to an environmental mixture of persistent organic pollutants triggers an increase in anxiety-like syndrome but does not affect boldness in unexposed offspring

Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are persistent organic pollutants (POPs) that are present as complex mixtures in all environmental compartments, including aquatic ecosystems. However, little is known about the effects of such complex mixtures on teleost behaviour. In this study, zebrafish (Danio rerio) were chronically exposed to an environmentally relevant mixture (MIX) containing 22 PCB and 7 PBDE congeners through diet from 5 days post fertilization onwards. MIX-exposed F0 fish produced offspring (F1 and F2 generations) that were fed using plain food and grown until adulthood. In each generation, five behavioural traits (i.e. boldness, activity, sociality, exploration and anxiety) were evaluated by the mean of different experimental set-ups. Two distinct behavioural syndromes were identified: boldness, positively correlated to activity and exploration; and anxiety, associated with low sociality. F0 fish did not display any behavioural disruption resulting from POP exposure whereas F1 MIX fish were bolder than fish from other generations but did not differ significantly from F1 controls. F2 MIX fish displayed a higher anxiety syndrome than F2 controls. This is of particular importance since such behavioural changes in offspring generations may have persistent ecological consequences, may affect fitness and hence cause detrimental effects on wild fish populations exposed to POP mixtures.

Using zebrafish embryo bioassays to identify chemicals modulating the regulation of the epigenome: a case study with simvastatin

Contaminants of emerging concern have been increasingly associated with the modulation of the epigenome, leading to potentially inherited and persistent impacts on apical endpoints. Here, we address the performance of the OECD Test No. 236 FET (fish embryo acute toxicity) in the identification of chemicals able to modulate the epigenome. Using zebrafish (Danio rerio) embryos, acute and chronic exposures were performed with the pharmaceutical, simvastatin (SIM), a widely prescribed hypocholesterolemic drug reported to induce inter and transgenerational effects. In the present study, the epigenetic effects of environmentally relevant concentrations of SIM (from 8 ng/L to 2000 ng/L) were addressed following (1) an acute embryo assay based on OECD Test No. 236 FET, (2) a chronic partial life-cycle exposure using adult zebrafish (90 days), and (3) F1 embryos obtained from parental exposed animals. Simvastatin induced significant effects in gene expression of key epigenetic biomarkers (DNA methylation and histone acetylation/deacetylation) in the gonads of exposed adult zebrafish and in 80 hpf zebrafish embryos (acute and chronic parental intergenerational exposure), albeit with distinct effect profiles between biological samples. In the chronic exposure, SIM impacted particularly DNA methyltransferase genes in males and female gonads, whereas in F1 embryos SIM affected mostly genes associated with histone acetylation/deacetylation. In the embryo acute direct exposure, SIM modulated the expression of both genes involved in DNA methylation and histone deacetylase. These findings further support the use of epigenetic biomarkers in zebrafish embryos in a high throughput approach to identify and prioritize epigenome-modulating chemicals.

Behavioral changes and transcriptomic effects at embryonic and post-embryonic stages reveal the toxic effects of 2,2',4,4'-tetrabromodiphenyl ether on neurodevelopment in zebrafish (Danio rerio)

Polybrominated biphenyl ethers (PBDEs) are new persistent pollutants that are widely exist in the environment and have many toxic effects. However, their toxicity mechanisms on neurodevelopment are still unclear. In this study, zebrafish embryos were exposed to 2, 2', 4, 4'-tetrabromodiphenyl ether (BDE-47) (control, 10, 50 and 100 μg/L) at 2 h postfertilization (hpf) - 7 dpf. Locomotion analysis indicated that BDE-47 increased spontaneous coiling activity in zebrafish embryos under high-intensity light stimuli and decreased locomotor in zebrafish larvae. RNA-Seq analysis revealed that most of the up-regulated pathways were related to the metabolism of cells and tissues, while the down-regulated pathways were related to neurodevelopment. Consistent with the locomotion and KEGG results, BDE-47 affected the expression of genes for central nervous system (gfap, mbpa, bdnf & pomcb), early neurogenesis (neurog1 & elavl3), and axonal development (tuba1a, tuba1b, tuba1c, syn2a, gap43 & shha). Furthermore, BDE-47 interfered with gene expression of the Wnt signaling pathway, especially during embryonic stages, suggesting that the mechanisms of BDE-47 toxicity to zebrafish at various stages of neurodevelopment may be different. In summary, early neurodevelopment effects and metabolic disturbances may have contributed to the abnormal neurobehavioral changes induced by BDE-47 in zebrafish embryos/larvae, suggesting the neurodevelopmental toxicity of BDE-47.

Toxicity of polychlorinated biphenyls in aquatic environments - A review

The assessment of polychlorinated biphenyls (PCBs) and their congeners resulting from the pollution of all environmental media is inherently related to its persistence and ubiquitous nature. In principle, determination of this class of contaminants are limited to the determination of their concentrations in the various environmental matrices. For solving many problems in this context, knowledge of the emission sources of PCBs, transport pathways, and sites of contamination and biomagnification is of great benefit to scientists and researchers, as well as many regulatory organizations. By far the largest amounts of PCBs, regardless of their discharged points, end up in the soil, sediment and finally in different aquatic environments. By reviewing relevant published materials, the source of origin of PCBs in the environment particularly from different pollution point sources, it is possible to obtain useful information on the nature of different materials that are sources of PCBs, or their concentrations and their toxicity or health effects and how they can be removed from contaminated media. This review focuses on the sources of PCBs in aquatic environments and critically reviews the toxicity of PCBs in aquatic animals and plants. The review also assesses the toxicity equivalency factors (TEFs) of PCBs providing valuable knowledge to other scientists and researchers that enables regulatory laws to be formulated based on selective determination of concentrations regarding their maximum permissible limits (MPLs) allowed. This review also supplies a pool of valuable information useful for designing decontamination technologies for PCBs in media like soil, sediment, and wastewaters.

DE-71 affected the cholinergic system and locomotor activity via disrupting calcium homeostasis in zebrafish larvae

Polybrominated diphenyl ethers (PBDEs) can induce neurotoxicity, but the mechanism of their toxicity on the cholinergic system and locomotion behavior remains unclear. In this paper, zebrafish embryos were exposed to DE-71 (0, 1, 3, 10, 30, and 100 µg/L) until 120 h post fertilization, and its effects on the behavior and cholinergic system of zebrafish larvae and its possible mechanism were investigated. Results indicated a general locomotor activity impairment in the light-dark transition stimulation without affecting the secondary motoneurons. However, with the extension of test time in the dark or light, the decreased locomotor activity was diminished, a significant decrease only observed in the 100 µg/L DE-71 exposure groups in the last 10 min. Furthermore, whole-body acetylcholine (ACh) contents decreased after DE-71 exposure, whereas no changes in NO contents and inducible nitric oxide synthase activity were found. The expression of certain genes encoding calcium homeostasis proteins (e.g., grin1a, camk2a, and crebbpb) and the concentrations of calcium in zebrafish larvae were significantly decreased after DE-71 exposure. After co-exposure with calcium channel agonist (±)-BAY K8644, calcium concentrations, ACh contents, and locomotor activity in the light-dark transition stimulation was significantly increased compared with the same concentrations of DE-71 exposure alone, whereas no significant difference was observed compared with the control, indicating that calcium homeostasis is involved in the impairment of cholinergic neurotransmission and locomotor activity. Overall, our results suggested that DE-71 can impair the cholinergic system and locomotor activity by impairing calcium homeostasis. Our paper provides a better understanding of the neurotoxicity of PBDEs.

Sex-specific differences in zebrafish brains

In this systematic review, we highlight the differences between the male and female zebrafish brains to understand their differentiation and their use in studying sex-specific neurological diseases. Male and female brains display subtle differences at the cellular level which may be important in driving sex-specific signaling. Sex differences in the brain have been observed in humans as well as in non-human species. However, the molecular mechanisms of brain sex differentiation remain unclear. The classical model of brain sex differentiation suggests that the steroid hormones derived from the gonads are the primary determinants in establishing male and female neural networks. Recent studies indicate that the developing brain shows sex-specific differences in gene expression prior to gonadal hormone action. Hence, genetic differences may also be responsible for differentiating the brain into male and female types. Understanding the signaling mechanisms involved in brain sex differentiation could help further elucidate the sex-specific incidences of certain neurological diseases. The zebrafish model could be appropriate for enhancing our understanding of brain sex differentiation and the signaling involved in neurological diseases. Zebrafish brains show sex-specific differences at the hormonal level, and recent advances in RNA sequencing have highlighted critical sex-specific differences at the transcript level. The differences are also evident at the cellular and metabolite levels, which could be important in organizing sex-specific neuronal signaling. Furthermore, in addition to having one ortholog for 70% of the human gene, zebrafish also shares brain structural similarities with other higher eukaryotes, including mammals. Hence, deciphering brain sex differentiation in zebrafish will help further enhance the diagnostic and pharmacological intervention of neurological diseases.

Neurotoxicity assessment of QoI strobilurin fungicides azoxystrobin and trifloxystrobin in human SH-SY5Y neuroblastoma cells: Insights from lipidomics and mitochondrial bioenergetics

Strobilurin fungicides are quinone outside inhibitors (QoI) used to treat fungal pathogens for agricultural and residential use. Here, we compared the potential for neurotoxicity of the widely used strobilurins, azoxystrobin (AZS) and trifloxystrobin (TFS), in differentiated human SH-SY5Y cells. Fungicides did not include cytotoxicity up to 200 µM but both induced loss of cell viability at 48 h, with TFS showing slightly higher toxicity that AZS. Caspase 3/7 activity was induced in SH-SY5Y cells by both fungicides at 48 h (50 µM for AZS and 25 µM for TFS). ATP levels were reduced following a 24-hour exposure to > 25 µM AZS and > 6.25 µM TFS and both fungicides rapidly impaired oxidative respiration (~12.5 µM for AZS and ~3.125 µM TFS) and decreased oligomycin-induced ATP production, maximal respiration, and mitochondrial spare capacity. AZS at 100 µM showed a continual impairment of mitochondrial membrane potential (MMP) between 4 and 48 h while TFS at > 50 µM decreased MMP at 24 h. Taken together, TFS exerted higher mitochondrial toxicity at lower concentrations compared to AZS in SH-SY5Y cells. To discern toxicity mechanisms of strobilurin fungicides, lipidomics was conducted in SH-SY5Y cells following exposure to 6.25 µM and 25 µM AZS, and a total of 1595 lipids were detected, representing 49 different lipid classes. Lipid classes with the largest proportion of lipids detected in SH-SY5Y cells included triglycerides (17%), phosphatidylethanolamines (8%), ether-linked triglycerides (8%), phosphatidylcholines (7%), ether-linked phosphatidylethanolamines (6%), and diacylglycerols (5%). Together, these 5 lipid classes accounted for over 50% of the total lipids measured in SH-SY5Y cells. Lipids that were increased by AZS included acyl carnitine, which plays a role in long chain fatty acid utilization for mitochondrial β-oxidation, as well as non-modified, ether linked, and oxidized triacylglycerols, suggesting compensatory upregulation of triglyceride biosynthesis. The ceramide HexCer-NS, linked to neurodegenerative diseases, was decreased in abundance following AZS exposure. In summary, strobilurin fungicides rapidly inhibit mitochondrial oxidative respiration and alter the abundance of several lipids in neuronal cells, relevant for understanding environmental exposure risks related to their neurotoxicity.

Maternal genetic effect on apoptosis of ovarian granulosa cells induced by cadmium

To investigate the maternal genetic effects of cadmium (Cd) -induced apoptotic in ovarian granulosa cells (OGCs). Herein, pregnant Sprague-Dawley (SD) rats were treated with CdCl₂ from day 1 to day 20, F1 and F2 female rats were mated with untreated males to produce F2 and F3 generations. Under this model, significant apoptotic changes were observed in F1 OGCs induced by Cd (Liu et al., 2021). In this study, no apoptotic bodies were found in F2 while the mitochondrial membrane potential level decreased significantly but not in F3. Moreover, significant changes in bcl-xl and Cle-CASPASE-9/Pro-CASPASE-9 ratio were observed in F2 which disappears in F3. The DNA methylation sequencing and microRNAs (miRNAs) microarray reveals different gene methylation and miRNAs changes in F2 and F3. Notably, miR-132-3p, miR-199a-5p, and miR-1949 were upregulated in F1 while downregulated in F2 and F3 in which apoptosis gradually disappeared. Further, miRNA maturation-related genes and transcription factors have different expression patterns in F1-F3. These results indicate that maternal genetic intergenerational/transgenerational effect of Cd-induced OGCs apoptotic was significantly attenuated and disappeared, which was related to self-repair regulation of apoptosis-related genes. The changes in apoptosis-related miRNAs and DNA methylation may be important, and the role of transcription factors deserve attention.

Toxic effect of BDE-47 on the marine alga Skeletonema costatum: Population dynamics, photosynthesis, antioxidation and morphological changes

The toxic effects of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) on the marine alga Skeletonema costatum were studied, including the population dynamics, chlorophyll fluorescence characteristics, pigment content, superoxide dismutase (SOD) activity, malondialdehyde (MDA) content and morphology. High doses (200-600 μg L^-1) of BDE-47 significantly suppressed the population growth of S. costatum, with a 96 h EC₅₀ value of 293 μg L^-1. Photosynthetic parameters (F_v/F_m, rETR_max and Φ_PSⅡ) of photosystem II (PSII) were significantly inhibited with increasing BDE-47 concentrations. The chlorophyll c (chl c) concentration was also inhibited by exposure to BDE-47. In contrast, chl a and carotenoid concentrations were elevated after exposure to high concentrations of BDE-47 for 72 and 96 h. The SOD activity was generally higher at concentrations of 100-600 μg L^-1 than those of the control when the exposure time was less than 48 h. With increasing time, the SOD activity generally decreased, and significantly higher SOD activity only occurred in the treatment with high doses of BDE-47. High MDA contents occurred after exposure for 96 h in all BDE-47 treatments. With increasing BDE-47 concentrations, drastic deformation of the silicious valve and detachment of the strutted processes were found. In addition, drastic decreases in the BDE-47 concentration in culture medium indicated the bioaccumulation of BDE-47 by S. costatum. Our results revealed multiple responses of S. costatum to BDE-47 exposure, and indicated the potential risk of BDE-47 in the East China Sea based on these responses.

The insecticide permethrin induces transgenerational behavioral changes linked to transcriptomic and epigenetic alterations in zebrafish (Danio rerio)

The pyrethroid insecticide permethrin is widely used for agricultural and domestic purposes. Previous data indicated that it acts as a developmental neurotoxicant and can induce transgenerational effects in non-target organisms. However, associated underlying mechanisms remain unclear. The aim of this study was to investigate permethrin-related transgenerational effects in the zebrafish model, and to identify possible molecular mechanisms underlying inheritance. Zebrafish (F0) were exposed to permethrin during early-life (2 h post-fertilization up to 28 days). The F1 and F2 offspring generations were obtained by pairing exposed F0 males and females, and were bred unexposed. Locomotor and anxiety behavior were investigated, together with transcriptomic and epigenomic (DNA methylation) changes in brains. Permethrin exposed F0 fish were hypoactive at adulthood, while males from the F1 and F2 generations showed a specific decrease in anxiety-like behavior. In F0, transcriptomic data showed enrichment in pathways related to glutamatergic synapse activity, which may partly underlie the behavioral effects. In F1 and F2 males, dysregulation of similar pathways was observed, including a subset of differentially methylated regions that were inherited from the F0 to the F2 generation and indicated stable dysregulation of glutamatergic signaling. Altogether, the present results provide novel evidence on the transgenerational neurotoxic effects of permethrin, as well as mechanistic insight: a transient exposure induces persistent transcriptional and DNA methylation changes that may translate into transgenerational alteration of glutamatergic signaling and, thus, into behavioral alterations.

Pesticide-induced multigenerational effects on amphibian reproduction and metabolism

Underlying drivers of species extinctions need to be better understood for effective conservation of biodiversity. Nearly half of all amphibian species are at risk of extinction, and pollution may be a significant threat as seasonal high-level agrochemical use overlaps with critical windows of larval development. The potential of environmental chemicals to reduce the fitness of future generations may have profound ecological and evolutionary implications. This study characterized effects of male developmental exposure to environmentally relevant concentrations of the anti-androgenic pesticide linuron over two generations of offspring in Xenopus tropicalis frogs. The adult male offspring of pesticide-exposed fathers (F1) showed reduced body size, decreased fertility, and signs of endocrine system disruption. Impacts were further propagated to the grand-offspring (F2), providing evidence of transgenerational effects in amphibians. The adult F2 males demonstrated increased weight and fat body palmitoleic-to-palmitic acid ratio, and decreased plasma glucose levels. The study provides important cross-species evidence of paternal epigenetic inheritance and pollutant-induced transgenerational toxicity, supporting a causal and complex role of environmental contamination in the ongoing species extinctions, particularly of amphibians.

Epigenetic biomarkers as tools for chemical hazard assessment: Gene expression profiling using the model Danio rerio

Recent reports raise the concern that exposure to several environmental chemicals may induce persistent changes that go beyond the exposed organisms, being transferred to subsequent generations even in the absence of the original chemical insult. These changes in subsequent non-exposed generations have been related to epigenetic changes. Although highly relevant for hazard and risk assessment, biomarkers of epigenetic modifications that can be associated with adversity, are still not integrated into hazard assessment frameworks. Here, in order to validate new biomarkers of epigenetic modifications in a popular animal model, zebrafish embryos were exposed to different concentrations of Bisphenol A (0.01, 0.1, 1 and 10 mg/L) and Valproic Acid (0.8, 4, 20 and 100 mg/L), two chemicals reported to alter the modulation of the epigenome. Morphological abnormalities and epigenetic changes were assessed at 80 hours-post fertilization, including DNA global methylation and gene expression of both DNA and histone epigenetic modifications. Gene expression changes were detected at concentrations below those inducing morphological abnormalities. These results further support the importance of combining epigenetic biomarkers with apical endpoints to improve guidelines for chemical testing and hazard assessment, and favour the integration of new biomarkers of epigenetic modifications into the standardized OECD test guideline 236 with zebrafish embryos.