Effects of Dechlorane Plus exposure on axonal growth, musculature and motor behavior in embryo-larval zebrafish

Photoaged polystyrene microplastics result in neurotoxicity associated with neurotransmission and neurodevelopment in zebrafish larvae (Danio rerio)

Microplastics (MPs) are emerging pollutants widely distributed in the environment, inducing toxic effects in various organisms. However, the neurotoxicity and underlying mechanisms of simulated sunlight-aged MPs have rarely been investigated. In this study, zebrafish (Danio rerio) were exposed to environmentally relevant concentrations (0, 0.1, 1, 10, and 100 μg/L) of virgin polystyrene (V-PS) and aged polystyrene (A-PS) for 120 hpf to evaluate the neurotoxicity. The results demonstrated that simulated sunlight irradiation altered the physicochemical properties (morphology, functional groups, and chemical composition) of V-PS. Exposure to A-PS causes greater toxicity on locomotor ability in larval zebrafish than V-PS. Motor neuron development was disrupted by transgenic (hb9-GFP) zebrafish larvae exposed to A-PS, with significant alterations in neurotransmitter levels (ACh, DA, 5-HT, and GABA) and enzyme activity (AChE, ChAT, and ChE). Further investigation found that exposure to A-PS had a significantly impact on the expression of neurotransmission and neurodevelopment-related genes in zebrafish. These findings suggest that A-PS induces neurotoxicity by its effects on neurotransmission and neurodevelopment. This study highlights the neurotoxic effects and mechanisms of simulated sunlight irradiation of MPs, providing new insights for assessing the ecological risks of photoaged MPs in the environment.

Comparing the Developmental Toxicity Delay and Neurotoxicity of Benzothiazole and Its Derivatives (BTHs) in Juvenile Zebrafish

In this study, a semi-static water exposure method was employed to investigate the early developmental and neurotoxic effects of four benzothiazole substances (BTHs), namely benzothiazole (BTH), 2-mercaptobenzothiazole (MBT), 2-hydroxybenzothiazole (BTON), and 2-aminobenzothiazole (2-ABTH), on zebrafish at an equimolar concentration of 10 μM. The findings revealed that all four BTHs exerted certain impacts on early development in zebrafish. MBT stimulated spontaneous movement in juvenile zebrafish, whereas BTON inhibited such movements. Moreover, all four BTHs hindered the hatching process of zebrafish larvae, with MBT exhibiting the strongest inhibition at 24 h post-fertilization (hpf). Notably, MBT acted as a melanin inhibitor by suppressing melanin production in juvenile zebrafish eyes and weakening phototaxis. Additionally, both BTH and BTON exhibited significantly lower speeds than the control group and other test groups under conditions without bright field stimulation; however, their speeds increased to average levels after percussion stimulation, indicating no significant alteration in motor ability among experimental zebrafish groups. Short-term exposure to these four types of BTHs induced oxidative damage in zebrafish larvae; specifically, BTH-, MBT-, and BTON-exposed groups displayed abnormal expression patterns of genes related to oxidative damage. Exposure to both BTH and MBT led to reduced fluorescence intensity in transgenic zebrafish labeled with central nervous system markers, suggesting inhibition of central nervous system development. Furthermore, real-time quantitative PCR results demonstrated abnormal gene expression associated with neural development. However, no significant changes were observed in 2-ABTH gene expression at this concentration. Overall findings indicate that short-term exposure to BTHs stimulates neurodevelopmental gene expression accompanied by oxidative damage.

Probiotic Lactobacillus rhamnosus alleviates the neurotoxicity of microcystin-LR in zebrafish (Danio rerio) through the gut-brain axis

Microcystin-LR (MCLR) is one of the most toxic cyanobacterial toxins and is harmful to the central nervous system of fish. Probiotic additives can improve neuroendocrine function in fish. Although both MCLR and probiotics aim at the nervous system, whether they interact with each other and the mechanisms remain unexplored. In the present study, 4-month-old zebrafish were exposed to 0, 2.2, and 22 μg/L of MCLR for 28 days with or without the probiotic L. rhamnosus. We found that MCLR exposure could inhibit the swimming speed of zebrafish, while the presence of L. rhamnosus mitigated this abnormality. To elucidate the mechanism of how L. rhamnosus alleviates MCLR-induced neurotoxicity, we examined the bioaccumulation of MCLR, changes in neurotransmitters, immune biochemical indicators, and hormone content of the hypothalamic-pituitary-interrenal (HPI) axis in zebrafish along the gut-brain axis. Our results showed L. rhamnosus could reverse the abnormal swimming behavior and eventually alleviate neurotoxicity in zebrafish by modulating intestinal and brain neural signaling, neuroinflammation, and HPI axis responses. This study provides implications for the application of probiotics in the aquaculture industry.

Levels, tissue distribution and isomer stereoselectivity of Dechlorane Plus in humans: A critical review

Exposure of human tissues to Dechlorane Plus (DP) has raised public concern because of the multiple health threats it may pose to humans. Therefore, it is important to summarize the main findings of previous studies on DP in human tissues and to provide potential guidance for future studies. In this paper, DP levels in different populations and human tissues worldwide since 2009 were systematically reviewed. DP levels in human tissues of workers in e-waste dismantling sites in Guangdong Province, China (median 190 ng·g-1 lw in serum) and DP manufacturing plants in Jiangsu Province, China (mean 857 ng·g-1 lw in whole-blood) are the highest reported worldwide. DP levels in tissues of the general population in recent studies are close to those of residents near e-waste dismantling sites, which should be of concern. DP levels in different human tissues were found to be positively correlated with a pattern of blood > breast milk > adipose tissue. The distribution of DP in different human tissues is mainly lipid-driven and may also be influenced by the interaction of DP with proteins such as human serum albumin. Most of the past studies determined the isomer stereoselectivity of DP in human tissues only by comparing the composition of DP in commercial DP products and human tissues, which lacks evidence of mechanism. Recently, a significantly different affinity of DP isomers for proteins was found, which seems to confirm the isomer selectivity of DP in human tissues. We simulated the binding of DP to human serum albumin and DP to thyroid hormone receptor β by molecular docking and found differences in the binding behavior of syn-DP and anti-DP to the selected proteins. Molecular docking seems to be a feasible approach for future studies to predict and reveal the mechanisms of DP behavior and health effects in human tissues.

Ephedrine and cocaine cause developmental neurotoxicity and abnormal behavior in zebrafish

Ephedrine (EPH) and cocaine (COC) are illegal stimulant drugs, and have been frequently detected in aquatic environments. EPH and COC have negative effects on the nervous system and cause abnormal behaviors in mammals and fish at high concentrations, but their mechanisms of neurotoxicity remain unclear in larvae fish at low concentrations. To address this issue, zebrafish embryos were exposed to EPH and COC for 14 days post-fertilization (dpf) at 10, 100, and 1000 ng L-1. The bioaccumulation, development, behavior, cell neurotransmitter levels and apoptosis were detected to investigate the developmental neurotoxicity (DNT) of EPH and COC. The results showed that EPH decreased heart rate, while COC increased heart rate. EPH caused cell apoptosis in the brain by AO staining. In addition, behavior analysis indicated that EPH and COC affected spontaneous movement, touch-response, swimming activity and anxiety-like behaviors. EPH and COC altered the levels of the neurotransmitters dopamine (DA) and γ-aminobutyric acid (GABA) with changes of the transcription of genes related to the DA and GABA pathways. These findings indicated that EPH and COC had noticeable DNT in the early stage of zebrafish at environmentally relevant concentrations.

Aflatoxin B1 exposure induced developmental toxicity and inhibited muscle development in zebrafish embryos and larvae

The prevalence of aflatoxin B1 (AFB1), one of the most toxic mycotoxins that contaminates feedstock and food is increasing worldwide. AFB1 can cause various health problems in humans and animals, as well as direct embryotoxicity. However, the direct toxicity of AFB1 on embryonic development, especially foetal foetus muscle development, has not been studied in depth. In the present study, we used zebrafish embryos as a model to study the mechanism of the direct toxicity of AFB1 to the foetus, including muscle development and developmental toxicity. Our results showed that AFB1 caused motor dysfunction in zebrafish embryos. In addition, AFB1 induces abnormalities in muscle tissue architecture, which in turn causes abnormal muscle development in larvae. Further studies found that AFB1 destroyed the antioxidant capacity and tight junction complexes (TJs), causing apoptosis in zebrafish larvae. In summary, AFB1 may induce developmental toxicity and inhibit muscle development through oxidative damage, apoptosis and disruption of TJs in zebrafish larvae. Our results revealed the direct toxicity effects of AFB1 on the development of embryos and larvae, including inhibition of muscle development and triggering neurotoxicity, induction of oxidative damage, apoptosis and disruption of TJs, and fills the gap in the toxicity mechanism of AFB1 on foetal development.

Molecular, morphological and behavioral alterations of zebrafish (Danio rerio) embryos/larvae after clorprenaline hydrochloride exposure

Chlorprenaline hydrochloride (CLOR) is a typical representative of β-adrenergic agonists that may be used illegally as a livestock feed additive and may have adverse impacts on the environment. In the present study, zebrafish embryos were exposed to CLOR to investigate its developmental toxicity and neurotoxicity. The results demonstrated that CLOR exposure led to adverse effects on developing zebrafish, such as morphological changes, a high heart rate, and increased body length, resulting in developmental toxicity. Moreover, the up-regulation of activities of superoxide dismutase (SOD) and catalase (CAT) and the enhancement of malondialdehyde (MDA) content illustrated that CLOR exposure activated oxidative stress in exposed zebrafish embryos. Meanwhile, CLOR exposure also caused alterations in locomotive behavior in zebrafish embryos, including an increase in acetylcholinesterase (AChE) activity. Quantitative polymerase chain reaction (QPCR) results showed that the transcription of genes related to the central nervous system (CNS) development, namely, mbp, syn2a, α1-tubulin, gap43, shha, and elavl3, indicated that CLOR exposure could lead to neurotoxicity in zebrafish embryos. These results showed that CLOR exposure could cause developmental neurotoxicity in the early stages of zebrafish development and that CLOR might induce neurotoxicity by altering the expression of neuro-developmental genes, elevating AChE activity, and activating oxidative stress.

Toxic effects of isofenphos-methyl on zebrafish embryonic development

Isofenphos-methyl (IFP) is widely used as an organophosphorus for controlling underground insects and nematodes. However, excessive use of IFP may pose potential risks to the environment and humans, but little information is available on its sublethal toxicity to aquatic organisms. To address this knowledge gap, the current study exposed zebrafish embryos to 2, 4, and 8 mg/L IFP within 6-96 h past fertilization (hpf) and measured mortality, hatching, developmental abnormalities, oxidative stress, gene expressions, and locomotor activity. The results showed that IFP exposure reduced the rates of heart and survival rate, hatchability, and body length of embryos and induced uninflated swim bladder and developmental malformations. Reduction in locomotive behavior and inhibition of AChE activity indicated that IFP exposure may induce behavioral defects and neurotoxicity in zebrafish larvae. IFP exposure also led to pericardial edema, longer venous sinus-arterial bulb (SV-BA) distance, and apoptosis of the heart cells. Moreover, IFP exposure increased the accumulation of reactive oxygen species (ROS) and the content of malonaldehyde (MDA), also elevated the levels of antioxidant enzymes of superoxide dismutase (SOD) and catalase (CAT), but decreased glutathione (GSH) levels in zebrafish embryos. The relative expressions of heart development-related genes (nkx2.5, nppa, gata4, and tbx2b), apoptosis-related genes (bcl2, p53, bax, and puma), and swim bladder development-related genes (foxA3, anxa5b, mnx1, and has2) were significantly altered by IFP exposure. Collectively, our results indicated that IFP induced developmental toxicity and neurotoxicity to zebrafish embryos and the mechanisms may be relevant to the activation of oxidative stress and reduction of acetylcholinesterase (AChE) content.

Ecological risk assessment of environmentally relevant concentrations of propofol on zebrafish (Danio rerio) at early life stage: Insight into physiological, biochemical, and molecular aspects

Propofol is an intravenous anesthetic injection extensively used in clinic, which has been proved to be neurotoxic in humans. Improper use and disposal of propofol may lead to its release into the aquatic environment, but the potential ecological risk of propofol to aquatic organisms remains poorly understood. For this study, we comprehensively explored the ecotoxicological effects and potential mechanisms of propofol (0.04, 0.2 and 2 mg L^-1) on 120 hpf zebrafish (Danio rerio) embryos from physiological, biochemical, and molecular perspectives. The results showed that propofol has moderate toxicity on zebrafish embryos (96 h LC₅₀ = 4.260 mg L^-1), which could significantly reduce the hatchability and delay the development. Propofol can trigger reactive oxygen species (ROS) generation, lipid peroxidation (Malondialdehyde, MDA) and DNA damage (8-hydroxy-2-deoxyguanosine, 8-OHdG). The glutathione peroxidase (GPX) activity of zebrafish embryos in 0.04 and 0.2 mg L^-1 propofol treatment group was activated in response to oxidative damage, while activities of superoxide dismutase (SOD), catalase (CAT) and GPX in zebrafish treated with 2 mg L^-1 was significant inhibited compared with the control group (p＜0.05). Moreover, the expression of antioxidant genes and related pathways was inhibited. Apoptosis was investigated at genes level and histochemistry. Molecular docking confirmed that propofol could change in the secondary structure of acetylcholinesterase (AChE) and competitively inhibited acetylcholine (ACh) binding to AChE, which may disturb the nervous system. These results described toxic response and molecular mechanism in zebrafish embryos, providing multiple aspects about ecological risk assessment of propofol in water environment.

Exploring specific biomarkers regarding neurobehavioral toxicity of lead dioxide nanoparticles in medaka fish in different water matrices

Nano-scale lead dioxide (nPbO₂) is an industrial metal oxide nanoparticle that can be also formed as a corrosion by-product from chlorination of Pb-containing plumbing materials. nPbO₂ governs release of toxic lead ion in drinking water and receiving organisms; however, its modes of toxic action regarding neurobehavioral toxicity remain unclear. This study evaluated the toxicity mechanism of nPbO₂ (10 and 20 mg/L) versus its released Pb(II)_aq (100 μg/L) in terms of aqueous chemistry, bioavailability and neurobehavioral toxicity to medaka fish in different water matrices. In very hard water (VHW), dissolved salts enhanced the aggregation and sedimentation of nPbO₂, resulting in higher bioavailability and altered locomotion of treated fish than those fish exposed to nPbO₂ in soft water with humic acid (SW + HA). Transcriptomic results identified six differentially expressed genes with greater altered expression with nPbO₂ than the control or Pb(II)_aq exposure. With VHW exposure, nPbO₂ caused greater altered expression of genes involved in cell adhesion (nlgn1 and epd), cell cytoskeleton (α1-tubulin), and relevant apoptosis (c-fos, birc5.1-a and casp3), as compared with SW + HA or Pb(II)_aq exposure. This study provides novel molecular mechanistic insights into the neurobehavioral nanotoxicity using nPbO₂ and medaka fish as surrogates, suggesting nPbO₂ promotes neurobehavioral dysfunction, leading to adverse outcomes from gene alteration to the organismal level. The identified biomarkers responded specifically to the nPbO₂-induced neurotoxicity in different water matrices can be used for evaluating toxicity risks of small metal oxide particulates on human or aquatic life under environmentally relevant exposures.

Environmentally relevant concentrations of organic (benzophenone-3) and inorganic (titanium dioxide nanoparticles) UV filters co-exposure induced neurodevelopmental toxicity in zebrafish

UV filters, widely used in personal care products, are ubiquitous environmental pollutants detected and pose a significant public health concern. Benzophenone-3 (BP3) and titanium dioxide nanoparticles (nano-TiO₂) are the predominant organic and inorganic UV filters in environmental media. However, few studies have explored the combined developmental neurotoxic (DNT) effects and the underlying mechanisms when co-exposed to BP3 and nano-TiO₂. In the present study, zebrafish (Danio rerio) embryos were exposed to environmentally relevant concentrations of BP3 (10 μg/L), nano-TiO₂ (100 μg/L), and mixtures starting from 6 h post fertilization (hpf), respectively. Developmental indicators and motor behaviors were investigated at various developmental stages. Our results showed that BP3 alone or co-exposed with nano-TiO₂ increased spontaneous movement at 24 hpf, co-exposure decreased touch response at 30 hpf and hatching rate at 60 hpf. Consistent with these motor deficits, co-exposure to BP3 and nano-TiO₂ inhibited relative axon length of primary motor neuron during the early developmental stages, disturbed the expression of axonal growth-related genes at 30 and 48 hpf, increased cell apoptosis on the head region and mRNA levels of apoptosis-related genes, and also increased reactive oxygen species (ROS) levels in zebrafish, suggesting the functional relevance of structural changes. Taken together, our findings demonstrated that BP3 alone or in combination with nano-TiO₂ at environmentally relevant concentrations induced evident neurotoxic effects on the developing embryos in zebrafish.

Neurotoxicity of tetrabromobisphenol A and SiO2 nanoparticle co-exposure in zebrafish and barrier function of the embryonic chorion

Silicon dioxide nanoparticles (n-SiO₂) absorb tetrabromobisphenol A (TBBPA) and modify its bioavailability and toxicity in the aquatic phase; embryonic chorion is an efficient barrier against nanoparticles (e.g., SiO₂) and influences their toxicity. However, few studies have investigated developmental neurotoxicity in fish after co-exposure to TBBPA and n-SiO₂, especially considering the barrier function of the chorion. In the present study, zebrafish embryos were exposed to TBBPA (50, 100, and 200 μg/L) alone or in combination with n-SiO₂ (25 mg/L) until 24 or 120 h post fertilization (hpf), in the presence and absence of the chorion. The results confirmed that TBBPA exposure alone significantly downregulated the expression of neurodevelopment marker genes (mbp, alpha-tubulin, shha, and gfap), altered acetylcholinesterase activity and acetylcholine content, and affected locomotor behavior at different developmental stages. Moreover, the results indicated that n-SiO₂ promoted TBBPA-induced neurotoxic effects in zebrafish larvae at 120 hpf, including further repression of the transcription of CNS-related genes, disruption of the cholinergic system, and decrease in the average swimming speed under dark/light stimulation. However, scanning electron microscopy/energy dispersive spectroscopy analysis revealed that at 24 hpf, the embryonic chorion efficiently blocked n-SiO₂ and consequently decreased the bioaccumulation of TBBPA and TBBPA-induced neurotoxicity in dechorionated zebrafish embryos. Taken together, the results demonstrate that n-SiO₂ affected the bioavailability and neurodevelopmental toxicity of TBBPA, and their combined toxicity to zebrafish embryos was mitigated by embryonic chorion, which will facilitate risk assessment on n-SiO₂ and TBBPA and improve understanding the function of the fish embryonic chorion.

Decabromodiphenyl ethane induced hyperactivity in developing zebrafish at environmentally relevant concentrations

Decabromodiphenyl ethane (DBDPE), a widely used novel brominated flame retardant, is gaining concerns due to rapidly increased contents in various environmental and biota samples. In the present study, zebrafish (Danio rerio) embryos were exposed to 2.91, 9.71, 29.14 and 97.12 μg/L of DBDPE until 120 h post-fertilization (hpf) to investigate the potential developmental neurotoxicity and underlying mechanisms. Chemical analysis revealed concentration-dependently increased body burdens of DBDPE in zebrafish larvae, with bioaccumulation factors (BCFs) ranging from 414 to 726. Embryonic exposure to DBDPE caused hyperactivity without affecting the development of secondary motoneuron axons and muscle fibers. However, further results implicated that DBDPE may affect the locomotor regulatory network via different mechanisms at lower and higher concentrations. On the one hand, embryonic exposure to 2.91 μg/L DBDPE transiently promoted spontaneous coiling contractions, but showed no effects on touch-response and swimming activity in zebrafish larvae. The whole-body contents of neurotransmitters were significantly decreased. Significant decreased protein abundances of α1-TUBULIN and SYN2a and molecular docking results pointed out possible interactions of DBDPE with these two proteins. However, these changes may be unconcerned with the transient hyperactivity, and the exact molecular mechanisms need further investigation. On the other hand, 29.14 and 97.12 μg/L DBDPE exposure caused longer-lasting effects in promoting spontaneous coiling contractions, and also touch-response and swimming activity. At the same time, increased ACh contents (without changes of other neurotransmitters) and ChAT activity and inhibited transcription of nAChRs were observed at higher concentrations. Molecular docking indicated direct interaction of DBDPE with ChAT. The results suggested that DBDPE induced hyperactivity at higher concentrations was probably involved with disrupted cholinergic system, with ChAT as a potential target. Given that the body burden of DBDPE in lower concentration group was comparable with those detected in wild fish, the current results may provide useful information for ecological risk assessment.

Hormetic dose-response of halogenated organic pollutants on Microcystis aeruginosa: Joint toxic action and mechanism

Quinolones (QNs), dechloranes (DECs), and chlorinated paraffins (CPs) are three kinds of new halogenated organic pollutants (HOPs), which originate from the use of flame retardants, lubricants and pesticides. Since QNs, DECs, and CPs are frequently detected in waters and sediments, it is necessary to investigate the toxic effects of these HOPs with dwelling phytoplankton, especially for cyanobacteria, to explore their potential hormetic effects and contributions to algal blooms. In the present study, we investigate single and joint toxicity of QNs, DECs and CPs on Microcystis aeruginosa (M. aeruginosa), a cyanobacterium that is frequently implicated with algal blooms. The results indicate single QNs and DECs induce marked hormetic effects on the proliferation of M. aeruginosa but CPs do not. The stimulatory effect of hormesis is linked with accelerated replication of DNA, which is considered to stem from the moderate rise in intracellular reactive oxygen species (ROS). Joint toxicity tests reveal that both QNs & CPs mixtures and DECs & CPs mixtures show hormetic effects on M. aeruginosa, but QNs & DECs mixtures show no hormetic effect. QNs & DECs mixtures exhibit synergistic toxic actions, which may be caused by a sharp rise in intracellular ROS simultaneously produced by the agents. Joint toxic actions of both QNs & CPs, and DECs & CPs shift from addition to antagonism as concentration increases, and this shift may mainly depend on the influence of CPs on cell membrane hydrophobicity of M. aeruginosa. This study provides data and toxic mechanisms for the hormetic phenomenon of single and joint HOPs on M. aeruginosa. The hormetic effects of HOPs may benefit the proliferation of M. aeruginosa in the aquatic environment, aggravating the formation of algal blooms. This study also reflects the important role of hormesis in environmental risk assessment of pollutants.

Comparison of Dechlorane Plus Concentrations in Sequential Blood Samples of Pregnant Women in Taizhou, China

To develop an appropriate sampling strategy to assess the intrauterine exposure to dechlorane plus (DP), we investigated DP levels in sequential maternal blood samples collected in three trimesters of pregnancy, respectively, from women living in Taizhou. The median concentration of DPs (sum of syn-DP and anti-DP) in all samples was 30.5 pg g−1 wet-weight and 5.01 ng g−1 lipid-adjusted weight, respectively. The trimester-related DP concentrations were consistently strongly correlated (p < 0.01), indicating that a single measurement of DP levels could represent intrauterine exposure without sampling from the same female repeatedly; however, the wet-weight levels significantly increased across trimesters (p < 0.05), while the lipid-adjusted levels did not significantly vary. Notably, whether lipid-adjusted weight or wet-weight levels, the variation extent of DP across trimesters was found to be less than 41%, and those for other persistent organic pollutants (POPs) reported in the literature were also limited to 100%. The limitation in variation extents indicated that, regardless of the time of blood collection during pregnancy and how the levels were expressed, a single measurement could be extended to screen for exposure risk if necessary. Our study provides different strategies for sampling the maternal blood to serve the requirement for assessment of in utero exposure to DP.

Dechloranes exhibit binding potency and activity to thyroid hormone receptors

Dechloranes are a group of halogenated flame retardants with a basic bicyclo[2.2.1]heptene, including Dechlorane Plus (DP), Dechlorane 602 (Dec 602), Dechlorane 603 (Dec 603) and Dechlorane 604 (Dec 604). A few epidemiological investigations and animal experiments have shown that DP exhibited thyroid-interfering effects. In the present study, we investigated whether DP and three other dechloranes could interfere the thyroid function through thyroid hormone receptors (TRs, TRα and TRβ) signaling pathways. The binding affinities of the four dechloranes to the two TRs were determined by fluorescence competitive binding assay. It was found that all the four dechloranes could bind with the two TRs. The relative potency (RP) values ranged from nd (not detectable) to 0.0667. Between the two TRs, dechloranes were more inclined to bind with TRβ, which implies that the thyroid interference effect of dechloranes may have selectivity in different tissues and organs. TRs-mediated luciferase reporter gene assay and T-screen assay showed that all the four dechloranes exhibited antagonistic activity to TRs in the cells. Taken together, our results demonstrated that dechloranes might interfere with thyroid function by binding with TRs and acting as TR antagonists. The health risk of highly exposed human populations should be of serious concern because of the high hazard quotient calculated from our cell assay results.

Effects of common environmental endocrine-disrupting chemicals on zebrafish behavior

Environmental endocrine-disrupting chemicals (EDCs), a type of exogenous organic pollutants, are ubiquitous in natural aquatic environments. Therefor, this review focused on the use of the zebrafish as a model to explore the effect of different EDCs on behavior, as well as the molecular mechanisms that drive these effects. Furthermore, our study summarizes the current knowledge on the neuromodulatory effects of different EDCs in zebrafish. This study also reviews the current state of zebrafish behavior research, in addition to the potential mechanisms of single and mixed pollutant-driven behavioral dysregulation at the molecular level, as well as the applications of zebrafish behavior experiments for neuroscience research. This review broadens our understanding of the influence of EDCs on zebrafish behavior and provides guidance for future research.

Nano-TiO2 aggravates bioaccumulation and developmental neurotoxicity of triphenyl phosphate in zebrafish larvae

This study explored the combined effects of titanium dioxide nanoparticles (nano-TiO₂) and triphenyl phosphate (TPhP) on the neurodevelopment of zebrafish larvae as well as the underlying mechanisms. With this regard, zebrafish embryos were exposed to nano-TiO₂ of 100 μg·L^-1, TPhP of 0, 8, 24, 72, and 144 μg·L^-1, or their combinations until 120 h post-fertilization (hpf). Results indicated 100 μg·L^-1 nano-TiO₂ alone to be nontoxic to zebrafish larvae. However, obvious developmental toxicity manifested as inhibition of surviving rate, heart rate and body length as well as increased malformation was observed in the higher concentrations of TPhP (72 and 144 μg·L^-1) alone and the co-exposure groups. Additionally, results suggested that nano-TiO₂ significantly enhanced the bioaccumulation of TPhP in zebtafish larvae, and thus aggravated the abnormities of spontaneous movement and swimming behavior in zebrafish larvae induced by TPhP. Nano-TiO₂ also exacerbated the TPhP-induced inhibition of the axonal growth on the secondary motor neuron, and aggravated the TPhP-induced decrease on expressions of neuron-specific green fluorescent protein (GFP) and neuronal marker genes (ngn1 and elavl3). Further, the content of neurotransmitter serotonin was not altered by TPhP alone exposure, but was decreased significantly in the co-exposure group of 144 μg·L^-1 TPhP and nano-TiO₂. Our data indicated that nano-TiO₂ might aggravate the neuron abnormities and serotonin system dysfunction by enhancing the TPhP accumulation, leading to exacerbated abnormal locomotors in zebrafish larvae.

Toxicity of 2-methyl-4-chlorophenoxy acetic acid alone and in combination with cyhalofop-butyl to Cyprinus carpio embryos

Herbicides may pose considerable danger to non-target aquatic organisms and further threaten human health. The present investigation was aimed to assess the effects of 2-methyl-4-chlorophenoxy acetic acid (MCPA-Na) on Cyprinus carpio embryos. Embryos were exposed to six concentrations of MCPA-Na (0, 52, 54, 56, 58 and 60 mg/L) for 96 h. A series of symptoms were observed in developmental embryos during MCPA-Na exposure, including increased death, hatching inhibited and morphological deformities. Further, MCPA-Na exposure leading to a series of morphological changes (pericardial edema, tail deformation, and spine deformation) in embryos, which were consistent with modifications in the associated genes. In this work, we also investigated the joint toxicity of herbicides (MCPA-Na and cyhalofop-butyl) commonly used in paddy fields on carp embryos, using the 96 h-LC₅₀ of herbicides (59.784 mg/L MCPA-Na and 1.472 mg/L cyhalofop-butyl) and confirmed that a synergistic effect existing in the binary mixtures.

Mechanisms of parental co-exposure to polystyrene nanoplastics and microcystin-LR aggravated hatching inhibition of zebrafish offspring

The combined toxicity effects of microcystins-LR (MCLR) and polystyrene nanoplastics (PSNPs) on the hatching of F1 zebrafish (Danio rerio) embryos were investigated in this study due to the increasing concerns of both plastic pollution and eutrophication in aquatic environments. Three-month-old zebrafish were used to explore the molecular mechanisms underlying the combined effect of MCLR (0, 0.9, 4.5, and 22.5 μg/L) on egg hatching in the existence of PSNPs (100 μg/L). The results demonstrated the existence of PSNPs further increased the accumulation of MCLR in F1 embryos. The hatching rates of F1 embryos were inhibited after exposure to 22.5 μg/L MCLR, and the presence of PSNPs aggravated the hatching inhibition induced by MCLR. The decrease of hatching enzyme activity and the abnormality of spontaneous movement were observed. We examined the altered expression levels of the genes associated with the hatching enzyme (tox16, foxp1, ctslb, xpb1, klf4, cap1, bmp4, cd63, He1.2, zhe1, and prl), cholinergic system (ache and chrnα7), and muscle development (Wnt, MyoD, Myf5, Myogenin, and MRF4). The results suggested the existence of PSNPs exacerbated the hatching inhibition of F1 embryos through decreasing the activity of enzyme, interfering with the cholinergic system, and affecting the muscle development.

Bioconcentration and developmental neurotoxicity of novel brominated flame retardants, hexabromobenzene and pentabromobenzene in zebrafish

The flame retardants hexabromobenzene (HBB) and pentabromobenzene (PBB) have been extensively used and become ubiquitous pollutants in the aquatic environment and biota, but their potential toxic effects on wildlife remained unknown. In this study, by using zebrafish (Danio rerio) as a model, the bioconcentration and developmental neurotoxicity were investigated. Zebrafish embryos were exposed to HBB and PBB (0, 30, 100 and 300 μg/L) from 2 until 144 h post-fertilization (hpf). Chemical analysis showed bioconcentrations of both chemicals, while HBB is readily metabolized to PBB in zebrafish larvae. Embryonic exposure to both chemicals did not cause developmental toxicity, but induced locomotor behavioral anomalies in larvae. Molecular docking results indicated that both chemicals could bind to zebrafish acetylcholinesterase (AChE). Furthermore, HBB and PBB significantly inhibited AChE activities, accompanied by increased contents of acetylcholine and decreased choline in larvae. Downregulation of the genes associated with central nervous system (CNS) development (e.g., mbp, α1-tubulin, gfap, shha) as well as the corresponding proteins (e.g., Mbp, α1-Tubulin) was observed, but gap-43 was upregulated at both gene and protein levels. Together, our results indicate that both HBB and PBB exhibit developmental neurotoxicity by affecting various parameters related to CNS development and indications for future toxicological research and risk assessment of the novel brominated flame retardants.

Developmental neurotoxicity of low concentrations of bisphenol A and S exposure in zebrafish

The vulnerability to environmental insults is heightened at early stages of development. However, the neurotoxic potential of bisphenol A (BPA) and bisphenol S (BPS) at developmental windows remains unclear. To investigate the mechanisms mediating the developmental neurotoxicity, zebrafish embryos were treated with 0.01, 0.03, 0.01, 0.3, 1 μM BPA/BPS. Also, we used Tg(HuC:GFP) zebrafish to investigate whether BPA/BPS could induce neuron development. The reduction in body length, and increased heart rate were significant in 0.3 and 1 μM BPA/BPS groups. The green fluorescence protein (GFP) intensity increased at 72 hpf and 120 hpf in Tg(HuC:GFP) larvae which was consistent with the increased mRNA expression of elval3 following BPS treatments, an indication of the plausible effect of BPS on embryonic neuron development. Additionally, BPA/BPS treatments elicited hyperactivity and reduced static time in zebrafish larvae, suggesting behavioral alterations. Moreover, qRT-PCR results showed that BPA and BPS could interfere with the normal expression of development-related genes vegfa, wnt8a, and mstn1 at the developmental stages. The expression of neurodevelopment-related genes (ngn1, elavl3, gfap, α1-tubulin, mbp, and gap43) were significantly upregulated in BPA and BPS treatments, except for the remarkable downregulation of mbp and gfap elicited by BPA at 48 (0.03 μM) and 120 hpf (0.3 μM) respectively; ngn1 at 48 hpf for 0.1 μM BPS. Overall, our results highlighted that embryonic exposure to low concentrations of BPA/BPS could be deleterious to the central nervous system development and elicit behavioral abnormalities in zebrafish at developmental stages.

Parental exposure to environmental concentrations of tris(1,3-dichloro-2-propyl)phosphate induces abnormal DNA methylation and behavioral changes in F1 zebrafish larvae

Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) has been demonstrated to be transferred from parental animals to their offspring. However, whether parental exposure to environmental concentrations of TDCIPP show neurodevelopmental toxicity in the F1 generation and the possible underlying mechanism remain unclear. Therefore, in this study, zebrafish embryos were exposed to environmental concentrations of TDCIPP (3, 30 and 300 ng L^-1) for 120 days. The effects of exposure on motor behaviors, neurotransmitter levels, DNA methylation, and gene expression of F1 larvae were investigated. Parental exposure left TDCIPP residues in F1 eggs as well as reduced body length of F1 larvae. Moreover, parental exposure significantly reduced swimming activity in F1 5 dpf larvae, although it did not significantly alter serotonin, dopamine, 3,4-dihydroxyphenylacetic acid, γ-aminobutyrate, and acetylcholine levels. Genes encoding DNA methylation transferases (dnmt3aa and dnmt1) were downregulated in F1 larvae. Reduced representation bisulfite sequencing analysis revealed 446 differentially methylated regions and enriched neuronal cell body Gene Ontology term in F1 generation. Correlation analysis between the expression of genes related to neural cell body and swimming speed indicated that solute carrier family 1 member 2b (slc1a2b) downregulation might be responsible for the inhibition of motor behaviors. Furthermore, bisulfite amplicon sequencing analysis confirmed hypermethylation of the promoter region of slc1a2b in F1 larvae following parental exposure to 300 ng L^-1 TDCIPP, which might have led to significant downregulation of gene expression and, in turn, influenced the motor behaviors. These results indicate that parental exposure to environmental concentrations of TDCIPP alters DNA methylation, downregulates gene expressions and, thus inducing developmental neurotoxicity, in F1 larvae.

Effects of dechlorane plus on intestinal barrier function and intestinal microbiota of Cyprinus carpio L

Dechlorane Plus (DP) is a typical polychlorinated flame retardant that has been emerged in chemical products. Due to its accumulation and amplification effect, the toxicity of DP has become a widespread environmental safety issue. However, whether DP can affect the intestinal tract of teleost fish remains largely unclear. To understand its effects on the intestinal barrier, morphological characteristics and intestinal microbiome of common carp, different concentrations (30, 60 and 120 μg/L) of DP were exposed to common carps for 4 weeks. The results indicated that DP evidently shortened the intestinal folds and damaged the intestinal epithelium layer. In addition, the mRNA expression levels of occludin, claudin-2 and zonula occludens-1 (ZO-1) were significantly decreased with increasing DP concentrations. Furthermore, the relative abundance of some microbiota species were also changed significantly. Our study first demonstrated that DP could cause damage to the intestinal epithelium and destroy the intestinal barrier and increase the relative abundance of pathogenic bacteria, thereby increasing the probability of contact between intestinal epithelium and pathogenic bacteria, which in turn lead to an increased susceptibility to various diseases and poor health. In summary, our findings reveal that chronic DP exposure can have a harmful effect on the intestinal flora balance and is potentially linked to human disease.

Transfer of dechlorane plus between human breast milk and adipose tissue and comparison with legacy lipophilic compounds

In this study, levels of dechlorane plus (DP) in breast milk and matched adipose tissue samples were measured from 54 women living in Wenling, China. Polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) were measured simultaneously for comparison. The levels of ∑DPs/∑PBDEs varied from less than one to several dozens of ng g^-1 lipid weight (lw) in matrices and the levels of ∑PCBs varied between several to hundreds of ng g^-1 lw. In the same matrix, ∑DPs and ∑PCBs/∑PBDEs showed a significant relationship (p < 0.05), indicating that they shared common sources. Accordingly, there was a strong association of lipid-adjusted concentrations of individual compounds (BDE-209 excluded) between matrices (p < 0.001), suggesting that breast milk could be a proxy for adipose tissue in human bioburden monitoring of these compounds. The predicted lipid-adjusted milk/adipose ratios varied from 0.62 to 1.5 but showed significant differences (p<0.001) between compounds, suggesting a compound-specific transfer between milk lipids and adipose tissue lipids. Specifically, the milk/adipose ratios for syn-DP and anti-DP (-1.40 and 1.3, respectively) were significantly higher than those of CB congeners and hexa/hepta-BDE congeners (p < 0.05). In addition, unlike PCBs/PBDEs (excluding BDE-209), DP's hydrophobicity might not be responsible for its preferable distribution in milk lipids. Instead, the interaction with nonlipid factors played a key role. The fraction of anti-DP between the two kinds of matrices was not significantly different, suggesting that the biochemical transfer processes may not be efficient enough to distinguish DP isomers. Nevertheless, the congener patterns of PCBs/PBDEs gave a clue about the compound-specific transfer between milk and adipose tissue. To our knowledge, this is the first to report the relationships of DP between adipose tissue and breast milk. These results could provide useful and in-depth information on biomonitoring of DP and facilitate the understanding of the accumulation and excretion potentials of DP and its distribution-related mechanism in humans.

Environmental relevant concentrations of benzophenone-3 induced developmental neurotoxicity in zebrafish

Benzophenone-3 (BP3 or oxybenzone) is an organic UV filter that has been widely used in personal care products. Its frequent detection in the environment and humans as well as its structural similarity to estradiol have prompted most research focus on its endocrine effect. However, these effects are usually associated with concentrations 10-100 fold higher than its environmental relevant concentrations. Few studies explore its adverse effects at environmental relevant concentrations. In the present study, we evaluated the developmental neurotoxic (DNT) effects of low concentration BP3 exposure during a sensitive developmental window in zebrafish. Our findings revealed that BP3 exposure at 10 μg/L (0.04 μM) during 6-24 h post fertilization (hpf) led to various DNT effects such as increased spontaneous movement at 21 and 24 hpf, decreased touch response at 27 hpf, heightened hyperactivity in locomotor response at 5 day post fertilization (dpf), decreased shoaling behavior at 11 dpf and decreased mirror attacks at 12 dpf. These effects were accompanied with decreased axonal growth at 27 hpf, decreased cell proliferation and increased cell apoptosis in the head region of larval zebrafish immediately after BP3 exposure at 24 hpf, and increased expression of retinoid X receptor gene rxrgb at 5 dpf. Interestingly, rxrgb knockdown through morpholino injection largely restored most of BP3-induced DNT effects, axonal growth delay, cell proliferation and cell apoptosis, suggesting that BP3-induced DNT effects are likely mediated through the Rxrgb receptor. In considering with recent findings on the endocrine effects of BP3, we conclude that BP3 at environmental relevant concentrations has limited estrogenic effect, but is neurotoxic to developing embryos in zebrafish.

Toxic effects of dechlorane plus on the common carp (Cyprinus carpio) embryonic development

Dechlorane Plus (DP) is a widely used chlorinated flame retardant, which has been extensively detected in the environment. Although DP content in the surface water is low, it can pose a continuous exposure risk to aquatic organisms due to its strong bioaccumulation. Considering that the related studies on the toxicity mechanism of DP exposure are limited, the effect of DP on carp embryo development was evaluated. In the present work, carp embryos were exposed to different concentrations (0, 30, 60, and 120 μg/L) of DP at 3 h post-fertilization (hpf). The expression levels of neural and skeletal development-associated genes, such as sox2, sox19a, Mef2c and BMP4, were detected with quantitative PCR, and the changes in different developmental toxicity endpoints were observed. Our results demonstrated that the expression levels of sox2, sox19a, Mef2c and BMP4 were significantly altered and several developmental abnormalities were found in DP-exposed carp embryos, such as DNA damage, increased mortality rate, delayed hatching time, reduced hatching rate, decreased body length, and increased morphological deformities. In addition, the activities of reactive oxygen species and malondialdehyde were remarkably higher in 60 and 120 μg/L DP exposure groups than in control group. These results suggest that DP can exhibit a unique modes of action, which lead to aberration occurrence in the early development stage of common carps, which may be related to some gene damage and oxidative stress. Besides, the parameters evaluated here can be used as tools to access the environmental risk for biota and humans exposed to DP.

Bioaccumulation and transfer characteristics of dechlorane plus in human adipose tissue and blood stream and the underlying mechanisms

In this study, bioaccumulation and transfer characteristics of dechlorane plus (DP) were examined between human adipose tissue and matched maternal serum, and the possible transfer mechanism between tissues was further discussed. The median level of total DP was 971 pg g^-1 wet weight (ww) and 1.22 ng g^-1 lipid weight (lw) in adipose tissue, respectively, and was 34.7 pg g^-1 ww and 3.98 ng g^-1 lw for serum, respectively. DP wet levels' positive association with fat contents of five types of human tissues indicated that DP distribution might be related to lipid-driven mechanism. However, the lipid-adjusted adipose-serum partitioning ratios were estimated to be 0.35 for syn-DP and 0.35 for anti-DP, accordingly, which implied that the DP distribution between serum and adipose tissues, was not only regulated by the tissue lipid contents. Both the internal mono-dechlorination of anti-DP, and stereo-selective behavior of DP isomers were not found in DP transfer from blood to adipose tissue. The marginal positive relationship was observed between serum levels and apolipoprotein A concentrations (p = 0.095 for total DP and 0.045 for syn-DP), and neither association was found between serum levels and thyroid hormone concentrations (THs). To our best knowledge, this is the first report about the accumulation relationship of DP between human adipose tissue and blood stream with the corresponding distribution-related mechanism.

Effects of dechlorane plus on oxidative stress, inflammatory response, and cell apoptosis in Cyprinus carpio

The levels of the chlorinated organic compound Dechlorane Plus (DP) are increasing in aquatic ecosystems. To investigate the adverse effects of DP on aquatic animals, common carp (Cyprinus carpio) were subjected to three different DP concentrations (30 μg L^-1, 60 μg L^-1, and 120 μg L^-1) for 1 d, 15 d, and 30 d. Histology and the hepatic and cerebral expression levels of several key antioxidant, detoxification, and apoptotic factors were then examined. Histopathological inspections showed that the liver and brain were severely damaged in carp exposed to 60 μg L^-1 and 120 μg L^-1 DP. Relative to the controls, the superoxide dismutase and glutathione activity levels and the malondialdehyde content were also changed in livers and brains exposed to DP. Besides, significant alterations in the expression levels of the inflammatory cytokines IL-1β, IL-6, and IL-10 were observed in the livers of carp subjected to DP. Relative to the control, the brains of DP-exposed carp presented with significantly upregulated IL-1β and IL-6 in carp treated with 120 μg L^-1 DP for 30 d. The transcription levels of hepatic cyp2b4, cyp1b1, and cyp3a138 were all increased compared with the untreated at all DP exposure concentrations. The aforementioned results suggest that DP exposure perturbs fish metabolism and causes liver injury by inhibiting antioxidant enzyme activity, increasing lipid peroxidation, promoting inflammation, and inducing cell apoptosis. This information and the analytical methodology used to acquire it may form the basis for future ecological risk assessments on DP and related xenobiotics in aquatic animals.

Neurodevelopmental toxicity assessments of alkyl phenanthrene and Dechlorane Plus co-exposure in zebrafish

Alkyl phenanthrene (A-Phen) and Dechlorane Plus (DP) are ubiquitous environmental pollutants that widely co-exist in the environment. It has been established that both A-Phen and DP elicit neurotoxicity, but the potential interactive toxicity of these contaminants is not well-known. To determine whether a mixture of A-Phen and DP would exhibit interactive effects on neurodevelopment, we co-exposed 3-methylphenanthrene (3-MP), a representative of A-Phen, with DP. Our results illustrated that exposure to 5 or 20 μg/L 3-MP alone or in combination with 60 μg/L DP caused neurobehavioral anomalies in zebrafish. In accordance with the behavioral deficits, 3-MP alone or co-exposed with DP significantly decreased axonal growth of secondary motoneurons, altered intracellular Ca²⁺ homeostasis and induced cell apoptosis in the muscle of zebrafish. Additionally, 3-MP alone or co-exposed with DP significantly increased reactive oxygen species (ROS) and the mRNA levels of apoptosis-related genes. These findings indicate that 3-MP alone or co-exposed with DP induces neurobehavioral deficits through the combined effects on neuronal connectivity and muscle function. Chemical analysis revealed significant increases in 3-MP and DP bioaccumulation in zebrafish co-exposed with 3-MP and DP. Elevated bioaccumulation resulting from mixture exposure may represent a significant contribution of the synergistic effects observed in combined chemical exposure.

Isoliquiritigenin as an antioxidant phytochemical ameliorates the developmental anomalies of zebrafish induced by 2,2',4,4'-tetrabromodiphenyl ether

2,2',4,4'-Tetrabromodiphenyl ether (BDE47) is the most abundant PBDE congeners in biological samples. It has strong tendencies to bioaccumulate and potentially endangers development of mammals through oxidative stress. Isoliquiritigenin (ISL), an emerging natural chalcone-type flavonoid, possesses various biological and pharmacological properties, including antioxidant, anti-allergic, anti-inflammatory, anti-tumor and estrogenic activities. The purpose of the study is to explore the antioxidant effect of ISL on the amelioration of developmental anomalies induced by BDE47. Zebrafish (Danio rerio) embryos were exposed to BDE47 (1 and 10 μM) and/or ISL (4 μM) for 4 to 120 hours post fertilization (hpf), and the morphology, development, behavior, oxidative stress status and related genes expression were assessed. The results showed that BDE47 contributed to dose-dependent growth retardation and deformities, including delayed hatching, spinal curvature, reduced body length, increased death rate, aberrant behaviors and impaired dark-adapted vision, which were significantly mitigated by ISL. Besides, ISL ameliorated excessive ROS accumulation, and exaggerated the expressions of apoptosis-related genes p53, Bcl-2, caspase 3 and caspase 9 induced by BDE47, suggesting that ISL protected zebrafish from the developmental toxicity of BDE47 by inactivation of programmed apoptosis and activation of antioxidant signaling pathways. Taken together, developing ISL as a dietary supplement might be a promising preventive strategy for the amelioration of developmental toxicity induced by environmental pollutants.

Pine needles as biomonitors of polybrominated diphenyl ethers and emerging flame retardants in the atmosphere of Shanghai, China: occurrence, spatial distributions, and possible sources

In this study, pine needles were used as biomonitors to investigate the levels, spatial distributions, and possible sources of polybrominated diphenyl ethers (PBDEs) and four emerging halogenated flame retardants (HFRs) in the atmosphere of Shanghai, China. The four emerging HFRs were hexabromocyclododecane (HBCD), decabromodiphenylethane (DBDPE), 1,2-bis(2,4,6-tribromophenoxy) ethane (BTBPE), and dechlorane plus (DP), with the first 3 HFRs being non-polybrominated diphenyl ether brominated flame retardants (non-PBDE BFRs). The total concentrations ranged from 3.71 to 4020 ng g^-1 dry weight (dw) for 52 PBDE congeners (Σ₅₂BDEs), < MDL (method detection limit) to 15.2 ng g^-1 dw for three non-PBDE BFRs (Σ₃non-PBDE BFRs), and 0.815 to 1090 pg g^-1 dw for two DP isomers (ΣDP), respectively. High levels of PBDEs, three non-PBDE BFRs, and DP were found in pine needles from suburbs and Pudong, which was a consequence of industrial activities. The fraction of anti-DP isomer (f_anti) in pine needles ranged from 0.515 to 0.939 with a mean value of 0.721, and most of the f_anti values were consistent with those of technical DP formulations. Principal component analysis-multiple linear regression (PCA-MLR) model identified four sources of PBDEs in pine needles with the quantified contributions: degradation of technical PBDE formulations (49.5%), technical deca-BDE (6.9%), technical penta-BDE (25.1%), and technical octa-BDE (18.5%). These findings are expected to help understand the pollution level, fate, and possible sources of HFRs in the atmosphere of Shanghai and provide a basis for air pollution control and management in Shanghai.

Comparative biomarker responses in Japanese medaka (Oryzias latipes) exposed to benzo[a]pyrene and challenged with betanodavirus at three different life stages

It is now well documented that several contaminants can modulate the fish immune system, leading to disrupted host resistance against pathogens and increased incidence of disease. Since fish are usually co-exposed to chemicals and pathogens in the natural environment, analysis of the immunotoxic effects of pollutants is particularly relevant. The authorities in the European Union have recommended the development of toxicity assays on cell cultures and embryos, as an alternative to testing in vertebrates. This is why in our study, a fish immune challenge assay was developed for the early life stages of Japanese medaka to evaluate and compare the relevance of new biomarkers. Fish were exposed to benzo[a]pyrene (BaP), a model pollutant, for 8days at the embryonic stage, or for 48h at the larvae and juvenile stages, and fish were infected with betanodavirus by bath-challenge of 10⁶TCID₅₀/mL. Biometric changes and induction of malformations were observed after embryonic exposure. DNA damage and induction of EROD activity were recorded at the end of all chemical exposures. Viral infection increased the mortality rate significantly and disturbed the behavior of fish after light stimulation. While BaP exposure increased swimming speed, betanodavirus infection slowed swimming activity. In larvae co-exposed to BaP and the virus, the viral titer in the whole body was higher than in fish infected only with the virus. This study highlighted the sensitivity and usefulness of the immune challenge assay on the early life stages of Japanese medaka to evaluate the toxic effects of pollutants.

Dechlorane Plus flame retardant in a contaminated frog species: Biomagnification and isomer-specific transfer from females to their eggs

While flame retardant Dechlorane Plus (DP) and its dechlorinated analogs have been frequently detected in wildlife, knowledge is limited on their bioaccumulation and maternal transfer in amphibians. In the present study, the occurrence of syn- and anti-DP isomers and a DP dechlorinated compound, anti-Cl₁₁-DP, were investigated in frogs and insects collected from the paddy field of a highly contaminated site. The concentrations of ∑DP (the sum concentrations of syn- and anti-DP) in the frog muscle, liver, and eggs were 141 ± 24.7, 454 ± 73.9, and 184 ± 31.1 ng/g lipid weight, respectively; with significantly higher levels in the males than females. The syn-, anti- and anti-Cl₁₁-DP were all detectable in the frog eggs, demonstrating their maternal transfer in female frogs. The concentration ratios between eggs and liver pairs were 0.49 ± 0.01, 0.35 ± 0.01, and 0.53 ± 0.06 for syn-DP, anti-DP, and anti-Cl₁₁-DP, respectively. The values of f_anti (the concentration of anti-DP relative to the sum concentration of DP) differed significantly between frog tissues (0.33-0.79) and insects (0.71-0.74), indicating isomer-specific bioaccumulation of DP in the frogs. The concentration ratios of the frogs to the insects were greater than 1 for all the DP-related compounds, suggesting a possibility of biomagnification of these chemicals in the frogs.

Perfluorododecanoic acid exposure induced developmental neurotoxicity in zebrafish embryos

Perfluorododecanoic acid (PFDoA), an artificial perfluorochemical, has been widely distributed in different ambient media and has been reported to have the potential to cause developmental neurotoxicity. However, the specific mechanism is largely unknown. In the current study, zebrafish embryos were treated with 0, 0.24, 1.2, and 6 mg/L PFDoA for 120 h. Exposure to PFDoA causes serious decreases in hatching delay, body length, as well as decreased locomotor speed in zebrafish larvae. Additionally, the acetylcholine (ACh) content as well as acetylcholinesterase (AChE) activity were determined to be significantly downregulated in PFDoA treatment groups. The level of dopamine was upregulated significantly after treating with 1.2 and 6 mg/L of PFDoA. Gene expressions related to the nervous system development were also analyzed, with the exception of the gene mesencephalic astrocyte-derived neurotrophic factor (manf), which is upregulated in the 6 mg/L treatment group. All other genes were significantly downregulated in larvae in the PFDoA group in different degrees. In general, the results demonstrated that PFDoA exposure could result in the disruption of the cholinergic system, dopaminergic signaling, and the central nervous system.

Distributions, influencing factors, and risk assessment of Dechlorane Plus and related compounds in surficial water and sediment from the Jiulong River Estuary, Southeast China

Dechloranes, a type of additive polychlorinated flame retardant, which include Dechlorane (Dec) Plus (DP), Dec 602, Dec 603, and Dec 604, were detected in surficial water and sediment from the Jiulong River Estuary (JRE). The total concentration of dechloranes in the water and sediments ranged from 1.4 to 4.1 ng/L and 9.3 to 36.2 ng/g dry weight, respectively. The distribution patterns of dechloranes in the water and sediments were both dominated by DP. The average values of the anti-DP fractional abundances (f_anti) in the water and sediment samples both were fell in the range of commercial DP mixtures. The relationships of DP in the water with suspended particulate matter (SPM), total organic carbon (TOC), and tides indicated that the combined actions of these environmental factors influenced the distribution of DP in the JRE. The deleterious risk associated with exposure to dechloranes via the water for adults was very low, suggesting that exposure of the local population of dechloranes via water is relatively safe in the JRE.

Neurological responses of embryo-larval zebrafish to short-term sediment exposure to decabromodiphenylethane

Decabromodiphenylethane (DBDPE) has been widely used as an alternative flame retardant due to the restriction or phase-out of traditional polybrominated diphenyl ethers (PBDEs), and is of increasing concern regarding its ubiquity, persistence, and potential adverse effects. In the present study, the toxicological effects of DBDPE were evaluated using zebrafish as an in vivo model. Upon being exposed to DBDPE-polluted sediments for a short term, it was found that the mortality and malformation of zebrafish (including edema, bent notochord, and bent tail) were not affected even at the highest concentration tested (1000.0 µg/kg dry sediment). Regarding behavioral responses, it was found that zebrafish larvae of 48 hours post fertilization (hpf) in all groups escaped successfully with a touch to the dorsal fin. However, when exposed to the highest DBDPE concentration, the larvae of 120 hpf exhibited significantly smaller distances as compared to the control. Moreover, the results of the acetylcholinesterase (AChE) activity, the expression levels of two important nerve-related genes, and the cell apoptosis all indicated that DBDPE posed low neurotoxicity in embryo-larval zebrafish. The results in this study shed some light on the potential risks of DBDPE in the real environment and highlight the application of the sediment exposure route in the future.

Transchem project - Part II: Transgenerational effects of long-term exposure to pendimethalin at environmental concentrations on the early development and viral pathogen susceptibility of rainbow trout (Oncorhynchus mykiss)

In the Transchem project, rainbow trout genitors were exposed to environmental concentrations of pendimethalin over a period of 18 months and two new first generations of offspring, F1_2013 and F1_2014, were obtained. We investigated the impact of direct chemical exposure on juveniles as well as the potential cumulative transgenerational and direct effects on the larval development and on the pathogen susceptibility of offspring. Depending on the chemical treatment or not of the adults, their offspring were distributed in the tanks of our experimental system, in two batches i.e. juveniles from the control genitors (G-) and others from the contaminated ones (G+), and then, half of the tanks were exposed daily to pendimethalin (Off+) while the others were used as controls (Off-). Viral challenges were performed on the offspring, before and after three months of direct chemical exposure, with strains of infectious hematopoietic necrosis virus (IHNV), viral haemorrhagic septicemia virus (VHSV) and sleeping disease alphavirus (SDV). Direct and transgenerational macroscopic effects were observed on offspring, with a percentage of abnormalities in offspring derived from the genitors exposed to pendimethalin (G+) significantly higher compared to those from the genitors from non-exposed group (G-). Before the direct chemical exposure, similar kinetics of mortality was observed between the offspring from the contaminated or control genitors after VHSV infection. With IHNV, the G+ group died in a slightly larger proportion compared to the G- group and seroconversion was greater for the G- group. For the SDV challenge, the mortality was delayed for the G+ offspring compared to the G- and seroconversion reached 65% in the G+ group compared to 45% in the G-, with similar antibody titres. After three months of direct chemical exposure, kinetics of mortality induced by IHNV infection were similar for all groups studied. Infection with SDV resulted in a cumulative mortality of 40% for the G- groups (Off- and Off+), significantly higher than those observed from the contaminated genitors G+. Proportion of seropositivity for SDV varied from 24 to 47% depending on the group, with very low quantities of secreted antibodies. Lastly, the direct exposure of offspring could impact the capacity of fish to adapt their haematological parameters to environmental and physiological changes, and underlines the potential toxic effects on the next generations.

Tissue regeneration promotion effects of phenanthroimidazole derivatives through pro-inflammatory pathway activation

A chemotherapeutic drug exerts favorable antitumor activity and simultaneously exhibits expectable inhibition on wound healing process. Phenanthroimidazole derivatives possess potent anticancer activity. However, only a few studies focused on the discovery of its potential effects on promoting tissue regeneration. In this study, four novel phenanthroimidazole derivatives were synthesized and characterized, and they exhibited evident inhibition on different tumor cells; compound 3 is the most active one. Moreover, 3 can promote wound healing of zebrafish in a dose-dependent manner. Further study demonstrated that 3 promoted the recruitment of inflammatory cells, formation of angiogenesis, and generation of reactive oxygen species and also influenced the motor behavior of zebrafish. Results indicated that 3 can accelerate the occurrence of pro-inflammation, angiogenesis, oxidative stress, and innervation, which play key roles in the facilitation of wound healing. Therefore, 3 can act as a bifunctional drug in inhibiting tumor and promoting tissue regeneration.

Tris (2-butoxyethyl) phosphate affects motor behavior and axonal growth in zebrafish (Danio rerio) larvae

Tris (2-butoxyethyl) phosphate (TBOEP) is an environmental contaminant that poses serious risks to aquatic organisms and their associated ecosystem. Recently, the reproductive and developmental toxicology of TBOEP has been reported. However, fewer studies have assessed the neurotoxic effects in zebrafish (Danio rerio) larvae. In this study, zebrafish embryos were subjected to waterborne exposure of TBOEP at 0, 50, 500, 1500 and 2500 μg/L from 2 to 144-h post-fertilization (hpf). Behavioral measurements showed that TBOEP exposure reduced embryonic spontaneous movement and decreased swimming speed of larvae in response to dark stimulation. In accordance with these motor effects, TBOEP treatment reduced neuron-specific GFP expression in transgenic Tg (HuC-GFP) zebrafish larvae and inhibited the growth of secondary motoneurons, as well as decreased expression of marker genes related to central nervous system development in TBOEP treated group. Furthermore, increased concentrations of reactive oxygen species (ROS) and malondialdehyde (MDA), as well as reduction of SOD activity were detected in TBOEP exposure group. The present results showed that the alteration in motor neuron and oxidative stress could together lead to the motor behavior alterations induced by TBOEP.

Emerging brominated flame retardants and dechlorane-related compounds in European eels (Anguilla anguilla) from Latvian lakes

Fifteen halogenated flame retardants (HFRs) including seven emerging brominated flame retardants (EBFRs) and eight dechlorane-related compounds (DRCs) were analyzed in eels (Anguilla anguilla) sampled from five Latvian lakes. Out of the seven EBFRs, hexabromocyclododecane (HBCD) and decabromodiphenyl ethane (DBDPE) were found in eels in quantifiable concentrations, up to 6.58 and 33.0 ng g^-1 lipid weight (l.w.), respectively. The mean total concentration of DRCs (∑_DRC) in the samples was 0.62 ng g^-1 l.w. and the geographical distribution of DRC contamination was nearly uniform among the selected lakes. Dechlorane 602 (Dec 602) was the predominant component, whereas the composition of mixture containing syn- and anti-Dechlorane Plus (DP) stereoisomers showed a pronounced enrichment of the anti-DP isomer and was close to the composition of OxyChem^® DP commercial product. The determined concentrations of HFRs were lower than in other studies of aquatic biota from Europe and Asia, and the obtained results reflect the acceptable environmental status of Latvian lakes with regard to the total content of HBCD (∑_HBCD), considering the environmental quality standards (EQS) stated in the Directive 2013/39/EU. The highest ∑_HBCD levels were observed in eels from lakes corresponding to the industrialization of those areas, while the results of principal component analysis (PCA) showed that the concentration of HBCD depended on the particular sampling lake, reflecting non-uniform contamination of the Latvian environment with this EBFR.

Developmental toxicity induced by PM2.5 through endoplasmic reticulum stress and autophagy pathway in zebrafish embryos

The aims of this study were to investigate the mechanism underlying the developmental toxicity of fine particulate matter (PM_2.5) and provide a more thorough understanding of the toxicity of PM_2.5 in an ecological environment. Zebrafish embryos at 4 h post-fertilization were exposed to PM_2.5 at doses of 200, 300, 400, 500, 600 and 800 μg/mL for 120 h. The mortality, hatching rate, morphology score, body length, locomotor capacity, histological changes, antioxidant defense system, leukocyte migration, inflammation-related gene mRNA expression, endoplasmic reticulum stress (ERS) and autophagy were evaluated to study PM_2.5-induced developmental toxicity and its underlying mechanisms. PM_2.5 exposure significantly increased the mortality and malformations and reduced the hatching rate and body length of the zebrafish. PM_2.5 significantly reduced the locomotor capacity of zebrafish larvae, increased the levels of ROS and disturbed the antioxidant defense system in zebrafish larvae. In addition, a histological examination showed that the heart, liver, intestines and muscle of the PM_2.5-treated zebrafish exhibited abnormal changes and a significant increase in cellular autophagic accumulation. RT-PCR showed that the expression of genes related to inflammation (tgfβ and cox2), ERS (hspa5, chop, ire1, xbp1s, and atf6) and autophagy (lc3, beclin1 and atg3) pathways was significantly increased in the PM_2.5-treated zebrafish, indicating that PM_2.5 induced inflammation and promoted ERS and autophagy responses via the activation of the IRE1-XBP1 and ATF6 pathways. Together, our data indicate that PM_2.5 induced a dose- and time-dependent increase in developmental toxicity to zebrafish embryos. Additionally, ERS and autophagy may play important roles in PM_2.5-induced developmental toxicity.

Tris(1,3-dichloro-2-propyl) phosphate disrupts axonal growth, cholinergic system and motor behavior in early life zebrafish

Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) could have neurotoxic effects and alter motor behaviors in zebrafish (Danio rerio) larvae, however, the underlying mechanisms are still unknown. In this study, zebrafish embryos were subjected to waterborne exposure of TDCIPP at 100, 300, 600, 900μg/L from 2 to 120-h post-fertilization (hpf). Behavioral measurements indicate that TDCIPP exposure significantly elevated spontaneous movement, and altered swimming behavior response of larvae to both light and dark stimulation. Interestingly, in accordance with these motor effects, TDCIPP significantly decreased expression of the neuron-specific GFP in transgenic (HuC-GFP) zebrafish larvae as well as decreased expression of the neural marker genes elavl3 and ngn1, inhibited the axonal growth of the secondary motoneurons and altered the expressions of axon-related genes (α1-tubulin, shha and netrin2) in zebrafish larvae. Furthermore, TDCIPP exposure at 900μg/L significantly increased the activity of acetylcholinesterase (AChE) enzyme, and decreased the total acetylcholine (ACh) concentration. Our data indicate that the alteration in motor neuron and inhibition of cholinergic system could together lead to the TDCIPP induced motor behavior alterations in zebrafish larvae.