[en] Highlights: • Acute embryotoxicity: 2,7-DBCZ >> 3,6-DBCZ ≅ 3,6-DCCZ. • Zebrafish embryos exposed to 2,7-DBCZ develop significant malformation, especially pericardial edema. • Transcriptomics assay shows that 2,7-DBCZ induced developmental toxicity in zebrafish by AhR activation. -- Abstract: Polyhalogenated carbazoles (PHCZs), which have the similar structure of dioxin, have been reported ubiquitous in the environments and drawn wide concerns. However, their potential ecological and health risks are still poorly understood. Here, wildtype zebrafish embryos were used to evaluate the environmental risks of 2,7-dibromocarbazole (2,7-DBCZ), 3,6-dibromocarbazole (3,6-DBCZ), and 3,6-dichlorocarbazole (3,6-DCCZ). 2,7-DBCZ was the most toxic compound with the 96-h LC₅₀ value of 581.8 ± 29.3 μg·L⁻¹ and the EC₅₀ value of 201.5 ± 6.5 μg·L⁻¹ for pericardial edema. The teratogenic effects of 2,7-DBCZ were tested using transgenic zebrafish larvae. The transcriptomic analysis revealed that 90 genes in zebrafish expressed differently after exposure to 2,7-DBCZ, and many pathways were related to aryl hydrocarbon receptor (AhR) activation. The qRT-PCR also showed that expression levels of AhR1 and CYP1 A in zebrafish were significantly up-regulated after exposure to 2,7-DBCZ. In conclusion, 2,7-DBCZ exhibited more potent toxicity and cardiac teratogenic effects, and presented developmental toxicity partially consistent with AhR activation. Our results will be of great help to the risk assessment and regulation-making of PHCZs. Meanwhile, further studies should be promoted to illustrate the potential mechanism between PHCZs and AhR in the near future.

[en] Highlights: • Hepatotoxicity of TBBPA and Cd aerosol co-exposure was evaluated in CD-1 male mice. • Hepatic changes include focal necrosis, increased organ weight, and elevated enzymes. • TBBPA group exhibited highest hepatic toxicity followed by co-exposure and Cd groups. • We did not observe any synergistic effect of hepatic toxicity between TBBPA and Cd. • TBBPA/Cd suppressed antioxidant defensive mechanisms and increased oxidative stress. - Abstract: Cadmium (Cd) and tetrabromobisphenol A (TBBPA) are two prevalent contaminants in e-waste recycling facilities. However, the potential adversely health effect of co-exposure to these two types of pollutants in an occupational setting is unknown. In this study, we investigated co-exposure of these two pollutants on hepatic toxicity in CD-1 male mice through a whole-body aerosol inhalation route. Specifically, mice were exposed to solvent control (5% DMSO), Cd (8 μg/m"3), TBBPA (16 μg/m"3) and Cd/TBBPA mixture for 8 h/day and 6 days a week for 60 days. Hepatic changes include increased organ weight, focal necrosis, and elevated levels of liver enzymes in serum. These changes were most severe in mice exposed to TBBPA, followed by Cd/TBBPA mixture and Cd. These chemicals also led to suppressed antioxidant defensive mechanisms and increased oxidative stress. Further, these chemicals induced gene expression of apoptosis-related genes, activated genes encoding for phase I detoxification enzymes and inhibited genes encoding for phase II detoxification enzymes. These findings indicate that the hepatic damages induced by subchronic aerosol exposure of Cd and TBBPA may result from the oxidative damages caused by excessive ROS production when these chemicals were metabolized in the liver.

[en] Highlights: • We developed an in vivo DNA mismatch repair (MMR) measurement assay in zebrafish embryos. • This assay involves microinjection of homo- and heteroduplex EGFP plasmids into zebrafish embryos. • This novel assay was validated with embryos from the MMR-deficient mlh1 mutant fish. • We successfully applied this assay for detecting environmental chemicals with carcinogenic effect. • This novel assay can be used for screening of environmental carcinogens. - Abstract: Impairment of DNA mismatch repair (MMR) function leads to the development and progression of certain cancers. Many environmental contaminants can target DNA MMR system. Currently, measurement of MMR activity is limited to in vitro or in vivo methods at the cell line level, and reports on measurement of MMR activity at the live organism level are lacking. Here, we report an efficient method to measure DNA MMR activity in zebrafish embryos. A G-T mismatch was introduced into enhanced green fluorescent protein (EGFP) gene. Repair of the G-T mismatch to G-C in the heteroduplex plasmid generates a functional EGFP expression. The heteroduplex plasmid and a similarly constructed homoduplex plasmid were injected in parallel into the same batch of embryos at 1-cell stage and EGFP expression in EGFP positive embryos was quantified at 24 h after injection. MMR efficiency was calculated as the total fluorescence intensity of embryos injected with the heteroduplex construct divided by that of embryos injected with the homoduplex construct. Our results showed 73% reduction of MMR activity in embryos derived from MMR-deficient mlh1 mutant fish (positive control) when compared with embryos from MMR-competent wild type AB line fish, indicating feasibility of in vivo MMR activity measurement in zebrafish embryos. We further applied this novel assay for measurement of MMR efficiency in embryos exposed to environmental chemicals such as cadmium chloride (CdCl_2), benzo[a]pyrene (BaP), and perfluorooctanesulphonic acid (PFOS) from 6 hpf to 24 hpf. We observed significant reductions of MMR efficiency in embryos exposed to 0.1 μM CdCl_2 (52%) and 0.5 μM BaP (34%), but no effect in embryos exposed to PFOS. Our study for the first time provides a model system for in vivo measurement of DNA MMR activity at the organism level, which has important implications in risk assessment of various environmental carcinogens.

[en] Highlights: • PFOS chronic exposure induces sex-dependent hepatic steotosis in zebrafish. • PFOS interferes with β-oxidation, lipid synthesis, and lipid hepatic export process. • Zebrafish could be used as an alternative model for PFOS chronic toxicity screening. - Abstract: Perfluorooctane sulfonate (PFOS), one persistent organic pollutant, has been widely detected in the environment, wildlife and human. Currently few studies have documented the effects of chronic PFOS exposure on lipid metabolism, especially in aquatic organisms. The underlying mechanisms of hepatotoxicity induced by chronic PFOS exposure are still largely unknown. The present study defined the effects of chronic exposure to low level of PFOS on lipid metabolism using zebrafish as a model system. Our findings revealed a severe hepatic steatosis in the liver of males treated with 0.5 μM PFOS as evidenced by hepatosomatic index, histological assessment and liver lipid profiles. Quantitative PCR assay further indicated that PFOS significantly increase the transcriptional expression of nuclear receptors (nr1h3, rara, rxrgb, nr1l2) and the genes associated with fatty acid oxidation (acox1, acadm, cpt1a). In addition, chronic PFOS exposure significantly decreased liver ATP content and serum level of VLDL/LDL lipoprotein in males. Taken together, these findings suggest that chronic PFOS exposure induces hepatic steatosis in zebrafish via disturbing lipid biosynthesis, fatty acid β-oxidation and excretion of VLDL/LDL lipoprotein, and also demonstrate the validity of using zebrafish as an alternative model for PFOS chronic toxicity screening.

[en] Developmental neurobehavioral toxicity of Dechlorane Plus (DP) was investigated using the embryo-larval stages of zebrafish (Danio rerio). Normal fertilized embryos were waterborne exposed to DP at 15, 30, 60 μg/L beginning from 6 h post-fertilization (hpf). Larval teratology, motor activity, motoneuron axonal growth and muscle morphology were assessed at different developmental stages. Results showed that DP exposure significantly altered embryonic spontaneous movement, reduced touch-induced movement and free-swimming speed and decreased swimming speed of larvae in response to dark stimulation. These changes occurred at DP doses that resulted no significant teratogenesis in zebrafish. Interestingly, in accord with these behavioral anomalies, DP exposure significantly inhibited axonal growth of primary motoneuron and induced apoptotic cell death and lesions in the muscle fibers of zebrafish. Furthermore, DP exposure at 30 μg/L and 60 μg/L significantly increased reactive oxygen species (ROS) and malondialdehyde (MDA) formation, as well as the mRNA transcript levels of apoptosis-related genes bax and caspase-3. Together, our data indicate that DP induced neurobehavioral deficits may result from combined effects of altered neuronal connectivity and muscle injuries. - Highlights: • DP exposure induced neurobehavioral toxicity was evaluated in zebrafish. • DP exposure altered motor behavior, inhibited axonal growth and induced lesions in muscle fibers. • DP exposure induced oxidative stress and apoptotic cell death in larval zebrafish. • DP exposure altered mRNA transcript levels of apoptosis-related genes. - This study demonstrates that DP exposure induces neurobehavioral toxicity in zebrafish and the developmental zebrafish model will be useful for ecological risk assessments of DP in aquatic ecosystem.

[en] Perfluorooctanesulphonic acid (PFOS) is a ubiquitous contaminant in the aquatic environment and our earlier studies demonstrated that chronic PFOS exposures lead to a female-biased sex ratio and decreased sperm quality in male zebrafish. The underlying mechanism for these reproductive effects is unknown. In the present study, 8 h post-fertilization (hpf) zebrafish were exposed to PFOS at 250 μg/L for 5 months, and the levels of sex hormones, expression of sex determination related genes, and histological and ultrastructural changes of gonads were fully characterized. During the sex differentiation period, we observed elevated estradiol (E2) and decreased testosterone (T) levels in whole tissue homogenates from PFOS exposed juveniles. In fully mature adult male fish, serum E2 levels were slightly increased, however, the estrogen receptor alpha (esr1) was significantly elevated in PFOS treated male gonads. Histological and electron microscopic examinations revealed structural changes in the gonads of PFOS exposed male and female adult zebrafish. In summary, chronic PFOS exposure disrupts sex hormone level and related gene expression and impairs gonadal development, which may contribute to the previously reported PFOS reproductive toxicity. - Highlights: • Chronic PFOS exposure produces a female-biased sex ratio in zebrafish. • Chronic PFOS exposure reduces sperm quality in zebrafish. • Chronic PFOS exposure increases estrogen level in juvenile and adult zebrafish. • Chronic PFOS exposure alters expression of key genes involved hormone pathways. • Chronic PFOS exposure alters male and femalegonadal structures in zebrafish.

[en] Tetrabromobisphenol A (TBBPA), one of the most widely used brominated flame retardants (BFRs), is a ubiquitous contaminant in the environment and in the human body. This study demonstrated that zebrafish embryos exposed to TBBPA during a sensitive window of 8–48 h post-fertilization (hpf) displayed morphological malformations and mortality. Zebrafish exposed exclusively between 48 and 96 hpf were phenotypically normal. TBBPA was efficiently absorbed and accumulated in zebrafish embryos, but was eliminated quickly when the exposure solution was removed. Larval behavior assays conducted at 120 hpf indicated that exposure to 5 μM TBBPA from 8 to 48 hpf produced larvae with significantly lower average activity and speed of movement in the normal condition than in those exposed from 48 to 96 hpf. Specifically, 8–48 hpf-exposed larvae spent significantly less time in both activity bursts and gross movements compared to control or 48–96 hpf exposed larvae. Consistent with the motor deficits, TBBPA induced apoptotic cell death, delayed cranial motor neuron development, inhibited primary motor neuron development and loosed muscle fiber during the early developmental stages. To further explore TBBPA-induced developmental and neurobehavioral toxicity, RNA-Seq analysis was used to identify early transcriptional changes following TBBPA exposure. In total, 1969 transcripts were significantly differentially expressed (P < 0.05, FDR < 0.05, 1.5-FC) upon TBBPA exposure. Functional and pathway analysis of the TBBPA transcriptional profile identified biological processes involved in nerve development, muscle filament sliding and contraction, and extracellular matrix disassembly and organization changed significantly. In addition, TBBPA also led to an elevation in the expression of genes encoding uridine diphosphate glucuronyl transferases (ugt), which could affect thyroxine (T4) metabolism and subsequently lead to neurobehavioral changes. In summary, TBBPA exposure during a narrow, sensitive developmental window perturbs various molecular pathways and results in neurobehavioral deficits in zebrafish. - Highlights: • 8–48 hpf is the sensitive exposure window for neurodevelopmental and behavioral toxicities of TBBPA. • TBBPA induced apoptotic cell death and affected motor neuron and muscle fiber development. • Zebrafish embryos rapidly absorbed and accumulated TBBPA, and eliminated it quickly. • TBBPA induced ugt genes expression, which increased T4 metabolism and subsequently induced neurobehavior defects.

[en] Highlights: ► We examined PBDE concentrations in various matrices from different industrial areas. ► Elevated PBDE levels were found in areas with low-voltage electrical manufactures. ► Areas with e-waste recycling activities also had higher PBDE concentrations. ► PBDE content and composition in water samples varied from one area to another. ► PBDE composition in sediment/soil and biological samples was predominated by BDE-209. - Abstract: Polybrominated diphenyl ethers (PBDEs) have been used extensively in electrical and electronic products, but little is known about their distribution in the environment surrounding the manufacturing factories. This study reports PBDE contamination in various matrices from the location (Liushi, Zhejiang province) that produces more than 70% of the low-voltage electrical appliances in China. Additionally, PBDE contamination was compared with other industries such as the e-waste recycling business (Fengjiang) in the same region. Specifically, we measured seven PBDE congeners (BDEs – 47, 99, 100, 153, 154, 183, and 209) in water, sediment, soil, plant, and animal tissues from four different areas in this region. The present study revealed elevated PBDE concentrations in all matrices collected from Liushi and Fengjiang in comparison with highly industrialized areas without significant PBDE contamination sources. In water samples, there were large variations of PBDE content and composition across different areas. In sediment/soil and biological samples, BDE-209 was the predominant congener and this could be due to the abundant usage of deca-BDE mixtures in China. Our findings provide the very first data on PBDE contamination in the local environments surrounding the electronics industry, and also reveal widespread PBDE contamination in highly industrialized coastal regions of China.

[en] Highlights: ► The LC₅₀ of TGA-CdTe for zebrafish at 120 hpf was 185.9 nM. ► Zebrafish exposed to TGA-CdTe resulted in lower hatch rate and more malformation. ► Body length and heart beat of zebrafish declined after exposure to TGA-CdTe. ► Larvae exposure to TGA-CdTe elicited a higher basal swimming rate. ► Abnormal vascular of FLI-1 transgenic zebrafish larvae exposed to TGA-CdTe occurred. - Abstract: CdTe quantum dots (QDs) are nanocrystals of unique composition and properties that have found many new commercial applications; therefore, their potential toxicity to aquatic organisms has become a hot research topic. The lab study was performed to determine the developmental and behavioral toxicities to zebrafish under continuous exposure to low concentrations of CdTe QDs (1–400 nM) coated with thioglycolic acid (TGA). The results show: (1) the 120 h LC₅₀ of 185.9 nM, (2) the lower hatch rate and body length, more malformations, and less heart beat and swimming speed of the exposed zebrafish, (3) the brief burst and a higher basal swimming rate of the exposed zebrafish larvae during a rapid transition from light-to-dark, and (4) the vascular hyperplasia, vascular bifurcation, vascular crossing and turbulence of the exposed FLI-1 transgenic zebrafish larvae.