Chronic exposure of 2,2',4,4'-tetrabromodiphenyl ether (PBDE-47) alters locomotion behavior in juvenile zebrafish (Danio rerio)

Stereoselective toxicity of acetochlor chiral isomers on the nervous system of zebrafish larvae

Acetochlor (ACT) is a widely detected pesticide globally, and the neurotoxic effects of its chiral isomers on humans and environmental organisms remain uncertain. Zebrafish were used to study the neurotoxicity of ACT and its chiral isomers. Our study reveals that the R-ACT, Rac-ACT, and S-ACT induce neurotoxicity in zebrafish larvae by impairing vascular development and disrupting the blood-brain barrier. These detrimental effects lead to apoptosis in brain cells, hindered development of the central nervous system, and manifest as altered swimming behavior and social interactions in the larvae. Importantly, the neurotoxicity caused by the S-ACT exhibits the most pronounced impact and significantly diverges from the effects induced by the R-ACT. The neurotoxicity associated with the Rac-ACT falls intermediate between that of the R-ACT and S-ACT. Fascinatingly, we observed a remarkable recovery in the S-ACT-induced abnormalities in BBB, neurodevelopment, and behavior in zebrafish larvae upon supplementation of the Wnt/β-catenin signaling pathway. This observation strongly suggests that the Wnt/β-catenin signaling pathway serves as a major target of S-ACT-induced neurotoxicity in zebrafish larvae. In conclusion, S-ACT significantly influences zebrafish larval neurodevelopment by inhibiting the Wnt/β-catenin signaling pathway, distinguishing it from R-ACT neurotoxic effects.

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.

A hypothetical model of multi-layered cost-effective wastewater treatment plant integrating microbial fuel cell and nanofiltration technology: A comprehensive review on wastewater treatment and sustainable remediation

Wastewater management has emerged as an uprising concern that demands immediate attention from environmentalists worldwide. Indiscriminate and irrational release of industrial and poultry wastes, sewage, pharmaceuticals, mining, pesticides, fertilizers, dyes and radioactive wastes, contribute immensely to water pollution. This has led to the aggravation of critical health concerns as evident from the uprising trends of antimicrobial resistance, and the presence of xenobiotics and pollutant traces in humans and animals due to the process of biomagnification. Therefore, the development of reliable, affordable and sustainable technologies for the supply of fresh water is the need of the hour. Conventional wastewater treatment often involves physical, chemical, and biological processes to remove solids from the effluent, including colloids, organic matter, nutrients, and soluble pollutants (metals, organics). Synthetic biology has been explored in recent years, incorporating both biological and engineering concepts to refine existing wastewater treatment technologies. In addition to outlining the benefits and drawbacks of the current technologies, this review addresses novel wastewater treatment techniques, especially those using dedicated rational design and engineering of organisms and their constituent parts. Furthermore, the review hypothesizes designing a multi-bedded wastewater treatment plant that is highly cost-efficient, sustainable and requires easy installation and handling. The novel setup envisages removing all the major wastewater pollutants, providing water fit for household, irrigation and storage purposes.

A Realistic Mixture of Persistent Organic Pollutants Affects Zebrafish Development, Behavior, and Specifically Eye Formation by Inhibiting the Condensin I Complex

Persistent organic pollutants (POPs) are posing major environmental and health threats due to their stability, ubiquity, and bioaccumulation. Most of the numerous studies of these compounds deal with single chemicals, although real exposures always consist of mixtures. Thus, using different tests, we screened the effects on zebrafish larvae caused by exposure to an environmentally relevant POP mixture. Our mixture consisted of 29 chemicals as found in the blood of a Scandinavian human population. Larvae exposed to this POP mix at realistic concentrations, or sub-mixtures thereof, presented growth retardation, edemas, retarded swim bladder inflation, hyperactive swimming behavior, and other striking malformations such as microphthalmia. The most deleterious compounds in the mixture belong to the per- and polyfluorinated acids class, although chlorinated and brominated compounds modulated the effects. Analyzing the changes in transcriptome caused by POP exposure, we observed an increase of insulin signaling and identified genes involved in brain and eye development, leading us to propose that the impaired function of the condensin I complex caused the observed eye defect. Our findings contribute to the understanding of POP mixtures, their consequences, and potential threats to human and animal populations, indicating that more mechanistic, monitoring, and long-term studies are imperative.

The effect of 2,2',4,4'-Tetrabromodiphenyl ether (BDE-47) on locomotor behaviour and muscle physiology of the sea cucumber Apostichopus japonicus

The 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) is the predominant congener of polybrominated diphenyl ethers, and it is also a persistent organic pollutant that with a higher detection rate in samples from environment and animals. To date, there have been few studies of the effects of BDE-47 on locomotion in sea cucumbers. In this study, we investigated the influence of different concentrations of BDE-47 (low: 0.1 μg/L; moderate: 1.0 μg/L; high: 10.0 μg/L) on locomotion of Apostichopus japonicus and evaluated changes in their muscle physiology using ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry. The behavioural studies showed that the average and maximum velocity of movement decreased significantly in both the moderate and high BDE-47 groups after 1 day of exposure. In addition, levels of 55 metabolites were identified and characterized in the longitudinal muscle of A. japonicus exposed to BDE-47. The alteration of taurine and norepinephrine levels indicated that BDE-47 had drastic physiological effects on the longitudinal muscle of A. japonicus.

Hormetic dose responses induced by organic flame retardants in aquatic animals: Occurrence and quantification

The organic flame retardants (OFRs) have attracted global concerns due to their potential toxicity and ubiquitous presence in the aquatic environment. Hormesis refers to a biphasic dose response, characterized by low-dose stimulation and high-dose inhibition. The present study provided substantial evidence for the widespread occurrence of OFRs-induced hormesis in aquatic animals, including 202 hormetic dose response relationships. The maximum stimulatory response (MAX) was commonly lower than 160% of the control response, with a combined value of 134%. Furthermore, the magnitude of MAX varied significantly among multiple factors and their interactions, such as chemical types and taxonomic groups. Moreover, the distance from the dose of MAX to the no-observed-adverse-effect-level (NOAEL) (NOAEL: MAX) was typically below 10-fold (median = 6-fold), while the width of the hormetic zone (from the lowest dose inducing hormesis to the NOAEL) was approximately 20-fold. Collectively, the quantitative features of OFRs-induced hormesis in aquatic animals were in accordance with the broader hormetic literature. In addition, the implications of hormetic dose response model for the risk assessment of OFRs were discussed. This study offered a novel insight for understanding the biological effects of low-to-high doses of OFRs on aquatic animals and assessing the potential risks of OFRs in the aquatic environment.

Feeding behavior toxicity in the marine rotifer Brachionus plicatilis caused by 2,2',4,4'-tetrabromodiphenyl ether (BDE-47): Characteristics and mechanisms

Polybrominated diphenyl ether contamination in marine environments has received special attention due to its accumulation and magnification in the marine food web and toxicity to organisms. In the present study, a series of short-term toxicological tests were conducted with the marine rotifer Brachionus plicatilis to assess the effects on ingestion and digestive performance after treatment with 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) at nonlethal concentrations under controlled laboratory conditions and to analyze the possible mechanism. The results showed that with accumulation in rotifers, BDE-47 caused a significant decline in the filtration and feeding rates in a concentration-dependent manner. Moreover, the activities of amylase (AMS) and protease were affected, indicating that BDE-47 impaired ingestion and digestion efficiency. BDE-47 exposure did not lead to abnormal microstructures in the main digestive tract (e.g., cilia around the corona, mastax, stomach, digestive gland and esophagus), but the gastric parietal cells shrank, suggesting nutritional deficiency. BDE-47 prominently induced the occurrence of irregular mitochondria at the cilia root, and mitochondrial and isocitrate dehydrogenase activity declined, indicating mitochondrial dysfunction. Furthermore, the activity of ATPase, which catalyzes ATP hydrolysis, decreased as the BDE-47 concentration rose, implying that BDE-47 retarded rotifer ATP dynamics, inevitably interfering with cilia movement to ingest food. Additionally, a significant decline in acetylcholine esterase activity was observed, which led to a hindrance in neurotransmission involved in food intake and digestion. Altogether, our results demonstrated that nonlethal concentrations of BDE-47 could induce feeding depression in rotifers, which is mainly attributed to stymied energy metabolism and nerve conduction.

Zebrafish Embryonic Exposure to BPAP and Its Relatively Weak Thyroid Hormone-Disrupting Effects

Safe endocrine-disrupting alternatives for bisphenol A (BPA) are needed because its adverse health effects have become a public concern. Some bisphenol analogues (bisphenol F and S) have been applied, but their endocrine-disrupting potential is either not negligible or weaker than that of BPA. However, the endocrine-disrupting potential of bisphenol AP (BPAP), another BPA alternative, has not yet been fully assessed. Hence, we evaluated the thyroid hormone (TH)-disrupting potency of BPAP because THs are essential endocrine hormones. Zebrafish embryos were exposed to BPAP (0, 18.2, 43.4, or 105.9 μg/L) for 120 h, and TH levels, the transcription of 16 TH-related genes, the transcriptome, development, and behavior were evaluated. In our study, a decrease in T4 level was observed only at the maximum nonlethal concentration, but significant changes in the T3 and TSHβ levels were not detected. BPAP did not cause significant changes in transcription and gene ontology enrichment related to the TH system. Developmental and behavioral changes were not observed. Despite T4 level reduction, other markers were not significantly affected by BPAP. These might indicate that BPAP has weak or negligible potency regarding TH disruption as a BPA alternative. This study might provide novel information on the TH-disrupting potential of BPAP.

Characterization of pharmaceuticals, personal care products, and polybrominated diphenyl ethers in lake sturgeon serum and gametes

Recent research suggests contaminants of emerging concern (CECs) are widespread and environmentally relevant concentrations can impact fishes. However, little is known about impacts of CECs to long-lived or rare species. The objective of this study was to characterize CEC concentrations in lake sturgeon (Acipenser fulvescens) serum and gametes. Blood serum was collected non-lethally from lake sturgeon at four lower Great Lakes basin sites: Detroit, upper Niagara, lower Niagara, and St. Lawrence rivers; additionally, gametes were collected from lake sturgeon in the St. Lawrence River. Samples were analyzed for pharmaceuticals and personal care products (PPCPs) and polybrominated diphenyl ethers (PBDEs). Overall, 44 different PPCPs were identified in serum and gamete samples across sites, with 22 PPCPs identified in at least 25% of serum samples and three PPCPs identified in 25% of gamete samples. PPCP concentrations in serum and gametes ranged from 0.00208 to 130 ppb and 0.00538-190 ppb, respectively. NMDS ordination revealed differences in the presence and concentrations of PPCPs in lake sturgeon serum across sites, however, N,N-diethyl-meta-toluamide (DEET), hydrocortisone, benztropine, and amitriptyline were detected in at least one serum sample at all sites. Additionally, DEET, 10-hydroxy-amitriptyline, and sertraline were detected in ≥25% of gamete samples collected from the St. Lawrence River. Twenty-six PBDE congeners were identified in 25% of serum samples and 24 were identified in 25% of gamete samples. PBDEs in serum were present across all sites and in gametes of St. Lawrence River lake sturgeon, and total PBDE concentrations in serum and gametes ranged from 0.184 to 12.7 ppb and 0.0826-0.44 ppb, respectively. Managers of lake sturgeon populations may need to consider the impacts of CECs if reproductive, developmental, behavioral, growth effects, or mortality are observed in the Great Lakes basin or other areas that are impacted by increased exposures to PPCPs and PBDEs.

Developmental exposure to BDE-99 hinders cerebrovascular growth and disturbs vascular barrier formation in zebrafish larvae

Polybrominated diphenyl ethers (PBDEs) are distributed throughout the environment. Despite a moratorium on their use, concentrations of PBDEs in the atmosphere and in residential environments remain high due to their persistence. The environmental health risks remain concerning and one of the major adverse effects is neurodevelopmental toxicity. However, the early response and effects of PBDEs exposure on the developing brain remain unknown. In the present study, we investigated the impacts of 2,2',4,4',5-pentabrominated diphenyl ether (BDE-99) on vascular growth and vascular barrier function with an emphasis on cerebral blood vessels, in the early life stages, using a zebrafish model. No general toxicity was observed in exposing zebrafish larvae to 0-0.5 μM BDE-99 at 72 hpf. BDE-99 exposure resulted in neither general toxicity nor pronounced developmental impairment in somatic blood vessels, including intersegmental vessels (ISV) and common cardinal veins (CCV). Meanwhile, both 0.05 μM and 0.5 μM of BDE-99 reduced cerebrovascular density as well as down-regulation of VEGFA and VEGFR2 in the head. In addition, BDE-99 exposure increased vascular leakage, both in cerebral and truncal vasculature at 72 hpf. The accentuated vascular permeability was observed in the head. The mRNA levels of genes encoding tight junction molecules decreased in the BDE-99-exposed larvae, and more robust reductions in Cldn5, Zo1 and Jam were detected in the head than in the trunk. Moreover, proinflammatory factors including TNF-α, IL-1β and ICAM-1 were induced, and the expression of neurodevelopment-related genes was suppressed in the head following BDE-99 exposure. Taken together, these results reveal that developmental exposure to BDE-99 impedes cerebrovascular growth and disturbs vascular barrier formation. The cerebral vasculature in developing zebrafish, a more sensitive target for BDE-99, may be a promising tool for the assessment of the early neurodevelopmental effects due to PBDEs exposure.

Bioconcentration, depuration and toxicity of Pb in the presence of titanium dioxide nanoparticles in zebrafish larvae

The interactions between nanoparticles (NPs) and metals in aquatic environments may modify the bioavailability and toxicity of metals to organisms. In this study, we investigated the effects of titanium dioxide NPs (n-TiO₂) on the bioconcentration, depuration, and neurotoxic effects of lead (Pb) in zebrafish larvae. Transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy showed that Pb²⁺ was adsorbed by n-TiO₂ to form NP-Pb complexes in suspension, and these complexes were observed in larval tissues. The bioconcentration of Pb in larvae along with the depuration rates of Pb were higher in the presence of n-TiO₂ compared to when n-TiO₂ was absent. Exposure to Pb alone induced the expression of the biomarker metallothionein, downregulated neurodevelopment-related genes, and reduced swimming activity of larvae. However, the addition of n-TiO₂ to the exposure solution alleviated these effects. The results suggest that n-TiO₂ can act as a carrier of Pb to increase its bioconcentration; however, the formation of NP-Pb complexes likely reduces the amount of free Pb²⁺, thereby reducing toxicity to larvae.

Long-term exposure to the non-steroidal anti-inflammatory drug (NSAID) naproxen causes thyroid disruption in zebrafish at environmentally relevant concentrations

The presence of trace levels of pharmaceuticals is an emerging issue impacting the aquatic ecosystem. Naproxen (NPX) is a nonsteroidal anti-inflammatory drug (NSAID) that has been frequently detected in aquatic environments worldwide. Recently, concerns regarding endocrine disruption by NSAIDs have increased; however, their effects on the thyroid system have yet to be understood. In this study, zebrafish were utilized to evaluate the thyroid-disrupting effects of NPX. After a 60-day exposure to various concentrations of NPX (0.1, 1, 10 and 100 μg/L), the body length and weight of the zebrafish were significantly decreased. The decrease of cytochrome P450 gene expression and enzyme activity might inhibit the metabolism of NPX, which might result in the significant bioconcentration in zebrafish. Thyroid hormone (TH) analysis showed that both triiodothyronine (T3) and thyroxine (T4) levels were substantially decreased. Gene transcription expressions along the hypothalamic-pituitary-thyroid (HPT) axis were also markedly affected. Significant downregulation of dio1, dio2, nis, nkx2.1, pax8, tg, tpo, trβ and ttr levels, along with the stimulation of the tshβ gene, were also observed in exposed fish compared to controls. Western blot analysis indicated that expression of the TTR protein was significantly decreased, which coincides with the results of the gene expression analysis. Collectively, our observations show that NPX increases the risk of bioconcentration and thyroid disruption in zebrafish. Given the continued increasing consumption and emission of pharmaceuticals, thyroid disruption should be considered when assessing the aquatic risk of long-term exposure to environmentally relevant concentrations of pharmaceuticals.

Effects of 25 thyroid hormone disruptors on zebrafish embryos: A literature review of potential biomarkers

It is estimated that many organic compounds found in our environment can interfere with the thyroid system and act as thyroid hormone (TH) disruptor. Despite that, there is a clear lack of assays to identify TH disruptors. Recently zebrafish embryos were suggested as screening tool to identify compounds which impact thyroid synthesis. Effects on hormone level, gene transcript expression, eye development and swim bladder inflation are suggested as potential biomarker for TH disruptors. In order to assess the applicability of these biomarkers we performed a literature review. The effects of 25 known TH disrupting compounds were compared between studies. The studies were limited to exposures with embryos prior 7 days of development. The different study designs and the lack of standardized methods complicated the comparison of the results. The most common responses were morphological alterations and gene transcript expression changes, but no specific biomarker for TH disruption could be identified. In studies addressing TH disruption behavioral effects were more commonly monitored than in studies not mentioning the TH pathway. TH disruption in developing zebrafish embryos might be caused by different modes of action e.g. disruption of follicle development, binding of TH, activation of TH receptors causing different effects. Timing of developmental processes in combination with exposure duration might also play a role. On the other side compound characteristics (uptake, stability, metabolization) could also cause differences between substances. Further studies are necessary to gain better understanding into the mechanisms of TH disruption in early zebrafish development.

Neurobehavioral effects of two metabolites of BDE-47 (6-OH-BDE-47 and 6-MeO-BDE-47) on zebrafish larvae

Two metabolites, OH-BDEs and MeO-BDEs, of polybrominated diphenyl ethers (PBDEs) were ubiquitously detected in animal tissues and environmental samples, drawing a widely public concern to their toxicity. The comparison of toxicity between PBDEs and their metabolites has been a focus in recent years, however, comparisons seldom involve neurobehavioral toxicity of PBDEs metabolites in published works. In this study, zebrafish larvae were exposed to 6-OH-BDE-47 and 6-MeO-BDE-47 and their neurobehavioral traits (including locomotion, path angle, and social activity) were recorded using the instrument Zebrabox; meanwhile, light illumination was used as stimuli in the test duration. The results showed larvae were more active in dark periods than light periods, and preferred turning right (+) to left (-). Effects of the two metabolites varied in different behavioral indicators. They induced different effects on path angle but did not reverse the left-right asymmetry. 6-OH-BDE-47 did not induce the effects on larval locomotion and social activity, but mainly decreased average and routine turn numbers; 6-MeO-BDE-47 promoted larvae responsive turns but inhibited social activity. This study offered new experimental means to the neurobehavioral toxicity of various PBDE metabolites. Further studies may focus on the toxic mechanisms of specific neurobehavioral traits.

Illicit drug ketamine induces adverse effects from behavioral alterations and oxidative stress to p53-regulated apoptosis in medaka fish under environmentally relevant exposures

With increasing problems of drug abuse worldwide, aquatic ecosystems are contaminated by human pharmaceuticals from the discharge of hospital or municipal effluent. However, ecotoxicity data and related toxic mechanism for neuroactive controlled or illicit drugs are still lacking, so assessing the associated hazardous risk is difficult. This study aims to investigate the behavioral changes, oxidative stress, gene expression and neurotoxic or apoptosis effect(s) in larvae of medaka fish (Oryzias latipes) with environmentally relevant exposures of ketamine (KET) solutions for 1-14 days. KET exposure at an environmentally relevant concentration (0.004 μM) to 40 μM conferred specific patterns in larval swimming behavior during 24 h. At 14 days, such exposure induced dose- and/or time-dependent alteration on reactive oxygen species induction, the activity of antioxidants catalase and superoxide dismutase, glutathione S-transferase and malondialdehyde contents in fish bodies. KET-induced oxidative stress disrupted the expression of acetylcholinesterase and p53-regulated apoptosis pathways and increased caspase expression in medaka larvae. The toxic responses of medaka larvae, in terms of chemical effects, were qualitatively analogous to those of zebrafish and mammals. Our results implicate a toxicological impact of waterborne KET on fish development and human health, for potential ecological risks of directly releasing neuroactive drugs-containing wastewater into the aquatic environment.

Transgenerational impairments of reproduction and development of the marine invertebrate Crepidula onyx resulted from long-term dietary exposure of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47)

Polybrominated diphenyl ethers have become ubiquitous in the environment and elevated concentrations have often been found in marine organisms. Using the gastropod Crepidula onyx as a study model, this multigenerational study sets out to test the hypotheses that 1) parental dietary exposure to environmentally realistic levels of 2,2',4,4'-tetrabrominated diphenyl ether (BDE-47) would lead to transgenerational impairments on fitness traits of marine invertebrates, and 2) the organisms might develop adaptation/acclimation after exposure for one or more generations. F₀ generation of C. onyx was fed with the dinoflagellate Isochrysis galbana encapsulated with two concentrations of BDE-47 (1.78 and 16.0 ng million cells^-1, respectively), and half of the F₁ offspring from the higher concentration treatment was returned to control condition (transgenerational group), while the other half received BDE-47 treatment continuously (continuous treatment group). Bioaccumulation and maternal transfer of BDE-47 were evident in all life stages of the F₀ generation and in F₁ eggs, respectively. Exposure to BDE-47 reduced fecundity, delayed sexual maturity, and impeded embryonic development in F₀ to F₂. In particular, developmental toxicity of F₂ embryos was apparent in the transgenerational group, but not in the continuous treatment group, even when BDE-47 was not detected in the F₂ embryos nor in their mothers and they have never been exposed to the chemical. This study also suggested that the offspring might have developed adaptation/acclimation to the exposure of BDE-47 within two generations of exposure, and that the physiological alterations associated with acclimation/adaptation might have hindered the normal larval development under a stress free condition. These findings highlighted the need for long-term multigenerational studies in the ecological risk assessment of chemicals alike.

Tetrabromobisphenol A caused neurodevelopmental toxicity via disrupting thyroid hormones in zebrafish larvae

Tetrabromobisphenol A (TBBPA), one of the most widely used brominated flame retardants (BFRs), has resulted in worldwide environmental contamination. TBBPA has been reported as a thyroid endocrine disruptor and a potential neurotoxicant. However, the underlying mechanism is still not clear. In this study, zebrafish (Danio rerio) embryos (2 h post-fertilization, hpf) were exposed to different concentrations of TBBPA (50, 100, 200 and 400 μg/L) alone or in combination with 3,3',5-triiodo-l-thyronine (T3, 20 μg/L + TBBPA, 200 μg/L). The results confirmed that TBBPA could evoke thyroid disruption by observations of increased T4 contents and decreased T3 contents, accompanied by up-regulated tshβ, tg mRNA and down-regulated ttr and trβ mRNA levels in zebafish larvae. TBBPA-induced neurodevelopmental toxicity was also indicated by down-regulated transcription of genes related to central nervous system (CNS) development (e.g., α1-tubulin, mbp and shha), and decreased locomotor activity and average swimming speed. Our results further demonstrated that treatment with T3 could reverse or eliminate TBBPA-induced effects on thyroidal and neurodevelopmental parameters. Given the above, we hypothesize that the observed neurodevelopmental toxicity in the present study could be attributed to the thyroid hormone disruptions by TBBPA.

Effects of dietary 2,2', 4,4'-tetrabromodiphenyl ether (BDE-47) exposure on medaka (Oryzias latipes) swimming behavior

A diet fortified with 2,2', 4,4'-tetrabromodiphenyl ether (BDE-47: 0, 10, 100, and 1000 ng/g) was dosed to 4-7-day-old post-hatch medaka fish for 40 days to evaluate the effects on the swimming activity of fish using a miniaturized swimming flume. Chlorpyrifos (CF)-exposed fish were selected as the positive control to assess the validity and sensitivity of the behavioral findings. After 20 and 40 days of exposure, the locomotor activity was analyzed for 6 min in a flume section (arena). The CF positive control for each time point were fish exposed to 50 ng CF/ml for 48 h. Swimming patterns, presented as two-dimensional heat maps of fish movement and positioning, were obtained by geostatistical analyses. The heat maps of the control groups at time point 20 revealed visually comparable swimming patterns to those of the BDE-47-treated groups. For the comparative fish positioning analysis, both the arenas were divided into 15 proportional areas. No statistical differences were found between residence times in the areas from the control groups and those from the BDE-47-treated groups. At time point 40, the heat map overall patterns of the control groups differed visually from that of the 100-ng BDE-47/g-treated group, but a comparative analysis of the residence times in the corresponding 15 areas did not reveal consistent differences. The relative distances traveled by the control and treated groups at time points 20 and 40 were also comparable. The heat maps of CF-treated fish at both time points showed contrasting swim patterns with respect to those of the controls. These differential patterns were statistically supported with differences in the residence times for different areas. The relative distances traveled by the CF-treated fish were also significantly shorter. These results confirm the validity of the experimental design and indicate that a dietary BDE-47 exposure does not affect forced swimming in medaka at growing stages.

Fish life-history traits are affected after chronic dietary exposure to an environmentally realistic marine mixture of PCBs and PBDEs

Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are persistent organic pollutants that have been shown to affect fish life-history traits such as reproductive success, growth and survival. At the individual level, their toxicity and underlying mechanisms of action have been studied through experimental exposure. However, the number of experimental studies approaching marine environmental situations is scarce, i.e., in most cases, individuals are exposed to either single congeners, or single types of molecules, or high concentrations, so that results can hardly be transposed to natural populations. In the present study, we evaluated the effect of chronic dietary exposure to an environmentally realistic marine mixture of PCB and PBDE congeners on zebrafish life-history traits from larval to adult stage. Exposure was conducted through diet from the first meal and throughout the life cycle of the fish. The mixture was composed so as to approach environmentally relevant marine conditions in terms of both congener composition and concentrations. Life-history traits of exposed fish were compared to those of control individuals using several replicate populations in each treatment. We found evidence of slower body growth, but to a larger asymptotic length, and delayed spawning probability in exposed fish. In addition, offspring issued from early spawning events of exposed fish exhibited a lower larval survival under starvation condition. Given their strong dependency on life-history traits, marine fish population dynamics and associated fisheries productivity for commercial species could be affected by such individual-level effects of PCBs and PBDEs on somatic growth, spawning probability and larval survival.

Cd36 is a candidate lipid sensor involved in the sensory detection of fatty acid in zebrafish

Recently more and more evidences raise the possibility for the taste system in the role of the perception of lipids in mammals, and the fatty acid receptor CD36 has been proved to be as an important candidate receptor of fat taste. Fish has different taste modality with mammals. No information was known about the function of cd36 in fish taste till now. Here, using in situ hybridization and immunofluorescence technologies, we showed that fish cd36/Cd36 localized in taste buds. Real-time PCR technology demonstrated that, in zebrafish cd36 (zcd36)-transfected cells, linoleic acid (LA) increased the expression level of tryptophan hydroxylase-1 (TPH-1), which encodes the enzyme involved in the biosynthesis of monoamine neurotransmitter of 5-HT. Moreover, the LA-induced up-regulation expression of TPH-1 was significantly curtailed by SSO, a specific inhibitor of LCFA binding to CD36, suggesting zCd36 is implicated in the LA-induced release of neurotransmitter. Importantly, we observed that zcd36 gene knockout zebrafish reduced the preference for LA contrast to wild-type zebrafish. Together, our findings indicate that Cd36 is a candidate lipid sensor involved in the sensory detection of fatty acid in zebrafish.

Effects of ibuprofen, diclofenac and paracetamol on hatch and motor behavior in developing zebrafish (Danio rerio)

Non-steroidal anti-inflammatory drugs (NSAIDs) which are widely used as pain relief medicines are causing increasing environmental concern due to their incomplete removal in wastewater treatment plant and potential toxicity on endocrine, kidney and reproduction in teleost fish. This study focused on the effects of widely used ibuprofen, diclofenac and paracetamol on the hatch and motor ability of early-stage zebrafish, by exposing embryos to the target chemicals at 5, 50 and 500 μg/L starting from 6 h postfertilization (hpf). A significant reduction in hatch rate at 55 hpf was caused by both ibuprofen (-63%) and diclofenac (-58%) at 500 μg/L. Exposure to high concentration of ibuprofen significantly decreased the spontaneous movement by 25%, and reduced the free swimming distance, duration and speed under dark condition by 41%, 29% and 30%, respectively. High concentration of diclofenac also caused 23% decrease in spontaneous movement, and reduced the swimming distance as well as active duration by 17% and 13% under light stimulation. In comparison, the exposure to paracetamol did not cause any notable effect. Among neuron related genes tested, the expression of neurog1 was down-regulated from ibuprofen and diclofenac exposure by 19% and 26%, while the expression of neurod1 was up-regulated only by ibuprofen (31%). These findings indicated that ibuprofen and diclofenac significantly affected embryo locomotivity and were potentially neurotoxic, thus posing threats to zebrafish development.

Preliminary screening of polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane (HBCDD) and tetrabromobisphenol A (TBBPA) flame retardants in landfill leachate

The occurrence of selected brominated flame retardants, including nine polybrominated diphenyl ether (PBDE) congeners, hexabromocyclododecane (HBCDD) and tetrabromobisphenol A (TBBPA) in leachate samples from eight landfill sites in South Africa, were investigated. In addition, the possible influences of dissolved organic carbon on their levels were also evaluated. Filtered leachate samples were subjected to solid-phase extraction to isolate the various target compounds. PBDEs with six bromine substituents and above, as well as α-HBCDD, β-HBCDD and TBBPA, were generally found below the detection limit. However, the mean value of the total lower PBDE congeners ranged between 0.04 and 0.48 μg L^-1, and the concentrations of γ-HBCDD ranged from not detectable (ND) to 0.05 μg L^-1. No significant correlation was observed between the target compounds and dissolved organic carbon, although weak to moderate correlations were mostly observed for the lower PBDEs.

Tissue Contaminant Burdens in San Francisco Estuary White Sturgeon (Acipenser transmontanus): Implications for Population Recovery

The San Francisco Estuary (SFE) is heavily influenced by anthropogenic activities, including historic and chronic contaminant inputs. These contaminants can adversely affect SFE fish populations, particularly white sturgeon, because they are a benthic dwelling, long-lived species. We measured a suite of metals and organic contaminants in liver and gonad tissues of 25 male and 32 female white sturgeon as well as several physiological indicators of sturgeon health. Most sturgeon (68% of males and 83% of females) were estimated to be between 13 and 17 years of age. Sturgeon tissues had elevated concentrations of several metals, including As, Ba, Cd, Cu, Cr, Pb, Hg, Ni, Se, and Zn. The most frequently detected organic contaminants in sturgeon livers and gonads were DDE, PCBs, PBDEs, and galaxolide. Selenium was detected at levels similar to those shown to cause impaired liver physiology and reproductive success in white sturgeon. Observed Hg levels were higher than those shown to result in lower condition factor and gonadosomatic indices in white sturgeon. Liver galaxolide levels correlated with decreased plasma estradiol levels in female sturgeon. The Cd, As, and Cu warrant further investigation, because they were detected at levels known to impair fish health. Our results suggest contaminants are negatively affecting SFE white sturgeon health and fitness. Future SFE white sturgeon contaminant research is suggested.

Endocrine disruption by Bisphenol A, polychlorinated biphenyls and polybrominated diphenyl ether, in zebra fish (Danio rerio) model: an in silico approach

Endocrine disrupting chemicals may induce adverse health effects in humans and wildlife. Recent studies demonstrate that endocrine disrupting chemicals like Bisphenol A (BPA), polychlorinated biphenyls (PCBs) and polybrominated diphenyl ether (PBDE) affect the reproductive characters shared by wide range of creatures including fish. An attempt was made to evaluate the toxicity of these chemicals on the vitellogenin protein of zebra fish (Danio rerio) using in silico approach. The protein structure of zebra fish vitellogenin was predicted using homology modelling, and the stereochemical quality of the model was validated by Ramachandran plot. The 3-D structure of vitellogenin was docked with the aforementioned chemicals that have demonstrated endocrine-disrupting activity. The pair-wise alignments between vitellogenin with phosvitin, lipovitellin-2 and YGP40 obtained by CLUSTALW alignment suggest that the vitellogenin contained lipovitellin-2- phosvitin- and YGP40-related amino acid sequences. Based on the prediction of CASTp and CLUSTALW, BPA and PCB predominantly interacted with lipovitellin-2 site of the protein, while PBDE interacts predominantly with the YGP40 site of the vitellogenin protein. The results indicate that the endocrine-disrupting chemicals (BPA, PCB and PBDE) dock with the vitellogenin cleavage sites lipovitellin-2 and YGP40 that play a crucial role in lipid-protein complex formation in the egg yolk. We hypothesize that these chemicals could potentially impair the egg yolk formation and eventually impact the zebra fish population which occupies an important niche among testing models used in drug discovery and related toxicity studies.

Permanent Deiodinase Type 2 Deficiency Strongly Perturbs Zebrafish Development, Growth, and Fertility

Iodothyronine deiodinases are selenocysteine-containing enzymes that activate or inactivate thyroid hormones (THs). Deiodinase type 2 (Dio2) catalyzes the conversion of the prohormone T4 into the transcriptionally active T3 and is the predominant activating deiodinase in zebrafish. Using zinc finger nucleases, we generated two different dio2(-/-) mutant zebrafish lines to investigate the physiological function of this TH activator. The first line contains a deletion of 9 bp, resulting in an in-frame elimination of three conserved amino acids. The other line is characterized by an insertion of 4 bp, leading to the introduction of a premature stop-codon. Both lines completely lack Dio2 activity, resulting in a strong reduction of T3 abundancy in all tissues tested. Early development is clearly perturbed in these animals, as shown by a diverse set of morphometric parameters, defects in swim bladder inflation, and disturbed locomotor activity tested between 1 and 7 days after fertilization. Permanent Dio2 deficiency also provokes long-term effects because growth and especially fertility are severely hampered. Possible compensatory mechanisms were investigated in adult dio2(-/-) mutants, revealing a down-regulation of the inactivating deiodinase Dio3 and TH receptor transcript levels. As the first nonmammalian model with permanent Dio2 deficiency, these mutant zebrafish lines provide evidence that Dio2 is essential to assure normal development and to obtain a normal adult phenotype.

Effects of dietary 2,2', 4,4'-tetrabromodiphenyl ether (BDE-47) exposure in growing medaka fish (Oryzias latipes)

In this research work, we addressed the effects of a diet fortified with BDE-47 (0, 10, 100, 1000ng/g) dosed to 4-7 day-old post-hatch medaka fish for 40 days, followed by an 80-day depuration period. BDE-47 accumulation and overall growth were evaluated throughout the dosing period, and its elimination was quantified over the following 60 days. The histological condition of the thyroid gland, liver and gonads from the 1000ng BDE-47-treated fish were assessed 5 and 70days after exposures finished. The phenotypic males to females ratio was also quantified 70days after treatments finished. Sixty days after the BDE-47 exposures, reproductive capacity (i.e. fecundity, fertility and hatchability) was evaluated in mating groups for a 20-day period. BDE-47 exposure via food from larval through juvenile life stages of medaka fish resulted in steady accumulation with time dose-dependently. This accumulation tendency rapidly decreased after dosing ended. The growth rates showed a significant increase only at the highest concentration 70days after exposures finished. The histological survey did not reveal BDE-47-related alterations in the condition of the potential target organs. However, a morphometrical approach suggested BDE-47-related differences in the thickness of the epithelium that lines thyroid follicles. The reproduction studies showed comparable values for the fecundity, fertility and hatching rates. Dietary BDE-47 dosed for 40days to growing medaka fish did not alter the phenotypic sex ratios at maturity. The dietary approach used herein could not provide conclusive evidence of effects on medaka development and thriving despite the fact that BDE-47 underwent rapid accumulation in whole fish during the 40-day treatment.

Reproductive Effects of Two Polybrominated Diphenyl Ethers on the Rotifer Brachionus plicatilis

The effects of two polybrominated diphenyl ethers (PBDEs) on the reproduction of the rotifer Brachionus plicatilis were investigated. Results showed that sexual maturation was promoted by tetra-brominated diphenyl ether-47 (BDE-47) and deca-brominated diphenyl ether-209 (BDE-209), whereas fecundity was inhibited by BDE-47, but promoted by BDE-209. Additionally, both PBDEs affected the expression of two genes, vasa and nanos mRNA, related to rotifer reproduction. This suggests a possible regulatory molecular mechanism at the transcriptional level. Our research extends the current knowledge of the ecotoxicological mechanism induced by PBDEs and provides further essential information for assessing the risks of PBDE contamination in marine ecosystems.

Microcystin-LR exposure induces developmental neurotoxicity in zebrafish embryo

Microcystin-LR (MCLR) is a commonly acting potent hepatotoxin and has been pointed out of potentially causing developmental neurotoxicity, but the exact mechanism is little known. In this study, zebrafish embryos were exposed to 0, 0.8, 1.6 or 3.2 mg/L MCLR for 120 h. MCLR exposure through submersion caused serious hatching delay and body length decrease. The content of MCLR in zebrafish larvae was analyzed and the results demonstrated that MCLR can accumulate in zebrafish larvae. The locomotor speed of zebrafish larvae was decreased. Furthermore, the dopamine and acetylcholine (ACh) content were detected to be significantly decreased in MCLR exposure groups. And the acetylcholinesterase (AChE) activity was significantly increased after exposure to 1.6 and 3.2 mg/L MCLR. The transcription pattern of manf, chrnα7 and ache gene was consistent with the change of the dopamine content, ACh content and AChE activity. Gene expression involved in the development of neurons was also measured. ɑ1-tubulin and shha gene expression were down-regulated, whereas mbp and gap43 gene expression were observed to be significantly up-regulated upon exposure to MCLR. The above results indicated that MCLR-induced developmental toxicity might attribute to the disorder of cholinergic system, dopaminergic signaling, and the development of neurons.

Molecular cloning, characterization, and the response of Cu/Zn superoxide dismutase and catalase to PBDE-47 and -209 from the freshwater bivalve Anodonta woodiana

Polybrominated diphenyl ethers-47 (PBDE-47) and -209 are significant components of total PBDEs in water and can catalyze the production of reactive oxygen species (ROS) in the organisms. Anti-oxidant enzymes play an important role in scavenging the high level of ROS. In the current study, two full-length cDNAs of Cu/Zn superoxide dismutase (CuZnSODs) and catalase (CAT) were isolated from freshwater bivalve Anodonta woodiana by rapid amplification of cDNA ends approach and respectively named as AwSOD and AwCAT. The nucleotide sequence of AwSOD cDNA had an open reading frame (ORF) of 465 bp encoding a polypeptide of 155 amino acids in which signature 1 GKHGFHVHEFGDNT and signature 2 GNAGARSACGVI of SODs were observed. Deduced amino acid sequence of AwSOD showed a significant similarity with that of CuZnSODs. AwCAT had an ORF 1536 bp encoding a polypeptide of 512 amino acids which contains a conserved catalytic site motif, and a proximal heme-ligand signature motif of CATs. The time-course expressions of AwSOD and AwCAT in hepatopancreas were measured by quantitative real-time PCR. Expressions of AwSOD and AwCAT showed a significant up-regulation in groups at a low concentration treatment of PBDE-47, a biphasic pattern in groups with a high concentration treatment. Administration of PBDE-209 could result in an up-regulation of AwSOD and AwCAT expressions with time- and dose-dependent matter. These results indicate that up-regulations of AwSOD and AwCAT expression of hepatopancreas of freshwater bivalve A. woodiana contribute to eliminate oxidative stress derived from PBDE-47 and -209 treated.

Physiological effects of polybrominated diphenyl ether (PBDE-47) on pregnant gartersnakes and resulting offspring

Polybrominated diphenyl ethers (PBDEs) are used as flame retardants and are persistent contaminants found in virtually every environment and organism sampled to date, including humans. There is growing evidence that PBDEs are the source of thyroid, neurodevelopmental, and reproductive toxicity. Yet little work has focused on how this pervasive contaminant may influence the reproduction and physiology of non-traditional model species. This is especially critical because in many cases non-model species, such as reptiles, are most likely to come into contact with PBDEs in nature. We tested how short-term, repeated exposure to the PBDE congener BDE-47 during pregnancy affected physiological processes in pregnant female gartersnakes (thyroid follicular height, bactericidal ability, stress responsiveness, reproductive output, and tendency to terminate pregnancy) and their resulting offspring (levels of corticosterone, bactericidal ability, and size differences). We found potential effects of BDE-47 on both the mother, such as increased size and higher thyroid follicular height, and her offspring (increased size), suggesting the effects on physiological function of PBDEs do indeed extend beyond the traditional rodent models.

Video-tracking of zebrafish (Danio rerio) as a biological early warning system using two distinct artificial neural networks: Probabilistic neural network (PNN) and self-organizing map (SOM)

Biological early warning systems (BEWS) are becoming very important tools in ecotoxicological studies because they can detect changes in the behavior of organisms exposed to toxic substances. In this work, a video tracking system was fully developed to detect the presence of commercial bleach (NaOCl) in water in three different concentrations (0.0005%; 0.0010% and 0.0020% (v/v)) during one hour of exposure. Zebrafish was selected as the test organism because it is widely used in many different areas and studies. Two distinct statistical models were developed, using probabilistic neural network (PNN) and correspondence analysis associated with self-organizing map (SOM-CA). The diagnosis was based only in the analysis of a few behavioral components of the fish, namely: mean angular velocity, mean linear velocity, spatial dispersion, mean value of the X coordinate and mean value of the Y coordinate. Both models showed good results in their diagnosis capabilities. However, the overall performance (accuracy) was always superior in the PNN model. The worst result was with the SOM-CA model, at the lowest concentration (0.0005% v/v), achieving only 65% of correct diagnosis. The best result was with the PNN model, at the highest concentration (0.0020% v/v), achieving 94% of correct diagnosis.

Developmental exposures to waterborne abused drugs alter physiological function and larval locomotion in early life stages of medaka fish

Environmental pollution by neuroactive pharmaceuticals from wastewater discharge is a major threat to aquatic ecosystems. However, the ecotoxicologic effect of waterborne abused drugs remains unclear. Embryos of medaka fish (Oryzias latipes) were exposed to aqueous solutions of 2 hallucinogenic drugs, ketamine (KET) and methamphetamine (MET) (0.004-40μM) to assess developmental toxicity, oxidative stress and behavioral alteration in early life stages. The environmentally relevant concentration (0.004μM) of both KET and MET significantly delayed blood circulation and hatching time in embryos and altered larval swimming behavior (e.g., maximum velocity and relative turn angle). KET and MET induced similar oxidative stress responses in embryos, which were unrecoverable in hatchlings in drug-free solutions. Early life exposure to the 2 drugs conferred distinct patterns in larval locomotion: KET induced hyperactivity and a less tortuous swimming path, but MET-treated larvae showed hypoactivity and a clockwise swimming direction at high doses. The alteration in locomotor responses were generally similar in mammals and zebrafish. We report sensitive biomarkers (e.g., heartbeat, hatching and swimming behavior) by developmental stage of medaka that reflect environmentally relevant exposures of abused drugs. They could be useful for ecological risk assessment of waterborne neuroactive drugs. The toxicity results implicate a potential ecotoxicological impact of controlled or abused drugs on fish development and populations in aquatic environments.

Neurotoxicity of FireMaster 550® in zebrafish (Danio rerio): Chronic developmental and acute adolescent exposures

BACKGROUND

FireMaster® 550 (FM 550) is the second most commonly used flame retardant (FR) product in consumer goods and has been detected in household dust samples. However, neurobehavioral effects associated with exposure have not been characterized in detail. We investigated the behavioral effects of FM 550 in zebrafish to facilitate the integration of the cellular and molecular effects of FM 550 with its behavioral consequences. The effects of developmental FM 550 exposure on zebrafish larvae swimming shortly after the end of exposure as well as the persisting effects of this exposure on adolescent behavior were studied. In addition, the acute effects of FM 550 on behavior with exposure during adolescence in zebrafish were studied.

METHODS

Developmental exposure to 0, 0.01, 0.1 or 1 mg/L of FM 550 via immersion spanned 0-5 days post fertilization, with larval testing on day 6 and adolescent testing on days 40-45. Acute adolescent (45 dpf) exposure was to 0, 1.0 or 3.0 mg/L of FM 550 via immersion, for 24 h, with testing 2 h or 1 week later. The vehicle condition was colony tank water with .0004% (developmental) or .0012% (adolescent) DMSO. Zebrafish behavior was characterized across several domains including learning, social affiliation, sensorimotor function, predator escape, and novel environment exploration.

RESULTS

Persisting effects of developmental FM 550 exposure included a significant (p<0.01) reduction in social behavior among all dose groups. Acute FM 550 exposure during adolescence caused hypoactivity and reduced social behavior (p's<0.05) when the fish were tested 2 h after exposure. These effects were attenuated at the 1 week post exposure testing point

DISCUSSION

Taken together, these data indicate that FM 550 may cause persisting neurobehavioral alterations to social behavior in the absence of perturbations along other behavioral domains and that developmental exposure is more costly to the organism than acute adolescent exposure.

Persisting effects of a PBDE metabolite, 6-OH-BDE-47, on larval and juvenile zebrafish swimming behavior

Polybrominated diphenyl ethers (PBDEs) are persistent organic pollutants that are widely detected in the environment, biota, and humans. In mammals, PBDEs can be oxidatively metabolized to form hydroxylated polybrominated diphenyl ethers (OH-BDEs). While studies have examined behavioral deficits or alterations induced by exposure to PBDEs in both rodents and fish, no study to date has explored behavioral effects from exposure to OH-BDEs, which have been shown to have greater endocrine disrupting potential compared to PBDEs. In the present study, zebrafish (Danio rerio) were exposed during embryonic and larval development (0-6 days post fertilization, dpf) to a PBDE metabolite, 6-hydroxy, 2,2',4,4' tetrabromodiphenyl ether (10-50 nM) and then examined for short and long-term behavioral effects. Exposed zebrafish tested as larvae (6 dpf) showed an altered swimming response to light-dark transitions, exhibiting hypoactivity in light periods compared to control fish. When fish exposed from 0-6 dpf were tested as juveniles (45 dpf), they showed an increased fear response and hyperactivity in response to tests of novel environment exploration and habituation learning. These results demonstrate that early life exposure to a PBDE metabolite can have immediate or later life (more than a month after exposure) effects on activity levels, habituation, and fear/anxiety.

Effects of titanium dioxide nanoparticles on lead bioconcentration and toxicity on thyroid endocrine system and neuronal development in zebrafish larvae

Nanoparticles (NPs) have attracted considerable attention because of their wide range of applications. Interactions between heavy metals (e.g., Pb) and NPs in aquatic environments may modify the bioavailability and toxicity of heavy metals. Therefore, this study investigated the influence of NPs (e.g., nano-TiO2) on the bioavailability and toxicity of Pb and its effects in the thyroid endocrine and nervous systems of zebrafish (Danio rerio) larvae. Zebrafish embryos (2-h post-fertilization) were exposed to five concentrations of Pb alone (0, 5, 10, 20, and 30μg/L) or in combination with nano-TiO2 (0.1mg/L) until 6 days post-fertilization. Results showed that the bioconcentration of Pb was significantly enhanced when combined with nano-TiO2 than when used alone. Zebrafish exposure to Pb alone at 30μg/L significantly decreased the thyroid hormone levels (T4 and T3), whereas nano-TiO2 treatment alone did not produce detectable changes. The levels of T4 and T3 were further decreased when Pb was combined with nano-TiO2 than when used alone. The transcription of the thyroid hormone-related factor tg gene was remarkably down-regulated by Pb treatment alone but up-regulated when Pb was combined with nano-TiO2. The significant up-regulation of tshβ gene and the down-regulation of TTR gene expression in the hypothalamic-pituitary-thyroid were observed in Pb with or without nano-TiO2 treatment groups. In addition, the transcription of genes involved in central nervous system (CNS) development (α-tubulin, mbp, gfap and shha) were significantly down-regulated by Pb and nano-TiO2 co-exposure as compared with Pb exposure alone. The locomotion activity analyzes confirmed that nano-TiO2 might enhance the toxicity of Pb to CNS development. These results suggest that nano-TiO2 increase bioconcentration of lead, which lead to the disruption of thyroid endocrine and neuronal system in zebrafish larvae.

Bioaccumulation, biotransformation, and toxicity of BDE-47, 6-OH-BDE-47, and 6-MeO-BDE-47 in early life-stages of zebrafish (Danio rerio)

2,2',4,4'-Tetrabromodiphenyl ether (BDE-47), 6-hydroxy-tetrabromodiphenyl ether (6-OH-BDE-47), and 6-methoxy-tetrabromodiphenyl ether (6-MeO-BDE-47) are the most detected congeners of polybrominated diphenyl ethers (PBDEs), OH-BDEs, and MeO-BDEs, respectively, in aquatic organisms. Although it has been demonstrated that BDE-47 can interfere with certain endocrine functions that are mediated through several nuclear hormone receptors (NRs), most of these findings were from mammalian cell lines exposed in vitro. In the present study, embryos and larvae of zebrafish were exposed to BDE-47, 6-OH-BDE-47, and 6-MeO-BDE-47 to compare their accumulation, biotransformation, and bioconcentration factors (BCF) from 4 to 120 hpf. In addition, effects on expression of genes associated with eight different pathways regulated by NRs were investigated at 120 hpf. 6-MeO-BDE-47 was most bioaccumulated and 6-OH-BDE-47, which was the most potent BDE, was least bioaccumulated. Moreover, the amount of 6-MeO-BDE-47, but not BDE-47, transformed to 6-OH-BDE-47 increased in a time-dependent manner, approximately 0.01%, 0.04%, and 0.08% at 48, 96, and 120 hpf, respectively. Expression of genes regulated by the aryl hydrocarbon receptor (AhR), estrogen receptor (ER), and mineralocorticoid receptor (MR) was affected in larvae exposed to 6-OH-BDE-47, whereas genes regulated by AhR, ER, and the glucocorticoid receptor (GR) were altered in larvae exposed to BDE-47. The greatest effect on expression of genes was observed in larvae exposed to 6-MeO-BDE-47. Specifically, 6-MeO-BDE-47 affected the expression of genes regulated by AhR, ER, AR, GR, and thyroid hormone receptor alpha (TRα). These pathways were mostly down-regulated at 2.5 μM. Taken together, these results demonstrate the importance of usage of an internal dose to assess the toxic effects of PBDEs. BDE-47 and its analogs elicited distinct effects on expression of genes of different hormone receptor-mediated pathways, which have expanded the knowledge of different mechanisms of endocrine disrupting effects in aquatic vertebrates. Because some of these homologues are natural products, assessments of risks of anthropogenic PBDE need to be made against the background of concentrations from naturally occurring products. Even though PBDEs are being phased out as flame retardants, the natural products remain.

Effect of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) on sexual behaviors and reproductive function in male zebrafish (Danio rerio)

BACKGROUND

Polybrominated diphenyl ethers (PBDEs) are ubiquitous in various environmental matrices and organisms and pose a threat to reproductive systems of organisms. However, few studies have explored the effects of PBDEs on sexual and reproductive behaviors in animals. Here we evaluated the effect of BDE-47 exposure on sexual and reproductive behaviors in zebrafish (Danio rerio).

METHODS

We used a charge-coupled device camera to evaluate 3 standard male zebrafish sexual behaviors—chasing, female association and induced female spawning—and assessed effects on reproductive success in female zebrafish that mated with exposed males.

RESULTS

After 21-day BDE-47 exposure, the frequency and total time of males associating with females was dose-dependently decreased. With the highest BDE-47 exposure, 1000 µg/L, the frequency of inducing spawning was decreased. Sexual behaviors and spawning outcome were closely associated in both control and exposure groups. Logistic regression analysis revealed BDE-47 exposure and total time of female association as the main factors contributing to induced female spawning behaviors, which affected final egg production. Multiple stepwise regression analysis suggested that female association and induced spawning by males were associated with egg production. Meanwhile, fecundity was lower for BDE-47-treated groups than controls, with only a significant difference with the highest dose. BDE-47 exposure at 100 and 1000 µg/L in males decreased fertilization rate, but BDE47 had no effect on hatching rate.

CONCLUSIONS

Exposure to BDE-47 may affect sexual behavior and reproductive output in zebrafish.

Dietary exposure of BDE-47 and BDE-99 and effects on behavior, bioenergetics, and thyroid function in juvenile red-eared sliders (Trachemys scripta elegans) and common snapping turtles (Chelydra serpentina)

Juvenile red-eared sliders (Trachemys scripta elegans) and snapping turtles (Chelydra serpentina) were fed food dosed with brominated diphenyl ether-47 (BDE-47) or BDE-99 for 6 mo beginning approximately 9 mo posthatch. During the exposure period, measurements of growth, bioenergetics, and behavior were made; thyroid function and accumulation were quantified postexposure. Whole-body concentrations of both congeners were lower in red-eared sliders compared with snapping turtles after 6 mo of exposure. Snapping turtles receiving BDE-47 had significantly elevated standard metabolic rates after 3 mo and 4 mo of exposure (p = 0.014 and p = 0.019, respectively). When exposed to BDE-99, red-eared sliders were slower to right themselves after having been inverted (p < 0.0001). Total glandular thyroxine concentrations were significantly reduced in red-eared sliders exposed to BDE-47 (mean control, 8080 ng/g; mean BDE-47, 5126 ng/g; p = 0.034). These results demonstrate that dietary exposure to BDE-47 and BDE-99 can elicit a suite of responses in 2 species of turtles, but that the red-eared slider appears to be a more sensitive species to the measured end points.

Interactive effects of hypoxia and polybrominated diphenyl ethers (PBDEs) on microbial community assembly in surface marine sediments

Hypoxia alters the oxidation-reduction balance and the biogeochemical processes in sediments, but little is known about its impacts on the microbial community that is responsible for such processes. In this study, we investigated the effects of hypoxia and the ubiquitously dispersed flame-retardant BDE47 on the bacterial communities in marine surface sediments during a 28-days microcosm experiment. Both hypoxia and BDE47 alone significantly altered the bacterial community and reduced the species and genetic diversity. UniFrac analysis revealed that BDE47 selected certain bacterial species and resulted in major community shifts, whereas hypoxia changed the relative abundances of taxa, suggesting slower but nonetheless significant community shifts. These two stressors targeted mostly different taxa, but they both favored Bacteroidetes and suppressed Gammaproteobacteria. Importantly, the impacts of BDE47 on bacterial communities were different under hypoxic and normoxic conditions, highlighting the need to consider risk assessments for BDE47 in a broader context of interaction with hypoxia.

Fathead minnow (Pimephales promelas Rafinesque) exposure to three novel brominated flame retardants in outdoor mesocosms: bioaccumulation and biotransformation

The phaseout of polybrominated diphenyl ethers (PBDEs) has prompted the search for appropriate substitutes. These substitutes, referred to as novel brominated flame retardants (NBFRs), are poorly characterized in terms of their persistence, bioaccumulation, and toxicity. The authors assessed the bioaccumulation potential of 3 non-PBDE brominated flame retardants: 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), tetrabromobisphenol A bis(2,3-dibromopropylether) (TBBPA-BDBPE), and BZ-54, a mixture of bis(2-ethylhexyl)tetrabromophthalate) (BEH-TEBP) and 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (EH-TBB). Replicate outdoor aquatic mesocosms were treated individually at concentrations designed to give a maximum load of 500 ng/g of flame retardant in the upper 5 cm of the sediment. Caged fathead minnows (Pimephales promelas, 24 fish per replicate) were introduced to each mesocosm and acclimated for 10 d prior to exposure. The exposure period was 42 d, followed by 28 d of depuration after transfer to a control mesocosm, during which physical, reproductive, and biochemical end points were examined. Tissue samples were taken to measure the accumulation, depuration, and biotransformation of NBFRs. Fathead minnows were observed to accumulate, after growth adjustment, BTBPE (16-4203 ng/g lipid) and TBBPA-BDBPE (>1000 ng/g lipid) but with a lack of consistent accumulation observed for EH-TBB and BEH-TEBP. However, limited biologically meaningful or consistent responses were observed in the monitored physical, reproductive, and biochemical parameters. Fathead minnows from each treatment exhibited several brominated transformation products. The authors conclude that these NBFRs have the potential to be bioaccumulative and persistent in vivo and, therefore, warrant further study of physiological effects linked to chronic, sublethal responses.

Multigenerational effects of benzo[a]pyrene exposure on survival and developmental deformities in zebrafish larvae

In the aquatic environment, adverse outcomes from dietary polycyclic aromatic hydrocarbon (PAH) exposure are poorly understood, and multigenerational developmental effects following exposure to PAHs are in need of exploration. Benzo[a]pyrene (BaP), a model PAH, is a recognized carcinogen and endocrine disruptor. Here adult zebrafish (F0) were fed 0, 10, 114, or 1,012 μg BaP/g diet at a feed rate of 1% body weight twice/day for 21 days. Eggs were collected and embryos (F1) were raised to assess mortality and time to hatch at 24, 32, 48, 56, 72, 80, and 96 h post fertilization (hpf) before scoring developmental deformities at 96 hpf. F1 generation fish were raised to produce the F2 generation followed by the F3 and F4 generations. Mortality significantly increased in the higher dose groups of BaP (2.3 and 20 μg BaP/g fish) in the F1 generation while there were no differences in the F2, F3, or F4 generations. In addition, premature hatching was observed among the surviving fish in the higher dose of the F1 generation, but no differences were found in the F2 and F3 generations. While only the adult F0 generation was BaP-treated, this exposure resulted in multigenerational phenotypic impacts on at least two generations (F1 and F2). Body morphology deformities (shape of body, tail, and pectoral fins) were the most severe abnormality observed, and these were most extreme in the F1 generation but still present in the F2 but not F3 generations. Craniofacial structures (length of brain regions, size of optic and otic vesicles, and jaw deformities), although not significantly affected in the F1 generation, emerged as significant deformities in the F2 generation. Future work will attempt to molecularly anchor the persistent multigenerational phenotypic deformities noted in this study caused by BaP exposure.