Effects of BDE-209 contaminated sediments on zebrafish development and potential implications to human health

The role of chorion integrity on the bioaccumulation and toxicity of selenium nanoparticles in Japanese medaka (Oryzias latipes)

Selenium nanoparticles (nano-Se) have a wide range of biomedical and agricultural applications. However, there is little information on the potential toxicity of nano-Se once it enters the environment, particularly in fish. The first line of defense from contaminants that embryonic fish have is the chorion, but the degree to which the chorion protects the developing embryo is unknown. Japanese medaka (Oryzias latipes) embryos were exposed to nano-Se in a wide range of concentrations (0.1-400 µM). The importance of chorion integrity was evaluated by exposing embryos to 16 nm nano-Se under four degrees of dechorionation: intact, roughened, partially-dechorionated, fully-dechorionated. Then, effects of particle size on embryos and larvae were determined using four sizes of nano-Se particles (16, 25-50, 50, 100 nm). The results showed that nano-Se exposure reduced survival, development, and hatching. Nano-Se was observed to adsorb on the chorion, with the amount decreasing with increased degree of dechorionation. Toxicity increased with increasing degree of dechorionation, and smaller-sized nano-Se crossed intact chorion more readily and resulted in higher toxicity than larger ones. In larvae, nano-Se accumulated on the skin and was more toxic compared to embryos. This study demonstrated the importance of the chorion in protecting developing embryos and effects of nanoparticle size on its bioavailability and subsequent toxicity.

Endocytosis, endoplasmic reticulum, actin cytoskeleton affected in tilapia liver under polystyrene microplastics and BDE153 acute co-exposure

Studies showed that contaminants adhered to the surface of nano-polystyrene microplastics (NPs) have a toxicological effect. Juveniles tilapia were dispersed into four groups: the control group A, 75 nm NPs exposed group B, 5 ng·L-1 2,2',4,4',5,5'-hexabromodiphenyl ether group C (BDE153), and 5 ng·L-1 BDE153 + 75 nm MPs group D, and acutely exposed for 2, 4 and 8 days. The hepatic histopathological change, enzymatic activities, transcriptomics, and proteomics, have been performed in tilapia. The results showed that the enzymatic activities of anti-oxidative (ROS, SOD, EROD), energy (ATP), lipid metabolism (TC, TG, FAS, LPL, ACC), pro-inflammatory (TNFα, IL-1β) and apoptosis (caspase 3) significantly increased at 2 d in BDE153 and the combined group and together in BDE153 group at 8 d. Histological slice showed displaced nucleus by BDE153 exposure and vacuoles appeared in the combined groups. KEGG results revealed that pathways associated with endocytosis, protein processing in endoplasmic reticulum and regulation of actin cytoskeleton were significantly enriched. The selected genes associated with neurocentral development (ganab, diaph3/baiap2a/ddost decreased and increased), lipid metabolism (ldlrap1a decreased, stt3b increased), energy (agap2 decreased, uggt1 increased) were affected under co-exposure, and fibronectin significantly increased via proteome. Our study indicated that endocytosis, protein processing in endoplasmic reticulum, regulation of actin cytoskeleton were affected in tilapia liver under NPs and BDE153 co-exposure.

Recoverability of zebrafish from decabromodiphenyl ether exposure: The persisted interference with extracellular matrix production and collagen synthesis and the enhancement of arrhythmias

As a widely used brominated flame retardant, the widespread presence of decabromodiphenyl ether (BDE-209) in the natural environment and the toxicity risks it poses are well established, but the recoverability of BDE-209-induced individual injuries remains unknown. Therefore, a 7-day depuration experiment following a 4-day exposure of zebrafish to BDE-209 was conducted to confirm the recoverability and its mode of action. Oxidative stress after depuration was significantly reduced compared with BDE-209 exposure as indicated by the decreased expression level of oxidative stress-related genes and the reduced MDA, Gpx, and GST in zebrafish, indicating a gradual recovery of antioxidant activity. However, BDE-209 inhibition of extracellular matrix (ECM) proteins worsened after depuration. Mechanistically, BDE-209 mediated ECM production and secretion by down-regulating integrin expression. Furthermore, BDE-209 inhibition of collagen synthesis worsened after depuration. Biochemical assays and histopathological observations revealed a same result in zebrafish. Mechanistically, lysine hydroxylation is inhibited thereby affecting collagen synthesis. Interestingly, zebrafish showed arrhythmia after depuration compared to BDE-209 exposure, and abnormal changes in ATPase levels indicated that disturbances in Ca2+ homeostasis contributed to arrhythmia. Collectively, BDE-209-induced interference with ECM production and collagen synthesis persisted after depuration, which will provide new insights for understanding the recovery patterns of individuals under BDE-209 stress.

A critical review on BDE-209: Source, distribution, influencing factors, toxicity, and degradation

As the most widely used polybrominated diphenyl ether, BDE-209 is commonly used in polymer-based commercial and household products. Due to its unique physicochemical properties, BDE-209 is ubiquitous in a variety of environmental compartments and can be exposed to organisms in various ways and cause toxic effects. The present review outlines the current state of knowledge on the occurrence of BDE-209 in the environment, influencing factors, toxicity, and degradation. BDE-209 has been detected in various environmental matrices including air, soil, water, and sediment. Additionally, environmental factors such as organic matter, total suspended particulate, hydrodynamic, wind, and temperature affecting BDE-209 are specifically discussed. Toxicity studies suggest BDE-209 may cause systemic toxic effects on living organisms, reproductive toxicity, embryo-fetal toxicity, genetic toxicity, endocrine toxicity, neurotoxicity, immunotoxicity, and developmental toxicity, or even be carcinogenic. BDE-209 has toxic effects on organisms mainly through epigenetic regulation and induction of oxidative stress. Evidence regarding the degradation of BDE-209, including biodegradation, photodegradation, Fenton degradation, zero-valent iron degradation, chemical oxidative degradation, and microwave radiation degradation is summarized. This review may contribute to assessing the environmental risks of BDE-209 to help develop rational management plans.

Endocrine disrupting and carcinogenic effects of decabromodiphenyl ether

Background

Decabromodiphenyl ether (BDE209), an essential industrial flame retardant that is widely used, has recently been reported to be increasing in human serum. Due to the structural similarity between BDE209 and thyroid hormones, its toxic effects on the thyroid are of particular concern.

Methods

Original articles in the PubMed database were collected using the terms "BDE209", "decabromodiphenyl ether", "endocrine disrupting", "thyroid", "carcinogenesis", "polybrominated diphenyl ethers", "PBDEs," and their synonyms from inception up to October of 2022.

Results

Of the 748 studies initially identified, 45 were selected, which emphasized the adverse effects of BDE209 on endocrine system. BDE209 may have a toxic effect not only on thyroid function but also on thyroid cancer tumorigenesis at multiple levels, such as by directly interfering with the TR, hypothalamic-pituitary-thyroid (HPT) axis, enzyme activity, and methylation. However, it is impossible to draw a definitive conclusion on the exact pathway of thyroid toxicity from BDE209.

Conclusions

Although the toxic effects of BDE209 on the thyroid have been well investigated, its tumorigenic effects remain unclear and further research is necessary.

Combined effects of climate change and BDE-209 dietary exposure on the behavioural response of the white seabream, Diplodus sargus

Decabromodiphenyl-ether (BDE-209) is a persistent organic pollutant ubiquitously found in marine environments worldwide. Even though this emerging chemical contaminant is described as highly toxic, bioaccumulative and biomagnifiable, limited studies have addressed the ecotoxicological implications associated with its exposure in non-target marine organisms, particularly from a behavioural standpoint. Alongside, seawater acidification and warming have been intensifying their impacts on marine ecosystems over the years, compromising species welfare and survival. BDE-209 exposure as well as seawater acidification and warming are known to affect fish behaviour, but information regarding their interactive effects is not available. In this study, long-term effects of BDE-209 contamination, seawater acidification and warming were studied on different behavioural traits of Diplodus sargus juveniles. Our results showed that D. sargus exhibited a marked sensitivity in all the behaviour responses after dietary exposure to BDE-209. Fish exposed to BDE-209 alone revealed lower awareness of a risky situation, increased activity, less time spent within the shoal, and reversed lateralization when compared to fish from the Control treatment. However, when acidification and/or warming were added to the equation, behavioural patterns were overall altered. Fish exposed to acidification alone exhibited increased anxiety, being less active, spending more time within the shoal, while presenting a reversed lateralization. Finally, fish exposed to warming alone were more anxious and spent more time within the shoal compared to those of the Control treatment. These novel findings not only confirm the neurotoxicological attributes of brominated flame retardants (like BDE-209), but also highlight the relevance of accounting for the effects of abiotic variables (e.g. pH and seawater temperature) when investigating the impacts of environmental contaminants on marine life.

Developmental exposure to sertraline impaired zebrafish behavioral and neurochemical profiles

The number of people suffering from mental health problems is rising, with anxiety and depression now the most commonly diagnosed psychiatric conditions. Selective serotonin reuptake inhibitors (SSRIs) are one of the most prescribed pharmaceuticals to treat these conditions, which has led to their common detection in many aquatic ecosystems. As the monoaminergic system shows a high degree of structural conservation across diverse animal phyla, a reasonable assumption is that the environmental levels of SSRIs in surface water can lead to adverse effects on fish and other aquatic wildlife. For instance, Sertraline (SER), a widely prescribed SSRI, has been shown to induce adverse effects in fish, albeit most of the reports used exposure concentrations exceeding those occurring in natural environments. Therefore, there is still a great lack of knowledge regarding SERs effects in fish species, especially during early life stages. This study describes the evaluation of developmental exposure of zebrafish (Danio rerio) to environmentally relevant concentrations of SER (from 0.01 to 10 μg/L), using a battery of key survival behaviors and further relating them with the expression of genes and neurochemical profiles of the monoaminergic system. We found that developmental exposure to SER did not affect embryo morphogenesis and growth. However, concentrations as low as 0.1 μg/L induced hypolocomotion and delayed learning. The observed behavioral impairment was associated with augmented serotonin levels rather than other neurochemicals and molecular markers, highlighting the relationship between serotonin signaling and behavior in zebrafish.

Decabromodiphenyl ethane induces locomotion neurotoxicity and potential Alzheimer's disease risks through intensifying amyloid-beta deposition by inhibiting transthyretin/transthyretin-like proteins

As a major alternative to traditional brominated flame retardants (BFRs), decabromodiphenyl ethane (DBDPE) is widely used and has been commonly detected in various environmental media and organisms. Few previous studies have focused on DBDPE-induced locomotion neurotoxicity, and the exact molecular mechanisms and related health risks remain unclear. In this study, we first analyzed the locomotion indicators of nematodes following DBDPE exposure, demonstrated that DBDPE caused locomotion neurotoxicity, and identified that a series of the transthyretin (TTR)-like genes participated in the regulation of nematode motility by transcriptomic analysis, gene transcription validation and TTR-like mutant verification. Subsequently, this study demonstrated that DBDPE exacerbated amyloid-beta (Aβ) deposition by repressing TTR/TTR-like gene transcription based on Alzheimer's disease (AD) model nematodes and human SH-SY5Y cells following DBDPE exposure and further revealed that DBDPE reduced the binding between TTR and Aβ by competing with the strand G region sites on the TTR/TTR-like protein, ultimately exacerbating Aβ deposition and the risk of AD. In short, our study demonstrated that DBDPE induced locomotion neurotoxicity and potential AD risks through intensifying Aβ deposition by inhibiting TTR/TTR-like proteins, providing reference support for risk management and policy formulation related to DBDPE and similarly structured novel BFRs.

Comparative Effects of Brominated Flame Retardants BDE-209, TBBPA, and HBCD on Neurotoxicity in Mice

Brominated flame retardants (BFRs) are ubiquitous industrial chemicals. In China, BFRs that are applied in large quantities include decabromodiphenyl ether (BDE-209), tetrabromobisphenol A (TBBPA), and hexabromocyclododecane (HBCD). Although findings are not always unequivocal, mounting evidence in vivo suggests that the BFRs have potential neurotoxicity. The present study aimed to assess and compare the neurotoxic effects of these three BFRs' exposure. Male mice were orally exposed to BDE-209, TBBPA, or HBCD at 50 and 100 mg/kg bw/day for 28 days. The cognitive behavior, oxidative stress (ROS, MDA, and GSH), apoptosis-related genes (caspase-3, bax, and bcl-2), memory-related proteins (BDNF and PSD-95), and neurotransmitters (AChE and ChAT) were detected comparatively. Results showed that high doses of BDE-209, TBBPA, and HBCD exposure impaired spatial memory of mice, elevated ROS and MDA and reduced GSH levels of hippocampus, upregulated caspase-3 and bax expressions, decreased BDNF and PSD-95 levels, and disordered AChE and ChAT levels. Notably, BDE-209 caused greater adverse effects > HBCD > TBBPA. This study confirms and extends that these three BFRs had similar neurotoxic effects at current concentrations, although they may be more or less toxic.

Comprehensive evaluation of the toxicity of the flame retardant (decabromodiphenyl ether) in a bioindicator fish (Gambusia affinis)

In recent years, concerns have increased about the adverse effects on health and the environment of polybrominated diphenyl ethers (PBDEs), especially BDE-209, the most widely PBDE used globally. These pollutants derive from e-waste and present different adverse effects on biota. In this work, a toxicological study on mosquitofish (Gambusia affinis) using BDE-209 (2,2',3,3',4,4',5,'5',6,6'-decabromodiphenyl ether) was carried out. Acute toxicity bioassays were conducted with daily renewal of solutions, using different concentrations of environmental relevance, ranged between 10 and 100 μg L^-1 of BDE-209. At 48 and 96 h of exposure, several parameters were evaluated, such as mortality, individual activity (swimming), biochemical activity (catalase; thiobarbituric acid-reactive substances; and acetylcholinesterase), and cytotoxic responses (micronucleus frequencies). In addition, integrated biomarker response and multivariate analyses were conducted to study the correlation of biomarkers. The calculated Lethal Concentration-50 remained constant after all exposure times (24 to 96 h), being the corresponding value 27.79 μg L^-1 BDE-209. Furthermore, BDE-209 induced effects on the swimming activity of this species in relation to acetylcholine, since BDE-209 increased, producing oxidative damage at the biochemical level and genotoxicity after 48 h of exposure to 10 and 25 μg L^-1 BDE-209. The results indicate that BDE-209 has biochemical, cytotoxic, neurotoxic, and genotoxic potential on G. affinis. In addition, mosquitofish could be used as a good laboratory model to evaluate environmental stressors since they could represent a risk factor for Neotropical species.

Environmental levels of carbaryl impair zebrafish larvae behaviour: The potential role of ADRA2B and HTR2B

The insecticide carbaryl is commonly found in indirectly exposed freshwater ecosystems at low concentrations considered safe for fish communities. In this study, we showed that after only 24 h of exposure to environmental concentrations of carbaryl (0.066-660 ng/L), zebrafish larvae exhibit impairments in essential behaviours. Interestingly, the observed behavioural effects induced by carbaryl were acetylcholinesterase-independent. To elucidate the molecular initiating event that resulted in the observed behavioural effects, in silico predictions were followed by in vitro validation. We identified two target proteins that potentially interacted with carbaryl, the α2B adrenoceptor (ADRA2B) and the serotonin 2B receptor (HTR2B). Using a pharmacological approach, we then tested the hypothesis that carbaryl had antagonistic interactions with both receptors. Similar to yohimbine and SB204741, which are prototypic antagonists of ADRA2B and HTR2B, respectively, carbaryl increased the heart rate of zebrafish larvae. When we compared the behavioural effects of a 24-h exposure to these pharmacological antagonists with those of carbaryl, a high degree of similarity was found. These results strongly suggest that antagonism of both ADRA2B and HTR2B is the molecular initiating event that leads to adverse outcomes in zebrafish larvae that have undergone 24 h of exposure to environmentally relevant levels of carbaryl.

Oxyfluorfen induces hepatotoxicity through lipo-sugar accumulation and inflammation in zebrafish (Danio rerio)

Oxyfluorfen (OXY) is widely used in agriculture as a herbicide, resulting in its continuous accumulation in the environment. The presence of OXY can be detected in soil and rivers. However, until now, the potential toxicity of OXY to aquatic organisms has not been evaluated. In this study, zebrafish was used as a model animal to evaluate OXY-induced liver toxicity. The study found that 0.25, 0.5, and 1 mg/L of OXY affected the early development of zebrafish and severely damaged the lipid and sugar metabolism in the liver of zebrafish larvae. Furthermore, a metabolic function disorder caused liver damage. OXY also caused inflammation by upregulating the inflammatory factors IL-6, IL-8, and TNF-α, and activated the apoptotic pathway to inhibit hepatocyte proliferation, resulting in zebrafish liver toxicity. Our research showed that OXY had certain toxic effects on zebrafish development and liver and could cause potential harm to other aquatic organisms and humans.

Emerging investigator series: metal nanoparticles in freshwater: transformation, bioavailability and effects on invertebrates

MNPs may undergo different environmental transformations in aquatic systems, consequently changing their mobility, bioavailability and toxicity to freshwater invertebrates.

DNA methylation changes induced by BDE-209 are related to DNA damage response and germ cell development in GC-2spd

Decabrominated diphenyl ether (BDE-209) is generally utilized in multiple polymer materials as common brominated flame retardant. BDE-209 has been listed as persistent organic pollutants (POPs), which was considered to be reproductive toxin in the environment. But it still remains unclear about the effects of BDE-209 on DNA methylation and the induced-male reproductive toxicity. Due to the extensive epigenetic regulation in germ line development, we hypothesize that BDE-209 exposure impacts the statue of DNA methylation in spermatocytes in vitro. Therefore, the mouse GC-2spd (GC-2) cells were used for the genome wide DNA methylation analysis after treated with 32 μg/mL BDE-209 for 24 hr. The results showed that BDE-209 caused genomic methylation changes with 32,083 differentially methylated CpGs in GC-2 cells, including 16,164 (50.38%) hypermethylated and 15,919 (49.62%) hypomethylated sites. With integrated analysis of DNA methylation data and functional enrichment, we found that BDE-209 might affect the functional transcription in cell growth and sperm development by differential gene methylation. qRT-PCR validation demonstrated the involvement of p53-dependent DNA damage response in the GC-2 cells after BDE-209 exposure. In general, our findings indicated that BDE-209-induced genome wide methylation changes could be interrelated with reproductive dysfunction. This study might provide new insights into the mechanisms of male reproductive toxicity under the environmental exposure to BDE-209.

Sediment toxicity assessment using zebrafish (Danio rerio) as a model system: Historical review, research gaps and trends

Sediment is an important compartment in aquatic environments and acts as a sink for environmental pollutants. Sediment toxicity tests have been suggested as critical components in environmental risk assessment. Since the zebrafish (Danio rerio) has been indicated as an emerging model system in ecotoxicological tests, a scientometric and systematic review was performed to evaluate the use of zebrafish as an experimental model system in sediment toxicity assessment. A total of 97 papers were systematically analyzed and summarized. The historical and geographical distributions were evaluated and the data concerning the experimental design, type of sediment toxicity tests and approach (predictive or retrospective), pollutants and stressors, zebrafish developmental stages and biomarkers responses were summarized and discussed. The use of zebrafish to assess the sediment toxicity started in 1996, using mainly a retrospective approach. After this, research showed an increasing trend, especially after 2014-2015. Zebrafish exposed to pollutant-bound sediments showed bioaccumulation and several toxic effects, such as molecular, biochemical, morphological, physiological and behavioral changes. Zebrafish is a suitable model system to assess the toxicity of freshwater, estuarine and marine sediments, and sediment spiked in the laboratory. The pollutant-bound sediment toxicity in zebrafish seems to be overall dependent on physical and chemical properties of pollutants, experimental design, environmental factor, developmental stages and presence of organic natural matter. Overall, results showed that the zebrafish embryos and larvae are suitable model systems to assess the sediment-associated pollutant toxicity.

2,4,6-Tribromophenol is toxic to Oreochromis niloticus (Linnaeus, 1758) after trophic and subchronic exposure

The presence of 2,4,6-Tribromophenol (TBP) in the environment increased the risk of exposure to aquatic organisms affecting the animal development or metabolism. The current study investigated the low, subchronic and trophic effect of TBP in both, male and female adult of Oreochromis niloticus. The fish were exposed to 0.5 or 50 ng g^-1 of TBP every ten days for 70 days. Then, hepatosomatic (HSI) and gonadosomatic (GSI) indexes, erythrocyte parameters (hemoglobin content, nuclear morphology and morphometrical abnormalities), biochemical endpoints (glutathione S-Transferase and catalase activities, non-protein thiols, lipid peroxidation and protein carbonylation levels in the liver; and acetylcholinesterase activity in the brain and muscle), histopathological analysis (liver) and vitellogenin levels (plasma) were considered. TBP affected the HSI in male and female fish, but not the GSI. Principal Component Analysis revealed that erythrocytes from males are more sensitive to TBP exposure. Likewise, TBP induced the expression of vitellogenin, CAT activity and liver lesion in male fish comparatively with control group, but GST and NPT were influenced only by sex. Finally, the results showed that the antioxidant mechanism and cholinesterase activity effects were more pronounced in male than in female. The current data shows evidences of estrogenic endocrine disruption and toxicity in O. niloticus exposed to TBP, revealing the risk of exposure to biota.

Association between fetal growth restriction and maternal exposure to polybrominated diphenyl ethers

Humans are exposed to polybrominated diphenyl ethers (PBDEs) via ingestion of food, dust inhalation, and dermal absorption. Exposure to PBDEs via the placenta and breast milk is a special and important pathway in infants. This nested case-control study aimed to investigate the levels of PBDEs in maternal serum and colostrum, and to assess the association between the occurrence of fetal growth restriction (FGR) and prenatal exposure to PBDEs. We recruited 293 mother-newborn pairs, including 98 FGR cases and 195 healthy controls in Wenzhou, China. Maternal serum and colostrum samples were collected during pregnancy and after delivery, respectively, and the levels of PBDEs were measured by gas chromatography-tandem mass spectrometry. The total levels of PBDEs in maternal serum and colostrum were found to be in equilibrium, but congener profiles of PBDEs in these matrices were different. Increased BDE-207, BDE-209, ∑BDE196-209 and ∑PBDEs levels in maternal serum and BDE-99, ∑BDE17-154 and ∑PBDEs levels in colostrum were correlated with decreased birth weight Z score. Increased concentrations of higher brominated BDEs in maternal serum (odds ratio (OR) = 1.010, 95%CI = 1.003-1.018) and low-to moderately brominated BDEs in colostrum (OR = 1.004, 95%CI = 1.000-1.009) were associated with increased risk of FGR, which showed an exposure-response relationship. In addition, infants with FGR were more exposed to PBDEs in colostrum after birth than healthy infants. Longitudinal birth cohort studies are needed to determine the prolonged effect of PBDEs exposure on the growth of FGR infants in the future.

Thiophanate-methyl induces severe hepatotoxicity in zebrafish

Thiophanate-methyl (TM) is widely used all over the world and is a typical example of pesticide residues, which can be detected in the soil, and even in vegetables and fruits. However, the molecular mechanisms underlying the hepatotoxicity of TM are not well understood. In this study, we utilized zebrafish to comprehensively evaluate the hepatotoxicity of TM and explore how the molecular mechanisms of hepatotoxicity are induced. The zebrafish larvae were exposed in 6.25, 12.5 and 25 mg/L TM from 72 to 144 hpf, while the adults were exposed in 2, 4 and 6 mg/L TM for 28 days. Here, we found that 12.5 and 25 mg/L TM induces specifically serious hepatotoxicity but not the toxicity of other organs in zebrafish larvae and adults. Moreover, it might triggered hepatotoxicity by activating the caspase-3 through apoptotic pathways and oxidative stress in zebrafish. Subsequently, this resulted in a metabolic imbalance in the zebrafish's liver. In conclusion, our results disclosed the fact that TM may induce severe hepatotoxicity by mediating activation of caspase-3 and oxidative stress in zebrafish.

Examining multi- and transgenerational behavioral and molecular alterations resulting from parental exposure to an environmental PCB and PBDE mixture

Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are persistent organic pollutants extensively used during the 20^th century and still present in aquatic environments despite their ban. Effects of exposure to these compounds over generations are poorly documented. Therefore, our aims were to characterize behavioral responses and underlying molecular mechanisms in zebrafish exposed to an environmentally relevant mixture of PCBs and PBDEs as well as in four unexposed offspring generations. Zebrafish (F0) were chronically exposed from the first meal onward to a diet spiked with a mixture containing 22 PCB and 7 PBDE congeners in proportions and concentrations reflecting environmental situations (ΣPCBs = 1991 and ΣPBDEs = 411 ng/g). Four offspring generations (F1 to F4) were obtained from this F0 and were not further exposed. Behavior was assessed at both larval and adult stages. Mechanisms related to behavioral defects (habenula maturation and c-fos transcription) and methylation (dnmts transcription) were monitored in larvae. Exposed adult F0 as well as F1 and F3 adults displayed no behavioral change while F2 expressed anxiety-like behavior. Larval behavior was also disrupted, i.e. hyperactive after light to dark transition in F1 or hypoactive in F2, F3 and F4. Behavioral disruptions may be related to defect in habenula maturation (observed in F1) and change in c-fos transcription (observed in F1 and F2). Transcription of the gene encoding DNA methyltransferase (dnmt3ba) was also modified in all generations. Our results lead us to hypothesize that chronic dietary exposure to an environmentally relevant mixture of PCB and PBDE triggers multigenerational and transgenerational molecular and behavioral disruptions in a vertebrate model.

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.

Acetylcholinesterase Is a Potential Biomarker for a Broad Spectrum of Organic Environmental Pollutants

Acetylcholinesterase (AChE, EC 3.1.1.7) is a classical biomarker for monitoring contamination and intoxication of organophosphate (OP) and carbamate pesticides. In addition to these classical environmental AChE inhibitors, other organic toxic substances have been found to alter AChE activity in various species. These emerging organic AChE disruptors include certain persistent organic pollutants (POPs), polycyclic aromatic hydrocarbons (PAHs), and wildly used chemicals, most of which have received considerable public health concern in recent years. It is necessary to re-evaluate the environmental significances of AChE in terms of these toxic substances. Therefore, the present review is aiming to summarize correlations of AChE activity of certain organisms with the level of the contaminants in particular habitats, disruptions of AChE activity upon treatment with the emerging disruptors in vivo and in vitro, and action mechanisms underlying the effects on AChE. Over 40 chemicals belonging to six main categories were reviewed, including 12 POPs listed in the Stockholm Convention. AChE activity in certain organisms has been found to be well correlated with the contamination level of certain persistent pesticides and PAHs in particular habitats. Moreover, it has been documented that most of the listed toxic chemicals could inhibit AChE activity in diverse species ranging from invertebrates to mammals. Besides directly inactivating AChE, the mechanisms in terms of interference with the biosynthesis have been recognized for some emerging AChE disruptors, particularly for dioxins. The collected evidence suggests that AChE could serve as a potential biomarker for a diverse spectrum of organic environmental pollutants.

The Transcriptome of the Zebrafish Embryo After Chemical Exposure: A Meta-Analysis

Numerous studies have been published in the past years investigating the transcriptome of the zebrafish embryo (ZFE) upon being subjected to chemical stress. Aiming at a more mechanistic understanding of the results of such studies, knowledge about commonalities of transcript regulation in response to chemical stress is needed. Thus, our goal in this study was to identify and interpret genes and gene sets constituting a general response to chemical exposure. Therefore, we aggregated and reanalyzed published toxicogenomics data obtained with the ZFE. We found that overlap of differentially transcribed genes in response to chemical stress across independent studies is generally low and the most commonly differentially transcribed genes appear in less than 50% of all treatments across studies. However, effect size analysis revealed several genes showing a common trend of differential expression, among which genes related to calcium homeostasis emerged as key, especially in exposure settings up to 24 h post-fertilization. Additionally, we found that these and other downregulated genes are often linked to anatomical regions developing during the respective exposure period. Genes showing a trend of increased expression were, among others, linked to signaling pathways (e.g., Wnt, Fgf) as well as lysosomal structures and apoptosis. The findings of this study help to increase the understanding of chemical stress responses in the developing zebrafish embryo and provide a starting point to improve experimental designs for this model system. In future, improved time- and concentration-resolved experiments should offer better understanding of stress response patterns and access to mechanistic information.

Teratogenic responses of zebrafish embryos to decabromodiphenyl ether (BDE-209) in the presence of nano-SiO2 particles

This study investigated the influence of nano-SiO₂ particles (nSiO₂) on the teratogenic responses of zebrafish embryos to decabromodiphenyl ether (BDE-209). Zebrafish embryos were exposed to BDE-209 in the absence and presence of nSiO₂ for 96 h post fertilization (hpf). Results showed that formation of nSiO₂-BDE-209 associates promoted both extracellular and intracellular uptake of BDE-209 by zebrafish embryos, thereby increasing the bioconcentration of BDE-209 on the chorion surface and the embryos. Results also showed embryos delay hatching temporarily when co-exposure to BDE-209 and nSiO₂ at 60 hpf. Furthermore, there was heartbeat decline (28.3 beats/10s) and increase in irregular heartbeat (45.8%) in zebrafish larvae at 96 hpf, compared to the sole exposure to BDE-209 (32.7 beats/10s and 0%). Malformation in terms of spinal curvature (SC), pericardial edema (PE) and yolk sac edema (YSE) were observed on zebrafish larvae at 33.9, 23.4, and 18%, respectively. Overall, abnormal development of zebrafish was apparent when co-exposure to BDE-209 and nSiO₂. All relevant evidence considered, nSiO₂ could facilitate the transport of BDE-209 towards zebrafish embryos and negatively impact the development of zebrafish.

Bioaccumulation and toxic effects of decabromodiphenyl ether in the presence of nanoscale zero-valent iron in an earthworm-soil system

In this study, the bioaccumulation and toxic effects of decabromodiphenyl ether (BDE209) (1 and 10 mg kg^-1) were investigated in the earthworm Eisenia fetida in the presence of different levels of nanoscale zero-valent iron (nZVI) (100, 500, and 1000 mg kg^-1) in an earthworm-soil system. The results demonstrated that compared to single BDE209 exposure, the addition of high levels of nZVI significantly (P < 0.05) inhibited growth and respiration, while increased the avoidance response of earthworms. The perturbations of antioxidant enzyme activities (superoxide dismutase (SOD) and catalase (CAT)) and the malondialdehyde (MDA) content clearly revealed that oxidative stress was induced by the two chemicals. The histopathological observations of the body wall of earthworms under a combined exposure of 10 mg kg^-1 BDE209 with 500 or 1000 mg kg^-1 nZVI illustrated the presence of a serious injury in the intestinal tissues after a 28-day exposure. Additionally, a gas chromatography-mass spectrometry analysis revealed that the coexistence of high level of nZVI significantly (P < 0.05) decreased the bioaccumulation of BDE209 in earthworms; BDE208 and BDE206 were the predominant congeners of debrominated metabolites, and 4,6-dibromobenzene-1,2,3,5-tetraol along with benzene-1,2,4,5-tetraol were determined as the two main intermediates. The possible degradation pathways were proposed on the basis of the identified products. This work provides useful information on the biological effects of BDE209 and nZVI.

Substance flow analysis and environmental releases of PBDEs in life cycle of automobiles

Polybrominated diphenyl ethers (PBDEs), a class of brominated flame retardants, have been widely used in many applications in industry such as automobiles, textiles, and electronics. This study focused on a quantitative substance flow analysis (SFA) of PBDEs in automobiles in order to identify their flow by life cycle and treatment pathways of PBDEs-containing materials in end-of-life vehicles (ELVs) in Korea. In addition, this study has estimated environmental releases of PBDEs in automobiles by life cycle in Korea. During this study, PBDEs were analyzed for the samples collected from several ELVs treatment facilities using X-ray fluorescence and gas chromatography/mass spectrometry (GC/MS) methods. The system boundary for SFA of PBDEs ranged from manufacturing/trade to disposal stage of automobiles by life cycle. Based on the result of the SFA, it was found that the amount of PBDEs in automobiles were the highest in use stage (7748ton/year), followed by production stage (1743ton/year) in 2014. In disposal stage, automobile shredded residues (ASR) and seat fabrics were the main components with relatively high levels of PBDEs in ELVs. The major treatment methods of such components included incineration (84%), energy recovery (9%), and landfilling (6%). This research indicates that PBDEs were emitted the highest amount from interior components during the use stage of automobiles, followed by recycling processes such as dismantling and shredding. This study suggests that PBDEs in ASR and seat fabrics should be properly managed to prevent the widespread dispersion in the environment.

The occurrence of endocrine disrupting compounds in off-shore sediments from the southern Baltic Sea

This paper presents the study on the occurrence and spatial distribution of polybrominated diphenyl ethers (PBDEs), butyltin compounds (BTCs), bisphenol A (BPA), and alkylphenols (APs) in sediments. The study focused mainly on off-shore surface sediments collected from the southern Baltic Sea. The pollutant concentrations were as follows: <LOQ-0.158 μg kg(-1) dw ∑9PBDEs, 0.02-1.06 μg kg(-1) dw BDE-209; <LOQ-20.13 μg Sn kg(-1) dw ∑BTCs and 2.7-1001 μg kg(-1) dw nonylphenols (NPs). The spatial distribution of the analyzed compounds was highly related to the organic matter content in the sediments. Only BDE-209 concentrations were the highest in sandy sediments collected near the point source of pollution. This suggests the fresh anthropogenic input of BDE-209 into the marine environment. The principal component analysis (PCA) confirms these observations-the distribution of ∑BTCs, NPs, and ∑9PBDEs was mainly determined by the physicochemical properties of the sediments, while the distribution of BDE-209 was also related to other factors, such as proximity to the pollution source. According to the environmental standards applied in this work, NPs, and to a lesser extent TBT, might pose a risk to aquatic life in the present study area as they occur in some sediments in concentrations higher than those that might cause adverse effects on biota.

The protective effects of insulin-like growth factor-1 on neurochemical phenotypes of dorsal root ganglion neurons with BDE-209-induced neurotoxicity in vitro

Polybrominated diphenyl ethers (PBDEs) exist extensively in the environment as contaminants, in which 2,2',3,3',4,4',5,5',6,6'-decabrominated diphenyl ether (BDE-209) is the most abundant PBDE found in human samples. BDE-209 has been shown to cause neurotoxicity of primary sensory neurons with few effective therapeutic options available. Here, cultured dorsal root ganglion (DRG) neurons were used to determine the therapeutic effects of insulin-like growth factor-1 (IGF-1) on BDE-209-induced neurotoxicity. The results showed that IGF-1 promoted neurite outgrowth and cell viability of DRG neurons with BDE-209-induced neurotoxicity. IGF-1 inhibited oxidative stress and apoptotic cell death caused by BDE-209 exposure. IGF-1 could reverse the decrease in growth-associated protein-43 (GAP-43) and calcitonin gene-related peptide (CGRP), but not neurofilament-200 (NF-200), expression resulting from BDE-209 exposure. The effects of IGF-1 could be blocked by the extracellular signal-regulated protein kinase (ERK1/2) inhibitor PD98059 and the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002, either alone or in combination. IGF-1 may play an important role in neuroprotective effects on DRG neurons with BDE-209-induced neurotoxicity through inhibiting oxidative stress and apoptosis and regulating GAP-43 and CGRP expression of DRG neurons. Both ERK1/2 and PI3K/Akt signaling pathways were involved in the effects of IGF-1. Thus, IGF-1 might be one of the therapeutic agents on BDE-209-induced neurotoxicity.

Advancing toxicology research using in vivo high throughput toxicology with small fish models

Small freshwater fish models, especially zebrafish, offer advantages over traditional rodent models, including low maintenance and husbandry costs, high fecundity, genetic diversity, physiology similar to that of traditional biomedical models, and reduced animal welfare concerns. The Collaborative Workshop on Aquatic Models and 21st Century Toxicology was held at North Carolina State University on May 5-6, 2014, in Raleigh, North Carolina, USA. Participants discussed the ways in which small fish are being used as models to screen toxicants and understand mechanisms of toxicity. Workshop participants agreed that the lack of standardized protocols is an impediment to broader acceptance of these models, whereas development of standardized protocols, validation, and subsequent regulatory acceptance would facilitate greater usage. Given the advantages and increasing application of small fish models, there was widespread interest in follow-up workshops to review and discuss developments in their use. In this article, we summarize the recommendations formulated by workshop participants to enhance the utility of small fish species in toxicology studies, as well as many of the advances in the field of toxicology that resulted from using small fish species, including advances in developmental toxicology, cardiovascular toxicology, neurotoxicology, and immunotoxicology. We alsoreview many emerging issues that will benefit from using small fish species, especially zebrafish, and new technologies that will enable using these organisms to yield results unprecedented in their information content to better understand how toxicants affect development and health.

Evaluation of the Genotoxic and Physiological Effects of Decabromodiphenyl Ether (BDE-209) and Dechlorane Plus (DP) Flame Retardants in Marine Mussels (Mytilus galloprovincialis)

Dechlorane Plus (DP) is a proposed alternative to the legacy flame retardant decabromodiphenyl ether (BDE-209), a major component of Deca-BDE formulations. In contrast to BDE-209, toxicity data for DP are scarce and often focused on mice. Validated dietary in vivo exposure of the marine bivalve (Mytilus galloprovincialis) to both flame retardants did not induce effects at the physiological level (algal clearance rate), but induced DNA damage, as determined by the comet assay, at all concentrations tested. Micronuclei formation was induced by both DP and BDE-209 at the highest exposure concentrations (100 and 200 μg/L, respectively, at 18% above controls). DP caused effects similar to those by BDE-209 but at lower exposure concentrations (5.6, 56, and 100 μg/L for DP and 56, 100, and 200 μg/L for BDE-209). Moreover, bioaccumulation of DP was shown to be concentration dependent, in contrast to BDE-209. The results described suggest that DP poses a greater genotoxic potential than BDE-209.

Developmental neurotoxicity of polybrominated diphenyl ethers mixture de71 in Sprague-Dawley rats

Polybrominated diphenyl ethers (PBDE) are a class of brominated flame retardants that are recognized as global environmental contaminants and a potential adverse health risk. The objective of this study was to evaluate the developmental impacts on rat Sprague-Dawley (SD) pups at postnatal day (PND) 11, 21, 50, 105, and 250 after perinatal exposure to a DE71 mixture. These PNDs corresponded to juveniles, young, and mature adults, respectively. The analysis included histopathological, transcriptional evaluation, and Western blots in both hippocampus and midbrain. There were no marked histopathological changes, but significant transcriptional alterations were observed at PND 21 and 250 in midbrain. These changes occurred in a number of the markers of the cholinergic system, including acetylcholinesterase, muscarinic and nicotinic receptors, and structural gene,s including those of neurofilaments, cell adhesion molecules including N-cadherin and CAMKII, and cytokines. The markers were upregulated at least twofold or greater at PND 21. These biomarkers were predominantly altered in males at low dose (0.3 mg/kg), whereas females were affected only at high concentration (30 mg/kg). At PND 250 both males and females showed downregulation of markers in both intermediate- and high-dose groups. Our results support the findings that in utero and lactational exposure to DE71 mixture leads to transcriptional alterations in midbrain of adult SD rats.

Simulating long-term occupational exposure to decabrominated diphenyl ether using C57BL/6 mice: biodistribution and pathology

Decabrominated biphenyl ether (BDE-209) is a fully brominated diphenyl ether compound used widely as an additive brominated flame retardant in a variety of consumer products. In recent years, BDE-209 has been reported to be abundant and persistent in the environment, and comparatively high burdens have been found in occupational environmental compartments and exposed individuals. In the present study, an animal model for simulating long-term occupational exposure to BDE-209 was set up. Female C57BL/6 mice (n=10) were intragastrically administered BDE-209 at a dose of 800 mg kg(-1) bw at 2-d intervals for 2 years with an internal blood level of approximately 200 ng mL(-1), which was comparable to the high level of BDE-209 detected in the occupational population, and the biodistribution and biological effects were evaluated systematically. The results showed that large amounts of the chemical accumulated in most tissues, and the preferential organs were the ovary and uterus, liver and lung. Decreased survival was observed in the exposed mice. The subsequent pathological analysis revealed hepatomegaly in the exposed mice, accompanied by obvious histopathological changes in the liver, lung, brain, spleen, kidney and ovary. No neoplastic lesions were observed in this lifetime exposure study. Although the number of experimental mice was limited, our observations offer a comprehensive understanding of the chronic toxicology of BDE-209 after continuous high-dose exposure.

Oxidative degradation of decabromodiphenyl ether (BDE 209) by potassium permanganate: reaction pathways, kinetics, and mechanisms assisted by density functional theory calculations

This study found that decabromodiphenyl ether (BDE 209) could be oxidized effectively by potassium permanganate (KMnO4) in sulfuric acid medium. A total of 15 intermediate oxidative products were detected. The reaction pathways were proposed, which primarily included cleavage of the ether bond to form pentabromophenol. Direct oxidation on the benzene ring also played an important role because hydroxylated polybrominated diphenyl ethers (PBDEs) were produced during the oxidation process. The degradation occurred dramatically in the first few minutes and fitted pseudo-first-order kinetics. Increasing the water content decelerated the reaction rate, whereas increasing the temperature facilitated the reaction. In addition, density functional theory (DFT) was employed to determine the frontier molecular orbital (FMO) and frontier electron density (FED) of BDE 209 and the oxidative products. The theoretical calculation results confirmed the proposed reaction pathways.

Applying Adverse Outcome Pathways (AOPs) to support Integrated Approaches to Testing and Assessment (IATA)

Chemical regulation is challenged by the large number of chemicals requiring assessment for potential human health and environmental impacts. Current approaches are too resource intensive in terms of time, money and animal use to evaluate all chemicals under development or already on the market. The need for timely and robust decision making demands that regulatory toxicity testing becomes more cost-effective and efficient. One way to realize this goal is by being more strategic in directing testing resources; focusing on chemicals of highest concern, limiting testing to the most probable hazards, or targeting the most vulnerable species. Hypothesis driven Integrated Approaches to Testing and Assessment (IATA) have been proposed as practical solutions to such strategic testing. In parallel, the development of the Adverse Outcome Pathway (AOP) framework, which provides information on the causal links between a molecular initiating event (MIE), intermediate key events (KEs) and an adverse outcome (AO) of regulatory concern, offers the biological context to facilitate development of IATA for regulatory decision making. This manuscript summarizes discussions at the Workshop entitled "Advancing AOPs for Integrated Toxicology and Regulatory Applications" with particular focus on the role AOPs play in informing the development of IATA for different regulatory purposes.

A multi-biomarker risk assessment of the impact of brominated flame retardant-decabromodiphenyl ether (BDE209) on the antioxidant system of earthworm Eisenia fetida

Decabromodiphenyl ether (BDE209) is the major contaminant at e-waste recycling sites (EWRSs), and its potential toxicological effects on terrestrial organisms have received extensive attention. However, the impacts of BDE209 on the antioxidant defense system in terrestrial organisms remain vague. Therefore, indoor incubation tests were performed systematically on control and contaminated soil samples to determine the effects of BDE209 on the antioxidant system of earthworm Eisenia fetida. The results showed that compared to the controls, superoxide dismutase (SOD) activities in all treated groups were elevated significantly after 21 and 28 days exposure; catalase (CAT) activities were much higher in all tests during the entire exposure period; peroxidase (POD) and glutathione-s-transferase (GST) activities generally decreased and indicated contrary response trend; the total antioxidant capacity (T-AOC) after exposure to low level of BDE209 (1 mg kg(-1)) was induced, whereas at 10 and 100 mg kg(-1) concentrations it showed suppression status; electron paramagnetic resonance (EPR) spectra suggested that hydroxyl radicals (OH) in earthworms were significantly induced by BDE209; the changes in malondialdehyde (MDA) contents suggested that reactive oxygen species (ROS) might lead to cellular lipid peroxidation in earthworms. The results of these observations suggested that severe oxidative stress occurred in E. fetida, and it may play an important role in inducing the BDE209 toxicity to earthworms.

Differential effects and potential adverse outcomes of ionic silver and silver nanoparticles in vivo and in vitro

Nanoparticles are of concern because of widespread use, but it is unclear if metal nanoparticles cause effects directly or indirectly. We explored whether polyvinylpyrrolidone-coated silver nanoparticles (PVP-AgNPs) cause effects through intact nanoparticles or dissolved silver. Females of the model species fathead minnow (Pimephales promelas) were exposed to either 4.8 μg/L of AgNO3 or 61.4 μg/L of PVP-AgNPs for 96h. Microarray analyses were used to identify impacted receptors and toxicity pathways in liver and brain tissues that were confirmed using in vitro mammalian assays. AgNO3 and PVP-AgNP exposed fish had common and distinct effects consistent with both intact nanoparticles and dissolved silver causing effects. PVP-AgNPs and AgNO3 both affected pathways involved in Na(+), K(+), and H(+) homeostasis and oxidative stress but different neurotoxicity pathways. In vivo effects were supported by PVP-AgNP activation of five in vitro nuclear receptor assays and inhibition of ligand binding to the dopamine receptor. AgNO3 inhibited ligand binding to adrenergic receptors α1 and α2 and cannabinoid receptor CB1, but had no effect in nuclear receptor assays. PVP-AgNPs have the potential to cause effects both through intact nanoparticles and metal ions, each interacting with different initiating events. Since the in vitro and in vivo assays examined here are commonly used in human and ecological hazard screening, this work suggests that environmental health assessments should consider effects of intact nanoparticles in addition to dissolved metals.