Effects of BDE-209 and its mixtures with BDE-47 and BDE-99 on multiple biomarkers in Carassius auratus

A Dangerous Couple: Sequential Effect of Phosphorus Flame-Retardant and Polyurethane Decrease Locomotor Activity in Planarian Girardia tigrina

Understanding the interplay among organophosphorus flame retardants (OPFRs), microplastics, and freshwater organisms is crucial for unravelling the dynamics within freshwater environments and foreseeing the potential impacts of organic pollutants and plastic contamination. For that purpose, the present research assessed the exposure impact of 10 mg L-1 flame-retardant aluminium diethylphosphinate (ALPI), 10 μg mg-1liver microplastics polyurethane (PU), and the combination of ALPI and PU on the freshwater planarian Girardia tigrina. The exposure to both ALPI and PU revealed a sequential effect, i.e., a decrease in locomotor activity, while oxidative stress biomarkers (total glutathione, catalase, glutathione S-transferase, lipid peroxidation) and metabolic responses (cholinesterase activity, electron transport system, and lactate dehydrogenase) remained unaffected. Despite this fact, it was possible to observe that the range of physiological responses in exposed organisms varied, in particular in the cases of the electron transport system, cholinesterase activity, glutathione S-transferase, catalase, and levels of total glutathione and proteins, showing that the energetic costs for detoxification and antioxidant capacity might be causing a lesser amount of energy allocated for the planarian activity. By examining the physiological, behavioural, and ecological responses of planarians to these pollutants, insights can be gained into broader ecosystem-level effects and inform strategies for mitigating environmental risks associated with OPFRs and microplastic pollution in freshwater environments.

Study on the Biomolecular Competitive Mechanism of Polybrominated Diphenyl Ethers and Their Derivatives on Thyroid Hormones

Polybrominated diphenyl ethers (PBDEs) are widely used brominated flame retardants. PBDEs and their derivatives, hydroxylated PBDEs (OH-PBDEs), can bind to hormone receptors and impact hormone secretion, transportation, and metabolism, leading to endocrine disruption and the development of various diseases. They have particularly strong interference effects on thyroid hormones. This study used decabromodiphenyl ether (BDE-209); 2,2',4,4'-tetrabromodiphenyl ether (BDE-47); and 6-OH-BDE-47 as representative compounds of PBDEs and their derivatives, OH-PBDEs. A fluorescence probe, fluorescein-isothiocyanate-L-thyroxine (FITC-T4, F-T4), specific for binding to transthyretin (TTR), a thyroid transport protein, was prepared. The binding capacity of PBDEs and their derivatives, OH-PBDEs, to TTR was quantitatively measured using fluorescence spectroscopy. The principle of quenching the fluorescence intensity of F-T4 after binding to TTR was used to analyze the competitive interaction between the probe and BDE-209, BDE-47, and 6-OH-BDE-47, thereby evaluating the toxic effects of PBDEs and their derivatives on the thyroid system. Additionally, AutoDock molecular docking software (1.5.6) was used to further analyze the interference mechanism of OH-PBDEs on T4. The results of the study are as follows: (1) Different types of PBDEs and OH-PBDEs exhibit varying degrees of interference with T4. Both the degree of bromination and hydroxylation affect their ability to competitively bind to TTR. Higher bromination and hydroxylation degrees result in stronger competitive substitution. (2) The competitive substitution ability of the same disruptor varies at different concentrations. Higher concentrations lead to stronger substitution ability, but there is a threshold beyond which the substitution ability no longer increases. (3) When OH-PBDEs have four or more bromine atoms and exhibit the most structural similarity to T4, their binding affinity to TTR is stronger than that of T4.

Comparative Assessment of the Toxicity of Brominated and Halogen-Free Flame Retardants to Zebrafish in Terms of Tail Coiling Activity, Biomarkers, and Locomotor Activity

BDE-47, a flame retardant that is frequently detected in environmental compartments and human tissues, has been associated with various toxic effects. In turn, information about the effects of aluminum diethyl-phosphinate (ALPI), a halogen-free flame retardant from a newer generation, is limited. This study aims to assess and compare the toxicity of BDE-47 and ALPI to zebrafish by analyzing the tail coiling, locomotor, acetylcholinesterase activities, and oxidative stress biomarkers. At 3000 µg/L BDE-47, the coiling frequency increased at 26-27 h post-fertilization (hpf), but the burst activity (%) and mean burst duration (s) did not change significantly. Here, we considered that the increased coiling frequency is a slight neurotoxic effect because locomotor activity was impaired at 144 hpf and 300 µg/L BDE-47. Moreover, we hypothesized that oxidative stress could be involved in the BDE-47 toxicity mechanisms. In contrast, only at 30,000 µg/L did ALPI increase the catalase activity, while the motor behavior during different developmental stages remained unaffected. On the basis of these findings, BDE-47 is more toxic than ALPI.

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.

BDE-99 (2,2',4,4',5 - pentain polybrominated diphenyl ether) induces toxic effects in Oreochromis niloticus after sub-chronic and oral exposure

PBDEs are toxic, lipophilic, hydrophobic, and persistent artificial chemicals, characterized by high physical and chemical stability. Although PBDEs are known to disturb hormone signaling, many effects of 2,2',4,4',5 - pentain polybrominated diphenyl ethers (BDE-99) in fish remain unclear. The current study investigates the effects of BDE-99 in Oreochromis niloticus where sixty-four juvenile fish were orally exposed to 0.294, 2.94, 29.4 ng g^-1 of BDE-99, every 10 days, during 80 days. The results showed histopathological findings in liver and kidney, increasing acetylcholinesterase activity in muscle, disturbs in the antioxidant system in liver and brain and decreasing the plasmatic levels of vitellogenin in females. According to multivariate analysis (IBR), the higher doses are related to the interaction of oxidative and non-oxidative enzymes. The present study provided evidence of deleterious effects after sub-chronic exposure of BDE 99 to O. niloticus, increasing the knowledge about its risk of exposure in fish.

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.

Use of enzymatic biomarkers of Labeo rohita to study the effect of polybrominated diphenyl ether (BDE- 209) via dietary exposure in laboratory conditions

Fishes have been widely used as a representative to estimate the health of an aquatic ecosystem. In the present study, Labeo rohita was selected for biomarker study against decabromodiphenyl ether (BDE-209), a persistent organic pollutant (POP), as it is a widely used Indian carp. The results suggested significant effects on the optimum metabolism of Labeo rohita. After 48 to 72 h of exposure, most of the biomarkers such as lactate dehydrogenase (LDH), creatine kinase (CK), serum glutamic pyruvic transaminase (SGPT), serum glutamic oxaloacetic transaminase (SGOT), and hepatosomatic index (HSI) increased drastically indicating the higher index of tissue and liver damage. On the contrary, succinic dehydrogenase (SDH), acetylcholinesterase (AChE), and alkaline phosphatase (ALP) showed a reverse trend suggesting the shifting of fish metabolism towards anaerobic respiration mode because of induced stress. Increased catalase (CAT) activity was also observed, which indicated increased abundance of reactive hydroxyl species and therefore a possible oxidative stress in fishes. It is further suggested to understand and examine the biotransformation characteristics and degradation pathways of polybrominated diphenyl ether (PBDE)s, which would be useful to comprehend their environmental fate.

Comparative effects of oral exposure to 2, 4, 6-tribromophenol and decabromodiphenyl ether in Nile tilapia

Flame retardants are compounds added to a high diversity of polymers used in electronics and furniture to decrease the risk of combustion. Decabromodiphenyl ether (BDE-209) is a polybrominated diphenyl ether (PBDE) congener still used worldwide, while 2, 4, 6-tribromophenol(TBP) is a PBDE metabolite used as a pesticide and flame retardant for wood conservation. These compounds have lipophilic properties and are easily bioaccumulated in the food chain. In the current study, the acute and chronic toxicity of BDE-209 and TBP was evaluated in Oreochromis niloticus through analyses of redox imbalance, neurotoxicity, and histopathological biomarkers after acute (24, 48, 72, and 96 h) and chronic (90 days) exposure to 0.5, 5, and 50 ng/g of the polybrominated compounds. The results showed effects on glutathione S-transferase(GST) activity and damage to biomolecules in both acute and chronic exposures. Liver histopathology and the ultrastructure of hepatocytes revealed alterations and damage in individuals from both experiments, but only BDE-209 led to neurotoxic effects. The current study revealed new endpoints related to polybrominated compounds in fish, highlighting the need to review the risk of exposure to biota.

The immunotoxicity of decabromodiphenyl ether (BDE-209) on broiler chicks by transcriptome profiling analysis

Decabromodiphenyl ether (BDE-209) has drawn significant attention due to its suppression of immune functions in animals and even humans. In order to explore the mechanism through which BDE-209 affects the immune system, broiler chicks were fed a diet containing various concentrations of BDE-209 (0, 0.004, 0.04, 0.4, and 4 g/kg) for 42 days. Histopathological observations of immune organs found damaged and necrotic lymphocytes in the spleen and bursa, and losses of lymphoid cells in thymic gland. The activities of catalase, glutathione, glutathione peroxidase, and superoxide dismutase in both the spleen and serum were affected by BDE-209. Obvious bioaccumulation effect was found in spleen tissues (high to 1339 ± 181.9 μg/kg). Furthermore, transcriptome sequencing analyses of the spleen identified 424 upregulated and 301 downregulated DEGs, and the cytokine-cytokine receptor interaction signal pathway was most significantly enriched based on the Kyoto Encyclopedia of Genes and Genomes database. Quantitative real-time PCR affirmed the decreased expressions of interleukin IL18, IL18R1, IL18RAP, IL21, as well as interferon gamma IFNG and tumor necrosis factor superfamily members TNFSF8, indicating significant interference to immunomodulation function and possible disease progression in inflammatory effects resulting from BDE-209 exposure. The immunotoxicity of BDE-209 may cause the suppression of immune and physiological functions of spleen cells, leading to inflammation and apoptosis and ultimately spleen atrophy.

Short-term exposure of decabromodiphenyl ether in female adult Balb/c mice: Immune toxicity and self-recovery

As a typical persistent organic pollutant, decabromodiphenyl ether (BDE-209) is associated with various health risks, especially on immune system, which is sensitive to environmental pollutants. In addition, there is a problem of multi-index estimation and lack of comprehensive evaluation in immune toxicity study. In this study, the immunotoxicity of BDE-209 was systematically estimated from the aspects of immunopathology, humoral immunity, cellular immunity and non-specific immunity, etc., and integrated biomarker responses (IBR) combined with principal component analysis was applied to comprehensively evaluate the immunotoxicity of BDE-209 and its self-recovery after discontinuation. Results showed that BDE-209 exposure could cause immunotoxicity. This response seems to depend on (1) atrophying immune organs (thymus and spleen), hepatomegaly accompanied by increasing aspartate aminotransferase and oxidative stress;(2) changing humoral (immunoglobulins) and cellular (lymphocyte proliferation and cytokine secretion) immunity indices; (3) altering related expressions of genes, and further leading to imbalance of Th1/Th2 (Th, helper T cell). Integrated biomarker responses (IBR) companied with principal component analysis selected five biomarkers (mRNA expression of GATA-3, malondialdehyde level in thymus, count of white blood cell, serum IgG and lipopolysaccharide-induced splenic lymphocyte proliferation) to clarify the immunotoxicity induced by BDE-209. Furthermore, IBR combined with factorial analysis revealed that the effect of BDE-209 could be dose-dependently reduced after withdrawal of BDE-209. Overall results suggested that BDE-209 has immunotoxicity on adult Balb/c mice, whereas this immunotoxicity could be reduced by the self-regulation of organisms to some extent.

Brominated flame retardants and heavy metals in common aquatic products from the pearl river delta, south china: Bioaccessibility assessment and human health implications

Aquatic products are an important source of environmental pollutants to humans. This study was conducted to assess the bioaccessibility of selected brominated flame retardants and heavy metals in common aquatic products from the Pearl River Delta, South China, as well as associated human health risks. Based on a questionnaire survey, ten of the most consumed aquatic products were collected from local markets. The bioaccessibility of polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane (HBCDDs), and heavy metals was assessed using an in vitro gastrointestinal model. Bioaccessibility of heavy metals (33.0-84.0%) and HBCDDs (38.5-68.4%) was significantly higher than that of PBDEs (13.4-65.4%). Total non-carcinogenic and carcinogenic risks from heavy metal consumption were much higher than the threshold values due to excessive abundances of arsenic in shellfish (HQ = 2.45, CR = 1.1 ×10^-3). Furthermore, middle-aged populations and females were subjected to greater health risks due to different intakes of aquatic products among age and gender groups. Significant difference in bioaccessibility among analytes indicated that bioaccessibility of pollutants is non-negligible in health risk assessment. This is the first study systematically investigating health risks of aquatic products consumption and concludes that shellfish is a great cause for concern for the PRD residents.

Two PBDEs exposure inducing feeding depression and disorder of digestive and antioxidative system of Daphnia magna

2,2',4,4'-tetrabrominated diphenyl ether (BDE-47) and 2,2',4,4',5-pentabromodiphenyl ether (BDE-99) are two typical polybrominated diphenyl ethers (PBDEs), and studies have proven that these PBDs can disrupt the behaviors and physical function of aquatic organisms. However, little is known about the compositional impacts of BDE-47/BDE-99 compound pollution on the feeding behavior of Daphnia magna. In this study, a response surface methodology (RSM) was introduced into the combined toxicity assessment of BDE-47 and BDE-99 on the feeding depression of D. magna. Low concentrations of BDE-47 (9.2 μg/L) and BDE-99 (5.4 μg/L) had no effect on the feeding behavior of D. magna; nevertheless, the feeding depression was strengthened, and a concentration-dependent effect was observed with increasing concentrations of BDE-47 and BDE-99. The results of RSM indicated that the mixture of BDE-47 and BDE-99 can enhance their toxicity on the feeding behavior of D. magna. Moreover, real-time PCR (qPCR) analysis showed that the down-regulation of α-amylase (AMS) appeared in most of the exposed D. magna. However, there were significant different in the gene expression of trypsin, superoxide dismutase (SOD) and catalase (CAT) between the exposure and control groups. The change in the enzyme activity of AMS, trypsin, SOD and CAT implied that BDE-47 and BDE-99 cause damage to the digestive and antioxidative systems of D. magna. Correlation analysis indicated that a significant positive correlation existed between the gene expression and enzyme activity of SOD and CAT. Our results contribute to the understanding of toxicity caused by BDE-47/BDE-99 compound pollution in D. magna and help to improve traditional toxicity assessment methods for aquatic environments.

Bioaccumulation of decabromodiphenyl ether affects the antioxidant system in the clam Mactra veneriformis

Antioxidant enzymes play vital roles against oxidative stress induced by decabromodiphenyl ether (BDE-209), being widespread in marine environment. However, the effect of BDE-209 on antioxidant enzymes remains poorly understood in marine bivalves. In this study, the clams Mactra veneriformis were exposed to 0.1, 1, and 10 μg/L BDE-209 for 7 days and then maintained in clean seawater for 3 days as the depuration. The bioaccumulation of BDE-209 and the effects on superoxide dismutase, catalase, and glutathione peroxidase were investigated. BDE-209 accumulation was concentration-dependent and decreased by 36%-52% after recovery. Malondialdehyde contents increased in a time- and dose-dependent manner. mRNA expression and activity of antioxidant enzymes changed with different patterns and recovered after depuration. These results suggested that antioxidant systems were triggered to protect the clams from oxidative damage caused by BDE-209. Thus, this research is helpful in elucidating the effect of BDE-209 on antioxidant system in marine bivalves.

Oxidative Stress, Induced by Sub-Lethal Doses of BDE 209, Promotes Energy Management and Cell Cycle Modulation in the Marine Fish Cell Line SAF-1

The effects of sub-lethal doses of polybrominated diphenyl ether (PBDE)-209 in terms of toxicity, oxidative stress, and biomarkers were evaluated in the Sparus aurata fibroblast cell line (SAF-1). Vitality and oxidative stress status were studied after incubation with PBDE for 72 h. Concomitantly, the quantification of proteins related to cell cycle and DNA repair (p53), cell proliferation (extracellular signal–regulated kinase 1 (ERK1)), energetic restriction (hypoxia-inducible factor 1 (HIF1)), and redox status (Nuclear factor erythroid 2–related factor 2 (NRF2)) was also determined after prolonged exposure (7–15 days) by immunoblotting. Our results demonstrated that rising concentrations of PBDEs exposure-induced oxidative stress, and that this event modulates different cell pathways related to cell cycle, cell signaling, and energetic balance in the long term, indicating the negative impact of sub-lethal dose exposure to cell homeostasis.

Evaluation of the oxidative stress in liver of crucian carp (Carassius auratus) exposed to 3,4,4'-tri-CDE, 2-MeO-3',4,4'-tri-CDE, and 2-HO-3',4,4'-tri-CDE

Polychlorinated diphenyl ethers (PCDEs) are a class of potential persistent organic contaminants, which have been widely detected in aquatic environment. In the present study, the effects of 3,4,4'-tri-CDE and its two possible metabolites (2-MeO-3',4,4'-tri-CDE and 2-HO-3',4,4'-tri-CDE) on oxidative stress biomarkers in liver of Carassius auratus were evaluated. The fish were treated with these three compounds at different doses (0.1, 1, and 10 μg/L) via semi-static water exposure. The liver samples were individually taken at 3, 7, and 21 days for analysis of oxidative stress indicators, including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), reduced glutathione (GSH), and malondialdehyde (MDA). Compare to the control group, the hepatic antioxidant enzyme activity and GSH contents showed significant decreases (p < 0.05) at high-dose treatment (10 μg/L) and prolonged exposure time (21 days) in most of the toxicant-treated groups, indicating the occurrence of oxidative stress in fish liver. However, no consistent trend of the variations of antioxidant parameters was observed at low doses (0.1 and 1 μg/L). Meanwhile, the lipid peroxidation was significantly induced with extending exposure time and increasing dose. In addition, the toxicity order of three compounds was discussed using the integrated biomarker response (IBR) index. Notably, 2-HO-3',4,4'-tri-CDE was indicated to cause the most severe hepatic oxidative stress.

Sublethal or not? Responses of multiple biomarkers in Daphnia magna to single and joint effects of BDE-47 and BDE-209

Polybrominated diphenyl ethers (PBDEs) are extremely incessant anthropogenic contaminants found in the environment, with dreadful risk to aquatic ecosystems. However, there is a limited amount of data concerning their impacts on freshwater organisms. 2,2',3,3',4,4',5,5',6,6'-decabromodiphenyl ether (BDE-209) and 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) are significant components of total PBDEs in water. The sublethal effects of BDE-47, BDE-209 and their binary mixtures on the aquatic organism Daphnia magna were investigated in acute and chronic exposure experiments. Immobilization and heartbeat were studied in daphnids after 48 h of exposure. Mortality rate, breed number, Cholinesterase (ChE), Glutathione S-transferases (GST) and Catalase (CAT) activities were evaluated after 21 days of exposure. The results showed that at 100 and 200 μg/L concentration of BDE-47, immobilization rate of daphnids were inhibited by 44.0 ± 16.7% and 88.0 ± 10.9%, respectively. The binary mixture of BDE-47 and BDE-209 had uncongenial effects on immobilization of D. magna under acute toxicity test. BDE-209 significantly increased the heartbeat rate of daphnids, which increased even further when combined with BDE-47. After 21 days of exposure, daphnids exposed to single BDE-47 were physiologically altered. The combination of BDE-47 with BDE-209 significantly decreased the mortality rate of daphnids. Irrespective of the concentration, higher numbers of offsprings were produced in the mixtures compared to BDE-47 treatment alone. ChE activities significantly (p < 0.05) decreased at concentrations of 2 and 4 μg/L in single BDE-47 treatment, while GST activity significantly (p < 0.05) decreased at 0.5 μg/L. CAT activities significantly increased with BDE-47 treatments in all the tested concentrations (p < 0.05). The mixtures significantly affect ChE (p < 0.05), GST (p < 0.05) and CAT activities (p < 0.05). The results illustrated that the toxicity of the mixture of PBDE congeners exposed to aquatic organisms may have antagonistic effects. The 21 days chronic test in this study suggests that acute toxicity tests, i.e. 48-h tests, using Daphnia may lead to underestimation of risks associated with PBDEs, especially, BDE-209. Hence, there is a necessity to re-examine PBDE congeners' environmental risk in aquatic organisms.

Responses of antioxidant and biotransformation enzymes in Carassius carassius exposed to hexabromocyclododecane

The ubiquitous existence of hexabromocyclododecane (HBCD) in environmental matrices has made it attractive to both field investigators as well as laboratory researchers. However, literature on the biological effects caused by HBCD on aquatic vertebrates seldom exist. This has inevitably increased the difficulty of toxicological assessment in the aquatic environment. Juvenile crucian carp (Carassius carassius) were exposed (flow-through) to different concentrations of technical HBCD (nominal 2, 20, 200 μg L^-1) for 7 days to determine the responses of antioxidant and biotransformation enzymes. HBCD was found to be increasingly bioconcentrated in the fish livers as time proceeds. Also, the contribution of α-HBCD exhibited an enhancement from 13% in the exposure solutions to 24% in crucian carp, still much lower than in wild fishes (ca. 80%). HBCD induced activities of antioxidant enzymes in most cases, as well as increased level of lipid peroxidation. In contrast to the weak response of 7-ethoxyresorufin-O-deethylase (EROD), 7-pentoxyresorufin-O-depentylase (PROD) activity was generally induced in a time-dependent manner with peaks at day 2. Phase II enzyme Glutathione-S-transferase (GST) showed a dose-dependent induction with maximums in the 20 μg L^-1 treatment at all the four timepoints of 1, 2, 4 and 7 days. Some enzymatic responses showed good associations, indicating coordinated functions. To sum up, tHBCD exposure in the present circumstance had produced an ecological stress to crucian carp. The low levels of biotransformation and slow rates of bioisomerization suggest a possible long-term toxic effect, especially around HBCD point sources.

Bioconcentration and effects of hexabromocyclododecane exposure in crucian carp (Carassius auratus)

As a cycloaliphatic brominated flame retardant, hexabromocyclododecane (HBCD) has been widely used in building thermal insulation and fireproof materials. However, there is little information on the bioconcentration as well as effects with respect to HBCD exposure in the aquatic environment. To investigate the bioconcentration of HBCD in tissues (muscle and liver) and its biochemical and behavioural effects, juvenile crucian carp (Carassius auratus) were exposed to different concentrations of technical HBCD (nominal concentrations, 2, 20, 200 μg/L) for 7 days, using a flow-through exposure system. HBCD was found to concentrate in the liver and muscle with a terminal concentration of 0.60 ± 0.22 μg/g lw (lipid weight) and 0.18 ± 0.02 μg/g lw, respectively, at an environmentally-relevant concentration (2 μg/L). The total thyroxine and total triiodothyronine in the fish plasma were lowered as a result of exposure to the HBCD. Acetylcholinesterase activity in the brain was increased, while swimming activity was inhibited and shoaling inclination was enhanced after exposure to 200 μg/L HBCD. Feeding rate was suppressed in the 20 and 200 μg/L treatment groups. In summary, HBCD concentrations 10-100× higher than the current environmentally-relevant exposures induced adverse effects in the fish species tested in this study. These results suggest that increasing environmental concentrations and/or species with higher sensitivity than carp might be adversely affected by HBCD.

Biotransformation of the Flame Retardant 1,2-Dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH) in Vitro by Human Liver Microsomes

The technical mixture of 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH or DBE-DBCH) and the pure β-TBECH isomer were subjected to in vitro biotransformation by human liver microsomes (HLM). After 60 min of incubation, 5 potential metabolites of TBECH were identified in microsomal assays of both the TBECH mixture and β-TBECH using ultraperformance liquid chromatography-Q-Exactive Orbitrap mass spectrometry. These include mono- and dihydroxylated TBECH and mono- and dihydroxylated TriBECH as well as an α-oxidation metabolite bromo-(1,2-dibromocyclohexyl)-acetic acid. Our results indicate potential hepatic biotransformation of TBECH via cyctochrome P450-catalyzed hydroxylation, debromination, and α-oxidation. Kinetic studies revealed that the formation of monohydroxy-TBECH, dihydroxy-TBECH, and monohydroxy-TriBECH were best fitted to a Michaelis-Menten enzyme kinetic model. Respective estimated V_max values (maximum metabolic rate) for these metabolites were 11.8 ± 4, 0.6 ± 0.1, and 10.1 ± 0.8 pmol min^-1 mg protein^-1 in TBECH mixture and 4992 ± 1340, 14.1 ± 4.9, and 66.1 ± 7.3 pmol min^-1 mg protein^-1 in β-TBECH. This indicates monohydroxy-TBECH as the major metabolite of TBECH by in vitro HLM-based assay. The estimated in vitro intrinsic clearance (Cl_int) of TBECH mixture was slower (P < 0.05) than that of pure β-TBECH. While the formation of monohydroxy-TBECH may reduce the bioaccumulation potential and provide a useful biomarker for monitoring TBECH exposure, further studies are required to fully understand the levels and toxicological implications of the identified metabolites.

A study of oxidative stress induced by two polybrominated diphenyl ethers in the rotifer Brachionus plicatilis

Polybrominated diphenyl ethers (PBDEs) are widely dispersed persistent organic pollutants in the marine ecosystem. However, their toxic mechanisms in marine organisms, especially invertebrates, remain poorly understood. Two common congeners of PBDEs, tetrabrominated diphenyl ether-47 (BDE-47) and decabrominated diphenyl ether-209 (BDE-209), were investigated. Their toxic mechanisms, with a focus on oxidative stress, were examined in rotifer Brachionus plicatilis. Overproduction of reactive oxygen species (ROS) was induced by two PBDEs. The expression of superoxide dismutase (SOD) mRNA was increased, suggesting SOD play a main role in ROS-scavenging. The intercellular concentrations of calcium ([Ca²⁺]_in) and the expression of calmodulin (CaM) mRNA were increased. This indicates the calcium ion (Ca²⁺) signaling channel is involved in PBDEs stress. Further analysis showed that the reproductive system might be the target site for toxicity of PBDEs. Moreover, high value of detection indexes in BDE-47 experimental groups suggested BDE-47 might cause higher oxidative damage than BDE-209 in rotifers.

Bioconcentration, metabolism and effects of diphenhydramine on behavioral and biochemical markers in crucian carp (Carassius auratus)

Diphenhydramine (DPH), an antihistamine used to alleviate human allergies, is widespread in aquatic environments. However, little is known about the biochemical and behavioral effects of DPH on non-target aquatic animals. In the present study, the tissue distribution, bioconcentration, metabolism, biochemical and behavioral effects were investigated in crucian carp (Carassius auratus) exposed to various concentrations of DPH (0.84, 4.23, 21.7 and 112 μg L(-1)) for 7d. DPH can accumulate in crucian carp, and high concentrations have been observed in the liver and brain with maximum bioconcentration factors of 148 and 81.6, respectively. A portion of the absorbed DPH was metabolized by the crucian carp to N-demethyl DPH and N,N-didemethyl DPH via N-demethylation. Direct fluorimetric assay was employed to assess metabolic activity, while oxidative stress and neurotransmission biomarkers were determined by Diagnostic Reagent Kits. DPH was found to increase hepatic 7-ethoxyresorufin O-deethylase activity in crucian carp with maximal induction of 119%. Concerning the oxidative stress status, DPH significantly inhibited superoxide dismutase (SOD, 37-58%) and glutathione S-transferase (GST, 43-65%) activities and led to a significant increase in malondialdehyde (MDA, 67-140%) levels and catalase (CAT, 38-143%) and glutathione peroxidase (GPx, 39-189%) activities in fish liver. Brain acetylcholinesterase activity was also induced in DPH-exposed crucian carp with maximal induction of 174%. In addition, shoaling was significantly enhanced, while swimming activity and feeding rates were markedly suppressed at DPH concentrations equal to or higher than 21.7 μg L(-1). Furthermore, significant correlations were found between oxidative stress biomarkers (SOD, CAT, GPx, GST and MDA) and behavioral parameters. Collectively, our results confirmed that DPH can accumulate and be metabolized in fish and exert a negative effect at different levels of biological organization.

Behavioral and biochemical responses in freshwater fish Carassius auratus exposed to sertraline

Sertraline is one of the most commonly prescribed selective serotonin reuptake inhibitors and is frequently detected in the aquatic environment. However, knowledge regarding relationships among molecular or biochemical endpoints involved in modes of action (MOAs) of sertraline and ecologically important behavioral responses of fish is insufficient. The present study aimed to investigate the bioconcentration and possible adverse outcomes pathways (AOPs) in crucian carp (Carassius auratus) exposed to various concentrations of sertraline (4.36, 21.3 and 116 μg L(-1)) for 7 d. Bioconcentration factor values were in the range of 19.5-626 in liver, 6.94-285 in brain, 4.01-146 in gill and 0.625-43.1 in muscle during the entire period of exposure. Liver superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione-S-transferase (GST) activities and brain acetylcholinesterase (AChE) activity were selected as biochemical endpoints associated with MOAs. Swimming activity, shoaling, feeding rate and food consumption were determined to assess behavioral responses. Fish plasma levels of sertraline exceeding human therapeutic doses were also predicted from external exposure concentrations. Significant enhancements in CAT, GPx, AChE and swimming activities and decreases in shoaling tendency, feeding rate and food consumption were observed when fish plasma levels exceeded human therapeutic thresholds. Shoaling, feeding rate and food consumption were correlated with the activities of SOD, CAT and GST. A significant positive correlation between swimming activity and AChE activity was also observed. As such, our study provides important AOPs linking biochemical responses with ultimate ecologically relevant behavioral endpoints.

Changes in antitoxic defense systems of the freshwater amphipod Gammarus pulex exposed to BDE-47 and BDE-99

Polybrominated diphenyl ethers (PBDEs) are emerging pollutants widely distributed in aquatic environment. Although the bioaccumulation of this compound has been well studied, few studies have investigated their impacts on antitoxic systems of invertebrates, considering both genders. Here, we have evaluated the effects of BDE-47 and BDE-99 congeners on the antitoxic defence systems of the freshwater amphipod Gammarus pulex, and especially on the multixenobiotic resistance (MXR) activity, as well as the activities of two antitoxic enzymes, the glutathione-S-transferase (GST) and the glutathione peroxidases (GPx). Results revealed that BDE-47 and BDE-99 have inhibited the MXR activity whatever the gammarid gender, which could lead to a reduction of the pollutant elimination from the organism. In addition, a gender-biased response and a congener-biased effect on the antitoxic enzymes activities were observed. Indeed, both BDE congener exposures increased the GST activity in males, whereas in females, only BDE-99 congener modified this activity by decreasing it. On the contrary, BDE exposures did not impact the GPx activity in females, while in males BDE-99 has increased it. Results of the present study highlight that a PBDE exposure at 0.1 µg L(-1) modify antitoxic enzymes activities differently according to gender, which could lead to a change in G. pulex sensitivity on the long term. Finally, this work confirms the ecotoxicological implication of gender in the pollutant toxicity assessment, in order to evaluate impact on populations.

Metabolic pathways of decabromodiphenyl ether (BDE209) in rainbow trout (Oncorhynchus mykiss) via intraperitoneal injection

Decabromodiphenyl ether (BDE209) was of great concern due to its biotransformation in different organisms. However, most studies devoted to the metabolic intermediates of BDE209, less has been done on the metabolic pathways in vivo, especially on the relationships among debrominated-BDEs, OH-BDEs and MeO-BDEs. In this study, the metabolic pathways and intermediates of BDE209 in rainbow trout (Oncorhynchus mykiss) were investigated, and the time-dependent transformations of the metabolites were also examined. The primary debrominated metabolites were BDE47, 49, 99, 197, 207; the main MeO-BDEs were MeO-BDE47, MeO-BDE68 and MeO-BDE100; OH-BDEs were primarily composed of OH-BDE28 and OH-BDE42. From the time-dependent and dose-effect relationships, the debromination should be followed by hydroxylation, and then by methoxylation. The increasing in body burden of MeO-BDEs corresponded to the decreasing of OH-BDEs, which could indirectly prove the inter-conversion between OH-BDEs and MeO-BDEs. This study would motivate the future research of toxicological mechanisms of BDEs.