Toxic effects of brominated indoles and phenols on zebrafish embryos

Identification of Bromophenols' glucuronidation and its induction on UDP- glucuronosyltransferases isoforms

Bromophenols (BPs) are prominent environmental pollutants extensively utilized in aquaculture, pharmaceuticals, and chemical manufacturing. This study aims to identify UDP- glucuronosyltransferases (UGTs) isoforms involved in the metabolic elimination of BPs. Mono-glucuronides of BPs were detected in human liver microsomes (HLMs) incubated with the co-factor uridine-diphosphate glucuronic acid (UDPGA). The glucuronidation metabolism reactions catalyzed by HLMs followed Michaelis-Menten or substrate inhibition kinetics. Recombinant enzymes and inhibition experiments with chemical reagents were employed to phenotype the principal UGT isoforms participating in BP glucuronidation. UGT1A6 emerged as the major enzyme in the glucuronidation of 4-Bromophenol (4-BP), while UGT1A1, UGT1A6, and UGT1A8 were identified as the most essential isoforms for metabolizing 2,4-dibromophenol (2,4-DBP). UGT1A1, UGT1A8, and UGT2B4 were deemed the most critical isoforms in the catalysis of 2,4,6-tribromophenol (2,4,6-TBP) glucuronidation. Species differences were investigated using the liver microsomes of pig (PLM), rat (RLM), monkey (MyLM), and dog (DLM). Additionally, 2,4,6-TBP effects on the expression of UGT1A1 and UGT2B7 in HepG2 cells were evaluated. The results demonstrated potential induction of UGT1A1 and UGT2B7 upon exposure to 2,4,6-TBP at a concentration of 50 μM. Collectively, these findings contribute to elucidating the metabolic elimination and toxicity of BPs.

Toxicity evaluation of chlorinated natural water using Photobacterium phosphoreum: Implications for ballast water management

Chlorination of ballast water could produce harmful disinfection by-products (DBPs) and total residual oxidants. The International Maritime Organization calls for toxicity testing of discharged ballast water with fish, crustacea and algae to reduce the risk, but it is difficult to evaluate the toxicity of treated ballast water in a short time. Therefore, the purpose of this study was to analyze the applicability of luminescent bacteria to the assessment of residual toxicity of chlorinated ballast water. The toxicity unit for all treated samples were higher for Photobacterium phosphoreum than for microalgae (Selenastrum capricornutum and Chlorella pyrenoidosa), after adding neutralizer, all samples showed little effect on the luminescent bacteria and microalgae. For the DBPs, except for 2,4,6-Tribromophenol, Photobacterium phosphoreum could produce more sensitive and rapid test results than other species, the results in Photobacterium phosphoreum showed that the toxicity of DBPs in order of: 2,4-Dibromophenol > 2,6-Dibromophenol > 2,4,6-Tribromophenol > Monobromoacetic acid > Dibromoacetic acid > Tribromoacetic acid, and most binary mixtures (aromatic DBPs and aliphatic DBPs) presented synergistic effects based on the CA model. The aromatic DBPs in ballast water deserve more attention. In general, for ballast water management, the use of luminescent bacteria to evaluate the toxicity of treated ballast water and DBPs is desirable, this study could provide beneficial information for enhancing ballast water management.

Parental and transgenerational impairments of thyroid endocrine system in zebrafish by 2,4,6-tribromophenol

Many environmental contaminants could be transmitted from parents and generate impairments to their progeny. The 2,4,6-tribromophenol (TBP), a novel brominated flame retardant which has been frequently detected in various organisms, was supposed to be bioaccumulated and intergenerational transmitted in human beings. Previous studies revealed that TBP could disrupt thyroid endocrine system in zebrafish larvae. However, there is no available data regarding the parental and transgenerational toxicity of this contaminant. Thus, in this study adult zebrafish were exposed to environmental contaminated levels of TBP for 60 days to investigate the parental and transgenerational impairments on thyroid endocrine system. Chemical analysis verified the bioaccumulation of TBP in tested organs of parents (concentration: liver>gonads>brain) and its transmission into eggs. For adults, increased thyroid hormones, disturbed transcriptions of related genes and histopathological changes in thyroid follicles indicate obvious thyroid endocrine disruptions. Transgenerational effects are indicated by the increased thyroid hormones both in eggs (maternal source) and in developed larvae (newly synthesized), as well as disrupted transcriptional profiles of key genes in HPT axis. The overall results suggest that the accumulated TBP could be transmitted from parent to offspring and generate thyroid endocrine disruptions in both generations.

Antibiofilm and Antimicrobial Activities of Chloroindoles Against Uropathogenic Escherichia coli

Uropathogenic Escherichia coli (UPEC) is a nosocomial pathogen associated with urinary tract infections and expresses several virulence factors that cause recurring infections and cystitis of the bladder, which can lead to pyelonephritis. UPEC uses different types of extracellular appendages like fimbriae and pili that aid colonization and adherence to bladder epithelium and can form persistent biofilm-like bacterial communities that aid its survival after the deployment of host immune responses. We investigated the antibiofilm, antimicrobial, and antivirulence properties of three indole derivatives namely, 4-chloroindole, 5-chloroindole, and 5-chloro 2-methyl indole. All the three chloroindoles had MICs of 75 μg/ml and inhibited biofilm formation by an average of 67% at 20 μg/ml. In addition, they inhibited swarming and swimming motilities, which are essential for dissemination from bacterial communities and colonization, reduced cell surface hydrophobicity, and inhibited indole production and curli formation. Gene expression analysis showed all three chloroindoles significantly downregulated the expressions of virulence genes associated with adhesion, stress regulation, and toxin production. A 3D-QSAR analysis revealed substitutions at the fourth and fifth positions of the indole moiety favored antimicrobial activity. Furthermore, these chloroindoles potently inhibited biofilm formation in other nosocomial pathogens and polymicrobial consortia.

Effect of halogenated indoles on biofilm formation, virulence, and root surface colonization by Agrobacterium tumefaciens

Agrobacterium tumefaciens is a plant pathogen that causes crown gall disease in several plant species by transferring its T-DNA to the host genome. Its chemotactic response to a range of chemical compounds released by hosts facilitates its colonization to host surfaces, and thus, novel anti-agrobacterium compounds are needed to prevent its biofilm formation. Here, we investigated 83 indole derivatives against A. tumefaciens, and based on the screening, 4-chloroindole, 6-iodoindole, and 5-chloro-2-methyl indole were selected as candidates that at 50 μg mL^-1 significantly inhibited the adherence and biofilm formation of A. tumefaciens to abiotic (nitrocellulose and polystyrene) and biotic (roots of Brassica juncea) surfaces. Furthermore, they reduced bacterial growth in a time and concentration-dependent manner and significantly reduced log CFU mL^-1 and survival (%). Changes in biofilm morphologies and biomasses, thicknesses, and substratum coverages were determined, and 2-D and 3-D analyses were performed using a crystal violet assay and bright field, CLSM, and SEM microscopies. Virulence factors such as swimming motility, exopolysaccharide, and exo-protease production, and cell surface hydrophobicity were markedly inhibited by the three compounds. Transcriptional analysis showed multi-fold downregulation of biofilm, virulence, motility, and stress-related genes; however, the degrees of these downregulations were variably affected. B. juncea seed germination was only severely affected by 4-chloroindole. This study demonstrates the promising antibiofilm and antivirulence activities of the three indole derivatives tested and their potentials for targeting and curbing A. tumefaciens infections.

Identification of unknown disinfection byproducts in drinking water produced from Taihu Lake source water

Although disinfection byproducts (DBPs) in drinking water have been suggested as a cancer causing factor, the causative compounds have not yet been clarified. In this study, we used liquid chromatography quadrupole-time-of-flight spectrometry (LC-QTOF MS) to identify the unknown disinfection byproducts (DBPs) in drinking water produced from Taihu Lake source water, which is known as a convergence point for the anthropogenic pollutants discharged from intensive industrial activities in the surrounding regions. In total, 91 formulas of DBPs were discovered through LC-QTOF MS nontarget screen, 81 of which have not yet been reported. Among the 91 molecules, 56 only contain bromine, 15 only contain chlorine and 20 DBPs have both bromine and chlorine atoms. Finally, five DBPs including 2,4,6-tribromophenol, 2,6-dibromo-4-chlorophenol, 2,6-dichloro-4-bromophenol, 4-bromo-2,6-di-tert-butylphenol and 3,6-dibromocarbazole were confirmed using standards. The former three compounds mainly formed in the predisinfection step (maximum concentration, 0.2-2.6 µg/L), while the latter two formed in the disinfection step (maximum concentration, 18.2-33.6 ng/L). In addition, 19 possible precursors of the discovered DBPs were detected, with the aromatic compounds being a major group. 2,6-di-tert-butylphenol as the precursor of 4-bromo-2,6-di-tert-butylphenol was confirmed with standard, with a concentration of 20.3 µg/L in raw water. The results of this study show that brominated DBPs which are possibly formed from industrial pollutants are relevant DBP species in drinking water produced form Taihu source water, suggesting protection of Taihu Lake source water is important to control the DBP risks.

Embryotoxic effects of tribromophenol on early post-implantation development of mouse embryos in vitro

2,4,6-Tribromophenol (TBP, CAS No. 118-79-6), the most widely produced brominated phenol, is frequently detected in environmental components. The detection of TBP in human bodies has earned great concerns about its adverse effects on human beings, especially for early embryonic development. Here, we optimized the mouse embryo in vitro culture (IVC) system for early post-implantation embryos and employed it to determine the embryotoxicity of TBP. With this new research model, we revealed the dose-dependent toxic effects of TBP on mouse embryos from peri-implantation to egg cylinder stages. Furthermore, TBP exposure inhibited the differentiation and survival of epiblast (EPI) cells and extraembryonic endoderm (ExEn) cells, while those of extraembryonic ectoderm (ExEc) cells were not influenced. These results implied that TBP might inhibit embryonic development by influencing the generation of three primary germ layers and fetal membranes (the amnion, chorionic disk, umbilical cord, and yolk sac). In summary, we showed a proof of concept for applying mouse embryo IVC system as a novel research model for studying mammalian embryonic toxicology of environmental pollutants. This study also demonstrated the toxicity of TBP on early embryonic development of mammals.

Antibacterial and Antibiofilm Activities of Chloroindoles Against Vibrio parahaemolyticus

Vibrio parahaemolyticus is a food-borne pathogen recognized as the prominent cause of seafood-borne gastroenteritis globally, necessitating novel therapeutic strategies. This study examined the antimicrobial and antivirulence properties of indole and 16 halogenated indoles on V. parahaemolyticus. Among them, 4-chloroindole, 7-chloroindole, 4-iodoindole, and 7-iodoindole effectively inhibited planktonic cell growth, biofilm formation, bacterial motility, fimbrial activity, hydrophobicity, protease activity, and indole production. Specifically, 4-chloroindole at 20 μg/mL inhibited more than 80% of biofilm formation with a minimum inhibitory concentration (MIC) of 50 μg/mL against V. parahaemolyticus and Vibrio harveyi. In contrast, 7-chloroindole inhibited biofilm formation without affecting planktonic cell growth with a MIC of 200 μg/mL. Both chlorinated indoles caused visible damage to the cell membrane, and 4-chloroindole at 100 μg/mL had a bactericidal effect on V. parahaemolyticus within 30 min treatment, which is superior to the effect of tetracycline at the same dose. The quantitative structure-activity relationship (QSAR) analyses revealed that chloro and bromo at positions 4 or 5 of the indole are essential for eradicating the growth of V. parahaemolyticus. These results suggest that halogenated indoles have potential use in antimicrobial and antivirulence strategies against Vibrio species.

Rough sets and social ski-driver optimization for drug toxicity analysis

BACKGROUND AND OBJECTIVES

Toxicity testing is an important step for developing new drugs, and animals are widely used in this step by exposing them to the toxicants. Zebrafishes are widely used for measuring and detecting the toxicity. However, measuring and testing toxicity manually is not feasible due to the large number of embryos. This work presents an automated model to investigate the toxicity of two toxicants (3, 4-Dichloroaniline (34DCA) and p-Tert-Butylphenol (PTBP)).

METHODS

The proposed model consists of two steps. In the first step, a set of features is extracted from microscopic images of zebrafish embryos using the Segmentation-Based Fractal Texture Analysis (SFTA) technique. Secondly, a novel rough set-based model using Social ski-driver (SSD) is used to find a global minimal subset of features that preserves important information of the original features. In the third step, the AdaBoost classifier is used to classify an unknown sample to alive or coagulant after exposing the embryo to a toxic compound.

RESULTS

For detecting the toxicity, the proposed model is compared with (i) three deterministic rough set reduction algorithms and (ii) the PSO-based algorithm. The classification performance rate of our model was ranged from 97.1% to 99.5% and it outperformed the other algorithms.

CONCLUSIONS

The results of our experiments proved that the proposed drug toxicity model is efficient for rough set-based feature selection and it obtains a high classification performance.

Nitroaromatic compounds damage the DNA of zebrafish embryos (Danio rerio)

Lethal and sublethal effects of trinitrotoluene (TNT) and its degradation products 2-amino-4,6-dinitrotoluene (2-ADNT) and 4-amino-2,6-dinitrotoluene (4-ADNT) to zebrafish embryos (Danio rerio) were investigated in a 120 h exposure scenario. Lethal concentrations (LC50) were 4.5 mg/l for TNT, 13.4 mg/l for 2-ADNT and 14.4 mg/l for 4-ADNT. Embryos exposed to 2-ADNT or 4-ADNT revealed a high proportion of chorda deformations among the surviving individuals. Genotoxicity of the nitroaromatic compounds in zebrafish embryos was investigated by comet assay isolating cells from whole embryos after 48 h in vivo exposure. Significant genotoxicity was induced by all three compounds tested, in comparison to the corresponding controls at 0.1 mg/l and 1.0 mg/l as lowest tested concentrations. The genotoxicity caused by TNT was about three to four times higher than that of 2-ADNT and 4-ADNT. To our knowledge, this is the first study demonstrating the genotoxicity of TNT in fish embryos by in vivo exposure. The results are discussed in the context of dumped munition in the marine environment.

Phytotoxicity and genotoxicity evaluation of 2,4,6-tribromophenol solution treated by UV-based oxidation processes

The environmental detriment due to the presence of emerging contaminants has encouraged the development of advanced oxidation processes. Such methods deal with non-selective chemical reactions. Therefore, toxic byproducts can be generated and distinct post treatment toxicity levels can be expected. The present study investigates the phytotoxicity of 2,4,6-tribromophenol (TBP) to L. sativa seeds and A. cepa bulbs, as well as the TBP phytotoxicity and genotoxicity to A. cepa root. L. sativa seeds and A. cepa bulbs were germinated by being exposed to solutions containing TBP before and after treatment by UV-based processes: direct photolysis (DP), heterogeneous photocatalysis (HP) and photoelectrolysis (PEC). Subsequent analysis of the root length, to determine phytotoxicity, as well as evaluation of chromosomal abnormalities, revealed that the samples treated by DP presented higher phytotoxicity than the untreated ones. On the other hand, samples treated by HP and PEC did not present phytotoxicity. In fact, for the A. cepa assays, phytotoxicity was not observed, including the initial sample. However, genotoxicity assays showed a high frequency of chromosomal aberrations in the initial sample, before the UV-based process treatment. After 140 min of treatment by HP, there was a reduction in genotoxicity, while PEC treatment resulted in a sample with no genotoxicity. In contrast, DP presented high levels of phytotoxicity and genotoxicity. Additionally, DP shows similar degradation and debromination values, when compared to the HP and PEC processes, but less mineralization. Therefore, considering that the DP process did not deals with the HO^• radical, the oxidation pathway can generate byproducts with higher toxicity, which lead to higher levels of phytotoxicity and genotoxicity. These results show that different UV-based oxidation processes are associated to distinct byproducts and toxicity levels. In addition, a toxicity assessment with different organisms should be performed to ensure a safe outcome.

Trophic transfer of naturally produced brominated aromatic compounds in a Baltic Sea food chain

Brominated aromatic compounds (BACs) are widely distributed in the marine environment. Some of these compounds are highly toxic, such as certain hydroxylated polybrominated diphenyl ethers (OH-PBDEs). In addition to anthropogenic emissions through use of BACs as e.g. flame retardants, BACs are natural products formed by marine organisms such as algae, sponges, and cyanobacteria. Little is known of the transfer of BACs from natural producers and further up in the trophic food chain. In this study it was observed that total sum of methoxylated polybrominated diphenyl ethers (MeO-PBDEs) and OH-PBDEs increased in concentration from the filamentous red alga Ceramium tenuicorne, via Gammarus sp. and three-spined stickleback (Gasterosteus aculeatus) to perch (Perca fluviatilis). The MeO-PBDEs, which were expected to bioaccumulate, increased in concentration accordingly up to perch, where the levels suddenly dropped dramatically. The opposite pattern was observed for OH-PBDEs, where the concentration exhibited a general trend of decline up the food web, but increased in perch, indicating metabolic demethylation of MeO-PBDEs. Debromination was also indicated to occur when progressing through the food chain resulting in high levels of tetra-brominated MeO-PBDE and OH-PBDE congeners in fish, while some penta- and hexa-brominated congeners were observed to be the dominant products in the alga. As it has been shown that OH-PBDEs are potent disruptors of oxidative phosphorylation and that mixtures of different congener may act synergistically in terms of this toxic mode of action, the high levels of OH-PBDEs detected in perch in this study warrants further investigation into potential effects of these compounds on Baltic wildlife, and monitoring of their levels.

Induced production of brominated aromatic compounds in the alga Ceramium tenuicorne

In the Baltic Sea, high concentrations of toxic brominated aromatic compounds have been detected in all compartments of the marine food web. A growing body of evidence points towards filamentous algae as a natural producer of these chemicals. However, little is known about the effects of environmental factors and life history on algal production of brominated compounds. In this study, several congeners of methoxylated polybrominated diphenyl ethers (MeO-PBDEs), hydroxylated polybrominated diphenyl ethers (OH-PBDEs) and brominated phenols (BPs) were identified in a naturally growing filamentous red algal species (Ceramium tenuicorne) in the Baltic Sea. The identified substances displayed large seasonal variations in the alga with a concentration peak in July. Production of MeO-/OH-PBDEs and BPs by C. tenuicorne was also established in isolated clonal material grown in a controlled laboratory setting. Based on three replicates, herbivory, as well as elevated levels of light and salinity in the culture medium, significantly increased the production of 2,4,6-tribromophenol (2,4,6-TBP). Investigation of differences in production between the isomorphic female, male and diploid clonal life stages of the alga grown in the laboratory revealed a significantly higher production of 2,4,6-TBP in the brackish water female gametophytes, compared to the corresponding marine gametophytes. Even higher concentrations of 2,4,6-TBP were produced by marine male gametophytes and sporophytes.

Naturally occurring marine brominated indoles are aryl hydrocarbon receptor ligands/agonists

The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that mediates the toxic and biological effects of structurally diverse chemicals, including the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). As part of a larger effort to identify the full spectrum of chemicals that can bind to and activate the AhR, we have examined the ability of several naturally occurring marine-derived brominated indoles and brominated (methylthio)indoles (collectively referred to as brominated indoles) to bind to the AhR and stimulate AhR-dependent gene expression. Incubation of mouse, rat, and guinea pig recombinant cell lines containing a stably transfected AhR-responsive luciferase reporter gene with eight brominated indoles revealed that all compounds stimulated luciferase reporter gene activity, although some species-specific differences were observed. All compounds induced significantly more luciferase activity when incubated with cells for 4 h as compared to 24 h, demonstrating that these compounds are transient activators of the AhR signaling pathway. Three of the brominated indoles induced CYP1A1 mRNA in human HepG2 cells in vitro and Cyp1a mRNA in zebrafish embryos in vivo. The identification of the brominated indoles as direct ligands and activators/agonists of the AhR was confirmed by their ability to compete with [(3)H]TCDD for binding to the AhR and to stimulate AhR transformation and DNA binding in vitro. Taken together, these results indicate that marine-derived brominated indoles are members of a new class of naturally occurring AhR agonists.

Embryotoxicity of nitrophenols to the early life stages of zebrafish (Danio rerio)

The nitrophenols (NPs) are water-soluble compounds. These compounds pose a significant health threat since they are priority environmental pollutants. In this study, 2-Nitrophenol (2NP) and 2,4-dinitrophenol (DNP) were examined for embryo and early life stage toxicity in zebrafish ( Danio rerio). Acute toxicity and teratogenicity of 2NP and DNP were tested for 4 days using zebrafish embryos. The typical lesions observed were no somite formation, incomplete eye and head development, tail curvature, weak pigmentation (≤48 hours postfertilization (hpf)), kyphosis, scoliosis, yolk sac deformity, and nonpigmentation (72 hpf). Also, embryo and larval mortality increased and hatching success decreased. The severity of abnormalities and mortalities were concentration- and compound-dependent. Of the compounds tested, 2,4-DNP was found to be highly toxic to the fish embryos following exposure. The median lethal concentrations and median effective concentrations for 2NP are 18.7 mg/L and 7.9 mg/L, respectively; the corresponding values for DNP are 9.65 mg/L and 3.05 mg/L for 48 h. The chorda deformity was the most sensitive endpoint measured. It is suggested that the embryotoxicity may be mediated by an oxidative phosphorylation uncoupling mechanism. This article is the first to describe the teratogenicity and embryotoxicity of two NPs to the early life stages of zebrafish.

Oxidation of bromophenols and formation of brominated polymeric products of concern during water treatment with potassium permanganate

The extensive use of bromophenols (BrPs) in industrial products leads to their occurrence in freshwater environments. This study explored the oxidation kinetics of several BrPs (i.e., 2-BrP, 3-BrP, 4-BrP, 2,4-diBrP, and 2,6-diBrP) and potential formation of brominated polymeric products of concern during water treatment with potassium permanganate [Mn(VII)]. These BrPs exhibited appreciable reactivity toward Mn(VII) with the maxima of second-order rate constants (kMn(VII)) at pH near their pKa values, producing bell-shaped pH-rate profiles. The unusual pH-dependency of kMn(VII) was reasonably explained by a tentative reaction model, where the formation of an intermediate between Mn(VII) and dissociated BrP was likely involved. A novel and powerful precursor ion scan (PIS) approach was used for selective detection of brominated oxidation products by liquid chromatography/electrospray ionization-triple quadrupole mass spectrometry. Results showed that brominated dimeric products such as hydroxylated polybrominated diphenyl ethers (OH-PBDEs) and hydroxylated polybrominated biphenyls (OH-PBBs) were readily produced. For instance, 2'-OH-BDE-68, one of the most naturally abundant OH-PBDEs, could be formed at a relatively high yield possibly via the coupling between bromophenoxyl radicals generated from the one-electron oxidation of 2,4-diBrP by Mn(VII). Given the altered or enhanced toxicological effects of these brominated polymeric products compared to the BrP precursors, it is important to better understand their reactivity and fate before Mn(VII) is applied by water utilities for the oxidative treatment of BrP-containing waters.

Bromophenols in marine algae and their bioactivities

Marine algae contain various bromophenols that have been shown to possess a variety of biological activities, including antioxidant, antimicrobial, anticancer, anti-diabetic, and anti-thrombotic effects. Here, we briefly review the recent progress of these marine algal biomaterials, with respect to structure, bioactivities, and their potential application as pharmaceuticals.

Ecotoxicity of a brominated flame retardant (tetrabromobisphenol A) and its derivatives to aquatic organisms

The large use of tetrabromobisphenol A (B(4)BPA) in common products (plastics, electric and electronic equipments) has raised concern about its ecotoxicity. Physical and bio-degradations may lead to the formation of tetrabromobisphenol A derivatives like tri- (B(3)BPA), di- (B(2)BPA), monobromobisphenol A (B(1)BPA) and bisphenol A (BPA). However, little is known about the toxicity of these brominated derivatives. An appraisal on the ecotoxicity of B(4)BPA and its derivatives was carried out with several bioassays representing organisms (bacteria, algae, micro-invertebrates and fish) of different taxonomic groups present in aquatic ecosystems. Endpoint values showed that B(4)BPA was significantly less toxic than the other chemicals when tested with the Microtox and algal asssays. A similar trend was observed with other bioassays for BPA. One of the brominated derivatives was particularly toxic: B(2)BPA. The LuminoTox assay and the rainbow trout hepatocytes assay reported the most significant toxicity for this derivative. Its toxicity was also significantly higher than the other compounds barring B(3)BPA when tested with the micro-crustacean test.

Oral exposure of adult zebrafish (Danio rerio) to 2,4,6-tribromophenol affects reproduction

The bromophenol 2,4,6-tribromophenol (TBP) is widely used as an industrial chemical, formed by degradation of tetrabromobisphenol-A, and it occurs naturally in marine organisms. Concentrations of TBP in fish have been related to intake via feed, but little is known about effects on fish health after oral exposure. In this study, we exposed adult male and female zebrafish (Danio rerio) to TBP via feed in nominal concentrations of 33, 330, and 3300 μg/g feed (or control feed) for 6 weeks to assess the effects of TBP on reproductive output, gonad morphology, circulatory vitellogenin levels, and early embryo development. The aim was also to investigate the extent to which TBP was metabolised to 2,4,6-tribromoanisole (TBA) in dietary exposed zebrafish, and the amounts of TBP and TBA found in offspring. After 6 weeks of exposure, we found about 3% of the daily dose of TBP in adult fish and the mean concentration of TBA was 25-30% of the TBP concentration. TBP and TBA were detected in offspring with wet weight-based egg/fish concentration ratios well below one. Exposure to TBP significantly reduced the fertilization success and disturbed the gonad morphology, i.e. fewer spermatid cysts in males and increased presence of atretic follicles and oocytes with decreased vitellogenesis in females. In females, the disturbed gonad morphology was accompanied by increased levels of circulating vitellogenin. Significant effects were observed at 3300 μg/g feed. Offspring early development was not significantly affected, but yolk-sac oedema tended to increase in frequency in exposed groups with time. Our results show that dietary exposure to TBP, at concentrations found in marine organisms that are part of the natural diet of wild fish, can interfere with reproduction in zebrafish. We also observed low accumulation from feed of TBP in zebrafish and biotransformation of TBP to TBA. This is the first paper showing gonadal histopathological changes and effects on fertility in TBP exposed fish.

Developmental toxicity and brain aromatase induction by high genistein concentrations in zebrafish embryos

Genistein is a phytoestrogen found at a high level in soybeans. In vitro and in vivo studies showed that high concentrations of genistein caused toxic effects. This study was designed to test the feasibility of zebrafish embryos for evaluating developmental toxicity and estrogenic potential of high genistein concentrations. The zebrafish embryos at 24 h post-fertilization were exposed to genistein (1 × 10⁻⁴ M, 0.5 × 10⁻⁴ M, 0.25 × 10⁻⁴ M) or vehicle (ethanol, 0.1%) for 60 h. Genistein-treated embryos showed decreased heart rates, retarded hatching times, decreased body length, and increased mortality in a dose-dependent manner. After 0.25 × 10⁻⁴ M genistein treatment, malformations of survived embryos such as pericardial edema, yolk sac edema, and spinal kyphosis were also observed. TUNEL assay results showed apoptotic DNA fragments in brain. This study also confirmed the estrogenic potential of genistein by EGFP expression in the brain of the mosaic reporter zebrafish embryos. This study first demonstrated that high concentrations of genistein caused a teratogenic effect on zebrafish embryos and confirmed the estrogenic potential of genistein in mosaic reporter zebrafish embryos.

Chronic exposure to environmental levels of tribromophenol impairs zebrafish reproduction

Tribromophenol (2,4,6-TBP) is ubiquitously found in aquatic environments and biota. In this study, we exposed zebrafish embryos (F(0); 2"" days post-fertilization, dpf) to environmental concentration (0.3 microg/L) and a higher concentration (3.0 microg/L) of TBP and assessed the impact of chronic exposure (120 dpf) on reproduction. TBP exposure did not cause a significant increase in the malformation and reduction in the survival in the F(0)-generation fish. After TBP exposure, the plasma testosterone and estradiol levels significantly increased in males and decreased in females. The transcription of steroidogenic genes (3beta-HSD, 17beta-HSD, CYP17, CYP19A, CYP19B) was significantly upregulated in the brain and testes in males and downregulated in the brain and ovary in females. TBP exposure significantly downregulated and upregulated the expression of VTG in the liver of female and male fish, respectively. Meanwhile, TBP exposure altered the sex ratio toward a male-dominant state. The F(1)-generation larvae exhibited increased malformation, reduced survival, and retarded growth, suggesting that TBP in the aquatic environment has significant adverse effects on fish population.

Hazard identification of imidacloprid to aquatic environment

The use of a very effective insecticide against sucking pests, neonicotinoid imidacloprid, has been increasing extensively. For this reason elevated concentrations are expected in aquatic environment. Despite this fact, there is still a lack of data available on its possible risk for the environment. In this study, the potential hazards of imidacloprid and its commercial product Confidor SL 200 to aquatic environment were identified by the acute and chronic toxicity assessment using bacteria Vibrio fischeri, algae Desmodesmus subspicatus, crustacean Daphnia magna, fish Danio rerio and the ready biodegradability determination. We found out, that imidacloprid was not highly toxic to tested organisms in comparison to some other environmental pollutants tested in the same experimental set-up. Among the organisms tested, water flea D. magna proved to be the most sensitive species after a short-term (48 h EC50=56.6 mg L(-1)) and long-term exposure (21 d NOEC=1.25 mg L(-1)). On the contrary, the intensified toxicity of Confidor SL 200 in comparison to analytical grade imidacloprid was observed in the case of algae and slight increase of its toxicity was detected testing daphnids and fish. The activities of cholinesterase, catalase and glutathione S-transferase of daphnids were not early biomarkers of exposure to imidacloprid and its commercial product. Imidacloprid was found persistent in water samples and not readily biodegradable in aquatic environment. Due to increased future predicted use of commercial products containing imidacloprid and the findings of this work, we recommend additional toxicity and biodegradability studies of other commercial products with imidacloprid as an active constituent.

Assessing the toxicity of TBBPA and HBCD by zebrafish embryo toxicity assay and biomarker analysis

Tetrabromobisphenol A (TBBPA) and hexabromocyclododecane (HBCD) are two of the most widely used brominated flame retardants (BFRs). The biological toxicity effect of TBBPA and HBCD was studied by means of zebrafish embryo toxicity assays in combination with three biomarkers, including superoxide dismutase (SOD), lipid peroxidation, (LPO), and heat shock protein (Hsp70). The standard zebrafish embryo assay showed that high concentrations of TBBPA (> or =0.75 mg/L) can cause lethality or malformation. For HBCD within the concentration range (0.002-10 mg/L), no endpoint was observed. Furthermore, SOD activities of zebrafish embryos exposed to TBBPA were increased with the increasing concentrations. SOD activities in the group treated by HBCD showed an increase followed by a decline. Regardless of TBBPA or HBCD, LPO were increased along with the increase of the concentration. The change pattern of Hsp70 levels was the same with LPO. All these results showed that TBBPA and HBCD could cause oxidative stress and Hsp70 overexpression, inducing acute toxicity to zebrafish embryo in a short-term exposure. The study also indicates that the zebrafish embryo assay in combination with the biomarkers is effective in aquatic environmental toxicology and risk assessment.

Polybrominated diphenyl ethers in marine ecosystems of the American continents: foresight from current knowledge

Polybrominated diphenyl ethers (PBDEs) are a class of synthetic halogenated organic compounds used in commercial and household products, such as textiles, furniture, and electronics, to increase their flame ignition resistance and to meet fire safety standards. The demonstrated persistence, bioaccumulation, and toxic potential of these compounds in animals and in humans are of increasing concern. The oceans are considered global sinks for PBDEs, as higher levels are found in marine organisms than in terrestrial biota. For the past three decades, North America has dominated the world market demand for PBDEs, consuming 95% of the penta-BDE formulation. Accordingly, the PBDE concentrations in marine biota and people from North America are the highest in the world and are increasing. Despite recent restrictions on penta- and octa-BDE commercial formulations, penta-BDE containing products will remain a reservoir for PBDE release for years to come, and the deca-BDE formulation is still in high-volume use. In this paper, we review all available data on the occurrence and trends of PBDEs in the marine ecosystems (air, water, sediments, invertebrates, fish, seabirds, and marine mammals) of North and South America. We outline here our concerns about the potential future impacts of large existing stores of banned PBDEs in consumer products, and the vast and growing reservoirs of deca-BDE as well as new and naturally occurring brominated compounds on marine ecosystems.

Acute toxicity of 353-nonylphenol and its metabolites for zebrafish embryos

BACKGROUND, AIM AND SCOPE

Nonylphenol (NP) can be detected in the aquatic environment all over the world. It is applied as a technical mixture of isomers of which 353-NP is the most relevant both in terms of abundance (about 20% of total mass) and endocrine potential. 353-NP is metabolised in sewage sludge. The aims of the present study were to determine and to compare the acute toxicity of t-NP, 353-NP and its metabolites as well as to discuss if the toxicity of 353-NP changes during degradation.

MATERIALS AND METHODS

353-NP and two of its metabolites were synthesised. The zebrafish embryo test was performed according to standard protocols. Several lethal and non-lethal endpoints during embryonal development were reported. NOEL, LOEL and EC50 were calculated.

RESULTS

All tested compounds caused lethal as well as non-lethal malformations during embryo development. 353-NP showed a higher toxicity (EC50 for lethal endpoints 6.7 mg/L) compared to its metabolites 4-(3.5-dimethyl-3-heptyl)-2-nitrophenol (EC50 13.3 mg/L) and 4-(3,5-dimethyl-3-heptyl)-2-bromophenol (EC50 27.1 mg/L).

DISCUSSION

In surface water, concentrations of NP are far below the NOEC identified by the zebrafish embryo test. However, in soils and sewage sludge, concentrations may reach or even exceed these concentrations. Therefore, sludge-treated sites close to surface waters should be analysed for NP and its metabolites in order to detect an unduly high contamination due to runoff events.

CONCLUSIONS

The results of the present study point out that the toxicity of 353-NP probably declines during metabolisation in water, sediment and soil, but does not vanish since the major metabolites exhibit a clear toxic potential for zebrafish embryos.

RECOMMENDATIONS AND PERSPECTIVES

Metabolites of environmental pollutants should be included in the ecotoxicological test strategy for a proper risk assessment.

Is the fish embryo toxicity test (FET) with the zebrafish (Danio rerio) a potential alternative for the fish acute toxicity test?

The fish acute toxicity test is a mandatory component in the base set of data requirements for ecotoxicity testing. The fish acute toxicity test is not compatible with most current animal welfare legislation because mortality is the primary endpoint and it is often hypothesized that fish suffer distress and perhaps pain. Animal alternative considerations have also been incorporated into new European REACH regulations through strong advocacy for the reduction of testing with live animals. One of the most promising alternative approaches to classical acute fish toxicity testing with live fish is the fish embryo toxicity (FET) test. The FET has been a mandatory component in routine whole effluent testing in Germany since 2005 and has already been standardized at the international level. In order to analyze the applicability of the FET also in chemical testing, a comparative re-evaluation of both fish and fish embryo toxicity data was carried out for a total of 143 substances, and statistical approaches were developed to evaluate the correlation between fish and fish embryo toxicity data. Results confirm that fish embryo tests are neither better nor worse than acute fish toxicity tests and provide strong scientific support for the FET as a surrogate for the acute fish toxicity test.

PCB association with model phospholipid bilayers

We compare the association of an ortho-substituted and a planar PCB (polychlorinated biphenyls PCB-52 and PCB-77, respectively) with single-component phospholipid bilayers terminated with phosphocholine headgroups. First, fluorescence correlation spectroscopy (FCS) studies of diffusion on supported fluid-phase DLPC show that the ortho-substituted PCB diffuses more slowly, indicating either complex formation or obstructed diffusion. Differential scanning calorimetry (DSC) of vesicles formed from DMPC shows that the gel-to-fluid phase transition temperature is lower for vesicles containing this ortho-substituted PCB. Atomic force microscopy (AFM) shows that, whereas supported bilayers of DMPC containing this ortho-substituted PCB display two melting points, bilayers containing the coplanar PCB display just a single melting point. A model is proposed in which the ortho-substituted PCB resides within the lipid tails of these phospholipid bilayers but the coplanar PCB associates preferentially with the headgroups. This model is consistent with the known membrane disruptive ability of the ortho substituted isomer.

Maternal transfer of brominated flame retardants in zebrafish (Danio rerio)

In many species reproduction and embryonic development have been shown to be sensitive to environmental contaminants. Understanding embryonic exposure to environmental contaminants is thus highly important. In this study concentrations of brominated flame retardants (BFRs) were measured in zebrafish eggs after parental exposure for 42 days via the diet. Zebrafish were exposed to two doses of eleven structurally-diverse BFRs. Eight BFRs were detected in the female zebrafish and maternal transfer to eggs was evident for all eight compounds. The highest concentrations in eggs were observed for hexabromocyclododecane (HBCD) and 2,4,4'-tribromodiphenyl ether (BDE 28), followed by 2,2',3,4,4',5',6-heptabromodiphenyl ether (BDE 183) and tetrabromobisphenol A 2,3-dibromopropyl ether (TBBPA DBPE). Five potential BFR metabolites were tentatively identified in female fish and maternal transfer was observed also for these compounds. The lipid adjusted concentrations in eggs were significantly higher than the concentrations in female fish for several of the BFRs. Further, the results showed a generally higher transfer in the lower exposure level and also indicated a dependency on the physico-chemical properties of the compounds.

The Sensitivity and Reproducibility of the Zebrafish (Danio rerio) Embryo Test for the Screening of Waste Water Quality and for Testing the Toxicity of Chemicals

The sensitivity of the zebrafish embryo test, a test proposed for routine waste water control, was compared with the acute fish toxicity test, in the determination of six types of waste water and ten different chemicals. The waste water was sampled from the following industrial processes: paper and cardboard production, hide tanning, metal galvanisation, carcass treatment and utilisation, and sewage treatment. The chemicals tested were: dimethylacetamide, dimethylsulphoxide, cadmium chloride, cyclohexane, hydroquinone, mercuric chloride, nickel chloride, nonylphenol, resmethrin and sodium nitrite. For many of the test substances, the zebrafish embryo test and the acute fish toxicity test results showed high correlations. However, there were certain environmentally-relevant substances for which the results of the zebrafish embryo test and the acute fish toxicity test differed significantly, up to 10,000-fold (Hg2+ > 150fold difference; NO2- > 300-fold; Cd2+ > 200-fold; resmethrin > 10,000-fold). For the investigated waste water samples and chemicals, the survival rate of the zebrafish embryos showed high variations between different egg samples, within the range of the EC50 concentration. Subsequently, 5–6 parallel assays were deemed to be the appropriate number necessary for the precise evaluation of the toxicity of the test substances. Also, it was found that the sensitivities of different ontogenetic stages to chemical exposure differed greatly. During the first 12 hours after fertilisation (4-cell stage to the 5-somite stage), the embryos reacted most sensitively to test substance exposure, whereas the later ontogenetic stages showed only slight or no response, indicating that the test is most sensitive during the first 24 hours post-fertilisation.