benzofurans and diphenyl

Apple replant disease (ARD) is a severe soil-borne disease frequently observed in apple tree nurseries and orchards worldwide. One of the responses of apple trees to ARD is the formation of biphenyl and dibenzofuran phytoalexins in their roots. However, there is no information on whether or not these phytoalexins are exuded into the soil. To answer this open question, a model system was established using the ARD-sensitive apple rootstock M26 (Malus × domestica Borkh. Rosaceae) and GC-MS analysis in combination with an in-house GC-MS database including retention indices. We have detected a total of 35 phytoalexins, i.e. 10 biphenyls and 25 dibenzofurans in root samples, thereby adding eight compounds to the previously reported 27 phytoalexins of Malinae species. When in vitro cultured M26 plantlets were treated with yeast extract, all the 35 phytoalexins were formed in the roots and 85.2% of the total phytoalexin amount was exuded into the culture medium. In roots of M26 plants grown in ARD soil in pot, 26 phytoalexins were detected and their exudation was demonstrated using two independent approaches of collecting root exudates. In a modified dipping experiment and a soil-hydroponic hybrid setup, the exudation rate was 39.5% and 20.6%, respectively. The exudation rates for individual phytoalexins differed, indicating controlled exudation processes. The exuded phytoalexins may play an important role in shaping the soil microbiome, which appears to greatly influence the development and severity of ARD.

Topics: Benzofurans; Biphenyl Compounds; Dibenzofurans; Malus; Phytoalexins; Plant Roots; Sesquiterpenes; Soil

All the possible polychlorinated aromatic compounds in the classes of dibenzodioxins (PCDDs), dibenzofurans (PCDFs), and biphenyls (PCBs) were studied by the quantum chemical methods of HF/6-311++G(d,p), B3LYP/6-311++G(d,p), and MP2/cc-pVTZ. The calculated stabilities and structures of these compounds were compared with the available data on their abundance and toxicity. Prediction models for trends in energy and planarity among these congeners were proposed. The results discussed here can help contribute to the understanding of the role of dioxin-like compounds (DLCs) in the environment.

Topics: Benzofurans; Biphenyl Compounds; Dibenzofurans; Dioxins; Polychlorinated Biphenyls; Polychlorinated Dibenzodioxins

Topics: Antioxidants; Benzofurans; Biphenyl Compounds; Dalbergia; Free Radical Scavengers; Molecular Structure; Spectrum Analysis; Structure-Activity Relationship

Fire blight is a devastating disease of Rosaceae plants, such as apple and pear trees. It is characterized by necrosis of plant tissue, caused by the phytopathogenic bacterium Erwinia amylovora. The plant pathogen produces the well-known antimetabolite 6-thioguanine (6TG), which plays a key role in fire blight pathogenesis. Here we report that YcfR, a member of the LTTR family, is a major regulator of 6TG biosynthesis in E. amylovora. Inactivation of the regulator gene (ycfR) led to dramatically decreased 6TG production. Infection assays with apple plants (Malus domestica cultivar Holsteiner Cox) and cell cultures of Sorbus aucuparia (mountain ash, rowan) revealed abortive fire blight pathogenesis and reduced plant response (biphenyl and dibenzofuran phytoalexin production). In the presence of the ΔycfR mutant, apple trees were capable of activating the abscission machinery to remove infected tissue. In addition to unveiling the regulation of 6TG biosynthesis in a major plant pathogen, we demonstrate for the first time that this antimetabolite plays a pivotal role in dysregulating the plant response to infection.

Topics: Bacterial Outer Membrane Proteins; Base Sequence; Benzofurans; Biphenyl Compounds; Erwinia amylovora; Molecular Sequence Data; Multigene Family; Mutation; Phytoalexins; Plant Cells; Plant Diseases; Rosaceae; Sesquiterpenes; Thioguanine

The remote oceans are among the most pristine environments in the world, away from sources of anthropogenic persistent organic pollutants (POP), but nevertheless recipients of atmospheric deposition of POPs that have undergone long-range atmospheric transport (LRAT). In this work, the background occurrence of gas and aerosol phase polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and dioxin like polychlorinated biphenyls (dl-PCB) is evaluated for the first time in the atmosphere of the tropical and subtropical Atlantic, Pacific, and Indian oceans. Thirty-nine air samples were collected during the eight-month Malaspina circumnavigation cruise onboard the R/V Hespérides. The background levels of dioxins and dl-PCBs remained very low and in many cases very close to or below the limit of detection. Expectedly, the levels of PCBs were higher than dioxins, PCB#118 being the most abundant compound. In the particular case of dioxins, octachlorodibenzo-p-dioxin (OCDD) was the most abundant PCDD/F congener. Distribution of dl-PCB is dominated by the gas phase, while for PCDD/F the aerosol phase concentrations were higher, particularly for the more hydrophobic congeners. The Atlantic Ocean presented on average the highest PCDD/F and dl-PCB concentrations, being lower in the southern hemisphere. The assessment of air mass back trajectories show a clear influence of continental source regions, and lower concentrations when the air mass has an oceanic origin. In addition, the samples affected by an oceanic air mass are characterized by a lower contribution of the less chlorinated dioxins in comparison with the furans, consistent with the reported higher reaction rate constants of dibenzo-p-dioxins with OH radicals than those of dibenzofurans. The total dry atmospheric deposition of aerosol-bound ∑PCDD/F and ∑dl-PCB to the global oceans was estimated to be 354 and 896 kg/year, respectively.

Topics: Aerosols; Air; Air Pollutants; Atlantic Ocean; Atmosphere; Benzofurans; Biphenyl Compounds; Gases; Geography; Indian Ocean; Oceans and Seas; Pacific Ocean; Polychlorinated Dibenzodioxins; Ships

The occurrence of nineteen mixed halogenated (bromo-chloro) dibenzo-p-dioxins, dibenzofurans (PXDD/Fs) and biphenyls (PXBs) in a range of foods (n>100) was investigated. The analytical methodology used dual activated carbon column fractionation with high resolution mass spectrometric measurement (13,500-15,000 res). Occurrence was observed in most commonly consumed foods but the most frequent detections of these environmental contaminants were made in shellfish and offal. The concentrations of the individual compounds were condensed into toxic equivalents (TEQs) using recently reported relative potency values. Although representing only a small subset of the full range of toxic PXDD/Fs and PXBs, the TEQs estimated for these compounds ranged from 0.2% to approximately 15% (depending on the food matrix) of the corresponding TEQ for the fully chlorinated analogues. This finding is of great toxicological importance as it implies that a potentially greater magnitude of TEQ could be associated with the full range of toxic PXDD/Fs and PXBs, thus making a significant contribution to dioxin-like toxicity from the diet, to human exposure.

Topics: Benzofurans; Biphenyl Compounds; Dioxins; Environmental Pollutants; Food Contamination; Furans; Humans; Hydrocarbons, Brominated; Hydrocarbons, Chlorinated; Polychlorinated Dibenzodioxins

Aucuparin is the most widely distributed biphenyl phytoalexin in the rosaceous subtribe Pyrinae, which includes the economically important fruit trees apple and pear. The biphenyl scaffold is formed by biphenyl synthase, which catalyzes biosynthesis of 3,5-dihydroxybiphenyl. Conversion of this precursor to aucuparin (3,5-dimethoxy-4-hydroxybiphenyl) was studied in cell cultures of Sorbus aucuparia after treatment with an elicitor preparation from the scab-causing fungus Venturia inaequalis. The sequence of the biosynthetic steps detected was O-methylation - 4-hydroxylation - O-methylation. The two alkylation reactions were catalyzed by distinct methyltransferases, which differed in pH and temperature optima as well as stability. Biphenyl 4-hydroxylase was a microsomal cytochrome P450 monooxygenase, whose activity was appreciably decreased by the addition of established P450 inhibitors. When fed to V. inaequalis-treated S. aucuparia cell cultures, radioactively labeled 3,5-dihydroxybiphenyl was not only incorporated into aucuparin but also into the dibenzofuran eriobofuran, the accumulation of which paralleled that of aucuparin. However, biphenyl 2'-hydroxylase activity proposed to be involved in dibenzofuran formation was detected in neither microsomes nor cell-free extracts in the presence of NADPH and 2-oxoglutarate, respectively. Nevertheless, a basis for studying biphenyl biosynthesis at the gene level is provided.

Topics: Ascomycota; Benzofurans; Biphenyl Compounds; Cells, Cultured; Cytochrome P-450 Enzyme System; Ketoglutaric Acids; Malus; Multienzyme Complexes; Phytoalexins; Pyrus; Sesquiterpenes; Sorbus

The biphenyl dioxygenase of Burkholderia xenovorans LB400 (BphAE(LB400)) catalyzes the dihydroxylation of biphenyl and of several polychlorinated biphenyls (PCBs) but it poorly oxidizes dibenzofuran. In this work we showed that BphAE(RR41), a variant which was previously found to metabolize dibenzofuran more efficiently than its parent BphAE(LB400), metabolized a broader range of PCBs than BphAE(LB400). Hence, BphAE(RR41) was able to metabolize 2,6,2',6'-, 3,4,3',5'- and 2,4,3',4'-tetrachlorobiphenyl that BphAE(LB400) is unable to metabolize. BphAE(RR41) was obtained by changing Thr335Phe336Asn338Ile341Leu409 of BphAE(LB400) to Ala335Met336Gln338Val341Phe409. Site-directed mutagenesis was used to create combinations of each substitution, in order to assess their individual contributions. Data show that the same Asn338Glu/Leu409Phe substitution that enhanced the ability to metabolize dibenzofuran resulted in a broadening of the PCB substrates range of the enzyme. The role of these substitutions on regiospecificities toward selected PCBs is also discussed.

Topics: Benzofurans; Biphenyl Compounds; Burkholderia; Catalysis; Dioxygenases; Escherichia coli; Mutagenesis, Site-Directed; Oxidation-Reduction; Polychlorinated Biphenyls; Recombinant Proteins

The formation of mono- to octachlorinated dibenzo-p-dioxins (PC₁₋₈DD) and dibenzofurans (PC₁₋₈DF) was studied using a model waste in a laboratory-scale combustion reactor with simultaneous collection of flue gas at three different temperatures (450 °C, 300 °C, and 200 °C) in the post-combustion zone. To investigate the influence of chlorination reactions and the effects of carbon backbone-containing compounds present in the flue gases, five aromatic compounds were injected into the flue gas, namely dibenzofuran (DF), biphenyl (BP), naphthalene, phenanthrene and fluorene. The injection of DF induced a reduction in the concentration of PC₃₋₅DD, but did not significantly influence the concentration of PCDF. A reduction in the concentration of PC₃₋₅DD was also observed during the injection of fluorene, which is structurally very similar to DF. The injection of biphenyl, naphthalene and phenanthrene had less pronounced effects on the formation of PCDD and PCDF. A possible explanation of the observed changes during injection of DF and fluorene, based on homologue profiles and affected congeners, involves formation of radical species from fluorene and/or dibenzofuran. The fluorene radical is stabilized by the delocalization of electrons across the aromatic ring structure and has the propensity to react with highly abundant hydrogen chloride, whereas the molecular species would require reaction with Cl₂ or chlorine radicals.

Topics: Air Pollutants; Air Pollution; Benzofurans; Biphenyl Compounds; Dibenzofurans, Polychlorinated; Incineration; Polychlorinated Dibenzodioxins; Polycyclic Aromatic Hydrocarbons

Bioassay-guided fractionation of the methanolic extract of the roots of Rhaphiolepis indica var. tashiroi afforded four new dibenzofurans, 2-hydroxy-3,4,6-trimethoxydibenzofuran (1), 2-hydroxy-3,4,9-trimethoxydibenzofuran (2), 2-hydroxy-3,4,6,9-tetramethoxydibenzofuran (3), and 1,2-methylenedioxy-3,4,6-trimethoxydibenzofuran (4), two new biphenyls, 3-hydroxy-2',5-dimethoxybiphenyl (5) and 2',3-dihydroxy-5-methoxybiphenyl (6), and 3-hydroxy-5-methoxybiphenyl (7). Among the isolates, 3, 5, and 6 exhibited inhibitory effects on N-formyl-methionyl-leucyl-phenylalanine (fMLP)-induced superoxide production, with in vitro IC50 values < 8.36 μM.

Topics: Anti-Inflammatory Agents; Benzofurans; Biphenyl Compounds; Humans; Inhibitory Concentration 50; Molecular Structure; N-Formylmethionine Leucyl-Phenylalanine; Neutrophils; Nuclear Magnetic Resonance, Biomolecular; Plant Roots; Rosaceae; Superoxides; Taiwan

The Rosaceous subtribe Pyrinae (formerly subfamily Maloideae) is well-known for its economically important fruit trees, such as apple and pear, and also includes Sorbus aucuparia. Elicitor-treated S. aucuparia cell cultures are used to study the biosynthesis of the Pyrinae-specific phytoalexins, biphenyls and dibenzofurans. Three biphenyls (aucuparin, noraucuparin, 2'-hydroxyaucuparin) and a dibenzofuran (eriobofuran) were isolated and structure elucidated using GC-MS and NMR. A second dibenzofuran of low abundance was tentatively assigned as noreriobofuran. Treatment of S. aucuparia cell cultures with yeast extract induced the formation of aucuparin as the major phytoalexin. In contrast, addition of preparations from the fire blight bacterium, Erwinia amylovora, and the scab-causing fungus, Venturia inaequalis, resulted in accumulation of eriobofuran as the major inducible constituent. Methyl jasmonate was a poor elicitor. The observations are suggestive of a biogenic relationship between biphenyls and dibenzofurans. Elicitor-treated S. aucuparia cell cultures provide an interesting in vitro system for studying biphenyl and dibenzofuran metabolism in the economically valuable Pyrinae.

Topics: Ascomycota; Benzofurans; Biphenyl Compounds; Cells, Cultured; Erwinia amylovora; Phytoalexins; Sesquiterpenes; Sorbus

This study was intended to determine the background levels of PCDD/PCDFs and PCBs in the Taiwanese population and to investigate factors potentially related to PCDD/PCDF and PCB levels. The levels of seventeen PCDD/PCDFs in the 251 serum samples collected from the general population in Taiwan ranged from 4.92 to 26.7 pg WHO(1998)-TEQ/g lipid (median: 11.5) and those of the twelve dioxin-like PCBs ranged between 1.74 and 21.6 pg WHO(1998)-TEQ/g lipid (median: 6.14). Five factors, age, gender, region of residence, dietary status, and smoking status, showed statistically significant association with the TEQ level of PCDD/PCDFs. The TEQ level of PCBs was statistically associated with age only, but not with the other four factors. The trends observed between age and the levels of PCDD/PCDFs and PCBs were not parallel in young subjects (<30 years old) and old subjects (>30 years old). The levels of PCDD/PCDFs and PCBs increased by 0.16 and 0.03 WHO(1998)-TEQ/g lipid per year for subjects above the age of 30, but there was no evidence of any association between age and the levels for subjects below the age of 30 years. These factors should be considered when investigating relationships between background serum levels of persistent organic pollutants and parameters associated with exposure sources or health outcomes.

Topics: Adolescent; Adult; Age Factors; Benzofurans; Biphenyl Compounds; Blood Chemical Analysis; Dioxins; Female; Humans; Male; Middle Aged; Risk Factors; Taiwan; Young Adult

Fish from Dutch markets were analysed for concentrations of polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (DL-PCBs) and compared with the new European maximum residue levels (MRLs), set in 2006. In a first study on 11 different fish and shellfish from various locations, concentrations of PCDD/Fs were nearly all below the MRL for PCDD/Fs [4 pg toxic equivalents (TEQ) per gram wet weight (ww)] and nearly all below 8 pg total TEQ/g ww, the new MRL for the sum of PCDD/Fs and DL-PCBs. Some samples exceeded the total TEQ MRL, such as anchovy, tuna and sea bass. Furthermore, 20 (out of 39) wild eel samples exceeded the specific MRL for eel (12 pg total TEQ/g ww), as the study revealed PCDD/F TEQ levels of 0.2-7.9 pg TEQ/g ww and total TEQ values of 0.9 to 52 pg/g ww. TEQ levels in farmed and imported eel were lower and complied with the MRLs. Smoking eel, a popular tradition in the Netherlands, only had marginal effects on PCDD/F and DL-PCB concentrations. Owing to volatilization, concentrations of lower-chlorinated PCBs were reduced to below the limit of quantification after smoking. DL-PCBs contributed 61-97% to the total TEQ in all eel samples. This also holds for other fish and shellfish (except shrimps): DL-PCB contributed (on average) from 53 (herring) to 83% (tuna) to the total TEQ. Principal-component analysis revealed distinctive congener profiles for PCDD/Fs and non-ortho PCBs for mussels, pikeperch, herring and various Mediterranean fish. The application of new TCDD toxic equivalency factors (TEFs) set by the World Health Organization in 2006 (to replace the 1997 TEFs) resulted in lower TEQ values, mainly owing to a decreased mono-ortho PCB contribution. This decrease is most pronounced for eel, owing to the relative high mono-ortho PCB concentrations in eel. Consequently, a larger number of samples would comply with the MRLs when the new TEFs are applied. The DR CALUX(R) assay may be used for screening total TEQ levels in eel, in combination with gas chromatography-high resolution mass spectrometry confirmation of suspected samples. An almost 1:1 correlation was found when the 1997 TEFs were applied, but, surprisingly, a 1.4-fold overestimation occurred with application of the 2006 TEFs.

Topics: Animals; Benzofurans; Biological Assay; Biphenyl Compounds; Dioxins; Fishes; Food Analysis; Hydrocarbons, Chlorinated; Netherlands; Shellfish; Smoking; Time Factors; World Health Organization

Although the metabolism of dibenzofuran by the biphenyl catabolic enzymes had been inferred in previous reports, the metabolic pattern has never been determined unambiguously. In this work, we describe the evolved biphenyl dioxygenase (BPDO) RR41 that exhibits a higher turnover rate of metabolism toward dibenzofuran and chlorodibenzofurans than the parental Burkholderia xenovorans LB400 BPDO. We used RR41 BPDO to identify unambiguously the metabolites produced from the oxygenation of dibenzofuran by LB400 BPDO, and we evaluated their further metabolism by the biphenyl catabolic pathway enzymes of strain LB400. RR41 BPDO was obtained by saturation mutagenesis of targeted amino acid residues. I335F336N338I341L409 of LB400 BphA were replaced by A335M336Q338V341F409 in RR41 BphA. Data confirm the critical role played by these amino acid residues for substrate specificity and regiospecificity.

Topics: Amino Acids; Benzofurans; Biotransformation; Biphenyl Compounds; Burkholderia; Catalysis; Cells, Cultured; Dibenzofurans, Polychlorinated; Dioxygenases; Escherichia coli; Mass Spectrometry; Mutagenesis; Oxidation-Reduction; Substrate Specificity

Polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs) were extracted by accelerated solvent extraction from animal feed samples and analysed by high-resolution gas chromatography/high-resolution mass spectrometry (HRGC/HRMS). In all of the feed samples analysed, the concentrations of PCDD/Fs and PCBs were below the existing tolerance limit of 5 pg I-TEQ g(-1) and 200 ng g(-1) fat, respectively. The mean concentrations of the total PCDDs, total PCDFs and total PCBs were 1.73-11.50 pg g(-1), 0.23-11.91 pg g(-1) and 60.00-234.40 pg g(-1) feed, respectively. Investigation of the correlations among the concentrations of PCDDs, PCDFs and PCBs showed that samples containing increased amounts of PCDFs also contained higher concentrations of PCDDs, with an average ratio of PCDF:PCDD of about 1.23:1 (r(2)=0.72, p<0.05). The correlation between the concentrations of PCDD/Fs and PCBs was positive but not significant.

Topics: Animal Feed; Animals; Benzofurans; Biphenyl Compounds; Cattle; Dioxins; Food Contamination; Fungicides, Industrial; Gas Chromatography-Mass Spectrometry; Korea; Poultry; Swine

In the present study, a dialytic method that uses a DNA aqueous solution to remove and enrich dioxins from polluted water was proposed. Circular dichroism (CD) and fluorescent spectra indicated that dibenzo-p-dioxin (DD), dibenzofuran (DF) and biphenyl (BP), which are dioxin derivatives, form complexes with DNA. Their experimental dialytic sorption coefficients were measured by quantifying the concentrations of DD, DF, and BP in aqueous solutions before and after dialysis of the DNA solution, and the values were 2.1x10(5), 1.3x10(5), and 1.5x10(7), respectively. As a simulated water treatment model, DNA solution was dialyzed in an aqueous mixture of DD, DF, and BP for 96h, the HPLC studies showed that the dioxin derivatives have been concentrated in the DNA solution about 200 times. The dialyzed DNA solution was reusable by an extraction with hexane.

Topics: Benzofurans; Biphenyl Compounds; Circular Dichroism; Dialysis; Dioxins; DNA; Metals; Molecular Structure; Solutions; Spectrometry, Fluorescence

The biotransformation of biphenyl, dibenzofuran, and diphenyl ether by 24 strains belonging to 18 species of the genus Trichosporon was investigated to assess the taxonomic relevance of this property at species and genus level. With the exceptions of T. brassicae and T. porosum CBS 2040, all other strains were able to transform the parent compounds to monohydroxylated intermediates. A second hydroxylation on the same aromatic ring was carried out by fewer strains and depended on the substrate. It appears that this step is the rate-limiting one in the biotransformation of the biarylic compounds tested. Ring fission of dihydroxylated derivatives of biphenyl was observed within 12 species. The aromatic ring system of dihydroxylated dibenzofuran was cleaved by strains of 5 species, while strains of 13 species were able to cleave the aromatic ring system of dihydroxylated diphenyl ether. Only 4 strains out of 18 species were able to cleave the aromatic ring system of all three parent compounds. These most active yeasts belong to the species T. coremiiforme, T. montevideense, T. mucoides, and T. sporotrichoides. In addition, strains of the species Cryptococcus curvatus and Cryptococcus humicola, closely related to the genus Trichosporon, were tested in parallel.

Topics: Benzofurans; Biodegradation, Environmental; Biphenyl Compounds; DNA, Fungal; DNA, Ribosomal; Mycological Typing Techniques; Phenyl Ethers; Phylogeny; RNA, Ribosomal; Trichosporon

Three strains of " Agrobacterium sanguineum", an aerobic marine bacterial species described previously, were re-characterized from phylogenetic and taxonomic viewpoints. 16S rDNA sequence comparisons showed that the " A. sanguineum" strains belong to the alpha-4 subgroup of alpha-Proteobacteria, with members of the genera Erythromicrobium and Porphyrobacter as their closest relatives. DNA-DNA hybridization studies indicated that the " A. sanguineum" strains were distinguishable from any previously known species of these genera. Bacteriochlorophyll a, monosaccharide-type glycosphingolipids, 2-OH fatty acids of C14:0, C15:0, C16:0, and C16:1, and ubiquinone-10 were detected in the " A. sanguineum" strains. The G+C of the DNA was 63.8-64.0 mol%. Two of the " A. sanguineum" strains, IAM 12620 (=ATCC 25659) and ATCC 25661, were able to grow with biphenyl and dibenzofuran as sole carbon source in the presence of 0.05% yeast extract. The medium in these cultures turned yellowish-orange at the exponential phase of growth due to the release of soluble chromogenic metabolites. The remaining " A. sanguineum" strain, ATCC 25660, and all test strains of Erythromicrobium and Porphyrobacter neither grew nor produced yellow-orange pigment with biphenyl or dibenzofuran. In PCR experiments, bphA1 gene, coding for the large subunit protein of biphenyl dioxygenase, was detected in " A. sanguineum" IAM 12620 and ATCC 25661. Based on these results, we propose classifying " A. sanguineum" IAM 12620 and ATCC 25661 as a new species of the genus Porphyrobacter with the name Porphyrobacter sanguineus sp. nov.

Topics: Bacteria, Aerobic; Bacteriochlorophylls; Benzofurans; Biphenyl Compounds; Fatty Acids; Photosynthesis; Phylogeny; Proteobacteria; RNA, Ribosomal, 16S; Species Specificity

Cells of the gram-negative bacterium Ralstonia sp. strain SBUG 290 grown in the presence of biphenyl are able to cooxidize dibenzofuran which has been 1,2-hydroxylated. Meta cleavage of the 1, 2-dihydroxydibenzofuran between carbon atoms 1 and 9b produced 2-hydroxy-4-(3'-oxo-3'H-benzofuran-2'-yliden)but-2-enoic acid, which was degraded completely via salicylic acid. The presence of these intermediates indicates a degradation mechanism for dibenzofuran via lateral dioxygenation by Ralstonia sp. strain SBUG 290.

Topics: Benzofurans; Biodegradation, Environmental; Biphenyl Compounds; Hydroxylation; Oxidation-Reduction; Proteobacteria

Polybrominated and polychlorinated biphenyls (PBBs/PCBs), dibenzo-p-dioxins (PBDDs/PCDDs), dibenzofurans (PBDFs/PCDFs), and diphenyl ethers (PBDEs/PCDEs) are persistent, lipophilic environmental contaminants that may pose a risk to fish early life stage survival. To determine this potential risk, a rainbow trout early life stage mortality bioassay was used in which the potency of individual polybrominated chemicals was compared to the potency of the most potent polychlorinated chemical in these classes, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Following injection of newly fertilized rainbow trout eggs, fish-specific toxic equivalency factors (TEFs) were calculated as the molar ratio of TCDD LD50 to brominated compound LD50. Signs of toxicity were identical to those produced by polychlorinated TCDD-like chemicals and included yolk sac edema, pericardial edema, multifocal hemorrhages, reduced growth, and craniofacial malformations. Polybrominated dibenzo-p-dioxins, dibenzofurans, and biphenyls exhibited decreased potency with increased bromine substitution. Only 2,3,7,8-TBDD was more potent than 2,3,7,8-TCDD, whereas other polybrominated dibenzo-p-dioxins were equipotent or less potent than identically substituted polychlorinated dibenzo-p-dioxins in this assay. Although two PBDF congeners were equipotent to identically substituted PCDFs, 2,3,7,8-TBDF was 9-fold more potent than 2,3,7,8-TCDF. Both 3,3',4,4'-TBB and 3,3',4,4',5,5'-HxBB were 10-fold more potent than identically substituted polychlorinated biphenyls. The halogenated diphenyl ethers and di-ortho polybrominated biphenyls were inactive in this assay. Thus, in this in vivo assay the polybrominated and polychlorinated TCDD-like chemicals were not always equally potent. To assess the risk posed by mixtures of these chemicals to feral fish populations, fish-specific TEFs for both polybrominated and polychlorinated chemicals should be used.

Topics: Animals; Benzofurans; Biphenyl Compounds; Embryo, Nonmammalian; Halogenated Diphenyl Ethers; Hydrocarbons, Brominated; Lethal Dose 50; Oncorhynchus mykiss; Ovum; Phenyl Ethers; Polybrominated Biphenyls; Polychlorinated Dibenzodioxins

Use of fish-specific toxic equivalency factors (TEFs) to estimate the risk that exposure to polybrominated dibenzo-p-dioxins (PBDDs), dibenzofurans (PBDFs), and biphenyls (PBBs) pose to fish early life stage survival depends on validation of the hypothesis that these chemicals act additively to produce mortality. A rainbow trout early life stage bioassay was used to determine how pairs of PBDD, PBDF, and PBB congeners interact to produce 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-like toxicity associated with sac fry mortality. The congener pairs tested were 2,3,7,8-tetrabromodibenzo-p-dioxin (2,3,7,8-TBDD)/1,2,3,7,8-pentabromodibenzo-p-dioxin [correction of pentabromodibenzop-dioxin] (1,2,3,7,8-PBDD); 2,3,7,8-TBDD/1,2,3,7,8-pentabromodibenzofuran (1,2,3,7,8-PBDF); 1,2,3,7,8-PBDD/2,3,4,7,8-pentabromodibenzofuran (2,3,4,7,8-PBDF); and 2,3,4,7,8-PBDF/ 3,3',4,4'-tetrabromobiphenyl (3,3',4,4'-TBB). Graded doses of each congener alone, or graded doses of fixed ratios of paired congeners were injected into newly fertilized rainbow trout eggs. In all cases, interactions between congener pairs were additive as tested by a probit model. Isobolographic analysis also supported the hypothesis that the PBDD, PBDF, and PBB congeners act additively. Thus, the use of fish-specific TEFs to convert fish tissue concentrations of individual PBDD, PBDF, and PBB congeners to TCDD equivalents (TEs) and then adding the TEs contributed by the various congeners to give the total TCDD equivalents concentration (TEC) in the tissue is supported by these results. By comparing the TEC in feral fish eggs to the fish egg TCDD no-observed-effect level (NOEL) and lowest-observed-effect level (LOEL) for early life stage mortality, the risk that complex mixtures of these polybrominated chemicals in eggs pose to sac fry survival can be estimated.

Topics: Animals; Benzofurans; Biphenyl Compounds; Drug Synergism; Embryo, Nonmammalian; Embryonic Development; Oncorhynchus mykiss; Polybrominated Biphenyls; Polychlorinated Dibenzodioxins; Survival Analysis