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At least 145 records · Page 8Linked to original sources
PubMed2000

Competitive behavior in the interactive toxicology of halogenated aromatic compounds.

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that binds and mediates responses to many halogenated aromatic compounds (HACs). Exposure to mixtures of HACs frequently results in nonadditive behavior in both in vivo and in vitro assays. One cause is antagonism, which results when two or more ligands compete for a limited supply of the AhR; one interacts agonistically to induce a strong response, and the other interacts unproductively, eliciting little or no response. This study involves the mechanism by which HACs induce CYP 1A1. Agonistic (e.g., TCDD) and unproductive (e.g., PCB 153) HACs behaved similarly through the stages of initial AhR binding and conversion of the initial AhR-ligand complex to the form that possesses increased affinity for the bound ligand. They diverged in the ability of the AhR-HAC complex to bind to a synthetic oligonucleotide containing the consensus dioxin response enhancer sequence, as studied by the gel retardation assay. Competition for the Ah receptor was used to explain antagonistic behavior between TCDD and other HACs in both the gel retardation assay and the downstream response of CYP 1A1 induction in primary rat hepatocytes.

Animals↗
PubMed1990

Degradation of halogenated aliphatic compounds by the ammonia- oxidizing bacterium Nitrosomonas europaea.

Suspensions of Nitrosomonas europaea catalyzed the ammonia-stimulated aerobic transformation of the halogenated aliphatic compounds dichloromethane, dibromomethane, trichloromethane (chloroform), bromoethane, 1,2-dibromoethane (ethylene dibromide), 1,1,2-trichloroethane, 1,1,1-trichloroethane, monochloroethylene (vinyl chloride), gem-dichloroethylene, cis- and trans-dichloroethylene, cis-dibromoethylene, trichloroethylene, and 1,2,3-trichloropropane, Tetrachloromethane (carbon tetrachloride), tetrachloroethylene (perchloroethylene), and trans-dibromoethylene were not degraded.

Ammonia↗
PubMed1989

Microbiological methods for the cleanup of soil and ground water contaminated with halogenated organic compounds.

There is growing interest in the enhancement of microbial degradative activities as a means of bringing about the in situ cleanup of contaminated soils and ground water. The halogenated organic compounds are likely to be prime targets for such biotechnological processes because of their widespread utilisation and the biodegradability of many of the most commonly used compounds. The aim of this review is to consider the potential for microbiological cleanup of haloorganic-contaminated sites. The technologies available involve the provision of suitable environmental conditions to facilitate maximum biodegradation rates either in the subsurface or in on-site bioreactors. Methodologies include the supply of inorganic nutrients, the supply of oxygen gas, the addition of degradative microbial inocula and the introduction of co-metabolic substrates. The potential efficiencies and limitations of the methods are critically discussed from a microbiological viewpoint with respect to substrate degradability and population responses to supplementation.

Bacteria↗
PubMed2004

Screening of halogenated aromatic compounds in some raw material lots for an aluminium recycling plant.

Four samples of scrap raw materials for an aluminium recycling plant were screened for the occurrence of persistent halogenated aromatic compounds. The samples contained waste from handling of electric and electronic plastics, filter dust from electronic crusher, cyclone dust from electronic crusher and light fluff from car shredder. In our screening analyses, brominated flame retardants were observed in all samples. Polybrominated diphenyl ethers (PBDE) were identified in all samples in amounts of 245-67450 ng/g. The major PBDE congeners found were decabromo- and pentabromodiphenyl ethers. 1,1-bis(2,4,6-tribromophenoxy)ethane, hexabromobenzene, ethyl-pentabromobenzene, tetrabromobisphenol-A, pentabromotoluene and dimethyl tetrabromobenzene were observed in all scrap samples. The concentrations of PCBs, PCNs (polychlorinated naphthalenes) and nona- to undecachlorinated terphenyls in some of these scrap samples were remarkably high.

Aluminum↗
PubMed2006

Development of a purge and trap continuous flow system for the stable carbon isotope analysis of volatile halogenated organic compounds in water.

A purge and trap (P&T) continuous flow system was developed in order to concentrate high volumes of water for trace analyses and stable carbon isotope measurements of volatile halogenated organic compounds (VHOCs) in seawater. The P&T parameters were evaluated regarding quality parameters, extraction efficiency and isotope fractionation. Precision (about 20%), linearity (>0.9676), and recoveries (between 75% and 99%) were reasonable within the large concentration range tested. Isotope fractionation was between 1 per thousand and 3 per thousand. Finally, the developed system was successfully applied to the quantitative and stable carbon isotope analysis of three water samples of different origin.

Carbon Isotopes↗
PubMed2006

Flavin-dependent halogenases involved in secondary metabolism in bacteria.

The understanding of biological halogenation has increased during the last few years. While haloperoxidases were the only halogenating enzymes known until 1997, it is now clear that haloperoxidases are hardly, if at all, involved in biosynthesis of more complex halogenated compounds in microorganisms. A novel type of halogenating enzymes, flavin-dependent halogenases, has been identified as a major player in the introduction of chloride and bromide into activated organic molecules. Flavin-dependent halogenases require the activity of a flavin reductase for the production of reduced flavin, required by the actual halogenase. A number of flavin-dependent tryptophan halogenases have been investigated in some detail, and the first three-dimensional structure of a member of this enzyme subfamily, tryptophan 7-halogenase, has been elucidated. This structure suggests a mechanism involving the formation of hypohalous acid, which is used inside the enzyme for regioselective halogenation of the respective substrate. The introduction of halogen atoms into non-activated alkyl groups is catalysed by non-heme FeII alpha-ketoglutarate- and O2-dependent halogenases. Examples for the use of flavin-dependent halogenases for the formation of novel halogenated compounds in in vitro and in vivo reactions promise a bright future for the application of biological halogenation reactions.

Bacteria↗
PubMed1981

Analysis of volatile halogenated organic compounds in fish.

A method for the analysis of volatile halogenated hydrocarbons in biological samples has been developed. Extraction efficiencies for various C1 and C2 halocarbons were found to be in the range of 63--82%, and recoveries were fairly good. The detection limits lie in the sub-ppb range (0.1--1 ppb). The method has been used to analyse fish samples from both unpolluted and polluted areas in Norway. The compounds most frequently found were chloroform, trichloroethylene and tetrachloroethylene in concentrations ranging from 10--1000 ppb. From one area, corresponding water and fish samples were analysed which made it possible to estimate accumulation factors for chloroform and trichloroethylene, which were found to be 200--500 and 1400 respectively.

Animals↗
PubMed2002

Inhibition of quorum sensing in Pseudomonas aeruginosa biofilm bacteria by a halogenated furanone compound.

Novel molecular tools have been constructed which allow for in situ detection of N-acyl homoserine lactone (AHL)-mediated quorum sensing in Pseudomonas aeruginosa biofilms. The reporter responds to AHL activation of LasR by expression of an unstable version of the green-fluorescent protein (Gfp). Gfp-based reporter technology has been applied for non-destructive, single-cell-level detection of quorum sensing in laboratory-based P. aeruginosa biofilms. It is reported that a synthetic halogenated furanone compound, which is a derivative of the secondary metabolites produced by the Australian macroalga Delisea pulchra, is capable of interfering with AHL-mediated quorum sensing in P. aeruginosa. It is demonstrated that the furanone compound specifically represses expression of a PlasB-gfp reporter fusion without affecting growth or protein synthesis. In addition, it reduces the production of important virulence factors, indicating a general effect on target genes of the las quorum sensing circuit. The furanone was applied to P. aeruginosa biofilms established in biofilm flow chambers. The Gfp-based analysis reveals that the compound penetrates microcolonies and blocks cell signalling and quorum sensing in most biofilm cells. The compound did not affect initial attachment to the abiotic substratum. It does, however, affect the architecture of the biofilm and enhances the process of bacterial detachment, leading to a loss of bacterial biomass from the substratum.

4-Butyrolactone↗
PubMed2006

Sonolytic degradation of halogenated organic compounds in groundwater: mass transfer effects.

Organic pollutants in liquid exposed to acoustic waves behave differently according to their physical and chemical properties. Laboratory batch experiments of sonication for the degradation of trichloroethylene (TCE) and ethylene dibromide (EDB) were carried out in groundwater at 20 kHz, and 12.5 and 35 W/cm(2). A theoretical model for the batch sonication system was derived to examine the mass transfer dependency of the ultrasonic degradation. Experimental results were supported with model predictions suggesting that both liquid phase diffusion coefficient and Henry's law constant are important parameters for the sonolytic degradation of the halogenated organic compounds in groundwater. When compared with the effect of the diffusion coefficient, Henry's constant exerts a greater influence on sonolytic degradation. When Henry's constant exceeds a value of 1 (volume/volume ratio), however, it no longer has much influence on the degradation process. The results also suggest that degradation is enhanced with an increase in ultrasonic power probably due to a greater bubble residence time and the formation of larger bubble at high-energy intensities.

Computer Simulation↗
PubMed1987

Developmental toxicity of halogenated acetonitriles: drinking water by-products of chlorine disinfection.

The developmental toxicity of acetonitrile and 5 halogenated derivatives was examined with an in vivo teratology screen adapted for use in the Long-Evans rat. The screen was extended to an evaluation of growth till postnatal Days 41-42, and weight of several organs at sacrifice. Acetonitrile was without developmental effects even at doses toxic to the dam. Of the halogenated compounds, treatment with trichloroacetonitrile (TCAN) and dichloroacetonitrile (DCAN) resulted in reduced fertility and increased early implantation failure. There was no effect on litter size in females bearing live litters, but pup birth weight was reduced in all litters exposed to halogenated compounds. Perinatal survival of the pups was adversely impacted by DCAN and TCAN. Postnatal growth till Day 4 was reduced by DCAN and bromochloroacetonitrile (BCAN) while growth till Day 42 was consistently affected only by TCAN. Some general observations were made on the usefulness of the criteria used in the screen, and TCAN, the most toxic of the halogenated compounds, was selected for further in-depth evaluation.

Abnormalities, Drug-Induced↗
PubMed2004

Development of fluorinated low temperature glassy carbon films for solid-phase microextraction.

Solid-phase microextraction (SPME) fibers with supported fluorinated glassy carbon are demonstrated for the first time. Oligo[1,3-dibutadiynylene-1,3-(tetrafluoro)phenylene] was synthesized and heated to temperatures that varied from 200 to 1000 degrees C to produce the fluorinated glassy carbon. The extent of graphitization of the glassy carbon increased as the processing temperature increased. The fluorinated glassy carbon selectively extracted monohalogenated benzenes from an aqueous solution when compared to the extraction of toluene. The selectivity increased in the order of phi-F < phi-Cl < phi-Br < phi-I. The selectivity for the halogenated compounds was greatest for the fluorinated glassy carbon phase processed at temperature below approximately 400 degrees C. Preliminary studies on the retention mechanism of the LTGC phase show that dispersive interactions are very important to the retention of halocarbons on the fluorinated LTGC. Finally, the selectivity of the fluorinated LTGC for halogenated compounds was compared to that of commercially available SPME fibers, such as poly(dimethylsiloxane), poly(dimethylsiloxane)/divinylbenzene (PDMS/DVB), and poly(dimethylsiloxane)/Carboxen (PDMS/Carboxen) fibers. As expected the fluorinated LTGC was more selectivity for the halogenated compounds. Interestingly the order of the increase in selectivity is opposite when comparing the fluorinated-LTGC and the three commercial fibers. A decrease in selectivity was observed going from fluorobenzene to iodobenzene using PDMS/DVB and PDMS/Carboxen fibers. While for the pure PDMS phase, there is a slight increase in selectivity from fluorobenzene to chlorobenzene but the remaining trend shows little change for bromobenzene and iodobenzene.

Carbon↗
PubMed1994

Reductive dehalogenation as a respiratory process.

Anaerobic bacteria can reductively dehalogenate aliphatic and aromatic halogenated compounds in a respiratory process. Only a few of these bacteria have been isolated in pure cultures. However, long acclimation periods, substrate specificity, high dehalogenation rates, and the possibility to enrich for the dehalogenation activity by subcultivation in media containing an electron donor indicate that many of the reductive dehalogenations in the environment are catalyzed by specific bacteria. Molecular hydrogen or formate appear to be good electron donors for the enrichment of such organisms. Furthermore, systems have to be employed which supply the cultures with the halogenated compounds beyond their toxicity level. All bacteria that are presently available in pure culture and grow with a halogenated compound as electron acceptor are members of new genera. Based on experimental results with the membrane-impermeable electron mediator methyl viologen, a model of the respiration system of Dehalobacter restrictus, a tetrachloroethene-dechlorinating bacterium, is presented. Further studies of the biochemistry and energetics of respiratory-dehalogenating strains will help to understand the mechanisms involved and perhaps reveal the evolutionary origin of the dehalogenating enzyme systems.

Anaerobiosis↗
PubMed1985

Degradation of halogenated aliphatic compounds by Xanthobacter autotrophicus GJ10.

A bacterium that is able to utilize a number of halogenated short-chain hydrocarbons and halogenated carboxylic acids as sole carbon source for growth was identified as a strain of Xanthobacter autotrophicus. The organism constitutively produces two different dehalogenases. One enzyme is specific for halogenated alkanes, whereas the other, which is more heat stable and has a higher pH optimum, is specific for halogenated carboxylic acids. Haloalkanes were hydrolyzed in cell extracts to produce alcohols and halide ions, and a route for the metabolism of 1,2-dichlorethane is proposed. Both dehalogenases show a broad substrate specificity, allowing the degradation of bromine- and chlorine-substituted organic compounds. The results show that X. autotrophicus may play a role in the degradation of organochlorine compounds and that hydrolytic dehalogenases may be involved in the microbial metabolism of short-chain halogenated hydrocarbons in microorganisms.

Biodegradation, Environmental↗
PubMed1978

Chemical structure and biodegradability of halogenated aromatic compounds. Substituent effects on 1,2-dioxygenation of catechol.

1. The influence of halogen substituents on the 1,2-dioxygenation of catechols was investigated. The results obtained with the two isoenzymes pyrocatechase I and pyrocatechase II from the haloarene-utilizing Pseudomonas sp. B 13 and the pyrocatechase from benzoate-induced cells of Alcaligenes eutrophus B.9 were compared. 2. Substituents on catechol were found to interfere with O2 binding by the two isoenzymes from Pseudomonas sp. B 13, whereas the Km value for catechol kept constant at different O2 concentrations. 3. Electron-attracting substituents decreased the Km values for catechols. 4. Results from binding studies with substituted catechols demonstrated narrow stereospecificities of pyrocatechase I from pseudomonas sp. B 13 and the pyrocatechase from alcaligenes eutrophus B.9. In contrast, a low steric hindrance by substituents in the binding of catechols with pyrocatechase II was observed. 5. Low pK'1 values of substituted catechols resulted in low Michaelis constants. 6. Electron-attracting substituents such as halogen decreased the reaction rates of catechol 1,2-dioxygenation. The correlation of the Vmax. values observed with pyrocatechase II from Pseudomonas sp. B 13 with the substituent constant sigma+ (Okamoto--Brown equation) was distinctly greater than with Hammett's sigma values. The corresponding logVmax. against sigma+ correlation for pyrocatechase I was considerably disturbed by steric influences of the substituents.

Alcaligenes↗