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Dechlorination
Kinds of Dechlorination Selected AbstractsGround Water Transfer Initiates Complete Reductive Dechlorination in a PCE-Contaminated AquiferGROUND WATER MONITORING & REMEDIATION, Issue 3 2007R. Lookman We conducted a field test to investigate whether ground water transfer from one site (showing complete natural reductive dechlorination of chlorinated ethenes to ethene) could induce full reductive dechlorination at another site polluted with tetrachloroethene and its partial dechlorination products trichloroethene and cis -dichloroethene (cDCE). Addition of electron donor (lactate) at the test site established low redox conditions but did not stimulate further dechlorination past cDCE. After transferring 2 m3 of ground water from the first site to the test site, full dechlorination commenced and high levels of ethene were measured to distances up to 6 m downstream of the injection location within 7 months. Ground water samples from monitoring wells were analyzed before and after inoculation of the test site for the presence of Dehalococcoides species (16S ribosomal RNA) and vinyl chloride reductase (vCRA) genes using the polymerase chain reaction. These tests showed that Dehalococcoides species were present both before and after ground water transfer, while vCRA genes were detected at the test site only after ground water transfer. The vCRA genes were detected in ground water samples collected 6 m downstream of the injection locations 7 months after ground water transfer, suggesting that the microorganisms carrying the dehalogenase genes were effectively transported in the aquifer. [source] Olefin Cyclopropanation by a Sequential Atom-Transfer Radical Addition and Dechlorination in the Presence of a Ruthenium Catalyst,ANGEWANDTE CHEMIE, Issue 43 2009Katrin Thommes Ganz ohne Diazo: Die reduktive Kupplung von Olefinen mit Dichlorverbindungen in Gegenwart von Magnesium und einem Rutheniumkatalysator liefert in guter Ausbeute Cyclopropane (siehe Schema). [source] Electrocatalytic Dechlorination of Chloroform in Aqueous Solution on Palladium/Titanium ElectrodeCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 1 2009Z. Sun Abstract Electrochemical dechlorination of chloroform in aqueous solution was investigated on a palladium-loaded meshed titanium electrode at ambient temperature. The palladium/titanium (Pd/Ti) electrode, which provided a catalytic surface for reductive dechlorination of chloroform in aqueous solution, was prepared with an electrodepositing method. Scanning electron microscope (SEM) micrographs show that Pd microparticles uniformly disperse on the meshed Ti electrode with spheroidal structure. Dechlorination experimental results indicate that, in aqueous solution with the high current efficiency of 33,%, the removal efficiency of chloroform on the Pd/Ti electrode was 37,%, under the conditions of a dechlorination current of 0.1,mA and dechlorination time of 180,min. [source] ChemInform Abstract: Olefin Cyclopropanation by a Sequential Atom-Transfer Radical Addition and Dechlorination in the Presence of a Ruthenium Catalyst.CHEMINFORM, Issue 4 2010Katrin Thommes Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Iron-Catalyzed Dechlorination of Aryl Chlorides.CHEMINFORM, Issue 13 2005Haiqing Guo Abstract For Abstract see ChemInform Abstract in Full Text. [source] An Efficient Synthesis of 2-Chloropyrimidines via Pd-catalyzed Regioselective Dechlorination of 2,4-Dichloropyrimidines in the Presence of NaHCO3CHINESE JOURNAL OF CHEMISTRY, Issue 5 2008Yang-Ming ZHANG Abstract An efficient synthesis of 2-chloropyrimidines from readily accessible 2,4-dichloropyrimidines was achieved via Pd-catalyzed regioselective dechlorination in the presence NaHCO3. [source] Bioreductive deposition of palladium (0) nanoparticles on Shewanella oneidensis with catalytic activity towards reductive dechlorination of polychlorinated biphenylsENVIRONMENTAL MICROBIOLOGY, Issue 3 2005Wim De Windt Summary Microbial reduction of soluble Pd(II) by cells of Shewanella oneidensis MR-1 and of an autoaggregating mutant (COAG) resulted in precipitation of palladium Pd(0) nanoparticles on the cell wall and inside the periplasmic space (bioPd). As a result of biosorption and subsequent bioreduction of Pd(II) with H2, formate, lactate, pyruvate or ethanol as electron donors, recoveries higher than 90% of Pd associated with biomass could be obtained. The bioPd(0) nanoparticles thus obtained had the ability to reductively dehalogenate polychlorinated biphenyl (PCB) congeners in aqueous and sediment matrices. Bioreduction was observed in assays with concentrations up to 1000 mg Pd(II) l,1 with depletion of soluble Pd(II) of 77.4% and higher. More than 90% decrease of PCB 21 (2,3,4-chloro biphenyl) coupled to formation of its dechlorination products PCB 5 (2,3-chloro biphenyl) and PCB 1 (2-chloro biphenyl) was obtained at a concentration of 1 mg l,1 within 5 h at 28°C. Bioreductive precipitation of bioPd by S. oneidensis cells mixed with sediment samples contaminated with a mixture of PCB congeners, resulted in dechlorination of both highly and lightly chlorinated PCB congeners adsorbed to the contaminated sediment matrix within 48 h at 28°C. Fifty milligrams per litre of bioPd resulted in a catalytic activity that was comparable to 500 mg l,1 commercial Pd(0) powder. The high reactivity of 50 mg l,1 bioPd in the soil suspension was reflected in the reduction of the sum of seven most toxic PCBs to 27% of their initial concentration. [source] Coexistence of a sulphate-reducing Desulfovibrio species and the dehalorespiring Desulfitobacterium frappieri TCE1 in defined chemostat cultures grown with various combinations of sulphate and tetrachloroetheneENVIRONMENTAL MICROBIOLOGY, Issue 2 2001Oliver Drzyzga A two-member co-culture consisting of the dehalorespiring Desulfitobacterium frappieri TCE1 and the sulphate-reducing Desulfovibrio sp. strain SULF1 was obtained via anaerobic enrichment from soil contaminated with tetrachloroethene (PCE). In this co-culture, PCE dechlorination to cis -dichloroethene was due to the activity of the dehalorespiring bacterium only. Chemostat experiments with lactate as the primary electron donor for both strains along with varying sulphate and PCE concentrations showed that the sulphate-reducing strain outnumbered the dehalogenating strain at relatively high ratios of sulphate/PCE. Stable co-cultures with both organisms present at similar cell densities were observed when both electron acceptors were supplied in the reservoir medium in nearly equimolar amounts. In the presence of low sulphate/PCE ratios, the Desulfitobacterium sp. became the numerically dominant strain within the chemostat co-culture. Surprisingly, in the absence of sulphate, strain SULF1 did not disappear completely from the co-culture despite the fact that there was no electron acceptor provided with the medium to be used by this sulphate reducer. Therefore, we propose a syntrophic association between the sulphate-reducing and the dehalorespiring bacteria via interspecies hydrogen transfer. The sulphate reducer was able to sustain growth in the chemostat co-culture by fermenting lactate and using the dehalogenating bacterium as a ,biological electron acceptor'. This is the first report describing growth of a sulphate-reducing bacterium in a defined two-member continuous culture by syntrophically coupling the electron and hydrogen transfer to a dehalorespiring bacterium. [source] Monitoring of Desulfitobacterium frappieri PCP-1 in pentachlorophenol-degrading anaerobic soil slurry reactorsENVIRONMENTAL MICROBIOLOGY, Issue 6 2000M. Lanthier Anaerobic biodegradation of pentachlorophenol (PCP) was studied in rotative bioreactors containing 200 g of PCP-contaminated soil and 250 ml of liquid medium. Reactors were bioaugmented with cells of Desulfitobacterium frappieri strain PCP-1, a bacterium able to dehalogenate PCP to 3-chlorophenol. Cells of strain PCP-1 were detected by quantitative PCR for at least 21 days in reactors containing 500 mg of PCP per kg of soil but disappeared after 21 days in reactors with 750 mg of PCP per kg of soil. Generally, PCP was completely removed in less than 9 days in soils contaminated with 189 mg of PCP per kg of soil. Sorption of PCP to soil organic matter reduced its toxicity and enhanced the survival of strain PCP-1. In some non-inoculated reactors, the indigenous microorganisms of some soils were also able to degrade PCP. These results suggest that anaerobic dechlorination of PCP in soils by indigenous PCP-degrading bacteria, or after augmentation with D. frappieri PCP-1, should be possible in situ and ex situ when the conditions are favourable for the survival of the degrading microorganisms. [source] Enhanced dechlorination of trichloroethylene by membrane-supported Pd-coated iron nanoparticlesENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 2 2008Linfeng Wu Abstract In this study, cellulose acetate (CA) supported iron and Pd/Fe nanoparticles were used for dechlorination of trichloroethylene (TCE) from water. Solution and microemulsion methods were used to synthesize the iron nanoparticles. Pd/Fe bimetallic particles were prepared by postcoating Pd on the prepared iron nanoparticles. These materials were then dispersed in CA solution, which was used to prepare the membrane-supported nanoparticles. TEM imaging confirmed that the iron and Pd/Fe bimetallic nanoparticles were ,10 nm in diameter. The results of dechlorination studies showed that the surface composition of the Pd/Fe bimetallic nanoparticles (microemulsion method) significantly affected the observed reduction rate constant. In addition, the rate constant was a nonlinear function of metal loading and initial TCE concentration. A comparative study for the Pd/Fe (Pd 1.9 wt %) nanoparticles from solution and microemulsion methods showed that the nanoparticles formed by the latter method gave superior performance for the dechlorination of TCE. © 2008 American Institute of Chemical Engineers Environ Prog, 2008 [source] Treatment of PCB-contaminated soils: I. Evaluation of in situ reductive dechlorination of PCBsENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 2 2001Robert C. Ahlert PhD PE Soil samples were obtained from a site contaminated with PCBs. PCB contamination is not uniform at the source of the samples. Some may be present as isolated "hot spots." The anaerobic phase of a two-stage bioremediation process was evaluated. Populations of native organisms were very low. Species capable of dechlorination of PCBs did not proliferate under anaerobic conditions in the laboratory. Reductive dechlorination did not occur. In-situ reductive dechlorination of heavily substituted PCB congeners is not likely to make a useful contribution to elimination at the site represented by the soil samples. [source] Enantiomeric composition of chiral polychlorinated biphenyl atropisomers in dated sediment coresENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2007Charles S. Wong Abstract ,Enantiomer fractions (EFs) of seven chiral poly chlorinated biphenyls (PCBs) were measured in dated sediment cores of Lake Hartwell (SC, USA) and Lake Ontario (USA) to detect, quantify, and gain insight regarding microbial reductive dechlorination of PCBs in lake sediments with high and low concentrations, respectively. Lake Hartwell sediments had high total PCBs (5,60 ,g/g), with significantly nonracemic EFs that generally were consistent with those from previous laboratory microcosm reductive dechlorination experiments using sediments from these sites. Thus, stereoselective reductive dechlorination had occurred in situ, including at total PCB concentrations of less than the threshold of approximately 30 to 80 ,g/g suggested as being necessary for reductive dechlorination. Enantiomer fractions of PCBs 91, 95, 132, and 136 in Lake Hartwell cores were significantly correlated both with concentrations of those individual congeners and with total PCB concentration for some sites. This result indicates that enantioselective microbial dechlorination activity increases with higher concentrations within sediments for these congeners. Enantiomer composition reversed with depth for PCBs 91, 132, and 176, suggesting that multiple microbial populations may be present within the same core that are enantioselectively dechlorinating PCBs. Such observations indicate that concentration and time are not the only factors affecting biotransformation, complicating prediction of enantioselectivity. Comparison of EFs with dates suggested biotransformation half-lives of approximately 30 years, which is on the same time scale as sequestration by burial. In contrast, Lake Ontario sediments (maximum total PCBs, 400 ng/g) had racemic or near-racemic amounts of most congeners throughout the core profile, which is consistent with achiral indicators suggesting no microbial biotransformation within Lake Ontario sediments. Thresholds for reductive dechlorination may exist, but they would be at concentrations of less than 30 to 80 ,g/g. [source] Metalloporphyrin solubility: A trigger for catalyzing reductive dechlorination of tetrachloroethyleneENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2004Ishai Dror Abstract Metalloporphyrins are well known for their electron-transfer roles in many natural redox systems. In addition, several metalloporphyrins and related tetrapyrrole macrocycles complexed with various core metals have been shown to catalyze the reductive dechlorination of certain organic compounds, thus demonstrating the potential for using naturally occurring metalloporphyrins to attenuate toxic and persistent chlorinated organic pollutants in the environment. However, despite the great interest in reductive dechlorination reactions and the wide variety of natural and synthetic porphyrins currently available, only soluble porphyrins, which comprise a small fraction of this particular family of organic macrocycles, have been used as electron-transfer shuttles in these reactions. Results from the present study clearly demonstrate that metalloporphyrin solubility is a key factor in their ability to catalyze the reductive dechlorination of tetrachloroethylene and its daughter compounds. Additionally, we show that certain insoluble and nonreactive metalloporphyrins can be activated as catalysts merely by changing solution conditions to bring about their dissolution. Furthermore, once a metalloporphyrin is fully dissolved and activated, tetrachloroethylene transformation proceeds rapidly, giving nonchlorinated and less toxic alkenes as the major reaction products. Results from the present study suggest that if the right environmental conditions exist or can be created, specific metalloporphyrins may provide a solution for cleaning up sites that are contaminated with chlorinated organic pollutants. [source] Anaerobic transformation of compounds of technical toxaphene.ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 11 2003Abstract Technical toxaphene (Melipax) and the single compounds of technical toxaphene (CTTs) 2,2,5- endo, 6- exo, 8,8,9,10- octachlorobornane (B8-806), 2,2,5- endo, 6- exo, 8,9,9,10-octachlorobornane (B8-809), 2,2,5,5,8,9,9,10,10-nonachlorobornane (B9- 1025), 2- endo, 3- exo, 5- endo, 6- exo, 8,8,9,10,10-nonochlorobornane (B9-1679), 2- endo, 3- exo, 5- endo, 6- exo, 8,9,10,10-octachlorobornane (B8-1414), 2- endo, 3- exo, 5- endo, 6- exo, 8,8,9,10-octachlorobornane (B8-1412), and 2- exo, 3- endo, 5- exo, 9,9,10,10-heptachlorobornane (B7-1453) were treated with suspensions of the anaerobic bacterium Dehalospirillum multivorans. After 7 d, more than 50% of technical toxaphene was transformed, and the relative amount of early eluting CTTs increased. After 16 d, only 2- exo, 3- endo, 6- exo, 8,9,10-hexachlorobornane (B6-923), 2- endo, 3- exo, 5- endo, 6- exo, 8,9,10-heptachlorobornane (B7-1001), and a few minor penta- and hexachloro-CTTs were detected in the samples. The result of the transformation was comparable with observations in naturally contaminated sediments and soil. However, the performance with D. multivorans was more simple and reproducible, as well as faster, than use of soil, sediment, or anaerobic sewage sludge. In agreement with reports in the literature, reductive dechlorination at geminal chlorine atoms (gem -Cls) was found to be the major CTT transformation pathway. Experiments conducted with CTTs and gem -Cls at both primary and secondary carbons clarified that the initial Cl -> H substitution takes place at the secondary carbon C2. Furthermore, the 2- endo -Cl position was preferably substituted with hydrogen. In the case of B8-806, the dechlorination at the secondary carbon C2 was approximately 20-fold faster than the subsequent, slow reduction at the primary carbon C8. The three different formerly unknown heptachloro-CTTs, 2- exo, 3- endo, 6- exo, 8,9,9,10-heptachlorobornane (B7-1473), 2- exo, 3- endo, 6- endo, 8,9,9,10-hepatchlorobornane (B7-1461), and 2- exo, 3- endo, 6- exo, 8,8,9,10-heptachlorobornane (B7-1470) were found as intermediates of the B8-806/809 transformation. Treatment of B9-1679 with D. multivorans indicated that gem -Cls on the bridge (C8 and C9) are dechlorinated faster than gem -Cls on the bridgehead (C10). [source] Biological activity associated with noncoplanar polychlorinated biphenyls after microbial dechlorination of aroclor 1242® and aroclor 1254®ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 5 2000Patricia E. Ganey Abstract Bioremediation of polychlorinated biphenyls (PCBs) byanaerobic microbial dechlorination occurring naturally in the subsurface and in engineered systems results in mixtures of lower-chlorinated, primarily ortho-substituted biphenyls. The purpose of this study was to determine whether this process of bacterial dechlorination results in a mixture that differs in biological activity from that of the parent PCB mixture. Two biological assays sensitive to the action of ortho-substituted PCBs were employed: insulin release by RINm5F cells, and superoxide anion (O2) production by rat neutrophils. The PCB mixtures Aroclor 1242® and Aroclor 1254® were incubated for nine months with microbes from PCB-contaminated sites (Silver Lake, MA, USA, or River Raisin, MI, USA), and the products of dechlorination were then extracted. Exposure of RINm5F cells to dechlorinated Aroclor 1242 or 1254 product mixtures caused an increase in insulin release similar to the hormone release from cells exposed to non-dechlorinated Aroclors. When tested alone, several of the major products identified in the dechlorination mixture (i.e., 2,2,,4,4,-tetrachlorobiphenyl, 2,2,,4-trichlorobiphenyl [TCB], 2,3,,4-TCB, 2,3,,5-TCB, and 2,2,-dichlorobiphenyl) caused an increase in insulin release. In studies using neutrophils isolated from rat peritoneum, the amount of O2 produced on exposure to product mixtures resulting from dechlorination of Aroclor 1242 was not different from the amount produced in nondechlorinated controls. The product mixture resulting from Aroclor 1254 dechlorination by organisms from River Raisin increased generation of O2, relative to the parent Aroclor. Taken together, these results suggest that anaerobic dechlorination of Aroclor mixtures of PCBs does not reduce the biological activities associated with lightly chlorinated and ortho -substituted PCBs. This observation has implications for the usefulness of PCB bioremediation efforts that involve only anaerobic dechlorination. [source] Activity of Adenosine Deaminase (ADA) and Adenylate Deaminase (AMPDA) Towards 6-Chloropurine Nucleosides Modified in the Ribose MoietyEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 21 2004Pierangela Ciuffreda Abstract The enzymes adenosine deaminase (ADA) and adenylate deaminase (AMPDA) are able to catalyze the hydrolytic dechlorination of 6-chloropurine riboside and the corresponding 2,,3,- O -isopropylidene derivative, but show no activity towards the 3,4- O -isopropylidene-1-methylriboside of 6-chloropurine and adenine. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Factors controlling the carbon isotope fractionation of tetra- and trichloroethene during reductive dechlorination by Sulfurospirillum ssp. and Desulfitobacterium sp. strain PCE-SFEMS MICROBIOLOGY ECOLOGY, Issue 1 2007Danuta Cichocka Abstract Carbon stable isotope fractionation of tetrachloroethene (PCE) and trichloroethene (TCE) was investigated during reductive dechlorination. Growing cells of Sulfurospirillum multivorans, Sulfurospirillum halorespirans, or Desulfitobacterium sp. strain PCE-S, the respective crude extracts and the abiotic reaction with cyanocobalamin (vitamin B12) were used. Fractionation of TCE (,C=1.0132,1.0187) by S. multivorans was more than one order of magnitude higher than values previously observed for tetrachloroethene (PCE) (,C=1.00042,1.0017). Similar differences in fractionation were observed during reductive dehalogenation by the close relative S. halorespirans with ,C=1.0046,1.032 and ,C=1.0187,1.0229 for PCE and TCE respectively. TCE carbon isotope fractionation (,C=1.0150) by the purified PCE-reductive dehalogenase from S. multivorans was more than one order of magnitude higher than fractionation of PCE (,C=1.0017). Carbon isotope fractionation of TCE by Desulfitobacterium sp. strain PCE-S (,C=1.0109,1.0122) as well as during the abiotic reaction with cyanocobalamin (,C=1.0154) was in a similar range to previously reported values for fractionation by mixed microbial cultures. In contrast with previous results with PCE, no effects due to rate limitations, uptake or transport of the substrate to the reactive site could be observed during TCE dechlorination. Our results show that prior to a mechanistic interpretation of stable isotope fractionation factors it has to be carefully verified how other factors such as uptake or transport affect the isotope fractionation during degradation experiments with microbial cultures. [source] Bacterial community analysis of shallow groundwater undergoing sequential anaerobic and aerobic chloroethene biotransformationFEMS MICROBIOLOGY ECOLOGY, Issue 2 2007Todd R. Miller Abstract At Department of Energy Site 300, beneficial hydrocarbon cocontaminants and favorable subsurface conditions facilitate sequential reductive dechlorination of trichloroethene (TCE) and rapid oxidation of the resultant cis- dichloroethene (cis -DCE) upon periodic oxygen influx. We assessed the geochemistry and microbial community of groundwater from across the site. Removal of cis -DCE was shown to coincide with oxygen influx in hydrocarbon-containing groundwater near the source area. Principal component analysis of contaminants and inorganic compounds showed that monitoring wells could be differentiated based upon concentrations of TCE, cis -DCE, and nitrate. Structurally similar communities were detected in groundwater from wells containing cis -DCE, high TCE, and low nitrate levels. Bacteria identified by sequencing 16S rRNA genes belonged to seven phylogenetic groups, including Alpha -, Beta -, Gamma - and Deltaproteobacteria, Nitrospira, Firmicutes and Cytophaga,Flexibacter,Bacteroidetes (CFB). Whereas members of the Burkholderiales and CFB group were abundant in all wells (104,109 16S rRNA gene copies L,1), quantitative PCR showed that Alphaproteobacteria were elevated (>106 L,1) only in wells containing hydrocarbon cocontaminants. The study shows that bacterial community structure is related to groundwater geochemistry and that Alphaproteobacteria are enriched in locales where cis -DCE removal occurs. [source] Contribution of ethylamine degrading bacteria to atrazine degradation in soilsFEMS MICROBIOLOGY ECOLOGY, Issue 2 2006Daniel Smith Abstract Bacterial communities that cooperatively degrade atrazine commonly consist of diverse species in which the genes for atrazine dechlorination and dealkylation are variously distributed among different species. Normally, the first step in degradation of atrazine involves dechlorination mediated by atzA, followed by stepwise dealkylation to yield either N -ethylammelide or N -isopropylammelide. As the liberated alkylamine moieties are constituents of many organic molecules other than atrazine, it is possible that a large number of alkylamine-degrading bacteria other than those previously described might contribute to this key step in atrazine degradation. To examine this hypothesis, we isolated 82 bacterial strains from soil by plating soil water extracts on agar media with ethylamine as a sole carbon source. Among the relatively large number of isolates, only 3 were able to degrade N -ethylammelide, and in each case were shown to carry the atzB gene and atzC genes. The isolates, identified as Rhizobium leguminosarum, Flavobacterium sp., and Arthrobacter sp., were all readily substituted into an atrazine-degrading consortium to carry out N -ethylammelide degradation. The distribution of these genes among many different species in the soil microbial population suggests that these genes are highly mobile and over time may lead to generation of various atrazine-degrading consortia. [source] Aerobic biodegradation of the chloroethenes: pathways, enzymes, ecology, and evolutionFEMS MICROBIOLOGY REVIEWS, Issue 4 2010Timothy E. Mattes Abstract Extensive use and inadequate disposal of chloroethenes have led to prevalent groundwater contamination worldwide. The occurrence of the lesser chlorinated ethenes [i.e. vinyl chloride (VC) and cis -1,2-dichloroethene (cDCE)] in groundwater is primarily a consequence of incomplete anaerobic reductive dechlorination of the more highly chlorinated ethenes (tetrachloroethene and trichloroethene). VC and cDCE are toxic and VC is a known human carcinogen. Therefore, their presence in groundwater is undesirable. In situ cleanup of VC- and cDCE-contaminated groundwater via oxidation by aerobic microorganisms is an attractive and potentially cost-effective alternative to physical and chemical approaches. Of particular interest are aerobic bacteria that use VC or cDCE as growth substrates (known as the VC- and cDCE-assimilating bacteria). Bacteria that grow on VC are readily isolated from contaminated and uncontaminated environments, suggesting that they are widespread and influential in aerobic natural attenuation of VC. In contrast, only one cDCE-assimilating strain has been isolated, suggesting that their environmental occurrence is rare. In this review, we will summarize the current knowledge of the physiology, biodegradation pathways, genetics, ecology, and evolution of VC- and cDCE-assimilating bacteria. Techniques (e.g. PCR, proteomics, and compound-specific isotope analysis) that aim to determine the presence, numbers, and activity of these bacteria in the environment will also be discussed. [source] Degradation of TCE with Iron: The Role of Competing Chromate and Nitrate ReductionGROUND WATER, Issue 3 2000Oliver Schlicker This study evaluates the potential of using granular iron metal for the abiotic removal of the organic ground water pollutant trichloroethene (TCE) in the presence of the common inorganic co-contaminants chromate and nitrate, respectively. Our long-term column experiments indicate a competitive process between TCE dechlorination and reductive transformation of chromate and nitrate, which is reflected in a significantly delayed onset of TCE dechlorination. Delay times and therefore the ranges of the nonreactive flowpaths increased with increasing experimental duration, resulting in a migration of the contaminants through the iron metal treatment zone. The present investigation also indicates that the calculated migration rates of TCE and the added cocontaminants chromate and nitrate are linearly related to the initial content of the cocontaminants. With an average pore water velocity of 0.6 m/d and a surface area concentration of 0.55 m2/mL in the column, the calculated migration rates varled between 0.10 cm/d and 5.86 cm/d. The particular similarity between the values of TCE migration and the migration of the strong oxidants chromate and nitrate and the long-term steady state of the TCE dechlorination in the absence of the chromate and nitrate indicates that these competitive transformations are the driving force for the gradual passivation of the granular iron due to the buildup of an electrically insulating Fe(III)-oxyhydroxide. Based on these passivation processes, general formulae were developed that allow a simplified approximation of breakthrough times for the contaminants TCE, chromate, and nitrate. [source] Ground Water Transfer Initiates Complete Reductive Dechlorination in a PCE-Contaminated AquiferGROUND WATER MONITORING & REMEDIATION, Issue 3 2007R. Lookman We conducted a field test to investigate whether ground water transfer from one site (showing complete natural reductive dechlorination of chlorinated ethenes to ethene) could induce full reductive dechlorination at another site polluted with tetrachloroethene and its partial dechlorination products trichloroethene and cis -dichloroethene (cDCE). Addition of electron donor (lactate) at the test site established low redox conditions but did not stimulate further dechlorination past cDCE. After transferring 2 m3 of ground water from the first site to the test site, full dechlorination commenced and high levels of ethene were measured to distances up to 6 m downstream of the injection location within 7 months. Ground water samples from monitoring wells were analyzed before and after inoculation of the test site for the presence of Dehalococcoides species (16S ribosomal RNA) and vinyl chloride reductase (vCRA) genes using the polymerase chain reaction. These tests showed that Dehalococcoides species were present both before and after ground water transfer, while vCRA genes were detected at the test site only after ground water transfer. The vCRA genes were detected in ground water samples collected 6 m downstream of the injection locations 7 months after ground water transfer, suggesting that the microorganisms carrying the dehalogenase genes were effectively transported in the aquifer. [source] Trichlorofluoroethene: A reactive tracer for evaluating reductive dechlorination in large-diameter permeable columnsGROUND WATER MONITORING & REMEDIATION, Issue 2 2005Jennifer A. Field Trichlorofluoroethene (TCFE) was used as a reactive tracer to determine the in situ rate of reductive dechlorination in treatment zones impacted by three large-diameter permeable columns (LDPCs) that were installed at a trichloroethene (TCE),contaminated site. The LDPCs were part of a pilot study to evaluate the effectiveness of hydrogen, lactate, and zero-valent iron for remediating TCE-contaminated ground water. The rate of TCFE reductive dechlorination was determined for each LDPC by means of push-pull tests conducted in each treatment layer. In addition, the distribution of TCFE's lesser chlorinated transformation products was determined. The rates of TCFE reductive dechlorination ranged from 0.05/d to 0.20/d and corresponded to half-lives ranging from 3.5 to 13.9 d. cis -Dichlorofluoroethene was the dominant transformation product detected in all the tests, which is consistent with the findings from pilot tests conducted in the LDPCs prior to the TCFE push-pull tests. cis -Chlorofluoroethene (CFE) and 1,1-CFE also were detected and indicate the potential for vinyl chloride to form under all treatment regimes. Significant production of fluoroethene (FE), the analog of ethene, was observed for only one of the hydrogen treatments. Unambiguous and sensitive detection of the lesser chlorinated products, such as CFE and FE, is possible because TCFE and its transformation products are not found in the background ground water at contaminated sites. Good agreement between the rates and transformation product profiles for TCFE and TCE in both field and laboratory experiments indicates the suitability of TCFE as a surrogate for predicting the rates of TCE reductive dechlorination. [source] Ground Water Chlorinated Ethenes in Tree Trunks: Case Studies, Influence of Recharge, and Potential Degradation MechanismGROUND WATER MONITORING & REMEDIATION, Issue 3 2004Don A. Vroblesky Trichloroethene (TCE) was detected in cores of trees growing above TCE-contaminated ground at three sites: the Carswell Golf Course in Texas, Air Force Plant PJKS in Colorado, and Naval Weapons Station Charleston in South Carolina. This was true even when the depth to water was 7.9 m or when the contaminated aquifer was confined beneath ,3 m of clay. Additional ground water contaminants detected in the tree cores were cis,1,2-dichloroethene at two sites and tetrachloroethene at one site. Thus, tree coring can be a rapid and effective means of locating shallow subsurface chlorinated ethenes and possibly identifying zones of active TCE dechlorination. Tree cores collected over time were useful in identifying the onset of ground water contamination. Several factors affecting chlorinated ethene concentrations in tree cores were identified in this investigation. The factors include ground water chlorinated ethene concentrations and depth to ground water contamination. In addition, differing TCE concentrations around the trunk of some trees appear to be related to the roots deriving water from differing areas. Opportunistic uptake of infiltrating rainfall can dilute prerain TCE concentrations in the trunk. TCE concentrations in core headspace may differ among some tree species. In some trees, infestation of bacteria in decaying heartwood may provide a TCE dechlorination mechanism within the trunk. [source] 2-Ethyl-2-phosphabicyclo[2.2.2]oct-7-ene derivatives: Synthesis and use in fragmentation-related phosphorylationsHETEROATOM CHEMISTRY, Issue 3 2005Helga Szelke A 2-phosphabicyclo[2.2.2]oct-7-ene oxide (2) and a 2-phosphabicyclo[2.2.2]octa-5,7-diene oxide (3) with ethyl substituent on the phosphorus atom was synthesized and their fragmentation properties were studied. The phosphabicyclooctadiene oxide (3) could be utilized in both the UV light-mediated phosphorylation of simple alcohols and in the thermoinduced phosphorylation of hydroquinone giving an easy access to P-ethylphosphinates (e.g., 4 and 6). The phosphabicyclooctene oxide (2) was, however, not useful in photoinduced phosphorylations; under such conditions the precursor (2) underwent dechlorination to afford 5. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:196,199, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20093 [source] Aerobic degradation by white-rot fungi of trichloroethylene (TCE) and mixtures of TCE and perchloroethylene (PCE)JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 9 2008Ernest Marco-Urrea Abstract BACKGROUND: Trichloroethylene (TCE) and perchloroethylene (PCE) are considered among the most important groundwater pollutants around the world. These compounds are usually found together in polluted environments but little is known about the ability of microorganisms to simultaneously degrade TCE and PCE. RESULTS: Data showed that several species of white-rot fungi, including Trametes versicolor, Ganoderma lucidum, and Irpex lacteus, degrade substantial levels of TCE in pure culture. T. versicolor was chosen for further study since it degraded higher levels of TCE than the other organisms. Initial glucose concentration and reoxygenation of samples increased the amount of TCE dechlorination, but no significant difference in percentage TCE degradation was observed. T. versicolor was able to degrade 34.1 and 47.7% of PCE and TCE added as mixtures (containing 5 and 10 mg L,1, respectively). CONCLUSIONS: The degradation ability of TCE was extended to other species of white-rot fungi. Percentage degradation as well as chloride release from mixtures of TCE and PCE showed that T. versicolor degrades mixtures of TCE and PCE almost as well as its ability to degrade individually added TCE or PCE. The results suggest the potential promise of T. versicolor for bioremediation of TCE and PCE in the environment. Copyright © 2008 Society of Chemical Industry [source] Catalytic conversion of waste plastics: focus on waste PVCJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 9 2007Mark A Keane Abstract Effective waste management must address waste reduction, reuse, recovery/recycling and, as the least progressive option, waste treatment. The increase in plastic waste production is a serious environmental issue. Plastics consumption continues to grow and while plastic recycling has seen a significant increase since the early 1990s, consumption still far exceeds recycling. Waste plastic can, however, serve as a potential resource and, with the correct treatment, can be reused or serve as hydrocarbon raw material or as a fuel. PVC, highly versatile with many applications, is non-biodegradable and has a high Cl content (56% of the total weight). Waste PVC incineration is highly energy demanding and can result in the formation of toxic chloro-emissions with adverse ecological, environmental and public health impacts. The Cl component must be removed from any waste PVC derived gas or oil before it can be used. An overview of the existing waste plastic treatment technologies is provided with an analysis of the available literature on thermal and catalytic PVC degradation. Thermal degradation results in random scissioning of the polymer chains generating products with varying molecular weights and uncontrolled Cl content. There is a dearth of literature dealing with the catalytic dechlorination of PVC. A case study is presented to illustrate the role heterogeneous catalysis can play in PVC waste treatment. The efficacy of Pd/Al2O3 to promote PVC dechlorination is demonstrated, where a significant decrease (by up to a factor of 560) in the liquid fraction Cl content is recorded in addition to differences (relative to thermal degradation) in the gas phase product, i.e. higher C1C4 content with preferential alkane formation. Copyright © 2007 Society of Chemical Industry [source] A review of catalytic approaches to waste minimization: case study,liquid-phase catalytic treatment of chlorophenolsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 11 2005Mark A Keane Abstract Effective waste management must address waste reduction, reuse, recovery/recycle and, as the least progressive option, waste treatment. Catalysis can serve as an integral green processing tool, ensuring lower operating pressures/temperatures with a reduction in energy requirements while providing alternative cleaner synthesis routes and facilitating waste conversion to reusable material. The case study chosen to illustrate the role that catalysis has to play in waste minimization deals with the conversion of toxic chlorophenols in wastewater. The presence of chloro-organic emissions is of increasing concern with mounting evidence of adverse ecological and public health impacts. A critical overview of the existing treatment technologies is provided with an analysis of the available literature on catalytic dechlorination. The efficacy of Pd/Al2O3 to promote the hydrogen-mediated dechlorination of mono- and dichlorophenols is demonstrated, taking account of both the physical and chemical contributions in this three-phase (solid catalyst and liquid/gaseous reactants) system. Hydrodechlorination activity and selectivity trends are discussed in terms of chloro-isomer structure, the influence of temperature is discussed, the role of base (NaOH) addition is examined and the feasibility of catalyst reuse is addressed. Copyright © 2005 Society of Chemical Industry [source] Oxidative polymerization and partial dechlorination of 2,4,6-trichlorophenol by a mixture of peroxidase isozymes from Vaccinium myrtillusJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2 2001Silvia Rita Stazi Abstract Plant peroxidases (EC 1.11.1.7) catalyze the oxidation of phenolic pollutants in the presence of hydrogen peroxide. In the present study, extracellular peroxidases from Vaccinium myrtillus cell suspension cultures (VMP) were evaluated for their ability to polymerize 2,4,6-trichlorophenol (TCP), a ubiquitous environmental contaminant. The effect of pH, temperature, reaction time, enzyme amount and initial pollutant concentration on the treatment efficiency was investigated in order to optimize the reaction conditions for TCP removal. An appreciable removal efficiency and a partial dehalogenation of TCP was observed over a wide range of initial pollutant concentrations (0.1,20,mmol,dm,3) and reaction conditions suggesting that VMP could be useful for potential decontamination applications. The use of polyethylene glycol in the reaction mixture allowed a reduction of the catalyst requirements needed to obtain well defined extents of TCP removal. © 2001 Society of Chemical Industry [source] Synthesis of 9-[2-(2-hydroxymethyl-2-methyl-, -(2-acetoxymethyl-2-methyl-, -(2,2-di(hydroxymethyl)-, and -(2,2-Di(acetoxymethyl)-1,3-dioxan-5-yl)ethyl] derivatives of guanine and 2-aminopurineJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 5 2000Dae-Kee Kim Synthesis of 9-[2-(2-hydroxymethyl-2-methyl-, -(2-acetoxymethyl-2-methyl-, -(2,2-di(hydroxymethyl)-, and -(2,2-di(acetoxymethyl)-1,3-dioxan-5-yl)ethyl] derivatives of guanine and 2-aminopurine, 2,9, has been accomplished in seven to eight step sequences from readily available 1-(tert -butyldiphenylsilyloxy)-acetone, 1,3-di(tert -butyldiphenylsilyloxy)acetone, and the diol 10. Formation of cyclic ketals 11 and 12 was carried out successfully under an acidic condition using a catalytic amount of methanesulfonic acid along with excess anhydrous copper(II) sulfate in toluene. Subsequent reactions of desilylation, acetylation, hydrogenolysis, and bromination afforded the key intermediates 19 and 20, which were coupled with 2-amino-6-chloropurine to produce the purine compounds 21 and 22 in good yields. Guanine derivatives 2,5 were obtained from 21 and 22 by hydrolysis and acetylation, while the dechlorination and hydrolysis of 21 and 22 yielded the 2-aminopurine compounds 6,9. [source] | ||||||||||||||||