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Query: EC:3.4.23.17 (PCE)
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Male albino rats of the Donryu strain were divided into 4 groups: the normal control group, tetrachloromethane (CCl4, TCM) group, tetrachloroethylene (CCl2 = CCl2, PCE) group and trichloroethylene (CHCl = CCl2, TCE) group. Each group was consisted of 6 animals. TCM, PCE and TCE were administered orally at a dosage of 13 mmoles/kg as a 50% v/v olive oil solution to rats 24 hours prior to an oral administration of m-xylene (8.2 mmoles/kg as a 50% v/v olive oil solution). The normal control group was administered only olive oil (2.5 ml/kg) 24 hours prior to m-xylene dose. Urine was collected 24, 48, 72 and 96 hours after administration of m-xylene. The urine was analysed for m-methylhippuric acid (m-MHA) by the paper chromatographic method of Ogata et al. The results obtained were as follows: 1) Total urinary excretion of m-MHA in the normal control group was equivalent on a molar basis to about 58% of m-xylene received, and the major portions of the metabolites were excreted on the 1st day. 2) In TCM group, total urinary excretion of m-MHA was about a half of that in the normal control group. It was equivalent on a molar basis to about 30% of m-xylene received (p less than 0.01), and the urinary excretion of m-MHA on the 1st day was significantly less than those of the normal control group (p less than 0.001) and TCE group (p less than 0.05). 3) In PCE group, urinary excretion of m-MHA on the 1st day was significantly less than that of the normal control group (p less than 0.01) and the excretion was delayed. 4) In TCE group, total urinary excretion of m-MHA was slightly but not significantly less than that of the normal control group (p less than 0.05). 5) In TCM-ip group of rats which were given TCM orally 24 hours prior to the administration of m-xylene by intraperitoneal injection, urinary excretion of m-MHA on the 1st day and in 4 days after administration of m-xylene was less than that of the control-ip group.
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PMID:[Metabolism of m-xylene in rats after administration of chlorinated hydrocarbons (author's transl)]. 61 80

Hydrocarbons such as TCE, PCE, TCA, gasoline and kerosene which are widely used in the industry, enter soils and groundwater from chemical waste disposal sites and from accidents. These types of substances are the most commonly encountered groundwater contaminants nationwide. Biotransformation of dissolved chlorinated hydrocarbons can provide complete mineralization to harmless end products such as CO2. It is the objective of this work to investigate the biodegradation and biotransformation, and transport of hydrocarbons in groundwater. This will be achieved first by defining and identifying relevant physical and biological processes which contribute to the fate of hydrocarbon contaminants in unsaturated/saturated soils, and providing a conceptual framework for incorporating these processes into a mathematical formulation. The conservation principles expressed in terms of quantifications of the physical, chemical and microbial processes described above lead to a system governing the phenomenon which consists of nonlinear partial differential equations. Microbial transformation conducted by both anaerobic and aerobic bacteria are considered.
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PMID:Theoretical modeling of biodegradation and biotransformation of hydrocarbons in subsurface environments. 233 35

Spinning drop tensiometry has been used in the past to determine low interfacial tension between aqueous surfactant solutions and organic phases that are lighter than water. In this work, we extend the use of the technique to measurement of low interfacial tension between aqueous surfactant solutions and organic phases that are denser than water by altering the wettability of the spinning glass tube. The interfacial tensions of water-SDS-PCE and water-SDS-TCE are determined using this new method. Copyright 1997 Academic Press. Copyright 1997Academic Press
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PMID:Interfacial Tension Measurement in DNAPL/Aqueous Surfactant Systems 944 43

The Department of Defense (DoD) has over 21,000 contaminated sites requiring some form of remediation. Contaminants on these sites include explosive compounds (i.e., TNT, RDX, HMX), chlorinated solvents (i.e., PCE, TCE, TCA), polycyclic aromatic hydrocarbons (i.e., benzo-a-pyrene), and polychlorinated biphenyls (i.e., aroclors). Current technology has centered around incineration, air stripping, and the use of activated carbon. Frequently, this technology is not cost effective nor publicly acceptable. Biotreatment offers a possible alternative. Biotreatment can cost effectively eliminate contaminants and avoid the use of harsh chemicals and physical treatments. However, special care must be employed to ensure that the proper remediation system is designed and engineered to optimize clean-up and minimize costs. Unfortunately, not all bioremediation efforts have been successful. In an attempt to develop bioremediation technology from the flask (bench scale) to the field (full-scale design), many scientists and engineers have failed to understand the phenomena that influence bioremediation. Issues such as additional mass transport mechanisms/limitations, the presence of multiple phases, spatial heterogeneities, and unfavorable factors for bacterial growth represent only a few of the phenomena that can limit or complicate biodegradation. Successful bioremediation requires a complete examination of the phenomena that can be observed as the scientist and engineer progress together from the bench to the field. An excellent way to examine these phenomena is by using the conceptual scales of observation: microscale, mesoscale, and macroscale. The microscale represents the level at which chemical/microbial species and reactions can be characterized independently of any transport phenomena. These activities are those occurring at the microbial cell level and generally are the focus of bench level work. The mesoscale is the level at which transport phenomena and system geometry are first apparent, with the exclusion of advective or mixing processes. This scale represents those activities that occur at the pore channel, soil particle or microbial aggregate level. The macroscale is the scale at which you have the ability to discern advective or mixing phenomena. These activities are generally associated on a site level and are the focus of the design engineer. The critical path as bioremediation technology is developed from flask to field is to observe and understand the phenomena that exert influence at each scale of observation so that its effects can be incorporated into the final remediation design.
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PMID:Roadblocks to the implementation of biotreatment strategies. 947 11

The effects of surfactants, sodium dodecyl sulfate (SDS) and Triton X-a00 (TX), and alcohols (methanol, ethanol, and propanol) on the dehalogenation of TCE and PCE by zero-valent iron were examined. Surface concentrations of PCE and TCE on the iron were dependent on aqueous surfactant concentrations. At concentrations above the CMC, sorbed halocarbon concentrations declined and concentrations associated with solution phase micelles increased. The anionic surfactant SDS ([SDS] < CMC) did not affect reduction rates, until the CMC was exceeded after which reactivity decreased, possibly due to sequestering of the TCE and PCE in mobile micelles. The nonionic TX showed a mixed effect on reactivity, increasing the PCE reduction rate, but not affecting TCE removal. Production of TCE from PCE increased in the presence of TX. Similar experiments showed that methanol, ethanol, and propanol inhibited reduction of TCE and PCE by metallic iron. Zero-valent iron may be useful in recycling soil washing effluents contaminated with TCE and PCE.
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PMID:Effects of alcohols, anionic and nonionic surfactants on the reduction of PCE and TCE by zero-valent iron. 1131 92

Area 6 at Dover Air Force Base (Dover, DE) has been the location of an in-depth study by the RTDF (Remediation Technologies Development Forum Bioremediation of Chlorinated Solvents Action Team) to evaluate the effectiveness of natural attenuation of chlorinated ethene contamination in groundwater. Compound-specific stable carbon isotope measurements for dissolved PCE and TCE in wells distributed throughout the anaerobic portion of the plume confirm that stable carbon isotope values are isotopically enriched in 13C consistent with the effects of intrinsic biodegradation. During anaerobic microbial reductive dechlorination of chlorinated hydrocarbons, the light (12C) versus heavy isotope (13C) bonds are preferentially degraded, resulting in isotopic enrichment of the residual contaminant in 13C. To our knowledge, this study is the first to provide definitive evidence for reductive dechlorination of chlorinated hydrocarbons at a field site based on the delta13C values of the primary contaminants spilled at the site, PCE and TCE. For TCE, downgradient wells show delta13C values as enriched as -18.0/1000 as compared to delta13C values for TCE in the source zone of -25.0 to -26.0/1000. The most enriched delta13C value on the site was observed at well 236, which also contains the highest concentrations of cis-DCE, VC, and ethene, the daughter products of reductive dechlorination. Stable carbon isotope signatures are used to quantify the relative extent of biodegradation between zones of the contaminant plume. On the basis of this approach, it is estimated that TCE in downgradient well 236 is more than 40% biodegraded relative to TCE in the proposed source area.
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PMID:Stable carbon isotope evidence for intrinsic bioremediation of tetrachloroethene and trichloroethene at area 6, Dover Air Force Base. 1134 96

Bioventing principles have been applied to completely dechlorinate tetrachloroethylene vapors in the unsaturated zone in a sequential anaerobic-aerobic pattern. The aerobic step yields trans-DCE and VC as PCE reductive dechlorination byproducts, while TCE and cis-DCE are observed as intermediates. The aerobic step results in rapid oxidation of the VC and trans-DCE to carbon dioxide. Hydrogen was delivered in the gas phase as a reducing agent for the anaerobic step at levels of 1%, and oxygen at 4.2% was used as an electron acceptor in the aerobic step. PCE and VC half lives in the anaerobic and aerobic steps respectively, where less than 10 min.
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PMID:Complete remediation of PCE contaminated unsaturated soils by sequential anaerobic-aerobic bioventing. 1137 54

The dissolved hydrogen concentrations under various redox processes were investigated based on batch experiments. Chloroethenes including tetrachloroethene (PCE), cis-dichloroethene (cis-DCE) and vinylchloride (VC) were respectively used as culture substrates. For each chloroethene, a series of bottles were prepared with the additions of different electron acceptors or donors such as nitrate, manganese oxide, ferrous iron, sulfate, carbondioxide and volatile fatty acids. Hydrogen concentrations as well as redox species were measured over time to ensure the achievements of characteristic hydrogen levels in various enrichment batches. The results showed that redox processes with nitrate, manganese oxide and ferric iron as the electron acceptors exhibited hydrogen threshold values close to PCE/TCE dechlorination, whereas cis-DCE and VC dechlorinations exhibited hydrogen threshold values in the range of sulfate reduction and methanogenesis, respectively. Characteristic hydrogen concentrations for various redox processes were as follows (nM): denitrification, 0.1-0.4; manganese reduction, 0.1-2.0; iron reduction, 0.1-0.4; sulfate reduction, 1.5-4.5; methanogenesis, 2.5-24; PCE/TCE dechlorination, 0.6-0.9; eis-DCE dechlorination, 0.1-2.5; and VC dechlorination, 2-24.
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PMID:Characteristic hydrogen concentrations for various redox processes in batch study. 1168 86

Fe(II)-based degradative solidification/stabilization (DS/S) is a modification of conventional solidification/stabilization (S/S) that uses Fe(II) as a reducing agent for chlorinated organics while immobilizing inorganic contaminants. Feasibility of the Fe(II)-based DS/S technology in treating soils contaminated with tetrachloroethylene (PCE) was tested in this study. The results of the PCE degradation experiments conducted in the presence of a humic acid suggest that natural organic matter would not significantly interfere with the degradative reaction by the Fe(II)-containing reactive species in DS/S systems. Solid-phase degradation experiments showed that the DS/S technology could effectively treat PCE in soils without substantial production of chlorinated intermediates. A pseudo-first-order rate law reasonably described degradation kinetics. The half-lives of PCE ranged from 13 to 335 days, which are within time spans allowable for typical in-situ DS/S application. Trichloroethylene (TCE) was the only chlorinated product observed in the solid-phase experiments, and its presence was generally transitory with the amount being less than 7% of the initial amount of PCE on a molar basis. A surface reaction appears to control observed PCE degradation kinetics rather than mass transfer to the reactive surface.
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PMID:Reductive dechlorination of tetrachloroethylene in soils by Fe(II)-based degradative solidification/stabilization. 1178 61

Chlorinated ethenes are pollutants in contaminated soil and groundwater, and one of the efficient way to remove them is biodegradation. In this paper, the microbial breakdown of PCE, cis-DCE and VC with initial concentrations of 100 mumol/L were studied under different redox conditions at temperature 20 degrees C. The results showed that in the presence of ferric iron and carbon dioxide, PCE were dechlorinated to TCE (0.26/day) and cis-DCE (0.31/day), respectively. In the presence of fatty acids and without competition from inorganic electron acceptors, all the studied chlorinated compounds were completely dechlorinated to ethenes. However, the degradation rates of cis-DCE and VC (0.04/day) were much lower than that of PCE (0.57/day). Under denitrifying, manganese reducing and sulfate reducing conditions, no degradation of chloroethenes was observed. When the temperature was lowered to 12 degrees C, the activities of dechlorinating microbes were also reduced, nevertheless, the completely reductive dechlorination of chloroethenes still occurred.
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PMID:[Dechlorination of chlorinated ethenes under different redox conditions]. 1204 14


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