Trichloroethylene degradation

Biological. Microbial degradation of trichloroethylene via sequential dehalogenation produced cis- and /ra/3s-l,2-dichloroethylene and vinyl chloride (Smith and Dragun, 1984). Anoxic microcosms in sediment and water degraded trichloroethylene to 1,2-dichloroethylene and then to vinyl chloride (Barrio-Lage et al., 1986). Trichloroethylene in soil samples collected from Des Moines, lA anaerobically degraded to 1,2-dichloroethylene. The production of 1,1-dichloroethylene was not observed in this study (Kleopfer et al., 1985). 

Xenobiotic compounds are usually attacked by enzymes whose primary function is to react with other compounds, a process that provides neither carbon nor energy called cometabolism. Cometabolism usually involves relatively small modifications of the substance that is cometabolized (the secondary substrate), compared to the primary substrate. The enzymes that carry out cometabolism tend to be relatively nonspecific. As an environmentally significant example of cometabolism, at least one strain of bacteria degrades trichloroethylene with an enzyme system that acts predominantly on phenol. The enzyme activity can be induced by exposure to phenol, after which it acts on trichloroethylene. 

H.-C. Tsien and R. S. Hanson. Soluble methane monooxygenase component B gene probe for identification of methanotrophs that rapidly degrade trichloroethylene. Appl. Environ. Microbiol., 58 953 (1992). 

This chapter describes an evanescent wave fiber optic biosensor and its application to immunoassays for rapid detection of bacterial cells and pollutants. Whole cells of Burkholderia cepacia G4 5223-PRl (G4) are of interest for their ability to degrade trichloroethylene (TCE) which is one of the most prevalent contaminants of ground water in the United States. The lower limit of detection of the G4 with this system is 10 - 10 cells/ml. In addition to TCE, the explosive trinitrotoluene (TNT) is a known contaminant of ground water. Limits of detection of TNT with this system is 10 ng/ml. 

Clapp, L. W., Regan, X M., Ah, E, Newman, X D., Park, X K. and Noguera, D. L. 1999. Activity, structure, and stratification of membrane-attached methanotrophic biofllms cometabohcally degrading trichloroethylene. Water Science and Technology,39,153-161. 

Nitric acid, cone. Completely degraded Trichloroethylene 14... 

Acetate and triacetate are essentially unaffected by dilute solutions of weak acids, but strong mineral acids cause serious degradation. The results of exposure of heat-treated and untreated triacetate taffeta fabrics to various chemical reagents have been reported (9). Acetate and triacetate fibers are not affected by the perchloroethylene dry-cleaning solutions normally used in the United States and Canada. Trichloroethylene, employed to a limited extent in the UK and Europe, softens triacetate. 

Pyrolysis. 1,1,2,2-Tetrachloroethane, like the 1,1,1,2-isomer, is thermally degraded with or without a catalytic agent to give trichloroethylene. 

The most important reactions of trichloroethylene are atmospheric oxidation and degradation by aluminum chloride. Atmospheric oxidation is cataly2ed by free radicals and accelerated with heat and with light, especially ultraviolet. The addition of oxygen leads to intermediates (1) and (2). 

In the presence of aluminum, oxidative degradation or dimerization supply HCl for the formation of aluminum chloride, which catalyzes further dimerization to hexachlorobutene. The latter is decomposed by heat to give more HCl. The result is a self-sustaining pathway to solvent decomposition. Sufficient quantities of aluminum can cause violent decomposition, which can lead to mnaway reactions (1,2). Commercial grades of trichloroethylene are stabilized to prevent these reactions in normal storage and use conditions. 

CHLORINATED HYDROCARBONS Hydrocarbons containing chlorine atoms, e.g. trichloroethylene. Some of these chemicals accumulate in the food chain and do not readily degrade. Some plastics which contain certain chlorinated hydrocarbons release dioxins into the air, when burnt at low temperatures. 

There has been an emphasis on recovery and recycling of trichloroethylene to reduce emissions of this photoreactive chemical to the atmosphere (CMR 1986 McNeill 1979). Photooxidative destruction has been successfully used in conjunction with air-stripping techniques to volatilize trichloroethylene from water and degrade it to nontoxic products (Bhowmick and Semmens 1994). If possible, recycling should be used instead of disposal. 

Most of the trichloroethylene used in the United States is released into the atmosphere by evaporation primarily from degreasing operations. Once in the atmosphere, the dominant trichloroethylene degradation process is reaction with hydroxyl radicals the estimated half-life for this process is approximately 7 days. This relatively short half-life indicates that trichloroethylene is not a persistent atmospheric compound. Most trichloroethylene deposited in surface waters or on soil surfaces volatilizes into the atmosphere, although its high mobility in soil may result in substantial percolation to subsurface regions before volatilization can occur. In these subsurface environments, trichloroethylene is only slowly degraded and may be relatively persistent. 

The relatively short predicted half-life of trichloroethylene in the atmosphere indicates that long-range global transport is unlikely (Class and Ballschmiter 1986). However, its constant release, as well as its role as an intermediate in tetrachloroethylene degradation, may account for its persistence and the fact that trichloroethylene is often present in remote areas. 

The reaction of volatile chlorinated hydrocarbons with hydroxyl radicals is temperature dependent and thus varies with the seasons, although such variation in the atmospheric concentration of trichloroethylene may be minimal because of its brief residence time (EPA 1985c). The degradation products of this reaction include phosgene, dichloroacetyl chloride, and formyl chloride (Atkinson 1985 Gay et al. 1976 Kirchner et al. 1990). Reaction of trichloroethylene with ozone in the atmosphere is too slow to be an effective agent in trichloroethylene removal (Atkinson and Carter 1984). 

Biotransformation was also strongly indicated as a factor in the degradation of trichloroethylene in a case of soil and groundwater pollution (Milde et al. 1988). The only ethylenes at the point source of pollution were tetrachloroethylene and trichloroethylene however, substantial amounts of known metabolites of these two compounds (dichloroethylene, vinyl chloride, and ethylene) were found at points far from the source. Data from laboratory studies by the same group supported the study authors contention that degradation was due... 

Degradation of trichloroethylene by anaerobes via reductive dehalogenation can be problematic because a common product is vinyl chloride, a known carcinogen (Ensley 1991). In an anaerobic colunm operated under methanogenic conditions, 100% transformation of injected tetrachloroethylene and trichloroethylene to... 

Aerobic biodegradation of trichloroethylene occurs by cometabolism with aromatie eompounds (Ensley 1991) and thus requires a cosubstrate such as phenol (Nelson et al. 1987, 1988) or toluene (Fan and Scow 1993). Trichloroethylene degradation by toluene-degrading baeteria has been demonstrated in the presence, but not absence, of toluene (Mu and Scow 1994). Isoprene, a structural analog of trichloroethylene, has also been used as a cosubstrate for triehloroethylene oxidation by some bacteria (Ewers et al. 1990). One source of inhibition of degradation in the absence of cosubstrate may be the toxieity of triehloroethylene itself to indigenous bacteria. 

Eng W, Palumbo AV, Sriharan S, et al. 1991. Methanol suppression of trichloroethylene degradation by Methylosinus trichosporium (OB3b) and methane-oxidizing mixed cultures. Appl Biochem Biotechnol 28/29 887-899. 

Mu DY, Scow KM. 1994. Effect of trichloroethylene (TCE) and toluene concentrations on TCE and toluene biodegradation and the population density of TCE and toluene degraders in soil. Appl Environ Microbiol 60 2661-2665. 

Nelson MJK, Montgomery SO, Pritchard PH. 1988. Trichloroethylene metabolism by microorganisms that degrade aromatic compounds. Appl Environ Microbiol 54 604-606. 

Walton BT, Anderson TA. 1990. Microbial degradation of trichloroethylene in the rhizosphere Potential application to biological remediation of waste sites. Appl Environ Microbiol 56 1012-1016. 

Hung C-H, BJ Marinas (1997) Role of chlorine and oxygen in the photocatalytic degradation of trichloroethylene vapor on TiOj films. Environ Sci Technol 31 562-568. 

Wackett LP, GA Brusseau, SR Householder, RS Hanson (1989) Survey of microbial oxygenases trichloroethylene degradation by propane-oxidizing bacteria. Appl Environ Microbiol 55 2960-2964. 

Sontoh S, JD Semrau (1998) Methane and trichloroethylene degradation by Methylosinus trichosporium OB3b expressing particulate methane monooxygenase. Appl Environ Microbiol 64 1106-1114. 

Folsom BR, PJ Chapman, PH Pritchard (1990) Phenol and trichloroethylene degradation by Pseudomonas cepacia G4 kinetics and interactions between substrates. Acinetobacter sp. strain A-CBl. Appl Environ Microbiol 56 1279-1285. 

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