Biotransformation Of Trichloroethylene Research Articles

Trichloroethylene biotransformation and its role in mutagenicity, carcinogenicity and target organ toxicity.

Metabolism is critical for the mutagenicity, carcinogenicity, and other adverse health effects of trichloroethylene (TCE). Despite the relatively small size and simple chemical structure of TCE, its metabolism is quite complex, yielding multiple intermediates and end-products. Experimental animal and human data indicate that TCE metabolism occurs through two major pathways: cytochrome P450 (CYP)-dependent oxidation and glutathione (GSH) conjugation catalyzed by GSH S-transferases (GSTs). Herein we review recent data characterizing TCE processing and flux through these pathways. We describe the catalytic enzymes, their regulation and tissue localization, as well as the evidence for transport and inter-organ processing of metabolites. We address the chemical reactivity of TCE metabolites, highlighting data on mutagenicity of these end-products. Identification in urine of key metabolites, particularly trichloroacetate (TCA), dichloroacetate (DCA), trichloroethanol and its glucuronide (TCOH and TCOG), and N-acetyl-S-(1,2-dichlorovinyl)-L-cysteine (NAcDCVC), in exposed humans and other species (mostly rats and mice) demonstrates function of the two metabolic pathways in vivo. The CYP pathway primarily yields chemically stable end-products. However, the GST pathway conjugate S-(1,2-dichlorovinyl)glutathione (DCVG) is further processed to multiple highly reactive species that are known to be mutagenic, especially in kidney where in situ metabolism occurs. TCE metabolism is highly variable across sexes, species, tissues and individuals. Genetic polymorphisms in several of the key enzymes metabolizing TCE and its intermediates contribute to variability in metabolic profiles and rates. In all, the evidence characterizing the complex metabolism of TCE can inform predictions of adverse responses including mutagenesis, carcinogenesis, and acute and chronic organ-specific toxicity.

Trichloroethylene biotransformation and its role in mutagenicity, carcinogenicity and target organ toxicity

Trichloroethylene biotransformation and its role in mutagenicity, carcinogenicity and target organ toxicity

Enhanced biotransformation of TCE using plant terpenoids in contaminated groundwater

To examine plant terpenoids as inducers of TCE (trichloroethylene) biotransformation by an indigenous microbial community originating from a plume of TCE-contaminated groundwater. One-litre microcosms of groundwater were spiked with 100 micromol 1(-1) of TCE and amended weekly for 16 weeks with 20 microl 1(-1) of the following plant monoterpenes: linalool, pulegone, R-(+) carvone, S-(-) carvone, farnesol, cumene. Yeast extract-amended and unamended control treatments were also prepared. The addition of R-carvone and S-carvone, linalool and cumene resulted in the biotransformation of upwards of 88% of the TCE, significantly more than the unamendment control (61%). The aforementioned group of terpenes also significantly (P < 0.05) allowed more TCE to be degraded than the remaining two terpenes (farnesol and pulegone), and the yeast extract treatment which biotransformed 74-75% of the TCE. The microbial community profile was monitored by denaturing gradient gel electrophoresis and demonstrated much greater similarities between the microbial communities in terpene-amended treatments than in the yeast extract or unamended controls. TCE biotransformation can be significantly enhanced through the addition of selected plant terpenoids. Plant terpenoid and nutrient supplementation to groundwater might provide an environmentally benign means of enhancing the rate of in situ TCE bioremediation.

Effect of biotransformation on multispecies plume evolution and natural attenuation

Biological transformation of volatile organic compounds is one of the key factors that influence contaminant-plume evolution and thus natural attenuation. In this study we investigate the effect of biological transformation on the transport of contaminants in the aqueous and gaseous phases. The analysis includes the study of the effect of density-driven advection of contaminants in the gaseous phase on multiphase and multispecies flow, fate and transport modeling in the subsurface. Trichloroethylene (TCE) and its two byproducts, dichloroethylene and vinyl chloride, are analyzed as the target contaminants. Our results indicate that density-driven advection of the gaseous phase, which is initiated by evaporation of TCE as a nonaqueous phase liquid, increases the downward and also the lateral migration of TCE within the unsaturated zone. This process also influences the location of high-concentration zones of the byproducts of TCE in the unsaturated and the saturated zones. Biotransformation of TCE contributes to the reduction of dissolved TCE plume development as expected. The daughter byproducts, which are introduced into the subsurface system, show distinct transport patterns as they are affected by their independent degradation kinetics and density-driven advection. These observations, which are based on our simulation results for biotransformation and transport of TCE and its byproducts, are useful in evaluating the natural attenuation processes, its potential health hazards and also the evaluation of potential plume development at contaminated sites.

Toxicokinetics of chloral hydrate in ad libitum-fed, dietary-controlled, and calorically restricted male B6C3F 1 mice following short-term exposure

Chloral hydrate is widely used as a sedative in pediatric medicine and is a by-product of water chlorination and a metabolic intermediate in the biotransformation of trichloroethylene. Chloral hydrate and its major metabolite, trichloroacetic acid, induce liver tumors in B6C3F 1 mice, a strain that can exhibit high rates of background liver tumor incidence, which is associated with increased body weight. This report describes the influence of diet and body weight on the acute toxicity, hepatic enzyme response, and toxickinetics of chloral hydrate as part of a larger study investigating the carcinogenicity of chloral hydrate in ad libitum-fed and dietary controlled mice. Dietary control involves moderate food restriction to maintain the test animals at an idealized body weight. Mice were dosed with chloral hydrate at 0, 50, 100, 250, 500, and 1000 mg/kg daily, 5 days/week, by aqueous gavage for 2 weekly dosing cycles. Three diet groups were used: ad libitum, dietary control, and 40% caloric restriction. Both dietary control and caloric restriction slightly reduced acute toxicity of high doses of chloral hydrate and potentiated the induction of hepatic enzymes associated with peroxisome proliferation. Chloral hydrate toxicokinetics were investigated using blood samples obtained by sequential tail clipping and a microscale gas chromatography technique. It was rapidly cleared from serum within 3 h of dosing. Trichloroacetate was the major metabolite in serum in all three diet groups. Although the area under the curve values for serum trichloroacetate were slightly greater in the dietary controlled and calorically restricted groups than in the ad libitum-fed groups, this increase did not appear to completely account for the potentiation of hepatic enzyme induction by dietary restriction.

Laboratory column studies for evaluating a barrier system for providing oxygen and substrate for TCE biodegradation

The industrial solvent trichloroethylene (TCE) is among the most ubiquitous chlorinated compounds found in groundwater contamination. The objective of this study was to develop a biobarrier system containing oxygen–organic releasing material to enhance the aerobic cometabolism of TCE in situ. The oxygen–organic material, which contains calcium peroxide and peat, is able to release oxygen and primary substrates continuously upon contact with water. Batch experiments were conducted to design and identify the components of the oxygen–organic releasing material, and evaluate the oxygen and organic substrate (presented as COD equivalent) release from the designed oxygen–organic material. The observed oxygen and chemical oxygen demand (COD) release rates were approximately 0.0246 and 0.052 mg/d/g of material, respectively. A laboratory-scale column experiment was then conducted to evaluate the feasibility of this proposed system for the bioremediation of TCE-contaminated groundwater. This system was performed using a series of continuous-flow glass columns including a soil column, an oxygen–organic material column, followed by two consecutive soil columns. Aerobic acclimated sludges were inoculated in all three soil columns to provide microbial consortia for TCE biodegradation. Simulated TCE-contaminated groundwater with a flow rate of 0.25 l/day was pumped into this system. Effluent samples from each column were analyzed for TCE and other indicating parameters (e.g., pH, dissolved oxygen). Results show that the decreases in TCE concentrations were observed over a 4-month operating period. Up to 99% of TCE removal efficiency was obtained in this passive system. Results indicate that the continuously released oxygen and organic substrates from the oxygen–organic materials enhanced TCE biotransformation. Thus, the biobarrier treatment scheme has the potential to be developed into an environmentally and economically acceptable remediation technology.

Enhanced Biotransformation of Trichloroethylene Under Mixed Electron Acceptor Conditions

The biotransformation of trichloroethylene (TCE) under various electron acceptor conditions was investigated by using enrichment cultures developed from the anaerobic digester sludge of Thibodaux sewage treatment plant. The results indicated that TCE was biotransformed under sulfate reducing, methanogenic, nitrate reducing, iron reducing, and fermenting conditions. However, the rates of TCE removal varied among the conditions studied. The fastest removal of TCE (100% removal in 9 days) was observed under mixed electron acceptor conditions, followed in order by methanogenic, fermenting, iron reducing, sulfate reducing, and nitrate reducing conditions. Under mixed electron acceptor conditions, the TCE was converted to ethene, which was further metabolized. Under sulfate and nitrate reducing conditions, the major metabolites produced from TCE metabolism were cis and trans dichloroethylene (DCE). Under methanogenic, iron reducing, and fermenting conditions, cis and trans DCE and ethene were produced from TCE metabolism. This study showed evidence for TCE metabolism in a mixed microbial population system similar to any contaminated field sites, where heterogeneous microbial population exists.

Biotransformation of trichloroethylene in collagen gel sandwich cultures of rat hepatocytes.

The collagen gel sandwich culture of hepatocytes has been proposed as one of the most suitable culture models available for biotransformation studies of xenobiotics. It is a complex model which imitates the cascade of enzymatic events of in vivo biotransformation and allows investigation of biological endpoints under realistic conditions. The biotransformation of trichloroethylene (TRI) has been studied in this model using rat hepatocytes. Headspace gas chromatographic measurements revealed that hepatocytes, cultured for 4 days in this in vitro system, metabolised TRI into the major oxidative metabolites trichloroacetic acid (TCA) and trichloroethanol (TCE). Cultured hepatocytes were exposed either to TRI, or to TCA and TCE. Endpoints studied were albumin secretion and the cytochrome P450 (CYP)-dependent enzymatic activities ethoxyresorufin O-deethylase (EROD), pentoxyresorufin O-depentylase (PROD) and N-nitrosodimethylamine demethylase (NDMA). The results show that both the parent compound and its metabolites exert specific effects on different CYP-dependent mono-oxygenase activities, as seen in vivo. It is suggested that collagen gel sandwich cultures represent a useful in vitro model for the investigation of metabolism-linked toxicity studies.

Production of Trichloroacetic Acid, Trichloroethanol and Dichloroacetic Acid from Trichloroethylene Degradation by Methylocystis sp. Strain M

The chlorinated organic compounds, trichloroacetic acid (TCAA), 2, 2, 2-trichloroethanol (TCAol), dichloroacetic acid (DCAA) and chloral were produced from the biotransformation of trichloroethylene (TCE) by a methane utilizing bacterium Methylocystis sp. strain M. The degradation of TCE by strain M was influenced by pH, with an optimum between 6 and 7. The conversions to TCAA, TCAol and DCAA derived from added TCE were 7.8%, 0.04% and 1.8%, respectively, at pH 7, and varied with pH. The reactions that convert chloral to these metabolites were also influenced by pH. The conversions to TCAA, TCAol and DCAA from added chloral were 77%, 0.6% and 6.0%, respectively, at pH 7. Strain M did not degrade TCAA, TCAol and DCAA, which were shown to be end products of TCE degradation by strain M. The production of DCAA from chloral suggested a new pathway for producing DCAA via chloral, in addition to that via TCEoxide. Thrity-four percent and 66% of DCAA produced from TCE were derived via chloral and TCEoxide, respectively.

Uptake and Biotransformation of Trichloroethylene by Hybrid Poplars

Poplar trees were found to be capable of taking up trichloroethylene (TCE) and degrading it to several known metabolic products: trichloroethanol, trichloroacetic acid, and dichloracetic acid. Poplars were also shown to transpire TCE in measurable amounts. To eliminate the possibility that the degradation we observed was produced solely by rhizosphere organisms, axenic poplar tumor cell cultures were tested; the cultures produced the same intermediate metabolic products. When dosed with [14C]TCE, cell cultures also produced low levels of radiolabeled carbon dioxide and a labeled insoluble residue. These results show that significant TCE uptake and biotransformation occurs in poplar, which demonstrates the potential for the use of poplars for in situ remediation of TCE.

Pseudomonas putida B2: a tod-lux bioluminescent reporter for toluene and trichloroethylene co-metabolism.

A tod-lux transcriptional fusion bioluminescent reporter strain, Pseudomonas putida B2, was developed to permit on-line analysis of trichloroethylene (TCE) transformation by toluene dioxygenase (todC1C2BA) in Pseudomonas putida F1. Strain B2 was exposed to toluene in growing and resting cell bioluminescence assays. The growing cells showed a direct correlation between bioluminescence and toluene concentration, while resting cells showed reproducible bioluminescence with repeated toluene exposures. In addition, P. putida B2 was encapsulated in alginate beads and used in a packed bed flow-through differential volume reactor. The TCE feed into the differential volume reactor was constant at 20 mg L-1 and toluene was pulsed in square-wave perturbations at 10 mg L-1. The system showed a direct correlation between the expression of the tod operon (as monitored by light output) and the co-metabolism of TCE. Approximately 20% of the TCE and 50% of the toluene was removed at a flow rate of 0.4 ml min-1. This approach allowed the on-line monitoring of tod gene expression and its relation to TCE biotransformation.

Biotransformation of Trichloroethylene by a Phenol-Induced Mixed Culture

Biodegradation of trichloroethylene (TCE) was studied using a mixed culture of aerobic, phenol-induced organisms. Abiotic experiments showed that sorption of TCE to biomass was negligible in the systems studied. The effects of influent phenol and TCE concentration on the TCE degradation capacity of the culture were studied using chemostats. A relationship exists between the influent phenol/TCE ratio and TCE biodegradation. TCE transformation yields ranged from 0.052 to 0.222 mg TCE removed/mg phenol removed. Monod kinetic coefficients for phenol degradation were determined. Monod kinetic coefficients were also determined for TCE biotransformation by resting cells. The concept of transformation capacity was used to model the decrease in active biomass concentration caused by TCE transformation. In mineralization studies using {sup 14}C-labeled TCE, 22% of the degraded mass of TCE was transformed to carbon dioxide, 8.8% was incorporated into biomass, 42% was transformed to nonvolatile products, with the remaining, unrecovered 27% most likely transformed into volatile or semivolatile products.

Batch cultivation ofMethylosinus trichosporium OB3b: V. Characterization of poly-β-hydroxybutyrate production under methane-dependent growth conditions

Methanotrophs have promising applications in the bioremediation of chlorinated hydrocarbons and in the production of a biopolymer, poly-beta-hydroxybutyrate (PHB). Batch bioreactor culture conditions were studied for the accumulation of PHB by methane-grown Methylosinus trichosporium OB3b, and to evaluate the effect of PHB on the bacterial capacity to degrade trichloroethylene (TCE), a common groundwater contaminant. The PHB content of the washed and lyophilized cells was measured by gas chromatography (GC), after hydrochloric acid (HCl) propanolysis. A differential GC-based assay was developed for the monomer and the polymer of beta-hydroxybutyrate utilizing 1% and 10% HCl (v/v) reaction mixtures, respectively. During bioreactor growth in a Cu-deficient modified Higgins' medium, the cells accumulated PHB upon depletion of nitrate. A biomass yield of 3.2 g dry wt/L and a PHB accumulation of approximately 10% (w/w) were reached after 140 to 160 h, without adversely affecting the propene or TCE epoxidation specific rate given by whole cells containing soluble methane monooxygenase (sMMO). The TCE biotransformation capacity ( approximately 0.25 mg TCE oxidized/mg dry cell wt) of resting cells containing approximately 10% PHB was consistently approximately 1.6-fold greater than that of cells containing only approximately 2% PHB. Higher levels (>10%) of accumulated PHB did not enhance this biotransformation capacity further. By replacing the bioreactor inlet air + CO(2) mixture with pure O(2) at approximately 85 h of batch operation, a PHB accumulation of approximately 45% was achieved after 160 h, but the whole-cell sMMO activity was markedly decreased. In contrast, cells grown in a 10 muM Cu-supplemented Higgins' nitrate minimal salts medium (particulate MMO formation) accumulated up to 50% PHB in only 120 h, coupled with a very high biomass yield of 18 g dry cell wt/L. High PHB accumulations above approximately 20% by both the -Cu and the +Cu grown cells resulted in a decreased ratio of the electronic cell count to the absorbance at 660 nm, which is commonly used to monitor bacterial growth. (c) 1996 John Wiley & Sons, Inc.

A Field Evaluation of In‐Situ Biodegradation of Chlorinated Ethenes: Part 2, Results of Biostimulation and Biotransformation Experiments

AbstractResults are presented from a field study that document the in‐situ biotransformation of trichloroethylene (TCE), cis‐dichLoroethylene (cis‐DCE), trans‐dichloroethylene (trans‐DCE), and vinyl chloride (VC) in a saturated, semiconfined aquifer. The enhanced biotransformation was accomplished by stimulating the growth of indigenous methane‐oxidizing bacteria (methanotrophs), which transform chlorinated aliphatic compounds by a cometabolic process to stable, nontoxic end products. Experiments were performed in the presence and absence of biostimulation by means of controlled chemical addition, frequent sampling, and quantitative analysis. The degree of biotransformation was assessed using mass balances and comparisons with bromide as a conservative tracer. Biostimulation of the test zone was successfully achieved by injecting methane‐ and oxygen‐containing ground water in alternating pulses under induced gradient conditions. After a few weeks of stimulation, methane concentrations gradually decreased below the detection limit within two meters of travel. Under active biostimulation conditions, 20 to 30% of the TCE was biotransformed during the first season of testing. Direct evidence for biotransformation of VC, trans‐DCE, cis‐DCE, and TCE was obtained in the second and third seasons of field testing. In the absence of biostimulation, the organic compounds concentrations at observation wells reached 95% of the injection concentration, demonstrating negligible losses due to abiotic processes. Biostimulation of the test zone resulted in a concurrent decrease in concentration of methane and the halogenated aliphatic compounds. The organic compounds were transformed within two meters of travel as follows: TCE, 20–30%; cis‐DCE, 45–55%; trans‐DCE, 80–90%; and VC, 90–95%. These results are in qualitative agreement with methane‐utilizing, mixed‐culture laboratory studies which indicate that the rate of biotransformation is more rapid when the molecules are less halogenated.A biotransformation intermediate was observed which was identified by GC‐MS analysis as trans‐dichloroethylene oxide (trans‐DCE epoxide), an expected intermediate based on laboratory studies. When methane addition was stopped, the concentration of the intermediate rapidly decreased, while halogenated compound concentrations slowly increased, indicating that active methane utilization was required for biotransformation to occur.

Trichloroethylene biotransformation in human and rat primary hepatocytes

The biotransformation of trichloroethylene (TCY) was studied in male Sprague-Dawley rats and in human hepatocyte suspensions to aid in estimating the potential for hepatocarcinogenesis in humans. The major metabolites were qualitatively identical in both species, but rat hepatocytes metabolized about four times more TCY than did human hepatocytes under the same experimental conditions. The quantities of chloral hydrate, trichloroethanol (free plus conjugated) and trichloroacetic acid (TCA) were 15, 5 and 20 times greater, respectively, in rat hepatocyte suspensions. Since the TCA metabolite has been implicated in TCY-induced peroxisomal proliferation and hepatocarcinogenesis and rats form less TCA than do mice, which are susceptible to these effects, the results suggest that humans are at low risk from TCY exposure.

Inhibition and stimulation of trichloroethylene biodegradation in microaerophilic microcosms

The possibility of increasing the biotransformation rate of trichloroethylene (TCE) in ground water and subsurface environments by nutrient addition to microcosms was studied. Three sets of microcosms made of sediment and water were prepared under a nitrogen atmosphere to preserve microacrophilic conditions; each set contained one of the following nutrients: sulfate, methane or ethylene. A control set of microcosms without nutrients was also prepared. The addition of methane was found to increase the biotransformation rate of TCE, allowing the depletion of 99.6% of the TCE in 6 months of incubation, with a lag time of 3 months. In the control microcosms, with no added nutrient, 78% of the TCE was depleted in 6 months of incubation. However, in the microcosms to which sulfate or ethylene was added, the half-life of TCE was appreciably increased. This indicates that methane addition increased the ability of the indigenous microorganisms to biodegrade TCE under microaerophilic conditions, and that sulfate addition inhibited the organisms responsible for the biotransformation of TCE or their biodegrading ability. The effect of ethylene was ambiguous; bacterial growth did not occur in sediment-water cultures supplied with ethylene as the sole carbon source. Hence ethylene either inhibited growth of indigenous bacteria or was not a suitable carbon source. The microcosm experiments suggest that biotransformation resulted from the action of methylotrophs, coexisting in microhabitats with methanogens, which cometabolize the chlorinated ethenes with methane.

Biotransformation of trichloroethylene in soil.

Biotransformation of trichloroethylene (TCE) in a soil sample was examined in sealed vials. A soil sample was collected from the ground inside the metal welfare factory ; it was located in the area where groundwater was contaminated by a degreaser, TCE, and cis-1, 2-dichloroethylene (cis-DCE), which had not been used in the vicinity. TCE was transformed into cis-DCE in 1 week in the collected unsterilized soil suspension. On the other hand, TCE did not degrade in the sterilized soil suspension. When 0.05 ml soil suspension was transferred to another sterilized soil suspension, this transformation was observed. This reaction was stopped by heating in boiling water for 10 min. Therefore, this transformation was considered to be due to a microbial dechlorination. The trans-1, 2-dichloroethylene, 1, 1-dichloroethylene and vinyl chloride were not detected by this TCE biotransformation. The cis-DCE did not further degrade at least in 3 weeks. It can therefore be presumed that cis-DCE contained in groundwater near the factory is a biotransformation product of TCE.

INHIBITION AND STIMULATION OF TRICHLOROETHYLENE BIODEGRADATION IN MICROAEROPHILIC MICROCOSMS

The possibility of increasing the biotransformation rate of trichloroethylene (TCE) in ground water and subsurface environments by nutrient addition to microcosms was studied. Three sets of microcosms made of sediment and water were prepared under a nitrogen atmosphere to preserve microacrophilic conditions; each set contained one of the following nutrients: sulfate, methane or ethylene. A control set of microcosms without nutrients was also prepared. The addition of methane was found to increase the biotransformation rate of TCE, allowing the depletion of 99.6% of the TCE in 6 months of incubation, with a lag time of 3 months. In the control microcosms, with no added nutrient, 78% of the TCE was depleted in 6 months of incubation. However, in the microcosms to which sulfate or ethylene was added, the half-life of TCE was appreciably increased. This indicates that methane addition increased the ability of the indigenous microorganisms to biodegrade TCE under microaerophilic conditions, and that sulfate addition inhibited the organisms responsible for the biotransformation of TCE or their biodegrading ability. The effect of ethylene was ambiguous; bacterial growth did not occur in sediment-water cultures supplied with ethylene as the sole carbon source. Hence ethylene either inhibited growth of indigenous bacteria or was not a suitable carbon source. The microcosm experiments suggest that biotransformation resulted from the action of methylotrophs, coexisting in microhabitats with methanogens, which cometabolize the chlorinated ethenes with methane.

Bacterial β-lyase mediated cleavage and mutagenicity of cysteine conjugates derived from the nephrocarcinogenic alkenes trichloroethylene, tetrachloroethylene and hexachlorobutadiene

The metabolism of β-lyase and the mutagenicity of the synthetic cysteine conjugates S-1,2-dichlorovinylcysteine (DCVC), S-1,2,2-trichlorovinylcysteine (TCVC), S-1,2,3,4,4-pentachlorobuta-1,3-dienylcysteine (PCBC) and S-3-chloropropenylcysteine (CPC) were investigated in Salmonella typhimurium strains TA100, TA2638 and TA98. The bacteria contained significantly higher concentrations of β-lyase than mammalian subcellular fractions. Bacterial 100 000 × g supernatants cleaved benzthiazolylcysteine to equimolar amounts of mercaptobenzthiazole and pyruvate. DCVC, TCVC and PCBC produced a linear time-dependent increase in pyruvate formation when incubated with bacterial 100 000 × g supernatants; pyruvate formation was inhibited by the β-lyase inhibitor aminooxyacetic acid (AOAA). CPC was not cleaved by bacterial enzymes to pyruvate. DCVC, TCVC and PCBC were mutagenic in three strains of S. typhimurium (TA100, TA2638 and TA98) in the Ames-test without addition of mammalian subcellular fractions; their mutagenicity was decreased by the addition of AOAA to the preincubation mixture. CPC was not mutagenic in any of the strains of bacteria tested. These results indicate that β-lyase plays a key role in the metabolism and mutagenicity of haloalkenylcysteines when tested in S. typhimurium systems. The demonstrated formation in mammals of the mutagens DCVC, TCVC and PCBC during biotransformation of trichloroethylene (Tri), tetrachloroethylene (Tetra) and hexachlorobutadiene (HCBD) may provide a molecular explanation for the nephrocarcinogenicity of these compounds.

Biotransformation of trichloroethylene in soil.

Trichloroethylene was shown to degrade aerobically to carbon dioxide in an unsaturated soil column exposed to a mixture of natural gas in air (0.6%).