Trichloroethylene Vapor Research Articles

A Human Physiologically Based Pharmacokinetic Model for Trichloroethylene and Its Metabolites, Trichloroacetic Acid and Free Trichloroethanol

Nine male and eight female healthy volunteers were exposed to 50 or 100 ppm trichloroethylene vapors for 4 h. Blood, urine, and exhaled breath samples were collected for development of a physiologically based pharmacokinetic (PBPK) model for trichloroethylene and its two major P450-mediated metabolites, trichloroacetic acid and free trichloroethanol. Blood and urine were analyzed for trichloroethylene, chloral hydrate, free trichloroethanol and trichloroethanol glucuronide, and trichloroacetic acid. Plasma was analyzed for dichloroacetic acid. Trichloroethylene was also measured in exhaled breath samples. Trichloroethylene, free trichloroethanol, and trichloroacetic acid were found in blood samples of all volunteers and only trace amounts of dichloroacetic acid (4–12 ppb) were found in plasma samples from a few volunteers. Trichloroethanol glucuronide and trichloroacetic acid were found in urine of all volunteers. No chloral hydrate was detected in the volunteers. Gender-specific PBPK models were developed with fitted urinary rate constant values for each individual trichloroethylene exposure to describe urinary excretion of trichloroethanol glucuronide and trichloroacetic acid. Individual urinary excretion rate constants were necessary to account for the variability in the measured cumulative amount of metabolites excreted in the urine. However, the average amount of trichloroacetic acid and trichloroethanol glucuronide excreted in urine for each gender was predicted using mean urinary excretion rate constant values for each sex. A four-compartment physiological flow model was used for the metabolites (lung, liver, kidney, and body) and a six-compartment physiological flow model was used for trichloroethylene (lung, liver, kidney, fat, and slowly and rapidly perfused tissues). Metabolic capacity (Vmaxc) for oxidation of trichloroethylene was estimated to be 4 mg/kg/h in males and 5 mg/kg/h in females. Metabolized trichloroethylene was assumed to be converted to either free trichloroethanol (90%) or trichloroacetic acid (10%). Free trichloroethanol was glucuronidated forming trichloroethanol glucuronide or converted to trichloroacetic acid via back conversion of trichloroethanol to chloral (trichloroacetaldehyde). Trichloroethanol glucuronide and trichloroacetic acid were then excreted in urine. Gender-related pharmacokinetic differences in the uptake and metabolism of trichloroethylene were minor, but apparent. In general, the PBPK models for the male and female volunteers provided adequate predictions of the uptake of trichloroethylene and distribution of trichloroethylene and its metabolites, trichloroacetic acid and free trichloroethanol. The PBPK models for males and females consistently overpredicted exhaled breath concentrations of trichloroethylene immediately following the TCE exposure for a 2- to 4-h period. Further research is needed to better understand the biological determinants responsible for the observed variability in urinary excretion of trichloroethanol glucuronide and trichloroacetic acid and the metabolic pathway resulting in formation of dichloroacetic acid.

E-beam treatment of trichloroethylene-air mixtures: Products and rates

Electron beam (E-beam) treatment of 3000 ppmv trichloroethylene (TCE) vapor in dry and wet air led to rapid, nearly quantitative, conversion of TCE to dichloroacetyl chloride, plus small amounts of phosgene. Higher E-beam doses, up to 110 kGy, led to oxidation of the initial products to CO, CO 2, HCl and Cl 2. The results parallel results found for photo- and Cl-atom initiated oxidation of TCE vapor, and are accounted for by an efficient Cl-atom chain oxidation. Lack of effect of 28,000 ppmv water vapor (90% RH) on rates or products reflects a very high efficiency for the Cl-atom chain oxidation and the very slow reaction of vapor phase water with acyl halides. Irradiation experiments conducted with TCE dissolved in aerated and deaerated water at 10 and 300 ppm showed marked differences in radiolytic products from those found in the vapor phase. A preliminary cost estimate indicates that E-beam treatment of TCE vapor is very competitive with conventional activated carbon treatment and catalytic oxidation.

Vacuum Photocatalytic Oxidation of Trichloroethylene

The combination of physical removal methods such as soil vapor vacuum extraction or vacuum air stripping with gas-solid heterogeneous photocatalytic oxidation of the off-gases produced may be an effective remediation technology for a variety of soil and water contamination problems, particularly those involving chlorinated ethylenes. To test the hypothesis that reduced pressure operation of the photocatalytic unit could enhance reactor performance, a bench-scale annular photocatalytic reactor operating in the vacuum range was designed, built, and evaluated. The reactor inner wall was coated with sol-gel-derived titania to provide a uniform, adherent, photocatalytically active thin film. Photocatalytic oxidation of trichloroethylene (TCE) in humid airstreams was employed as a model chemistry. Reduction of the operating pressure at fixed feed conditions and molar feed rate significantly enhanced PCO performance as measured by the observed TCE conversion. Higher conversions were obtained in spite of a reduction in the residence time accompanying the lower pressure operation. The greatest enhancements in the TCE destruction efficiency occurred for low TCE feed concentrations and high water vapor levels. The performance enhancement appears to be linked to reduction in the absolute water vapor concentration and competition between TCE and water vapor for adsorption sites on the catalyst.

Role of Water in the Photocatalytic Degradation of Trichloroethylene Vapor on TiO2 Films

The focus of this study was to investigate the role of water vapor in the photocatalytic degradation of trichloroethylene (TCE) on anatase titanium dioxide films immobilized on the surfaces of ring-roughened annular reac tors. Experimental variables included TCE concentration (0.7−7 parts per million by volume or ppmv), oxygen concentration (13−120 000 ppmv), residence time (2.77−9.81 s), relative humidity (0−100%), and reactor length. TCE conversion was not affected by relative humidities up to 20%, but it deteriorated as the gas mixture approached saturation with respect to water vapor. Major intermediates and products from TCE degradation were the same as those previously reported for dry conditions: carbon tetrachloride, chloroform, hexachloroethane, pentachloroethane, and tetrachloroethylene. The formation rates for these compounds increased with increasing water vapor concentrations at relatively low humidities as a result of a stronger deteriorating rate effect of water vapor on atomic oxygen oxid...

Concentration-time relationships for the effects of inhaled trichloroethylene on signal detection behavior in rats.

The risk from inhaled volatile organic compounds (VOCs) is presently assessed on the basis of lifetime exposure to average concentrations of the vapor. This strategy yields rational predictions of risk if the product of concentration (C) and the duration of exposure (t) yields constant effects on health (Haber's Rule). The validity of this assumption was evaluated by assessing the acute behavioral effects of inhaled trichloroethylene (TCE) vapor at various values of C and t. Adult male Long-Evans rats (n = 11) were trained to perform a signal detection task in which a press on one lever produced food on trials containing a signal (a brief, unpredictable light flash); a press on a second lever produced food on trials lacking a signal. Response time (RT) and indices of sensitivity (SI) and bias (RI) derived from the theory of signal detection were calculated at three times during repeated daily 60-min tests conducted in air containing 0, 400, 800, 1200, 1600, 2000, or 2400 ppm TCE. Behavior remained stable during tests in air. In TCE, SI declined and RT increased as functions of both C and t. RI was not affected by TCE. Effects on SI and RT were not predictable from the C x t product: both endpoints were more affected by C than by t. To quantify the change in the effect of TCE across exposure times, concentration-effect relationships for inhaled TCE on SI and RT were modeled with cubic polynomial functions at each of the three exposure durations. Concentrations of inhaled TCE associated with preselected changes in SI and RT were then estimated for each animal from these functions. Criterion concentrations, SI0.1 and RT100, were defined as the concentration of TCE associated with a 0.1-unit decrease in SI or a 100-msec increase in RT, respectively. Both SI0. 1 and RT100 increased as exposure duration decreased, but did so more slowly than would be predicted by Haber's Rule. This pattern indicates that application of Haber's Rule overestimates the concentration of inhaled TCE associated with changes in signal detection and thus underestimates the risk of behavior change from short-term exposures to TCE. On the other hand, the fact that SI0.1 and RT100 did increase with shorter exposure times indicates that the converse assumption, that the toxicity of inhaled TCE is independent of the duration of exposure, yields an overly conservative estimate of risk.

Role of Chlorine and Oxygen in the Photocatalytic Degradation of Trichloroethylene Vapor on TiO2 Films

The photocatalytic degradation of trichloroethylene (TCE) was investigated with ring-roughened annular reactors. Anatase titanium dioxide films were immobilized by chemical vapor deposition using titanium tetraisopropoxide as the source of titanium. Experimental variables included TCE concentration (0.1−10 parts per million by volume or ppmv), oxygen content (20−200 000 ppmv), residence time (2.46−9.57 s), and reactor length. In general, TCE conver sion increased with increasing values of all of these variables up to a maximum of 99.4% within the range investigated. Ten chlorinated organic intermediates/products were observed primarily at low oxygen concentrations. Among these compounds, carbon tetrachloride, chloroform, hexachloroethane, pentachloroethane, and tetrachloroethylene were present at quantifiable levels. Additional experiments revealed that pentachloroethane and tetrachloroethylene also decomposed with degradation efficiencies (up to 98 and 94%, respectively) being somewhat lower than that for TCE. Chloroform conversions were low (up to 30%), and no appreciable degradation of carbon tetrachloride was observed for the range of operating conditions investigated. Chlorinated organic intermediate/product formation was the result of various reactions involving chlorine and hydrogen atom extractions and additions. Chlorine atom attack reactions were inhibited in the presence of relatively high oxygen concentrations including that in ambient air due to the predominance of competing oxidation reactions involving unidentified reactive oxygen species.

Automated Detection of Trichloroethylene by Fourier Transform Infrared Remote Sensing Measurements

Passive Fourier transform infrared (FT-IR) remote sensing measurements are used to implement the automated detection of trichloroethylene (TCE) vapor in the presence of a variety of infrared background signatures. Through the use of a combination of bandpass digital filtering and piecewise linear discriminant analysis, this detection procedure is applied directly to short segments of the interferogram data collected by the FT-IR spectrometer. Data employed in this work were collected during open-air/passive cell terrestrial and passive cell laboratory measurements. Infrared backgrounds employed included terrain, low-angle sky, and water backgrounds, in addition to laboratory blackbody measurements. Other potentially interfering chemical species present were carbon tetrachloride, acetone, methyl ethyl ketone, and sulfur hexafluoride (SF6). These data are used to assemble two data sets of differing complexity. Optimization studies are performed separately with each data set to study the influence of filter bandpass position, bandpass width, interferogram segment location, and segment size on the ability to detect TCE. The optimal parameters found consist of a Gaussian-shaped filter positioned at 939.5 cm-1, with a width at half-height of 123.4 cm-1. This filter is applied to interferogram points 111−220 (relative to the centerburst). When applied to a prediction set of 60 000 interferograms, the piecewise linear discriminant developed on the basis of these optimal parameters is found to detect TCE successfully in 96.2% of the cases in which it is present. The overall rate of false detections is 0.5%. The limit of detection of TCE is found to be 102 ppm-m at a temperature difference of 10.5 °C between the infrared background and the analyte. SF6 is observed to provide the greatest spectral interference among the compounds tested, producing a false detection rate of 8.6%. It is found that this false detection rate can be reduced to 1.5% through the development of a probability-based interpretation of the piecewise linear discriminant results. These results are observed to compare favorably with those obtained in a separate analysis of filtered single-beam spectra.

Concentration-Time Relationships for the Effects of Inhaled Trichloroethylene on Signal Detection Behavior in Rats

The risk from inhaled volatile organic compounds (VOCs) is presently assessed on the basis of lifetime exposure to average concentrations of the vapor. This strategy yields rational predictions of risk if the product of concentration (C) and the duration of exposure (t) yields constant effects on health (Haber's Rule). The validity of this assumption was evaluated by assessing the acute behavioral effects of inhaled trichloroethylene (TCE) vapor at various values of C and t. Adult male Long-Evans rats (n = 11) were trained to perform a signal detection task in which a press on one lever produced food on trials containing a signal (a brief, unpredictable light flash); a press on a second lever produced food on trials lacking a signal. Response time (RT) and indices of sensitivity (SI) and bias (RI) derived from the theory of signal detection were calculated at three times during repeated daily 60-min tests conducted in air containing 0, 400, 800, 1200, 1600, 2000, or 2400 ppm TCE. Behavior remained stable during tests in air. In TCE, SI declined and RT increased as functions of both C and t. RI was not affected by TCE. Effects on SI and RT were not predictable from the C x t product: both endpoints were more affected by C than by t. To quantify the change in the effect of TCE across exposure times, concentration-effect relationships for inhaled TCE on SI and RT were modeled with cubic polynomial functions at each of the three exposure durations. Concentrations of inhaled TCE associated with preselected changes in SI and RT were then estimated for each animal from these functions. Criterion concentrations, SI0.1 and RT100, were defined as the concentration of TCE associated with a 0.1-unit decrease in SI or a 100-msec increase in RT, respectively. Both SI0. 1 and RT100 increased as exposure duration decreased, but did so more slowly than would be predicted by Haber's Rule. This pattern indicates that application of Haber's Rule overestimates the concentration of inhaled TCE associated with changes in signal detection and thus underestimates the risk of behavior change from short-term exposures to TCE. On the other hand, the fact that SI0.1 and RT100 did increase with shorter exposure times indicates that the converse assumption, that the toxicity of inhaled TCE is independent of the duration of exposure, yields an overly conservative estimate of risk.

Model development for subsurface organic compound vapor diffusion using geographic information systems: A feasibility assessment

Abstract The feasibility of using a geographic information system (GIS) to evaluate the subsurface transport of volatile organic compounds (VOCs) is evaluated. A GIS analysis based on selected soil properties and a flow path model were used to demonstrate the visualization of a probable path taken by diffusing VOC vapors in the vadose zone. The model uses soil properties such as texture, organic matter content, water content, bulk density, and permeability as path finding indices. The values of the soil properties used in the validation of this model were obtained from the respective County Soil Survey Reports. The various combinations of these soil properties resulted in deviations from the anticipated path taken by the diffusing organic vapors as they migrated through the subsurface. The model was evaluated using two soil systems and estimated diffusion coefficients. A proportionality constant (k) was calculated and used in conjunction with the assigned soil property values in the calculation of diffusion coefficients (Df) for trichloroethylene (TCE) vapors for each soil system. For each case, the model depicts the probable path taken by the VOC vapors as being the route through the soils having characteristics most favorable for chemical migration. Specifically, the soils along the predicted flow path have combinations of high moisture contents, low bulk densities, clay and organic matter contents as well as higher porosity and permeability than soils along any other possible flow path in the given soil systems.

Vapor Transport of Trichloroethylene in the Unsaturated Zone: Field and Numerical Modeling Investigations

Vapor transport of chlorinated solvents in the unsaturated zone may be an important mechanism for the spread of contamination at spill sites and may be a significant factor controlling the extent of groundwater contamination. Two field experiments were carried out at the Canadian Forces Base Borden field site to provide detailed monitoring of the transport behavior of trichloroethylene vapors in the unsaturated zone. Experiments were conducted for both winter and summer conditions and under different surface boundary conditions. The observed results were simulated using a Fickian‐based numerical model with linear equilibrium phase partitioning. The model includes both diffusion and density‐induced advection and allows for the incorporation of spatial heterogeneities and nonisothermal conditions. Numerical sensitivity analyses were conducted to further evaluate the relative influence of various transport parameters on vapor migration. Use of measured field values as input parameters resulted in a very good match between the experimental results and numerical simulations. In both experiments, vapor plumes spread several meters from the source and downward to the capillary fringe within only a few days. Seasonal temperature variations were found to have a significant impact on the rate and total mass of vapor transport, and variations in organic carbon content, and to a lesser extent moisture content, exerted the greatest control on retardation of vapor migration. Transport was diffusion dominated, but density‐induced advection was an appreciable component of net transport under summer conditions, when vapor concentrations were higher. Geologic conditions at the site made overall transport relatively insensitive to the ground surface boundary condition.

Novel Products in the CO2-Laser Induced Reaction of Trichloroethylene

Previous reports on the thermal or CO2-laser induced decomposition of trichloroethylene have identified only one condensible product, hexachlorobenzene (in addition to HCl and mono- and dichloroacetylene). We have found that trichloroethylene vapor exposed to cw irradiation on the P(24) line of the (001 - 100) band of the CO2 laser at incident power levels from 8 - 17 W produces numerous products, of which the 13 major ones have been identified using IR, GC/MS, GC/FTIR, and NMR methods. All of these products have 4, 6, or 8 carbons, are highly unsaturated, and are completely chlorinated or contain a single hydrogen. C4HCl5 and C6Cl6 isomers (three of each) account for S 55% to 85% of total products (based on peak areas in the total ion chromatograms in GC/MS runs), depending on reaction conditions. In addition to characterizing the products, we discuss the dependence of the product distribution on laser power, irradiation time, and cell geometry, and we outline a possible mechanism.

Detection of low levels of trichloroethylene vapor with Raman spectrometry

The response of a novel fiber-optic Raman probe to low levels of trichloroethylene (TCE) vapors is characterized. The detection limit of the current probe for TCE vapor is 34 mg/L, and the probe exhibits a fully reversible response. The probe uses an organic-polymer, low-density polyethylene to concentrate TCE vapors in the optical path of the fiber-optic Raman spectrometer. The relative standard deviation for measurement of 677 mg/L of TCE in the vapor is 0.3%.

Vapor Adsorption of Trichloroethylene on Quartz Sands of Varying Grain Size

Laboratory measurements were carried out to determine the vapor adsorption of the solvent trichloroethylene (TCE) on a dry quartz sand of two different mesh sizes. Using a static adsorption laboratory procedure and inverse gas chromatography (IGC), the sorption of TCE vapor in nitrogen was measured at concentration ranges of approximately 0.1 to 440,000 ppm by volume. Adsorption was measured on 30/40 and 100/200 mesh dry quartz sand, with the finer material created by mechanically crushing and sieving coarser material. The observed sorption isotherms fit a Freundlich isotherm and are also well represented by a simple linear sorption isotherm.

Gas-sensing properties of SnO 2 pyrolytic films subjected to ultrviolet radiation

Chemisorption of different species changes the electrical resistivity of many semiconductor films. In this work we have studied the behavior of thermally treated SnO 2 films. At room temperature thermal desorption of many species is negligible in this material, so the electrical resistivity of the SnO 2 films remains invariant with various gas compositions in the surrounding. To operate a gas sensor at room temperature with this material, we have used UV-radiation to produce photodesorption. At the same time this radiation produces photodissociation of the chemisorbed molecules. Using nitrogen as a carrier gas, small amounts of acetone and trichloroethylene vapors are injected into the system, measuring the current through the films with a constant applied voltage. Selectivity is achieved in this case by using filters that modify the IV excitation spectrum. The short-wavelength cut-off of this spectrum should be no longer than about 3200 Å, corresponding to the minimum photon energy to excit electron-hole pairs in the SnO 2 films. Nitrogen/oxygen gas transitions have been investigated.

Modeling multicomponent volatile organic and water vapor adsorption on soils

Volatile organic chemical (VOC) and water vapors are present simultaneously in the soil gas phase. Any modeling of VOC vapor flow must account for the strong competition they experience from water and any competition between themselves. To account for these competitions, the multicomponent form of the Brunauer—Emmett—Teller equation with finite number of adsorption layers was tested. Of the three input constants required in the multicomponent model, two can be obtained from single species adsorption experiments. The third constant was found to be bounded within a fairly narrow range; although its physical meaning is debatable, its value can be approximated fairly accurately. The data used to check the applicabi- lity of this model were for the adsorption of trichloroethylene and toluene on a sand and Yolo silt loam (fine-silty, mixed, nonacid, thermic Typic Xerorthent). For relative humidities (RHs) corresponding to less than one molecular layer of water coverage and at low to very low toluene and trichloro ethylene (TCE) vapor pressures, it underpredicted the adsorbed amounts of both species from their binary mixtures with water on both soils. At RHs corresponding to between one and two molecular layers of water coverage, predictions compared well with data. At RHs corres- ponding to about two layers of water, the model overpredicted the adsorbed amounts. At toluene relative vapor pressures above 0.1 the model reasonably described the adsorbed amount on sand at two RHs corresponding to one to two water layers. This model was further tested on published adsorption data of para-xylene and water on soil. It was reasonably successful in describing adsorption of para-xylene from its binary mixture with water above para-xylene relative vapor pressure of 0.069 and water relative humidity of 0.084. No competition between TCE and toluene was observed at the low vapor pressures in our experiments. Simulations of adsorption in the ternary systems of TCE, toluene, and water followed the same pattern as the binary simulations.

Effect of subchronic inhalation exposure to low-level trichloroethylene on heart rate and wakefulness-sleep in freely moving rats.

Electroencephalographic (EEG) and heart rate (HR) responses to repeated 8-h exposure for 6 weeks to trichloroethylene (TRI) vapor of 50, 100 and 300 ppm were examined in freely moving rats with chronically implanted electrodes for polygraphic recordings. Exposure to all the TRI levels significantly decreased amount of time spent in wakefulness (W) during the exposure period. Exposure to 100 ppm and higher levels significantly decreased the time-averaged HR during the post-exposure period. The HRs during the stages of slow-wave sleep (SWS) and paradoxical sleep (PS) were significantly lowered after cessation of exposure to 50 ppm. When compared with the previously reported responses to short-term exposure to TRI (Arito H, et al. Arch Toxicol 1993; 67: 193-199), significant changes in wakefulness-sleep and HR elicited by the long-term exposure appeared at lower exposure levels. The EEG and HR effects of long-term exposure to TRI of 50 ppm or higher levels are discussed for their causative factors on the basis of the reported findings and for validity of the ongoing biological exposure limit value of TRI with reference to documentations enlisted for ACGIH's TLV of 50 ppm (ACGIH. Documentation of the threshold limit values and biological exposure indices, 5th ed. 1986: 595-597).

Decomposition of halogenated hydrocarbons using intense, penetrating bremsstrahlung

Radiolytic decomposition of chlorinated hydrocarbons and other toxic compounds has been experimentally measured using ionizing radiation produced by electron accelerator and nuclear isotope sources. Decomposition products have been identified. A portable, commercially available electron accelerator was set up at a Superfund site where vapor extraction wells were removing trichloroethylene (TCE) from a spill into the unsaturated soil. The extraction vapor was passed through the accelerator beam to decompose the TCE. On site radiolytic decomposition of TCE vapor using an accelerator is shown to be significantly less expensive than filtration of TCE vapor using activated charcoal.

Characterization of Calcium-Deficient Hydroxyapatite after a Catalytic Reaction with Trichloroethylene Vapor

Abstract Calcium-deficient hydroxyapatite (DAp) was characterized both before and after an oxidative catalytic reaction with trichloroethylene (TCE) vapor at 450 °C. Most of the Cl in the TCE which decomposed by the reaction was captured as Cl− in DAp. This result supports the assumption reported in a previous paper. On the basis of infrared spectroscopic and X-ray photoelectron spectroscopic results, the captured Cl species was assumed to replace OH− in DAp and to form chloroapatite.

Radiolytic decomposition of environmental contaminants and site remediation using an electron accelerator

AbstractHalogenated and nonhalogenated hydrocarbon contaminants are currently found in natural waterways, groundwater, and soils as a result of spills and careless disposal practices. The development of proper treatment methodologies for the waste streams producing this environmental damage is now a subject of growing concern. A significant number of these waste stream compounds are chemically stable and are thus resistant to environmental degradation.Numerous researchers have investigated the use of ionizing radiation to decompose chlorinated hydrocarbons in diverse matrices and have proposed various free‐radical‐induced reaction mechanisms.This article is divided into two sections. First, we present data on experimentally measured, radiolytically induced decomposition of hazardous wastes and toxic substances using accelerator‐generated bremsstrahlung sources and gamma radiation from cobalt‐60. Data are presented on the radiolytically induced reduction in concentration of volatile organic compounds (VOCs) dissolved in water and in air, polychlorinated biphenyls (PCBs) dissolved in oil, high explosives dissolved in groundwater, and chemical weapon surrogates. The results of these studies suggest the potential use of ionizing radiation as a method of hazardous waste treatment.The second section of this article describes the technical aspects of a field‐scale radiolytic decomposition site cleanup demonstration using an electron accelerator. A portable, commercially available electron accelerator was set up at the Lawrence Livermore National Laboratory's (LLNL's) Site 300, a Superfund site, where vacuum extraction wells were removing trichloroethylene (TCE) vapor from a ground spill into the unsaturated soil zone. The accelerator was retrofitted into the existing vacuum extraction system such that the extracted TCE‐containing vapor passed through the accelerator beam for treatment. The concentration of TCE in the vapor was reduced by an amount dependent on the accelerator beam power. Production of reaction products in the vapor was measured as a function of absorbed dose.

Acute effects of trichloroethylene on blood concentrations and performance decrements in rats and their relevance to humans.

This study was designed to clarify the nature of effects of trichloroethylene (TCE) on the central nervous system, and to determine the critical concentrations in blood associated with specific behavioural changes. This was achieved by a follow up of the whole time course of TCE intoxication during and after exposure. The effects of a single four hour exposure to TCE on signalled bar press shock avoidance in rats were tested by methods previously applied to investigate the acute neurobehavioural effects of exposure to toluene. Even low exposure to TCE induced shock avoidance performance decrements in rats. Rats exposed to 250 ppm TCE showed a significant decrease both in the total number of lever presses and in avoidance responses at 140 minutes of exposure compared with controls. The rats did not recover their pre-exposure performance until 140 minutes after the exhaustion of TCE vapour. Exposures in the range 250 ppm to 2000 ppm TCE for four hours produced concentration related decreases in the avoidance response rate. No apparent acceleration of the reaction time was seen during exposure to 1000 or 2000 ppm TCE. The latency to a light signal was somewhat prolonged during the exposure to 2000 to 4000 ppm TCE. It is estimated that there was depression of the central nervous system with slight performance decrements and the corresponding blood concentration was 40 micrograms/ml during exposure. Depression of the central nervous system with anaesthetic performance decrements was produced by a blood TCE concentration of about 100 micrograms/ml. These results showed effects of TCE on the central nervous system that were considered to be a function of both the exposure concentration and the duration of exposure, which are closely related to the TCE concentration in blood.