Human Toxic Chemical Exposure - 1,1,1-trichloroethane

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Reference Summary

The solvent 1,1, l-trichloroethane (or methyl chloroform) is a chlorinated hydrocarbon solvent in wide spread use because of its low explosion risk and relative safety compared to other solvents in the same class. It is used as a degreaser, a dry-cleaning agent and a propellant. NIOSH has estimated worker exposure to 1,1,1-trichloroethane at about 3 million per year (1). 1,1,1-trichloroethane has the following structure:



Symptoms of acute exposure to l, l, l-trichloroethane include dizziness, incoordination, and drowsiness. It has been subject to a carcinogenesis bioassay by NCI and found not to be carcinogenic (2). However, chronic, low-level exposure to l, l, l-trichloroethane has been found to cause decreased memory and impairment of the central nervous system (3).

Uptake and Metabolism

Intake of l, l, l-trichloroethane can occur either by breathing the solvent vapor or by skin contact. Immersion of one hand in the solvent for 30 minutes is approximately equivalent to breathing 50 ppm for the same length of time.

An accompanying graph details levels of l, l, l-trichloroethane in blood following exposure for one day (a 6 hour exposure). The data are derived from exposure to human volunteers, at rest during exposure (4). Exercise during exposure increases uptake, so that levels can be from 10% to 50% higher if the exposed individual was engaged in strenuous work during the exposure period (5). This solvent accumulates to a small extent in the body fat; thus, repeated exposures will lead to levels about 10% to 20% higher than those attained during a single exposure episode (6).



Biological Monitoring

Most of the l, l, l-trichloroethane that is absorbed by the body is excreted unchanged by the lungs. About 2%-5% is metabolized to trichloroethanol and to trichloroacetic acid. These metabolites can be detected in the blood or urine. Trichloroacetic acid, because of its binding to serum albumin, will persist in the blood stream with a half-life of about 3 days. Short term, very high exposures to l, l, l-trichloroethane will generally not produce detectable elevations of trichloroethanol or trichloroacetic acid; thus, measurements of these compounds are fairly ineffective in the identification of brief overexposures.

The Biological Exposure Indices (BEIs) recommended by the ACGIH for l, l, l-trichloroethane are: 10mg/L trichloroacetic acid in urine, 30mg/L trichloroethanol in urine and 1mg/L trichloroethanol in blood when collected at the end of shift at the end of workweek (7). Trichloroethanol in urine can be used as a fairly sensitive measure of overexposures to l, l, l-trichloroethane provided that urine specimens are obtained both on the day before and the day after exposure. As a gross measure, trichloroethanol levels in the urine will be, under 40 mg/l at the end of a workshift, if the air levels were under 350 ppm. By the next morning, the urinary levels of trichloroethanol will decline by about 30%.

Trichloroacetic acid levels in urine will generally stay under 8 mg/l unless there is consistent exposure to solvent levels over 350 ppm for 2 to 5 days.

The evidence that l, l, l-trichloroethane can produce significant neurobehavioral effects at a levels of 350 ppm in the air is spotty. However, some countries have called for a lowering of the standard to 200 ppm. Lauwerys has recommended that the level of l, l, l-trichloroethane in expired air be kept under 50 ppm during exposure (8). This level would correspond with an exposure level of under 150 ppm and less if there were significant skin contact.

For more information on sampling procedures, please see the Pacific Toxicology Laboratories collection and shipping instructions for urine and blood volatiles.

References

1. Settig, M., Handbook of Toxic and Hazardous Chemicals, Noyes Publications, 1981.

2. National Cancer Institute, Bioassay of I, l, l-Trichloroethane for Possible Carcinogenicity, Carcinog. Tech. Rept. Ser. NCI-CG-TR-3, Washington, DC, 1977.

3. Axelson, O., et. al., Current Aspects of Solvent Related Disorders. In Developments in Occupational Medicine (ed. Carl Zenz), Yearbook Medical Publishers inc. , Chicago, Pp. 237-59. 1977.

4. Nolan, R.J., et. al., Kinetics and metabolism of inhaled methylchloroform (1, 1, I-trichloroethane) in male volunteers, Fund. App. Toxic., 4: 654-62, 1984.

5. Monster, A.C., l, l, l-Trichloroethane in Biological Monitoring and Surveillance of Workers Exposed to Chemicals, Eds: Aitio, A., Riihimake, V., and Vainio, H., McGraw-Hill, 1984.

6. Savolained, H., Pharmacokinetics, pharmacoynamics, and aspects of neurotoxic effects of four inhaled aliphatic chlorohydrocarbon solvents as relevant in man, fur. J. Drug metab. Pharm. 6:85-90, 1981.

7. American Conference of Governmental Industrial Hygenists, Inc.: Documentation of the Biological Exposure Indices (BEIs), Cincinnati, OH, 1991.

8. Lauwerys, R.W., Industrial Chemical Exposure: Guidelines for Biological Monitoring, Biomedical Publications, Davis, California, 1983.

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