Tetrachloroethylene toxicity

AH volatile organic solvents are toxic to some degree. Excessive vapor inhalation of the volatile chloriaated solveats, and the central nervous system depression that results, is the greatest hazard for iadustrial use of these solvents. Proper protective equipment and operating procedures permit safe use of solvents such as methylene chloride, 1,1,1-trichloroethane, trichloroethylene, and tetrachloroethylene ia both cold and hot metal-cleaning operations. The toxicity of a solvent cannot be predicted from its chlorine content or chemical stmcture. For example, 1,1,1-trichloroethane is one of the least toxic metal-cleaning solvents and has a recommended threshold limit value (TLV) of 350 ppm. However, the 1,1,2-trichloroethane isomer is one of the more toxic chloriaated hydrocarboas, with a TLV of only 10 ppm. 

Inhibited grades of 1,1,1-trichloroethane are used in hundreds of different industrial cleaning appHcations. 1,1,1-Trichloroethane is preferred over trichloroethylene or tetrachloroethylene because of its lower toxicity. Additional advantages of 1,1,1-trichloroethane include optimum solvency, good evaporation rate, and no fire or flash point as determined by standard test methods. Common uses include cleaning of electrical equipment, motors, electronic components and instmments, missile hardware, paint masks, photographic film, printed ckcuit boards, and various metal and certain plastic components during manufacture (see Metal surface treatments). 

The only significant use of 1,1,2,2-tetrachloroethane is as a feedstock in the manufacture of trichloroethylene, tetrachloroethylene, and 1,2-dichloroethylene. Although it is an excellent solvent, its use should be discouraged in view of its high toxicity. 

Pentachloroethane is a good solvent for cellulose acetate, certain cellulose ethers, and for natural gums and resins, but its high toxicity has discouraged these uses. Pentachloroethane is still used as an intermediate in some tetrachloroethylene processes. 

Hexachloroethane is considered to be one of the more toxic chlorinated hydrocarbons. The 1991 ACGIH recommended time-weighted average (TWA) for hexachloroethane was 1 ppm or 10 mg /m of air. Skin adsorption is a route of possible exposure ha2ard. The primary effect of hexachloroethane is depression of the central nervous system (147). Pentachloroethane and tetrachloroethylene are primary metaboHtes of hexachloroethane in sheep (148). 

Other chlorinated solvents such as tetrachloroethylene or chloroform may be used in place of carbon tetrachloride. Caution The reaction of sulfur trioxide with chlorinated solvents has been reported to give phosgene and other toxic products. Adequate venting of all by-product gases is essential. 

Distillation of tetrachloroethylene (formerly a dry-cleaning solvent) in new galvanised steel equipment produces traces of dichloroacetylene. This is toxic and may cause ill-health in those exposed. Should the acetylene chance to be concentrated (as in the sub-entry above), it is also very explosive. The galvanised metal becomes passivated in a few days and the effect was not found with other steels. 

Perchloroethylene (tetrachloroethylene) is a nonflammable solvent of low toxicity that dissolves and removes H blister and V nerve agents but does not neutralize them. NIOSH has recommended that this substance be treated as a potential human carcinogen. It does not work with G nerve agents. 

I now shall present a summary of an application of decision analysis to a specific chemical, perchloroethylene (PCE), a widely used dry cleaning solvent (also called tetrachloroethylene). Full details of this application are presented in an EPA report (5). Perchloroethylene was selected for us by the staff of the EPA Office of Toxic Substances as representative of chemicals on which EPA needed to make an unreasonable risk determination under TSCA. Our analysis was carried out as an exercise in methodology development and not to support any specific regulatory activities by EPA concerning perchloroethylene. 

Friberg, L., Kylin, B., and Nystrom, A. Toxicities of trichloroethylene and tetrachloroethylene and Fujiwara s p3n idine-alkali reaction. Acta Pharmacol. Toxicol, 9 303-312,1953. 

Richter. J.E., Peterson. S.F., and Kleiner. C.F. Acute and chronic toxicity of some chlorinated benzenes, chlorinated ethanes, and tetrachloroethylene to Daphnia magna. Arch. Environ. Contam. Toxicol, 12(6) 679-684,1983. 

U.S. EPA. Preliminary study of selected potential environmental contaminants - Optical brighteners, methyl chloroform, trichloroethylene, tetrachloroethylene, ion exchange resins. Office of Toxic Snbstances, Report 560/2-75-002,1975,286 p. U.S. EPA. Report on the problem of halogenated air pollntants and stratigraphic ozone. Office of Research and Development, Report-600/9-75-008, 1975a, 55 p. 

Hexachlorobutadiene was first prepared in 1877 by the chlorination of hexyl oxide (lARC 1979). Commercial quantities of hexachlorobutadiene have never been produced in the United States. The primary source of hexachlorobutadiene found in the United States is inadvertent production as a waste by-product of the manufacture of certain chlorinated hydrocarbons, such as tetrachloroethylene, trichloroethylene, and carbon tetrachloride (ERA 1980 Yang 1988). In 1982, ERA reported an annual volume of about 28 million pounds of hexachlorobutadiene inadvertently produced as a waste by- product from this source (ERA 1982b HSDB 1993). Table 4-1 summarizes information on U.S. companies that reported the production, import, or use of hexachlorobutadiene in 1990 based on the Toxics Release Inventory TRI90 (1992). The TRI data should be used with caution since only certain types of facilities are required to report. This is not an exhaustive list. 

Manufacturing processes in which organic products are made are of special interest to green chemists for a variety of reasons, largely because so many of the raw materials used to make such products, the by-products formed in the reactions, and the final products themselves are likely to he toxic or hazardous in other ways. Historically, the problem with such manufacturing processes is that they have required the use of organic solvents, such as carbon tetrachloride, chloroform, tetrachloroethylene, trichloroethylene, 1,1,1-trichloro-ethane, benzene, toluene, and xylene. A major thrust, then, has been to find satisfactory substitutes for these organic solvents. 

Groups of 90 male and 90 female Sprague-Dawley rats, 12 weeks of age, were exposed to concentrations of 5,10, 50 or 250 ppm [20,40,200 or 1000 mg/ni ] 1,2-dichloroethane (purity, 99.82% 1,1-dichloroethane, 0.02% carbon tetrachloride, 0.02% trichloroethylene, 0.02% tetrachloroethylene, 0.03% benzene, 0.09%) in air for 7 h per day on five days per week for 78 weeks. After several days of exposure to 250 ppm, the concentration was reduced to 150 ppm because of severe toxic effects. A group of 90 males and 90 females kept in an exposure chamber under the same conditions for the same amount of... 

ATSDR (Agency for Toxic Substances and Disease Registry). Toxicological Profile for Tetrachloroethylene Draft for Public Comment Public Health Service Atlanta, GA, 1995. 

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