Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants Volume 3 (1996) / Chapter Skim
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B11: Trichloroethylene
B11: Trichloroethylene
Pages 292-320
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Coleman, Ph.D. Johnson Space Center Toxicology Group Biomedical Operations and Research Branch National Aeronautics and Space Administration Houston, Texas PHYSICAL AND CHEMICAL PROPERTIES TrichIoroethylene (TCE)
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In an experiment by the Toxicology Laboratory at the National Aeronautics and Space Administration, all Me TCE disappeared upon passage over heated alkaline adsorbent, with at least 75% conversion to DCA (Rippstein, 1980~. The SMAC limits developed here are only applicable to a spacecraft environment in which an alkaline air scrubber is not present.
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are oxidation to TCA and excretion of unchanged trichIoroethano} in the urine. The proportion of urinary metabolites excreted as TCA was predicted to increase in a chronic exposure.
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In one TCE exposure accident, two workmen rapidly lost consciousness upon re-entry into an atmosphere containing TCE at an estimated 3000 ppm after an earlier, less severe exposure (Longley and [ones, 1963~. In a controlled laboratory study with a human volunteer, a 2.75-h exposure to TCE at 100 ppm did not cause any significant effects on psychomotor performance (Stopps and McLaughlin, 19671.
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Whether spaceflight-associated conditions, such as gravitational stress, thermal load, electrolyte changes, fluid shifts, or catecholamine alterations, caused those cardiac rhythm irregularities is unknown at this time (NASA, 1991~. Short-Telm and Subchronic Exposures Repeated exposures for 7 hid for 5 consecutive days to TCE at 200 ppm did not adversely affect performance or neurological or biochemical tests in human volunteers, but they elicited a consistent subjective response of a sensation of mild fatigue and sleepiness during the fourth and fifth days (Stewart et al., 1970~.
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In one investigation, the TCE exposures were confounded by the presence of other chemicals, and the magnitude of worker complaints did not compare well with the exposure concentrations (Bloom et al., 1974~. Three workers reported occasional lightheadedness and headache in a degreasing operation, which had a TWA TCE concentration at 47 ppm, with I-h maximum exposures up to 94 ppm (Hervin et al., 1974~.
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Exposure of these species for 7 in/d, 5 d/w, for 161 to 175 ~ at 400 ppm caused increased liver and kidney weights in rats, increased liver weights in male and female guinea pigs, depressed growth in male guinea pigs, and a slight increase in liver weights of rabbits, but no adverse effects in monkeys (Adams et al., 195 1~. Carcinogenicity The results of most of the carcinogenicity studies with animals show that TCE is a potential carcinogen.
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Many of the studies did not report purity of test material; hence, it is possible that mutagenic epoxide stabilizers caused false positives (Brown et al., 1990~. Reproductive and Developmental Effects TCE was found not to be a developmental toxicant in mice or rats exposed to TCE by inhalation at 300 ppm (Schwetz et al., 1975~.
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(Muller et al., 1975~. In Wistar rats, pre-exposure with ethanol or phenobarbital can enhance hepatic damage induced by exposure to TCE vapor (Okino et al., 1991~.
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301 Pa Cal C)
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303 oo oo _ _- ~a, cry <:~N (~\ Ce Cd Cd ~O ~ Cd ~C,)
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TABLE Il-3 Spacecraft Maximum Allowable Concentrations Exposure Concentration, Concentration, Duration ppm mg/m3 1 h 50 270 60 50 20 10 Target Toxicity Cardiac arrhythmias, CNS effects CNS effects Liver and kidney effects Liver and kidney effects Liver and kidney effects, cancer 24 h 11 7 d 30 d 180 d 9 4 2 RATIONALE FOR ACCEPTABLE CONCENTRATIONS CNS Effects Five available human inhalation studies could potentially provide data pertinent to setting short-term SMACs for ICE. Each of the human inhalation studies was reviewed for a number of quality factors as follows: purity of test material, method of exposure-concentration measurement, appropriateness of toxic end point, number of subjects, and statistical methods.
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were reported at concentrations below 1000 ppm; however, one subject with a preexisting visual perception deficit was found to be more susceptible to TCE as measured in a Howard-Dolman depth perception test. Because 1000 ppm caused significant effects in visual perception, steadiness, and coordination, 300 ppm was concluded to be a no-observed-adverse-effect level (NOAEL)
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Questionable statistical analysis of the data, inaccurate TCE vapor exposure, or poor experimental execution was suggested as responsible for the positive effects in the original study (Stewart et al., 1974~. Other investigators have also been unable to confirm decremental performance effects at 100 to 300 ppm (Annau, 1981~.
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because the extended length of exposure is not a major factor in the cardiac sensitizing potential of ICE. Hepat ot oxi city and Nephrot om city Setting longer-term SMACs is complicated by the fact that the only long-term continuous inhalation exposure study is of limited quality.
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Unfortunately, the magnitude of the TCE exposures could be estimated only in relative terms (Stewart et al., 1991~. The studies with positive results are of limited value because of poorly characterized exposure history or small sample sizes.
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, the adjustment factor was calculated to be 26,082 for a near instantaneous exposure concentration that would yield the same excess tumor risk as a continuous lifetime exposure. The 24-h TCE exposure concentration that would yield an excess tumor risk of 10-4 was equal to the follow~ng: I.9 x 10~4 ppm x 26082 x 10~4 .
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might be more appropriate than a linear extrapolation to low doses to set exposure limits (Steinberg and DeSesso, 19931. Summary The I-h SMAC of 50 ppm was based on cardiac sensitization in dogs and the occurrence of arrhythmias in some crew members during missions.
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In Documentation of the Threshold Limit Values and Biological Exposure Indices, 5th Ed. American Conference of Governmental Industrial Hygienists, Cincinnati, Ohio.
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1987. Addendum to the Health Assessment Document for Trichioroethylene: Update Carcinogenicity Assessment for Trichioroethylene.
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1990. Physiologically based pharmacokinetic modeling of the lactating rat and nursing pup: A multiroute exposure mode} for trichIoroethylene and its metabolite, trichIoroacetic acid.
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1989. Relationship between vapor exposure and urinary metabolite excretion among workers exposed to trichIoroethylene.
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1992. Guidelines for Developing Spacecraft Maximum Allowable Concentrations for Space Station Contaminants.
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1973. Epinephrine-induced cardiac arrhythmia potential of some common industrial solvents.
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1981. Halogenated aliphatic hydrocarbons containing chlorine, bromine and iodine.
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320 SMACS FOR SELECTED AIRBORNE CONTAMINANTS Section 1910.1000. Washington, D.C.
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