Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants Volume 3 (1996) / Chapter Skim
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B5: Dichloroacetylene
B5: Dichloroacetylene
Pages 117-134
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solvents Spontaneously combustible OCCURRENCE AND USE c DCA is the major product formed from trichIoroethylene (TCE) in carbon dioxide scrubbers containing alkaline materials (Saunders, 1967~.
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In a National Aeronautics and Space Administration (NASA) Toxicology Laboratory experiment, all the TCE disappeared when passed over heated alkaline adsorbent, with at least 75 % conversion to DCA (Rippstein, 1980~.
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Predominant symptoms reported include headache, nausea, and vomiting, which are followed, some hours later, by numbness in the perioral region, anesthesia throughout the facial skin and mucosa, and analgesia or reduced sensitivity over the entire distribution of the trigeminal nerve, with loss of the corneal reflex (Carder, 1944; Humphrey and McClelland, 1944; Reichert et al., 1976~. In addition, labial sores, visual disturbances, and impaired taste and smell sensations frequently occur (Carder, 1944; Humphrey and McClelland, 1944; Reichert et al., 1976~.
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Histological changes in the brains of New Zealand albino rabbits after a 1-h exposure to DCA at 126, 202, or 307 ppm were evident in the sensory cortical regions and were concentration-related (Reichert et al., 1976~. The most severe injury was to the sensory trigeminal nucleus, followed in decreasing intensity by the facial and oculomotor nerves and the motor trigeminal nucleus.
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et al., 1971~. In addition, some animals exposed continuously developed weakness in the hind legs and had difficulty walking, indicating neurological effects.
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Malignant {ymphomas were much more common in male and female controls for group i, with incidences of 14/30 and 17/30, respectively, versus incidences of 1/30 and 2/30 in exposed male and female mice, respectively. Harderian gland tumors, commonly seen in this strain of mice, were increased in DCA-exposed mice, but this gland is not present in human beings.
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Biological Interactions Lethality data suggest possible biological interactions between DCA and TCE or ether, but the data are sparse (Siege!
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124 4 ._ Cat ._ o pa C)
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126 .§ In Cat sit V, C)
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TABLE 5-3 Spacecraft Maximum Allowable Concentrations Exposure Concentration, Concentration, Duration ppm mg/m3 Target Toxicity 1 h 0.6 2.4 Neurotoxicity, kidney, and liver 24 h 0.04 0.16 Neurotoxicity, kidney, and liver 7 d 0.03 0.12 Neurotoxicity and kidney 30 d 0.025 0.1 Neurotoxicity and kidney 180 d 0.015 0.06 Neurotoxicity and kidney RATIONALE FOR ACCEPTABLE CONCENTRATIONS Based on accidental exposures of human beings to DCA during trichioroethylene anesthesia and during closed environmental testing, it is apparent that the principal target organ of DCA is the nervous system for exposures of a few days or less. The human data cannot be used to set safe exposure concentrations because the DCA concentrations were never reported in descriptions of the accidents.
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exposures in rats. Exposure concentrations causing mild-to-moderate effects, as evident by serum urea nitrogen increases and histopathological changes, were reduced by a factor of 10 to reach a no-observed-adverse-effect level (NOAEL)
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The resulting values were not used because the estimated concentrations to protect against lethality were far below concentrations estimated to protect against neurotoxicity, the major effect seen in human beings. Estimates for the 7-d, 30-d, and iS0-d ACs
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Analysis of acute lethality data in mice led to values that were inconsistent with sublethal effects, so the lethality results were not used. Data on carcinogenic potential were not used because there was not an appropriate way to apply the linearized multistage mode!
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132 IS .S t In V' A: .° Cd= m o Cd 'C;, oo 1 ° _ o no 1 to.
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In Documentation of the Threshold Limit Values and Biological Exposure Indices, 6th Ed. American Conference of Governmental Industrial Hygienists, Cincinnati, Ohio.
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1981. Halogenated aliphatic hydrocarbons containing chlorine, bromine and iodine.
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