Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants Volume 5 (2008) / Chapter Skim
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9 1,2 - Dichloroethane
9 1,2 - Dichloroethane
Pages 144-161
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From page 144... ...
Committee on Toxicology, and published by the National Academy Press in 1996 in Volume 3, Appendix B6, of Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants (Wong 1996)
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derived ACs for critical effects including CNS effects, GI symptoms, liver toxicity, and impaired immune defenses. He reviewed the data from a Russian paper (Kozik 1957)
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Even though this study is not an acute exposure study, because exposure continued over several months and perhaps years, Wong (1996) concluded that this level of EDC can be used to evaluate CNS effects for all exposure durations.
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in guinea pigs and rats and stated that they had measured several parameters to assess toxicity, the only quantitative data they presented were changes in body weight and tissue weight. In general, the NRC SMAC and spacecraft water exposure guideline committees do not consider body weight changes or organ weight changes to be robust variables for calculating ACs (NRC 1992, 2000)
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The two estimated TWA doses were 47 and 97 mg per kg of body weight for male and female rats, 97 and 195 mg/kg for male mice, and 149 and 299 mg/kg for female mice. Observed tumors included squamous cell carcinomas of the forestomach, hemangiosarcomas of the circulatory system, and fibrosarcomas of the subcutaneous tissue.
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classified EDC as B2, a probable human carcinogen. They extrapolated the gavage data to an inhalation exposure scenario and calculated an inhalation unit risk (unit risk = upper-bound excess lifetime cancer risk estimated to result from continuous exposure to an agent at a concentration of 1 microgram [µg]
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Inhalation unit risk represents the potential excess cancer risk for a person exposed for a lifetime to EDC at 1 µg/m3 and is at most 22 in 1,000,000. The EPA's estimated inhalation carcinogenic risks and associated EDC air concentrations, summarized in IRIS (1991)
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. Abbreviations: ACGIH, American Conference of Governmental Industrial Hygienists; IDLH, immediately dangerous to life and health; NIOSH, National Institute for Occupational Safety and Health; OSHA, Occupational Safety and Health Administration; PEL, permissible exposure limit; ; REL, recommended exposure limit; STEL, short-term exposure limit; TLV, threshold limit value; TWA, time-weighted average.
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Relevant Data Since 1996 NASA reviewed the literature to find a long-term EDC inhalation exposure study to use for deriving a 1,000-d AC (and a SMAC) for both a noncarcinogenic toxicity end point and, if applicable, a carcinogenic risk factor for 1 in 10,000.
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The 1,000-d AC for GI disturbances and neurotoxicity can be calculated based on a LOAEL of 15 ppm as follows. AC is derived for a prolonged continuous duration of 1,000 d, and for GI effects and neurological effects the concentration was adjusted for discontinuous-to-continuous exposures.
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, the NRC Committee on Spacecraft Exposure Guidelines recommends modifying the previous approach so that when data are extrapolated from a chronic-duration animal study (especially a 2-y study) to 1,000 d for human exposure an additional time factor of 728 d (2 y)
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Although no adverse effects were found in rats exposed to 200 ppm for 30 wk, mild hepatotoxic effects were noted in the guinea pigs (such as parenchymatous degeneration with some vacuolization)
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Differences in the internal dose and pharmacokinetics between these two routes of exposure, the confounding factor of pharmacokinetic changes due to the use of corn oil for the gavage, the metabolic saturation behavior and potential consequences, and the levels of DNA alkylations, DNA damage, and in vitro and in vivo genotoxicity are the factors NASA considered in its decision. Supporting evidence includes pharmacokinetic data and comparative toxicity studies of bolus dosing of solvents in corn oil versus administration in drinking water (more similar to dosing associated with inhalation)
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Whether the positive results for tumor incidence in the NTP oral ingestion study might be due to the vehicle used for administration has been questioned. NASA reviewed studies in which a few volatile organics were administered by gavage in corn oil that resulted in a large amount in the system in a short period of time, and in drinking water, which delivered the chemical in small doses over an extended time.
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(2004) reported that two other haloalkanes, bromodichloromethane and tribromomethane, which produced neoplasia in the large intestine when given as a corn oil gavage, failed to elicit such effects in male rats when given via drinking water for 26 wk.
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1988. Physiological model for tissue glutathione depletion and increased resynthesis after ethylene dichloride exposure.
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Cold Spring Harbor, NY: Cold Spring Harbor Laboratory Press.
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Pp.135-170 in Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants, Vol.
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