Methods for Developing Spacecraft Water Exposure Guidelines (2000) / Chapter Skim
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Executive Summary
Executive Summary
Pages 1-8
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To prevent adverse health effects and degradation of work performance, it will be necessary to minimize space crews' exposures to those contam~nants. NASA has established exposure guidelines for airborne contam~nants, called spacecraft maximum allowable concentrations (SMACs)
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The NRC assigned this task to the Committee on Toxicology. The Subcommittee on Spacecraft Water Exposure Guidelines, a multidisciplinary group of experts, was convened to develop the guidelines presented in this report for calculating exposure levels that will prevent adverse health effects and degradation in crew performance.
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The air and water systems of the International Space Station constitute a single life support system, and the use of condensate from inside the cabin as a source of drinking water could introduce unwanted substances into the water system. RANKING CONTAMINANTS FOR RISK ASSESSMENT IdeaDy, SWEGs should be established for all chemical substances that might be found in spacecraft water.
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All observed toxic effects should be considered, including mortality, morbidity, functional impairment, neurotoxicity, immunotoxicity, reproductive toxicity, genotoxicity, and carcinogenicity. Data from oral exposure studies should be used, particularly drinking water and feed studies, in which the duration of exposure approximates anticipated human exposure times.
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An alternative to the traditional carcinogenic and noncarcinogenic risk assessment methods is the benchmark-dose (BMD) approach.
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The latter factors are used to account for uncertainties associated with m~crogravity, radiation, and stress. Some of the ways astronauts can be physically, physiologically, and psychologically compromised include decreased muscle mass, decreased bone mass, decreased red blood cell mass, depressed immune systems, altered nutritional requirements, behavioral changes, shift of body fluids, altered blood flow, altered hormonal status, altered enzyme concentrations, increased sensitization to cardiac arrhythmia, and altered drug metabolism.
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Those guidance levels should be reviewed before SWEGs are established. The purpose of this comparison would not be simply to mimic the regulatory guidelines set elsewhere, but to determine how and why other exposure guidelines might differ from those of NASA and to assess whether those differences are reasonable in light of NASA's special needs.
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That chapter also discusses ways to account for uncertainties associated with spaceflight, such as microgravity. Because it is not possible to conduct risk assessments on all the potential water contaminants, the subcommittee also considered prioritizing the contaminants for risk assessment.
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