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Water must be recycled in long duration manned space missions (Silverstein et al., 1992). The research of the Center for Space Environmental Health (CSE!-I) is focused on two health aspects of water recycling. First, water-borne contaminants in a closed loop system must be identified and exposure to these contaminants quantified for a risk-based evaluation of the impact of water recycling on crew health, both acute and long-term effects. Second, special attention must be given to water contaminants which are characteristic of the recycle system itself, that is, contaminants generated in water storage, water distribution, and long-term wear on recycle system elements.

Inhalation risks on long-duration manned spaced flight include gasses chronically released by outgassing of materials, gasses released during spills, thermodegradation events (including fires) with their attendant particulates, and fire extinguishment. As an example, an event in which electronic insulation consisting of polytetrafluoroethylene undergoes thermodegradation on the Space Station Freedom was modeled experimentally and theoretically from the initial chemistry and convective transport through pulmonary deposition in humans. The low-gravity environment was found to impact various stages of event simulation. Critical unknowns were identified, and these include the extent of production of ultrafine particles and polymeric products at the source in low gravity, the transport of ultrafine particles in the spacecraft air quality control system, and the biological response of the lung, including alveolar macrophages, to this inhalation risk in low gravity.

This paper reviews the issues that must be addressed to define and integrate technologies, countermeasures, and medical care systems into space systems which will be developed for long duration space flight. This paper considers combined and cumulative effects, the broad range of space environmental health issues, including some examples, and a discussion of a management approach to these risks. While the primary emphasis is on space environmental health issues, other aspects of the space environment are also considered. Allocation of finite resources for optimal risk management is also considered.

Recent trends toward prolonged space flights have highlighted concern over potential health hazards for crews occupying a confined habitat for an extended duration mission. Previous spaceflight and remote habitat experiences have identified a large number of compounds that pose potential hazards as space habitat contaminants. A project is underway to prioritize these compounds according to: 1) the degree of potential exposure, 2) known or potential health risks, 3) process- and mission-specific determination of sources of contamination, and 4) preliminary evaluation of mission performance degradations associated with compound containment or substitution. An effort is underway to establish a comprehensive database making use of all available national and international data in order to provide a basis from which to evaluate both the impact and the likelihood of long term or transient exposure to these agents. The database will define projected capabilities of Space Station Freedom from early assembly phase through man-tended and permanently-manned capability, previous knowledge of the lunar base environment, and the limited data available from the Viking mission for the Mars environment. This information will then form the basis for mitigation measures including: 1) future process modification or substitution, 2) special provisions for compound containment or use restrictions, 3) re-evaluation of current exposure standards, and 4) reprioritization of information needs (e.g., toxicology, effects on human performance, or re-evaluation of alternative-process mission requirements).