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The safety of astronauts in habitats beyond Earth has always represented a challenge to the disciplines of environmental health and occupational medicine. The forthcoming long duration missions present new challenges in space environmental health. The space habitat is similar to a small tight building. Both chemical and microbial contaminants have the potential to accumulate in an atmosphere of limited volume and turnover. Microgravity and the absence of convection currents will produce unusual behavior of suspended particles and of fluid and mass transport in the habitat and life systems. The response of astronauts to both toxic chemicals and infective biota may differ from the Earth-based situation. Their physiological status is altered in not totally understood ways in microgravity, and there is the potential of additional stress from solar and cosmic radiation. They will be exposed to a diverse range, concentration and type of potential contaminants.

Human scalp hair is increasingly regarded as a valuable indicator tissue for biological monitoring of environmental exposure to toxic substances. Hair provides both current and past records of exposure during prolonged periods of time. To validate hair monitoring for assessment of toxic substances in space, a unique biological model was developed. Human scalp grafts were transplanted to athymic BALB/c-nu/nu nude mice and then animals were exposed continuously over 2 months, using implanted osmotic pumps, to methylmercury (MeHg), a substance known to be incorporated into hair. Mercury concentrations in hairs were determined using X-ray fluorescence (XRF) spectrometry by segmental analysis of single strands. Blood, skin and brain concentrations of methylmercury were measured by cold vapor analysis. Human scalp hair grown in nude mice showed long-term persistence of human characteristics.