APPENDIX B RADIATION HEALTH EFFECTS IN THE SPACE ENVIRONMENT Radiation doses and dose rates which may be encountered in space present potential health risks to space workers. This section discusses the biological and health effects of the different radiations encountered in the space environment and is based upon data currently available from human epidemiological surveys, laboratory animal studies, and space experimentation. The effects on health are considered in two general categories: early or acute effects, and late or delayed effects. Early effects are those occurring within hours, days, or a few weeks following high-dose, whole-body exposure. Late or delayed effects usually occur months to years following exposure and include cancer-induction, developmental abnormalities in the newborn, genetically related ill-health, lens cataracts, shortened lifespan, and impairment of fertility. The special problems of HZE-particle induced health effects are also discussed. EARLY EFFECTS Early radiation health effects assume clinical significance only with whole-body dose equivalent greater than 150 rem received in relatively short time periods (minutes to hours). Such exposure levels are likely to be encountered only during major solar particle events or during nuclear detonations in space. Radiation is similar to other potentially hazardous physical or chemical agents in that high doses can produce tissue and organ injury, illness, and possibly death. The principle site of biological action of ionizing radiation is the proliterating cells of the renewal system of the organism, such as the bone marrow and intestinal epithelium and spermatogonia. Within these cell renewal populations, the most sensitive cell is the progenitor or stem cell. When the supply of functional cells is temporarily disrupted, the result is impaired function of that tissue or organ and potentially serious injury to the individual. If the therapeutic measures are inadequate or regeneration of the depleted cell population does not occur soon enough, the individual may die. Damage to bone marrow and the intestine may cause death within 7 to 60 days after acute exposure to whole-body dose of radiation greater than a few hundred rad of low-LET radiation. Cellular depletion in tissues and organs that contain large numbers of dividing cells, e.g., in the bone marrow, lymphopoietic tissues, and testis, can be detected at doses as low as 50 rad delivered in short time periods, and are readily evident at doses of 100 to 150 rad. Death does not occur at these dose levels, although severe cellular depletion can be observed in some non-vital renewing organs, such as the testis. Whole-body radiation doses in the 200- to 400-rad
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