Acute Effects of Exposure to Ionizing Radiation Dose (rem) Effect 25-50 Blood changes. For example, white blood cells begin to disappear. Temporary sterility in men. 75 Vomiting in 10 percent of those exposed. 200 Depression or ablation of bone marrow. Nausea and vomiting within hours. Epilation (loss of hair) within 2 or 3 weeks. 300 Erythema (reddening of the skin). 450 Lethal dose for 50 percent of those exposed. Death within 30 days. 1000 Loss of intestinal wall. weeks. 2000 Unconscious within minutes, death within a few Death within 1 or 2 hours. ¢ Examples of delayed effects include cataracts, several forms of cancer, and genetic disorders in offspring. Cataracts appear after a latency period of several years and require a threshold dose of at least 200 rem. Genetic effects have been demonstrated only in animal studies; they have not been observed in humans. For example, data collected on more than 30,000 offspring of people irradiated at Hiroshima and Nagasaki did not reveal statistically significant increases in stillbirths, neonatal deaths, birth weight, or congenital malformations (2; 3). According to current medical knowledge, no threshold dose is required for cancer induction. Since cancer occurs naturally in the general population and cannot be distinguished from radiation-induced disease, the problem of risk assessment, especially at low doses, is complex. The only way to determine the magnitude of the cancer risk is to study large groups of exposed personnel and compare their cancer incidence with that of a similar, unexposed group. 179