radiological half-life of 1357Cs and where the initial intake is the same regardless of age, the integral 30-, 50-, and 70-y dose equivalents are slightly greater when intake begins as an adult than for intake beginning at any other age. This results from the combination of changing body weights, fractional deposits, and biological 30-, 50-, and 70-y dose equivalents are less when concentration of 137Cs in food with time. For example, when intake begins as an infant, the 137Cs_ concentration in food has declined by about 35% by the time the infant reaches 18 y of age, whenthe dietary intake is greater and the longer. for infants and children because !37Cs accounts for about 97% of the total estimated effective dose equivalent at the atolls via the ingestion pathway and 90Sr for less than 3%. Doses from 137Cs and %Srare insignificant through the inhalation pathway as compared Consequently, if the intake of 137Cs for an infant to that via ingestion (Robison et al., 1987; ICRP, or child were equal to that for the adult (which it is not based on available dietary information from the Marshall Islands), the estimated integral 30-, 50-, and 70-y dose equivalent would Consequently, the relative magnitude of the integral dose equivalent among infants, intake begins as an infant or child than when intake begins as an adult. . Even if the ?9Sr intake for infants and children were significantly higher than what we have estimated, the total integral 30-, 50-, and 70-y effective dose equivalent from both 137Cs and %Sr would be greater for adults than half-life for 137Cs_ with age and the reduced biological half-life of 137Cs 1979; Cristy et al., 1984; Kendall, 1986). children, and adults can be determined by still be similar to that estimated for adults. evaluating the ingestion pathway; that analysis indicates that the estimated effective In the case of 90S,, the dose commitment per integral dose equivalents for adults due to unit intake is greater by about a factor of 5 for intake beginning at ages 0 to 5 y than for intake beginning as an adult. However, when agedependent differences in intake of 90Sr via the ingestion of 137Cs and 99Sr is a conservative estimate for intake beginning in infancy and childhood. diet are accounted for, the estimated integral References Aarkrog, A. (1963), "Caesium-37 from Fall-out in Human Milk," Nature 197, 667-668. Abraham, S., M.D. Carroll, C.L. Johnson, and C.M. Villa Dresser (1979), Caloric and Selected Nutrient Values for Persons 1-74 years of Age: First Health and Nutrition Examination Survey, United States 1971-1974, U.S. Department of Health, Education and Welfare, DHEW Publication No. (DHS) 79-1657, Series 11, No. 209. Adams,N. (1981), "Dependence on Ageat Intake of Committed Dose Equivalents from Radionuclides,” Phys. Med. Biol. 26, 1019-1034. Bengtsson, L.G., Y. Naversten, and K.G. Svensson (1964), "Maternal and Infantile Metabolism of Caesium," Assessment of Radioactivity in Man, Vol. II, International Atomic Energy Agency, Vienna, Austria, pp. 21-32. IO0EZbO 22