118 RADIATION STANDARDS, INCLUDING FALLOUT BIBLIOGRAPHY 1. L. Van Middlesworth, Nucleonics 12, No. 9, 56 (1954). 2. Gunther, R. L., and Jones, H.B.: Confirmation of radioactivity in Thyrvids of Various Animals, July 15 to Sept. 10, 1954. University of California Radiation Laboratory Report (UCRIL 2689) Berkeley, 1954. 3. White, M. R., and Dobson, E. L.: California Cattle Thyroid Activity Associated With Fallout: 1955. University of California Radiation Laboratory Report (UCRL 3355) Berkeley, 1956. 4. Comar, C. L, et al: Thyroid Radioactivity After Nuclear Weapons Tests. Science 126: 16-18, July 5, 1957. 5. Wolff, A. H.: Radioactivity in Animal Thyroid Glands. Public Health Rept. G2; 1121-1126. December 1957. 6. Ibid. 7. L. Van Middlesworth: Radioactivity in Thyroid Glands Following Nuclear WeaponsTest, Science, vol. 123, pp. 982-983, June 1, 1956. 8. Campbell, J. E., et al.: The Occurrence of Strontium 90, Iodine 131 and Other Radionuclides in Milk, May 1957 through April 1958, American Journal of Public Health, vol. 49, No. 2, pp. 225-235, February 1959. 9. Beierwaltes, W. H., et al., J.A.M.A. 173; 1895-1902 (1960). 10. Eisenbud, M., et al., Science, vol. 136, pp. 370-374, May 4, 1962. 11. Radiological Health Data, vol. III, Nos. 1, 2,3, 4,5, and 6. 12, U.S. Summary—General Population Characteristics, U.S. Census Populalation, 1960, T.C. (1), 1B, U.S. Department of Commerce. THE INTAKE OF STRONTIUM 90 AND CERTAIN OTHER RADIONUCLIDES BY THE U.S. POPULATION INTRODUCTION The Public Health Service has in recent years been developing surveillance systems with the objective of measuring and evaluating the levels of radioactivity in the environment. This program is described in other material submitted for the record. Among the radionuclides of health significance which have been determined in this surveillance effort is strontium 90. Milk has been used as the principal index to strontium 90 intake. Before summarizing the results of the program for monitoring of strontium 90, it is important to consider the rela- tive contributions of different sources of intake to total human intake of this radionuclide in order to evaluate the use of milk as an indicator. SOURCES OF INTAKE OF STRONTIUM 0 In the situation of general environmental contamination strontium 90 may enter the human body from all three of the environmental media: air, water, and food. Various studies have provided estimates of the relative contributions of these three media, and within the category of food the relative contribution of various food items. The results of one such study by Straub, Murthy, and Campbell are summarized in table IIT. The estimate for air is based upon analysis of composite Cincinnati air samples from February to June 1959. Similarly, the contribution of water is based upon an analysis of strontium 90 content of drinking water in Cincinnati during this period. The contribution from various Kinds of foods is based upon composite analysis of typical diets and data on food samples purchased in the Cincinnati area, These data indicate that milk and dairy products consumed at the rate of approximately 550 grams per day would contribute about 50 percent of the total daily intake of strontium 90. These data agree in general with results of similar studies in other countries in which milk and dairy products represcut an important element in the diet. MILK AS AN INDICATOR OF STRONTIUM9) The data on contributions of various sources of intake of strontium 90 sug- gest that milk can serve as a useful indicator of the levels of total daily intake of strontium 90. (1) There are several advantages of milk as such an indicator: The biochemistry of milk production is such that it serves as a biological sampling and concentration mechanism, drawing its raw materials from the environment serving as sources for air, water, and food for the cow. Thus, SURATARE.SERRASABRESEEC gidgeshrine