Kendall Peterson of Lawrence Livermore National Laboratory, Dr. Charles Sondhausof the University of California, William Adams, M.D., Dr. John Baum,Victor Bond, M.D., Donald Borg, M.D., Robert Conard, M.D., Eugene Cronkite, M.D., Andrew Hull, Edward Lessard, Charles Meinhold, Robert Miltenberger, Stephen Musolino, and Dr. Jan Naidu,all from Brookhaven National Laboratory, Nathanial Green- range associated with the contents of the stomach in cases of sudden death’ were usedtoesti- mate maximum thyroid-absorbed dose. The average dose was based on the average ly activity in urine collected from people exposed at Rongelap Island. The contribution to thyroid dose from external sources was estimated by us from the air exposure created by 142 nuclides estimated from results of fallout composition. The external dose estimated by us was similar to original estimates by Sondhausfor persons exposed at Rongelap and Utirik Islands. The original external dose estimates at these islands, 1.75 gray and 0.14 gray (175 rad and 4 rad), respectively, were derived from survey instrument readings taken at evacuation and film badge data from a nearby military outpost.” Our external dose value at Sifo Island, 1.1 gray (110 rad), was greater than the 0.69 gray (69 rad) originally estimated by Sondhaus from postevacuation surveys of exposure rate. Thedifference wasdue to the presence of very short-lived activation and transuranic nuclides which, accordingto the nuclide composition, must have been present prior to evacuation of Sifo Island. Medical observations concerning thyroid abnormalities have been tabulated by us along with the new thyroid dose. From theseresults, we estimate the mean cancer risk rate in the exposed population of 251 people to be 150 thyroid cancers per million-person gray years at risk (1.5+2.5 thyroid cancers per million-person rad years at risk). The mean time at risk for thyroid cancer was 19 years. We estimated the mean thyroid nodule risk rate to be 830 nodules per million-person gray yearsat risk (8.30 + 14 per million-person rad years at risk), The mean time at risk for a thyroid nodule was 18 years. The uncertainty derived for the estimate of risk was based on the standard deviation in adult mean urine activity concentration, the standard deviation in thyroid-absorbed dose per unit intake, and the standard deviation in the spontaneous frequency of thyroid nodules or lesions in the unexposed comparison group. house from Lawrence Berkeley Laboratory, Dr. Bruce Wachholz from the National Cancer Institute, Thomas McCraw and Roger Ray from the Departmentof Energy, and Barbara Boccia, M.D., a physician in private practice. References 1. Lessarp, E.T., MILTENBERGER, R.P., MusoLINO, S.V., NAIDU, J.R., AND CONARD, R.A., Thyroid-Absorbed Dose for Rongelap and Utirik Residents. BNL, in press. 2. CRONKITE, E.P., Bonp, V.P., AND DUNHAM, C.L., (Eds.), Some Effects of Ionizing Radia- | tion on Human Beings. United States Atomic Energy Commission Report, Washington, DC, 1956. 3. JAMES, R.A., Estimate of Radiation Dose to Thyroid of Rongelap Children Following the BRAVOEvent, UCRL-12278, 1964. 4. ConarRD, R.A. ET AL., A Twenty- Year Review of Medical Findings in a Marshallese Popula- tion Accidentally Exposed to Radioactive 5. 6. 7. . 8. Acknowledgments 9. The reexamination was accomplished because of the fine efforts of Dr. Fred Brauer of Battelle Pacific Northwest Laboratory, Dr. 26 SOC 7824 Fallout, BNL 50424, 1974. Committee on the Biological Effects of Ionizing Radiation. The Effects on Populations of Exposure to Low Levels of Ionizing Radiation, National Research Council Report, National Academy Press, Washington, DC, 1980. LessARD, E.T. MILTENBERGER, R.P., COHN, S.H., Muso.ino, 8.V., anD CoNaARD, R.A., Protracted exposure to fallout, the Rongelap and Utirik experience, Health Phys. 46, 511-27 (1984), MILTENBERGER, R.P., GREENHOUSE, N.A., AND LESSARD, E.T., Whole body counting results from 1974 to 1979 for Bikini Island Residents, Health Phys. 39 (3), 395-408 (1979). Eve, LS., A review of the physiology of the gastrointestinal tract in relation to radiation doses from radioactive materials, Health Phys. 12, 131-61 (1966). SonpHaus, C.A. AND Bonn, V.P., Physical Factors and Dosimetry in the Marshall Islands Radiation Exposures, Naval Medical Research . Institute Report, Bethesda, MD, WT-939, 1955.