Thyroid-Absorbed Dose for Rongelap and Utirik Residents Persons who were present on March 1, 1954, at Rongelap Island, Rongelap Atoll, Sifo Island, Ailingnae Atoll, and Utirik Island, Utirik Atoll in the Marshall Islands have been examined by medicalspecialists to determine if any observable effects occurred as a result of exposure to radioactive fallout from the Pacific weapon test known as Operation Castle BRAVO. Medical specialists have reported short-term effects exhibited over a period of many months andpossible long-term effects exhibited over many years. A study was undertaken to reexamine thyroidabsorbed dose estimates for people who were exposed accidentally at Rongelap,Sifo, and Utirik Islands. Four methods were examined: 1) reevaluation of radiochemical analysisto relate results from pooled urineto intake, retention, and excretion functions; 2) analysis of neutron-irradiation studies of archival soil samples to estimate areal activities of the iodine isotopes; 3) analysis of source term, weather data, and meteorology functions predicting atmospheric diffusion and fallout deposition to estimate airborne concentrations of the iodine isotopes; and 4) reevaluation of radioactive fall-out contaminating a Japanese fishing vessel in the vicinity of Rongelap Island on March 1, 1954, to determine fallout components. Details of this research are to be published in a Brookhaven National Laboratory report by Lessard etal.’ The original estimate of external whole-body dose from the acute exposure was1.75 gray (175 rad) at Rongelap and 0.14 gray (14 rad) at Utirik.? Thefirst estimate of thyroid dose from internal emitters in Rongelap people was 100 to 150 rep.” Thusthefirst estimate of total thyroidabsorbed dose was2.68 to 3.15gray (268 to 315 rad) for Rongelap people in general and for internal plus external exposure. In 1964, three teenage girls who were exposed in 1954 underwent surgery for benign thyroid nodules. In 1964, the 3- to 4-year-old child thyroid dose was reexamined by Jameson the basis internal emitters was estimated at 2 to 33 gray (200-3300 rad). The most probable total thyroid dose was in the rangeof 7 to 14 gray (700-1400 rad). The James estimate of most probable total thyroid-absorbed dose to the child was 2 to 5 times higher than the estimate reported by Cronkite for Rongelap people. The value for the James estimate of total thyroid dose was extrapolated to other ages and to the Utirik people and reported along with medical effects by Conard.’ The numberof radiationinduced thyroid lesions per million-person rad years at risk was tabulated by Conard for the Rongelap- and Utirik-exposed populations. It was clear that the risks of radiation-induced benign and cancerous lesions were not comparable between the two atolls for any age grouping. The thyroid cancer risk for the Japanese population exposed at Nagasaki and Hiroshima reported by the National Research Council’s Committee on the Biological Effects of Ionizing Radiation was 1.89 excess cases per millionperson rad yearsof tissue dose. This parameter was 7.0 at Rongelap and 17.8 at Utirik for the 10-year and older age grouping in 1974." Variation in risk of radiation-induced thyroid cancer between atolls and the difference when comparedto otherirradiated groups became an important scientific and health-related question with considerable political overtones. Early in 1977, Bond, Borg, Conard, Cronkite, Greenhouse, Naidu, and Meinhold, all members of Brookhaven National Laboratory, and Sondhaus, University of California, College of Medicine, initiated a reexamination of the technical issues. In 1978, formal program objectives and funding were supplied by the Department of Energy’s Division of Biological and Environmental Research. In June 1978, the Meteorology Division at Lawrence Livermore National Laboratory was subcontracted to provide a computer simulation of the dispersion, transport, and deposition of fallout from the 1954 atmospheric nucleartest, BRAVO. A subcontract to provide neutron activation analysis of archival soil samples was given to the Radiological Sciences Department, Batelle-Pacific Northwest Laboratory. Soil samples were provided by Seymour, the director of 1) urine bioassay results and 2) a range of values for thyroid burden of 1317 thyroid mass, and uptake retention functions for iodine.® In addition two modes of intake were considered, inhalation and ingestion. For 3- to 4-year-old girls the extreme range of thyroid dose from 23 V0 1d26