1 ( \ \ . « ‘ \ Table 1. Dosimetric conclusions for the protracted exposure of Rongelap and Utirik adults from day of return to 50 years. Rongelap Committed Effective Utirik Committed Effective Dose Equivalent, Sv+S.E. Dose Equivalent, SvtS.E. Nuclide Fe-55 4.8xl07) + 2.5x107/ Co-6n zZn-65 Sr-90 Cs-137 External External 3.4x10_, 1.9x10_;, 5.3x10_, 2.2x10_, 1.7x10 + + + + + 3.6x107/ + 2.0x1077 1.3x10_, 1.0x10_7 &.0x10_, 1.1x10_, 3.4x10 4.4x10_, 3.0x10_, 1.9x10_, 1.3x19_, 4.1x1n + + + + + 3.3x10_, 4.4x10_¢ 5-9x10_5, 1.0x10_3 &.2x10 A decline in the daily activity ingestion rate greater than that due solely to radioactive decay was estimated to be 9 % per year for Cs-137, 8% per year for Sr-90, 80% per year for Zn-65 and 60% per year for Co-60. A tentative value of 3% per year for Pu was estimated from sparse data. Current studies are ained at determining more accurately the dosimetric impact of Pu. These values for the % per year decline in activity ingestion rate were observed at both atolls and do not account for the additional decline due to radioactive decay. The accidental acute exposure during March 1 and 2, 1954 was considered separately from the protracted post-return exposure. The thyroid absorbed dose was reevaluated due to the fact that incidence of thyroid nodules, benign and malignant, in the exposed populations of Utirik and Rongelap has indicated critical differences relative to that reported for other radiation exposed groups. Reanalyses of thyroid absorbed dose was based on a conprehensive fallout model in conjunction with dietary and living pattern data at the tine of acute exposure. Four studies were used to generate thyroid absorbed dose estimates, they were: (1) archival soil-sample analysis for 1-129, (2) evaluation of radiochemical analyses data for “Bikini Ash", the BRAVO fallout which fell on a Japanese fishing vessel in the vicinity of RongePap Atoll on March 1, 1954, (3) weather and source-tem data for BRAVO coupled with current fallout transport and deposition models and (4) evaluation of the radioiodine analysis of the single initial pooled urine sample reported for the Rongelap people. Tentative results indicate thyroid doses were underestimated for the Rongelap people by a factor of 2 to 10. Thyroid nodule incidence will be evaluated in terms of new estinates for thyroid absorbed dose for both atoll populations. ACKNOWLEDGEMENTS Research carried out under the auspices of the Contract NO. DE-~ACO2-76CHOOO16. The full text of printed as a Brookhaven National Laboratory report. U.S. Deparment of Energy, this communication will be