body burden means for adults on Utirik and the observed K, rate constant from Rongelap. It was observed on Rongelap that .031% of 6520 was removed from the diet pathway each day in addition to radioactive decay. Additionally, reduction . . . . 137 90 60 in dietary radioactivity on Rongelap had been observed for Cs, Sr, and Co to be greater than that predicted by radioactive decay alone. Instantaneous re- duction fractions very similar to those at Rongelap were observed at Utirik for 90 the Sr, and 137 . Cs nuclides. The lower curve on Figure 16 reflects the dose equivalent, dose equivalent rate, and body burden which would have occurred had . . radioactive decay alone accounted for the removal of ronment. 6 . . en from the Utirik envi- Since additional mechanisms could be measured for other nuclides at Utirik and for the °° Zn nuclide on a nearby atoll, the upper curve was chosen as the most likely body burden history for adults post return to Utirik Atoll. Figure 17 indicates the Utirik adult mean total body dose equivalent rate for each nuclide. An obvious difference relative to the Rongelap history exists; 6525 not 1376, was the major nuclide contributing to the dose equivalent rate. This was due to the Utirik population returning 3 to 4 months after the initial contaminating event, and the Rongelap population returning after 3 years. The age of the fallout had a dramatic influence on the importance of each nuclide contributing to the internal dose equivalent. In fact 60c, and 6575 played major roles during the first 3 years, a time interval that corresponded to the period during which field whole body counting facilities were being developed at Brookhaven National Laboratory and when medical examinations for people on Utirik Atoll were not done. Additionally, pooled and/or in- dividual radiochemical analysis of urine was not performed during this period. The impact of 6500 and 6006 was such that even if the least conservative rate