Appendix I INCIDENCE OF THYROID DISEASE IN THE COMPARISON POPULATIONS In Section IX.A the importance of obtaining an "unexposed" comparison population for evaluation of thyroid findings in the exposed Rongelap and Utirik people was discussed. The purpose of this appendix is to examine the usefulness of the comparison populations used in these studies with regard to possible thyroid effects from residual radiation exposure during their habitation on Rongelap and Utirik Atolls. The expected occurrence of radiationinduced thyroid nodularities and cancer in this population will be calculated by using available risk data on thyroid findings in the exposed Rongelap people and in persons receiving thyroid irradiation from x~ray treatment. The observed thyroid findings in the comparison population will be compared with findings from U.S. A. statistics. Thyroid Findings in Comparison Populations Table 1 lists the percents of positive thyroid findings in exposed and comparison populations, and Table 2 the individual cases within the comparison populations with length of stay on the home island. These latter data are incomplete and uncertain in many cases, but tend to show that an average esti- mated stay of one-half time (10 to 12 yrs) on their island is not unreasonable. Some people with thyroid nodules have never lived on their home island since 1954, + B. Expected Cases of Thyroid Nodules in Comparison Populations Based on Estimated Radiation Exposure Levels In Appendix II data are presented indicating that if people lived continuously to 1979 on Rongelap since their return in 1957, and on Utirik since July 1954, they might have received an average thyroid dose of about 4.5 rem on Rongelap and 16 rem on Utirik.* However, a more realistic dose is thought to be roughly half of these values (2.25 rem for Rongelap and 8 rem for Utirik), mainly because of absences from the home island on visits to other atolls. On the average the children probably received about half the adult thyroid exposure because their lower ages result in shorter residence time. In the case of the Utirik people, food subsidization during the first few years, when 6527n was by far the greatest contributor to the internal dose, reduced the dependence on fish, which was the major source of that radionuclide. Also, many of the unexposed Utirik people probably did not return until later, when the °°zn contribution was less. Since risk data for radiation effects to be used below are necessarily derived from acute exposures, the contributions *Since radioiodines had virtually decayed by the time the people moved back to Rongelap and Utirik, this exposure was due almost entirely to other radionuclides. - 104 -