58 not very reliable. From our surveys of the unexposed people of Rongelap and Likiep (a nearby atoll not exposed to fallout), the incidence appears to be about 5%, mostly presentin older age groups (see Figure 29 and Table 25). We haveseen a few cases of hvperthvroidism and myxedema at the a = 50 = » +0 z = 20 1962) for the Marshall Islands, the population 8 parisons). Data on iodine intake and excretion in the Marshallese (tabulated below and presented in detail in Appendix 9) indicate that iodine-deficiency goiter would not be expected in this population. Sample 28 Urines 19 Urines 7 Diets (1965) (1974)" (1974)* lodine, av. ug/day (range) 105 (19-279) 127 (25-266) 70 (48-152) The urinary iodine excretion is somewhat lower than the U.S. mean of 190 ug/day (18-483) in 1941.94 On the basis of the few diets analyzed, the daily iodine intake seems to be within the recom- mended rangeof 50 to 75 yg.95 These iodinelevels are somewhatlower than would be expected in an oceanic popuiation but are much higherthan seen in areas of endemic goiter.96 The Marshallese diet contains no knowgoitrogens, and diffuse goiters (typical of endemic goiter) have not been observed. Thehigh incidence of both benign and malignant thyroid nodules in the exposed Rongelap people appears to be clearly related to radiation exposure with a large component due to radiotodine in thefallout. Numerous studies on animals have shownthat thyroid neoplasia follows exposure both to x-irradiation and to radioiodines.97-99 Such tumors may be benign or malignantand appear to be dose-dependent to some degree. The incidence of thyroid tumorsis increased in Japanese atom bomb survivors!00-103 (Figure 43). There is a considerable amount of data showing that children who were given radiation to the head and neck region for treatment of thymic hyper*The iodine analyses were done by M.T. Kinsley and DF Leahy at BNL. EQ Nagasak: = 30 Majuro Hospital, but no statistics are available. Two cases of thyroid cancer are reported from hospital admissions for a 10-year period (1952varying between 15,000 and 20,000 during that period. This has been estimated by Trust Territory medical personnel to be abouthalf the actual number of cases (therefore 8 cases per 20,000 people per 20 years was used for statistical com- (2 Hiroshima 10 Notincity 0-9 10-99 T65 dose Figure 43. Prevalence of diseases of the thyroid. fifth examination cycle, by radiation dose and city for females age 0 to L9 at time of bomb.(From Belsky et al. 104) trophy, acne, and fungusof the scalp have an in- creased incidence of both benign and malignant thyroid lesions in later years.195-112 Reports of tumorigenic effects of radioiodine in man are more limited. Sheline et al.,!!3 in their follow-up study of 250 patients treated for hyperthyroidism, re- ported 8 having nodular goiter, of whom 6 had been irradiated at age <20 and 4 at age <10. Morerecently a numberof cancers of the thyroid have been reported in patients previously treated with radioiodine for hyperthyroidism. !14-116 The numberof such cases reported is, however, lower than might be expected on the basis of the widespread use of 131], perhaps because the cells are morelikely to undergo lethal damage.!17-122 In the more heavily exposed Rongelap group the adult thyroids received a dose (335 rads) about twice that to the whole body and those of smal! children (700 to 1400 rads) about 8 times that to the whole body. On the basis of the incidence of benign nodules in the unexposed MarshallIslands populations examined, about 3 to 4 cases would be expected during the 20 vears in the Rongelap exposed group, whereas 24 occurred. In the Utirik group about6 would be expected, and 6 occurred. Regarding cancerof the thyroid, on the basis of Marshall Islandsstatistics, about 0.033 cases would be expected in the Rongelap group overthe 20year period, whereas 3 occurred. In the Uurik population about 0.06 cases would be expected, and 1 occurred; in view of the low doseofradia- tion it is unlikely that this case is radiation induced. Tables 33 and 34 show the incidence and the risk per rad in the Marshallese compared with that in other populations for both benign and malignant thyroid neoplasms. Data on benign thv- roid nodularity are scarce, but the incidence in