58 not very reliable. From our surveys of the unex- posed people of Rongelap and Likiep (a nearby atoll not exposed to fallout), the incidence appears to be about 5%, mostly present in older age groups (see Figure 29 and Table 25). We haveseen a few cases of hyperthyroidism and myxedema atthe Majuro Hospital, but no statistics are available. Two cases of thyroid cancer are reported from hospital admissions for a 10-vear period (1952- 1962) for the Marshall Islands, the population varving between 15,000 and 20,000 during that period. This has been estimated by Trust Territory medical personnel to be about half the actual number of cases (therefore 8 cases per 20,000 people per 20 years was used for statistical com- parisons). Data on iodine intake and excretion in the Marshallese (tabulated below and presented in detail in Appendix 9) indicate that iodine-deficlency goiter would not be expected in this population. Sample 28 Urines 19 Urines 7 Diets (1965) (1974)* (1974)* Todine, av. ug/day (range) 105 (19-279) 127 (25-266) 70 (48-152) The urinary iodine excretion is somewhatlower than the U.S. mean of 190 wg/day (18-483) in 1941.94 On the basis of the few diets analyzed, the daily iodine intake seemsto be within the recommended range of 50 to 75 wg.These iodinelevels are somewhatlower than would be expected in an oceanic population 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. The high 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 dueto radioiodine in the fallout. Numerous studies on animals have shownthat thyroid neoplasia follows exposure both to x-irradiation and to radioiodines.9?-9? Such tumors may be benign or malignant and appear to be dose-dependent to some degree. The incidence of thyroid tumorsis increased in Japanese atom bomb survivors!09-103 (Figure 43). Thereis a considerable amount of data showing that children who were given radiation to the head and neckregion for treatment of thymic hyper“The iodine analyses were done by M.T. Kinsley and DF. Leahy at BNL. 1 60 + = 530 => (| Hiroshima Nagasaki = 2g e x T65 dose Figure 43. Prevalence of diseases of the thyroid. fifth ex- amination cycle, by radiation dose and city for females age 0 to 19 at time of bomb. (From Belskyet ai.!°*) trophy, acne, and fungus of the scalp have an tn- creased incidence of both benign and malignant thyroid lesions in later years.!95-112 Reports of tumorigenic effects of radioiodine in man are more limited. Shelineet al.,14 in their follow-up study of 250 patients treated for hyperthyroidism, reported 8 having nodular goiter, of whom 6 had been irradiated at age <20 and 4 at age <10. Morerecently a number of cancersof the thyroid have been reported in patients previously treated with radioiodine for hyperthyroidism. !14-!16 The numberof such cases reported is, however, lower than might be expected on the basis of the widespread use of 1311, perhaps becausethe 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 andthose of small . children (700 to 1400 rads) about 8 timesthat to the whole body. On the basis ofthe incidence of benign nodules in the unexposed Marshall Islands populations examined, about 3 to 4 cases would be expected during the 20 years in the Rongelapexposed group, whereas 24 occurred. In the Utirik group about 6 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 over the 20year period, whereas 3 occurred. In the Utirik population about 0.06 cases would be expected, and 1 occurred; in view of the low dose of radia- tionit is unlikely thatthis 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 thyroid nodularity are scarce, but the incidencein