10. Fallout in Utah In May 1953, Washington County, Utah, was thought to have received an unusual amount of radioactive fallout from a nuclear test at the Nevada test site. The exact dosage of iodine-131 from this fallout is not known but estimates for the dose from iodine-131 to the thyroid gland range from less than 10 rad to above 400 rad. Examination conducted in 1965 of school children in Washington County, Utah, revealed several thyroid ab‘normalities but nothing which can be specifically ascribed to radiation as an etiological agent. Because of the fact that Washington County residents seem, historically, to have had a relatively high prevdlence of thyroid disease and because children in Utah outside Washington County and in Northern Arizona at the time of fallout showed the same frequency of the more severe thyroid abnormalities as did the children who were in residence within the County, it is not possible, from this particular study, to ascribe any degree of significance to radiation exposure. If indeed the exposures to iodine-131 from fallout through the past several years were of significance throughout the State of Utah rather than confined to Washington County, the question of residence in Washington County, in May 1953, may be of little or no importance. ANIMAL DATA Data from animal experiments indicate that thyroid tumors originate spontaneously less frequently and may be less easily induced by radiation than tumors of some other organs. Thus leukemia is frequent in numerous strains of mice, breast tumors common in rats, squamous cell carcinoma in white-faced cattle and mast cell tumor in dogs, whereas thyroid tumors were infrequent in all except in regions where goiter is endemic. The two general types of thyroid tumors are: (1) rounded, circumscribed, benign nodules: adenomas; and (2) invasive, destructive growths: carcinomas., Adenomas do not necessarily develop into cancers but may precede them. Ionizing radiation, as well as a number of chemical agents, may induce either. Most animal experiments with radiation have been done when the ani- mals were young, though not in infancy. However, a limited number of sheep at Battelle-Northwest (formerly Hanford Laboratories) have been continuously exposed to various levels of iodine-131 from conception to death (up to 10 to 12 years of age). These animals have shown no thyroid tumors at dose levels giving 150 rads per year, but have shown adenomas after several years, with accumulated thyroid doses of 5000 to 40,000 rads. Two cancers involving the thyroid gland were seen at cumulative doses of 10,000 and 30,000 rads. Thyroid exposures of 30,000 to 40,000 rads as a result of single doses of iodine-131 to young adult sheep also resulted in many adenomas after 4 to 5 years. When rats were subjected to radiation combined with substances producing goiter (which act by reducing thyroid hormonal production and stimulating the pituitary), a few thyroid cancers were produced by 1100 rads of X-ray. About 15,000 rads were required to produce a comparable tumor incidence when iodine-131 was used as the source of radiation. DOE ARCHIVES Wt