¥. RADIOIODINE Summary Jodine-131 is the primary radioiodine that is of importance in radioactive fallout. It has an 8-day physical half-life and is a beta and ganme emitter. The thyroid gland is the principal target organ of 13/1, | The metabolism of fodine and effects of 1311, espectfally for high doses, were known in the Jate 1940s as a result of medica! uses of radioiodine. Hy pothyrofdism was the primary radfofodine exposure effect, while thyroid carcinogenesis came to be appreciated as a late effect of thyroid irradiation in the 1950s. Isotopes of fodine were known to be components of radioactive contamination fran atomic weapons and nuclear facilities by 1950, and were reported to be in precipitation in the open literature in 1951 and in animal thyroids in 1956. | From the 1950s into the 180s, radiojodtnes have been the subject of research, not only because of their role as 3a canponent of radioactive fallout, but also because of their position as potential environmental contaminants fron nuclear reactors. Their use in medicine, as diagnostic ani therapeutic tools. has led to an even greater understanding of their biological significance. Environmental Pathways A review of the literature indicates that little information on V3! in the environment existed until the mid-1950s. Nevertheless, in the late 1941s there was concern about the hazard to animals grazing on land that was cont rinated with radioactivity from airborne wastes from the production of nuctear matertals. Out of this concern, experimental plans to eveluate the effects of VST tn sheep were made in 1948 frornberg, 1964), Im afdttion, by 1940