Radioiodine in Colorado Deer and Elk Thyroids during 1964-65

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Abstract
This paper reports and discusses the levels of radioactive iodine-131 in thyroids of Rocky Mountain mule deer (Odocoileus hemionus) and elk (Cervus canadensis) in Colorado following an underground explosion at the Nevada test site, and the Chinese tests in 1964 and 1965. Seventy-nine deer thyroids and 11 elk thyroids were obtained from animals collected throughout the 2-year period and quantitatively assayed for I131 . Four significant responses in the I131 concentrations were measured, with 3 of the peaks being attributed to the 2 Chinese tests and an underground test at the Nevada test site which reportedly vented. The other response could not be traced to any announced release of radioactivity. Radioiodine levels subsequent to each peak declined with half-times ranging from 8 to 11 days. Integrated thyroid doses calculated for each response ranged from approximately 12 to 254 mrads, which appears far below a dose required to produce thyroid adenomas. The data readily demonstrate the high sensitivity of deer and elk thyroids for environmental monitoring of I 131.