Factors Influencing the Accumulation of 131I in Colorado Deer Thyroids Following 1961–1962 Nuclear Weapons Tests

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Abstract
Radioiodine concentrations were measured in the thyroids of north-central Colorado mule deer which were collected singly each week and in larger numbers during the hunting seasons from October 1961 through May 1963. The trends in thyroid radioiodine concentrations were reflective of atmospheric nuclear tests and levels of environmental fallout contamination throughout the study. Variation in thyroid activity between individuals was studied by analysis of thyroids from numerous deer taken on selected days during hunting seasons. The frequency distribution of radioiodine levels was skewed with the greater proportion of the values falling below the mean. An analysis of variance indicated that age had a significant effect upon radioiodine accumulation, with the higher burdens occurring in the younger age groups, but that there was no significant difference between sexes. The analysis also indicated no significant interaction between sex and age. Fetal thyroids contained radioiodine in levels which increased exponentially with age. Near-term fetuses had thyroid radioiodine concentrations up to ten times greater than those of their dams. No activity was found in the thyroids of fetuses in the embryonic stage.