Assessment of thyroid doses due to 131I from atmospheric nuclear weapons tests in Nevada

About 100 of the atmospheric nuclear weapons tests carried out at the Nevada Test Site (NTS) resulted in off-site detection of radioactive materials. These tests released about 5 EBq of 131I in the atmosphere, predominantly in 1952, 1953, 1955 and 1957. Radioiodine was deposited across the United States of America, with the highest values immediately downwind of the NTS and the lowest values of the west coast. In the 1980s, three major dose reconstruction studies were undertaken in order to address the assessment of thyroid doses due to 131I fallout from the NTS: (1) the ORERP study of the US Department of Energy; (2) the Utah thyroid cohort study; and (3) the NCI thyroid study. The first two studies are concerned with doses received by 'local' populations (less than 800 km from the NTS), while the third study deals with the estimation of thyroid doses received by populations across the continental USA. In all three studies, uncertainty estimates were attached to the calculated doses. The second and third studies specifically addressed the assessment of thyroid doses from radioiodines, whereas the first study has a much wider scope, in that it considers both external and internal irradiation of the main organs and tissues of the body from all radionuclides produced by nuclear weapons tests. The thyroid doses from NTS fallout resulted essentially from the ingestion of milk contaminated with 131I; other, usually less important, pathways of exposure are the consumption of leafy vegetables and eggs. Because children generally drink more milk than adults, and because of the smaller mass of their thyroid gland, children received higher doses than adults for a given deposition of 131I. The thyroid doses are estimated to have ranged up to a few grays for small children in south-western Utah who drank milk from a family owned goat. A preliminary estimate of the collective thyroid dose to the US population from NTS fallout is 4 x 106 man·Gy, corresponding to a per capita thyroid dose of about 20 mGy. (author). 30 refs, 6 tabs