Radiation Exposure and Thyroid Disease in Kazakhstan

The proposed work will improve our understanding of historical, fallout-related radiation doses received by residents of villages in Kazakhstan immediately downwind from the Semipalatinsk Nuclear Test Site (SNTS), where multiple nuclear test explosions were carried out between 1949 and 1962. In collaboration with scientists at the Institute for Biophysics in Moscow, NCI has developed a combined bi-national dose reconstruction methodology based on lessons learned from studying radioactive fallout from tests at the SNTS in Kazakhstan, the Nevada Test Site in the United States, and other test sites. Gamma rays from radionuclides such as cesium 137 in fallout are highly penetrating and can affect all organs even when the radioactive source is outside the body, whereas less-penetrating beta particles from iodine 131, also plentiful in fallout, mainly affect the thyroid gland when ingested in milk from dairy animals grazing on contaminated pasture. We are particularly interested in both kinds of radiation doses to children, because their thyroid glands are small and very active, tend to concentrate ingested iodine, and are highly sensitive to radiation carcinogenesis. The conditions of fallout exposure in Kazakhstan are directly relevant to those following a hypothetical nuclear accident or radiation terrorism incident involving high levels of local fallout. We propose a field study in Kazakhstan to investigate aspects of typical daily village life in areas affected by fallout that might influence individual radiation doses to the thyroid gland. Using focus group interviews, we will collect retrospective information about factors influencing radiation dose to the thyroid gland in children of two distinct ethnic groups (Kazakh and European). These factors include milk and milk product consumption, dependence on different species of dairy animals known to differ with respect to concentration of iodine in milk, seasonal practices of pasturing and supplemental feeding of dairy animals at the time of the nuclear tests, time children typically spent outdoors, and radiation shielding provided by dwellings and other buildings. We will also ask about protective measures taken at the time, such as details of temporary evacuations of villages predicted to be in the fallout paths from particular tests. These data will fill key gaps in the current dose-reconstruction methodology and should result in improved dose estimates, as well as a basis for evaluating and quantifying dosimetric uncertainty and related biases in risk estimates.