Thyroid doses of the population after the Chernobyl accident

Abstract

The accident at the Chernobyl nuclear power plant (NPP) in Ukraine on 26 April 1986 resulted in a significant release of radioactivity to the atmosphere, particularly of Iodine-131 (131I), with the greatest contamination occurring in Belarus, Ukraine, and western part of Russia. Increase in thyroid cancer and other thyroid diseases incidence in exposed population in these counties was the main health consequence of Chernobyl accident. Therefore, much attention was paid to the thyroid doses, mainly due to the 131I intake with foodstuffs during two months after the accident. This paper reviews the thyroid doses received by the population of the affected countries, both individual doses for subjects of radiation epidemiological studies and average doses for the population. Individual thyroid doses due to 131I intake varied up to 42 Gy and depended on the age of the person, region of residence at the time of the accident and cow’s milk consumption habits. The population-average thyroid doses among young children reached 0.75 Gy in the most contaminated area, Gomel Oblast, in Belarus. Intake of 131I was the main exposure pathway to the thyroid gland: its average contribution to the thyroid dose was more than 90 %. In addition to exposure from 131I, the intake of short-lived radioiodine (132I, 133I, 135I) and radiotellurium (131mTe, 132Te) isotopes, external irradiation from gamma-emitting radionuclides deposited on the ground, and 134Cs, 137Cs ingestion contributed to the thyroid doses, typically, not more than 10 %. Uncertainties associated with dose estimates, in terms of mean geometric standard deviation of individual stochastic doses, varied in range from 1.6 for doses based on individual-radiation measurements to 2.6 for ‘modelled’ doses. From a radiological point of view, 131I was the most important radionuclide that caused radiation exposure to the thyroid gland after the Chernobyl accident and an increase in the incidence of thyroid cancer and other thyroid diseases among the exposed population.