A 24-year follow-up of malignancies in Sweden after the Chernobyl nuclear power accident in 1986

Abstract

A 24-year follow-up of total malignancies in Sweden after the Chemobyl nuclear power plant accident in 1986 shows a small increase in the incidence of malignancies when the average deposition of caesium-137 for each parish was used to classifY the exposure. Background: The accident at the Chernobyl nuclear power plant in Ukraine, USSR occurred on 26 April, 1986. Five percent out of the total 85 PBq released caesium-13 7 from the Chernobyl reactor was deposited in Sweden during the ensuing days, especially during the heavy rainfall on April 28-29, with an unequal distribution in the eastern coastal regions from Stockholm in the south to Umea in the north [I]. The main contributors to the dose rate in the first weeks were short-lived nuclides replaced by the long-lived caesium-134 and caesium-l37 [2]. Two studies in Sweden have shown a slight increase in total malignancies related to caesium-137 deposition after the Chemobyl accident. In the initial study the inhabitants in the 450 parishes in 7 counties in Northern Sweden were classified using an analogous map on the deposition of caesium-I 37 in these parishes, the excess relative risk (ERR) was calculated to 0.11 per 100 kBq/m' (95% Confidence Interval 0.03-0.20) [3]. In the second study a digital map was used instead to match each person 's dwelling coordinate to the exposure of caesium-137 with a similar result of ERR 0.10 per 100 kBq/m' (95% CI 0.00-0.23) [4]. Methods: The population in nine out of Sweden's 21 counties was included in this 24-year follow-up study: Norrbotten, Viisterbotten, Jiimtland, Viistemorrland, Giivleborg, Dalarna, Viistmanland, Uppsala and S6derrnanland. These counties had the highest fallout of radionuclides in Sweden after the Chernobyl accident, but had also areas with no fallout. The total population was annually retrieved from the National Archives 1986-1992. Each individual was classified annually with their address to the parish. [n all, 612 parishes and 2,183 ,212 individuals were included in the study. The average deposition of caesium-137 for each parish was given by the Swedish Radiation Safety Authority from the lowest average of 1 to the highest of 85 kBq/m' in May 1986. By assignment with the Swedish Radiation Safety Authority, the Geological Survey of Sweden had performed aerial gamma measurements over the whole of Sweden creating a grid of 200.200 meter of caesium-I 37 deposition. This digital map was used by the Swedish Radiation Safety Authority to calculate the parish average. Using the annual address for the individuals each person could be followed over time. Taking into account both the half-life of caesium-137 of 30 years and if a person changed address a cumulative exposure estimate could be created in kSq.years/m2 for 1986-1992. Cases of malignancies and deaths with date of