A countrywide survey of radon concentrations in Estonian dwellings was carried out during the period 1998-2001. The survey formed a part of the cooperation program on radiation protection between the Estonian Radiation Protection (Kiirguskeskus) Centre and the Swedish Radiation Protection Authority (SSI). The Estonian Environmental Foundation and the Swedish Ministry for Foreign Affairs have given financial support for the survey.
The survey included measurements in a number of dwellings representative for Estonia in detached houses and multifamily buildings (only dwellings on the bottom floor were included in the survey). Altogether, radon concentrations were measured in 515 dwellings, a number large enough to be statistically significant.
All measurements were made with alphatrack film detectors of the same type that SSI uses in Sweden. The measurements were made during a 2-3 month period during the winter halfyear. Two detectors were used in each dwelling. In Estonia there are 0.17 dwellings in detached houses and 0.45 million in multiapartment buildings. Of the 1.26 million inhabitants in Estonia. 0.36 million live in detached houses and 0.90 million in multiapartment buildings. Most of the latter were built during the Soviet occupation. Of the dwellings in multifamily buildings 30 % are assumed to be situated on the first floor. The mean radon concentration in dwellings in detached hoses, according to the survey results, is 103 Bq/m3, in dwellings on the bottom floor in multiapartment buildings it is 78 Bq/m3. In 1% of the dwellings the radon concentration exceeded 400 Bq/m3. The highest radon concentration found in the study was 1040 Bq/m3.
Approximately 70% of the Estonian population lives in apartments in multiapartment buildings. Based on the assumption that the average radon concentration in the dwellings in multi-apartment buildings that are not situated on the bottom floor is 30 Bqm3, and that these dwellings constitute 70% of all dwellings in multiapartment buildings, the mean radon concentration in dwellings in multiapartment buildings is calculated to be 44 Bq/m3. The mean value for all Estonia dwellings is calculated to be 60 Bqm3. Using the detriment factor given by ICRP, annually about 90 Estonians are expected to develop lung cancer due to exposure to radon in their homes. Most of them, about 75, are smokers, which are affected by the synergetic effect of the two carcinogens, smoking and radon. In Estonia the source of indoor radon is radoncontaining soil air that is transported into the buildings from the ground. Building materials with enhanced radium concentrations are not known in Estonia. In this survey, the highest indoor radon concentrations have been found in the northern part of Estonia where uraniumrich Dictyonema shale and uraniumcontaining phosphorous Glauconite sandstone exist in the bedrock and as fragments in the soils. Radon concentrations higher than 400 Bqm3 have also been measured in buildings situated in areas with karst formations. Areas with Dictyonema shale, Glauconite sandstone and karst are areas with a special risk for radon.