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RADON CONTROL IN ESTONIA

L. Pahapill 1 , G.Åkerblom 2
1 Estonian Radiation Protection Centre, Kopli 76 Tallinn 10416 Estonia 2 Swedish Radiation Protection Institute, SE-17116 Stockholm, Sweden

Radon surveys started in Estonia in 1989. The Department Building Physics at the Estonian Building
Research Institute measured radon levels in dwellings, in building materials produced in the country,
and in the soil. The indoor radon concentrations in more than 400 houses were measured under grab-sampling
techniques using Lucas cells. The highest measured radon level was 6700 Bqm -3 . The results
of these measurements made during 1989-91 showed that the main source of indoor radon is the soil
underneath buildings. No building materials with elevated radium concentrations have been found so
far.
A new nation wide radon-monitoring program within the Estonian Environmental Monitoring Program
started in 1994. The main objectives of this program were to identify radon risk areas
in the country and radon risk housing construction types.
The bedrock in Estonia consists of sediments from the Cambrian to Devonian periods. These
sediments have low to normal uranium concentrations with the exceptions of the Ordovician
Dictyonema black shale and phosphorous-rich Glauconite sand that are exposed mostly in the northern
part of the country. The Dictyonema shale is similar to the uranium-rich black alum shale found in
Sweden and Norway. Till, silt, clay, sand and gravel are the main soil types. The coastal regions of
northern Estonia have the greatest radon problem in the country; many coastal houses are constructed
on ground that contains Dictyonema shale, either in the bedrock or as fragments in the soil.
During the five year (1994 - 1998) radon-monitoring program, the indoor radon concentrations in 700
dwellings that were located in the expected radon prone areas were measured. The measurements were
made with passive alpha-track detectors, the measurements’ period was three months during heating
seasons. The maximum measured values of indoor radon concentrations exceeded 12,000 Bqm -3 . The
arithmetical mean of these measurements was 102 Bqm -3 . Approximately 65% of the measured
dwellings had radon levels below 100 Bqm -3 . In 3 % of the houses, radon concentration exceeded 800
Bqm -3 .
In 1997, a national survey of radon in randomly selected dwellings across the entire country was
started. This survey includes radon measurements in 500 dwellings.
Key words: radon, dwellings, radon in soil air, Dictyonema shale, measurements.