RADON CONTROL IN ESTONIA. L. Pahapill 1, G.Åkerblom 2. Estonian Radiation Protection Centre, Kopli 76 Tallinn Estonia

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1 Radon in the Living Environment, 066 RADON CONTROL IN ESTONIA L. Pahapill 1, G.Åkerblom 2 1 Estonian Radiation Protection Centre, Kopli 76 Tallinn Estonia 2 Swedish Radiation Protection Institute, SE Stockholm, Sweden Radon surveys started in Estonia in 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 grabsampling techniques using Lucas cells. The highest measured radon level was 6700 Bqm -3. The results of these measurements made during 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 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 ( ) 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. INTRODUCTION Elevated indoor radon concentration as a risk factor for human health was recognised in Estonia at the end of the 1980s. Information about radon problems was mainly acquired from Western Europe, especially through publications from Sweden and Finland. Public attention was drawn to the problems of natural radioactivity and to the possible existence of high indoor radon concentrations by the so-called Sillamäe-case of Since December 1989, the Department of Building Physics at the Estonian Building Research Institute (EBRI) has carried out radon measurements. The results of the measurements made from show that the main source of indoor radon in Estonia is the ground under buildings (Pahapill et. al 1993). 597

2 066 Radon in the Living Environment, The Estonian-Swedish Radon Project made it possible to start a radon-monitoring program within the Estonian Environmental Monitoring program in The main objectives of this program were to investigate radon levels in dwellings and to identify radon risk areas and radon risk housing construction types. The first part of this radon project was completed in 1996 and includes measurements from randomly selected dwellings in areas considered to be radon risk areas (Pahapill et. al 1996). In 1997, a national survey of radon in randomly selected dwellings across the entire country was started. This survey includes radon measurements in 500 of the 160,000 dwellings in Estonia and is the second part of the Estonian-Swedish Radon Project. The main goals of the survey are: 1) estimation of the national radon situation for calculation of public health risk created by indoor radon and, 2) to provide a basis for work on protective measures against radon. In 1997 soil air radon measurements commenced at the test sites representing the prevailing soil types of radon prone areas. Testing was implemented to initiate the state s interest in geologically oriented radon risk mapping. MEASUREMENTS The radon measurements taken from by the Department of Building Physics at the EBRI used the grab sampling method, with Lucas cells. The instrument used was a Pylon AB-5 (Pylon Electronic Development Company, Canada). Since then, most of the measurements for the Swedish- Estonian Radon Projects have been made with passive alpha-track detectors. The CR-39 (polyallyl diglycol carbonate) alpha-track detector material from TASL Ltd. of Bristol, UK was used. The film was placed in a closed cup holder of electrically conductive plastic. After chemical etching in a 20% NaOH solution (17 hours, etching temperature 68 0 C), the detectors were evaluated in an image analysis system. The detectors were originally designed by the National Radiological Protection Board (NRPB), UK, but they have been further developed by Swedish Radiation Protection Institute (SSI). The etching and reading films was done in the Estonian Radiation Protection Centre. Sensitivity calibration of the detectors was performed at SSI (Mellander and Enflo, 1992). The usual measurement period is three months during winter heating season. Two detectors are placed in each dwelling, usually, one in a bedroom and living room. In two story single-family houses, one detector is placed on each level. Soil air radon measurements were performed using an emanometer of type Markus 10 (Gammadata Mätteknik AB, Sweden), in-situ determinations of the concentrations of radium-226, thorium-232 and potassium-40 in the soil were made using a portable gamma-ray spectrometer of type GR-256 (Exploranium G.S. Ltd., Canada), equipped with a 3 x3 NaI (TI) crystal detector. The spectrometer was calibrated at the Borlänge calibration facility, owned by the Geological Survey of Sweden. ESTONIAN DWELLINGS Multi-family houses are dominant in the Estonian dwelling stock. One million or 2/3 of the Estonian population live in apartment houses. Single-family houses are more common in rural areas, 598

3 Radon in the Living Environment, 066 but almost half of the rural population also lives in multi-family houses. Today s dwelling stock consists of three major types of houses-brick walls, concrete panel buildings, and wood constructions. Wood construction is more dominant in rural areas and among the buildings built before Concrete panel building construction began in the early sixties. Most urban residents live in apartment houses built after 1950; 26% of Estonia s apartment buildings were built after These flats typically have 2-3 rooms, plus a kitchen, hall, bathroom and toilet. The average floor space per capita is about 20 m 2. The houses are, for the most part, provided with district central heating, water supply, and natural chimney ventilation. The estimated average ventilation rate in the heating season is about exchanges per hour. The ventilation rate of 1.0 times per hour was established in the construction rules (SNiP) for the dwellings in the Former Soviet Union. The percentage of single-family houses among dwellings is approximately 30%. They are more common in rural areas and smaller towns. Most houses are 1-2 story wooden or brick houses, with 3-4 rooms, a kitchen, hall and toilet. In towns, there is public tap-water and drainage. They have stove heating or their own heating system and natural ventilation. Saunas are more widespread in single-family houses in rural areas. Private houses built after 1950 are often self-made - built by the people living in them. The insulation standard of these houses is often better than apartment buildings, but the ventilation rates may be lower than in the standard houses. SOURCES OF RADON, THE GROUND Soil air is the main source of radon gas in Estonia. As far as is known, no building materials with elevated radium concentrations have been used in the construction of dwellings. The water used in the households generally have low radon concentrations. The bedrock in Estonia consists of sediments from the Cambrian to Devonian periods, underlain by the Precambrian basement, consisting of crystalline rocks belonging to the Baltic shield. The sediments have been penetrated down to the basement by numerous bore holes. The basement rocks are not exposed anywhere in Estonia. The sedimentary rocks consist mainly of sandstones, shales, limestones, siltstones and clays. These sediments dip gently southward. Thus, the oldest sediments are located on the northern coast of Estonia, where the oldest sediments are of Precambrian age (590 m.y.). The thickness of the sediments is m. The sediments are often unconsolidated, and sequences of clays and sands exist. The sedimentary rocks have low to normal uranium concentrations, usually less than 2.5 ppm uranium (30 Bq kg -1 ), with the exceptions of the Ordovician Dictyonema black shale and phosphorous-rich Glauconite sand in northern Estonia. The Dictyonema shale is 2-6 m thick and is from the Lower Ordovician period (490 m.y.). It is a kerogen-rich shale with enhanced uranium contents; on average, the uranium concentration is 30 ppm (ca. 400 Bq kg -1 ), but it ranged as high as ppm ( Bq kg -1 ). The Dictyonema shale is similar to the Upper Cambrian uranium-rich, black alum shale found in Sweden and Norway. Directly above the Dictyonema shale lies the phosphorous-rich Glauconite sand that forms a layer of varying thickness, from just a few centimeters to more than 5 meters. The Glauconite sand also has an enhanced uranium concentration, which is however, much lower than that of the Dictyonema shale. The Glauconite sand has been extensively mined for its phosphorous especially east of Tallinn where there are large excavations. The Dictyonema shale and the Glauconite sand are only exposed in the klint and in a few other areas along the northern coast of Estonia, e.g. in the eastern districts of Tallinn and the 599

4 066 Radon in the Living Environment, towns of Toila, Kunda and Sillamäe, where large parts of the towns are built on the Dictyonema shale. Glacial ice covered nearly the entire region during the last glacial period. Thus, the soil in large parts of the country consists of moraine and glacial deposits of gravel, sand, silt and clay. The glacial soil consist mainly of material from the underlying rock units and to a large extent, of Precambrian rocks transported by the glacial ice from the bottom of the Baltic Sea and from Finland. Some of this rock material contains stones and fragments of uranium-rich granites. In some parts of northern Estonia, the glacial soils contain Dictyonema shale fragments and Glauconite sand. As a complement to the radon measurement projects, reconnoitring surveys were made to the northern regions of Estonia to study the geology and locate areas with special geologic features that may promote the risk of radon in buildings. During these surveys, measurements were made with portable gamma-ray spectrometers and emanometers to determine the concentration of radium-226, thorium-232 and potassium-40 in soils, as well as the radon concentration in the soil air. The measurements were made a depths of cm. A compilation of results is given in Table 1. Radon risk areas in Estonia (Figure 1), where indoor radon could create a health risk, are found predominantly along the northern coast, where the risk is connected with soils containing Dictyonema shale fragments and Glauconite sand. The karst regions have a high incidence of fractures, and underground streams and caves formed by the weathering of the limestones bedrock. When atmospheric pressure changes occur, air moves in and out of these underground cavities and although the radon concentration in the air is not more than 1,000-10,000 Bqm -3, the large volumes of air that can be transported into buildings from these cavities can result in high indoor radon concentrations. Karst areas exist in Estonia and it is, therefore, expected that more buildings with high radon concentrations will be found in future surveys of limestone areas too. RESULTS Measurements made from by the Estonian Building Research Institute showed that the main source of indoor radon in buildings is the ground. The indoor radon concentrations in more than 400 houses (90% of them being dwellings and 10 % kindergartens, schools and hospitals) were measured by grab sampling. The maximum measured level was 6700 Bqm -3. In 72 % of houses the radon concentration was below 100 Bqm -3, and in 4 % it exceeded 800 Bqm -3. During the five year ( ) radon-monitoring program, the indoor radon concentrations in 700 dwellings that are 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 (Pahapill et. al 1998). A summary of these measurements is presented in Table 2. The type of dwelling that was at greatest risk for indoor radon exposure was determined to be the two-story apartment houses with crawl-spaces built in the 1950s. The crawl spaces of these buildings lack external ventilation outlets. However, the floors on the first story have indoor 600

5 Radon in the Living Environment, 066 ventilation outlets that lead to the crawl spaces, creating excellent conditions for the influx of radon gas (Figure 2). The highest level of indoor radon measured in this project was 12,000 Bqm -3, recorded in one two-story apartment house. This type of dwelling had the highest radon levels in all areas where it was founded. The radon levels in single-family houses were higher than in apartment buildings in all areas. The results of radon measurements made in different types of buildings are presented in Table 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. During the first year of this survey, measurements in 200 randomly selected dwellings in the three counties were carried out. Two of the counties, Lääne-Virumaa and Ida-Virumaa, are situated in the northern part of the country and were expected to be radon prone areas. The third county Saaremaa is the largest Estonian island in Baltic Sea (2671 km 2 ), which due to the geological situation is not likely to be a radon risk area (there is no Dictyonema shale and no phosphorous-rich Glauconite sand layers in the sediments). Soils in all three counties consists of moraine and glacial deposits of gravel, sand and clay, the thickness of Quaternary deposits is usually 5-10 m. Saaremaa and Lääne- Virumaa are rural counties, where single-family houses are more common. A survey form was used to collect data on each dwelling measured and to form the database. A summary of the measurements is presented in Table 4. The results of surveys in two of the counties (Saaremaa and Ida-Virumaa) are similar: the maximum measured level is 320 Bqm -3. The arithmetical mean in Ida-Virumaa is 70 Bqm -3 and 66 Bqm -3 in Saaremaa. The percentage of dwellings below 100 Bqm -3 in Ida-Virumaa is 82 %, in Saaremaa 71 %. Of the dwellings in Saaremaa 8 % exceed 200 Bqm -3 as do 5% of the dwellings in Ida-Virumaa. The radon levels measured in dwellings of Lääne-Virumaa are higher: the maximum 1040 Bqm -3, the arithmetical mean is 137 Bqm % of the dwellings have radon levels below 100 Bqm -3. In 18% of houses, the radon concentration is higher than 400 Bqm -3. The 1997 radon-monitoring program the radon levels in the small town Loksa along the northern coast were also measured. The results of these measurements are given in Table 4. They show the importance of permeability of soils to indoor air radon concentrations. Loksa is situated in varved clays filled with groundwater. All measured radon levels in the houses were very low: the arithmetical mean was 28 Bqm -3, the maximum measured value was 70 Bqm -3, measured in a dwelling that as described above ought to be classified a radon risk house (Figure 2). CONCLUSIONS There are potentially high radon risk areas in Estonia, mostly in the northern part of the country. Radon investigations must be continued in order to identify radon risk areas and radon risk types of buildings. The Radiation Act was enforced in 1997 in Estonia, now there is a need for national regulations on radon. There is a need to work out recommendations for remedial and preventive actions against radon in Estonia building practices. 601

6 066 Radon in the Living Environment, ACKNOWLEDGEMENTS This work was supported by Estonian State Environmental Monitoring Program, Estonian Environmental Foundation and by the Swedish Project Radiation Protection East (EST-6.01 and EST-6.05). The authors are grateful to Anne Rulkov for her excellent work in the measuring programs. REFERENCES [1] Mellander H, Enflo A The alpha track method used in the Swedish radon epidemiological study. Radiation Protection Dosimetry. Vol. 45, No. 1/4, 1992, [2] Pahapill L, Jõgioja E, Rohumäe T. Indoor radon in Estonia. In: Kallikoski P, Jantunen M, Seppänen O, editors. Proc.of the 6 th Int. Conf. on Indoor Air Quality and Climate, Vol. 4, 1993, [3] Pahapill L, Rulkov A, Swedjemark GA. Radon in Estonian Buildings. Establishment of a measurements system and obtained results. Swedish Radiation Protection Institute. SSI-report 1996:13. Stockholm, 1996, p 19. [4] Pahapill L, Dambis M, Morkunas G, Åkerblom G. Radon in the Baltic States. In: Sorgaad-Hansen J, Damkjear A, editors. Radiation Protection Issues in the Baltic Region with Emphasis on Co-operative Projects with Estonia, Latvia and Lithuania. Proc. of the Regional IRPA Congress held in Stockholm June , Riso National Laboratory, Denmark, 1998,

7 Radon in the Living Environment, 066 Table 1: Range of activity concentrations of 226 Ra 232 Th, 40 K in soil and 222 Rn in soil air. 226 Ra, Bq kg Th, Bq kg K, Bq kg Rn, kbqm -3 Northern Estonia Sand Thin layer of till above karst Till in phosphorous-rich area Till with Dictyonema shale ,500 fragments 603

8 066 Radon in the Living Environment, Table 2. Indoor radon in the dwellings measured Arithmetical mean (Am), geometrical mean (Gm), maximum values (Max) of radon levels found indoors and distribution (%) of the indoor radon concentration (Bqm -3 ) are presented. Area Tallinn Kunda Aseri Rakvere Toila Paldiski Raasiku Narva Indoor 222 Rn, Bq/m 3 Am Gm Max The distribution of indoor 222 Rn concentrations, % < > Table 3: Indoor radon concentrations by type of Estonian dwelling. Type of dwelling No of houses Am, Bq/m 3 Max, Bq m -3 Single-family houses, with cellars Single-family houses, without cellars Apartment houses, with cellars Apartment houses, without cellars Multi apartment buildings

9 Radon in the Living Environment, 066 Table 4: Indoor radon concentrations in the dwellings measured Number of measured dwellings, arithmetical mean (Am), geometrical mean (Gm), maximum values (Max) of radon levels found indoors and distribution (%) of the indoor radon concentrations (Bqm -3 ) are presented. Area No. of flats Indoor 222 Rn, Bq/m 3 Am Gm Max The distribution of indoor 222 Rn concentrations, % < >801 Lääne-Viru Ida-Viru Saaremaa Loksa

10 066 Radon in the Living Environment, Figure 1: Areas in Estonia chosen for radon measurements Figure 2: Two-story apartment house with crawl space that is ventilated through openings in the bottom floor 606