Journal of Environmental Radioactivity 150 (2015) 99e103
Contents lists available at ScienceDirect
Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad
Reconstruction of national distribution of indoor radon concentration in Russia using results of regional indoor radon measurement programs I. Yarmoshenko*, G. Malinovsky, A. Vasilyev, M. Zhukovsky Institute of Industrial Ecology UB RAS, S. Kovalevskoy St., 20, Ekaterinburg 620219, Russia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 8 June 2015 Received in revised form 6 August 2015 Accepted 15 August 2015 Available online xxx
The aim of the paper is a reconstruction of the national distribution and estimation of the arithmetic average indoor radon concentration in Russia using the data of official annual 4-DOZ reports. Annual 4DOZ reports summarize results of radiation measurements in 83 regions of Russian Federation. Information on more than 400 000 indoor radon measurements includes the average indoor radon isotopes equilibrium equivalent concentration (EEC) and number of measurements by regions and by three main types of houses: wooden, one-storey non-wooden, and multi-storey non-wooden houses. To reconstruct the national distribution, all-Russian model sample was generated by integration of sub-samples created using the results of each annual regional program of indoor radon measurements in each type of buildings. According to indoor radon concentration distribution reconstruction, all-Russian average indoor radon concentration is 48 Bq/m3. Average indoor radon concentration by region ranges from 12 to 207 Bq/m3. The 95-th percentile of the distribution is reached at indoor radon concentration 160 Bq/m3. © 2015 Published by Elsevier Ltd.
Keywords: Radon Russia Distribution
1. Introduction Survey of indoor radon concentrations in a representative sample of houses is a significant stage of national and regional programs dealing with population radon exposure. Indoor radon survey provides the information on distribution of indoor radon concentrations in dwellings and other locations and retrieves the factors most influencing on indoor radon level. The results of indoor radon survey constitute the base for strategy of protection against radon and effective protection measures. According to its mission, UNSCEAR periodically reviews the results of national indoor radon surveys and estimates average worldwide indoor radon concentration as well as effective dose due to radon. Totally, results of indoor radon surveys from more than 60 countries were included in 2006 report (UNSCEAR, 2009). The UNSCEAR 2000 report gives population-weighted worldwide arithmetic and geometric mean (GM) values 39 and 30 Bq/m3 respectively with corresponding geometric standard deviation (GSD) 2.3 (UNSCEAR, 2000). In Russia, protection against radon is required by Federal Law
* Corresponding author. E-mail address: [email protected] (I. Yarmoshenko). http://dx.doi.org/10.1016/j.jenvrad.2015.08.007 0265-931X/© 2015 Published by Elsevier Ltd.
“On protection of population against radiation”. Since 1990, Russian Radiation Safety Standards (RRSS) include restriction on indoor annual equivalent equilibrium concentration of radon isotopes. This quantity is calculated as 222Rn EEC þ 4.6 220Rn EEC. In existing dwellings, the restriction is EEC of radon isotopes ¼ 200 Bq/m3. For new buildings, the more strength restriction is established, EEC of radon isotopes ¼ 100 Bq/m3. Protection of population of Russia against indoor radon is the responsibility of Russian Federal Service for Surveillance on Consumer Rights Protection and Human Wellbeing (Rospotrebnadzor). The approach to indoor radon problem in Russia, developed by Rospotrebnadzor in 1990-s and 2000-s, does not include the indoor radon survey in the national representative sample of buildings. The indoor radon measurements, which were performed in the frames of regional annual radiation monitoring programs, were focused on searching for high radon areas (Kormanovskaya and Stamat, 2010; Svetovidov et al., 2012). In order to control compliance with the restrictions of the RRSS, the measurements in all new buildings were another important task. According to these priorities, regional departments of Rospotrebnadzor were equipped mostly with short term radon measurements devices (grab sampling). Totally eleven types of devices for short term measurements of ECC of radon isotopes and eight types of devices for short term measurements of radon
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concentration are used (ISSDCR, 2014; Zhukovsky and Yarmoshenko, 1997; Zhukovsky et al., 2010). Such devices are relatively cheap and allow prompt control of exposure to radon progeny. Measurements of thoron ECC may be performed using the most of grab sampling devices. In Russia, exposure to thoron progeny is not considered to be an important problem in comparison with the radon progeny. In average, EEC of thoron with the factor 4.6 contributes only few Bq/m3 to ECC of radon isotope (Zhukovsky and Yarmoshenko, 1998; Yarmoshenko et al., 2002). Only few laboratories were equipped with long term nuclear track detectors (Marenny et al., 2000, 2005). In case of radon gas measurements, equilibrium factor F ¼ 0.5 is used in Russia (Yarmoshenko et al., 2014). Since 2001, Rospotrebnadzor established the Joint system of the control of the individual doses to the population and an information bank to collect the data of radiation measurements performed by regional departments and other laboratories (Svetovidov et al., 2012). Instructions and guidelines on reporting results of the population radon exposure control were developed by StPetersburg Research Institute of Radiation Hygiene after Professor P.V. Ramzaev (Stamat et al., 2014). Data in the information bank are annually reviewed and summary is published. Indoor radon data are presented in 4-DOZ Report (Rospotrebnadzor, 2007). Now, information of the 4-DOZ annual reports becomes the largest source of data on indoor radon exposure of population of the Russian Federation. The data collecting system is based on the average values by regions and doesn't include the information on dispersion of indoor concentration. Thus, there is no possibility to analyze the distribution of radon isotopes ECC radon exposure in Russian Federation that is important for optimization of protection against radon exposure (ICRP, 2014). The aim of our analysis is to reconstruct the national distribution of indoor radon concentration using these data. 2. Materials and methods For our analysis, we used 4-DOZ Reports issued by St-Petersburg Research Institute of Radiation Hygiene after Professor P.V. Ramzaev in the period from 2008 to 2013 (ISSDCR, 2009, 2011a, 2011b, 2012, 2013, 2014). The annual reports summarize the results of radiation measurements and dose assessment in 83 regions of the Russian Federation, which were presented to national data bank according to the requirements of special guidelines (Rospotrebnadzor, 2007). Measurements of indoor radon (222Rn) and thoron (220Rn) EEC and/or radon (222Rn) gas concentration are conducted within the regional radiation measurement programs of most of the regions. Annual summary 4-DOZ Report includes the average EEC of indoor radon isotopes (222Rn EEC þ 4.6 220Rn EEC) and the number of measurements by regions and by three main types of houses: wooden house, one-storey non-wooden house and multi-storey non-wooden house. The last two groups include houses built using mineral materials such as stone, brick, concrete etc. Thus, the average indoor radon isotopes EEC and the number of measurements represent results of annual regional program of radiation measurements in corresponding type of buildings. The distribution of indoor radon isotopes EEC in dwellings of Russia was reconstructed considering each annual regional program of measurements in the each type of buildings as the radon survey of a rural territory or a district of urban territory. For the purposes of the analysis, it was suggested that such quasi-surveys conducted over the period of 2008e2013 cover all territory of Russia. Consequently, all-Russian model sample can be generated by integration of sub-samples created using results of the quasisurveys.
In order to generate the sub-sample of indoor radon isotopes EEC under suggestion on lognormal distribution, it is necessary to know GM and GSD of radon isotopes EEC and the number of generated values (N). For the case of lognormal distribution, the GM can be calculated using the following equation:
! s2LN GM ¼ exp lnðAMÞ ; 2
(1)
where AM is arithmetic mean of radon isotopes EEC (Bq/m3) for each quasi-survey obtained from the 4-DOZ annual reports, sLN is the natural logarithm of the GSD. As mentioned above, the exact values of GSD for each quasisurvey are unknown. Therefore, we used some typical values, which were chosen depending on the number of measurements. The dependence of dispersion of indoor radon concentration values on number of measurements reflects higher variability of radon sources in larger territory. Factors influencing the variability are associated with both variation of radon geogenic potential and diversity of types of buildings (the detailed report devoted to factors influencing GSD is under publication). Accepted values of GSD are presented in Table 1. The number of generated values of radon isotopes EEC in the sub-samples was normalized by population of the region and the number of measurements in the frame of regional radiation monitoring program:
N
Npop $Nmeas ; Ntotal
(2)
where Npop is the population of the region; Nmeas is the number of measurements in this region in certain type of building in a certain year; Ntotal is the number of measurements in this region in all type of building for the period of 2008e2013. With regard to available computational resources the total size of modeled sample to reconstruct distribution of indoor radon concentrations in dwellings of Russia was limited by 60004. Then, the number of generated values for each i-th quasi-survey is chosen based on the condition SNi ¼ 60004. Totally data on 874 quasi-surveys were included to the analysis (surveys with Nmeas1000
235 445 89 105
1.8 2.1 2.7 3.0
Table 2 The number of the quasi-surveys and average size of sub-samples, (N, in brackets). Type of building
Year 2008
2009
2010
2011
2012
2013
Wooden houses One-storey brick and stone houses Multi-storey brick and stone houses
24 (42) 37 (11) 76 (152)
24 (31) 34 (12) 76 (110)
27 (25) 38 (13) 75 (111)
34 (22) 44 (14) 77 (108)
37 (20) 43 (11) 77 (99)
32 (26) 43 (14) 77 (105)
departments of Rospotrebnadzor of Russia requires special consideration with regard to applicability for the reconstruction of the national distribution of indoor radon concentration. The weak points that diminish reliability of the data are summarized below. Absence of common rigorous requirements on inclusion of the dwellings to annual regional radon measurements program decreases the quality of regional surveys. Application of short term indoor radon measurements increases the uncertainty of results, including both possible overestimation and underestimation of arithmetic mean. Absence of information on dispersion of indoor radon isotopes EEC in annual reports detracts accuracy of reconstruction of national distribution. It is necessary to say that each regional annual data set on indoor radon measurements can not be considered as a high quality representative indoor radon survey. The regional measurements programs are directed to search high radon dwellings and, to a lesser extent, to control radon in new buildings. Nevertheless, there are few reasons to undertake the reconstruction on the base of the regional measurements
100 p, % 90 80 70 60 50 40 30 20 10 0
5
10
50 Radon concentration, Bq/m3
100
200
Fig. 1. Reconstructed cumulative distribution of indoor radon concentration in dwellings of Russia.
programs. The measurements of indoor radon concentrations are conducted in most of regions of the country. At least 200 measurements are performed in 59 regions of 83 and more than 400 measurements e in the half of regions annually. The total number of indoor radon EEC measurements, over 400 000 during six years, is significant. Few regions where indoor radon measurements are not performed regularly are low populated. It is important that there are national scheme of metrological support and traceability of radon concentration measurements and national guidance system on protection against radon (Stamat et al., 2014). The national collecting of indoor radon measurements results was established about 15 years ago and current requirements for presentation of regional data to national data bank were issued in 2007. Thus, the national system of indoor radon control sustainably works for a quite long period. By results of reconstruction of the national distribution, allRussian average indoor radon concentration is 48 Bq/m3. Additional contribution of thoron EEC to indoor exposure is supposed to be low (Zhukovsky and Yarmoshenko, 1998; Yarmoshenko et al., 2002). If average thoron EEC is about 0.5 Bq/m3, then average radon isotopes EEC is 26 Bq/m3. The modeled indoor radon concentrations depend on the equilibrium factor, F. UNSCEAR (2000) considers F ¼ 0.4 as world typical value. However, for countries with climate colder than the planet average, higher equilibrium factor is expected. Our previous investigations in typical Russian dwellings (Zhukovsky and Yarmoshenko, 1998) and analyses of other authors have shown the lower disequilibrium between radon gas and radon daughters at low air exchange rate (Swedjemark, 1983). According to these investigations F ¼ 0.5 can be applied to estimate the average indoor radon concentration in Russian dwelling. Exposure of Russian population to indoor radon was previously estimated by Marenny et al. (2000, 2005). Marenny et al. (2005) divided the population into several categories depending upon two grades of radon geogenic potential (high and moderate), type of settlement (urban and rural) and floor (the ground floor, the first
Table 3 Parameters of the distributions of generated values of EEC of radon isotopes. Type of building
Arithmetic mean, Bq/m3
Geometric mean, Bq/m3
GSD
Percentage above 300 Bq/m3
Wooden houses One-storey brick and stone houses Multi-storey brick and stone housesa All types
75 59 46 48
37 32 24 25
3.1 3.0 3.0 3.1
3.5% 2.1% 1.1% 1.3%
a
Average over all floors.
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floor and higher floors). The values of GM and GSD for each category were derived from the radon surveys conducted using long term measurements in 2709 dwellings in seven regions of Russia in 1990-s (Marenny et al., 2000). Population weighted average indoor radon concentration was estimated to be about 52 Bq/m3 (Marenny et al., 2005). The advantage of analysis performed by Marenny et al. (2005) is the possibility to take into account the characteristics of dispersion of indoor radon concentration. At the same time that analysis was restricted only to few regions where long term measurements were conducted. All-Russian data were considered previously by Zhukovsky et al. (2011) and Baryshkov et al. (2013). Zhukovsky et al. (2011) reviewed 2009 annual 4-DOZ report (ISSDCR, 2011a) and suggested an average indoor radon EEC of 30 Bq/m3 for estimation of lung cancer risk associated with indoor radon exposure in Russia. According to the Joint system of the control of the individual doses to the population the total effective dose due to indoor and outdoor inhalation of short lived radon and thoron progeny is 1.97 mSv/year (Baryshkov et al., 2013; Onishenko and Romanovich, 2014), which corresponds indoor EEC of radon isotopes 28 Bq/m3. Thus, on the one hand, the previous estimations have provided quite consistent assessments of indoor radon exposure of population in range of indoor radon concentration from 50 to 60 Bq/m3. On the other hand, the dispersion of indoor radon concentration in dwellings was not considered in the previous assessments of the most recent and complete data. New analysis performed taking into account such dispersion resulted in slightly lower estimation (indoor radon concentration 48 Bq/m3) and allowed to reconstruct the distribution of indoor radon concentration in Russian dwellings. In comparison with other countries indoor radon concentration 48 Bq/m3 is moderate. It corresponds to 53rd percentile of national average indoor radon concentrations presented in UNSCEAR review and to 60th percentile if only large countries (area >200 000 km2) are considered (UNSCEAR, 2000, 2009). As can be seen in Table 3, higher average indoor radon concentration is observed in wooden houses (Table 3), which are usual in rural settlements. High radon concentration is considered to be associated with convective entry from the soil. More air-tight construction causes lower concentration in one-storey brick and stone houses. The lowest average indoor radon concentration is obtained in multi-storey apartment buildings, where the diffusion from building materials dominates over convection as the radon source (Vasilyev and Zhukovsky, 2013). Obtained value of GSD ¼ 3.1 reflects both the dispersion of reported average values and model dispersion of indoor radon concentration in the regions. The GSD values accepted to generate the model regional samples are rough approximation which is based on the dispersions typically observed in radon surveys, including regional surveys performed in some Russian region. For example, GSD value in Ekaterinburg was 3.0. According to UNSCEAR review (UNSCEAR, 2009) world average value of GSD is 2.2 and the range is from about 1 to 3.9. Researchers who developed Europe map of indoor radon accepted value GSD ¼ 1.8 as typical value to be applied for 10 10 km2 cell for dwellings on the first floor (Tollefsen et al., 2011). Dispersion of the results of radon measurements using the short term measurements, which are common in Rospotrebnadzor regional departments, should be higher than it is expected for long term measurements (Zhukovsky et al., 2010). Above considerations on current knowledge on dispersion of indoor radon concentration in different regions give evidences that uncertainty of accepted GSD is relatively high. Nevertheless, despite the high uncertainty, reconstructed percentiles of indoor radon isotopes concentration distribution (Fig. 1) can be applied to preliminary consideration of the strategy of protection of population of Russia against indoor radon. As can be
seen from Table 3 indoor radon isotopes EEC exceeds the restriction level 200 Bq/m3 in 0.71% of dwellings in Russia. This value together with average indoor radon concentration is important starting point for planning the remediation measures in the country. Reconstructed distribution can be used to discuss possible derived reference level of indoor radon concentration that can be introduced in Russia according to recent ICRP recommendations (ICRP, 2014). According to approach presented by Yarmoshenko et al. (2013, 2014) to establish the national derived reference level some percentile of the national distribution of indoor radon concentration can be used. For example, reconstructed 95-th percentile of indoor radon concentration in Russia is about 160 Bq/m3 and this level can be suggested as the optimized reference level of radon concentration. Performed reconstruction of indoor radon concentration distribution allows preliminary estimation of indoor radon concentration distribution in Russia. However it cannot substitute for the conventional national indoor radon survey. Reliable estimates of national average indoor radon concentration and pattern of distribution should be obtained by means of survey which is based on measurements on indoor radon concentration in a representative sample of dwellings using unified, preferably long term measurements technique. 5. Conclusion Since about 70 000 measurements of indoor radon concentration as well as radon and thoron EEC are conducted in dwellings annually in Russia, the total number of measurements performed during last years allows assessment of some average characteristics of population exposure. According to our estimations, average national indoor radon concentration is 48 Bq/m3. The 95th percentile of reconstructed distribution is about 160 Bq/m3. These figures can be applied for justification of population protection against radon in Russia. The most important weak points of available information about exposure are associated with the applied method of selecting the houses for measurements and application of grab sampling measurements. Average value of radon concentration may be biased due to large number of measurements both in potential radon affected areas and in new buildings. Short term grab sampling measurements introduce greater uncertainty to the results in comparison with nuclear track method. With regard to these limitations, proper optimization of the protection against radon within the system of radiation protection (justification, optimization and application of reference levels) could not be achieved. Conventional national indoor radon survey in Russia is necessary. The main task of such survey is to obtain unbiased estimate of average value and distribution of indoor radon concentration. At the same time the task of revealing radon affected areas can be considered to be already accomplished in Russia. Correct sampling of dwellings and using of long term measurements are the most important for designing national survey in Russia. Acknowledgments The research has been made under the financial support of Institute of Industrial Ecology, Project 15-IIE-01. References Baryshkov, N.K., Bratilova, A.A., Karmanovskaia, A.A., et al., 2013. Doses to the Population of the Russian Federation in 2012. Information Handbook. SPb, p. 67 (in Russian).
I. Yarmoshenko et al. / Journal of Environmental Radioactivity 150 (2015) 99e103 ICRP, 2014. Radiological protection against radon exposure. ICRP publication 126. Ann. ICRP 43 (3). ISSDCR, 2009. Results of unified system of individual dose control functioning during 2008. Radiat. Hyg. 4 (2), 46e67 (in Russian). ISSDCR, 2011a. Results of functioning of the integrated state system for doses control and registration (ESKID) according to the data for 2009. Radiat. Hyg. 1 (4), 55e77 (in Russian). ISSDCR, 2011b. Integrated state system for doses control and registration (Forms No. 3-DOZ and No. 4-DOZ) on the basis of 2010 data. Radiat. Hyg. 4 (4), 51e69 (in Russian). ISSDCR, 2012. Integrated state system for doses control and registration (Forms No. 1-DOZ and No. 2-DOZ) on the basis of 2011 data. Radiat. Hyg. 3 (5), 68e76 (in Russian). ISSDCR, 2013. Integrated state system for doses control and registration (Forms No.1- DOS, No. 3-DOS and No. 4 DOS) on the basis of 2012 data. Radiat. Hyg. 3 (6), 63e86 (in Russian). ISSDCR, 2014. Integrated state system for doses control and registration (Forms No.1- DOS, No. 3-DOS and No. 4 DOS) on the basis of 2013 data. Radiat. Hyg. 3 (7), 54e81 (in Russian). Kormanovskaya, T.A., Stamat, I.P., 2010. Results of the integrated system of individual dose control sybsystem functioning on the base of statistical report forms N4 DOZ in 2001-2009. Radiat. Hyg. 4 (3), 10e14 (in Russian with English abstract). Marenny, A.M., Savkin, M.N., Shinkarev, S.M., 2000. Estimation of the radoninduced dose for Russia's population: methods and results. Rad. Prot. Dos. 90 (4), 403e408. Marenny, A.M., Shinkarev, S.M., Penezev, A.V., Savkin, M.N., Hoshi, M., 2005. Assessment of exposure to the population of Russia from radon. Int. Congr. Ser. 1276, 352e353. Onishenko, G.G., Romanovich, I.K., 2014. Current trends of the provision for radiation safety of the population of the Russian Federation. Radiat. Hyg. 7 (4), 14e22. Rospotrebnadzor, 2007. Form of Federal State Statistical Observation No.4-DOZ “Information on Radiation Doses of the Population Due to Natural and Technogenic Modified Radiation Background”. Guidelines. Russian Federal Service for Surveillance on Consumer Rights Protection and Human Wellbeing, Moscow (in Russian). Stamat, I.P., Kormanovskaya, T.A., Gorskiy, G.A., 2014. Russian Federation population radiation protection during the exposure from natural ionizing irradiation
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sources: modern state and directions for development and optimization. Radiat. Hyg. 1 (7), 54e62 (in Russian with English abstract). Svetovidov, A.V., Stamat, I.P., Kormanovskaya, T.A., Kononenko, D.V., 2012. Main results and ways to improve the uniform state system for population exposure doses control and registration on the basis of state statistical surveillance forms N. 4-DOZ. Radiat. Hyg. 1 (5), 52e59 (in Russian with English abstract). Swedjemark, G.A., 1983. The equilibrium factor-F. Health Phys. 45 (2), 453e462. Tollefsen, T., Gruber, V., Bossew, P., De Cort, M., 2011. Status of the European indoor radon map. Radiat. Prot. Dosim. 145 (2e3), 110e116. UNSCEAR (United Nations Scientific Committee on the Effects Atomic Radiations), 2000. Sources and Effects of Ionizing Radiation, UNSCEAR 2000 Report to the General Assembly, vol. I. Annex B, United Nations (NY). UNSCEAR (United Nations Scientific Committee on the Effects Atomic Radiations), 2009. Effects of Ionizing Radiation, UNSCEAR 2006 Report to the General Assembly, vol. II. Annex E: Source-to-effects Assessment for Radon in Homes and Workplaces, United Nations (NY). Vasilyev, A.V., Zhukovsky, M.V., 2013. Determination of mechanisms and parameters which affect radon entry into a room. J. Environ. Radioact. 124, 185e190. Yarmoshenko, I., Zhukovsky, M., Ekidin, A., Kirdin, I., Pavlyuk, A., 2002. An indoor thoron survey performed in the Central Urals. In: Peter, J., Schneider, G., Bayer, A. (Eds.), Proceedings of the 5-th International Conference on High Levels of Natural Radiation and Indoor Radon Areas, vol. II, pp. 223e226. Salzgitter, Germany. Yarmoshenko, I., Onishchenko, A., Zhukovsky, M., 2013. Establishing regional reference indoor radon level on the base of radon survey data. J. Radiol. Prot. 33, 329e338. Yarmoshenko, I.V., Onishchenko, A.D., Zhukovsky, M.V., 2014. Problems of establishing national reference level for radon. Radiat. Hyg. 7 (4), 69e71. Zhukovsky, M.V., Yarmoshenko, I.V., 1997. Radon: Izmerenie, Dozy, Otsenka Riska (Radon: Measurement, Doses, Risk Assessment). UrO RAN, Ekaterinburg, p. 230 (in Russian). Zhukovsky, M., Yarmoshenko, I., 1998. Radon survey in the Ural region of Russia: results and analysis. Radiat. Prot. Manag. 2, 34e42. Zhukovsky, M., Onischenko, A., Bastrikov, V., 2010. Radon measurements e discussion of error estimates for selected methods. Appl. Radiat. Isot. 68 (4e5), 816e820. Zhukovsky, M.V., Yarmoshenko, I.V., Kiselev, S.M., 2011. Modern approach to regulation of radon exposure and analysis of consequences of its application in Russia. ANRI 4, 18e25 (in Russian).
Contents lists available at ScienceDirect
Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad
Reconstruction of national distribution of indoor radon concentration in Russia using results of regional indoor radon measurement programs I. Yarmoshenko*, G. Malinovsky, A. Vasilyev, M. Zhukovsky Institute of Industrial Ecology UB RAS, S. Kovalevskoy St., 20, Ekaterinburg 620219, Russia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 8 June 2015 Received in revised form 6 August 2015 Accepted 15 August 2015 Available online xxx
The aim of the paper is a reconstruction of the national distribution and estimation of the arithmetic average indoor radon concentration in Russia using the data of official annual 4-DOZ reports. Annual 4DOZ reports summarize results of radiation measurements in 83 regions of Russian Federation. Information on more than 400 000 indoor radon measurements includes the average indoor radon isotopes equilibrium equivalent concentration (EEC) and number of measurements by regions and by three main types of houses: wooden, one-storey non-wooden, and multi-storey non-wooden houses. To reconstruct the national distribution, all-Russian model sample was generated by integration of sub-samples created using the results of each annual regional program of indoor radon measurements in each type of buildings. According to indoor radon concentration distribution reconstruction, all-Russian average indoor radon concentration is 48 Bq/m3. Average indoor radon concentration by region ranges from 12 to 207 Bq/m3. The 95-th percentile of the distribution is reached at indoor radon concentration 160 Bq/m3. © 2015 Published by Elsevier Ltd.
Keywords: Radon Russia Distribution
1. Introduction Survey of indoor radon concentrations in a representative sample of houses is a significant stage of national and regional programs dealing with population radon exposure. Indoor radon survey provides the information on distribution of indoor radon concentrations in dwellings and other locations and retrieves the factors most influencing on indoor radon level. The results of indoor radon survey constitute the base for strategy of protection against radon and effective protection measures. According to its mission, UNSCEAR periodically reviews the results of national indoor radon surveys and estimates average worldwide indoor radon concentration as well as effective dose due to radon. Totally, results of indoor radon surveys from more than 60 countries were included in 2006 report (UNSCEAR, 2009). The UNSCEAR 2000 report gives population-weighted worldwide arithmetic and geometric mean (GM) values 39 and 30 Bq/m3 respectively with corresponding geometric standard deviation (GSD) 2.3 (UNSCEAR, 2000). In Russia, protection against radon is required by Federal Law
* Corresponding author. E-mail address: [email protected] (I. Yarmoshenko). http://dx.doi.org/10.1016/j.jenvrad.2015.08.007 0265-931X/© 2015 Published by Elsevier Ltd.
“On protection of population against radiation”. Since 1990, Russian Radiation Safety Standards (RRSS) include restriction on indoor annual equivalent equilibrium concentration of radon isotopes. This quantity is calculated as 222Rn EEC þ 4.6 220Rn EEC. In existing dwellings, the restriction is EEC of radon isotopes ¼ 200 Bq/m3. For new buildings, the more strength restriction is established, EEC of radon isotopes ¼ 100 Bq/m3. Protection of population of Russia against indoor radon is the responsibility of Russian Federal Service for Surveillance on Consumer Rights Protection and Human Wellbeing (Rospotrebnadzor). The approach to indoor radon problem in Russia, developed by Rospotrebnadzor in 1990-s and 2000-s, does not include the indoor radon survey in the national representative sample of buildings. The indoor radon measurements, which were performed in the frames of regional annual radiation monitoring programs, were focused on searching for high radon areas (Kormanovskaya and Stamat, 2010; Svetovidov et al., 2012). In order to control compliance with the restrictions of the RRSS, the measurements in all new buildings were another important task. According to these priorities, regional departments of Rospotrebnadzor were equipped mostly with short term radon measurements devices (grab sampling). Totally eleven types of devices for short term measurements of ECC of radon isotopes and eight types of devices for short term measurements of radon
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I. Yarmoshenko et al. / Journal of Environmental Radioactivity 150 (2015) 99e103
concentration are used (ISSDCR, 2014; Zhukovsky and Yarmoshenko, 1997; Zhukovsky et al., 2010). Such devices are relatively cheap and allow prompt control of exposure to radon progeny. Measurements of thoron ECC may be performed using the most of grab sampling devices. In Russia, exposure to thoron progeny is not considered to be an important problem in comparison with the radon progeny. In average, EEC of thoron with the factor 4.6 contributes only few Bq/m3 to ECC of radon isotope (Zhukovsky and Yarmoshenko, 1998; Yarmoshenko et al., 2002). Only few laboratories were equipped with long term nuclear track detectors (Marenny et al., 2000, 2005). In case of radon gas measurements, equilibrium factor F ¼ 0.5 is used in Russia (Yarmoshenko et al., 2014). Since 2001, Rospotrebnadzor established the Joint system of the control of the individual doses to the population and an information bank to collect the data of radiation measurements performed by regional departments and other laboratories (Svetovidov et al., 2012). Instructions and guidelines on reporting results of the population radon exposure control were developed by StPetersburg Research Institute of Radiation Hygiene after Professor P.V. Ramzaev (Stamat et al., 2014). Data in the information bank are annually reviewed and summary is published. Indoor radon data are presented in 4-DOZ Report (Rospotrebnadzor, 2007). Now, information of the 4-DOZ annual reports becomes the largest source of data on indoor radon exposure of population of the Russian Federation. The data collecting system is based on the average values by regions and doesn't include the information on dispersion of indoor concentration. Thus, there is no possibility to analyze the distribution of radon isotopes ECC radon exposure in Russian Federation that is important for optimization of protection against radon exposure (ICRP, 2014). The aim of our analysis is to reconstruct the national distribution of indoor radon concentration using these data. 2. Materials and methods For our analysis, we used 4-DOZ Reports issued by St-Petersburg Research Institute of Radiation Hygiene after Professor P.V. Ramzaev in the period from 2008 to 2013 (ISSDCR, 2009, 2011a, 2011b, 2012, 2013, 2014). The annual reports summarize the results of radiation measurements and dose assessment in 83 regions of the Russian Federation, which were presented to national data bank according to the requirements of special guidelines (Rospotrebnadzor, 2007). Measurements of indoor radon (222Rn) and thoron (220Rn) EEC and/or radon (222Rn) gas concentration are conducted within the regional radiation measurement programs of most of the regions. Annual summary 4-DOZ Report includes the average EEC of indoor radon isotopes (222Rn EEC þ 4.6 220Rn EEC) and the number of measurements by regions and by three main types of houses: wooden house, one-storey non-wooden house and multi-storey non-wooden house. The last two groups include houses built using mineral materials such as stone, brick, concrete etc. Thus, the average indoor radon isotopes EEC and the number of measurements represent results of annual regional program of radiation measurements in corresponding type of buildings. The distribution of indoor radon isotopes EEC in dwellings of Russia was reconstructed considering each annual regional program of measurements in the each type of buildings as the radon survey of a rural territory or a district of urban territory. For the purposes of the analysis, it was suggested that such quasi-surveys conducted over the period of 2008e2013 cover all territory of Russia. Consequently, all-Russian model sample can be generated by integration of sub-samples created using results of the quasisurveys.
In order to generate the sub-sample of indoor radon isotopes EEC under suggestion on lognormal distribution, it is necessary to know GM and GSD of radon isotopes EEC and the number of generated values (N). For the case of lognormal distribution, the GM can be calculated using the following equation:
! s2LN GM ¼ exp lnðAMÞ ; 2
(1)
where AM is arithmetic mean of radon isotopes EEC (Bq/m3) for each quasi-survey obtained from the 4-DOZ annual reports, sLN is the natural logarithm of the GSD. As mentioned above, the exact values of GSD for each quasisurvey are unknown. Therefore, we used some typical values, which were chosen depending on the number of measurements. The dependence of dispersion of indoor radon concentration values on number of measurements reflects higher variability of radon sources in larger territory. Factors influencing the variability are associated with both variation of radon geogenic potential and diversity of types of buildings (the detailed report devoted to factors influencing GSD is under publication). Accepted values of GSD are presented in Table 1. The number of generated values of radon isotopes EEC in the sub-samples was normalized by population of the region and the number of measurements in the frame of regional radiation monitoring program:
N
Npop $Nmeas ; Ntotal
(2)
where Npop is the population of the region; Nmeas is the number of measurements in this region in certain type of building in a certain year; Ntotal is the number of measurements in this region in all type of building for the period of 2008e2013. With regard to available computational resources the total size of modeled sample to reconstruct distribution of indoor radon concentrations in dwellings of Russia was limited by 60004. Then, the number of generated values for each i-th quasi-survey is chosen based on the condition SNi ¼ 60004. Totally data on 874 quasi-surveys were included to the analysis (surveys with Nmeas1000
235 445 89 105
1.8 2.1 2.7 3.0
Table 2 The number of the quasi-surveys and average size of sub-samples, (N, in brackets). Type of building
Year 2008
2009
2010
2011
2012
2013
Wooden houses One-storey brick and stone houses Multi-storey brick and stone houses
24 (42) 37 (11) 76 (152)
24 (31) 34 (12) 76 (110)
27 (25) 38 (13) 75 (111)
34 (22) 44 (14) 77 (108)
37 (20) 43 (11) 77 (99)
32 (26) 43 (14) 77 (105)
departments of Rospotrebnadzor of Russia requires special consideration with regard to applicability for the reconstruction of the national distribution of indoor radon concentration. The weak points that diminish reliability of the data are summarized below. Absence of common rigorous requirements on inclusion of the dwellings to annual regional radon measurements program decreases the quality of regional surveys. Application of short term indoor radon measurements increases the uncertainty of results, including both possible overestimation and underestimation of arithmetic mean. Absence of information on dispersion of indoor radon isotopes EEC in annual reports detracts accuracy of reconstruction of national distribution. It is necessary to say that each regional annual data set on indoor radon measurements can not be considered as a high quality representative indoor radon survey. The regional measurements programs are directed to search high radon dwellings and, to a lesser extent, to control radon in new buildings. Nevertheless, there are few reasons to undertake the reconstruction on the base of the regional measurements
100 p, % 90 80 70 60 50 40 30 20 10 0
5
10
50 Radon concentration, Bq/m3
100
200
Fig. 1. Reconstructed cumulative distribution of indoor radon concentration in dwellings of Russia.
programs. The measurements of indoor radon concentrations are conducted in most of regions of the country. At least 200 measurements are performed in 59 regions of 83 and more than 400 measurements e in the half of regions annually. The total number of indoor radon EEC measurements, over 400 000 during six years, is significant. Few regions where indoor radon measurements are not performed regularly are low populated. It is important that there are national scheme of metrological support and traceability of radon concentration measurements and national guidance system on protection against radon (Stamat et al., 2014). The national collecting of indoor radon measurements results was established about 15 years ago and current requirements for presentation of regional data to national data bank were issued in 2007. Thus, the national system of indoor radon control sustainably works for a quite long period. By results of reconstruction of the national distribution, allRussian average indoor radon concentration is 48 Bq/m3. Additional contribution of thoron EEC to indoor exposure is supposed to be low (Zhukovsky and Yarmoshenko, 1998; Yarmoshenko et al., 2002). If average thoron EEC is about 0.5 Bq/m3, then average radon isotopes EEC is 26 Bq/m3. The modeled indoor radon concentrations depend on the equilibrium factor, F. UNSCEAR (2000) considers F ¼ 0.4 as world typical value. However, for countries with climate colder than the planet average, higher equilibrium factor is expected. Our previous investigations in typical Russian dwellings (Zhukovsky and Yarmoshenko, 1998) and analyses of other authors have shown the lower disequilibrium between radon gas and radon daughters at low air exchange rate (Swedjemark, 1983). According to these investigations F ¼ 0.5 can be applied to estimate the average indoor radon concentration in Russian dwelling. Exposure of Russian population to indoor radon was previously estimated by Marenny et al. (2000, 2005). Marenny et al. (2005) divided the population into several categories depending upon two grades of radon geogenic potential (high and moderate), type of settlement (urban and rural) and floor (the ground floor, the first
Table 3 Parameters of the distributions of generated values of EEC of radon isotopes. Type of building
Arithmetic mean, Bq/m3
Geometric mean, Bq/m3
GSD
Percentage above 300 Bq/m3
Wooden houses One-storey brick and stone houses Multi-storey brick and stone housesa All types
75 59 46 48
37 32 24 25
3.1 3.0 3.0 3.1
3.5% 2.1% 1.1% 1.3%
a
Average over all floors.
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floor and higher floors). The values of GM and GSD for each category were derived from the radon surveys conducted using long term measurements in 2709 dwellings in seven regions of Russia in 1990-s (Marenny et al., 2000). Population weighted average indoor radon concentration was estimated to be about 52 Bq/m3 (Marenny et al., 2005). The advantage of analysis performed by Marenny et al. (2005) is the possibility to take into account the characteristics of dispersion of indoor radon concentration. At the same time that analysis was restricted only to few regions where long term measurements were conducted. All-Russian data were considered previously by Zhukovsky et al. (2011) and Baryshkov et al. (2013). Zhukovsky et al. (2011) reviewed 2009 annual 4-DOZ report (ISSDCR, 2011a) and suggested an average indoor radon EEC of 30 Bq/m3 for estimation of lung cancer risk associated with indoor radon exposure in Russia. According to the Joint system of the control of the individual doses to the population the total effective dose due to indoor and outdoor inhalation of short lived radon and thoron progeny is 1.97 mSv/year (Baryshkov et al., 2013; Onishenko and Romanovich, 2014), which corresponds indoor EEC of radon isotopes 28 Bq/m3. Thus, on the one hand, the previous estimations have provided quite consistent assessments of indoor radon exposure of population in range of indoor radon concentration from 50 to 60 Bq/m3. On the other hand, the dispersion of indoor radon concentration in dwellings was not considered in the previous assessments of the most recent and complete data. New analysis performed taking into account such dispersion resulted in slightly lower estimation (indoor radon concentration 48 Bq/m3) and allowed to reconstruct the distribution of indoor radon concentration in Russian dwellings. In comparison with other countries indoor radon concentration 48 Bq/m3 is moderate. It corresponds to 53rd percentile of national average indoor radon concentrations presented in UNSCEAR review and to 60th percentile if only large countries (area >200 000 km2) are considered (UNSCEAR, 2000, 2009). As can be seen in Table 3, higher average indoor radon concentration is observed in wooden houses (Table 3), which are usual in rural settlements. High radon concentration is considered to be associated with convective entry from the soil. More air-tight construction causes lower concentration in one-storey brick and stone houses. The lowest average indoor radon concentration is obtained in multi-storey apartment buildings, where the diffusion from building materials dominates over convection as the radon source (Vasilyev and Zhukovsky, 2013). Obtained value of GSD ¼ 3.1 reflects both the dispersion of reported average values and model dispersion of indoor radon concentration in the regions. The GSD values accepted to generate the model regional samples are rough approximation which is based on the dispersions typically observed in radon surveys, including regional surveys performed in some Russian region. For example, GSD value in Ekaterinburg was 3.0. According to UNSCEAR review (UNSCEAR, 2009) world average value of GSD is 2.2 and the range is from about 1 to 3.9. Researchers who developed Europe map of indoor radon accepted value GSD ¼ 1.8 as typical value to be applied for 10 10 km2 cell for dwellings on the first floor (Tollefsen et al., 2011). Dispersion of the results of radon measurements using the short term measurements, which are common in Rospotrebnadzor regional departments, should be higher than it is expected for long term measurements (Zhukovsky et al., 2010). Above considerations on current knowledge on dispersion of indoor radon concentration in different regions give evidences that uncertainty of accepted GSD is relatively high. Nevertheless, despite the high uncertainty, reconstructed percentiles of indoor radon isotopes concentration distribution (Fig. 1) can be applied to preliminary consideration of the strategy of protection of population of Russia against indoor radon. As can be
seen from Table 3 indoor radon isotopes EEC exceeds the restriction level 200 Bq/m3 in 0.71% of dwellings in Russia. This value together with average indoor radon concentration is important starting point for planning the remediation measures in the country. Reconstructed distribution can be used to discuss possible derived reference level of indoor radon concentration that can be introduced in Russia according to recent ICRP recommendations (ICRP, 2014). According to approach presented by Yarmoshenko et al. (2013, 2014) to establish the national derived reference level some percentile of the national distribution of indoor radon concentration can be used. For example, reconstructed 95-th percentile of indoor radon concentration in Russia is about 160 Bq/m3 and this level can be suggested as the optimized reference level of radon concentration. Performed reconstruction of indoor radon concentration distribution allows preliminary estimation of indoor radon concentration distribution in Russia. However it cannot substitute for the conventional national indoor radon survey. Reliable estimates of national average indoor radon concentration and pattern of distribution should be obtained by means of survey which is based on measurements on indoor radon concentration in a representative sample of dwellings using unified, preferably long term measurements technique. 5. Conclusion Since about 70 000 measurements of indoor radon concentration as well as radon and thoron EEC are conducted in dwellings annually in Russia, the total number of measurements performed during last years allows assessment of some average characteristics of population exposure. According to our estimations, average national indoor radon concentration is 48 Bq/m3. The 95th percentile of reconstructed distribution is about 160 Bq/m3. These figures can be applied for justification of population protection against radon in Russia. The most important weak points of available information about exposure are associated with the applied method of selecting the houses for measurements and application of grab sampling measurements. Average value of radon concentration may be biased due to large number of measurements both in potential radon affected areas and in new buildings. Short term grab sampling measurements introduce greater uncertainty to the results in comparison with nuclear track method. With regard to these limitations, proper optimization of the protection against radon within the system of radiation protection (justification, optimization and application of reference levels) could not be achieved. Conventional national indoor radon survey in Russia is necessary. The main task of such survey is to obtain unbiased estimate of average value and distribution of indoor radon concentration. At the same time the task of revealing radon affected areas can be considered to be already accomplished in Russia. Correct sampling of dwellings and using of long term measurements are the most important for designing national survey in Russia. Acknowledgments The research has been made under the financial support of Institute of Industrial Ecology, Project 15-IIE-01. References Baryshkov, N.K., Bratilova, A.A., Karmanovskaia, A.A., et al., 2013. Doses to the Population of the Russian Federation in 2012. Information Handbook. SPb, p. 67 (in Russian).
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