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Population exposure to inhaled radon and thoron progeny
232
Population exposure to inhaled radon and thoron progeny O. Iacob, C. Grecea, E. Botezatu Radiation Protection Department, Institute of Public Health, 14, Victor Babes Street, Iasi 6600, Romania
The radiation dose from inhaled radon and thoron progeny indoors is the dominant component of population exposure to natural radiation sources accounting for about 60 per cent in Romania. The radon and thoron short-lived decay product concentrations were measured in 760 typical urban and rural Romanian houses, randomly selected throughout the country.The method used to determine the volumetric activity of 218 Po, 214 Pb, 214 Bi and 212 Pb is the active one of sucking a known volume of air through an open-faced high-efficiency filter paper and counting the deposited activity with a ZnS(Ag) alpha scintillation counter. The detection limits were of 1 Bq m−3 for each of 218 Po, 214 Pb, 214 Bi and 0.1 Bq m−3 for 212 Pb. Internal exposures due to inhalation of radon and thoron progeny indoors and outdoors were expressed in terms of effective dose, individual and collective. The population-weighted averages of equilibrium equivalent concentration (EEC) of radon and thoron indoors were 25 Bq m−3 and 1.1 Bq m−3 respectively, with the corresponding average annual per capita effective dose of 1.88 mSv and 0.37–2.25 mSv in total. Outdoors values of EEC, were 5.7 Bq m−3 for radon progeny and 0.3 Bq m−3 for thoron progeny and the corresponding annual per capita effective doses were 0.14 mSv and 0.04 mSv, 0.18 mSv in total. The overall annual per capita effective dose arising from internal exposure to inhaled radon isotopes was estimated at 2.43 mSv with an associated annual collective effective dose of 55 112 man Sv.
1. Introduction The radiation dose from inhaled radon and thoron progeny indoors is the dominant component of population exposure to natural radiation sources accounting for about 60 per cent in Romania [1]. The objectives of our work were to determine the general distributions of radon and thoron progeny concentrations in dwellings, the magnitude of individual and collective exposures and to assess the potential lung cancer risk. Since our last study [2], we have extended the indoor radon and thoron progeny measurements in rural areas. The rural houses differ from those built in urban areas in structure, construction technology, design, building RADIOACTIVITY IN THE ENVIRONMENT VOLUME 7 ISSN 1569-4860/DOI 10.1016/S1569-4860(04)07026-3
© 2005 Elsevier Ltd. All rights reserved.
Population exposure to inhaled radon and thoron progeny
233
materials, and heating. They are usually single-family dwellings where raised levels of radon and thoron progeny are expected to occur because of their activity concentrations in subjacent ground and surrounding soil [3].
2. Materials and methods The radon and thoron short-lived decay product concentrations have been measured in 760 typical urban and rural Romanian houses, randomly selected throughout the country. The standardized method used to determine the volumetric activity of 218 Po, 214 Pb, 214 Bi and 212 Pb is the active one of grabbing a known volume of air (about 0.6 m3 ) through an open-faced highefficiency filter paper (98%) at known flow rate (0.01–0.08 m3 min−1 ) for a certain collection time (usually 10 minutes) and counting the deposited activity with a ZnS alpha scintillation counter (40% efficiency) during four counting intervals. A computer program, very versatile in handling multiple input parameters, has been developed to solve the decay equations for obtaining the activity concentrations of daughters in air, to calculate the equilibrium equivalent concentration (EEC), the potential alpha energy concentrations and the equilibrium factor F , for radon daughters. The detection limits of our method are, in optimum sampling and counting conditions, 1 Bq m−3 for each of 218 Po, 214 Pb, 214 Bi and 0.1 Bq m−3 for 212 Pb [4]. Internal exposure due to inhalation of radon and thoron progeny indoors and outdoors has been expressed in terms of effective dose [5]. In dose estimates, the dose conversion coefficients adopted by the UNSCEAR-2000 Report of 9 nSv (Bq h m−3 )−1 has been used for radon daughters, indoors and outdoors, and, for thoron progeny, of 40 nSv (Bq h m−3 )−1 indoors as well as outdoors [6]. An indoor occupancy factor of 0.75 and a population size of 22.68 million inhabitants have been considered in all calculations.
3. Results and discussion The results of all measurements show a log-normal distribution, as is illustrated in Fig. 1 for 222 Rn progeny and in Fig. 2 for 212 Pb, the most important short lived decay product of thoron. The average value of equilibrium factor F for indoor radon short-lived decay products was 0.51 ± 0.19, ranging from 0.1 to 0.9. The value of F varies in dwellings with ventilation rate and presence of aerosol sources such as smoking or cooking and is affected to some extent by the incoming air. High ventilation rate and low aerosol concentration give values of F significantly lower than 0.5. When ventilation is low and aerosol concentration is high the value of F is higher and so is also the dose. Figure 3 shows the results in histogram form. The results of our study, as equilibrium equivalent concentrations of radon and thoron and the resulting annual effective dose for an adult, are presented in Table 1. In detached houses, the average values of EEC of radon and thoron were 36.3 Bq m−3 and 1.4 Bq m−3 , respectively. In blocks of flats, these average values were approximately two times lower, 11.7 Bq m−3 for radon progeny and 0.8 Bq m−3 for thoron progeny. The population-weighted averages of the EEC of radon and thoron indoors have been estimated
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Fig. 1. Log-normal cumulative frequency plot of radon daughter concentrations.
Fig. 2. Log-normal cumulative frequency plot of 212 Pb concentrations.
Fig. 3. Distribution of equilibrium factor F for indoor radon daughters.
Population exposure to inhaled radon and thoron progeny
235
Table 1 EECs of radon and thoron and the resulting annual individual exposures (adult) Source of exposure
Location
Equilibrium equivalent concentration (Bq m−3 ) average
222 Rn daughters
220 Rn daughters
Indoors Detached house Block of flats Outdoors Indoors Detached house Block of flats Outdoors
25.0∗ 36.3 11.7 5.7 1.1∗ 1.4 0.8 0.3
range 10–564 3.8–21.6 2.0–8.3 0.2–6.4 0.2–2.8 0.1–0.6
Annual individual effective dose (mSv) average 1.48∗ 2.15 0.69 0.11 0.29∗ 0.37 0.21 0.03
range 0.59–33.3 0.22–1.28 0.04–0.17 0.05–1.68 0.05–0.59 0.01–0.05
∗ Population-weighted average.
Table 2 EECs of radon and thoron with respect to building materials Building material
Equilibrium equivalent concentration (Bq m−3 ) Radon daughters Thoron daughters average range average range
Brick Wood Adobe Raw clay Hollow masonry blocks Autoclaved concrete
19.0 ± 14.4 8.3 ± 5.8 18.5 ± 10.2 26.4 ± 16.2 13.7 ± 11.8 7.0 ± 3.5
2.3–564 1.6–37.8 2.5–101 5.5–375 2.7–39.0 3.4–13.3
0.68 ± 0.52 1.11 ± 0.79 1.46 ± 1.04 1.66 ± 1.27 0.77 ± 0.48 0.46 ± 0.27
0.1–5.9 0.2–6.4 0.1–12.8 0.1–6.1 0.3–1.9 0.2–0.9
at 25 Bq m−3 and 1.1 Bq m−3 , respectively. The corresponding values for outdoors were 5.7 Bq m−3 and 0.3 Bq m−3 for radon and thoron progeny, about 5 times smaller than indoors. Table 2 presents the average equilibrium equivalent concentrations of radon and thoron determined with respect to building materials. The average values of EEC of radon in rural dwellings varied from 7.0 to 26.4 Bq m−3 as a function of building materials used, with individual values ranging from 1.6 Bq m−3 to 564 Bq m−3 . The average values of EEC of thoron were between 0.46 Bq m−3 and 1.66 Bq m−3 taking into account the building materials. The individual values ranged from 0.1 Bq m−3 to 12.8 Bq m−3 . Data in Table 2 clearly indicate that rural houses built of raw clay in a wooden framework presented substantially higher radon and thoron levels than houses constructed of wood, brick or concrete blocks. The corresponding average individual annual effective doses are listed in Table 3. The average annual effective doses received by people living in houses constructed of different types of building materials had values between 0.53 mSv in cellular autoclaved concrete houses and 2.0 mSv in houses built of raw clay in a wooden framework from both radon and
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Table 3 Annual effective doses from 222 Rn and 220 Rn progeny with respect to building materials Building material Radon daughters average limits Brick Wood Adobe Raw clay Hollow masonry blocks Autoclaved concrete
1.12 ± 0.85 0.49 ± 0.34 1.09 ± 0.60 1.56 ± 0.96 0.81 ± 0.70 0.41 ± 0.21
Annual effective doses (mSv) Thoron daughters average limits
0.14–33.3 0.09–2.24 0.15–5.97 0.33–22.2 0.16–2.21 0.20–0.70
0.18 ± 0.14 0.29 ± 0.21 0.38 ± 0.27 0.44 ± 0.33 0.20 ± 0.13 0.12 ± 0.07
0.03–1.55 0.05–1.68 0.03–3.36 0.03–1.60 0.08–0.50 0.05–0.24
Total 1.30 ± 0.89 0.78 ± 0.39 1.47 ± 0.65 2.0 ± 1.37 1.01 ± 0.71 0.53 ± 0.22
Table 4 Annual effective doses and the estimated health effects Location
Exposure source
Annual per capita (mSv)
Effective dose collective (man Sv)
Potential number of radioinduced lung cancers
Indoors
222 Rn progeny
1.88 0.37 2.25
42 638 8392 51 030
3725
Total outdoors
0.14 0.04 0.18
3175 907 4082
298
Total
2.43
55 112
4023
220 Rn progeny
Total indoors Outdoors
222 Rn progeny 220 Rn progeny
thoron progeny inhalation. Table 3 also confirms that radon and thoron progeny inhaled in detached houses is the most variable source of human exposure, with annual exposures ranging over three orders of magnitude: from 0.09 mSv to 33.3 mSv for radon daughters and from 0.03 mSv to 3.36 mSv for thoron daughters. The estimated overall effective dose arising from internal exposure to inhaled radon isotopes in the course of a year is summarized in Table 4. The average annual per capita effective doses received by the population indoors were estimated at 1.88 mSv and 0.37 mSv from radon and thoron progeny respectively, 2.25 mSv in total. Exposures for children have been calculated on the assumption that effective doses for the age group of up to ten years might on average be a factor of 2 higher than for adults. The corresponding values outdoors (0.14 mSv and 0.04 mSv) are much smaller. The overall annual per capita effective dose arising from internal exposure to inhaled radon isotopes was estimated at 2.43 mSv with an associated annual collective effective dose of 55 112 man Sv. Implications for public health of radon and thoron progeny exposure indoors can be estimated from this collective dose by applying the nominal fatality and detriment coefficient of 7.3 × 10−2 Sv−1 adopted by the ICRP in its Publication 65 for risk assessment [7]. As an estimate, 4023 lifetime radio-induced lung cancers each year might be attributed to inhalation of radon and thoron short-lived decay products.
Population exposure to inhaled radon and thoron progeny
237
4. Conclusions This study on the population exposure to inhaled radon and thoron progeny in Romania led to the following results: – The values of indoor equilibrium equivalent concentrations of radon and thoron presented a log-normal distribution. – The average values of EEC of radon were 36.3 Bq m−3 in detached houses and 11.7 Bq m−3 in a block of flats with individual values ranging from 3.8 to 564 Bq m−3 . – The average values of EEC of thoron were 1.4 Bq m−3 in detached houses and 0.8 Bq m−3 in a block of flats, with individual values ranging from 0.2 to 6.4 Bq m−3 . – The indoor population-weighted average of the EECs of radon and thoron were estimated at 25.0 and 1.1 Bq m−3 , respectively. – The average annual effective dose for an adult was 1.48 mSv from indoor inhaled radon progeny, individual values ranging between 0.22 and 33.3 mSv. – The average annual effective dose for an adult from thoron progeny inhalation indoors was 0.29 mSv, individual values ranging between 0.05 and 1.68 mSv. – The corresponding average annual per capita effective doses were 1.88 and 0.37 mSv, 2.25 mSv in total. – Outdoors values of EEC of 5.7 for radon and 0.3 Bq m−3 for thoron and, consequently, the corresponding annual per capita effective doses (0.14 and 0.04 mSv, 0.18 mSv in total) are much smaller. – The overall annual per capita effective dose arising from internal exposure to inhaled radon isotopes was estimated at 2.43 mSv with an associated annual collective effective dose of 55 112 man Sv. As an estimate, 4023 lifetime radio-induced lung cancers each year might be attributed to inhalation of radon and thoron short-lived decay products by the Romanian population.
References [1] O. Iacob, J. Prev. Med. 4 (2) (1996) 73–82. [2] O. Iacob, C. Grecea, O. Capitanu, V. Rascanu, J. Prev. Med. 9 (2) (2001) 5–12. [3] O. Iacob, C. Grecea, in: International Conference of High Levels of Natural Radiation and Radon Areas, vol. 2, Munich, 2002, pp. 156–158. [4] ICRP Publication 60: 1990 Recommendations of the International Commission on Radiological Protection, Ann. ICRP 21 (1–3) (1991). [5] IRS, Romanian Standard SR-13397, 1997. [6] UNSCEAR, Exposures from natural radiation sources, Annex B in: Sources and Effects of Ionizing Radiation, UNSCEAR 2000 Report to the General Assembly, with Scientific Annexes, United Nations, New York, 2000, pp. 50–123. [7] ICRP Publication 65: Protection against radon-222 at home and at work, Ann. ICRP 23 (2) (1993).
Population exposure to inhaled radon and thoron progeny O. Iacob, C. Grecea, E. Botezatu Radiation Protection Department, Institute of Public Health, 14, Victor Babes Street, Iasi 6600, Romania
The radiation dose from inhaled radon and thoron progeny indoors is the dominant component of population exposure to natural radiation sources accounting for about 60 per cent in Romania. The radon and thoron short-lived decay product concentrations were measured in 760 typical urban and rural Romanian houses, randomly selected throughout the country.The method used to determine the volumetric activity of 218 Po, 214 Pb, 214 Bi and 212 Pb is the active one of sucking a known volume of air through an open-faced high-efficiency filter paper and counting the deposited activity with a ZnS(Ag) alpha scintillation counter. The detection limits were of 1 Bq m−3 for each of 218 Po, 214 Pb, 214 Bi and 0.1 Bq m−3 for 212 Pb. Internal exposures due to inhalation of radon and thoron progeny indoors and outdoors were expressed in terms of effective dose, individual and collective. The population-weighted averages of equilibrium equivalent concentration (EEC) of radon and thoron indoors were 25 Bq m−3 and 1.1 Bq m−3 respectively, with the corresponding average annual per capita effective dose of 1.88 mSv and 0.37–2.25 mSv in total. Outdoors values of EEC, were 5.7 Bq m−3 for radon progeny and 0.3 Bq m−3 for thoron progeny and the corresponding annual per capita effective doses were 0.14 mSv and 0.04 mSv, 0.18 mSv in total. The overall annual per capita effective dose arising from internal exposure to inhaled radon isotopes was estimated at 2.43 mSv with an associated annual collective effective dose of 55 112 man Sv.
1. Introduction The radiation dose from inhaled radon and thoron progeny indoors is the dominant component of population exposure to natural radiation sources accounting for about 60 per cent in Romania [1]. The objectives of our work were to determine the general distributions of radon and thoron progeny concentrations in dwellings, the magnitude of individual and collective exposures and to assess the potential lung cancer risk. Since our last study [2], we have extended the indoor radon and thoron progeny measurements in rural areas. The rural houses differ from those built in urban areas in structure, construction technology, design, building RADIOACTIVITY IN THE ENVIRONMENT VOLUME 7 ISSN 1569-4860/DOI 10.1016/S1569-4860(04)07026-3
© 2005 Elsevier Ltd. All rights reserved.
Population exposure to inhaled radon and thoron progeny
233
materials, and heating. They are usually single-family dwellings where raised levels of radon and thoron progeny are expected to occur because of their activity concentrations in subjacent ground and surrounding soil [3].
2. Materials and methods The radon and thoron short-lived decay product concentrations have been measured in 760 typical urban and rural Romanian houses, randomly selected throughout the country. The standardized method used to determine the volumetric activity of 218 Po, 214 Pb, 214 Bi and 212 Pb is the active one of grabbing a known volume of air (about 0.6 m3 ) through an open-faced highefficiency filter paper (98%) at known flow rate (0.01–0.08 m3 min−1 ) for a certain collection time (usually 10 minutes) and counting the deposited activity with a ZnS alpha scintillation counter (40% efficiency) during four counting intervals. A computer program, very versatile in handling multiple input parameters, has been developed to solve the decay equations for obtaining the activity concentrations of daughters in air, to calculate the equilibrium equivalent concentration (EEC), the potential alpha energy concentrations and the equilibrium factor F , for radon daughters. The detection limits of our method are, in optimum sampling and counting conditions, 1 Bq m−3 for each of 218 Po, 214 Pb, 214 Bi and 0.1 Bq m−3 for 212 Pb [4]. Internal exposure due to inhalation of radon and thoron progeny indoors and outdoors has been expressed in terms of effective dose [5]. In dose estimates, the dose conversion coefficients adopted by the UNSCEAR-2000 Report of 9 nSv (Bq h m−3 )−1 has been used for radon daughters, indoors and outdoors, and, for thoron progeny, of 40 nSv (Bq h m−3 )−1 indoors as well as outdoors [6]. An indoor occupancy factor of 0.75 and a population size of 22.68 million inhabitants have been considered in all calculations.
3. Results and discussion The results of all measurements show a log-normal distribution, as is illustrated in Fig. 1 for 222 Rn progeny and in Fig. 2 for 212 Pb, the most important short lived decay product of thoron. The average value of equilibrium factor F for indoor radon short-lived decay products was 0.51 ± 0.19, ranging from 0.1 to 0.9. The value of F varies in dwellings with ventilation rate and presence of aerosol sources such as smoking or cooking and is affected to some extent by the incoming air. High ventilation rate and low aerosol concentration give values of F significantly lower than 0.5. When ventilation is low and aerosol concentration is high the value of F is higher and so is also the dose. Figure 3 shows the results in histogram form. The results of our study, as equilibrium equivalent concentrations of radon and thoron and the resulting annual effective dose for an adult, are presented in Table 1. In detached houses, the average values of EEC of radon and thoron were 36.3 Bq m−3 and 1.4 Bq m−3 , respectively. In blocks of flats, these average values were approximately two times lower, 11.7 Bq m−3 for radon progeny and 0.8 Bq m−3 for thoron progeny. The population-weighted averages of the EEC of radon and thoron indoors have been estimated
234
O. Iacob et al.
Fig. 1. Log-normal cumulative frequency plot of radon daughter concentrations.
Fig. 2. Log-normal cumulative frequency plot of 212 Pb concentrations.
Fig. 3. Distribution of equilibrium factor F for indoor radon daughters.
Population exposure to inhaled radon and thoron progeny
235
Table 1 EECs of radon and thoron and the resulting annual individual exposures (adult) Source of exposure
Location
Equilibrium equivalent concentration (Bq m−3 ) average
222 Rn daughters
220 Rn daughters
Indoors Detached house Block of flats Outdoors Indoors Detached house Block of flats Outdoors
25.0∗ 36.3 11.7 5.7 1.1∗ 1.4 0.8 0.3
range 10–564 3.8–21.6 2.0–8.3 0.2–6.4 0.2–2.8 0.1–0.6
Annual individual effective dose (mSv) average 1.48∗ 2.15 0.69 0.11 0.29∗ 0.37 0.21 0.03
range 0.59–33.3 0.22–1.28 0.04–0.17 0.05–1.68 0.05–0.59 0.01–0.05
∗ Population-weighted average.
Table 2 EECs of radon and thoron with respect to building materials Building material
Equilibrium equivalent concentration (Bq m−3 ) Radon daughters Thoron daughters average range average range
Brick Wood Adobe Raw clay Hollow masonry blocks Autoclaved concrete
19.0 ± 14.4 8.3 ± 5.8 18.5 ± 10.2 26.4 ± 16.2 13.7 ± 11.8 7.0 ± 3.5
2.3–564 1.6–37.8 2.5–101 5.5–375 2.7–39.0 3.4–13.3
0.68 ± 0.52 1.11 ± 0.79 1.46 ± 1.04 1.66 ± 1.27 0.77 ± 0.48 0.46 ± 0.27
0.1–5.9 0.2–6.4 0.1–12.8 0.1–6.1 0.3–1.9 0.2–0.9
at 25 Bq m−3 and 1.1 Bq m−3 , respectively. The corresponding values for outdoors were 5.7 Bq m−3 and 0.3 Bq m−3 for radon and thoron progeny, about 5 times smaller than indoors. Table 2 presents the average equilibrium equivalent concentrations of radon and thoron determined with respect to building materials. The average values of EEC of radon in rural dwellings varied from 7.0 to 26.4 Bq m−3 as a function of building materials used, with individual values ranging from 1.6 Bq m−3 to 564 Bq m−3 . The average values of EEC of thoron were between 0.46 Bq m−3 and 1.66 Bq m−3 taking into account the building materials. The individual values ranged from 0.1 Bq m−3 to 12.8 Bq m−3 . Data in Table 2 clearly indicate that rural houses built of raw clay in a wooden framework presented substantially higher radon and thoron levels than houses constructed of wood, brick or concrete blocks. The corresponding average individual annual effective doses are listed in Table 3. The average annual effective doses received by people living in houses constructed of different types of building materials had values between 0.53 mSv in cellular autoclaved concrete houses and 2.0 mSv in houses built of raw clay in a wooden framework from both radon and
236
O. Iacob et al.
Table 3 Annual effective doses from 222 Rn and 220 Rn progeny with respect to building materials Building material Radon daughters average limits Brick Wood Adobe Raw clay Hollow masonry blocks Autoclaved concrete
1.12 ± 0.85 0.49 ± 0.34 1.09 ± 0.60 1.56 ± 0.96 0.81 ± 0.70 0.41 ± 0.21
Annual effective doses (mSv) Thoron daughters average limits
0.14–33.3 0.09–2.24 0.15–5.97 0.33–22.2 0.16–2.21 0.20–0.70
0.18 ± 0.14 0.29 ± 0.21 0.38 ± 0.27 0.44 ± 0.33 0.20 ± 0.13 0.12 ± 0.07
0.03–1.55 0.05–1.68 0.03–3.36 0.03–1.60 0.08–0.50 0.05–0.24
Total 1.30 ± 0.89 0.78 ± 0.39 1.47 ± 0.65 2.0 ± 1.37 1.01 ± 0.71 0.53 ± 0.22
Table 4 Annual effective doses and the estimated health effects Location
Exposure source
Annual per capita (mSv)
Effective dose collective (man Sv)
Potential number of radioinduced lung cancers
Indoors
222 Rn progeny
1.88 0.37 2.25
42 638 8392 51 030
3725
Total outdoors
0.14 0.04 0.18
3175 907 4082
298
Total
2.43
55 112
4023
220 Rn progeny
Total indoors Outdoors
222 Rn progeny 220 Rn progeny
thoron progeny inhalation. Table 3 also confirms that radon and thoron progeny inhaled in detached houses is the most variable source of human exposure, with annual exposures ranging over three orders of magnitude: from 0.09 mSv to 33.3 mSv for radon daughters and from 0.03 mSv to 3.36 mSv for thoron daughters. The estimated overall effective dose arising from internal exposure to inhaled radon isotopes in the course of a year is summarized in Table 4. The average annual per capita effective doses received by the population indoors were estimated at 1.88 mSv and 0.37 mSv from radon and thoron progeny respectively, 2.25 mSv in total. Exposures for children have been calculated on the assumption that effective doses for the age group of up to ten years might on average be a factor of 2 higher than for adults. The corresponding values outdoors (0.14 mSv and 0.04 mSv) are much smaller. The overall annual per capita effective dose arising from internal exposure to inhaled radon isotopes was estimated at 2.43 mSv with an associated annual collective effective dose of 55 112 man Sv. Implications for public health of radon and thoron progeny exposure indoors can be estimated from this collective dose by applying the nominal fatality and detriment coefficient of 7.3 × 10−2 Sv−1 adopted by the ICRP in its Publication 65 for risk assessment [7]. As an estimate, 4023 lifetime radio-induced lung cancers each year might be attributed to inhalation of radon and thoron short-lived decay products.
Population exposure to inhaled radon and thoron progeny
237
4. Conclusions This study on the population exposure to inhaled radon and thoron progeny in Romania led to the following results: – The values of indoor equilibrium equivalent concentrations of radon and thoron presented a log-normal distribution. – The average values of EEC of radon were 36.3 Bq m−3 in detached houses and 11.7 Bq m−3 in a block of flats with individual values ranging from 3.8 to 564 Bq m−3 . – The average values of EEC of thoron were 1.4 Bq m−3 in detached houses and 0.8 Bq m−3 in a block of flats, with individual values ranging from 0.2 to 6.4 Bq m−3 . – The indoor population-weighted average of the EECs of radon and thoron were estimated at 25.0 and 1.1 Bq m−3 , respectively. – The average annual effective dose for an adult was 1.48 mSv from indoor inhaled radon progeny, individual values ranging between 0.22 and 33.3 mSv. – The average annual effective dose for an adult from thoron progeny inhalation indoors was 0.29 mSv, individual values ranging between 0.05 and 1.68 mSv. – The corresponding average annual per capita effective doses were 1.88 and 0.37 mSv, 2.25 mSv in total. – Outdoors values of EEC of 5.7 for radon and 0.3 Bq m−3 for thoron and, consequently, the corresponding annual per capita effective doses (0.14 and 0.04 mSv, 0.18 mSv in total) are much smaller. – The overall annual per capita effective dose arising from internal exposure to inhaled radon isotopes was estimated at 2.43 mSv with an associated annual collective effective dose of 55 112 man Sv. As an estimate, 4023 lifetime radio-induced lung cancers each year might be attributed to inhalation of radon and thoron short-lived decay products by the Romanian population.
References [1] O. Iacob, J. Prev. Med. 4 (2) (1996) 73–82. [2] O. Iacob, C. Grecea, O. Capitanu, V. Rascanu, J. Prev. Med. 9 (2) (2001) 5–12. [3] O. Iacob, C. Grecea, in: International Conference of High Levels of Natural Radiation and Radon Areas, vol. 2, Munich, 2002, pp. 156–158. [4] ICRP Publication 60: 1990 Recommendations of the International Commission on Radiological Protection, Ann. ICRP 21 (1–3) (1991). [5] IRS, Romanian Standard SR-13397, 1997. [6] UNSCEAR, Exposures from natural radiation sources, Annex B in: Sources and Effects of Ionizing Radiation, UNSCEAR 2000 Report to the General Assembly, with Scientific Annexes, United Nations, New York, 2000, pp. 50–123. [7] ICRP Publication 65: Protection against radon-222 at home and at work, Ann. ICRP 23 (2) (1993).