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Soil and building material as main sources of indoor radon in Băiţa-Ştei radon prone area (Romania)
Journal of Environmental Radioactivity 116 (2013) 174e179
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it¸a-S¸tei radon Soil and building material as main sources of indoor radon in Ba prone area (Romania) Constantin Cosma a, Alexandra Cucos¸-Dinu a, Botond Papp a, *, Robert Begy a, Carlos Sainz a, b a b
Faculty of Environmental Science and Engineering, “Babes¸-Bolyai” University, Cluj-Napoca RO-400294, Romania Department of Medical Physics, Faculty of Medicine, Univ. of Cantabria, Santander ES-39011, Spain
a r t i c l e i n f o
a b s t r a c t
Article history: Received 4 November 2011 Received in revised form 10 September 2012 Accepted 12 September 2012 Available online 17 November 2012
Radon contributes to over than 50% of the natural radiation dose received by people. In radon risk areas this contribution can be as high as 90e95%, leading to an exposure to natural radiation 5e10 times higher than normal. This work presents results from radon measurements (indoor, soil and exhalation from building materials) in B ait¸a-S¸tei, a former uranium exploitation area in NW Romania. In this region, indoor radon concentrations found were as high as 5000 Bq m3 and soil radon levels ranged from 20 to 500 kBq m3. An important contribution from building materials to indoor radon was also observed. Our results indicate two independent sources of indoor radon in the surveyed houses of this region. One source is coming from the soil and regular building materials, and the second source being uranium waste and local radium reached material used in building construction. The soil as source of indoor radon shows high radon potential in 80% of the investigated area. Some local building materials reveal high radon exhalation rate (up to 80 mBq kg1 h1 from a sandy-gravel material, ten times higher than normal material). These measurements were used for the radon risk classification of this area by combining the radon potential of the soil with the additional component from building materials. Our results indicate it¸a-S¸tei area can be categorized as a radon prone area. that Ba Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved.
Keywords: Indoor radon Soil radon Soil permeability Radon potential Radon prone area Radon risk
1. Introduction Radon (222Rn) is present in both indoor and outdoor air because the parent radionuclide of it (226Ra) in the 238U decay series occurs in trace amounts throughout the Earth’s crust. Once formed, 222Rn, (with a half life of about 3.82 days), because it is chemically inert, can migrate through soil or foundation material, to reach the indoor atmosphere. Radon gas from soil, considered the most important source, enters house mainly through cracks in the building structure. Moreover, radon also enters from building material and from the water supply, and the concentration can reach high levels if air exchange is reduced (Cosma et al., 1996 a). Radon contribute in average with about 50% at the natural exposure of people in the whole world and it is considered as responsible for between 3 and 14% of lung cancer death, being proved the second main cause for this illness after smoking (WHO, 2009). In radon risk areas (radon prone areas) this contribution can be much higher, growing the natural dose exposure of 5e10 times. Over time, epidemiological studies have demonstrated an evidence
* Corresponding author. Tel.: þ40 264 307030; fax: þ40 264 307032. E-mail address: [email protected] (B. Papp).
of correlation between radon exposure and lung cancer, even in case of low levels of radon in residential buildings. Unfortunately, the effort of the authorities to work towards in order to reduce the number of lung cancers related to radon exposures is still far from successful in some countries (WHO, 2009). Radon concentration in indoor air has been measured in many countries worldwide in a large number of buildings mostly as a result of the application of radon policies and regulation requirements (WHO, 2009; UNSCEAR, 2006; ICRP 115, 2010). The approach of indoor radon studies in connection with radon gas from soil and building material are due to presence of such factors linked to the underlying geological formations and building structure, which could lead to increased levels of radon inside houses (Barros-Dios et al., 2007). Several studies have performed radiological measurements in areas with a former uranium mine and have revealed a significant association between the uranium content of soil and high indoor radon concentration (Singh et al., 2002; Somlai et al., 2006; Barros-Dios et al., 2007). Although, radon from soil and rocks and from the basement of the buildings represents the main radon sources. Another study in UK indicates that radon emanation from building materials have significant contribution to increased indoor radon concentrations in some houses (Denman et al., 2007).
0265-931X/$ e see front matter Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jenvrad.2012.09.006
C. Cosma et al. / Journal of Environmental Radioactivity 116 (2013) 174e179
The present study represents a part of an extensive research on indoor radon exposure in the region of Transylvania-Romania. The most important high background radiation area in Transylvania it¸a-S¸tei (Bihor County), where the highest indoor was located in Ba radon concentrations have been found (Cosma et al., 2009; Sainz -Popa et al., 2010; Cucos¸-Dinu et al., 2012). et al., 2009; Trut¸a Another radon prone area was identified at Herculane Spa situated in a granitic zone (Cosma et al., 1996 a, Cosma et al., 1996 b). The aim of this work is to highlight a connection between the high indoor radon levels and the underlying soil and building material identified both as the main radon sources for houses of B ait¸a-S¸tei radon-prone area. 2. Material and methods it¸a-S¸tei is located in the Bihor Mountains (NW part The area of Ba it¸a” of Romania) in the neighborhood of “Avram Iancu” and “Ba it¸auranium mines. This includes the town S¸tei and few villages (Ba Plai, B ait¸a-Sat, Nucet, Fânat¸e, Cîmpani etc.), with a total of approximately 15.000 inhabitants (see Fig.1). 2.1. Indoor radon measurements Integrated indoor radon measurements were performed in 335 it¸a-S¸tei area between 2008 and 2010, in randomly dwellings of Ba selected houses. For indoor radon level measurements CR-39 tracketched detectors were used, according to the NRPB Measurements Protocol (Sainz et al., 2009; Miles and Howarth, 2000). Solid state track detector CR-39 is used widely in the field of health physics, such as for radon monitoring or neutron dosimetry. Alpha track detectors are not expensive, reliable and easy to use. Every CR-39 detector was placed under the cap of a cylindrical polypropylene container of 5.5 cm height and 3.5 cm diameter, with a small opening in its upper part which prevents radon decay products and also thoron (220Rn) entering (RADOPOT). Only alpha particles from 222 Rn that diffuse into the container and from the two polonium isotopes (218Po and 214Po) produced inside, can hit the detector (Sainz et al., 2009). In order to evaluate average indoor radon concentrations, the detectors were exposed in the inhabited areas of dwellings, such as bedrooms and living-rooms, at a height of 1.0e1.5 m from the floor, and for a time of 2 or 3 months. After the exposure, the etching process and the automatic reading of all detectors have been made in the Laboratory of Environmental Radioactivity of Babes¸-Bolyai University, using RadoSys-2000 equipment (Elektronika, Budapest, Hungary).
it¸a-S¸tei radon-prone area (in Bihor County). Fig. 1. The zone of Ba
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Radon concentration can be determined by counting the tracks in a given area. The individual error of radon measurements was estimated at less than 10%. The accuracy of the detection system has been periodically checked by the successful participation in national and international radon intercomparison exercises with National Institute of Physics and Nuclear Engineering (IFIN) of Bucharest, Radon Laboratory of Cantabria University, Spain and National Institute of Radiological Sciences of Chiba, Japan, during the period 2007e2011 (Cosma et al., 2009; Janik et al., 2009). 2.2. Radon in soil measurements it¸aThe preliminary radon in soil measurements in the area of Ba S¸tei were performed in 2010 autumn, when relatively dry conditions prevailed in the area. The aim of the measurements was the determination of the radon potential of soil, in order to classify this area from the point of view of radon risk. For this, 30 measurements of radon concentration in soil and of the soil permeability were performed, at 10 places in the whole area. 2.2.1. Method for measuring radon activity concentration in soil The experimental method of the radon concentration measurements was based on the sampling of the soil gas and measuring the activity concentration of 222Rn gas, using the LUK3C radon detector and accessories. The measurement principle of the LUK3C device lays on a scintillation detection technique with Lucas cells, by determining the activity directly from the alpha decay of 222 Rn and progeny. The efficiency of this technique is (2.2 counts sec1) to 1 Bq of radon activity deposited into the Lucas cell, when 222Rn is in equilibrium with its progeny (Plch, 1997). For the extraction of soil gas, a steel sampling probe was used. The probe was inserted into the soil to a minimum depth of 50 cm, and was retracted some cm back, in order to create a small cavity in soil for gas extraction. For soil gas sampling was used a Janet syringe with the volume of 150 ml (same volume as that of the Lucas cell). The syringe was connected to the upper end of the sampling probe. Before the measurement of the activity of the radon gas, the flux of radon gas from soil must forced by three consecutively extractions to avoid contaminating with atmospheric air. Only the third extraction of the soil gas (with volume of the syringe equal of Lucas cell) was introduced into the detector cell with the help of a preliminary vacuum technique. Before inserting the soil gas sample into the Lucas cell a delay time of about 3e4 min was used, for the decaying of 220Rn (thoron) gas below to 10% of its initial content. Because the half-life of 220Rn (55.6 s) is much shorter than the half-life of 222Rn (3.82 days), thoron effectively decays in short time (5 min). After the insertion of the soil gas sample into the Lucas cell, the detector starts several countings (from 1 to 10) of the alpha decays from 222Rn, and it stops when statistic errors become lower than 5%. Finally, the detector gives an average radon concentration, which was corrected by the background of the measurement process (Cosma et al., 2010). In this way, the total time of a single measurement is no more than 10 min. The scheme for the soil gas sampling and its insertion into the detector is shown in Fig. 2. 2.2.2. Method of measuring permeability of soil Permeability measurements were performed by a method based on the measuring the empty time (i.e. flow rate) of a water column from a bottle, that was connected directly to the same probe inserted in soil, described in the method for measuring radon concentration in soil (see Fig. 2). For this, the two extremities of the bottle were equipped with two valves and the top part of the bottle (through the tap) was connected directly to the soil probe (see Fig. 3).
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time is short (in the order of seconds), the permeability is high, and if the measured empty-time is long (in the order of tens of minutes), the permeability is low (Cosma et al., 2010; Papp et al., 2009). The principle and the theory for the determination of soil permeability k [m2] from the empty-time t[s] of water from the bottle is similar with the Radon-Jok permeameter, which represents an international reference in the field (Neznal et al., 2004; Barnet et al., 2008; Neznal and Neznal, 2005). The range for the measured permeability values by this method are from very high permeability (in the order of 108 m2), corresponding to an emptytime of 11 s, to ultra low permeability (in the order of 1014 m2), corresponding to an empty time of 40 min.
Fig. 2. The schemes for the sampling of soil gas and its insertion into the Lucas cell of the LUK3C detector.
2.2.3. Determination of the radon potential and the radon index of soil For the radon risk estimation of a given place or building site, the radon potential of the soil (RP), can be defined by the following expression (Neznal et al., 2004; Barnet et al., 2008):
RP ¼ ðCRn 1Þ=ðlog k 10Þ The depth of the probe inserted in the soil was the same as at radon concentration measurements in soil gas (minimum 50 cm). In the case of soil permeability measurements it is important the geometrical sizes of the active space created in the soil, in order to determine quantitatively the permeability of the soil. In the process of the permeability measurements, the gravitational flow-out of the water column (through a second tap on the bottom part of the bottle) creates a pressure difference in the bottle, that depends on the extraction rate of the soil gas. By measuring the empty-time (t [sec]) of a known water quantity from the bottle it can be determined the permeablity of the soil (k [m2]). As the measured empty-
where, CRn [kBq m3] is the measured radon concentration in soil, and k [m2] is the permeability of soil. In these estimations, radon concentration values lower than 1 kBq m3 were excluded, which is not characteristic for radon levels in soil. Also, radon concentration values higher than other values (of three times) measured at the same place were excluded, as local anomalies of a site (Neznal et al., 2004; Barnet et al., 2008). Because most of the soils in B ait¸a-S¸tei area having high permeability (for sandy soils), values lower than 4,1013 m2 were excluded. From the remaining values for radon concentrations and permeability, the highest was decisive for radon potential calculations (Neznal et al., 2004; Barnet et al., 2008). According to “The new method of the radon risk assessment of the building sites”, the values for radon potential of soil can be classified in the following ranges: low risk (for RP < 10), medium risk (for 10<¼RP < 35), and high risk (for RP>¼35), and it is dimensionless (Neznal et al., 2004; Barnet et al., 2008). 2.3. Radon exhalation measurements from building material
Fig. 3. The system for soil permeability measurements, consist from a soil probe inserted in soil, and the bottle filled with water and equipped with the two valves.
In order to measure radon exhalation rate from building materials, bricks, gravels or stones, radon concentration is determined in a tight vessel into which radon diffuse. The increase of the radon concentration in time was measured by Radim3A radon monitor, in Eman version. In this case, the vessel was mounted and sealed to the detection chamber of the Radim-Eman radon monitor, which is screwed to the base plate. On the base plate, is glued a gasket, made of soft rubber. When exhalation from the material (stones or bricks) is measured, the sample is inserted into the vessel and the vessel is mounted up to the base plate of the detection chamber (see Fig. 4). (Radim 3A-Eman, 2004). The analyzed building material sample comes from a village of it¸a-S¸tei area (in the name Fanate), from a dump of gravel-stone. Ba The sample was dried at a temperature of w70 C, and was divided into three grain fractions. The first was a sample from sandy-gravel fraction with grains diameter of 1e2 mm, the second was a sample of gravel fraction with grains diameter between 5 mm and 2 cm, and the third was a sample from stone fraction with grains diameter larger then 2 cm. The exhalation rate of radon gas from the sample (ER) is given in unit as [Bq kg1 h1]. During the measurements, radon concentration growing in time, and tends to an equilibrium value. This equilibrium value depends on the grail size dependence (Morawska
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Fig. 5. The distribution of the measured indoor radon concentrations in the 335 dwellings from Bait¸a-S¸tei area.
Fig. 4. Scheme of the system for radon exhalation measurements: radon monitor (RADIM-EMAN, in the upper part), closed to the radon receiver container (in the middle part) and the vessel that contains the sample as radon source (in the bottom part).
and Phillips, 1993; Breitner et al., 2010), on the emanation factor of 222 Rn atoms from the sample (i.e. from the mineral grains), on the 226 Ra (radium) content of the sample. As importance is the dependence on the moister content and pore characterization, and the tightness of the vessel and detection chamber (Nazaroff and Nero, 1988; Cosma et al., 2001). Through the radon exhalation measurement, the first part it can be considered to have a constantly linear increasing rate. Therefore, the rate of the increase can be the slope of the fitted line, denoted as r [Bq m3 h1]. From the slope r [Bq m3 h1] of the fitted line we determined the exhalation rate of radon gas (ER) by the:
ER ¼ r$Vair =Ms where, Vair [m3] is the volume of the air inside the vessel, that is determined from the total volume of the entire container (radon receiver and radon source containers, Vtot ¼ 4.0 L), reduced by the volume of the sample (Vs), and Ms [kg] is the mass of the sample.
exposure of population (WHO, 2009). For about 30% of all studied dwellings the radon concentration exceeds the threshold of 300 Bq,m3 recently recommended as a reference level by ICRP in the latest Statement on Radon (ICRP 115, 2010). From the radon distribution dataset it can be observed a double log-normal distribution. The statistical calculations for the first part of the distribution gives the following parameters: geometric mean of 135 Bq m3, median of 123 Bq m3, arithmetic mean of 202.2 Bq m3, and for the second part: geometric mean of 764 Bq m3, median of 736 Bq m3, arithmetic mean of 858 Bq m3. The double log-normal distribution can be related the existence of two independent sources of indoor radon in the houses of the area. The first maximum (81e 120 Bq m3) could be explained from the source of soil and normal building material and the second (601e3000 Bq m3) could come from uranium waste used in building constructions or/and building local materials with high uranium and radium content. The main reasons for high indoor radon concentrations in this region could be explained by the using of uranium tailings from the area of uranium mines. The mine was operated in the period of 1952e1998 when many houses were built using radioactive tailings from mine or building material (sand, gravel, etc) from the Cris¸it¸a river bad having increased amounts of radium and uranium Ba (Sandor et al., 1999). 3.2. Radon potential and the radon index results
3. Results and discussions 3.1. Indoor radon results The distribution of the measured indoor radon concentrations by solid state track detectors are shown on Fig. 5, where the concentration values were in the wide range from 15 to 2200 Bq m3, depending on the ventilation rate, construction material of the houses and of the soil permeability under the building. Considering the geological and the seasonal corrections, the annual average value of the radon concentration for B ait¸a-S¸tei area is 343.5 Bq m3, which is 4.16 times higher than the average indoor radon concentration of 82.5 Bq m3 reported for Transylvania (Cosma et al., 2009; Sainz et al., 2009). This value confirms previous studies which have classified this region as a radon-prone area (Cosma et al., 2009; Sainz et al., 2009; Trut¸ a-Popa et al., 2010; Cucos¸-Dinu, et al., 2012). Indoor radon concentrations in monitored region are significantly higher than the recommended level of 100 Bq m3 for residential
The results of the radon concentration measurements in soil and it¸a-S¸tei area are summaof soil permeability measurements in Ba rized in the Table 1. The radon risk category (i.e. radon index (RI)) of the investigated sites are shown in the last column of the Table 1. According to “The new method of the radon risk assessment of the building sites”, the majority of the investiganted places show high radon risk (RI), for which the radon potential RP > 35 (Neznal et al., 2004; Barnet et al., 2008). This can be explained in one hand by the high soil permeabilities of the investigated places (78% of the places having permeabilities over than 4,1012 m2). On the other hand, places take part to this category of permeability, radon concentrations higher than 30 kBq m3 resulting high radon risk (86% from concentration values), and concentrations bettween 10 and 30 kBq m3 resulting medium radon risk (14% from the values). As we mention, the last place Bǎit¸a-Plai (see last line in Table 1) shown very high radon risk (with RP ¼ 1607.2). This is characteristic for the place, because closed to this (at a distance of 1000 m) is
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Table 1 The measured soil radon concentration values and errors (CRn dCRn) with the soil permeability values (k), and the calculated values of the radon potential (RP) with the radon indexes (RI). (The number in bellow the name of each site represent the number of measurements performed at the site. The parameter D[m] is the depth from that the soil gas was sampled). place
D [m]
CRn dCRn [kBq m3]
S¸tei (3)
0.8 0.8 0.8 0.8 0.8 0.7 0.7 0.7 0.8 0.6 0.6 0.5 0.65 0.7 0.8 0.8 0.8 0.8 0.8 0.8 0.6 0.8 0.8 0.8 0.4 0.4 0.4 0.5
44.1 40.2 22.3 22.0 30.1 53.5 54.5 63.4 159.5 58.1 59.1 61.3 46.9 27.1 11.9 7.9 45.4 128.7 23.1 5.5 7.6 42.2 35.2 16.6 462.9 398.5 446.1 512.0
Lunca S¸tei (2) Cîmpani (4)
Fânat¸e 68 (2) Nucet Popas (2) Nucet Cris¸ (1) Bǎit¸a 204 (5)
Bǎit¸a 206 (5)
Bǎit¸a Plai (4)
2.0 2.0 1.0 1.2 1.5 2.6 2.6 2.9 7.8 2.7 2.6 2.8 2,1 1.3 0.7 0.5 2.0 5.1 1.1 0.5 0.5 1.2 1.5 0.8 13.3 12.0 13.0 14.0
k [m2] 1.7E-12 2.4E-12 2.4E-11 1.9E-13 3.0E-13 1.2E-11 2.4E-11 2.4E-11 7.1E-12 6.8E-13 e 9.8E-12 2.4E-11 5.2E-11 High High High 1.8E-11 2.8E-13 1.3E-11 High 2.7E-11 High High 3.3E-11 e e 4.8E-11
RP
RI
69.8
High
11.5
Medium
101.1
High
26.8
Medium
59.8
High
93.2 59.1
High High
73.0
High
1607.2
High
it¸a-Plai”, where the soil has very situated the old uranium mine “Ba high uranium content. 3.3. Radon exhalation results The results of the radon exhalation measurements (i.e. radon concentration versus time) of the three samples having different grains fractions are shown in Fig. 6. The radon concentration growing during the measurement and tends to an equilibrium value. From Fig. 6 it can be seen that in the first part of the measurements (in about the first 18 h) the growing rate of the radon concentration can be considered to be constantly linear, in all three cases. The results of the linear fits and of the calculations are shown in the Table 2, which contains the values of the radon exhalation rates (ER) for the three fractions, which depends on the values of the slopes (r), on the air volume inside the vessel (Vair) and on the mass of the samples (M). Results of the laboratory measurements on the three samples of different grain size and calculations show different exhalation rates. The first two samples (sandy gravel with smallest grain sizes and gravel with grain size of some cm) had the same radon exhalation rates, while the third (normal stone with big grain size) sample have lower radon exhalation rate. The radon exhalation of
Table 2 Results of the slope (r) of the increasing radon concentrations from the linear fits, and the determined radon exhalation rate (ER) with errors, for the three samples (i.e.grain size). Samples
r dr [Bq m3 h1] Vair [L] M [kg] ER dER [mBq kg1 h1]
Sandy gravel 34.2 1.5 Gravel 41.4 1.6 Stone 4.3 1.3
3.4 3.3 3.3
1.4 1.7 1.7
84.1 3.7 81.4 3.1 8.4 2.6
Fig. 6. The increasing of the radon concentration (CRn) in time (t) for the first part (linear part) of the measurement. The squares corresponds to the data from sandygravel sample, the circles corresponds to the data from gravel sample, and the triangles corresponds to the data from stone sample, with the corresponding error bars. The lines are the linear fits to the three concentration data sets for which the values of the correlation coefficients (R2) are: 0.98 (for sandy-gravel), 0.97 (for gravel) and 0.40 (for stone).
the sandy gravel and gravel was of ten times higher (i.e. with one order) then the exhalation of the stones. It is well known that the exhalation rate (i.e. radon exhalation) depends on the emanation factor of 222Rn atoms from the sample (i.e. from the mineral grains), on the 226Ra (radium) content of the sample, on the moisture content, (Nazaroff and Nero, 1988; Cosma et al., 2001) and also from the grain size of the samples, which is well described in Morawska and Phillips (1993) and Breitner et al., 2010. Consistent with our results, several studies have carried out regarding the soil and indoor radon measurements in areas of former uranium mines and have pointed out a significant association between the uranium content of soil and high indoor radon concentration (Somlai et al., 2006; Abdallah and Khalid, 2008; Khan and Puranik, 2011). The annual average indoor radon concentration for all our measurements (the both two groups) of 345 Bq m3 is similar to value found in a Hungarian uranium mine area (Somlai et al., 2006) of about 400 Bq m3 and higher than those of 100 Bq m3 reported for an Indian uranium mining area (Khan and Puranik, 2011). If we refer only to the first group from Fig. 2 (an average of w100 Bq m3) it can be seen that our results are similar to those from Indian area. The Jordanian study about soil radon and indoor radon connection (Abdallah and Khalid, 2008) performed in a non uranium area is rather relevant also in our case (100 Bq m3 radon in soil produces 1 Bq m3 indoor radon). The similarities and the difference of these annual average results comming firstly from the geological characteristics of the mentioned uranium areas (i.e. amount of uranium content of the soils and permeability of the soils. The uranium content of the soils determines the concentration of radon gas in soil, and the permeability of the soils is an important parameter which determines the entry rate of radon gas to the buildings indoor. 4. Conclusions The paper presents integrated indoor radon levels from 335 dwellings performed in several villages of Bǎit¸a-S¸tei radon prone area (in Bihor County), near an old uranium mine, during 2008e 2010. The results indicate an annual average value of indoor
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radon concentrations of about 343.5 Bq m3, which is 4.16 times higher than the average indoor radon concentration of 82.5 Bq m3estimated for Transylvania (e.g. NW part of Romania). Statistical calculations on the distribution of the indoor radon values give a double lognormal distribution. This double distribution means that there are two independent sources of indoor radon in the houses of the area. The first source coming from soil and normal building material and the second is coming from uranium waste and high uranium content of material used in building constructions. For characterizing radon potential of soil, were performed radon in soil and permeability of soil measurements at 10 selected places. The results of the estimations provide that the majority of the investigated places shown high radon risk (80% having high radon it¸a-S¸tei potential). The second main source of the indoor radon in Ba uranium area is building materials and uranium waste. The material containing a mixture of sandy-gravel and stone, used as building material in the area shows highest radon exhalation. Therefore, this material has an important contribution to radiation doses for population in houses which uses as building material. This survey has been carried out within the framework of a European Research Project focused on the reduction of radon exposure received by population living in surroundings of a former uranium mine in Bǎit¸a-S¸tei radon prone area. The project fulfills the requirements of a national radon program including detailed indoor radon campaigns together with radiological characterizations of the soil and building materials as a radon sources. In the near future, this study will also covering the testing and implementation of the most effective remedial solutions in 20 homes with the highest indoor radon levels. Acknowledgment This work represents a part of research study supported by the project 586-12487, Contract No. 160/15.06.2010 with the title “IMPLEMENTATION OF RADON REMEDIATION TECHNIQUES IN DWELLINGS OF BǍIT¸A URANIUM MINE AREA/IRART” of the Sectoral Operational Programme “Increase of Economic Competitiveness” co-financed by The European Regional Development Fund. References Abdallah, I.M., Khalid, M.A., 2008. Evaluation of radon gas concentration in the air of soil and dwellings of Hawar and Foara villages, using (CR-39) detectors. Radiation Measurements 43 (1), 452e455. Barnet, I., Pacherová, P., Neznal, M., Neznal, N., 2008. Radon in Geological Environment e Czech Experience, Special Papers No. 19. Czech Geological Survey, Prague, pp. 25e30. Barros-Dios, J.M., Ruano-Ravina, A., Gastelu-Iturri, J., Figueiras, A., 2007. Factors underlying residential radon concentration: results from Galicia, Spain. Environmental Research 103 (2), 185e190. Breitner, D., Arvela, H., Hellmuth, K.H., Renvall, T., 2010. Effect of moisture content on emanation at different grain size fractions e a pilot study on granitic esker sand sample. Journal of Environmental Radioactivity 101 (11), 1002e1006. Cosma, C., Ristoiu, D., Cozar, O., Znamirovschi, V., Daraban, L., Râmboiu, S., Chereji, I., 1996 a. Studies on the occurence of radon in selected sites of Romania. Environment International 22 (1), 61e65.
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Cosma, C., Ristoiu, D., Poffijn, A., Meesen, G., 1996 b. Radon in various environmental samples in the Herculane Spa, Cerna Valley, Romania. Environment International 22 (1), 383e388. Cosma, C., Dancea, F., Jurcut, T., Ristoiu, D., 2001. Determination of 222Rn emanation fraction and diffusion coefficient in concrete using accumulation chambers and the influence of humidity and radium distribution. Applied Radiation and Isotopes 54, 467e473. Cosma, C., Szacsvai, K., Dinu, A., Ciorba, D., Dicu, T., Suciu, L., 2009. Preliminary integrated indoor radon measurements in Transylvania (Romania). Isotopes in Environmental and Health Studies 45 (3), 259e268. Cosma, C., Papp, B., Moldovan, M., Cosma, V., Cindea, C., Suciu, L., Apostu, A., 2010. Measurement of radon potential from soil using a Special method of sampling. Acta Geophysica 58 (5), 947e956. , D., Cucos¸ (Dinu), A., Cosma, C., Dicu, T., Begy, R., Moldovan, M., Papp, B., Nit¸a it¸a Burghele, B., Sainz, C., 2012. Thorough investigations on indoor radon in Ba radon-prone area (Romania). Science of the Total Environment 431, 78e83. Denman, A.R., Groves-Kirkby, N.P., Groves-Kirkby, C.J., Crockett, R.G.M., Phillips, P.S., Woolridge, A.C., 2007. Health implications of radon distribution in living rooms and bedrooms in U.K. dwellings e a case study in Northamptonshire. Environment International 33 (8), 999e1011. ICRP 115 (International Commission on Radiological Protection), 2010. Lung Cancer Risk From Radon and Progeny and Statement on Radon. ICRP Publication 115 Ann. ICRP, p. 40. Janik, M., Tokonami, S., Kovács, T., Kávási, N., Kranrod, C., Sorimachi, A., Takahashi, H., Miyahara, N., Ishikawa, T., 2009. International intercomparisons of integrating radon detectors in the NIRS radon chamber. Applied Radiation and Isotopes 67 (9), 1691e1696. Khan, A.H., Puranik, V.D., 2011. Radon in the environment and in dwellings in a uranium mining area in Eatern India: an overview. Radiation Protection Dosimetry 145 (2e3), 198e201. Miles, J.C.H., Howarth, C.B., 2000. Validation Scheme for Laboratories Making Measurements of Radon in Dwelling: 2000. Revision NRPB e M1140. National Radiological Protection Board, Chilton, p. 11. Morawska, L., Phillips, C.R., 1993. Dependence of the radon emanation on radium distribution and internal structure of the material. Geochimica et Cosmochimica Acta 57 (8), 1783e1797. Nazaroff, W.W., Nero, A.V., 1988. Soil as a Source of Indoor Radon: Generation, Migration and Entry: Radon and Its Decay Products in Indoor Air. A WileyInterscience Publication, pp. 57e112. Neznal, M., Neznal, M., 2005. Permeability as an important parameter for radon risk classification of foundation soils. Annals of Geophysics 48 (1), 175e180. Neznal, M., Neznal, N., Matolín, M., Barnet, I., Miksova, J., 2004. The New Method for Assessing the Radon Risk of Building Sites. Special Papers No. 16. Czech Geological Survey, Prague. , C.D., Moldovan, M., 2009. Soil Radon Measurements in Papp, B., Cosma, C., Nit¸a Cluj-napoca (Romania). 5th Hungarian Radon Forum. Pannon Univ. Press. 47e52. Plch, J., 1997. Manual for Operating LUK 3C Device, Jiri Plch, M. Eng. SMM, Prague. Sainz, C., Dinu, A., Dicu, T., Szacsvai, K., Cosma, C., Quindós, L.S., 2009. Comparative risk assessment of residential radon exposures in two radon-prone areas, S¸tei (Romania) and Torrelodones (Spain). Science of the Total Environment 407 (15), 4452e4460. Sandor, G.N., Poffijn, A., Cosma, C., 1999. Indoor radon survey in an uranium area from Romania. In: Radon in the Living Environment, pp. 1101e1104. Athens, Greece. Singh, S., Kumar, A., Singh, B., 2002. Radon level in dwellings and its correlation with uranium and radium content in some areas of Himachal Pradesh India. Environment International 28 (1e2), 97e101. Somlai, J., Gorjanacz, Z., Varhegyi, A., Kovacs, T., 2006. Radon concentration in houses over a closed Hungarian uranium mine. Science of the Total Environment 367 (2e3), 653e665. -Popa, L.A., Dinu, A., Dicu, T., Szacsvai, K., Cosma, C., Hofmann, W., 2010. Trut¸a Preliminary lung cancer risk assessment of exposure to radon progeny for Transylvania, Romania. Health Physics 99 (3), 301e307. UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation), 2006. Annex E: Sources-to-effects Assessment for Radon in Homes and Workplaces. United Nations, New York. WHO (World Health Organization), 2009. Who handbook on indoor radon. A public health perspective (available online).
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Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad
it¸a-S¸tei radon Soil and building material as main sources of indoor radon in Ba prone area (Romania) Constantin Cosma a, Alexandra Cucos¸-Dinu a, Botond Papp a, *, Robert Begy a, Carlos Sainz a, b a b
Faculty of Environmental Science and Engineering, “Babes¸-Bolyai” University, Cluj-Napoca RO-400294, Romania Department of Medical Physics, Faculty of Medicine, Univ. of Cantabria, Santander ES-39011, Spain
a r t i c l e i n f o
a b s t r a c t
Article history: Received 4 November 2011 Received in revised form 10 September 2012 Accepted 12 September 2012 Available online 17 November 2012
Radon contributes to over than 50% of the natural radiation dose received by people. In radon risk areas this contribution can be as high as 90e95%, leading to an exposure to natural radiation 5e10 times higher than normal. This work presents results from radon measurements (indoor, soil and exhalation from building materials) in B ait¸a-S¸tei, a former uranium exploitation area in NW Romania. In this region, indoor radon concentrations found were as high as 5000 Bq m3 and soil radon levels ranged from 20 to 500 kBq m3. An important contribution from building materials to indoor radon was also observed. Our results indicate two independent sources of indoor radon in the surveyed houses of this region. One source is coming from the soil and regular building materials, and the second source being uranium waste and local radium reached material used in building construction. The soil as source of indoor radon shows high radon potential in 80% of the investigated area. Some local building materials reveal high radon exhalation rate (up to 80 mBq kg1 h1 from a sandy-gravel material, ten times higher than normal material). These measurements were used for the radon risk classification of this area by combining the radon potential of the soil with the additional component from building materials. Our results indicate it¸a-S¸tei area can be categorized as a radon prone area. that Ba Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved.
Keywords: Indoor radon Soil radon Soil permeability Radon potential Radon prone area Radon risk
1. Introduction Radon (222Rn) is present in both indoor and outdoor air because the parent radionuclide of it (226Ra) in the 238U decay series occurs in trace amounts throughout the Earth’s crust. Once formed, 222Rn, (with a half life of about 3.82 days), because it is chemically inert, can migrate through soil or foundation material, to reach the indoor atmosphere. Radon gas from soil, considered the most important source, enters house mainly through cracks in the building structure. Moreover, radon also enters from building material and from the water supply, and the concentration can reach high levels if air exchange is reduced (Cosma et al., 1996 a). Radon contribute in average with about 50% at the natural exposure of people in the whole world and it is considered as responsible for between 3 and 14% of lung cancer death, being proved the second main cause for this illness after smoking (WHO, 2009). In radon risk areas (radon prone areas) this contribution can be much higher, growing the natural dose exposure of 5e10 times. Over time, epidemiological studies have demonstrated an evidence
* Corresponding author. Tel.: þ40 264 307030; fax: þ40 264 307032. E-mail address: [email protected] (B. Papp).
of correlation between radon exposure and lung cancer, even in case of low levels of radon in residential buildings. Unfortunately, the effort of the authorities to work towards in order to reduce the number of lung cancers related to radon exposures is still far from successful in some countries (WHO, 2009). Radon concentration in indoor air has been measured in many countries worldwide in a large number of buildings mostly as a result of the application of radon policies and regulation requirements (WHO, 2009; UNSCEAR, 2006; ICRP 115, 2010). The approach of indoor radon studies in connection with radon gas from soil and building material are due to presence of such factors linked to the underlying geological formations and building structure, which could lead to increased levels of radon inside houses (Barros-Dios et al., 2007). Several studies have performed radiological measurements in areas with a former uranium mine and have revealed a significant association between the uranium content of soil and high indoor radon concentration (Singh et al., 2002; Somlai et al., 2006; Barros-Dios et al., 2007). Although, radon from soil and rocks and from the basement of the buildings represents the main radon sources. Another study in UK indicates that radon emanation from building materials have significant contribution to increased indoor radon concentrations in some houses (Denman et al., 2007).
0265-931X/$ e see front matter Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jenvrad.2012.09.006
C. Cosma et al. / Journal of Environmental Radioactivity 116 (2013) 174e179
The present study represents a part of an extensive research on indoor radon exposure in the region of Transylvania-Romania. The most important high background radiation area in Transylvania it¸a-S¸tei (Bihor County), where the highest indoor was located in Ba radon concentrations have been found (Cosma et al., 2009; Sainz -Popa et al., 2010; Cucos¸-Dinu et al., 2012). et al., 2009; Trut¸a Another radon prone area was identified at Herculane Spa situated in a granitic zone (Cosma et al., 1996 a, Cosma et al., 1996 b). The aim of this work is to highlight a connection between the high indoor radon levels and the underlying soil and building material identified both as the main radon sources for houses of B ait¸a-S¸tei radon-prone area. 2. Material and methods it¸a-S¸tei is located in the Bihor Mountains (NW part The area of Ba it¸a” of Romania) in the neighborhood of “Avram Iancu” and “Ba it¸auranium mines. This includes the town S¸tei and few villages (Ba Plai, B ait¸a-Sat, Nucet, Fânat¸e, Cîmpani etc.), with a total of approximately 15.000 inhabitants (see Fig.1). 2.1. Indoor radon measurements Integrated indoor radon measurements were performed in 335 it¸a-S¸tei area between 2008 and 2010, in randomly dwellings of Ba selected houses. For indoor radon level measurements CR-39 tracketched detectors were used, according to the NRPB Measurements Protocol (Sainz et al., 2009; Miles and Howarth, 2000). Solid state track detector CR-39 is used widely in the field of health physics, such as for radon monitoring or neutron dosimetry. Alpha track detectors are not expensive, reliable and easy to use. Every CR-39 detector was placed under the cap of a cylindrical polypropylene container of 5.5 cm height and 3.5 cm diameter, with a small opening in its upper part which prevents radon decay products and also thoron (220Rn) entering (RADOPOT). Only alpha particles from 222 Rn that diffuse into the container and from the two polonium isotopes (218Po and 214Po) produced inside, can hit the detector (Sainz et al., 2009). In order to evaluate average indoor radon concentrations, the detectors were exposed in the inhabited areas of dwellings, such as bedrooms and living-rooms, at a height of 1.0e1.5 m from the floor, and for a time of 2 or 3 months. After the exposure, the etching process and the automatic reading of all detectors have been made in the Laboratory of Environmental Radioactivity of Babes¸-Bolyai University, using RadoSys-2000 equipment (Elektronika, Budapest, Hungary).
it¸a-S¸tei radon-prone area (in Bihor County). Fig. 1. The zone of Ba
175
Radon concentration can be determined by counting the tracks in a given area. The individual error of radon measurements was estimated at less than 10%. The accuracy of the detection system has been periodically checked by the successful participation in national and international radon intercomparison exercises with National Institute of Physics and Nuclear Engineering (IFIN) of Bucharest, Radon Laboratory of Cantabria University, Spain and National Institute of Radiological Sciences of Chiba, Japan, during the period 2007e2011 (Cosma et al., 2009; Janik et al., 2009). 2.2. Radon in soil measurements it¸aThe preliminary radon in soil measurements in the area of Ba S¸tei were performed in 2010 autumn, when relatively dry conditions prevailed in the area. The aim of the measurements was the determination of the radon potential of soil, in order to classify this area from the point of view of radon risk. For this, 30 measurements of radon concentration in soil and of the soil permeability were performed, at 10 places in the whole area. 2.2.1. Method for measuring radon activity concentration in soil The experimental method of the radon concentration measurements was based on the sampling of the soil gas and measuring the activity concentration of 222Rn gas, using the LUK3C radon detector and accessories. The measurement principle of the LUK3C device lays on a scintillation detection technique with Lucas cells, by determining the activity directly from the alpha decay of 222 Rn and progeny. The efficiency of this technique is (2.2 counts sec1) to 1 Bq of radon activity deposited into the Lucas cell, when 222Rn is in equilibrium with its progeny (Plch, 1997). For the extraction of soil gas, a steel sampling probe was used. The probe was inserted into the soil to a minimum depth of 50 cm, and was retracted some cm back, in order to create a small cavity in soil for gas extraction. For soil gas sampling was used a Janet syringe with the volume of 150 ml (same volume as that of the Lucas cell). The syringe was connected to the upper end of the sampling probe. Before the measurement of the activity of the radon gas, the flux of radon gas from soil must forced by three consecutively extractions to avoid contaminating with atmospheric air. Only the third extraction of the soil gas (with volume of the syringe equal of Lucas cell) was introduced into the detector cell with the help of a preliminary vacuum technique. Before inserting the soil gas sample into the Lucas cell a delay time of about 3e4 min was used, for the decaying of 220Rn (thoron) gas below to 10% of its initial content. Because the half-life of 220Rn (55.6 s) is much shorter than the half-life of 222Rn (3.82 days), thoron effectively decays in short time (5 min). After the insertion of the soil gas sample into the Lucas cell, the detector starts several countings (from 1 to 10) of the alpha decays from 222Rn, and it stops when statistic errors become lower than 5%. Finally, the detector gives an average radon concentration, which was corrected by the background of the measurement process (Cosma et al., 2010). In this way, the total time of a single measurement is no more than 10 min. The scheme for the soil gas sampling and its insertion into the detector is shown in Fig. 2. 2.2.2. Method of measuring permeability of soil Permeability measurements were performed by a method based on the measuring the empty time (i.e. flow rate) of a water column from a bottle, that was connected directly to the same probe inserted in soil, described in the method for measuring radon concentration in soil (see Fig. 2). For this, the two extremities of the bottle were equipped with two valves and the top part of the bottle (through the tap) was connected directly to the soil probe (see Fig. 3).
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time is short (in the order of seconds), the permeability is high, and if the measured empty-time is long (in the order of tens of minutes), the permeability is low (Cosma et al., 2010; Papp et al., 2009). The principle and the theory for the determination of soil permeability k [m2] from the empty-time t[s] of water from the bottle is similar with the Radon-Jok permeameter, which represents an international reference in the field (Neznal et al., 2004; Barnet et al., 2008; Neznal and Neznal, 2005). The range for the measured permeability values by this method are from very high permeability (in the order of 108 m2), corresponding to an emptytime of 11 s, to ultra low permeability (in the order of 1014 m2), corresponding to an empty time of 40 min.
Fig. 2. The schemes for the sampling of soil gas and its insertion into the Lucas cell of the LUK3C detector.
2.2.3. Determination of the radon potential and the radon index of soil For the radon risk estimation of a given place or building site, the radon potential of the soil (RP), can be defined by the following expression (Neznal et al., 2004; Barnet et al., 2008):
RP ¼ ðCRn 1Þ=ðlog k 10Þ The depth of the probe inserted in the soil was the same as at radon concentration measurements in soil gas (minimum 50 cm). In the case of soil permeability measurements it is important the geometrical sizes of the active space created in the soil, in order to determine quantitatively the permeability of the soil. In the process of the permeability measurements, the gravitational flow-out of the water column (through a second tap on the bottom part of the bottle) creates a pressure difference in the bottle, that depends on the extraction rate of the soil gas. By measuring the empty-time (t [sec]) of a known water quantity from the bottle it can be determined the permeablity of the soil (k [m2]). As the measured empty-
where, CRn [kBq m3] is the measured radon concentration in soil, and k [m2] is the permeability of soil. In these estimations, radon concentration values lower than 1 kBq m3 were excluded, which is not characteristic for radon levels in soil. Also, radon concentration values higher than other values (of three times) measured at the same place were excluded, as local anomalies of a site (Neznal et al., 2004; Barnet et al., 2008). Because most of the soils in B ait¸a-S¸tei area having high permeability (for sandy soils), values lower than 4,1013 m2 were excluded. From the remaining values for radon concentrations and permeability, the highest was decisive for radon potential calculations (Neznal et al., 2004; Barnet et al., 2008). According to “The new method of the radon risk assessment of the building sites”, the values for radon potential of soil can be classified in the following ranges: low risk (for RP < 10), medium risk (for 10<¼RP < 35), and high risk (for RP>¼35), and it is dimensionless (Neznal et al., 2004; Barnet et al., 2008). 2.3. Radon exhalation measurements from building material
Fig. 3. The system for soil permeability measurements, consist from a soil probe inserted in soil, and the bottle filled with water and equipped with the two valves.
In order to measure radon exhalation rate from building materials, bricks, gravels or stones, radon concentration is determined in a tight vessel into which radon diffuse. The increase of the radon concentration in time was measured by Radim3A radon monitor, in Eman version. In this case, the vessel was mounted and sealed to the detection chamber of the Radim-Eman radon monitor, which is screwed to the base plate. On the base plate, is glued a gasket, made of soft rubber. When exhalation from the material (stones or bricks) is measured, the sample is inserted into the vessel and the vessel is mounted up to the base plate of the detection chamber (see Fig. 4). (Radim 3A-Eman, 2004). The analyzed building material sample comes from a village of it¸a-S¸tei area (in the name Fanate), from a dump of gravel-stone. Ba The sample was dried at a temperature of w70 C, and was divided into three grain fractions. The first was a sample from sandy-gravel fraction with grains diameter of 1e2 mm, the second was a sample of gravel fraction with grains diameter between 5 mm and 2 cm, and the third was a sample from stone fraction with grains diameter larger then 2 cm. The exhalation rate of radon gas from the sample (ER) is given in unit as [Bq kg1 h1]. During the measurements, radon concentration growing in time, and tends to an equilibrium value. This equilibrium value depends on the grail size dependence (Morawska
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Fig. 5. The distribution of the measured indoor radon concentrations in the 335 dwellings from Bait¸a-S¸tei area.
Fig. 4. Scheme of the system for radon exhalation measurements: radon monitor (RADIM-EMAN, in the upper part), closed to the radon receiver container (in the middle part) and the vessel that contains the sample as radon source (in the bottom part).
and Phillips, 1993; Breitner et al., 2010), on the emanation factor of 222 Rn atoms from the sample (i.e. from the mineral grains), on the 226 Ra (radium) content of the sample. As importance is the dependence on the moister content and pore characterization, and the tightness of the vessel and detection chamber (Nazaroff and Nero, 1988; Cosma et al., 2001). Through the radon exhalation measurement, the first part it can be considered to have a constantly linear increasing rate. Therefore, the rate of the increase can be the slope of the fitted line, denoted as r [Bq m3 h1]. From the slope r [Bq m3 h1] of the fitted line we determined the exhalation rate of radon gas (ER) by the:
ER ¼ r$Vair =Ms where, Vair [m3] is the volume of the air inside the vessel, that is determined from the total volume of the entire container (radon receiver and radon source containers, Vtot ¼ 4.0 L), reduced by the volume of the sample (Vs), and Ms [kg] is the mass of the sample.
exposure of population (WHO, 2009). For about 30% of all studied dwellings the radon concentration exceeds the threshold of 300 Bq,m3 recently recommended as a reference level by ICRP in the latest Statement on Radon (ICRP 115, 2010). From the radon distribution dataset it can be observed a double log-normal distribution. The statistical calculations for the first part of the distribution gives the following parameters: geometric mean of 135 Bq m3, median of 123 Bq m3, arithmetic mean of 202.2 Bq m3, and for the second part: geometric mean of 764 Bq m3, median of 736 Bq m3, arithmetic mean of 858 Bq m3. The double log-normal distribution can be related the existence of two independent sources of indoor radon in the houses of the area. The first maximum (81e 120 Bq m3) could be explained from the source of soil and normal building material and the second (601e3000 Bq m3) could come from uranium waste used in building constructions or/and building local materials with high uranium and radium content. The main reasons for high indoor radon concentrations in this region could be explained by the using of uranium tailings from the area of uranium mines. The mine was operated in the period of 1952e1998 when many houses were built using radioactive tailings from mine or building material (sand, gravel, etc) from the Cris¸it¸a river bad having increased amounts of radium and uranium Ba (Sandor et al., 1999). 3.2. Radon potential and the radon index results
3. Results and discussions 3.1. Indoor radon results The distribution of the measured indoor radon concentrations by solid state track detectors are shown on Fig. 5, where the concentration values were in the wide range from 15 to 2200 Bq m3, depending on the ventilation rate, construction material of the houses and of the soil permeability under the building. Considering the geological and the seasonal corrections, the annual average value of the radon concentration for B ait¸a-S¸tei area is 343.5 Bq m3, which is 4.16 times higher than the average indoor radon concentration of 82.5 Bq m3 reported for Transylvania (Cosma et al., 2009; Sainz et al., 2009). This value confirms previous studies which have classified this region as a radon-prone area (Cosma et al., 2009; Sainz et al., 2009; Trut¸ a-Popa et al., 2010; Cucos¸-Dinu, et al., 2012). Indoor radon concentrations in monitored region are significantly higher than the recommended level of 100 Bq m3 for residential
The results of the radon concentration measurements in soil and it¸a-S¸tei area are summaof soil permeability measurements in Ba rized in the Table 1. The radon risk category (i.e. radon index (RI)) of the investigated sites are shown in the last column of the Table 1. According to “The new method of the radon risk assessment of the building sites”, the majority of the investiganted places show high radon risk (RI), for which the radon potential RP > 35 (Neznal et al., 2004; Barnet et al., 2008). This can be explained in one hand by the high soil permeabilities of the investigated places (78% of the places having permeabilities over than 4,1012 m2). On the other hand, places take part to this category of permeability, radon concentrations higher than 30 kBq m3 resulting high radon risk (86% from concentration values), and concentrations bettween 10 and 30 kBq m3 resulting medium radon risk (14% from the values). As we mention, the last place Bǎit¸a-Plai (see last line in Table 1) shown very high radon risk (with RP ¼ 1607.2). This is characteristic for the place, because closed to this (at a distance of 1000 m) is
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Table 1 The measured soil radon concentration values and errors (CRn dCRn) with the soil permeability values (k), and the calculated values of the radon potential (RP) with the radon indexes (RI). (The number in bellow the name of each site represent the number of measurements performed at the site. The parameter D[m] is the depth from that the soil gas was sampled). place
D [m]
CRn dCRn [kBq m3]
S¸tei (3)
0.8 0.8 0.8 0.8 0.8 0.7 0.7 0.7 0.8 0.6 0.6 0.5 0.65 0.7 0.8 0.8 0.8 0.8 0.8 0.8 0.6 0.8 0.8 0.8 0.4 0.4 0.4 0.5
44.1 40.2 22.3 22.0 30.1 53.5 54.5 63.4 159.5 58.1 59.1 61.3 46.9 27.1 11.9 7.9 45.4 128.7 23.1 5.5 7.6 42.2 35.2 16.6 462.9 398.5 446.1 512.0
Lunca S¸tei (2) Cîmpani (4)
Fânat¸e 68 (2) Nucet Popas (2) Nucet Cris¸ (1) Bǎit¸a 204 (5)
Bǎit¸a 206 (5)
Bǎit¸a Plai (4)
2.0 2.0 1.0 1.2 1.5 2.6 2.6 2.9 7.8 2.7 2.6 2.8 2,1 1.3 0.7 0.5 2.0 5.1 1.1 0.5 0.5 1.2 1.5 0.8 13.3 12.0 13.0 14.0
k [m2] 1.7E-12 2.4E-12 2.4E-11 1.9E-13 3.0E-13 1.2E-11 2.4E-11 2.4E-11 7.1E-12 6.8E-13 e 9.8E-12 2.4E-11 5.2E-11 High High High 1.8E-11 2.8E-13 1.3E-11 High 2.7E-11 High High 3.3E-11 e e 4.8E-11
RP
RI
69.8
High
11.5
Medium
101.1
High
26.8
Medium
59.8
High
93.2 59.1
High High
73.0
High
1607.2
High
it¸a-Plai”, where the soil has very situated the old uranium mine “Ba high uranium content. 3.3. Radon exhalation results The results of the radon exhalation measurements (i.e. radon concentration versus time) of the three samples having different grains fractions are shown in Fig. 6. The radon concentration growing during the measurement and tends to an equilibrium value. From Fig. 6 it can be seen that in the first part of the measurements (in about the first 18 h) the growing rate of the radon concentration can be considered to be constantly linear, in all three cases. The results of the linear fits and of the calculations are shown in the Table 2, which contains the values of the radon exhalation rates (ER) for the three fractions, which depends on the values of the slopes (r), on the air volume inside the vessel (Vair) and on the mass of the samples (M). Results of the laboratory measurements on the three samples of different grain size and calculations show different exhalation rates. The first two samples (sandy gravel with smallest grain sizes and gravel with grain size of some cm) had the same radon exhalation rates, while the third (normal stone with big grain size) sample have lower radon exhalation rate. The radon exhalation of
Table 2 Results of the slope (r) of the increasing radon concentrations from the linear fits, and the determined radon exhalation rate (ER) with errors, for the three samples (i.e.grain size). Samples
r dr [Bq m3 h1] Vair [L] M [kg] ER dER [mBq kg1 h1]
Sandy gravel 34.2 1.5 Gravel 41.4 1.6 Stone 4.3 1.3
3.4 3.3 3.3
1.4 1.7 1.7
84.1 3.7 81.4 3.1 8.4 2.6
Fig. 6. The increasing of the radon concentration (CRn) in time (t) for the first part (linear part) of the measurement. The squares corresponds to the data from sandygravel sample, the circles corresponds to the data from gravel sample, and the triangles corresponds to the data from stone sample, with the corresponding error bars. The lines are the linear fits to the three concentration data sets for which the values of the correlation coefficients (R2) are: 0.98 (for sandy-gravel), 0.97 (for gravel) and 0.40 (for stone).
the sandy gravel and gravel was of ten times higher (i.e. with one order) then the exhalation of the stones. It is well known that the exhalation rate (i.e. radon exhalation) depends on the emanation factor of 222Rn atoms from the sample (i.e. from the mineral grains), on the 226Ra (radium) content of the sample, on the moisture content, (Nazaroff and Nero, 1988; Cosma et al., 2001) and also from the grain size of the samples, which is well described in Morawska and Phillips (1993) and Breitner et al., 2010. Consistent with our results, several studies have carried out regarding the soil and indoor radon measurements in areas of former uranium mines and have pointed out a significant association between the uranium content of soil and high indoor radon concentration (Somlai et al., 2006; Abdallah and Khalid, 2008; Khan and Puranik, 2011). The annual average indoor radon concentration for all our measurements (the both two groups) of 345 Bq m3 is similar to value found in a Hungarian uranium mine area (Somlai et al., 2006) of about 400 Bq m3 and higher than those of 100 Bq m3 reported for an Indian uranium mining area (Khan and Puranik, 2011). If we refer only to the first group from Fig. 2 (an average of w100 Bq m3) it can be seen that our results are similar to those from Indian area. The Jordanian study about soil radon and indoor radon connection (Abdallah and Khalid, 2008) performed in a non uranium area is rather relevant also in our case (100 Bq m3 radon in soil produces 1 Bq m3 indoor radon). The similarities and the difference of these annual average results comming firstly from the geological characteristics of the mentioned uranium areas (i.e. amount of uranium content of the soils and permeability of the soils. The uranium content of the soils determines the concentration of radon gas in soil, and the permeability of the soils is an important parameter which determines the entry rate of radon gas to the buildings indoor. 4. Conclusions The paper presents integrated indoor radon levels from 335 dwellings performed in several villages of Bǎit¸a-S¸tei radon prone area (in Bihor County), near an old uranium mine, during 2008e 2010. The results indicate an annual average value of indoor
C. Cosma et al. / Journal of Environmental Radioactivity 116 (2013) 174e179
radon concentrations of about 343.5 Bq m3, which is 4.16 times higher than the average indoor radon concentration of 82.5 Bq m3estimated for Transylvania (e.g. NW part of Romania). Statistical calculations on the distribution of the indoor radon values give a double lognormal distribution. This double distribution means that there are two independent sources of indoor radon in the houses of the area. The first source coming from soil and normal building material and the second is coming from uranium waste and high uranium content of material used in building constructions. For characterizing radon potential of soil, were performed radon in soil and permeability of soil measurements at 10 selected places. The results of the estimations provide that the majority of the investigated places shown high radon risk (80% having high radon it¸a-S¸tei potential). The second main source of the indoor radon in Ba uranium area is building materials and uranium waste. The material containing a mixture of sandy-gravel and stone, used as building material in the area shows highest radon exhalation. Therefore, this material has an important contribution to radiation doses for population in houses which uses as building material. This survey has been carried out within the framework of a European Research Project focused on the reduction of radon exposure received by population living in surroundings of a former uranium mine in Bǎit¸a-S¸tei radon prone area. The project fulfills the requirements of a national radon program including detailed indoor radon campaigns together with radiological characterizations of the soil and building materials as a radon sources. In the near future, this study will also covering the testing and implementation of the most effective remedial solutions in 20 homes with the highest indoor radon levels. Acknowledgment This work represents a part of research study supported by the project 586-12487, Contract No. 160/15.06.2010 with the title “IMPLEMENTATION OF RADON REMEDIATION TECHNIQUES IN DWELLINGS OF BǍIT¸A URANIUM MINE AREA/IRART” of the Sectoral Operational Programme “Increase of Economic Competitiveness” co-financed by The European Regional Development Fund. References Abdallah, I.M., Khalid, M.A., 2008. Evaluation of radon gas concentration in the air of soil and dwellings of Hawar and Foara villages, using (CR-39) detectors. Radiation Measurements 43 (1), 452e455. Barnet, I., Pacherová, P., Neznal, M., Neznal, N., 2008. Radon in Geological Environment e Czech Experience, Special Papers No. 19. Czech Geological Survey, Prague, pp. 25e30. Barros-Dios, J.M., Ruano-Ravina, A., Gastelu-Iturri, J., Figueiras, A., 2007. Factors underlying residential radon concentration: results from Galicia, Spain. Environmental Research 103 (2), 185e190. Breitner, D., Arvela, H., Hellmuth, K.H., Renvall, T., 2010. Effect of moisture content on emanation at different grain size fractions e a pilot study on granitic esker sand sample. Journal of Environmental Radioactivity 101 (11), 1002e1006. Cosma, C., Ristoiu, D., Cozar, O., Znamirovschi, V., Daraban, L., Râmboiu, S., Chereji, I., 1996 a. Studies on the occurence of radon in selected sites of Romania. Environment International 22 (1), 61e65.
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