- Email: [email protected]
Indoor radon measurements in a Greek city located in the vicinity of lignite-fired power plants
Radiation Measurements 45 (2010) 1060e1067
Contents lists available at ScienceDirect
Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas
Technical Report
Indoor radon measurements in a Greek city located in the vicinity of lignite-fired power plants M. Manousakas a, A. Fouskas a, H. Papaefthymiou a, *, V. Koukouliou b, G. Siavalas c, P. Kritidis d a
Department of Chemistry, University of Patras, 26500 Patras, Greece International Atomic Energy Agency, Vienna c Department of Geology, University of Patras, 26500 Patras, Greece d NCSR “Demokritos”, 153 10 Aghia Paraskevi, Athens, Greece b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 June 2009 Received in revised form 27 April 2010 Accepted 31 July 2010
This work presents indoor radon measurements in 42 dwellings in the city of Megalopolis, Southern Greece, located in the vicinity of 2 lignite-fired power plants and examines the effect of season, floor level and age of the dwellings on indoor radon concentration. The radon measurements have been carried out using the LR-115, type II and CR-39 alpha track detectors in “closed-can” geometry. The average annual indoor radon concentration (GM) was found to be 52 Bq m3, which is well below the recommended action level of the European Union. This value corresponds to an annual effective dose to the population of 1.3 0.4 mSv. Season and age of the examined dwellings represent factors that affected significantly the indoor radon in Megalopolis, while the effect of floor level appeared to be not significant. Radium activity concentration values, measured by g-ray spectrometry in 20 sub-samples of six soil cores (60e135 cm depth), collected from the surrounding area of the city, were found to be consistent with the Greek and world average values. Based on the results of this study, it is concluded that the effect of the lignite-fired power plants on indoor radon concentration in Megalopolis’ dwellings was not significant. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Indoor radon Passive detectors Lignite-fired power plants Effective dose Greece
1. Introduction Radon (222Rn) is a decay product of 226Ra, which is in turn a decay product of 238U. Since uranium is present in all terrestrial materials, radon gas emanates from the bedrock underlying dwellings and can enter and reach high concentrations in indoor spaces mainly due to the lower pressure inside in relation to the atmosphere outside and in the ground. The diffusion of radon through the ground is related to permeability, which is dependent on grain-size distribution, degree of compaction and the water content of the soil (Durrani and Ilic, 1997). It is well established that the inhalation of radon (222Rn) and mainly its radioactive decay products, contributes more than 50% of the total radiation dose to the world population from natural sources (UNSCEAR, 2000). Many epidemiological case-control studies, which have been conducted in a number of countries, have shown a consistent statistically significant increase of lung cancer risk, due to exposure to radon in dwellings at even moderate levels of exposure and also a strong synergism with smoking (UNSCEAR, 2000; Krewski et al., 2005; Bochicchio, 2008).
* Corresponding author. Tel.: þ30 2610 997132; fax: þ30 2610 997118. E-mail address: [email protected] (H. Papaefthymiou). 1350-4487/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2010.07.024
Radon concentration varies from region to region and from country to country, depending on a number of factors e.g. geological characteristics of the underlying area, season of the year, meteorological parameters, type and construction characteristics of the house, building materials, ventilation, etc. (Durrani and Ili c, 1997). Large-scale radon surveys have been performed in many countries to estimate the indoor radon concentration and to determine the factors affecting its concentration (UNSCEAR, 2000; Langroo et al., 1991; Marcinowski et al., 1994; Sarrou and Pashalidis, 2003; Bochicchio et al., 2005). In Greece, the relatively larger radon survey has been carried out from 1995 to 1998 by Nikolopoulos et al. (2002). In this survey the arithmetic and geometric mean values for the indoor radon concentration were found to be 55 and 44 Bq m3, respectively. Additionally, according to UNSCEAR (2000), the arithmetic and geometric mean values for Greece are 73 and 52 Bq m3, respectively. Besides the natural sources of radiation, human activities, such as the burning of fossil fuels, can be a source of environmental radioactivity. It is well known that coal contains toxic trace elements along with naturally occurring radioactive elements, in concentrations, in some cases, higher than those in most sedimentary rocks (Seredin and Finkelman, 2008). During combustion, a considerable amount of toxic elements and radionuclides are released into the atmosphere as fly ash or vapors, while large
M. Manousakas et al. / Radiation Measurements 45 (2010) 1060e1067
amounts of these remain as bottom ash (Meij, 1995). The submicron fly ash particles, due to their high atmospheric mobility, can be transported over a wide range of distances and may constitute a potential hazard in the vicinity of the plant. Greek lignite, especially that of Megalopolis basin, contains high concentration of natural radionuclides, mainly that of the 238U decay series, while fly ash have been found to contain enhanced levels of 238U and 226Ra as compared to lignite (Papaefthymiou et al., 2007). The city of Megalopolis (Southern Greece) (Fig. 1) is located about 2.5 and 4 km NE to the lignite power plants A (Units I, II and III, 550 MW) and B (Unit IV, 300 MW), respectively, which are operated by the Public Power Corporation of Greece. The stack height of Units I and II is 120 m, while the heights of units III and IV are 180 and 206 m, respectively (Papaefthymiou et al., 2005). At full load, the units consume about 22e25 106 kg of pulverized lignite per day. Most of the produced fly ash is collected by electrostatic filters, which have a design collection efficiency of 99.6%, but in practice it falls to 95e96%. The lignite deposit of the Megalopolis basin is of very low gross calorific value (16.9 MJ kg1 on a dry basis) (Siavalas et al.,
1061
2007) and of high water and ash content (60% and 17%, respectively) (Papaefthymiou et al., 2007), reflecting its poor quality. Open fly ash deposits also exist around the power plants. Despite the relatively high height of the stacks, the 226Ra activity concentration in surface soil presented higher values within a distance of 0e5 km (26e337 Bq kg1) compared to that of 5e10 km (23e42 Bq kg1) from the power plants (Rouni et al., 2001). In addition, bulk deposition studies, which have been carried out in the city, showed significantly increased 238U-activity (Bq m2) in the deposited dust. About 70% of the uranium activity found in the fallout samples was attributed to the soil dust resuspension and 30% to the escaping fly ash from the power plants (Papaefthymiou et al., 2005). According to these results, the city of Megalopolis is located in the area of maximum deposition. Fly ash particles are also deposited inside dwellings, through doors and windows opened. The aims of this study were: to measure the indoor radon concentration levels in the city of Megalopolis, to assess the impact of the power plants operation on the radon concentration levels and to investigate the effect of season, floor level and age of the buildings
Fig. 1. Map of Greece showing the location of Megalopolis. The locations of the soil cores are shown in the amplification.
1062
M. Manousakas et al. / Radiation Measurements 45 (2010) 1060e1067
on radon levels. Activity concentration of 226Ra was also measured by g-spectrometry in sub-samples of six soil cores collected from the area around the city. Estimation of radiation dose to the population of Megalopolis due to indoor radon is also presented. In this survey, radon levels were monitored using the solid-state nuclear track detector (SSNTD) technique, which is the most reliable technique for integrated and long-term measurement of radon concentration inside dwellings (Durrani and Ili c, 1997). The measurements were performed over 1 year in four consecutive 3-month periods (seasons). 2. Experimental 2.1. Geology of the area Megalopolis is a small city (10,000 inhabitants) located on the Megalopolis basin at the centre of the Peloponnese Peninsula, Southern Greece (Fig. 1). Geologically, the margins of the basin consist of Mesozoic limestones, dolomites, cherts, and Upper Eocene to Upper Oligocene flysch (Vinken, 1965). The sediments filling the basin have been deposited from the Upper Pliocene until today and reflect a variety of terrestrial, fluvial, limnic, and telmatic palaeo-environments. At the central part of the basin the sediments reach their maximum thickness exceeding 500 m (Vinken, 1965). This sedimentary filling, which is mostly composed of fine sediments (clays and marls) along with the flysch formation constitute an impermeable cap for the permeable carbonate rocks outcropping at the western margins of the basin. Soil permeability values measured by Rouni et al. (2001) within a 10 km radius from the Megalopolis power pants were found to be 1015e109 m2 in the range 0e5 km and 1014e109 m2 in the range 5e10 km. These values show that the soil permeability is low and consistent with the geology of the area (Bowen, 1980). 2.2. Indoor radon measurements Indoor radon measurements were performed by means of the solid-state nuclear track detection technique, using the LR-115, type II detector in a “closed-can” geometry. The dosimeter was a metallic can (tin can, commercially available) in order to avoid the anisotropic deposition of radon decay products on the walls, which can be caused by static electric charges. The input of radon decay products in the dosimeter was avoided by use of black filter material (fabric), which also reduces the exposure of the detector to light and prevents the entry of dust and aerosol. A 10 mm 35 mm of the LR-115 detector material was used, of which a 10 mm 10 mm was exposed and a 10 mm 10 mm part, covered by a similar part of the detector, was used to determine the background track density. The rest part (5 mm 10 mm) was used to attach the film at the bottom of each dosimeter (Kritidis et al., 1994). A number of indoor radon measurements were also performed using the CR-39 detector. In this case, the dosimeter was a semi-cylindrical plastic cup with a base of 4.5 cm in diameter and a height of 2 cm. The cover of the cup contained a filter that prevented radon daughters from entering into the cup space. A piece of the CR-39 detector (13 37 mm) was attached at the bottom of the cup. Before exposure the holders and the detectors were dipped in a solution of a dilute detergent (1:5000) and allowed to dry before use to eliminate the electrostatic effects. Background checks were carried out on 10 randomly selected detectors per batch. The measurements were carried out for a 1 year (December 2005eNovember 2006) with the 3-month of the exposure time for each group of the detectors (December 2005eFebruary 2006, MarcheMay 2006, JuneeAugust 2006 and SeptembereNovember 2006). The aims of the measurements are to examine the seasonal
variations of the indoor radon levels and also to estimate the annual average radon concentration values. For this purpose, 50 dosimeters with the LR-115 detector were prepared for every season and distributed in 50 randomly selected dwellings in the city of Megalopolis. During summer and fall a second dosimeter with the CR-39 detector was placed side-by-side with the LR-115 one in 25 from a total of 50 dwellings for results’ comparison. The dosimeters were placed in the living room or bedroom, the two most frequently used rooms of each home, at 1 m height from the floor and away from windows and doors. In this way, a total of 4 LR-115 detectors were placed at each chosen dwelling (4 50 ¼ 200). In addition, a total of 50 (2 25 ¼ 50) CR-39 detectors were placed at each of the 25 selected dwellings. During the year, for various reasons, (dosimeters were lost or damaged, participants changed residence) a number of dosimeters failed to return or returned after the three-month exposure time. Complete data covering all four seasons were available for 42 sampling sites (4 42 ¼ 168). Our analysis was based on these dwellings that participated in all four seasons. Moreover, a total number of 8 CR-39 dosimeters were lost. Complete data for both detectors were available for 20 and 18 sampling sites during summer and fall, respectively. Most of the dwellings were made of fired clay bricks and reinforced concrete, while the oldest ones were made of stones with clay and/or cement and mainly wood for floors. The examined dwellings were mainly in different two to three storey buildings. The ventilation of all dwellings was natural, through open windows and doors. Most dwellings were heated by hot-water central heating system for about 5e6 months per year (NovembereApril). Full address and information concerning the characteristics of the dwellings (age of the building, heating system and type of building materials) were collected. After each 3-month exposure, the detectors were subjected to chemical processing with NaOH and then to track counting in a given area. The track counting was performed manually with a slide projector using an optimized technique for the LR-115 detectors (Kritidis et al., 1994), whereas an optical microscope was used for the CR-39 ones. Typical backgrounds for the LR-115 and the CR-39 detectors were 27 6 tracks cm2 and 20 4 tracks cm2, respectively. The calibration factors for converting the recorded track densities to Bq m3 were 2.3 103 tracks cm2 per Bq h m3 (with a standard deviation of 4%) and 2.6 103 tracks cm2 per Bq h m3 (with a standard deviation of 3%) for the LR-115 and CR-39 detectors, respectively. The statistical error of a single 3-month measurement at the average level of 40 Bq m3 was 9% (1s) and 8% for the LR-115 and CR-39 detectors, respectively. 2.3. Measurements of radium activity in soil samples Six soil cores (M1-M6) were collected from undisturbed sites around the city. The locations of the soil sampling sites are shown in Fig. 1. The sampling was performed with a steel corer tube placed vertically into the soil. The length of the soil cores ranged from 60 to 135 cm, depending on the ability of the corer to penetrate in the soil. After sampling, the cores were gently sliced to a resolution of 20e30 cm. All soil sub-samples were air dried, passed through a 2 mm sieve, homogenized and oven dried at a temperature of 105 C for 24 h. Then, the samples, ranging in mass from 50 to 70 g, were placed into cylindrical containers (20 mm height, 69 mm diameter), weighed, sealed hermetically and stored for 4 weeks prior to counting to establish secular radioactive equilibrium between 226Ra and its short-lived daughter products. Measurements of 226Ra activity concentration in soil samples were undertaken by means of a high-resolution g-ray detector (Canberra HPGe) coupled to a PC-based multichannel analyzer and the appropriate electronics. The detector has an efficiency of 25% and
M. Manousakas et al. / Radiation Measurements 45 (2010) 1060e1067
2.4. Statistical analysis
35
Frequency distribution (%)
an FWHM of 1.9 keV for the 60Co g-ray energy line at 1332 keV. The procedures of energy and efficiency calibrations are described in detail elsewhere (Papaefthymiou et al., 2007). The duration of measurements was 24 h to obtain satisfactory statistical precision. The 226Ra activity concentration was derived from the weighted mean of the photopeak of 214Bi (609.3 keV) and the two photopeaks of 214Pb (295.2 and 352.0 keV). The detection limits (2s) for a 24-h counting time were 0.8 and 0.7 Bq kg1 for 214Bi and 214Pb, respectively.
1063
30 25 20 15 10 5 0
2.5. Effective dose calculation The effective dose (ED) to the population of the Megalopolis city was calculated from the following formula according to (UNSCEAR, 2000):
ED mSv y1 ¼ CRn F OF DC 106 where CRn is the calculated geometric mean value (Bq m3) of the indoor radon concentration, OF is the indoor occupancy factor, F is the mean equilibrium factor indoors and DC is the dose conversion factor. 3. Results and discussion 3.1. Indoor radon concentrations Fig. 2 presents the frequency distribution histogram of the full year indoor radon concentration measurements. As shown in this figure, the distribution of the radon concentrations appears to be log-normal (highly skewed to the right), as confirmed by the applied KolmogoroveSmirnov normality test (Z ¼ 1.715, P ¼ 0.006). As a result, the geometric means were used for results’ description and statistical comparisons. Table 1 gives summary statistics for the measured 222Rn concentration levels in the surveyed dwellings during the examined four seasons, as well as for the estimated annual average concentrations. The annual geometric mean was found to be 52 Bq m3 with a GSD of 1 Bq m3 and varied from 29 to 164 Bq m3, while the arithmetic mean and the standard deviation were 56 and 24 Bq m3, respectively. These values are consistent with the Greek average values. None of the total 42 dwellings under consideration exceeded the action levels of 400 and 200 Bq m3, proposed by the European Commission (EC, 1990) for old (before 1990) and newer (after 1990) houses, respectively, while only one exceeds the recommendation by the US EPA action level of 150 Bq m3 (EPA, 2003).
0 26 024 0 24 022 0 22 020 0 20 018 0 18 016 0 16 014 0 14 012 0 12 010 00 -1 80 0 -8 60 0 -6 40 0 -4 20 20 0-
The KolmogoroveSmirnov normality test was applied to the log-transformed data to verify the hypothesis, that the data set follows log-normal distribution. Evaluation of the significance of the difference between means for the three examined factors (season, floor level and age of the dwellings) was performed using three-way analysis of variance (3-way ANOVA). The season factor had 4 levels (winter, spring, summer and fall), the location factor had 3 levels (ground, 1st floor, 2nd floor) and the age factor had also 3 levels (1st: dwellings constructed during the period 1930e1955, 2nd: dwellings constructed during the period 1956e1980 and 3rd: dwellings constructed during the period 1981e2005). The Tamhane test was used for multiple comparisons. Paired t-test was used to evaluate the significance of the difference between mean values (GM) in radon concentrations obtained for summer and fall by both types of detectors (LR-115 and CR-39). Statistical analysis was performed using the SPSS v.15 software package.
Indoor radon concentration (Bq m-3) Fig. 2. Frequency distribution of the indoor Megalopolis.
222
Rn concentration in the city of
Table 2 reports the mean temperature and wind velocity during the four seasons and the respective minimum and maximum values. As is the case in Mediterranean countries, winter presented the lowest mean and minimum temperatures, whereas summer the highest ones. On the other hand, wind velocity presented the highest mean value during winter and the lowest during summer. Radon concentrations in dwellings are subjected to seasonal variation due to a number of factors (e.g. geological and meteorological factors, dwelling characteristics and habits of the inhabitants). The main trend in Mediterranean countries, as well as in a number of other countries is maximum radon concentration values in winter and minimum in summer (Papastefanou et al., 1994; Ramola et al., 1998; Papaefthymiou et al., 2003; Zunic et al., 2007; Hadad et al., 2007; Faheem et al., 2007; Prasad et al., 2008; Ningappa et al., 2008; Udovi ci c et al., 2009). As shown in Table 1, the highest average radon concentration (GM) in Megalopolis was observed in winter followed by summer, while the lowest one was observed in spring. This trend differs to some extent with the general trend mentioned above. The average winter-to-summer ratio was 1.6 1.2 (varied from 0.3 to 6.5), while for Patras (Greece) the average ratio was 2.8 1.2 (Papaefthymiou et al., 2003). Results reported by a number of researchers also show that in some cases (e.g. houses situated on mountain slopes) radon values in summer are higher compared to those in winter (Arvela et al., ska et al., 2004; Friedmann, 2005). Also Miles (2001) 1988; Karpin reports that a significant minority of houses (10e20% in the UK) have no substantial seasonal variation or follow a different pattern. As mentioned earlier in the text, Megalopolis is located in the vicinity of 2 lignite-fired power plants. Measurements of natural radioactivity in bulk deposition samples collected in Megalopolis city on a monthly basis during 1997, showed enhanced activity concentration values of 238U. It is also worthy to notice that the uranium deposition rates were directly influenced by NW directed emissions, which was the prevailing wind direction during summer (Papaefthymiou, 2008). According to the inhabitants, during
Table 1 Annual average and seasonal indoor radon concentrations (Bq m3) during December 2006eNovember 2007 in the city of Megalopolis (N ¼ 42).
Winter Spring Summer Fall Annual
AM
SD
GM
GSD
Min
Max
74 40 61 48 56
39 27 40 21 24
65 33 51 45 52
2 2 2 2 1
25 12 13 21 29
241 121 218 116 164
AM: arithmetic mean; SD: standard deviation; GM: geometric mean; GSD: geometric standard deviation; Min: minimum value; Max: maximum value.
1064
M. Manousakas et al. / Radiation Measurements 45 (2010) 1060e1067
the
examined
Wind velocity (m s
AM SD
Min
Max
AM SD
1 0 5 0
16 24 32 27
1.44 1.23 1.10 1.22
7 14 24 16
4 5 3 5
during
December
1
Temperature ( C)
Winter Spring Summer Fall
area
1.00 0.49 0.49 0.53
)
Min
Max
0.06 0.33 0.19 0.59
4.41 3.49 2.81 3.22
AM: arithmetic mean; SD: standard deviation.
summer, due to the tendency to open windows, fly ash particles were deposited on the walls, floor and furniture inside dwellings. On the other hand, the open windows may decrease the indoor radon concentration. Although radium concentration is enhanced in Megalopolis fly ash samples, radon exhalation rates were found to be significantly lower than that of Megalopolis lignite. According to Karangelos et al. (2004), this could be attributed to the virtification of the produced fly ash, which results in a decrease of the emanation of radon from the grain. The data were divided into three categories according to the floor level of the house, where the dosimeter was placed: the first contains the measurements taken in the ground floor, the second in the 1st floor and the 3rd in the 2nd floor level. Summary statistics of radon measurements in ground, 1st and 2nd floor are presented in Table 3. As can be seen from Tables 1 and 3, the highest value of 241 Bq m3 was observed during winter in the ground floor, while the lowest one (12 Bq m3) during spring in the 1st floor. The average radon concentration (GM) decreases from ground to the 1st floor, whereas the values for the 1st and 2nd floor levels are more or less the same. Similar results are also reported by other researchers in Greece (Kritidis et al., 1994; Ioannides et al., 2000; Nikolopoulos et al., 2002; Papaefthymiou et al., 2003) and in other countries (Khan, 2000; Bochicchio et al., 2005; Zunic et al., 2007). Fig. 3 presents the seasonal averaged indoor radon concentrations in different floors. As shown in this figure, winter presents the highest radon values in all floors examined. The surveyed dwellings were also classified into three categories based on the age of the buildings, which is related to the type and quantity of material used and the building technique employed (Psichoudaki and Papaefthymiou, 2008): (1) those that were constructed during the period 1930e1955, (2) buildings that were constructed during the period 1956e1980 and (3) those that were constructed after 1980. The old buildings were constructed with stones, clay or/and cement and mainly wood for floors, while recent buildings were constructed with reinforced concrete and fired clay bricks and have thinner walls (categories II and III). The main difference between the last two categories is that category (III) contains buildings which were built with concrete made by cement, containing fly ash. Fig. 4 presents the dependence of radon concentration on construction materials in different seasons. As shown in this figure, old dwellings present higher radon concentration in all four seasons. Table 3 Variation of the indoor radon concentration (Bq m3) with the floor level.
Ground 1st floor 2nd floor
N
AM
SD
GM
GSD
Min
Max
60 88 24
60 54 50
41 32 21
51 45 46
2 2 2
13 12 15
241 147 110
N: number of measurements; AM: arithmetic mean; SD: standard deviation; GM: geometric mean; GSD: geometric standard deviation; Min: minimum value; Max: maximum value.
Radon concentration (Bq m–3)
75 concerning
70
Ground 1st 2nd
65 60 55 50 45 40 35 30 25 Winter
Spring
Summer
Fall
Fig. 3. Seasonal averaged indoor radon concentrations in different floors.
It is well known that building materials contribute to internal radiation exposure due to the exhalation of short-lived radon daughter products. Elevated radiation may arise when by-products with high natural radioactivity, such as fly ash from coal-fired power plants, are used in the production of building materials (UNSCEAR, 2000). In Greece, since the beginning of the 1980s, dwellings were constructed with concrete made by cement containing up to 20% fly ash containing high activity concentrations, mainly of 238U and 226Ra (Papaefthymiou et al., 2007). The addition of fly ash may enhance the radon exhalation from concrete, which will in turn increase the indoor radon concentrations. Table 4 contains the arithmetic and geometric means of radon concentration of each period, together with the minimum and the maximum values. As shown in this table, dwellings constructed during the period 1930e1955 seem to present the highest average radon concentration, which could be attributed to the higher permeability of old constructions or to the building movement over time. In addition, dwellings constructed after 1980 seem to present higher average radon concentration compared to those constructed during the period 1956e1980. This may be attributed to the higher 226Ra content in cement used for concrete production, due to the addition of fly ash (Papaefthymiou and Gouseti, 2008) or to better tightness of modern buildings. Similar results have been observed in Ptolemais, a city in Northern Greece (Psichoudaki and Papaefthymiou, 2008). Three-way analysis of variance was applied to the obtained data to examine the effect of the studied factors on radon concentration levels. The factors considered were season, floor level in which dosimeter was placed and the age of the examined dwellings. Statistical analysis showed that there is no statistically significant interaction between the three examined factors on radon concentrations (floor by age: F ¼ 0.330 on 3 and 168 df (degree of
Indoor radon concetration (Bq m–3)
Table 2 Meteorological data 2005eFebruary 2006.
85 1930-1955 1956-1980 1981-2005
80 75 70 65 60 55 50 45 40 35 30 Winter
Spring
Summer
Fall
Fig. 4. Seasonal averaged indoor radon concentrations in different ages of the dwellings.
M. Manousakas et al. / Radiation Measurements 45 (2010) 1060e1067 Table 4 Variation of the indoor radon concentration (Bq m3) with the age of the examined dwellings.
1930e1955 1956e1980 1981e2005
1065
Table 5 Comparison between indoor radon measurements obtained with the LR-115 and the CR-39 detectors.
N
AM
SD
GM
GSD
Min
Max
Summer
12 64 92
69 49 59
25 26 40
64 43 49
2 2 2
29 13 12
117 116 241
LR-115
CR-39
LR-115
CR-39
71 44 62 2
84 52 72 2
42 13 40 1
39 15 37 1
N: number of measurements; AM: arithmetic mean; SD: standard deviation; GM: geometric mean; GSD: geometric standard deviation; Min: minimum value; Max: maximum value.
freedom), P ¼ 0.803; floor by season: F ¼ 0.676 on 6 and 168 df, P ¼ 0.669; age by season: F ¼ 0.418 on 6 and 168 df, P ¼ 0.866; floor by season by age: F ¼ 1.037 on 9 and 168 df, P ¼ 0.414). Regarding main effects, the analysis showed a significant seasonal effect (F ¼ 4.774 on 3 and 168 df, P ¼ 0.003). The multiple comparison tests showed that the average radon concentration in winter was significantly higher than that of spring and fall (P < 0.005 and P ¼ 0.002, respectively), while the average concentration in summer was significantly higher compared to that of spring (P ¼ 0.007). At this time it is not entirely clear what causes the enhanced radon levels in summer compared to those of spring and fall. As shown in Table 2, these results could not be attributed to meteorological parameters such as temperature and wind velocity or to the presence of small amounts of fly ash inside dwellings. Occupant activities affecting ventilation could be possibly a reason for these results. Further investigations are needed to elucidate these findings. The effect of building age was also significant (F ¼ 3.172 on 2 and 168 df, P ¼ 0.045). Specifically, the average radon concentration in the old dwellings (51e76 years) was significantly higher compared to those 25e49 years old (P ¼ 0.024). Significant relation in radon concentration with the age of the buildings has been also found by other researchers (Galleli et al., 1998). This may be attributed to the higher air-tightness and to changes in building materials (e.g. use of concrete instead of wood for the construction of floors), which lead to a decrease in the permeability of the buildings. It seems that the presence of fly ash in cement, used for the construction of the newer dwellings, does not influence significantly the indoor radon concentration, although the radium content of cement used for concrete production (Portland cement type II and fly ash) is higher compared to other building materials used in Peloponnese, Greece (Papaefthymiou and Gouseti, 2008). This could be attributed to the fact that the radon exhalation from samples of concrete with fly ash as an additive is slightly influenced or even decreased, despite the higher 226Ra content (Stoulos et al., 2003; Kovler et al., 2005). The average radon concentration value in the ground floor was higher compared to those in the 1st and 2nd floor, but the statistical analysis showed that the differences in mean values were non significant (F ¼ 0.525 on 2 and 168 df, P ¼ 0.593). Given that the diffusion chambers were not exposed on different floors of the same buildings and the poor statistics of the sample, this could be considered as indicative and cannot be used for any detailed conclusion. Similar results have been found for Ptolemais (Northern Greece) (Psichoudaki and Papaefthymiou, 2008).
AM SD GM GSD
Fall
AM: arithmetic mean; SD: standard deviation GM: geometric mean; GSD: geometric standard deviation.
Paired t-test applied to the data set showed that the differences in mean radon concentration values (GM) obtained by the LR-115 and CR-39 detectors during summer and fall were not statistically significant (P ¼ 0.067 and P ¼ 0.435, respectively). Moreover, with regard to season, a significant difference was found between measurements obtained during summer and fall using the CR-39 (detector (P < 0.001), which is consistent with the results obtained using the LR-115 detector. 3.3. Activity concentration of
226
Ra in soil samples
The average activity concentrations of 226Ra in all 6 cores are presented in Table 6, along with the Greek and world average soil values. It is apparent from this table that radium is almost uniformly distributed with depth. The 226Ra activity concentration ranged from 22 to 29 Bq kg1 and all examined cores presented more or less the same average activity concentration value of 226Ra. The average 226Ra activity concentration for all six cores was found to be 25.0 1.5 Bq kg1, which is consistent with the Greek and world average values for soil (UNSCEAR, 2000). Given that the permeability of the geological substrate in the examined area is low, the average indoor radon concentration in the examined area seems to be consistent with the radium content of the soil underneath dwellings. Although the radium (uranium) content of the geological formations underneath dwellings is not the only parameter controlling the indoor radon, the knowledge of radium content in a region is useful information for predicting indoor radon concentrations, especially in substrates with high radium concentrations (Sachs et al., 1982). 3.4. Effective dose due to indoor radon To evaluate the annual effective dose for the adult inhabitants of the city of Megalopolis in the indoor environment, a dose conversion factor of 9 nSv per Bq m3, a mean equilibrium value of 0.4 and an occupancy factor of 80% were adopted according to UNSCEAR (2000). As mentioned above, the average annual radon concentration ranged from 29 to 164 Bq m3. These values correspond to an annual effective dose ranging from 0.73 to 4.1 mSv, with a mean value of 1.4 0.6 mSv. Based on the annual geometric mean value the effective dose is 1.3 0.4 mSv y1. This value is slightly higher than Table 6 Average activity concentration of
226
Ra in the collected soil cores. Bq kg1 d.w SD
3.2. Comparison of LR-115 and CR-39 radon measurements During summer and fall, two types of detectors (LR-115 and CR39) were placed side-by-side in a number of the examined dwellings for results’ comparison. Summary statistics of the obtained results are presented in Table 5. It is obvious from this table that the patterns of both detectors are quite similar: the average radon concentration during summer is higher as compared to the one during fall.
Core
Average Greek soila World soila a
UNSCEAR (2000).
M1 M2 M3 M4 M5 M6
23.3 1.5 24.1 0.5 24.6 2.5 24.7 2.2 27.8 0.9 25.2 1.8 25.0 1.5 25 (1e240) 35 (17e60)
1066
M. Manousakas et al. / Radiation Measurements 45 (2010) 1060e1067
the world average annual effective dose of 1 mSv for radon and its decay products (UNSCEAR, 2000). Moreover, it is also higher than the annual average value of 0.8 mSv found by Nikolopoulos et al. (2002) for Greece. On the basis of the ICRP (1993) recommendations for radon in dwellings, the estimated annual dose in all cases except one is well below the recommended action levels (3e10 mSv y1). Based on these estimates, it is concluded that the dwellings under investigation in the city of Megalopolis are generally characterized by low radon exposure dose. 4. Conclusions Indoor radon measurements were performed in 42 dwellings in the city of Megalopolis, Southern Greece, which is located in the vicinity of 2 lignite-fired power plants. Radon measurements have been carried out using solid-state nuclear track detectors during a whole year and conducted as four consecutive 3-month periods to obtain integrated 1-year concentrations. Since 222Rn is a decay product of 226Ra, the radium content was also measured in soil cores collected from the surrounding area. The average annual radon concentration (GM) was found to be well below the action levels recommended by European Commission and US EPA and is consistent with the 226Ra activity concentrations measured in soil cores taking into account the low permeability of the bedrock of the examined area. The calculated annual effective dose was found to be slightly higher than the Greek average value, but lower than the ICRP recommended action levels. The season of the year and the age of the buildings are factors that significantly influence the indoor radon levels in the city of Megalopolis, whereas the floor level does not. The seasonal pattern presented deviation from the general trend with higher values in winter and lower in summer. These results suggest that the seasonal correction factors should not be used everywhere in Greece. Based on the results of this study, no significant increase in indoor radon concentration in Megalopolis due to its vicinity with lignite-fired power plants could be detected. Acknowledgments The authors would like to thank the residents and the mayor of the Megalopolis city for their help during the radon measurements. References Arvela, H., Voutilainen, A., Mäkeläinen, I., Castren, O., Winqvist, K., 1988. Comparison of predicted and measured variations of indoor radon concentration. Radiat. Prot. Dosimetry 24, 231e235. Bochicchio, F., Campos-Venuti, G., Piermattei, S., Nuccetelli, C., Risica, S., Tommasino, L., Torri, G., Magnoni, M., Agnesod, G., Sgorbati, G., Bonomi, M., Minach, L., Trotti, F., Malisan, M.R., Maggiolo, S., Gaidolfi, L., Giannardi, C., Rongoni, A., Lombardi, M., Cherubini, G., D’Ostilio, S., Cristofaro, C., Pugliese, M., Martucci, V., Crispino, A., Cuzzocrea, P., Sansone Santamaris, A., Cappai, M., 2005. Annual average and seasonal variations of residential radon concentration for all the Italian Regions. Radiat. Meas. 40, 686e694. Bochicchio, F., 2008. The radon issue: considerations on regulatory approaches and exposure evaluations on the basis of recent epidemiological results. Appl. Radiat. Isot. 66, 1561e1566. Bowen, R., 1980. Ground Water. Applied Science Publ., London. Durrani, S.A., Ili c, R. (Eds.), 1997. Radon Measurements by Etched Track Detectors. World Scientific Publishing Co., Singapore. EPA, 2003. Assessment of risks from radon in homes. Air and Radiation, EPA 402-R03e003. EC (European Commission), 1990. Council Directive 90/143/EC of 21 February 1990 on the protection of the public against indoor exposure to radon. Official J. Eur. Commun.. Faheem, M., Mati, N., Matiullah, 2007. Seasonal variation in indoor radon concentrations in dwellings in six districts of the Punjab province, Pakistan. J. Radiol. Prot. 27, 493e500. Friedmann, H., 2005. Final results of the Austrian radon project. Health Phys. 89, 339e348.
Galleli, G., Panatto, D., Lai, P., Orlando, P., Risso, D., 1998. Relevance of main factors affecting radon concentration in multi-storey buildings in Liguria (Nothern Italy). J. Environ. Radioact. 39 (2), 117e128. Hadad, K., Doulatdar, R., Mehdizadeh, S., 2007. Indoor radon monitoring in Northern Iran using passive and active measurements. J. Environ. Radioact. 95, 39e52. International Commission on Radiological Protection (ICRP), 1993. Protection Against Radon at Home and Work. ICRP. Publication 65. Ioannides, K.G., Stamoulis, K.C., Papachristodoulou, C.A., 2000. A survey of 222Rn concentrations in dwellings of the town of Metsovo in North-Western Greece. Health Phys. 79, 697e702. Karangelos, D.J., Petropoulos, N.P., Anagnostakis, M.J., Hinis, E.P., Simopoulos, S.E., 2004. J. Environ. Radioact. 77, 233e246. ska, M., Mnich, Z., Kapa1a, J., 2004. Seasonal changes in radon concentrations Karpin in buildings in the region of northeastern Poland. J. Environ. Radioact. 77, 101e109. Khan, A.J., 2000. A study of indoor radon levels in Indian dwellings, influencing factors and lung cancer risks. Radiat. Meas. 32, 87e92. Kovler, K., Perevalov, A., Levit, A., Steiner, V., Metzger, L.A., 2005. Radon exhalation of cementitious materials made with coal fly ash: Part 2 e testing hardened cement-fly ash pastes. J. Environ. Radioact. 82, 335e350. Krewski, D., Lubin, J.H., Zielinski, J.M., Alavanja, M., Catalan, V.S., Field, R.W., Klotz, J.B., Létourneau, E.G., Lynch, C.F., Lyon, J.I., Sandler, D.P., Schoenberg, J.B., Steck, D.J., Stolwijk, J.A., Weinberg, C., Wilcox, H.B., 2005. Residential radon and risk of lung cancer. A combined analysis of 7 North American case-control studies. Epidemiology 16, 137e145. Kritidis, P., Kamenopoulou, V., Kallithrakas-Kontos, N., 1994. Indoor radon concentrations in Athens determined with an optimized etched track detector technique. Radiat. Prot. Dosimetry 55, 149e152. Langroo, M.K., Wise, K.N., Duggleby, J.C., Kotler, L.H., 1991. A nation wide survey of 222 Rn and g-radiation levels in Australian homes. Health Phys. 61, 753e761. Marcinowski, F., Lucas, R.M., Yeager, W.M., 1994. National and regional distribution of airborne radon concentrations in U.S. homes. Health Phys. 66, 699e706. Meij, R., 1995. The distribution of trace elements during the combustion of coal. In: Swaine, D.J., Goodarzi, F. (Eds.), Environmental Aspects of Trace Elements in Coal. Kluwer Academic Publishers, The Netherlands. Miles, J.C.H., 2001. Temporal variation of radon levels in houses and implications for radon measurement strategies. Radiat. Prot. Dosimetry 93, 369e375. Ningappa, C., Sannappa, J., Chandrashekara, M.S., Paramesh, L., 2008. Concentrations of radon and its daughter products in and around Bangalore city. Radiat. Prot. Dosimetry 130, 459e465. Nikolopoulos, D., Louizi, A., Koukouliou, V., Serefoglou, A., Georgiou, E., Ntalles, K., Proukakis, Ch, 2002. Radon survey in Greece-risk assessment. J. Environ. Radioact. 63, 173e186. Papaefthymiou, H., Mavroudis, A., Kritidis, P., 2003. Indoor radon levels and influencing factors in houses of Patras, Greece. J. Environ. Radioact. 66, 247e260. Papaefthymiou, H., Kritidis, P., Anousis, J., Sarafidou, J., 2005. Comparative assessment of natural radioactivity in fallout samples from Patras and Megalopolis, Greece. J. Environ. Radioact. 78, 249e265. Papaefthymiou, H., Symeopoulos, B.D., Soupioni, M., 2007. Neutron activation analysis and natural radioactivity measurements of lignite and ashes from Megalopolis basin, Greece. J. Radioanal. Nucl. Chem. 274 (1), 123e130. Papaefthymiou, H., 2008. Elemental deposition in the vicinity of a lignite power plant in Southern Greece. J. Radioanal. Nucl. Chem. 275 (2), 433e439. Papaefthymiou, H., Gouseti, O., 2008. Natural radioactivity and associated radiation hazards in building materials used in Peloponnese, Greece. Radiat. Meas. 43, 1453e1457. Papastefanou, C., Stoulos, S., Manolopoulou, M., Ioannidou, A., Charalambous, S., 1994. Indoor radon concentrations in Greek apartment dwellings. Health Phys. 66, 270e273. Prasad, G., Prasad, Y., Gusain, G.S., Ramola, R.C., 2008. Measurement of radon and thoron levels in soil, water and indoor atmosphere of Budhakedar in Garhwal Himalaya, India. Radiat. Meas. 43, S375eS379. Psichoudaki, M., Papaefthymiou, H., 2008. Natural radioactivity measurements in the city of Ptolemais (Northern Greece). J. Environ. Radioact. 99, 1011e1017. Ramola, R.C., Kandari, M.S., Rawat, R.B.S., Ramachandran, T.V., Choubey, V.M., 1998. A study of seasonal variations of radon levels in different types of houses. J. Environ. Radioact. 39 (1), 1e7. Rouni, P.K., Petropoulos, N.P., Anagnostakis, M.J., Hinis, E.P., Simopoulos, S.E., 2001. Radioenvironmental survey of the Megalopolis lignite field basin. Sci. Total Environ. 272, 261e272. Sachs, H.M., Hernandez, T.L., Ring, J.W., 1982. Regional geology and radon variability in buildings. Environ. Int. 8, 97e103. Sarrou, I., Pashalidis, I., 2003. Radon levels in Cyprous. J. Environ. Radioact. 68, 269e277. Seredin, V.V., Finkelman, R.B., 2008. Metalliferous coals: a review of the main genetic and geochemical types. Int. J. Coal Geol. 76, 253e289. Siavalas, G., Kalaitzidis, S., Cornelissen, G., Chatziapostolou, A., Christanis, K., 2007. Influence of lignite mining and utilization on organic matter budget in the Alfeios River Plain, Peloponnese (South Greece). Energ. Fuel. 21 (5), 2698e2709. Stoulos, S., Manolopoulou, M., Papastefanou, C., 2003. Assessment of natural radiation exposure and radon exhalation from building materials in Greece. J. Environ. Radioact. 69, 225e240.
M. Manousakas et al. / Radiation Measurements 45 (2010) 1060e1067 Udovi ci c, V., Grabe z, B., Dragi c, A., Banjanac, R., Jokovi c, D., Pani c, B., Joksimovi c, D., 2009. Radon problem in an underground low-level laboratory. Radiat. Meas. 44, 1009e1012. UNSCEAR, 2000. Sources and Effects of Ionizing Radiation. In: Report to the General Assembly with Scientific Annexes, vol. I. United Nations Scientific Committee on the Effects of Atomic Radiation, United Nations, New York (Sources).
1067
Vinken, R., 1965. Stratigraphie und Tektonik des Beckens von Megalopolis (Peloponnes, Griechenland). Geol. Jb 83, 97e148. Zunic, Z.S., Yarmoshenko, I.V., Birovljev, A., Bochicchio, F., Quarto, M., Obryk, B., Paszkowski, M., Celikovi c, I., Demajio, A., Uji c, P., Budzanowski, M., Olko, P., McLaughlin, J.P., Waligorski, M.P.R., 2007. Radon survey in the high natural radiation region of Niska Banja, Serbia. J. Environ. Radioact. 92, 165e174.
Contents lists available at ScienceDirect
Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas
Technical Report
Indoor radon measurements in a Greek city located in the vicinity of lignite-fired power plants M. Manousakas a, A. Fouskas a, H. Papaefthymiou a, *, V. Koukouliou b, G. Siavalas c, P. Kritidis d a
Department of Chemistry, University of Patras, 26500 Patras, Greece International Atomic Energy Agency, Vienna c Department of Geology, University of Patras, 26500 Patras, Greece d NCSR “Demokritos”, 153 10 Aghia Paraskevi, Athens, Greece b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 June 2009 Received in revised form 27 April 2010 Accepted 31 July 2010
This work presents indoor radon measurements in 42 dwellings in the city of Megalopolis, Southern Greece, located in the vicinity of 2 lignite-fired power plants and examines the effect of season, floor level and age of the dwellings on indoor radon concentration. The radon measurements have been carried out using the LR-115, type II and CR-39 alpha track detectors in “closed-can” geometry. The average annual indoor radon concentration (GM) was found to be 52 Bq m3, which is well below the recommended action level of the European Union. This value corresponds to an annual effective dose to the population of 1.3 0.4 mSv. Season and age of the examined dwellings represent factors that affected significantly the indoor radon in Megalopolis, while the effect of floor level appeared to be not significant. Radium activity concentration values, measured by g-ray spectrometry in 20 sub-samples of six soil cores (60e135 cm depth), collected from the surrounding area of the city, were found to be consistent with the Greek and world average values. Based on the results of this study, it is concluded that the effect of the lignite-fired power plants on indoor radon concentration in Megalopolis’ dwellings was not significant. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Indoor radon Passive detectors Lignite-fired power plants Effective dose Greece
1. Introduction Radon (222Rn) is a decay product of 226Ra, which is in turn a decay product of 238U. Since uranium is present in all terrestrial materials, radon gas emanates from the bedrock underlying dwellings and can enter and reach high concentrations in indoor spaces mainly due to the lower pressure inside in relation to the atmosphere outside and in the ground. The diffusion of radon through the ground is related to permeability, which is dependent on grain-size distribution, degree of compaction and the water content of the soil (Durrani and Ilic, 1997). It is well established that the inhalation of radon (222Rn) and mainly its radioactive decay products, contributes more than 50% of the total radiation dose to the world population from natural sources (UNSCEAR, 2000). Many epidemiological case-control studies, which have been conducted in a number of countries, have shown a consistent statistically significant increase of lung cancer risk, due to exposure to radon in dwellings at even moderate levels of exposure and also a strong synergism with smoking (UNSCEAR, 2000; Krewski et al., 2005; Bochicchio, 2008).
* Corresponding author. Tel.: þ30 2610 997132; fax: þ30 2610 997118. E-mail address: [email protected] (H. Papaefthymiou). 1350-4487/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2010.07.024
Radon concentration varies from region to region and from country to country, depending on a number of factors e.g. geological characteristics of the underlying area, season of the year, meteorological parameters, type and construction characteristics of the house, building materials, ventilation, etc. (Durrani and Ili c, 1997). Large-scale radon surveys have been performed in many countries to estimate the indoor radon concentration and to determine the factors affecting its concentration (UNSCEAR, 2000; Langroo et al., 1991; Marcinowski et al., 1994; Sarrou and Pashalidis, 2003; Bochicchio et al., 2005). In Greece, the relatively larger radon survey has been carried out from 1995 to 1998 by Nikolopoulos et al. (2002). In this survey the arithmetic and geometric mean values for the indoor radon concentration were found to be 55 and 44 Bq m3, respectively. Additionally, according to UNSCEAR (2000), the arithmetic and geometric mean values for Greece are 73 and 52 Bq m3, respectively. Besides the natural sources of radiation, human activities, such as the burning of fossil fuels, can be a source of environmental radioactivity. It is well known that coal contains toxic trace elements along with naturally occurring radioactive elements, in concentrations, in some cases, higher than those in most sedimentary rocks (Seredin and Finkelman, 2008). During combustion, a considerable amount of toxic elements and radionuclides are released into the atmosphere as fly ash or vapors, while large
M. Manousakas et al. / Radiation Measurements 45 (2010) 1060e1067
amounts of these remain as bottom ash (Meij, 1995). The submicron fly ash particles, due to their high atmospheric mobility, can be transported over a wide range of distances and may constitute a potential hazard in the vicinity of the plant. Greek lignite, especially that of Megalopolis basin, contains high concentration of natural radionuclides, mainly that of the 238U decay series, while fly ash have been found to contain enhanced levels of 238U and 226Ra as compared to lignite (Papaefthymiou et al., 2007). The city of Megalopolis (Southern Greece) (Fig. 1) is located about 2.5 and 4 km NE to the lignite power plants A (Units I, II and III, 550 MW) and B (Unit IV, 300 MW), respectively, which are operated by the Public Power Corporation of Greece. The stack height of Units I and II is 120 m, while the heights of units III and IV are 180 and 206 m, respectively (Papaefthymiou et al., 2005). At full load, the units consume about 22e25 106 kg of pulverized lignite per day. Most of the produced fly ash is collected by electrostatic filters, which have a design collection efficiency of 99.6%, but in practice it falls to 95e96%. The lignite deposit of the Megalopolis basin is of very low gross calorific value (16.9 MJ kg1 on a dry basis) (Siavalas et al.,
1061
2007) and of high water and ash content (60% and 17%, respectively) (Papaefthymiou et al., 2007), reflecting its poor quality. Open fly ash deposits also exist around the power plants. Despite the relatively high height of the stacks, the 226Ra activity concentration in surface soil presented higher values within a distance of 0e5 km (26e337 Bq kg1) compared to that of 5e10 km (23e42 Bq kg1) from the power plants (Rouni et al., 2001). In addition, bulk deposition studies, which have been carried out in the city, showed significantly increased 238U-activity (Bq m2) in the deposited dust. About 70% of the uranium activity found in the fallout samples was attributed to the soil dust resuspension and 30% to the escaping fly ash from the power plants (Papaefthymiou et al., 2005). According to these results, the city of Megalopolis is located in the area of maximum deposition. Fly ash particles are also deposited inside dwellings, through doors and windows opened. The aims of this study were: to measure the indoor radon concentration levels in the city of Megalopolis, to assess the impact of the power plants operation on the radon concentration levels and to investigate the effect of season, floor level and age of the buildings
Fig. 1. Map of Greece showing the location of Megalopolis. The locations of the soil cores are shown in the amplification.
1062
M. Manousakas et al. / Radiation Measurements 45 (2010) 1060e1067
on radon levels. Activity concentration of 226Ra was also measured by g-spectrometry in sub-samples of six soil cores collected from the area around the city. Estimation of radiation dose to the population of Megalopolis due to indoor radon is also presented. In this survey, radon levels were monitored using the solid-state nuclear track detector (SSNTD) technique, which is the most reliable technique for integrated and long-term measurement of radon concentration inside dwellings (Durrani and Ili c, 1997). The measurements were performed over 1 year in four consecutive 3-month periods (seasons). 2. Experimental 2.1. Geology of the area Megalopolis is a small city (10,000 inhabitants) located on the Megalopolis basin at the centre of the Peloponnese Peninsula, Southern Greece (Fig. 1). Geologically, the margins of the basin consist of Mesozoic limestones, dolomites, cherts, and Upper Eocene to Upper Oligocene flysch (Vinken, 1965). The sediments filling the basin have been deposited from the Upper Pliocene until today and reflect a variety of terrestrial, fluvial, limnic, and telmatic palaeo-environments. At the central part of the basin the sediments reach their maximum thickness exceeding 500 m (Vinken, 1965). This sedimentary filling, which is mostly composed of fine sediments (clays and marls) along with the flysch formation constitute an impermeable cap for the permeable carbonate rocks outcropping at the western margins of the basin. Soil permeability values measured by Rouni et al. (2001) within a 10 km radius from the Megalopolis power pants were found to be 1015e109 m2 in the range 0e5 km and 1014e109 m2 in the range 5e10 km. These values show that the soil permeability is low and consistent with the geology of the area (Bowen, 1980). 2.2. Indoor radon measurements Indoor radon measurements were performed by means of the solid-state nuclear track detection technique, using the LR-115, type II detector in a “closed-can” geometry. The dosimeter was a metallic can (tin can, commercially available) in order to avoid the anisotropic deposition of radon decay products on the walls, which can be caused by static electric charges. The input of radon decay products in the dosimeter was avoided by use of black filter material (fabric), which also reduces the exposure of the detector to light and prevents the entry of dust and aerosol. A 10 mm 35 mm of the LR-115 detector material was used, of which a 10 mm 10 mm was exposed and a 10 mm 10 mm part, covered by a similar part of the detector, was used to determine the background track density. The rest part (5 mm 10 mm) was used to attach the film at the bottom of each dosimeter (Kritidis et al., 1994). A number of indoor radon measurements were also performed using the CR-39 detector. In this case, the dosimeter was a semi-cylindrical plastic cup with a base of 4.5 cm in diameter and a height of 2 cm. The cover of the cup contained a filter that prevented radon daughters from entering into the cup space. A piece of the CR-39 detector (13 37 mm) was attached at the bottom of the cup. Before exposure the holders and the detectors were dipped in a solution of a dilute detergent (1:5000) and allowed to dry before use to eliminate the electrostatic effects. Background checks were carried out on 10 randomly selected detectors per batch. The measurements were carried out for a 1 year (December 2005eNovember 2006) with the 3-month of the exposure time for each group of the detectors (December 2005eFebruary 2006, MarcheMay 2006, JuneeAugust 2006 and SeptembereNovember 2006). The aims of the measurements are to examine the seasonal
variations of the indoor radon levels and also to estimate the annual average radon concentration values. For this purpose, 50 dosimeters with the LR-115 detector were prepared for every season and distributed in 50 randomly selected dwellings in the city of Megalopolis. During summer and fall a second dosimeter with the CR-39 detector was placed side-by-side with the LR-115 one in 25 from a total of 50 dwellings for results’ comparison. The dosimeters were placed in the living room or bedroom, the two most frequently used rooms of each home, at 1 m height from the floor and away from windows and doors. In this way, a total of 4 LR-115 detectors were placed at each chosen dwelling (4 50 ¼ 200). In addition, a total of 50 (2 25 ¼ 50) CR-39 detectors were placed at each of the 25 selected dwellings. During the year, for various reasons, (dosimeters were lost or damaged, participants changed residence) a number of dosimeters failed to return or returned after the three-month exposure time. Complete data covering all four seasons were available for 42 sampling sites (4 42 ¼ 168). Our analysis was based on these dwellings that participated in all four seasons. Moreover, a total number of 8 CR-39 dosimeters were lost. Complete data for both detectors were available for 20 and 18 sampling sites during summer and fall, respectively. Most of the dwellings were made of fired clay bricks and reinforced concrete, while the oldest ones were made of stones with clay and/or cement and mainly wood for floors. The examined dwellings were mainly in different two to three storey buildings. The ventilation of all dwellings was natural, through open windows and doors. Most dwellings were heated by hot-water central heating system for about 5e6 months per year (NovembereApril). Full address and information concerning the characteristics of the dwellings (age of the building, heating system and type of building materials) were collected. After each 3-month exposure, the detectors were subjected to chemical processing with NaOH and then to track counting in a given area. The track counting was performed manually with a slide projector using an optimized technique for the LR-115 detectors (Kritidis et al., 1994), whereas an optical microscope was used for the CR-39 ones. Typical backgrounds for the LR-115 and the CR-39 detectors were 27 6 tracks cm2 and 20 4 tracks cm2, respectively. The calibration factors for converting the recorded track densities to Bq m3 were 2.3 103 tracks cm2 per Bq h m3 (with a standard deviation of 4%) and 2.6 103 tracks cm2 per Bq h m3 (with a standard deviation of 3%) for the LR-115 and CR-39 detectors, respectively. The statistical error of a single 3-month measurement at the average level of 40 Bq m3 was 9% (1s) and 8% for the LR-115 and CR-39 detectors, respectively. 2.3. Measurements of radium activity in soil samples Six soil cores (M1-M6) were collected from undisturbed sites around the city. The locations of the soil sampling sites are shown in Fig. 1. The sampling was performed with a steel corer tube placed vertically into the soil. The length of the soil cores ranged from 60 to 135 cm, depending on the ability of the corer to penetrate in the soil. After sampling, the cores were gently sliced to a resolution of 20e30 cm. All soil sub-samples were air dried, passed through a 2 mm sieve, homogenized and oven dried at a temperature of 105 C for 24 h. Then, the samples, ranging in mass from 50 to 70 g, were placed into cylindrical containers (20 mm height, 69 mm diameter), weighed, sealed hermetically and stored for 4 weeks prior to counting to establish secular radioactive equilibrium between 226Ra and its short-lived daughter products. Measurements of 226Ra activity concentration in soil samples were undertaken by means of a high-resolution g-ray detector (Canberra HPGe) coupled to a PC-based multichannel analyzer and the appropriate electronics. The detector has an efficiency of 25% and
M. Manousakas et al. / Radiation Measurements 45 (2010) 1060e1067
2.4. Statistical analysis
35
Frequency distribution (%)
an FWHM of 1.9 keV for the 60Co g-ray energy line at 1332 keV. The procedures of energy and efficiency calibrations are described in detail elsewhere (Papaefthymiou et al., 2007). The duration of measurements was 24 h to obtain satisfactory statistical precision. The 226Ra activity concentration was derived from the weighted mean of the photopeak of 214Bi (609.3 keV) and the two photopeaks of 214Pb (295.2 and 352.0 keV). The detection limits (2s) for a 24-h counting time were 0.8 and 0.7 Bq kg1 for 214Bi and 214Pb, respectively.
1063
30 25 20 15 10 5 0
2.5. Effective dose calculation The effective dose (ED) to the population of the Megalopolis city was calculated from the following formula according to (UNSCEAR, 2000):
ED mSv y1 ¼ CRn F OF DC 106 where CRn is the calculated geometric mean value (Bq m3) of the indoor radon concentration, OF is the indoor occupancy factor, F is the mean equilibrium factor indoors and DC is the dose conversion factor. 3. Results and discussion 3.1. Indoor radon concentrations Fig. 2 presents the frequency distribution histogram of the full year indoor radon concentration measurements. As shown in this figure, the distribution of the radon concentrations appears to be log-normal (highly skewed to the right), as confirmed by the applied KolmogoroveSmirnov normality test (Z ¼ 1.715, P ¼ 0.006). As a result, the geometric means were used for results’ description and statistical comparisons. Table 1 gives summary statistics for the measured 222Rn concentration levels in the surveyed dwellings during the examined four seasons, as well as for the estimated annual average concentrations. The annual geometric mean was found to be 52 Bq m3 with a GSD of 1 Bq m3 and varied from 29 to 164 Bq m3, while the arithmetic mean and the standard deviation were 56 and 24 Bq m3, respectively. These values are consistent with the Greek average values. None of the total 42 dwellings under consideration exceeded the action levels of 400 and 200 Bq m3, proposed by the European Commission (EC, 1990) for old (before 1990) and newer (after 1990) houses, respectively, while only one exceeds the recommendation by the US EPA action level of 150 Bq m3 (EPA, 2003).
0 26 024 0 24 022 0 22 020 0 20 018 0 18 016 0 16 014 0 14 012 0 12 010 00 -1 80 0 -8 60 0 -6 40 0 -4 20 20 0-
The KolmogoroveSmirnov normality test was applied to the log-transformed data to verify the hypothesis, that the data set follows log-normal distribution. Evaluation of the significance of the difference between means for the three examined factors (season, floor level and age of the dwellings) was performed using three-way analysis of variance (3-way ANOVA). The season factor had 4 levels (winter, spring, summer and fall), the location factor had 3 levels (ground, 1st floor, 2nd floor) and the age factor had also 3 levels (1st: dwellings constructed during the period 1930e1955, 2nd: dwellings constructed during the period 1956e1980 and 3rd: dwellings constructed during the period 1981e2005). The Tamhane test was used for multiple comparisons. Paired t-test was used to evaluate the significance of the difference between mean values (GM) in radon concentrations obtained for summer and fall by both types of detectors (LR-115 and CR-39). Statistical analysis was performed using the SPSS v.15 software package.
Indoor radon concentration (Bq m-3) Fig. 2. Frequency distribution of the indoor Megalopolis.
222
Rn concentration in the city of
Table 2 reports the mean temperature and wind velocity during the four seasons and the respective minimum and maximum values. As is the case in Mediterranean countries, winter presented the lowest mean and minimum temperatures, whereas summer the highest ones. On the other hand, wind velocity presented the highest mean value during winter and the lowest during summer. Radon concentrations in dwellings are subjected to seasonal variation due to a number of factors (e.g. geological and meteorological factors, dwelling characteristics and habits of the inhabitants). The main trend in Mediterranean countries, as well as in a number of other countries is maximum radon concentration values in winter and minimum in summer (Papastefanou et al., 1994; Ramola et al., 1998; Papaefthymiou et al., 2003; Zunic et al., 2007; Hadad et al., 2007; Faheem et al., 2007; Prasad et al., 2008; Ningappa et al., 2008; Udovi ci c et al., 2009). As shown in Table 1, the highest average radon concentration (GM) in Megalopolis was observed in winter followed by summer, while the lowest one was observed in spring. This trend differs to some extent with the general trend mentioned above. The average winter-to-summer ratio was 1.6 1.2 (varied from 0.3 to 6.5), while for Patras (Greece) the average ratio was 2.8 1.2 (Papaefthymiou et al., 2003). Results reported by a number of researchers also show that in some cases (e.g. houses situated on mountain slopes) radon values in summer are higher compared to those in winter (Arvela et al., ska et al., 2004; Friedmann, 2005). Also Miles (2001) 1988; Karpin reports that a significant minority of houses (10e20% in the UK) have no substantial seasonal variation or follow a different pattern. As mentioned earlier in the text, Megalopolis is located in the vicinity of 2 lignite-fired power plants. Measurements of natural radioactivity in bulk deposition samples collected in Megalopolis city on a monthly basis during 1997, showed enhanced activity concentration values of 238U. It is also worthy to notice that the uranium deposition rates were directly influenced by NW directed emissions, which was the prevailing wind direction during summer (Papaefthymiou, 2008). According to the inhabitants, during
Table 1 Annual average and seasonal indoor radon concentrations (Bq m3) during December 2006eNovember 2007 in the city of Megalopolis (N ¼ 42).
Winter Spring Summer Fall Annual
AM
SD
GM
GSD
Min
Max
74 40 61 48 56
39 27 40 21 24
65 33 51 45 52
2 2 2 2 1
25 12 13 21 29
241 121 218 116 164
AM: arithmetic mean; SD: standard deviation; GM: geometric mean; GSD: geometric standard deviation; Min: minimum value; Max: maximum value.
1064
M. Manousakas et al. / Radiation Measurements 45 (2010) 1060e1067
the
examined
Wind velocity (m s
AM SD
Min
Max
AM SD
1 0 5 0
16 24 32 27
1.44 1.23 1.10 1.22
7 14 24 16
4 5 3 5
during
December
1
Temperature ( C)
Winter Spring Summer Fall
area
1.00 0.49 0.49 0.53
)
Min
Max
0.06 0.33 0.19 0.59
4.41 3.49 2.81 3.22
AM: arithmetic mean; SD: standard deviation.
summer, due to the tendency to open windows, fly ash particles were deposited on the walls, floor and furniture inside dwellings. On the other hand, the open windows may decrease the indoor radon concentration. Although radium concentration is enhanced in Megalopolis fly ash samples, radon exhalation rates were found to be significantly lower than that of Megalopolis lignite. According to Karangelos et al. (2004), this could be attributed to the virtification of the produced fly ash, which results in a decrease of the emanation of radon from the grain. The data were divided into three categories according to the floor level of the house, where the dosimeter was placed: the first contains the measurements taken in the ground floor, the second in the 1st floor and the 3rd in the 2nd floor level. Summary statistics of radon measurements in ground, 1st and 2nd floor are presented in Table 3. As can be seen from Tables 1 and 3, the highest value of 241 Bq m3 was observed during winter in the ground floor, while the lowest one (12 Bq m3) during spring in the 1st floor. The average radon concentration (GM) decreases from ground to the 1st floor, whereas the values for the 1st and 2nd floor levels are more or less the same. Similar results are also reported by other researchers in Greece (Kritidis et al., 1994; Ioannides et al., 2000; Nikolopoulos et al., 2002; Papaefthymiou et al., 2003) and in other countries (Khan, 2000; Bochicchio et al., 2005; Zunic et al., 2007). Fig. 3 presents the seasonal averaged indoor radon concentrations in different floors. As shown in this figure, winter presents the highest radon values in all floors examined. The surveyed dwellings were also classified into three categories based on the age of the buildings, which is related to the type and quantity of material used and the building technique employed (Psichoudaki and Papaefthymiou, 2008): (1) those that were constructed during the period 1930e1955, (2) buildings that were constructed during the period 1956e1980 and (3) those that were constructed after 1980. The old buildings were constructed with stones, clay or/and cement and mainly wood for floors, while recent buildings were constructed with reinforced concrete and fired clay bricks and have thinner walls (categories II and III). The main difference between the last two categories is that category (III) contains buildings which were built with concrete made by cement, containing fly ash. Fig. 4 presents the dependence of radon concentration on construction materials in different seasons. As shown in this figure, old dwellings present higher radon concentration in all four seasons. Table 3 Variation of the indoor radon concentration (Bq m3) with the floor level.
Ground 1st floor 2nd floor
N
AM
SD
GM
GSD
Min
Max
60 88 24
60 54 50
41 32 21
51 45 46
2 2 2
13 12 15
241 147 110
N: number of measurements; AM: arithmetic mean; SD: standard deviation; GM: geometric mean; GSD: geometric standard deviation; Min: minimum value; Max: maximum value.
Radon concentration (Bq m–3)
75 concerning
70
Ground 1st 2nd
65 60 55 50 45 40 35 30 25 Winter
Spring
Summer
Fall
Fig. 3. Seasonal averaged indoor radon concentrations in different floors.
It is well known that building materials contribute to internal radiation exposure due to the exhalation of short-lived radon daughter products. Elevated radiation may arise when by-products with high natural radioactivity, such as fly ash from coal-fired power plants, are used in the production of building materials (UNSCEAR, 2000). In Greece, since the beginning of the 1980s, dwellings were constructed with concrete made by cement containing up to 20% fly ash containing high activity concentrations, mainly of 238U and 226Ra (Papaefthymiou et al., 2007). The addition of fly ash may enhance the radon exhalation from concrete, which will in turn increase the indoor radon concentrations. Table 4 contains the arithmetic and geometric means of radon concentration of each period, together with the minimum and the maximum values. As shown in this table, dwellings constructed during the period 1930e1955 seem to present the highest average radon concentration, which could be attributed to the higher permeability of old constructions or to the building movement over time. In addition, dwellings constructed after 1980 seem to present higher average radon concentration compared to those constructed during the period 1956e1980. This may be attributed to the higher 226Ra content in cement used for concrete production, due to the addition of fly ash (Papaefthymiou and Gouseti, 2008) or to better tightness of modern buildings. Similar results have been observed in Ptolemais, a city in Northern Greece (Psichoudaki and Papaefthymiou, 2008). Three-way analysis of variance was applied to the obtained data to examine the effect of the studied factors on radon concentration levels. The factors considered were season, floor level in which dosimeter was placed and the age of the examined dwellings. Statistical analysis showed that there is no statistically significant interaction between the three examined factors on radon concentrations (floor by age: F ¼ 0.330 on 3 and 168 df (degree of
Indoor radon concetration (Bq m–3)
Table 2 Meteorological data 2005eFebruary 2006.
85 1930-1955 1956-1980 1981-2005
80 75 70 65 60 55 50 45 40 35 30 Winter
Spring
Summer
Fall
Fig. 4. Seasonal averaged indoor radon concentrations in different ages of the dwellings.
M. Manousakas et al. / Radiation Measurements 45 (2010) 1060e1067 Table 4 Variation of the indoor radon concentration (Bq m3) with the age of the examined dwellings.
1930e1955 1956e1980 1981e2005
1065
Table 5 Comparison between indoor radon measurements obtained with the LR-115 and the CR-39 detectors.
N
AM
SD
GM
GSD
Min
Max
Summer
12 64 92
69 49 59
25 26 40
64 43 49
2 2 2
29 13 12
117 116 241
LR-115
CR-39
LR-115
CR-39
71 44 62 2
84 52 72 2
42 13 40 1
39 15 37 1
N: number of measurements; AM: arithmetic mean; SD: standard deviation; GM: geometric mean; GSD: geometric standard deviation; Min: minimum value; Max: maximum value.
freedom), P ¼ 0.803; floor by season: F ¼ 0.676 on 6 and 168 df, P ¼ 0.669; age by season: F ¼ 0.418 on 6 and 168 df, P ¼ 0.866; floor by season by age: F ¼ 1.037 on 9 and 168 df, P ¼ 0.414). Regarding main effects, the analysis showed a significant seasonal effect (F ¼ 4.774 on 3 and 168 df, P ¼ 0.003). The multiple comparison tests showed that the average radon concentration in winter was significantly higher than that of spring and fall (P < 0.005 and P ¼ 0.002, respectively), while the average concentration in summer was significantly higher compared to that of spring (P ¼ 0.007). At this time it is not entirely clear what causes the enhanced radon levels in summer compared to those of spring and fall. As shown in Table 2, these results could not be attributed to meteorological parameters such as temperature and wind velocity or to the presence of small amounts of fly ash inside dwellings. Occupant activities affecting ventilation could be possibly a reason for these results. Further investigations are needed to elucidate these findings. The effect of building age was also significant (F ¼ 3.172 on 2 and 168 df, P ¼ 0.045). Specifically, the average radon concentration in the old dwellings (51e76 years) was significantly higher compared to those 25e49 years old (P ¼ 0.024). Significant relation in radon concentration with the age of the buildings has been also found by other researchers (Galleli et al., 1998). This may be attributed to the higher air-tightness and to changes in building materials (e.g. use of concrete instead of wood for the construction of floors), which lead to a decrease in the permeability of the buildings. It seems that the presence of fly ash in cement, used for the construction of the newer dwellings, does not influence significantly the indoor radon concentration, although the radium content of cement used for concrete production (Portland cement type II and fly ash) is higher compared to other building materials used in Peloponnese, Greece (Papaefthymiou and Gouseti, 2008). This could be attributed to the fact that the radon exhalation from samples of concrete with fly ash as an additive is slightly influenced or even decreased, despite the higher 226Ra content (Stoulos et al., 2003; Kovler et al., 2005). The average radon concentration value in the ground floor was higher compared to those in the 1st and 2nd floor, but the statistical analysis showed that the differences in mean values were non significant (F ¼ 0.525 on 2 and 168 df, P ¼ 0.593). Given that the diffusion chambers were not exposed on different floors of the same buildings and the poor statistics of the sample, this could be considered as indicative and cannot be used for any detailed conclusion. Similar results have been found for Ptolemais (Northern Greece) (Psichoudaki and Papaefthymiou, 2008).
AM SD GM GSD
Fall
AM: arithmetic mean; SD: standard deviation GM: geometric mean; GSD: geometric standard deviation.
Paired t-test applied to the data set showed that the differences in mean radon concentration values (GM) obtained by the LR-115 and CR-39 detectors during summer and fall were not statistically significant (P ¼ 0.067 and P ¼ 0.435, respectively). Moreover, with regard to season, a significant difference was found between measurements obtained during summer and fall using the CR-39 (detector (P < 0.001), which is consistent with the results obtained using the LR-115 detector. 3.3. Activity concentration of
226
Ra in soil samples
The average activity concentrations of 226Ra in all 6 cores are presented in Table 6, along with the Greek and world average soil values. It is apparent from this table that radium is almost uniformly distributed with depth. The 226Ra activity concentration ranged from 22 to 29 Bq kg1 and all examined cores presented more or less the same average activity concentration value of 226Ra. The average 226Ra activity concentration for all six cores was found to be 25.0 1.5 Bq kg1, which is consistent with the Greek and world average values for soil (UNSCEAR, 2000). Given that the permeability of the geological substrate in the examined area is low, the average indoor radon concentration in the examined area seems to be consistent with the radium content of the soil underneath dwellings. Although the radium (uranium) content of the geological formations underneath dwellings is not the only parameter controlling the indoor radon, the knowledge of radium content in a region is useful information for predicting indoor radon concentrations, especially in substrates with high radium concentrations (Sachs et al., 1982). 3.4. Effective dose due to indoor radon To evaluate the annual effective dose for the adult inhabitants of the city of Megalopolis in the indoor environment, a dose conversion factor of 9 nSv per Bq m3, a mean equilibrium value of 0.4 and an occupancy factor of 80% were adopted according to UNSCEAR (2000). As mentioned above, the average annual radon concentration ranged from 29 to 164 Bq m3. These values correspond to an annual effective dose ranging from 0.73 to 4.1 mSv, with a mean value of 1.4 0.6 mSv. Based on the annual geometric mean value the effective dose is 1.3 0.4 mSv y1. This value is slightly higher than Table 6 Average activity concentration of
226
Ra in the collected soil cores. Bq kg1 d.w SD
3.2. Comparison of LR-115 and CR-39 radon measurements During summer and fall, two types of detectors (LR-115 and CR39) were placed side-by-side in a number of the examined dwellings for results’ comparison. Summary statistics of the obtained results are presented in Table 5. It is obvious from this table that the patterns of both detectors are quite similar: the average radon concentration during summer is higher as compared to the one during fall.
Core
Average Greek soila World soila a
UNSCEAR (2000).
M1 M2 M3 M4 M5 M6
23.3 1.5 24.1 0.5 24.6 2.5 24.7 2.2 27.8 0.9 25.2 1.8 25.0 1.5 25 (1e240) 35 (17e60)
1066
M. Manousakas et al. / Radiation Measurements 45 (2010) 1060e1067
the world average annual effective dose of 1 mSv for radon and its decay products (UNSCEAR, 2000). Moreover, it is also higher than the annual average value of 0.8 mSv found by Nikolopoulos et al. (2002) for Greece. On the basis of the ICRP (1993) recommendations for radon in dwellings, the estimated annual dose in all cases except one is well below the recommended action levels (3e10 mSv y1). Based on these estimates, it is concluded that the dwellings under investigation in the city of Megalopolis are generally characterized by low radon exposure dose. 4. Conclusions Indoor radon measurements were performed in 42 dwellings in the city of Megalopolis, Southern Greece, which is located in the vicinity of 2 lignite-fired power plants. Radon measurements have been carried out using solid-state nuclear track detectors during a whole year and conducted as four consecutive 3-month periods to obtain integrated 1-year concentrations. Since 222Rn is a decay product of 226Ra, the radium content was also measured in soil cores collected from the surrounding area. The average annual radon concentration (GM) was found to be well below the action levels recommended by European Commission and US EPA and is consistent with the 226Ra activity concentrations measured in soil cores taking into account the low permeability of the bedrock of the examined area. The calculated annual effective dose was found to be slightly higher than the Greek average value, but lower than the ICRP recommended action levels. The season of the year and the age of the buildings are factors that significantly influence the indoor radon levels in the city of Megalopolis, whereas the floor level does not. The seasonal pattern presented deviation from the general trend with higher values in winter and lower in summer. These results suggest that the seasonal correction factors should not be used everywhere in Greece. Based on the results of this study, no significant increase in indoor radon concentration in Megalopolis due to its vicinity with lignite-fired power plants could be detected. Acknowledgments The authors would like to thank the residents and the mayor of the Megalopolis city for their help during the radon measurements. References Arvela, H., Voutilainen, A., Mäkeläinen, I., Castren, O., Winqvist, K., 1988. Comparison of predicted and measured variations of indoor radon concentration. Radiat. Prot. Dosimetry 24, 231e235. Bochicchio, F., Campos-Venuti, G., Piermattei, S., Nuccetelli, C., Risica, S., Tommasino, L., Torri, G., Magnoni, M., Agnesod, G., Sgorbati, G., Bonomi, M., Minach, L., Trotti, F., Malisan, M.R., Maggiolo, S., Gaidolfi, L., Giannardi, C., Rongoni, A., Lombardi, M., Cherubini, G., D’Ostilio, S., Cristofaro, C., Pugliese, M., Martucci, V., Crispino, A., Cuzzocrea, P., Sansone Santamaris, A., Cappai, M., 2005. Annual average and seasonal variations of residential radon concentration for all the Italian Regions. Radiat. Meas. 40, 686e694. Bochicchio, F., 2008. The radon issue: considerations on regulatory approaches and exposure evaluations on the basis of recent epidemiological results. Appl. Radiat. Isot. 66, 1561e1566. Bowen, R., 1980. Ground Water. Applied Science Publ., London. Durrani, S.A., Ili c, R. (Eds.), 1997. Radon Measurements by Etched Track Detectors. World Scientific Publishing Co., Singapore. EPA, 2003. Assessment of risks from radon in homes. Air and Radiation, EPA 402-R03e003. EC (European Commission), 1990. Council Directive 90/143/EC of 21 February 1990 on the protection of the public against indoor exposure to radon. Official J. Eur. Commun.. Faheem, M., Mati, N., Matiullah, 2007. Seasonal variation in indoor radon concentrations in dwellings in six districts of the Punjab province, Pakistan. J. Radiol. Prot. 27, 493e500. Friedmann, H., 2005. Final results of the Austrian radon project. Health Phys. 89, 339e348.
Galleli, G., Panatto, D., Lai, P., Orlando, P., Risso, D., 1998. Relevance of main factors affecting radon concentration in multi-storey buildings in Liguria (Nothern Italy). J. Environ. Radioact. 39 (2), 117e128. Hadad, K., Doulatdar, R., Mehdizadeh, S., 2007. Indoor radon monitoring in Northern Iran using passive and active measurements. J. Environ. Radioact. 95, 39e52. International Commission on Radiological Protection (ICRP), 1993. Protection Against Radon at Home and Work. ICRP. Publication 65. Ioannides, K.G., Stamoulis, K.C., Papachristodoulou, C.A., 2000. A survey of 222Rn concentrations in dwellings of the town of Metsovo in North-Western Greece. Health Phys. 79, 697e702. Karangelos, D.J., Petropoulos, N.P., Anagnostakis, M.J., Hinis, E.P., Simopoulos, S.E., 2004. J. Environ. Radioact. 77, 233e246. ska, M., Mnich, Z., Kapa1a, J., 2004. Seasonal changes in radon concentrations Karpin in buildings in the region of northeastern Poland. J. Environ. Radioact. 77, 101e109. Khan, A.J., 2000. A study of indoor radon levels in Indian dwellings, influencing factors and lung cancer risks. Radiat. Meas. 32, 87e92. Kovler, K., Perevalov, A., Levit, A., Steiner, V., Metzger, L.A., 2005. Radon exhalation of cementitious materials made with coal fly ash: Part 2 e testing hardened cement-fly ash pastes. J. Environ. Radioact. 82, 335e350. Krewski, D., Lubin, J.H., Zielinski, J.M., Alavanja, M., Catalan, V.S., Field, R.W., Klotz, J.B., Létourneau, E.G., Lynch, C.F., Lyon, J.I., Sandler, D.P., Schoenberg, J.B., Steck, D.J., Stolwijk, J.A., Weinberg, C., Wilcox, H.B., 2005. Residential radon and risk of lung cancer. A combined analysis of 7 North American case-control studies. Epidemiology 16, 137e145. Kritidis, P., Kamenopoulou, V., Kallithrakas-Kontos, N., 1994. Indoor radon concentrations in Athens determined with an optimized etched track detector technique. Radiat. Prot. Dosimetry 55, 149e152. Langroo, M.K., Wise, K.N., Duggleby, J.C., Kotler, L.H., 1991. A nation wide survey of 222 Rn and g-radiation levels in Australian homes. Health Phys. 61, 753e761. Marcinowski, F., Lucas, R.M., Yeager, W.M., 1994. National and regional distribution of airborne radon concentrations in U.S. homes. Health Phys. 66, 699e706. Meij, R., 1995. The distribution of trace elements during the combustion of coal. In: Swaine, D.J., Goodarzi, F. (Eds.), Environmental Aspects of Trace Elements in Coal. Kluwer Academic Publishers, The Netherlands. Miles, J.C.H., 2001. Temporal variation of radon levels in houses and implications for radon measurement strategies. Radiat. Prot. Dosimetry 93, 369e375. Ningappa, C., Sannappa, J., Chandrashekara, M.S., Paramesh, L., 2008. Concentrations of radon and its daughter products in and around Bangalore city. Radiat. Prot. Dosimetry 130, 459e465. Nikolopoulos, D., Louizi, A., Koukouliou, V., Serefoglou, A., Georgiou, E., Ntalles, K., Proukakis, Ch, 2002. Radon survey in Greece-risk assessment. J. Environ. Radioact. 63, 173e186. Papaefthymiou, H., Mavroudis, A., Kritidis, P., 2003. Indoor radon levels and influencing factors in houses of Patras, Greece. J. Environ. Radioact. 66, 247e260. Papaefthymiou, H., Kritidis, P., Anousis, J., Sarafidou, J., 2005. Comparative assessment of natural radioactivity in fallout samples from Patras and Megalopolis, Greece. J. Environ. Radioact. 78, 249e265. Papaefthymiou, H., Symeopoulos, B.D., Soupioni, M., 2007. Neutron activation analysis and natural radioactivity measurements of lignite and ashes from Megalopolis basin, Greece. J. Radioanal. Nucl. Chem. 274 (1), 123e130. Papaefthymiou, H., 2008. Elemental deposition in the vicinity of a lignite power plant in Southern Greece. J. Radioanal. Nucl. Chem. 275 (2), 433e439. Papaefthymiou, H., Gouseti, O., 2008. Natural radioactivity and associated radiation hazards in building materials used in Peloponnese, Greece. Radiat. Meas. 43, 1453e1457. Papastefanou, C., Stoulos, S., Manolopoulou, M., Ioannidou, A., Charalambous, S., 1994. Indoor radon concentrations in Greek apartment dwellings. Health Phys. 66, 270e273. Prasad, G., Prasad, Y., Gusain, G.S., Ramola, R.C., 2008. Measurement of radon and thoron levels in soil, water and indoor atmosphere of Budhakedar in Garhwal Himalaya, India. Radiat. Meas. 43, S375eS379. Psichoudaki, M., Papaefthymiou, H., 2008. Natural radioactivity measurements in the city of Ptolemais (Northern Greece). J. Environ. Radioact. 99, 1011e1017. Ramola, R.C., Kandari, M.S., Rawat, R.B.S., Ramachandran, T.V., Choubey, V.M., 1998. A study of seasonal variations of radon levels in different types of houses. J. Environ. Radioact. 39 (1), 1e7. Rouni, P.K., Petropoulos, N.P., Anagnostakis, M.J., Hinis, E.P., Simopoulos, S.E., 2001. Radioenvironmental survey of the Megalopolis lignite field basin. Sci. Total Environ. 272, 261e272. Sachs, H.M., Hernandez, T.L., Ring, J.W., 1982. Regional geology and radon variability in buildings. Environ. Int. 8, 97e103. Sarrou, I., Pashalidis, I., 2003. Radon levels in Cyprous. J. Environ. Radioact. 68, 269e277. Seredin, V.V., Finkelman, R.B., 2008. Metalliferous coals: a review of the main genetic and geochemical types. Int. J. Coal Geol. 76, 253e289. Siavalas, G., Kalaitzidis, S., Cornelissen, G., Chatziapostolou, A., Christanis, K., 2007. Influence of lignite mining and utilization on organic matter budget in the Alfeios River Plain, Peloponnese (South Greece). Energ. Fuel. 21 (5), 2698e2709. Stoulos, S., Manolopoulou, M., Papastefanou, C., 2003. Assessment of natural radiation exposure and radon exhalation from building materials in Greece. J. Environ. Radioact. 69, 225e240.
M. Manousakas et al. / Radiation Measurements 45 (2010) 1060e1067 Udovi ci c, V., Grabe z, B., Dragi c, A., Banjanac, R., Jokovi c, D., Pani c, B., Joksimovi c, D., 2009. Radon problem in an underground low-level laboratory. Radiat. Meas. 44, 1009e1012. UNSCEAR, 2000. Sources and Effects of Ionizing Radiation. In: Report to the General Assembly with Scientific Annexes, vol. I. United Nations Scientific Committee on the Effects of Atomic Radiation, United Nations, New York (Sources).
1067
Vinken, R., 1965. Stratigraphie und Tektonik des Beckens von Megalopolis (Peloponnes, Griechenland). Geol. Jb 83, 97e148. Zunic, Z.S., Yarmoshenko, I.V., Birovljev, A., Bochicchio, F., Quarto, M., Obryk, B., Paszkowski, M., Celikovi c, I., Demajio, A., Uji c, P., Budzanowski, M., Olko, P., McLaughlin, J.P., Waligorski, M.P.R., 2007. Radon survey in the high natural radiation region of Niska Banja, Serbia. J. Environ. Radioact. 92, 165e174.