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Journal of Environmental Radioactivity 63 (2002) 173–186 www.elsevier.com/locate/jenvrad

Radon survey in Greece—risk assesment Dimitrios Nikolopoulos a,∗, Anna Louizi a, Virginia Koukouliou b, Athina Serefoglou a, Evangelos Georgiou a, Konstantinos Ntalles a, Charalambos Proukakis a a

Medical Physics Department, Medical School University of Athens, Mikras Asias 75, 115 27, Goudi, Athens, Greece b Greek Atomic Energy Commission, 153 10, Agia Paraskevi, Athens,Greece Received 9 July 2001; received in revised form 17 February 2002; accepted 21 February 2002

Abstract A large scale radon survey using track etch detectors has been carried out from 1995 to 1998 in Greece in order to estimate the radon concentrations in Greek dwellings and the exposure of the Greek population to radon. The total data set consisted of 1277 samples. Residential potential alpha energy concentration values ranged between (0.024±0.009) and (8±1) WLM per year (P⬍0.05) and effective doses between (0.09±0.04) and (28±4) mSv (P⬍0.05). The mean lifetime risk for the Greek population due to radon was found to be 0.4%.  2002 Elsevier Science Ltd. All rights reserved. Keywords: Radon; Survey; Risk assessment; Greece

1. Introduction Human exposure to high concentrations of radon gas has been correlated to lung cancer incidence, although the effect of low doses is not well defined (Auvinen et al., 1996; Pershagen, Liang, Zdenek, Svensson, & Boice, 1992). Due to elevated concentrations frequently found indoors, residential radon research is still in progress

Corresponding author. Tel.: +3010-746-23-68/746-23-70; Fax: +3010-746-23-69. E-mail address: dnikolop@med.uoa.gr (D. Nikolopoulos).

0265-931X/02/$ - see front matter  2002 Elsevier Science Ltd. All rights reserved. PII: S 0 2 6 5 - 9 3 1 X ( 0 2 ) 0 0 0 2 6 - 7


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(Gerken, Kreienbrock, Wellmann, Kreuzer, & Wichmann, 2000; Yu, Lau, Guan, Lo, & Young, 2000). Small-scale measurements of radon gas concentration within dwellings in Greece have been reported (Proukakis, Molfetas, Ntalles, Georgiou, & Serefoglou, 1988; Georgiou, Ntalles, Molfetas, Athanassiadis, & Proukakis, 1988a; Georgiou, Ntalles, Anagnostopoulos, Proukakis, & Athanassiadis, 1988b; Papastefanou, Stoulos, Manolopoulou, Ioannidou, & Charalambous, 1994; Ioannides, Stamoulis, & Papachristodoulou, 2000). Continuing the radon investigation conducted by the Medical Physics Department-University of Athens (MPD-UOA) since 1988, a large-scale nationwide residential radon survey in Greece was designed and performed, using dosimeters of MPD-UOA construction, fully calibrated and tested by the MPD-UOA (Nikolopoulos, Louizi, Petropoulos, Simopoulos, & Proukakis, 1999). The main scope was to obtain an adequate estimation of the annual radon concentration distribution indoors, to assess the average risk, and to determine the percentage of dwellings in which radon concentrations exceed certain reference levels.

2. Materials and methods 2.1. Statistical data The most recently published demographical data is the 1991 census, according to which, Greece had a population of 10.4 million people (National Statistical Service of Greece, 1995). The population was highly concentrated in urban areas, and mainly in Athens where about 37% of the total population resided. The total number of buildings was 3.8 million. Approximately 75% (2.85 million) of the buildings were used as dwellings. The occupants per dwelling ratio was on average 3.0 and was subjected to small variations within urban, semi-urban and rural areas. The buildings were classified by the National Statistical Service of Greece (NSSG) according to their use. Those used as residencies, were distinguished in conventional and non-regular dwellings, regular rooms and institutional households. The residencies constituting by at least one room higher than 2 m and larger than 4 m2 with direct day light from window or glass door, were considered as conventional dwellings (National Statistical Service of Greece, 1995). Building data were provided nationwide according to an administrative partition proposed by the NSSG. The data about the number of stories, building attributes and occupational status of each separate conventional dwelling, provided by the NSSG, concerned only part of the capital (Athens). For the rest of the country the data were given only in an accumulative manner. Moreover, the NSSG provided no maps through which the geographical coordinates of each house could be found. 2.2. Sampling design Due to the limitations placed by the demographical data, and taking into account the financial and work power of the MPD-UOA, the radon survey was not based on


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a grid division but was administratively designed. The sampling design was based on the partition proposed by the NSSG. Ten administrative districts, called regions, were divided into prefectures, called departments, which were subdivided into provinces. These were organized in municipalities and communes, which included villages and city quarters. Sampling design was based on the following procedure: a sampling density of 1 per 1000 conventional dwellings was adopted, balancing both feasibility and precision of estimation. The number of samples was calculated for a department, according to the total number of its conventional dwellings. This number was further allocated to each province, in proportion to the fraction of the number of conventional dwellings of the province over the total number of conventional dwellings of the department. Continuing, the sample number of each province was allocated to its municipalities and communes, in proportion to the number of the conventional dwellings of the municipality or commune over the total number of conventional dwellings of the province. The procedure was followed, so as to allocate adequate number of samples to each village or city quarter (Nikolopoulos, Maddison, Louizi, & Proukakis, 1997).

2.3. Experimental apparatus

The experimental apparatus was the MPD radon dosimeter (Nikolopoulos, Louizi, Papadimitriou, & Proukakis, 1997). The dosimeter consisted of a cylindrical nonconductive plastic cup of 5 cm height and 1.5 cm radius. The cover had a 3 mm hole on the center and a filter that prevented radon daughters from entering. Radon was detected by a 2Ă—2 cm CR-39 nuclear track detector placed at the bottom of the cup. The overall uncertainty of radon measurement in the 95% confidence interval was below 10% (Nikolopoulos et al., 1999). The 12-mo exposure period was selected due to the best estimation of the average value it provides. One detector was installed in each sampled conventional dwelling, placed in the bedroom 1 m above the ground, near the wall.

2.4. Measurement procedure

Detectors were installed by trained personnel. A door-to-door approach was selected, so as to minimize non-response and bias. This scheme was generally followed and changed only by restrictions placed at the implementation stage (i.e. refusals and other difficulties). Within every sampling location, dwellings were selected by the personnel, so as to sample nationwide all types of buildings. In each case, a questionnaire was filled and the inhabitant was given informative brochures. At the end of the 12-mo period the dosimeters were collected, either via door-to-door approach or via post.


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3. Results The survey was carried out between July of 1995 and August 1998 with the installation of 1500 MPD dosimeters in 834 locations (i.e. villages and city quarters) resulting in the sampling of 1061 dwellings in 722 locations. The data included an additional 216 samples in 12 locations collected between 1988 and 1994 by other MPD-UOA investigators (Proukakis et al., 1988; Georgiou et al., 1988a; Georgiou et al., 1988b), resulting in a total of 1277 samples in 734 locations within Greece. The locations are presented in Fig. 1. As shown in Fig. 1, broad sampling was performed in South Greece, i.e. Attica Department, Peloponnese and the island of Crete covering about 40% of the Greek territory and about 50% of the Greek population, while local sampling occurred in all other investigated areas. The survey results in South Greece, added up to the level of a province, are given in Table 1. Sample density ranged between 1/271 conventional dwellings and 1/10003 conventional dwellings with an average of 1/2405 conventional dwellings excepting the

Fig. 1. Sampling locations, locations where elevated radon concentrations occurred and “radon prone” areas in Greece.


Area

Prefecture: IRAKLION Viannos Kenourgion Malevizion Monofatsion Pediada Pyrgiotissa Temenos Prefecture: LASITHI Ierapetra Lasithi Mirambelos Sitia Prefecture: RETHYMNON Agios Basilios Amarion Mylopotamos Rethymnon Prefecture: CHANIA Apokoronas Kissamos Kydonia Selinos Sfakia

Region

Crete

113901 3454 9679 9534 12159 19844 5069 54162 42532 11699 2495 14352 13986 33295 4530 3531 7800 17434 59039 6507 9382 38582 3415 1153

126 5 16 10 22 19 9 45 56 16 5 15 20 39 7 6 6 20 82 24 15 41 2 0

40 41 47 36 39 44 40 37 39 32 45 46 42 55 63 41 42 46 56 90 35 47 29 0

A.M. 34.9 30.2 39.1 30.3 33.9 38.1 22.0 37.1 34.1 30.0 43.0 39.8 35.8 38.6 39.5 29.6 41.3 37.5 43 59 31.6 40.3 27.6 0

G.M. 1.7 2.4 1.6 1.8 1.8 1.6 2.0 1.9 1.6 1.3 1.2 1.6 1.8 1.9 2.7 2.2 1.2 1.7 3 3 1.5 1.5 1.5 0

G.S.D

Dwellings Samples Concentration (Bq m-3)

11.0 11.0 15.3 12.4 15.9 13.6 14.4 13.2 7.2 18.2 29.4 15.7 13.2 12.8 12.8 18.1 33 13.6 11.5 16.3 17.6 11.5 20.8 0

Min

⏎200 Bq m-3

17.6 0 98 0 173 0 71 0 114 0 96 0 82 0 77 0 115 0 50 0 69 0 82 0 115 0 220 1 220 1 136 0 57 0 169 0 530 3 530 3 99 0 159 0 37 0 0 0 (continued on next page)

Max

Table 1 Survey results in South Greece. A.M. is the arithmetic mean, G.M. is the geometric mean, G.S.D. is the geometric standard deviation, Min is the minimum recorded value and Max is the maximum. The last column refers to the number of dwellings with concentrations above 200 Bq m-3

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Area

Prefecture:ARGOLIDA Argos Ermionida Nafplion Prefecture: ARKADIA Gortinia Kynoria Mantinia Megalopoli Prefecture:ACHAIA Egialida Kalavryta Patrai Prefecture: ILIA Ilia Olymbia Prefecture: KORINTHIA Korinthia Prefecture: LAKONIA Gythio Epidvrou Limniras Lakedemonos Itilou Prefecture: MESSINIA Kalame Messini Pylos Trifilia

Region

Peloponesse

Table 1 (continued)

41791 17481 8230 16080 56306 12209 14796 22168 7133 130950 26991 10383 93576 69094 54551 14543 76638 76638 53910 6435 18430 24802 4243 79336 31645 15260 14536 17895

16 7 0 9 41 5 10 20 6 29 10 9 10 47 40 7 32 32 36 2 14 15 5 58 24 10 12 12

49 71 0 21 60 36 53 83 30 35 64 17 16 24 25 25 38 38 31 151 32 34 21 39 24 31 40 51

A.M. 27.1 34 0 50.4 35.7 21.9 33.1 45 28.9 21.7 36.0 15.7 16.0 20.9 21.6 23.4 25.9 25.9 25.6 53 26.5 29.0 17.2 32.2 23.7 25.4 34.7 41.9

G.M. 2.3 3 0 1.3 2.7 2.9 2.4 4 1.5 2.7 2.2 2.7 1.2 1.6 1.7 1.4 2.6 2.6 2.2 3 1.6 2.3 1.8 1.8 1.7 2.0 1.9 1.7

G.S.D

Dwellings Samples Concentration (Bq m-3)

14.2 14.2 0 15.3 6.3 6.3 11.4 14.3 17.5 7.4 7.4 9.4 9.6 7.6 7.6 13.4 4.3 4.3 6.4 53 8.3 6.4 6.4 8.9 20.4 8.9 15.8 16.6

Min 272 272 0 29.2 630 87 231 630 37 289 289 32 20.3 98 98 40 228 228 93 249 90 93 49 140 32 76 100 140

Max 1 1 0 0 3 0 1 2 0 1 1 0 0 0 0 0 1 1 0 1 0 0 0 0 0 0 0 0

⬎200 Bq m-3

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Area

Prefecture: Capital Prefecture: Capital Remainder Prefecture: Capital Remainder Prefecture: Capital Remainder

Region

Attica

Table 1 (continued)

PEIRAEUS

WEST ATTICA

SOUTH ATTICA

ATHENS

547758 547758 359287 198522 160765 250762 184071 66691 431230 370103 61127

112 112 202 49 153 4 4 0 37 37 0

23 23 41 41 41 11 11 0 40 40 0

A.M. 16.7 16.7 33.6 35.6 32.2 10.8 10.8 0 26.2 26.2 0

G.M. 1.9 1.9 1.7 1.9 1.4 1.4 1.4 0 2.1 2.1 0

G.S.D

Dwellings Samples Concentration (Bq m-3)

3.7 3.7 5.3 8.6 5.3 6.7 6.7 0 9.9 9.9 0

Min

136 136 261 107 261 15.0 15.0 0 203 203 0

Max

0 0 2 0 2 0 0 0 1 1 0

⬎200 Bq m-3

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capital province within the West Attica prefecture where the sample density was 1/46,018 conventional dwellings and the four provinces where no dosimeters were finally collected. With the above exceptions, the sample density is representative according to UNSCEAR (1993) and is comparable to that of the other similarly designed surveys based on statistically representative sampling (McLaughlin & Wasiolek, 1988; Ulbak et al., 1988; Langroo, Wise, Duggleby, & Kotler, 1991; Marcinowski, Lucas, & Yeager, 1994; Bochicchio et al., 1996). Table 2 summarizes the results for the local sampling. The results of both Tables 1 and 2 are given as frequency distribution histogram in Fig. 2. Introducing c2 test, the overall results follow the lognormal distribution (P⬍0.01). Residential radon concentration ranged between 200 and 400 Bq m-3 in 22 dwellings (1.9%), 400 and 1000 Bq m-3 in eight (0.7%) dwellings, and above 1000 Bq m-3 in four (0.4%) dwellings. In the full data set, arithmetic mean was found to be equal to 55 Bq m-3 and the geometric mean equal to 44.0 Bq m-3 with a geometric standard deviation of 2.4 Bq m-3. In only a small percentage (1.1%) of dwellings in Greece did the measured radon concentrations exceed the European Commission (1990) action level (400 Bq m-3). Through the questionnaires it was found that the full data set consisted of 741 (58.0%) dwellings located on the ground floor, 320 (25.1%) on the first floor, 105 (8.2%) on the second floor, 64 (5.0%) on the third floor and, 47 (3.7%) above the third floor of a building. Among these categories the one-way analysis of variance (ANOVA) method was applied to the logarithms of the radon concentrations, which follow the Gauss distribution. Ground floor dwellings presented statistically significant higher radon concentrations but for the dwellings of the first floor and above, the differences were not significant (P⬍0.001). Applying the same method to ground floor dwelling radon concentration data of each surveyed area it was found that some areas presented statistically significant differences in radon concentrations (P⬍0.001). In some of these areas the residential radon concentrations lie in the tail (P⬍0.01) of the lognormal distribution (Fig. 1). From these only two, i.e. Arnea Chalkidikis and Vrisses Apokoronou Chanion are “radon prone” areas according to NRPB (1994). Residential Potential Alpha Energy Concentration (PAEC) and effective dose values may be calculated from the above data set by using appropriate values for the equilibrium, occupancy and dose conversion factor. Since no such values are available for Greece, a mean equilibrium value of 0.4 (ICRP, 1993) and an occupancy factor of 0.8 (UNSCEAR, 1993) respectively were used to estimate risks. PAEC values were calculated using 72 WLM y-1/Bq m-3 of mean annual equivalent radon concentration, while effective doses using 6 nSv h-1/Bq m-3 of mean annual equivalent radon concentration as a dose conversion factor. In South Greece, where broad area sampling was performed, residential PAEC values ranged between (0.024±0.009) and (2.8±1.0) WLM per year (P⬍0.05) with a mean of 0.2 WLM per year. Effective doses were between (0.09±0.04) and (11±4) mSv per year (P⬍0.05), with a mean of 0.8 mSv per year. These mean values lie far beyond the maximum values of (8±1) WLM per year and (28±4) mSv per year (P⬍0.05) that occurred in the radon prone area of Arnea Chalkidikis. Using an ICRP (1993) risk factor of 2.8×10-4 per WLM according to epidemiolog-


Prefecture: Evros Alexandroupolis Prefecture: Thessaloniki Thessaloniki Prefecture: Pierria Litochoro Leptokarya Prefecture: Serres Serres Gazoros Orea Eleni Prefecture: Drama Andriani Vathitolo Dasoto Domatia Katafygio Nikiforos Paliambela Perithorio Platanovrisi

Thraki

Macedonia

Area

Region

10 10 9 9 32 18 14 21 19 1 1 74 13 6 2 36 3 5 1 7 1

Samples

51 51 90 90 42 42 42 11 12 3.7 6.4 53 12 15 14 133 19 12 6.5 9 12.3

A.M. 47 47 71.3 71.3 38.4 36.9 38.7 8.4 8.8 3.7 6.4 15.3 11.0 13.9 12.2 90.0 12.7 12.4 6.5 8.8 12.3

G.M.

Concentration

3 3 2.2 2.2 1.5 1.2 1.3 2.1 2.2 0 0 2.1 1.7 1.4 2.0 3.0 2.9 1.5 0 1.4 0

G.S.D. 25.9 25.9 22.0 22.0 19.7 19.7 20.3 3.7 3.7 3.7 6.4 5.7 5.7 9.2 7.5 7.4 5.7 7.6 6.5 6.2 12.3

Min

⏎200 Bq m-3

89 0 89 0 189 0 189 0 137 0 97 0 137 0 27.0 0 27.0 0 3.7 0 6.4 0 492 2 18.6 0 26.4 0 19.8 0 492 2 42 0 17.4 0 6.5 0 15.4 0 12.3 0 (continued on next page)

Max

Table 2 Survey results in other locations in Greece. A.M. is the arithmetic mean, G.M. is the geometric mean, G.S.D. is the geometric standard deviation, Min is the minimum recorded value and Max is the maximum. The last column refers to the number of dwellings with concentrations above 200 Bq m-3

D. Nikolopoulos et al. / J. Environ. Radioactivity 63 (2002) 173–186 181


Aegean Islands

Central Greece

Thessalia

Epirus

Region

Table 2 (continued) Samples

22 10 5 5 1 1 47 47 18 18 26 26 22 11 11 8 8 46 46 25 12 1 2 1 9

Area

Prefecture: Kavala Kavala Eleftheropolis Moustheni Mesoropi Domatia Prefecture: Chalkidiki Arnea Prefecture: Ioannina Ioannina Prefecture: Magnisia Volos Prefecture: Viotia Tithorea Polydroso Prefecture: Kyklades Milos island Prefecture: Samos Ikaria isand Prefecture: Lesvos Mitilena Plomarion Megalochori Gera Limnos island

32 14 33 68 26.7 18.2 270 270 89 89 44 44 115 178 52 41 41 58 58 60 50 4.4 10 10.2 88

A.M. 25.5 13.9 21.8 39.6 26.7 18.2 108.2 108.2 59.6 59.6 42.4 42.4 86.7 151.2 49.7 39 39 63.6 63.6 20.7 29 4.4 9.4 10.2 63.6

G.M.

Concentration

2.2 1.4 2.3 2.8 0 0 3.2 3.2 2.4 2.4 1.4 1.4 1.9 1.7 1.4 1.4 1.4 2.2 2.2 1.3 3 0 1.0 0 2.2

G.S.D. 4.6 4.6 5.6 13.0 26.7 18.2 25.9 25.9 25.9 25.9 18.5 18.5 38 55 38 20.8 20.8 37 37 4.3 4.3 4.4 9.3 10.2 29.6

Min 141 23.8 65 141 26.7 18.2 1700 1700 600 600 65 65 500 500 88 59 59 200 200 310 310 4.4 9.6 10.2 310

Max 0 0 0 0 0 0 12 12 1 1 0 0 3 3 0 0 0 0 0 2 1 0 0 0 1

⏎200 Bq m-3

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Fig. 2.

183

Frequency distribution histogram of radon concentrations in Greek dwellings (1277 samples).

ical data, a mean PAEC value of 0.2 WLM per year assuming that this is representative for Greece, due to the broad sampling performed there and, the mean life expectancy of 74 y for men and 77 y for women in Greece (Katsougianni et al., 1990), the mean lifetime risk in Greece due to residential radon is 0.4% (0%–1.1% in the 95% confidence interval). This means that on average 40 over 10,000 inhabitants of Greece would die due to lung cancer caused by residential radon exposure. Since Greece had a population of 10.4 million people, it may be calculated that on average 400 mortal lung cancers due to residential radon are expected to occur each year in Greece. Mean lifetime risk was calculated excluding the data from the rest of the country because the sampling there, was not statistically representative according to UNSCEAR (1993). The uncertainties of PAEC and effective dose values were calculated taking into account the instrumental uncertainty of the MPD radon dosimeter and the statistical fluctuations of the recorded concentrations within every surveyed area of Tables 1 and 2. Mean lifetime risk uncertainty was calculated taking into account the fluctuations of the calculated PAEC values in South Greece. Both uncertainties are biased by uncertainties of the dosimetric conversion factors (Nazaroff & Nero, 1988; Louizi & Nikolopoulos, 1998). Moreover, mean lifetime risk is biased by age, smoking habits (Nazaroff & Nero, 1988) and by uncertainties of the mean life expectancy in Greece.


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4. Discussion The survey combined a number of designing and operating hypotheses that guided the project and allowed the establishment of a valid regional benchmark of radon levels mainly in South Greece but also in the rest of the country. It was found that the Greek population reacts positively and with great interest to subjects relevant to background radiation. The door-to-door approach was found to be very effective, minimizing refusals and bias. The loss of detectors was kept at a low percent of approximately 15%. In some areas the loss was greater, resulting in a sample density lower than the initially designed. On the other hand, in some provinces, constituting mainly by villages, the sample density was greater because the inhabitants showed great interest and wanted participation in the survey project. The building types were selected by the personnel, which may have biased the data. Unfortunately, at the design stage, a nationwide random selection of building types was not possible due to lack of statistical data on building attributes. For the same reason this bias cannot be estimated. On the other hand, an effort has been made by the personnel to limit the bias, by trying to include in the survey all types of buildings. According to the results obtained, it was found that only a small percentage of dwellings appeared to have annual average radon levels, above 400 Bq m-3, which is the action level proposed by the European Community. The survey supports the recommendation of testing mainly ground floor or first floor dwellings, since there were not found significant differences in radon concentrations among the dwellings of the rest floors. In addition, the radon estimates have shown geographic differences, leading to supporting the strategy of focusing to areas with high radon potential. “Radon prone� areas such as Arnea Chalkidikis lie on a granitic underground (Greek Institute of Geology and Mineral Exploration, 2000), which may be related to high radon potential. The survey is still progress, because on the one hand, different results may be obtained elsewhere and on the other hand a better estimation of the national average should be determined. Moreover, geological and other relevant data are being collected by MPD-UOA. These will be combined in the future with the questionnaire data, in order to investigate the factors that affect indoor radon concentrations in Greece. Comparing survey results with the results of other similar designed surveys (McLaughlin & Wasiolek, 1988; Ulbak et al., 1988; Langroo et al., 1991; Marcinowski et al., 1994; Bochicchio et al., 1996) and the results of other investigators for Greece (Papastefanou et al., 1994; Ioannides et al., 2000; Geranios et al., 2001) no particular differentiations occur. PAEC values and effective doses due to residential radon of Greek population are similar to other Europeans (McLaughlin & Wasiolek, 1988; Ulbak et al., 1988; Bochicchio et al., 1996; Ioannides, Stamoulis & Papachristodoulou, 2000; Geranios et al., 2001). The risk is age dependent and increases if the individual is a smoker (Nazaroff & Nero, 1988). Data on the age and smoking habits of the individuals were not collected in this survey. Efforts on these topics are being held by MPD-UOA now. The calculations of the mean nationwide annual risk due to residential radon were based only on broad area sampling (about 40% of the Greek territory and about 50%


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of the Greek population) because the use of data from local sampling may have introduced a systematic error if these had represented over- or under- estimation of the mean radon concentration of each surveyed area. Nevertheless, elevated residential radon concentrations may be found in non-broadly surveyed part of Greece. Moreover, the “radon prone” area of Arnea Chalkidikis is now under investigation by MPD-UOA.

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