radon survey in greece—risk assesment

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

Radon survey in Greece—risk assesment

Dimitrios Nikolopoulosa,∗, Anna Louizia,Virginia Koukoulioub, Athina Serefogloua,

Evangelos Georgioua, Konstantinos Ntallesa,Charalambos Proukakisa

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 to1998 in Greece in order to estimate the radon concentrations in Greek dwellings and theexposure 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 be0.4%. 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 lungcancer incidence, although the effect of low doses is not well defined (Auvinen etal., 1996; Pershagen, Liang, Zdenek, Svensson, & Boice, 1992). Due to elevatedconcentrations 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: [email protected] (D. Nikolopoulos).

0265-931X/02/$ - see front matter 2002 Elsevier Science Ltd. All rights reserved.PII: S0265 -931X(02)00026-7

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

(Gerken, Kreienbrock, Wellmann, Kreuzer, & Wichmann, 2000; Yu, Lau, Guan,Lo, & Young, 2000).

Small-scale measurements of radon gas concentration within dwellings in Greecehave been reported (Proukakis, Molfetas, Ntalles, Georgiou, & Serefoglou, 1988;Georgiou, Ntalles, Molfetas, Athanassiadis, & Proukakis, 1988a; Georgiou, Ntalles,Anagnostopoulos, Proukakis, & Athanassiadis, 1988b; Papastefanou, Stoulos, Mano-lopoulou, Ioannidou, & Charalambous, 1994; Ioannides, Stamoulis, & Papachristo-doulou, 2000). Continuing the radon investigation conducted by the Medical PhysicsDepartment-University of Athens (MPD-UOA) since 1988, a large-scale nationwideresidential radon survey in Greece was designed and performed, using dosimetersof MPD-UOA construction, fully calibrated and tested by the MPD-UOA(Nikolopoulos, Louizi, Petropoulos, Simopoulos, & Proukakis, 1999). The mainscope was to obtain an adequate estimation of the annual radon concentration distri-bution indoors, to assess the average risk, and to determine the percentage of dwell-ings 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 towhich, Greece had a population of 10.4 million people (National Statistical Serviceof Greece, 1995). The population was highly concentrated in urban areas, and mainlyin Athens where about 37% of the total population resided. The total number ofbuildings was 3.8 million. Approximately 75% (2.85 million) of the buildings wereused as dwellings. The occupants per dwelling ratio was on average 3.0 and wassubjected 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 conventionaland non-regular dwellings, regular rooms and institutional households. The resi-dencies constituting by at least one room higher than 2 m and larger than 4 m2 withdirect day light from window or glass door, were considered as conventional dwell-ings (National Statistical Service of Greece, 1995). Building data were providednationwide according to an administrative partition proposed by the NSSG. The dataabout the number of stories, building attributes and occupational status of each separ-ate 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 accumulativemanner. Moreover, the NSSG provided no maps through which the geographicalcoordinates of each house could be found.

2.2. Sampling design

Due to the limitations placed by the demographical data, and taking into accountthe financial and work power of the MPD-UOA, the radon survey was not based on

175D. Nikolopoulos et al. / J. Environ. Radioactivity 63 (2002) 173–186

a grid division but was administratively designed. The sampling design was basedon the partition proposed by the NSSG. Ten administrative districts, called regions,were divided into prefectures, called departments, which were subdivided into prov-inces. These were organized in municipalities and communes, which included vil-lages and city quarters.

Sampling design was based on the following procedure: a sampling density of 1per 1000 conventional dwellings was adopted, balancing both feasibility and pre-cision of estimation. The number of samples was calculated for a department, accord-ing to the total number of its conventional dwellings. This number was further allo-cated to each province, in proportion to the fraction of the number of conventionaldwellings of the province over the total number of conventional dwellings of thedepartment. Continuing, the sample number of each province was allocated to itsmunicipalities and communes, in proportion to the number of the conventional dwell-ings of the municipality or commune over the total number of conventional dwellingsof the province. The procedure was followed, so as to allocate adequate number ofsamples to each village or city quarter (Nikolopoulos, Maddison, Louizi, & Pro-ukakis, 1997).

2.3. Experimental apparatus

The experimental apparatus was the MPD radon dosimeter (Nikolopoulos, Louizi,Papadimitriou, & Proukakis, 1997). The dosimeter consisted of a cylindrical non-conductive plastic cup of 5 cm height and 1.5 cm radius. The cover had a 3 mmhole on the center and a filter that prevented radon daughters from entering. Radonwas detected by a 2×2 cm CR-39 nuclear track detector placed at the bottom of thecup. The overall uncertainty of radon measurement in the 95% confidence intervalwas below 10% (Nikolopoulos et al., 1999). The 12-mo exposure period was selecteddue to the best estimation of the average value it provides. One detector was installedin 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 selec-ted, so as to minimize non-response and bias. This scheme was generally followedand changed only by restrictions placed at the implementation stage (i.e. refusalsand other difficulties). Within every sampling location, dwellings were selected bythe personnel, so as to sample nationwide all types of buildings. In each case, aquestionnaire was filled and the inhabitant was given informative brochures. At theend of the 12-mo period the dosimeters were collected, either via door-to-doorapproach or via post.


3. Results

The survey was carried out between July of 1995 and August 1998 with the instal-lation 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 anadditional 216 samples in 12 locations collected between 1988 and 1994 by otherMPD-UOA investigators (Proukakis et al., 1988; Georgiou et al., 1988a; Georgiouet 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 wasperformed in South Greece, i.e. Attica Department, Peloponnese and the island ofCrete covering about 40% of the Greek territory and about 50% of the Greek popu-lation, while local sampling occurred in all other investigated areas. The surveyresults 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 conven-tional 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.

177D. Nikolopoulos et al. / J. Environ. Radioactivity 63 (2002) 173–186T

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

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capital province within the West Attica prefecture where the sample density was1/46,018 conventional dwellings and the four provinces where no dosimeters werefinally collected. With the above exceptions, the sample density is representativeaccording to UNSCEAR (1993) and is comparable to that of the other similarlydesigned surveys based on statistically representative sampling (McLaughlin &Wasiolek, 1988; Ulbak et al., 1988; Langroo, Wise, Duggleby, & Kotler, 1991; Mar-cinowski, Lucas, & Yeager, 1994; Bochicchio et al., 1996). Table 2 summarizes theresults for the local sampling. The results of both Tables 1 and 2 are given as fre-quency distribution histogram in Fig. 2. Introducing c2 test, the overall results followthe lognormal distribution (P�0.01). Residential radon concentration ranged between200 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 equalto 44.0 Bq m-3 with a geometric standard deviation of 2.4 Bq m-3. In only a smallpercentage (1.1%) of dwellings in Greece did the measured radon concentrationsexceed 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 thethird floor of a building. Among these categories the one-way analysis of variance(ANOVA) method was applied to the logarithms of the radon concentrations, whichfollow the Gauss distribution. Ground floor dwellings presented statistically signifi-cant 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 groundfloor dwelling radon concentration data of each surveyed area it was found that someareas 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. ArneaChalkidikis and Vrisses Apokoronou Chanion are “ radon prone” areas according toNRPB (1994).

Residential Potential Alpha Energy Concentration (PAEC) and effective dosevalues may be calculated from the above data set by using appropriate values forthe equilibrium, occupancy and dose conversion factor. Since no such values areavailable for Greece, a mean equilibrium value of 0.4 (ICRP, 1993) and an occupancyfactor of 0.8 (UNSCEAR, 1993) respectively were used to estimate risks. PAECvalues were calculated using 72 WLM y-1/Bq m-3 of mean annual equivalent radonconcentration, while effective doses using 6 nSv h-1/Bq m-3 of mean annual equival-ent radon concentration as a dose conversion factor. In South Greece, where broadarea 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 peryear. 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 maximumvalues of (8±1) WLM per year and (28±4) mSv per year (P�0.05) that occurred inthe radon prone area of Arnea Chalkidikis.

Using an ICRP (1993) risk factor of 2.8×10-4 per WLM according to epidemiolog-

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

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

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09.

39.

60

Ger

a1

10.2

10.2

010

.210

.20

Lim

nos

isla

nd9

8863

.62.

229

.631

01


Fig. 2. 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 representa-tive for Greece, due to the broad sampling performed there and, the mean life expect-ancy 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 the95% confidence interval). This means that on average 40 over 10,000 inhabitants ofGreece would die due to lung cancer caused by residential radon exposure. SinceGreece had a population of 10.4 million people, it may be calculated that on average400 mortal lung cancers due to residential radon are expected to occur each year inGreece. Mean lifetime risk was calculated excluding the data from the rest of thecountry because the sampling there, was not statistically representative according toUNSCEAR (1993).

The uncertainties of PAEC and effective dose values were calculated taking intoaccount the instrumental uncertainty of the MPD radon dosimeter and the statisticalfluctuations of the recorded concentrations within every surveyed area of Tables 1and 2. Mean lifetime risk uncertainty was calculated taking into account the fluctu-ations of the calculated PAEC values in South Greece. Both uncertainties are biasedby uncertainties of the dosimetric conversion factors (Nazaroff & Nero, 1988; Lou-izi & Nikolopoulos, 1998). Moreover, mean lifetime risk is biased by age, smokinghabits (Nazaroff & Nero, 1988) and by uncertainties of the mean life expectancyin Greece.


4. Discussion

The survey combined a number of designing and operating hypotheses that guidedthe project and allowed the establishment of a valid regional benchmark of radonlevels mainly in South Greece but also in the rest of the country. It was found thatthe Greek population reacts positively and with great interest to subjects relevant tobackground 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 ofapproximately 15%. In some areas the loss was greater, resulting in a sample densitylower than the initially designed. On the other hand, in some provinces, constitutingmainly by villages, the sample density was greater because the inhabitants showedgreat interest and wanted participation in the survey project. The building types wereselected by the personnel, which may have biased the data. Unfortunately, at thedesign stage, a nationwide random selection of building types was not possible dueto lack of statistical data on building attributes. For the same reason this bias cannotbe estimated. On the other hand, an effort has been made by the personnel to limitthe 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 ofdwellings appeared to have annual average radon levels, above 400 Bq m-3, whichis the action level proposed by the European Community. The survey supports therecommendation of testing mainly ground floor or first floor dwellings, since therewere not found significant differences in radon concentrations among the dwellingsof 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 (GreekInstitute of Geology and Mineral Exploration, 2000), which may be related to highradon potential. The survey is still progress, because on the one hand, different resultsmay be obtained elsewhere and on the other hand a better estimation of the nationalaverage should be determined. Moreover, geological and other relevant data are beingcollected by MPD-UOA. These will be combined in the future with the questionnairedata, in order to investigate the factors that affect indoor radon concentrations inGreece.

Comparing survey results with the results of other similar designed surveys(McLaughlin & Wasiolek, 1988; Ulbak et al., 1988; Langroo et al., 1991; Marcinow-ski et al., 1994; Bochicchio et al., 1996) and the results of other investigators forGreece (Papastefanou et al., 1994; Ioannides et al., 2000; Geranios et al., 2001) noparticular differentiations occur. PAEC values and effective doses due to residentialradon of Greek population are similar to other Europeans (McLaughlin & Wasiolek,1988; Ulbak et al., 1988; Bochicchio et al., 1996; Ioannides, Stamoulis & Papachris-todoulou, 2000; Geranios et al., 2001). The risk is age dependent and increases ifthe individual is a smoker (Nazaroff & Nero, 1988). Data on the age and smokinghabits of the individuals were not collected in this survey. Efforts on these topicsare being held by MPD-UOA now.

The calculations of the mean nationwide annual risk due to residential radon werebased only on broad area sampling (about 40% of the Greek territory and about 50%


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

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radon survey in greece—risk assesment

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