www.elsevier.com/locate/jenvrad

Journal of Environmental Radioactivity 78 (2005) 113–121

Short communication

An overview of an indoor radon study carriedout in dwellings in India and Bangladeshduring the last decade using solid state

nuclear track detectors

Alok Srivastava)

Department of Chemistry, Panjab University, Chandigarh-160014, India

Received 19 November 2003; received in revised form 29 March 2004; accepted 14 April 2004

Abstract

This paper reports on radon concentrations in dwellings from fifty different locations ofIndia. The incorporated data were obtained using the passive solid state nuclear track detector

technique. The estimated geometric mean value for India is 67.1 Bq m�3. Chuadanga inBangladesh had the lowest observed indoor radon concentration of 27.3 Bq m�3 and Una inthe northern part of India had the highest concentration of 281.5 Bq m�3. This paper discussesthe national geometrical mean value in terms of the national geometric mean values of other

countries and also in terms of the geological influence. The estimated indoor radon levels arecompared with the indoor radon levels as recommended by the International Commission onRadiation Protection (ICRP). It was observed that there are several locations in India where

dwellings have higher indoor radon levels than the ICRP recommended value and requiressome sort of intervention from regulating authorities. The mean value for indoor radon levelgiven in the report of UNSCEAR 2000 for India needs to be revised.

� 2004 Published by Elsevier Ltd.

Keywords: Indoor radon; Solid state nuclear track detectors (SSNTD); UNSCEAR; ICRP

) Fax: D91-172-545-074.

E-mail address: alokamla@hotmail.com.

0265-931X/$ - see front matter � 2004 Published by Elsevier Ltd.

doi:10.1016/j.jenvrad.2004.04.002

114 A. Srivastava / J. Environ. Radioactivity 78 (2005) 113–121

1. Introduction

The radiation dose from radon inhalation constitutes a major part of the totalnatural background dose received by man. The United Nations Scientific Committeeon the Effects of Atomic Radiation (UNSCEAR, 2000) reports that nearly half ofthe dose received by man from natural sources is due to breathing radon and itsprogenies present in the dwellings. Many developed countries have instituted largescale radon surveys because of certain reports (Rajeewsky, 1940; Sevc et al., 1976;Edling et al., 1986; Henshaw et al., 1990; Jacobi, 1991; Durrani, 1993) thatpathogenesis of lung, skin cancer and kidney diseases could be ascribed to itsexposure. But, very few such surveys have been carried out in developing countrieswhere some of the world’s highest natural radiation background areas are located.Such studies have become quite important for countries like India, Pakistan,Bangladesh and China which have very large populations.

Radon, the heaviest member of the inert gas family is produced in uranium andthorium bearing minerals as a result of radioactive decay. Among the three isotopesof radon (219Rn, 220Rn and 222Rn), 222Rn is considered to be the most toxic. It ispresent in the environment for long periods because of its half life of 3.82 days. It isestimated that around 1 GBq of 222Rn is released per ton of ore containing onepercent U3O8. The effect of this ubiquitous gas in indoor dwellings is dependent onseveral factors such as topography, soil characteristics, weather, constructionmaterials, ventilation, aerosols, life style of the inhabitants etc. The study of radonexposure can be carried out either by employing passive detection techniques or byusing active detection techniques.

One of the first systematic studies on radon levels in Indian dwellings (Subba-Ramu et al., 1990) was carried out using solid state nuclear track detectors. Theseauthors reported the indoor radon levels in dwellings located in 15 different cities ofIndia. This study was further extended (Srivastava et al., 1996) by carrying outadditional surveys in the north eastern region of India. The resulting data of radonlevels from 24 cities of India were thus compiled and the mean radon level of 81Bq.m�3 from the compiled data for India was derived (Srivastava et al., 1996). Thishigh value was attributed to the fact that most of the cities included in these surveyswere located in high radiation background areas.

Recent literature also reports additional data on indoor radon levels (Dwivedi et al.,1997; Narayana et al., 1998; Ramola et al., 1998; Virk, 1999; Khan, 2000; Virk andSharma, 2000; Dwivedi et al., 2001; Singh et al., 2001). These measurements were alsomade using solid state nuclear track detectors andwere fromareas not surveyed earlier.

In this study, an attempt has been made to have an overview of the indoor radonexposure in the last decade in India by collecting the data available in literature,the additional recent data obtained from Paud, a suburb of Pune city in India andthe data from Rajshahi and Chuadanga in Bangladesh (Srivastava et al., 2001). TheBangladesh data is included in the overall analysis as it represents a region which liesbetween the mainland of India and the north eastern region of India and showssimilarity in the geological features. The results are compared with results of similarstudies carried out in different parts of the world and are discussed in the light of

115A. Srivastava / J. Environ. Radioactivity 78 (2005) 113–121

exposure limits set up by the International Commission of Radiation Protection(ICRP, 1994).

2. Materials and methods

The measurement of indoor radon levels using passive techniques is carried out byexposing solid state nuclear track detectors to indoor radon and its progenies fora period of time normally ranging from three to six months. The tracks formed in thesaid detectors after being enhanced by suitable chemical treatment are counted eitherby optical microscope or by using a spark counter.

The two most commonly used solid state nuclear track detectors are CR-39 andLR-115 which have been found to be quite durable and stable. The CR-39 isa polymer of allyl diglycol carbonate in which the tracks formed can be made visibleby etching with 6N NaOH at 70 degrees centigrade for about 5–6 h. The LR-115film, on the other hand, is basically a thin cellulose nitrate film mounted on apolycarbonate backing.

The track formed on this film can be made visible by chemically etching it in 2.5 NNaOH at 60 (C for about 1–2 h. The measured track densities are converted to actualtrack densities using sensitivity factors which are estimated from controlled experi-ments carried out in the national calibration facility (Ramachandran et al., 1990) in theEnvironmental Assessment Division of Bhabha Atomic Research Centre in Mumbai.

This facility consists of an exposure chamber which is a 0.5 m3 painted box havingtwo inlet ports for introducing filtered air, aerosols and radon gas and an outlet tube todischarge the contents of the chamber. Monodispersive aerosols (di-2 ethtl hexylsebacate condensed on NaCl) of 0.2 mm aerodynamic size are introduced inside theexposure chamber using a Lemer–Sinclair type condensation aerosol generator.Radon gas of known concentration is introduced through a 226Ra source with anactivity of 1:85!105 Bq. The activity levels during the exposure of the detectors areestimated from the activity collected on a Millipore filter paper type AA by drawinga known volume of air from the chamber using a vacuum pump and then following thealpha decay of the sample collected on the filter paper using an alpha counting setup.

3. Results and discussion

Fig. 1 shows the locations from where the analysed radon exposure data werecollected. Table 1 shows the details of the sampling locations by name, with itslatitude and longitude and the number of measurements. It also shows the maximumand minimum value of the indoor radon levels obtained in that location, besides theestimated geometric mean value for the said location. In general, the experimentalcumulative uncertainty is estimated to be about 20 percent. This includes an error of13 percent in detector calibration and around 4–7 percent uncertainty in countingstatistics. Table 2 gives the population, maximum value of indoor radon level and thenational geometric mean value of indoor radon concentration of countries from thelast report of United Nations Scientific Committee on Effects of Atomic Radiation(UNSCEAR, 2000). In general, the radon data are expressed in terms of Bq.m�3

.

116 A. Srivastava / J. Environ. Radioactivity 78 (2005) 113–121

Therefore, data reported in terms of potential alpha energy level were converted toBq.m�3 using the equilibrium factor (F) of 0.4 (ICRP, 1994; UNSCEAR, 2000) tomake comparisons more meaningful. This value is quite close to the value of 0.39determined for a small amount of Indian dwellings (Subba-Ramu et al., 1990).

It can be observed from Fig. 1 that the radon work carried out in India is quitescant and scattered. A considerable amount of survey is still required to lead toa definitive conclusion. It is also observed from Fig. 1 that, so far, there have beenvery few surveys of the indoor radon concentration in Bangladesh. The analysis ofthe data collected from literature and the data from Pune, presented for the first timeshows that the lowest mean indoor radon for the Indian region (includingBangladesh) was 27.3 Bq.m�3 and the highest was 281.5 Bq.m�3. The minimumwas observed in Chuadanga in Bangladesh and the maximum was observed in Unain the Himalayan region of northern India.

The estimated national geometric mean for India using the compiled data is67.1 Bq.m�3. This value, when compared to geometrical mean values of other

Fig. 1. Locations in India and Bangladesh where the indoor radon concentrations were determined using

the passive detector technique.

117A. Srivastava / J. Environ. Radioactivity 78 (2005) 113–121

Table 1

Results of the indoor radon concentration measured in India and Bangladesh over the past decade

Location Latitude Longitude No. (Radon concentration Bq.m�3) Reference

Min. Max. GM

Trivandrum 08.29N 76.59E 12 31.5 183.2 98.1 Srivastava et al. (1996)

Manipal 12.25N 75.00E 10 18.5 180.4 105.5 Srivastava et al. (1996)

Chingelpet 12.45N 80.00E 12 18.5 183.1 67.5 Srivastava et al. (1996)

Ullal 12.80N 74.85E 9 39.6 63.6 50.3 Narayana et al. (1998)

Suratkal 13.00N 74.80E 9 49.5 83.2 63.6 Narayana et al. (1998)

Nandikur 13.20N 74.75E 9 54.3 71.1 62.5 Narayana et al. (1998)

Udupi 13.35N 74.70E 9 41.0 93.6 54.3 Narayana et al. (1998)

Coondapar 13.60N 74.65E 9 24.7 82.4 52.1 Narayana et al. (1998)

Bhatkal 13.97N 74.57E 9 39.6 75.0 52.0 Narayana et al. (1998)

Honnavar 14.30N 74.55E 9 29.7 75.0 41.6 Narayana et al. (1998)

Kumta 14.40N 74.50E 9 34.0 79.0 59.9 Narayana et al. (1998)

Karwar 14.80N 74.10E 9 30.8 63.6 43.4 Narayana et al. (1998)

Pune 18.31N 73.55E 23 25.3 192.3 67.2 Present Work

Allahabad 25.40N 81.90E 24 37.9 199.8 93.4 Dwivedi et al. (1997)

Mathura 27.28N 77.41E 18 36.1 125.8 69.4 Srivastava et al. (1996)

Kanpur 26.28N 80.24E 120 – – 33.0 Khan (2000)

Lucknow (I) 26.55N 80.59E 180 – – 34.0 Khan (2000)

Lucknow (II) 26.55N 80.59E 20 64.8 145.2 103.6 Srivastava et al. (1996)

Godhra 22.45N 73.40E 18 31.5 195.2 122.1 Srivastava et al. (1996)

Tuwa 22.46N 73.40E 17 33.3 193.3 102.7 Srivastava et al. (1996)

Nellore 14.27N 80.02E 14 39.8 197.0 106.4 Srivastava et al. (1996)

Hyderabad 17.20N 78.30E 7 29.6 202.6 98.9 Srivastava et al. (1996)

Vizag 17.70N 83.30E 14 20.4 75.9 29.6 Srivastava et al. (1996)

Nagpur 21.09N 79.09E 29 26.8 198.9 87.9 Srivastava et al. (1996)

Jodhpur 26.18N 73.04E – 12.0 189.6 74.9 Srivastava et al. (1996)

Udaipur 24.42N 73.33E 8 23.1 117.5 49.0 Srivastava et al. (1996)

Khetri 27.96N 75.52E 37 23.1 183.2 74.9 Srivastava et al. (1996)

Hamirpur 30.20N 80.12E 27 20.9 146.3 42.6 Virk and Sharma (2000)

Tehri 30.15N 79.30E 57 29.6 245.1 143.4 Ramola et al. (1998)

Garhwal 30.13N 79.30E 42 94.0 152.0 113.2 Ramola et al. (1998)

Dehradun 30.19N 78.04E 34 13.9 197.9 99.9 Srivastava et al. (1996)

Una 31.32N 76.18E 27 123.3 658.6 281.5 Singh et al. (2001)

Kulu 32.13N 77.24E 108 156.1 635.4 278.5 Singh et al. (2001)

Ramera 30.20N 80.12E 8 104.0 209.0 160.4 Virk and Sharma (2000)

Asthota 30.20N 80.12E 4 110.0 183.0 141.4 Virk and Sharma (2000)

Kumaon 30.20N 80.01E – 6.7 63.5 36.1 Ramola et al. (1998)

Rakha 22.80N 87.00E 5 35.2 202.6 121.2 Srivastava et al. (1996)

Jaduguda 22.30N 86.18E 32 14.8 202.6 76.8 Srivastava et al. (1996)

Saiha 22.49N 92.98E 13 16.7 146.2 48.1 Srivastava et al. (1996)

Aizawl (I) 23.36N 91.00E 10 40.3 68.2 52.4 Dwivedi et al. (2001)

Aizawl (II) 23.36N 91.00E 36 11.1 290.5 49.0 Srivastava et al. (1996)

Agartala 23.50N 91.25E 10 26.7 34.2 30.2 Dwivedi et al. (2001)

Khawlian 24.05N 93.50E 6 46.3 303.4 163.7 Srivastava et al. (1996)

Kailashahar 24.19N 92.01E 10 27.0 34.4 30.5 Dwivedi et al. (2001)

Kolasib 24.22N 92.70E 14 22.2 52.7 32.4 Srivastava et al. (1996)

Karimganj 24.40N 92.30E 10 29.9 47.1 37.5 Dwivedi et al. (2001)

Silchar 24.82N 92.73E 11 16.7 53.7 38.9 Srivastava et al. (1996)

(continued on next page )

118 A. Srivastava / J. Environ. Radioactivity 78 (2005) 113–121

countries shown in Table 2, indicates that India could very well be considered inthe group of countries like Estonia, Finland, Luxemburg, Hungary, Albania andSlovenia which have rather high mean indoor radon levels. The mean value forindoor radon levels given in the report of UNSCEAR (2000) for India needs tobe revised. This value corresponds to few measurements realized in the lateeighties.

The high value of the mean indoor radon level in India is due to the fact that themajority of the results collected for evaluating indoor radon levels come fromdwellings situated in locations that are already classified as high background areas(Subba-Ramu et al., 1990; Srivastava et al., 1996). Therefore, a definitive conclusionabout the general state of indoor radon levels in India requires more data to improvetheir spatial representativity.

An analysis of the data available in Bangladesh shows that indoor radon levelstudies have so far been carried out in 24 dwellings of Rajshahi and 19 dwellings ofChuadanga. The minimum indoor radon value was found to be 19.2 Bq.m�3 and themaximum value was 37.5 Bq.m�3. The geometrical mean value for the indoor radonlevel in Rajshahi has been estimated to be 32.4 Bq.m�3 and 27.3 Bq.m�3 forChuadanga resulting in an overall geometric mean of 29.7 Bq.m�3.

According to the regulations of the International Commission of RadiationProtection (ICRP, 1994) the indoor radon level should not exceed 200 Bq.m�3

for future houses. An intervention level is recommended if the houses have indoorradon levels in the range of 200–600 Bq.m�3. In the light of the above statedrecommendations, one can say that all the dwellings so far surveyed in Bangladeshare well within the prescribed limit.

However, in India there are certain locations such as Una and Kulu where eventhe mean indoor radon values are higher than that recommended by theInternational Commission for Radiation Protection (ICRP, 1994) for individualdwellings. It is well known that the geological formation of this particular region ofthe Himalayas is quartzite overlain by chlorite schists and gneisse with veins ofpitchblende occuring in the crests of the anticlinal folds of quartzite. Therefore, it isnot surprising if high indoor radon levels are observed in dwellings located in thisparticular region of India where some sort of intervention from regulating authori-ties may become mandatory.

Table 1 (continued)

Location Latitude Longitude No. (Radon concentration Bq.m�3) Reference

Min. Max. GM

Shillong (I) 25.34N 91.00E 10 29.8 108.3 60.1 Dwivedi et al. (2001)

Shillong (II) 25.34N 91.00E – 15.7 198.9 71.2 Srivastava et al. (1996)

Shillong(III) 25.34N 91.00E 10 46.3 263.6 104.2 Dwivedi et al. (2001)

Guwahati 26.11N 91.47E 10 29.1 70.4 48.5 Dwivedi et al. (2001)

Rajshahi 24.40N 88.70E 24 29.6 37.5 32.4 Srivastava et al. (2001)

Chuadanga 24.40N 88.65E 19 19.2 28.3 27.3 Srivastava et al. (2001)

119A. Srivastava / J. Environ. Radioactivity 78 (2005) 113–121

In the present work, no attempt has been made to analyse the data with a view tostudy the influence of seasons on the indoor radon levels though it is a well knownfact that indoor radon levels are subject to seasonal variations. It can, however, beobserved from the limited studies carried out by Ramola et al. (1998), Narayanaet al. (1998), Dwivedi et al. (2001) and Singh et al. (2001) that winter to summer ratiolies between 1.1 and 1.9 and for a definitive conclusion more data input is required.

Table 2

Radon concentrations in dwellings determined by indoor radon surveys (UNSCEAR, 2000) for 36

countries

Country Population (106) (Radon concentration Bq.m�3)

Maximum value Geometric mean value

Canada 29.68 1720 14

United States 269.40 – 25

Argentina 35.22 211 26

China 1232.00 382 20

India 944.60 210 42

Indiaa 1045.84 408 67

Japan 125.40 310 13

Thailand 58.70 480 16

Kuwait 1.69 120 6

Denmark 5.24 600 29

Estonia 1.47 1390 92

Finland 5.13 2000 84

Lithuania 3.73 1860 22

Norway 4.35 50000 40

Sweden 8.82 85000 56

Austria 8.11 190 15

Belgium 10.16 12000 38

France 58.33 4690 41

Germany 81.92 10000 40

Ireland 3.55 1700 37

Luxemburg 0.41 2500 70

Netherlands 15.58 380 18

Switzerland 7.22 10000 50

Bulgaria 8.47 250 22

Hungary 10.05 1990 82

Poland 38.60 432 32

Albania 3.40 270 105

Croatia 4.50 92 32

Cyprus 0.76 78 7

Greece 10.49 490 52

Italy 57.23 1040 57

Portugal 9.81 2700 45

Slovania 1.92 1330 60

Spain 39.67 15400 42

Australia 18.06 420 8

New Zealand 3.60 90 18

Bangladesha 133.40 38 30

a Present work.

120 A. Srivastava / J. Environ. Radioactivity 78 (2005) 113–121

4. Conclusions

In conclusion, it can be stated that the study on indoor radon carried out in Indiaover the last decade are based on data that are still scant and scattered. The meanindoor radon level value varies from 27.3 to 281.5 Bq.m�3. The national geometricmean value, which has been estimated as 67.1 Bq.m�3 in the present work placesIndia in the group of countries like Estonia, Finland, Luxemburg, Hungary, Albaniaand Slovenia which have rather high mean indoor radon level (UNSCEAR, 2000).The high average indoor radon level in the case of India may be related to the factthat most of the data obtained so far comes from dwellings located in highbackground radiation areas. There are dwellings in certain locations of India wheresome sort of intervention from regulating authorities may become mandatory. Themean value for indoor radon level given in the report of UNSCEAR (2000) for Indianeeds to be revised.

Acknowledgements

The author would like to express his deep sense of gratitude to Prof. Dr. U.W.Scherer of Aachen University of Applied Sciences, Juelich (Germany) and Prof.Dr. R. Prasad from University of Illinois at Chicago Circle, USA for their kindhospitality and for extending all possible assistance in the preparation of thismanuscript. The author would also like to thank Dr. T.V. Ramachandran ofEnvironmental Assessment Division, Bhabha Atomic Research Centre, Mumbai(India), Dr. K.K. Dwivedi of Department of Science and Technology, Governmentof India and Prof. C. Papastefanou from University of Thessaloniki, Thessaloniki(Greece) for their valuable help. The assistance provided by Mr. Albert Bayita in themeasurements of the Pune samples is gratefully acknowledged.

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