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ORIGINAL ARTICLE
Year : 2021  |  Volume : 44  |  Issue : 3  |  Page : 146-151  

Estimation of indoor 222Rn and 220Rn concentration and annual inhalation dose in the indoor environment around Kolar district of Karnataka state, India


1 Department of Physics, Government First Grade College, Sidlaghatta, Karnataka, India
2 Department of Physics, BMS College of Engineering, Bengaluru, Karnataka, India
3 Department of Physics, Government First Grade College, Tumakur, Karnataka, India
4 Department of Physics and RC, VVIET, Mysore, Karnataka, India
5 Department of Medical Electronics, BMS College of Engineering, Bengaluru, Karnataka, India
6 Department of Physics, IDSG Government College, Chikmagalur, Karnataka, India

Date of Submission29-Jul-2021
Date of Decision17-Aug-2021
Date of Acceptance27-Aug-2021
Date of Web Publication04-Jan-2022

Correspondence Address:
C S Kaliprasad
Department of Physics, BMS College of Engineering, Bengaluru - 560 019, Karnataka
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/rpe.rpe_33_21

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  Abstract 


The indoor 222Rn and 220Rn were measured by using deposition progeny sensors and single-entry pinhole dosimeter around Kolar Gold Fields of Karnataka state, India. The thirty different places were identified and fixed the dosimetry cups for the determination. The 222Rn and 220Rn concentrations of indoor environment range from 26.2 ± 1.3 to 138.4 ± 1.6 and 21.2 ± 0.8 to 133.3 ± 1.5 Bq/m3 with a mean value of 68.8 ± 1.6 and 61.8 ± 1.5 Bq/m3, respectively. The equivalent concentrations of 222Rn and 220Rn values vary from 0.9 ± 0.4 to 7.6 ± 1.1 and 6.8 ± 0.8 to 19.8 ± 1.8 Bq/m3 with a standard value of 4.3 ± 0.8 and 14.2 ± 1.3 Bq/m3, respectively. The values between the equilibrium factor between 222Rn, 220Rn, and their daughter were also calculated and found to be 0.23 and 0.07, respectively. The average annual intake of 222Rn, 220Rn, and their daughters' products is 2.28 mSv/y1, slightly below the global average of 2.4 mSv/y1 from all components. The data obtained compare average values in the world.

Keywords: Equilibrium equivalent concentration of 220Rn, equilibrium equivalent concentration of 222Rn, pinhole dosimeter, radon, solid-state nuclear track detectors, thoron


How to cite this article:
Reddy K U, Kaliprasad C S, Suresh C, Ningappa C, Mata B N, Srinivasa E. Estimation of indoor 222Rn and 220Rn concentration and annual inhalation dose in the indoor environment around Kolar district of Karnataka state, India. Radiat Prot Environ 2021;44:146-51

How to cite this URL:
Reddy K U, Kaliprasad C S, Suresh C, Ningappa C, Mata B N, Srinivasa E. Estimation of indoor 222Rn and 220Rn concentration and annual inhalation dose in the indoor environment around Kolar district of Karnataka state, India. Radiat Prot Environ [serial online] 2021 [cited 2022 Jun 27];44:146-51. Available from: https://www.rpe.org.in/text.asp?2021/44/3/146/334780




  Introduction Top


Inhalation of 222Rn, 220Rn, and its daughter products is responsible for over 52% of humanity's radiation dosage.[1],[2] Both the radionuclides are naturally occurring due to the dissolution of their parental radioactive decay series such as thorium and uranium, which can be found in water, building materials, soil, rocks, etc. The second most lung cancer causable thing is indoor radon, compared to smoking.[2] As a result, the determination of the activity concentration of 220Rn and 222Rn in the indoor atmosphere is very important. The WHO has advocated on lowering the 222Rn action threshold from 100 to 200 Bq/m3[3] based on epidemiological data in several countries. 220Rn and 222Rn daughter products, but not 222Rn and 220Rn, are the main contributors to lung cancer doses. As a result, it is critical to directly estimate the daughter products.[4] For the first time in this study area, equilibrium equivalent concentration of 222Rn and 220Rn (EERC and EETC, respectively) was estimated along with 222Rn and 220Rn concentrations.


  Materials and Methods Top


Study area

The current research area is centered on the Kolar Gold Fields (KGF), which nearly encompasses the Kolar district in Karnataka's easternmost region, also known as the “Golden Land of India.” It is located between the latitudes of 12° 4555.03 and 13° 3642.05 north and the longitudes of 77° 5025.06 and 78° 3512.24 east. It is bordered on the north by chikkaballapur district, on the east by Andhra Pradesh's Chittoor district, on the south by Tamil Nadu's Krishnagiri and Vellore districts, and on the west by Bangalore rural district.

Kolar is the administrative center of the Kolar district. This district has a total area of 3979 km2. The functioning of the mines was halted by the federal government in 2001 due to financial losses in gold production. The Indian government is considering the reopening of the mines and resuming its operations. Granite and hornblende gneiss are the majority rocks present in the research area. Red sandy or loamy and lateritic soil are the two types of soil found in the research region. Approximately 73% of the entire area is ideal for agriculture and horticulture; 3% for pasture and forestry; and the remainder is suitable for mining, quarrying, and wildlife habitat. The study locations are indicated in the geological map, as shown in [Figure 1].
Figure 1: Geological map of study area with study locations

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222Rn and 220Rn measurement

Pinhole dosimeters, the most modern and accurate equipment for estimating 222Rn and 220Rn concentrations in indoor atmosphere, were utilized at thirty different locations throughout the study region. It is made up of two cylindrical chambers, each measuring 4.1 cm in length and 3.1 cm in radius.[5],[6] It has two compartments separated by a central pinhole disc which acts as 222Rn discriminator. The gas enters the first chamber, known as the ”222Rn +220Rn” chamber, through a glass fibre filter paper with a thickness of 0.56 m and then diffuses to the other cup, which is fully covered with four holes of 1 mm diameter at the top to almost completely stop the entry of 220Rn gas into the second chamber, known as the “222Rn chamber.” The schematic diagram of pinhole dosimeter is shown in [Figure 2].
Figure 2: Schematic diagram of pinhole dosimeter

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The Bhabha Atomic Research Center has developed direct measurement technology for the concentration of 222Rn and 220Rn, i.e., direct radon progeny sensors (DRPSs) and direct thoron progeny sensors (DTPSs), respectively.[7] The absorber employed for thoron daughter products is aluminized Mylar film of 50-μm thickness, which detects only α-particles (8.78 MeV) produced from 212Po. For 222Rn daughter product measurement, a combination of aluminized Mylar with a thickness of 25 m and a cellulose nitrate film with a thickness of 12 μm and an effective thickness of 37 μm is used as an absorber, which primarily detects particles emitted from 214Po with an energy of 7.69 MeV and 212Po with an energy of 8.78 MeV. Because 37-μm aluminized Mylar is not available on the market, this absorber combination was created. [Figure 3] shows the schematic diagram of this sensor (DTPS/DRPS). The dosimeters were suspended 2.5 m above ground level in an indoor environment. Detector films are collected after 90 days of exposure to the environment and chemically treated in a 2.5 N NaOH solution at 60°C for 60 min using a spark calculator
Figure 3: Direct progeny sensor (DTPS/DRPS)

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Estimation of 222Rn and 220Rn concentration

The concentrations of 222Rn and 220Rn gases in the indoor environment are calculated using Equations (1) and (2)[8] based on measured track densities in 222Rn and “222Rn + 220Rn” compartments





where “T1” and “T2” are the track densities 222Rn and 222Rn+220Rn, respectively; “D” is the number of days exposed; “B” is the background track density (4 tracks/cm2); and KR and KT are the calibration factors for 22Rn and 222Rn+220Rn compartments, respectively.

Equilibrium Equivalent Radon Concentration and Equilibrium Equivalent Thoron Concentration

DTPS is used to identify thoron (222Rn) daughter products, whereas DRPS is used to detect 222Rn (220Rn) daughter products (DRPS). Equation (3)[9] is used to determine EETC.



where “T1” is the track densities recorded on DTPS, “D” is the number of days exposed, “B” is the background counts, and ST = (0.94 ± 0.027) tracks/cm2/day1/EETC (Bq/m3) is the sensitivity factor for thoron daughter products.[10]

EERC is calculated from exact track density from 222Rn daughter products in DRPS obtained from Equation (4).[11]



Where ƞRT = (0.01 ± 0.0004) is the track registration efficiency for 220Rn daughter products in DRPS and ƞTT = (0.083 ± 0.0004) is the track registration efficiency for thoron daughter products in DTPS, respectively.

The EERC is calculated using Equation (5).[9]



Where SR = (0.09 ± 0.0004) tracks/cm2/day/EERC (Bq/m3) is the sensitivity factor for 222Rn daughter products.[10]

Estimation of equilibrium Factors for 222Rn and 220Rn

Equilibrium factor (EF) is calculated by the ratio of their daughter product concentration to their concentration for individual dwellings and is given by Equations (6) and (7).[6]





Calculation of annual inhalation dose

Indoor inhalation dose is computed from 222Rn, 220Rn, and their daughter product concentration measurements using the conversion coefficient 9 nSv for 222Rn and 40 nSv for 220Rn from Equation (8).[11]



Where Din is the indoor inhalation dose and CR and CT are the 222Rn and 220Rn concentrations, respectively.


  Results and Discussion Top


222Rn and 220Rn activity concentration

The measured 222Rn, 220Rn, and their daughter product concentrations are presented in [Table 1]. The concentrations of 222Rn and 220Rn in indoor air range from 26.2 ± 1.3 to 138.4 ± 1.6 Bq/m3 and 21.2 ± 0.8 to 133.3 ± 1.5 Bq/m3 with an average value of 68.8 ± 1.6 and 61.8 ± 1.5 Bq/m3, respectively, which are both within the ICRP 2009 recommended range of 200–300 Bq/m3[12],[13] and higher than the global average value of 40 Bq/m3.[14] The homes chosen for indoor research are placed at random around the study area and are made of bricks and cement, with various types of flooring on the ground floor. The concentrations of 222Rn and 220Rn vary greatly from one location to the next, and the average 220Rn concentration is lower than the average 222Rn concentration. 220Rn concentrations are higher than 222Rn concentrations in some areas. This is due to a variety of factors, including variations in radium and thorium activity in soil, rocks, building materials used in house construction, ventilation, 222Rn in water, local geology, and meteorological conditions, among others.
Table 1: Variation of indoor 222Rn, 220Rn, and their daughter product concentration, equilibrium factor, and inhalation dose in and around Kolar Gold Fields

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Indoor EERC and EETC values varied from 6.8 ± 0.8 to 19.8 ± 1.8 Bq/m3 and 0.9 ± 0.4 to 7.6 ± 1.1 Bq/m3 with a standard value of 14.2 ± 1.3 and 4.3 ± 0.8 Bq/m3, with an average value of 4.3 ± 0.8 Bq/m3, respectively. The value of the EERC is higher than the EETC because the internal EERC and the EETC rely heavily on the 222Rn and 220Rn inhalation of materials used for wall and floor construction, low air intensity, etc.

In Nelavanki, Yalduru, Kolar town, and in Srinivaspur, the concentration of 222Rn indoors, 220Rn, and their birthdays is high. This is because these areas have granitic rocks that expose the earth's surface, which has increased radiation activity. As a result of the rock structure along the various layers and spaces, 222Rn and 220Rn gases can enter the structures, resulting in increased concentration.[15],[16],[17],[18],[19] Indoor 222Rn, 220Rn, and their daughter product concentrations are slightly higher in Bangaru tirupati, Mulbagal, Malur, Vokkaleri, Cheluvanayakana Halli, and Sugaturu. This is because these places consist of hornblende gneiss which has lesser activity compared to granitic rocks, and the ventilation conditions in the dwellings of these places are comparatively good. In addition to this, the building materials used for construction in these places are cement, vitrified tiles, bricks, and gray granite which has slightly lesser activity of radionuclides.[20]

Indoor 222Rn, 220Rn, and their daughter product concentrations are found in lower concentrations in Marikuppam, BEML Nagar, Andersonpet, Sambhram Hospital, and Robertsonpet. The geology of these places consists of metabasalt and metagabbro which have very less activity of radionuclides, and the ventilation condition of all the dwellings considered for the study is very good. In addition to this, the materials used for construction of houses have very less activity concentration of radionuclides. Due to this reason, these places have very less concentration of radon, thoron, and their daughter products. Indoor 222Rn, 220Rn, and their daughter products are found to be high in granitic rock areas, with high radiation activity. It also depends on the type of building materials used, the atmosphere, and the geography of the area. Low concentrations of radon, thoron, and their offspring are recorded in the rocky areas of metabasalt and metagabbro as well as good ventilation in all homes.

[Table 2] and [Figure 4] show the statistical analysis and frequency distribution of 222Rn and 220Rn concentrations. The skewness value for 222Rn and 220Rn is 0.498 and 0.801, which indicates that the distribution is log normal and more number of values above the mean value. The distribution tail is toward left. The kurtosis value for 222Rn and 220Rn is −0.357 and 0.326, respectively. The negative values indicate that the values are smaller than the mean values.[21],[22]
Table 2: Statistics of 222Rn and 220Rn in and around Kolar Gold Fields

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Figure 4: Frequency distribution curve of 222Rn and 220Rn

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Equilibrium factors for 222Rn and 220Rn

[Table 3] summarizes the estimated values of the equilibrium equals of 222Rn and 220Rn. The indoor 222Rn and 220Rn equilibrium ranged from 0.14 to 0.51 and 0.03 to 0.11, respectively, on a scale of 0.23 and 0.07. The average 222Rn value is lower than UNSCEAR's declared 222Rn value of 0.4,[14] but greater than the reported 220Rn value of 0.03.[2]
Table 3: Average indoor 222Rn, 220Rn, and their daughter product concentration and inhalation dose in and around Kolar Gold Fields

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Annual inhalation dose

The equilibrium of the coefficient of 222Rn and 220Rn in any place that is being used for the calculation of the inhaled dose is 222Rn, 220Rn, and their daughter products, which is included in [Table 3]. The annual dose from indoor inhalation ranges from 0.73 to 3.46 mSv/y, with an average cost of 2.28 mSv/y, in accordance with the received information. The obtained values are within the recommended ICRP action threshold of 3–10 mSv−1.[20] The overall mean of the total annual inhalation dose is 2.4 mSv−1,[14] whereas the mean annual indoor inhalation dose is reduced.





Pinhole dosimeters were used to determine the levels of 222Rn, 220Rn, and their daughter products in the indoor environment in thirty different areas around the study area. In the current investigation, the average indoor 222Rn was found to be 68.8 Bq/m3, which is higher than the national and global averages of 40 and 42 Bq/m3, but lower than the WHO standard of 100 Bq/m3. The normal 220Rn concentration is 61.8 Bq/m3, which is higher above the national and global averages of 42 and 10 Bq/m3, respectively. The average indoor inhalation exposure is 2.28 mSv/y1. Indoor levels are within the ICRP 2011 action level. In the study area, houses are safe from 222Rn and 220Rn exposure as per the standard recommendation.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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