|Year : 2020 | Volume
| Issue : 1 | Page : 21-25
Indoor222Rn exposure in selected schools and residential dwellings of Mandya, Karnataka
KN Narasimhamurthy1, GV Ashok2, N Nagaiah3, NG Shiva Prasad4, AN Prema5
1 Department of Physics, Government First Grade College, Tumkur, Karnataka, India
2 Department of Physics, Government College, Mandya, Karnataka, India
3 Department of Physics, Bangalore University, Jnanabharathi Campus, Bengaluru, Karnataka, India
4 Department of Physics, Government First Grade College, Srirangapatna, Karnataka, India
5 Department of Physics, Don Bosco Institute of Technology, Bengaluru, Karnataka, India
|Date of Submission||20-Jun-2018|
|Date of Decision||02-Jan-2020|
|Date of Acceptance||18-Jan-2020|
|Date of Web Publication||12-May-2020|
G V Ashok
Department of Physics, Government College, Mandya, Karnataka
Source of Support: None, Conflict of Interest: None
The people typically spend most of their time at home and schools and also it workplaces for teachers and administrators and service staff, who might spend even more time than children in school buildings. In view of this, indoor radon concentration has been carried out in selected residential and schools located in Mandya, Karnataka, using solid-state nuclear track detector technique. Annual mean values of222Rn in selected schools and houses were found to be 17.4 and 23.3 Bq/m3, respectively. The data distribution was discussed using lognormal probability plots. The doses to different organs and tissues were calculated using the ICRP model of the respiratory tract, and intercomparison of risk is discussed. It can be seen that the larger fraction of the dose is delivered to the lungs (69%) and extrathoracic region (31%) of the body.
Keywords: Houses, inhalation dose, radon, schools, solid-state nuclear track detector
|How to cite this article:|
Narasimhamurthy K N, Ashok G V, Nagaiah N, Shiva Prasad N G, Prema A N. Indoor222Rn exposure in selected schools and residential dwellings of Mandya, Karnataka. Radiat Prot Environ 2020;43:21-5
|How to cite this URL:|
Narasimhamurthy K N, Ashok G V, Nagaiah N, Shiva Prasad N G, Prema A N. Indoor222Rn exposure in selected schools and residential dwellings of Mandya, Karnataka. Radiat Prot Environ [serial online] 2020 [cited 2020 Jul 10];43:21-5. Available from: http://www.rpe.org.in/text.asp?2020/43/1/21/284232
| Introduction|| |
Natural radioactivity is the main source of population exposure to ionizing radiation. More than 80% of exposure comes from the natural radioactivity. Radon and its progenies contribute more than 50% to the annual effective dose received from all sources of ionizing radiation (UNSCEAR, 2008). Radon is a naturally occurring colorless and odorless gas. It was first discovered in the form of222 Rn in 1899, with two other isotopes of radon (220 Rn and219 Rn) discovered subsequently. In general,219 Rn and220 Rn are not significant public health concerns in modern, well-maintained architectural structures due to the short half-life (3.96 and 55.6 s, respectively).222 Rn, in contrast, has a half-life of 3.8 days, which allows it to travel some distance.222 Rn can seep into buildings through cracks in floors, construction joints, and/or around service pipes. Henceforward,222 Rn is referred to simply as “Radon.”
Laith et al. measured the radon concentration, the surface exhalation rate, and the mass exhalation rate in building construction materials commonly used in Iraq. Aswood et al. found that the mean radon concentrations in agricultural soil collected from the Cameron Highlands were 198.44 ± 59.44 Bq/m3. Radiation damage to bronchial cells can eventually be the second leading lung cancer risk next to smoking. Radon exposure at schools may have a considerable public health impact. The risk of lung cancer in children resulting from exposure to radon may be up to threefold higher than that of adults exposed to the same amount of radon due to the morphometric differences between the lungs of children and the lungs of adults., Schools are also workplaces for teachers and administrators and service staff, who might spend even more time than children in school buildings. The safety of children in schools is of utmost importance. Many organizations are working to assess radon exposure in homes and raise awareness about the importance of testing, given that children and staff spend a considerable amount of time indoors in schools where radon levels can accumulate to high levels. Therefore, high levels of radon in school buildings may pose significant health risks to those who spend many months, or years, at those schools.
In the present study, we reported222 Rn concentration in few selected residential places and schools in Mandya, Karnataka. Using the dosimetric approach of ICRP respiratory tract model, doses due to222 Rn to the different tissues and organs of the human body were calculated and discussed.
| Methodology|| |
Solid-state nuclear track detector technique
The concentrations of222 Rn in the dwellings were measured using solid-state nuclear track detectors (SSNTDs). For indoor radon measurements, 12-μm thick LR115 Type-II strippable cellulose nitrate films, supported on a transparent 100-μm thick polyester (cellulose acetate) sheet, made by Kodak Pathe, France, were used. The films are less influenced by the moderate humidity, heat, and light. The films were kept in the two compartments of single-entry twin-cup pinhole dosimeters which have a single entry where gas enters into the first chamber (radon) through a glass fiber filter paper and then into the second chamber through discriminating pinhole disc which separates the two chambers. The first chamber is the reference chamber and the second one is the pinhole chamber. Each chamber has a length of 4.1 cm and radius of 3.1 cm. On the other side of the compartment, only radon gas was allowed to enter which has a circular disc with four pinholes of 2 mm length and 1 mm diameter in it. This pinhole is designed in size and thickness of the cap to block thoron from entry inside by considering the diffusion length and half-life of thoron. These plastic dosimeters were developed and calibrated at Environmental Assessment Division, Bhabha Atomic Research Centre, Mumbai.
The dosimeters are hanged overhead on the ceiling at a height of about 2.5 m from the floor and at least 10 cm away from any surface. The films were retrieved after 90 days, etched in an etching bath unit, and tracks were counted using a spark counter. The radon gas concentrations were determined from the track densities obtained from “Radon chamber” (Tr), using the following relations.
Where CR is the radon concentration (Bq/m3), d is the number of exposure days, and Kr1 is the calibration factor for radon in the “Radon chamber” (0.0170 ± 0.002 tr/cm /Bq/d/m).
Area under the study
Mandya is a prominent agricultural district with land of sugar and rice formed in the year 1939. Blessed with the irrigation waters of river Cauvery and Hemavathi, half of the district countryside is lush in various hues of green throughout the year. About half of the agricultural land in the district receives assured irrigation from the Krishna Raj Sagar and the Hemavathi reservoirs. Groundwater contributes to about 80% of the drinking water requirements in the rural areas, 50% of the urban water requirements, and more than 50% of the irrigation requirements of the district.
Mandya comes under the group of districts known as the maidan (plain) districts and is situated in the Southern part of the Karnataka State and to the North of Mysore district, of which it once formed a part. The whole of Mandya district is a plateau of heights ranging from 2500 to 3000 ft above the sea level. The geology of Mandya consists several rocks and minerals. The main rock system has younger granites, granodiorite, pegmatite, schists, phyllite, shals, limestone/marbles, quartz, and unclassified crystallines (mainly gneisses). Furthermore, Mandya consists of minerals such as corundum, iron, gold, mica, China Clay, garnet kyanite, lead, zinc, and silver.
| Results and Discussion|| |
The measurement of concentration of222 Rn in indoor was carried out in few selected houses and schools in Mandya city. The twin-cup pinhole dosimeters loaded with SSNTD films were exposed for a period of 1 year (6 months duration, twice). The annual mean radon concentrations obtained in the present study are presented in [Figure 1]. The radon levels in the houses varied between 15.3 and 38.3 Bq/m3 with a mean value of 23.3 Bq/m3. The222 Rn concentrations in the schools varied between 5.4 and 36.5 Bq/m3 with a mean value of 17.4 Bq/m3 [Table 1]. The overall mean radon concentration is calculated as 20.3 Bq/m3. The observed mean value of 222Rn concentration is well within the world average 40 Bq m-3 for indoors and the Indian average of 42 Bq m-3.,
|Figure 1: Indoor radon concentrations at different schools (S) and houses (h)|
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|Table 1: The annual mean222Rn concentration in selected schools and houses|
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To determine the distribution of the data, the values of the measured results were compared with a normal [Figure 2]a and[Figure 2]b and log-normal distribution [Figure 3]a and [Figure 3]b in selected houses and schools, respectively. When combining all data points sampled at all times and locations, the resulting probability density functions p(x) for indoor radon concentration (x) appear approximately lognormal as shown in [Figure 2], which is expressed as:
|Figure 2: Normal probability distribution of222Rn concentration in selected (a) houses and (b) schools, respectively|
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|Figure 3: Lognormal probability distribution of222Rn concentration in selected (a) houses and (b) schools, respectively|
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Where s is the standard deviation and m is the mean of the log-transformed variable. In the present study, μ = 22.6 and σ = 8.519 for houses and μ =18.94 and σ = 11.36 for schools.
Many factors contribute to the entry of radon gas. Buildings in nearby areas can have significantly different radon levels from one another. Many schools and commercial buildings are constructed on concrete slabs that permit radon gas to enter through cracks and expansion joints between the slab and the ground soil. Other features such as the presence of basement areas, crawl spaces, utility tunnels, sub-slab Heating Ventilation and air conditioning (HVAC) ducts, cracks, or other penetrations in the slab (e.g., around pipes) also provide areas for radon to enter indoor spaces.222 Rn concentrations in selected houses and schools are below the action limit of the World Health Organization (40 Bq/m3).
Inhalation doses to different organs and tissues
Inhalation of radon delivers radiation dose not only to the lungs but also to different organs and tissues of the body. Based on the available information on the distribution and retention of radionuclides in different organs and tissues, many models have been developed to quantify the doses imparted to different organs and tissues and these are being used for intercomparisons of risks (human respiratory tract models). From the literature, it is found that two sets of calculations were generally performed for inhaled decay products: “Type M” and “Type F.” These differ in the rate with which material is taken up by body fluids from the lung. It is normally thought that the behavior of radon decay products is closer to Type M., Hence, in the present work, a new attempt has been made (using Type M) to compare the doses to different organs and tissues using the mean radon concentration of 20.3 Bq/m3, which are presented in [Table 2].
|Table 2: Summary of calculated annual doses (μv) from inhaling air containing radon at 20.3 Bq/m3 with radon decay products to different tissue organs in adults|
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In the present work, doses to different organs and tissues are estimated using the dose conversion factors reported by Kendall and Smith which are based on the internal dosimetry code PLEIADES., The annual inhalation doses to different organs and tissues are calculated using the formula:
Annula inhalation dose (μSv/y) = CR× (DCF)Organ × V × 106 (3)
Where CR is the concentration of radon (Bq/m3), (DCF)Organ is the dose coefficient for the organ (Sv/Bq), and V is the annual volume of air breathed (7300 m3). In the present work, a new attempt has been made (using Type M) to compare the doses to different organs and tissues using the value of mean radon concentration obtained from the study. The dose from radon alone to different organs is very low and is calculated by taking the dose conversion factor reported in Khursheed.
From the [Table 2], it can be observed that the kidney receives the highest dose (54.8 μSv/y) from decay products of222 Rn among all the organs present outside the respiratory tract and the other organs such as the stomach, liver, Red bone marrow (RBM), and intestine, receive very small amounts. [Table 2] reports the dose obtained from dosimetric calculations and these doses cannot be considered for risk assessments but which can only be used for intercomparisons of risks between different organs. The discrepancy between epidemiology and dosimetric calculation of dose is well known (ICRP, 1993), and dosimetric dose conversion factors are higher by a factor of 3–4.,, Due to this, the higher annual effective dose of 2324.79 μSv/y from radon decay products and 30.85 μSv/y from radon alone for a low radon exposure of 20.3 Bq/m3 was found (compared to 1150 μSv/y). It can be seen that the larger fraction of the dose is delivered to the lungs (69%) and extrathoracic region (31%) of the body.
| Conclusions|| |
Indoor radon concentration has been carried out in selected residential and schools located in Mandya, Karnataka, using the SSNTD technique. The radon levels in the houses varied between 15.3 and 38.3 Bq/m3 with a mean value of 23.6 Bq/m3. The222 Rn concentrations in the schools varied between 5.4 and 36.5 Bq/m3 with a mean value of 17.1 Bq/m3. The overall mean radon concentration is calculated as 20.3 Bq/m3. The data distribution was discussed by using normal and lognormal probability plots. The doses to different organs and tissues were calculated using the ICRP model of the respiratory tract and intercomparison and were discussed. It can be seen that the larger fraction of the dose is delivered to the lungs (69%) and extrathoracic region (31%) of the body. The annual concentrations of the222 Rn in the region of study are below the action limit of the World Health Organization (40 Bq/m3). To understand the actual contribution of the radon gas in causing lung cancer in the region of the study, it is important to conduct a case–control study. However, the derived data of measurement will be helpful in providing baseline data for further studies.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2]