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ORIGINAL ARTICLE
Year : 2018  |  Volume : 41  |  Issue : 1  |  Page : 20-25  

Measurement of ambient gamma radiation levels and radon concentration in drinking water of Koppa and Narasimharajapura taluks of Chikmagalur district, Karnataka, India


1 Department of Physics, IDSG Government College, Chikmagalur, Karnataka, India
2 Department of PG Studies and Research in Physics, Kuvempu University, Shimoga, Karnataka, India
3 Research and Development Centre, Bharathiar University, Coimbatore, Tamil Nadu, India

Date of Submission31-Jan-2018
Date of Decision17-Mar-2018
Date of Acceptance30-Mar-2018
Date of Web Publication31-May-2018

Correspondence Address:
Dr. J Sannappa
Department of PG Studies and Research in Physics, Kuvempu University, Shankaraghatta, Shimoga - 577 451, Karnataka
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/rpe.RPE_15_18

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  Abstract 

This study presents the results of indoor and outdoor ambient gamma dose rates and radon concentration in groundwater at different locations of Koppa and Narasimharajapura taluks of Chikmagalur district, (13°40' north latitude and 75° 62' east longitudes). The total annual effective dose ranged between 0.67 mSv/y and 1.76 mSv/y with an average value of 1.16 mSv/y. The calculated total annual effective dose was found to be higher than the world average. The radon concentration in groundwater was analyzed using radon emanometry technique. The measured radon concentrations ranged from 3.96 Bq/l to 90.63 Bq/l with an average value of 35.34 Bq/l. This study reveals that 80% of drinking water samples have radon levels higher than the maximum contaminant level of 11 Bq/l recommended by the United States Environmental Protection Agency. All the recorded radon concentration values were found to be well below the action level of 100 Bq/l recommended by the World Health Organization. It is also found that the dose due to borewell water samples is higher compared to dose due to water from other sources such as hand pump, open well, and tap water.

Keywords: Annual effective dose, emanometry, gamma radiation, radon concentration


How to cite this article:
Srinivasa E, Rangaswamy D R, Suresh S, Reddy K U, Sannappa J. Measurement of ambient gamma radiation levels and radon concentration in drinking water of Koppa and Narasimharajapura taluks of Chikmagalur district, Karnataka, India. Radiat Prot Environ 2018;41:20-5

How to cite this URL:
Srinivasa E, Rangaswamy D R, Suresh S, Reddy K U, Sannappa J. Measurement of ambient gamma radiation levels and radon concentration in drinking water of Koppa and Narasimharajapura taluks of Chikmagalur district, Karnataka, India. Radiat Prot Environ [serial online] 2018 [cited 2021 Feb 26];41:20-5. Available from: https://www.rpe.org.in/text.asp?2018/41/1/20/233646


  Introduction Top


The naturally occurring background radiation arises mainly from terrestrial radioactive nuclides present in varying amounts in soil, rocks, building materials, and water. These radionuclides are widely distributed in the earth's crust, atmosphere, and extraterrestrial sources arising from cosmic-ray bombardment. These natural background radiations can vary significantly depending on the geological and environmental factors. Significant portion of the background radiation arises from radionuclides such as 40 K,238 U,232 Th, radon, and thoron and their progeny present in indoor and outdoor atmosphere. Out of the total radiation exposure, nearly 97% is from natural sources and only about 3% is from artificial sources of radiation.[1],[2],[3]222 Rn and 220 Rn are ubiquitous and are produced in the course of decay of 238 U and 232 Th series. According to the United States Environmental Protection Agency (USEPA) and the WHO studies, radon is the second leading cause for lung cancer after tobacco smoking.[4] For the health and radiation protection point of view, many countries have been carrying out nationwide radon survey and case–control studies of residential radon and lung cancer risk.[5] Radon is soluble in cold water and its solubility decreases with increasing temperature. Groundwater can cause additional radon into homes and other buildings, creating health risk.[6] When radon and its progeny are inhaled, increased the risk of lung cancer, while ingestion of radon in water is suspected of being associated with increased risk of tumors of several internal organs, primarily the stomach.[7],[8],[9],[10] In the United States, about 168 cancer deaths per year are caused by radon gas present in the drinking water, 89% of lung cancer caused by breathing of radon gas released from water, and 11% of stomach cancer caused by drinking of radon-containing water.[11],[12] The radioactive contamination in the ground water is high as compared to surface water (such as lake and river water). From the health, hygiene, and also radiological point of view, the present study is very essential in order to assess the doses and health risk resulting from gamma radiation and also radon in drinking water of the study area.

Geology of the study area

Lithostratigraphy of Chikmagalur district belongs to Baba bhudan group-Mulaingiri formation with phyllites and rare ultramafic sill. Santaveri formation-Meta basalts, gabbros, layered basic complexes, siliceous phyllites, cross bedded quartzites, ultramafic schists, basal conglomerate. The major soil type in the district comprises red loamy and red sandy soil (mainly), hilly area soil, and mixed red and black soil.


  Materials and Methods Top


Ambient gamma absorbed dose rates in the air

In the present study, environmental radiation dosimeter (ER-709 radiation survey meter) with halogen-quenched gamma radiation detector type GM132 is used to measure the natural background radiation dose rate. The instrument was calibrated at the Radiation Standards and Calibration Laboratory, Nucleonix Systems Pvt., Ltd., using 137 Cs as a standard source. The instrument is calibrated to read exposure rate in two ranges with measuring sensitivity of 0.1 μR/h and 1 μR/h and exposure with measuring sensitivity of 1 μR and accuracy of ±10% with Cs-137. The ER709 manufactured by Nucleonix Systems Pvt., Ltd., Hyderabad, India, is exclusively designed to serve as low-level survey meter in indoor and outdoor atmosphere. The ambient gamma absorbed dose rates were measured, in situ, in the identified locations. In each location, 30–40 points were selected and at each point 10–20 readings were recorded. The arithmetic mean of the readings was taken as representative figure for location. All measurements were made 1 m above the ground surface, as is the standard practice. The exposure rate (μR/h) was converted into absorbed dose rate (nGy/h) using the conversion factor of 1 μR/h = 8.7 nGy/h, which stems from the definition of roentgen and gray.[13] The conversion coefficient of 0.7 Sv Gy -1 and occupation factors of 0.2 and 0.8 for outdoors and indoors, respectively, were used to convert the absorbed dose in air to the effective dose.[1]

The indoor annual effective dose rates (E) and outdoor annual effective dose were calculated using the equations (1) and (2):



Radon concentration in water

The activity concentration of 222 Rn in groundwater was estimated by the emanometry method. [Figure 1] and [Figure 2] show the schematic diagram of radon bubbler and Lucas cell, respectively. After collecting the water samples using the standard procedure, the samples were brought to the laboratory with minimal loss of time and were analyzed immediately. In this method, about 40–60 ml of the water samples was transferred into the bubbler by the vacuum transfer technique. The dissolved radon in the water was transferred into preevacuated and background-counted scintillation cell. The scintillation cell was stored for 3 h to allow radon to attain equilibrium with its daughters and then it was coupled to a photomultiplier and alpha-counting assembly. Studies on radon concentration in groundwater samples in and around the study area were calculated using the equation 3:[14]
Figure 1: Radon bubbler

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Figure 2: Schematic representation of Lucas cell

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where D = counts above background, V = volume of water, E = efficiency of the scintillation cell (74%), λ = decay constant for radon (2.098 × 10− 6 s − 1), T = counting delay after sampling, and t = counting duration(s).

The annual mean effective doses for inhalation and ingestion from radon in water were calculated using the parameter established in the UNSCEAR report 2000[1] as follows:



where DIn is the effective dose for inhalation, CRnW is the radon concentration in water (Bq/l or KBq/m 3), RaW is the radon in air to the radon in water ratio (10− 4), F is the equilibrium factor between radon and its progenies (0.4), I is the average indoor occupancy time per individual (7000 ha −1), and DCF is the dose conversion factor for radon exposure (9 nSv [Bq h m − 3]−1).[1]



where DIg is the effective dose for ingestion, CRnW is the radon concentration in water (Bq/l), Cw is the weighed estimate of water consumption (UNSCEAR 2000), and EDC is the effective dose coefficient for ingestion (3.5 nSvBq − 1).


  Results and Discussion Top


The average absorbed dose rates from indoor and outdoor terrestrial gamma radiation and radon concentration in groundwater at all the selected locations of the study area are summarized in [Table 1]. [Figure 3] gives indoor and outdoor gamma absorbed dose rates. The values of indoor gamma absorbed dose rates were found in the range of 87–295.8 nGy/h with an average value of 193.14 nGy/h. This value is approximately two times more than the world average of 84 nGy/h.[13] Similarly, outdoor gamma absorbed dose rates were found in the range of 78.3–252.3 nGy/h with an average value of 174 nGy/h. This value is approximately three times higher than the world average of 59 nGy/h. Except at some locations, the average indoor absorbed dose rates were higher than the outdoor atmosphere. The higher levels of indoor gamma absorbed dose may be due to contribution of gamma radiation from building materials. The higher gamma absorbed dose rates were observed at mud-typed houses and houses having flooring materials such as decorative granites, ceramic titles, and vitrified tiles and houses were constructed by local rocks and local mud bricks. The values of indoor gamma absorbed dose were higher where the outdoor gamma dose was also higher. Gamma absorbed dose rates in atmosphere mainly depend on geology of the area, use of soil, rocks, and building materials for the construction of buildings, types of construction, and ventilation condition of dwellings. The geology of these regions was mainly attributed by granodiorite and granite, quartz chlorite schist with orthoquartzite, and Shimoga granite type of rocks. The area belongs to Baba Budan mountain range and the Kudremukh-Gangamula succession of the Western Ghats. The dwellings with mud walls, floorings, and granite floorings have relatively higher value of radiation, which indicates that including construction materials, the soil and rocks underneath the dwellings are the main causative factors for the relatively higher natural background radiation level.
Table 1: Absorbed dose, annual effective dose, radon concentration, inhalation, ingestion, and total dose

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Figure 3: Indoor and outdoor gamma absorbed dose rate

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Estimated values of annual effective dose for indoor exposures range from 0.43 mSv/y to 1.45 mSv/y with an average value of 0.95 mSv/y. For outdoor exposure, annual effective dose ranges from 0.10 mSv/y to 0.31 mSv/y with an average value of 0.21 mSv/y. The average outdoor annual effective dose received by the inhabitants of the study area was higher than the world outdoor annual effective dose average value of 0.07 mSv/y.[14],[15] The total annual effective dose varies from 0.67 mSv/y to 1.76 mSv/y with an average value of 1.16 mSv/y.

The mean values of radon concentration of all the studied drinking water samples vary from 3.56 Bq/l to 90.63 Bq/l with an average value of 35.34 Bq/l. The higher radon concentration in drinking water was observed in borewell and hand pumps water, this is possibly because of its greater depth, which allows water to interact with a greater thickness of aquifer and thus more radon is expected in hand pumps and borewells waters.[16] The US Environment Protection Agency has proposed that the allowed maximum contamination level (MCL) for radon concentration in water is 11.1 Bq/l.[11] The UNSCEAR-2000 has suggested a value of radon concentration in water for human consumption between 4 and 40 Bq/l.[1] From experimental results, it is evident that 80% water samples from borewells and hand pumps have radon concentrations higher than the MCL of 11.1 Bq/l recommended by the EPA, and 60% of the recorded values were well within the safe limit when compared with the allowed MCL for radon concentration in water for human consumption (4–40 Bq/l) suggested by the UNSCEAR.[1] The European Commission and WHO recommended the action level of radon concentration in drinking water as 100 Bq/l. From the study, it is found that all the recorded values were well below the action level and hence safe for drinking purposes.[17],[18] The estimated inhalation and ingestion dose varies from 8.97 μSv/y to 228.40 μSv/y with an average value of 89.05 μSv/y and from 0.75 μSv/y to 19.00 μSv/y with an average value of 7.41 μSv/y, respectively. From the above results it can be concluded that, the inhalation of radon released from drinking water may cause higher radiation dose than the ingestion and as shown in [Figure 4]. The mean annual effective doses due to ingestion and inhalation from radon in water are 0.0074 and 0.089 mSv/y and these values are higher than the mean annual effective doses of 0.002 and 0.025 mSv/y of UNSCEAR due to ingestion and inhalation, respectively.[1] The estimated total annual effective dose due to radon inhalation and ingestion ranges from 9.71 μSv/y to 247.4 μSv/y with an average value of 96.46 μSv/y. The average value is well below the reference level of 0.1 mSv/y of the WHO and hence do not pose any health problem from radon dose received from drinking water in the study area. The value of radon concentrations obtained in groundwater was compared with those reported by the other investigators in different parts of the world as summarized in [Table 2].
Figure 4: Inhalation and ingestion dose due to radon

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Table 2: Comparison of radon concentration in groundwater with those reported by the other investigators in different parts of the world

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  Conclusions Top


In the present study, the indoor, outdoor, and total annual effective doses due to terrestrial gamma radiation and radon concentration in drinking water were estimated. The average value of ambient gamma absorbed dose rate in the study area measured from radiation survey meter was found to be higher when compared to the worldwide average value of 56 nGy/h (UNSCEAR, 2000) as well as the All-India average value of 80.7 nGy/h. It was found that the average indoor gamma absorbed dose is higher than outdoors. The obtained results reveal that the radon concentration in tap water is lower than that in borewell water and hand pumps. The recorded radon concentration values in drinking water samples are within the safe limits recommended by the WHO and EC. The results show no significant radiological risk for the inhabitants of the studied regions. [33]

Acknowledgments

The authors would like to express their sincere thanks to the Department of PG Studies and Research in Physics, Kuvempu University, for providing instrumentation facility to carry out the research work.

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]



 

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