INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 4, No 4, 2014 © Copyright by the authors - Licensee IPA- Under Creative Commons license 3.0 Research article ISSN 0976 – 4402 Distribution of 226Ra and 222Rn in bore well and lake water of Mysore Taluk, Karnataka State, India Rajesh. B.M1, Chandrashekara. M.S1, Nagaraja. P2, Chandrashekara. A3, Paramesh. L1 1- Department of Studies in Physics, University of Mysore, Manasagangotri, Mysore 570006, Karnataka State, India. 2- Department of Studies in Chemistry, University of Mysore, Manasagangotri, Mysore 570006, Karnataka State, India. 3- BARC, Yelawala, Mysore - 571130, Karnataka State, India. [email protected] doi: 10.6088/ijes.2014040400011 ABSTRACT The dose due to Ra-226 and Rn-222 concentration to the population of Mysore taluk through drinking water pathway was assessed using radon emanometry method. Radium-226 activity concentration varies from BDL to 73 mBql-1 with a median of 17.9 mBql-1 and Radon-222 concentration varies from 0.5 to 643.9 Bql-1 with a median of 23.8 Bql-1. Committed effective dose due to radium and radon concentration through drinking water path was found to vary from 15.6 to be 57.1 µSvy-1 with a geometric mean of 31.3 µSvy-1. Keywords: Ra-226, Rn-222, Effective dose, Emanometry, Mysore. 1. Introduction Radium-226 is one of major radioactive element found in water and food. Since it has a long half-life of 1622 years and its chemical behavior is similar to calcium, it can be accumulated in the human bones through ingestion of water. It can be measured directly using its α or γray emissions or indirectly by the emanation of its short-lived daughter product 222Rn. Maximum Contaminant Level for 226Ra in drinking water is reported as 740 mBql-1 (20 pCil1 ) (USEPA, 2000). Radon-222 is a chemically inert, colorless, odorless and a radioactive noble gas. It is a daughter product of radium-226 and has a half-life of 3.82 days. Radon is soluble in water and its mole fraction solubility is 2.3×10-4 at 15°C and 1.25×10-4 at 37°C and its solubility decreases with increase in temperature and increases with increase in pressure. This property allows a high concentration of radon in ground waters. Emanation of radon in the soil and water depends on the meteorological conditions like temperature, pressure and shows positive correlation with radon concentration and humidity, rainfall shows negative correlation (Iveta et al., 2009). Higher radon concentration in water depends on, groundwater which is extracted from drill holes in rocks or from springs flowing through crystalline rocks, because these have higher concentration of radium than the average bedrock. Radon gas can dissolve in groundwater and later be released into the air during normal household activities such as showering, dishwashing and doing laundry. When radon accumulates in indoor air, it can pose an increased health risk. It is a major contributor to the ionizing radiation dose received by the general population. Exposure to waterborne radon may occur by ingestion and inhalation. When inhaled over prolonged periods it is capable of causing lung cancer. One of the risks associated with ingestion of water containing radon and radon progeny is stomach and colon cancer. A study on dissolved radionuclides in aquatic environment gives the key aspect for evaluation and control of natural exposure (UNSCEAR, 2000). Received on November 2013 Published on January 2014 558 Distribution of 226Ra and 222Rn in bore well and lake water of Mysore Taluk, Karnataka State, India 2. Study area The study area is Mysore taluk, Karnataka State, India and it lies between 12°13″–12°25″N latitude and 76°27″– 76°45″E longitude, at an altitude of about 767 m amsl (Figure1) forming a part of the catchment zone of the Cauvery and Kabini rivers at north west and south east respectively. The archean rocks of south India are best developed in Mysore and are made up of schists, gnesis, pegmatites and granites. The soil in Mysore region is red sandy and loamy as in entire district. The population of Mysore taluk is about 10.38 lakhs. The study area consists of precambrian gneisses with enclaves of amphibolites and limited zones of ultramafic rocks. Pegmatitic intrusions into the Precambrian gneisses and schists have also been found in several areas. The occurrence of ground water is under unconfined aquifer conditions. The thickness of the weathered zone varied between 3 m and 5 m over much of the region. Outcrops of most of the rocks are present in almost all elevated regions and along valley cuts. Large diameter shallow (10–12 m depth) dug-wells and deep (35–60 m depth) bore wells provide the major source of water in the remaining portions of the study area. A masonry wall is normally constructed in the dug-wells to a depth of 1 to 2 m below ground level. In bore wells, depending upon the nature of rock formations, unslotted casing is installed up to a depth of 5 to 6 m below ground level and slotted casings from 6 to 15 m, depending upon the thickness of the weathered/fractured zones (Ramakrishnan and Swami Nath, 1981; Shashikumar et al., 2008). Figure 1: Study area Rajesh. B.M International Journal of Environmental Sciences Volume 4 No.4, 2014 559 Distribution of 226Ra and 222Rn in bore well and lake water of Mysore Taluk, Karnataka State, India 3. Materials and methods 3.1 Estimation of 222Rn and 226Ra activity by Emanometry Method Forty-five water samples were collected from ground water source like bore wells and surface water like lakes at different locations of Mysore taluk. The 226Ra and 222Rn activity concentration in water samples was estimated by the radon emanometry. Water sample was collected in pre acid cleaned airtight plastic bottles in a gentle manner to prevent the air bubbles inside the container and to control the aeration during the water sampling process, which might lead to out gassing resulting in improper radon estimation. For radium, about 20 liter of water was collected and pre concentrated to 70 ml. In this method, about 70 ml of the water sample was transferred into the bubbler of 100 ml size by the vacuum transfer technique (Figure2) and it kept for a known period of 21 days to attain equilibrium between radium and radon. The dissolved radon in the water was transferred into a pre-evacuated and background counted ZnS (Ag) scintillation cell of size 150 cc. The scintillation cell was stored for 180 minutes to allow radon to attain equilibrium with its daughters and then it was coupled to a photomultiplier and programmable alpha counting system. The concentration was calculated using the following equations (1) and (2) (Raghavayya et al., 1980; Shashikumar et al., 2011) . 6 . 97 × 10 − 2 × D 222 Rn Bql − 1 = V × E × e − λ T × 1 − e − λ t _________________________________ (1) 6 . 97 × 10 − 2 × D 226 Ra mBql − 1 = V × E × 1 − e − λ t × e − λ T × 1 − e − λθ ____________________ (2) ( ( ) ( ) ) ( ( ) ) ( ) ( ) Where, D = counts above background, V = Volume of water (70 ml), E = Efficiency of the scintillation cell (74 %), λ = decay constant for radon (2.098 x 10-6 s-1), T = Counting delay after sampling, t = Counting duration (s) and θ = build up time in the bubbler (s). Figure 2: Radon Bubbler Rajesh. B.M International Journal of Environmental Sciences Volume 4 No.4, 2014 560 Distribution of 226Ra and 222Rn in bore well and lake water of Mysore Taluk, Karnataka State, India 3.2 Dose due to 222Rn and 226Ra concentration in water The committed effective dose for the population of the region was estimated using the concentration of 222Rn and 226Ra in water samples. The parameters for the inhalation pathway were 222Rn concentration in water, air water concentration ratio of 10-4, indoor occupancy of 7,000 hours per year and inhalation dose coefficient applied is that for the gas. The effective dose to the ingestion mainly depends upon the amount of water consumed by a human being in a day. The dose due to inhalation and ingestion are calculated by the equation (3, 4 & 5) (Kovacs et al., 2003; UNSCEAR, 2000; Yu et al., 1994). Inhalation dose (Sv) = 222Rn conc. (Bq l-1) × 10-4 × 7,000 h × 0.4 × 9 nSv (Bq h m-3)-1____(3) Ingestion dose (Sv) = 222Rn conc. (Bq l-1) × 365 l y-1 × 3.5 nSv Bq-1_________________ (4) Ingestion dose (Sv) = 226Ra conc. (Bq l-1) × 365 l y-1 × 280 nSv Bq-1________________ (5) Committed effective dose (Sv) = Dose conversion factor × water consumption × duration of consumption × Concentration of 226Ra and 222Rn + Inhalation dose due to 222Rn 4. Results and discussion The radon and radium concentration in different types of water samples was estimated using radon emanometry. Radium concentration varies from 0.72 to 72.9 mBql-1 with a median of 17.9 mBql-1 and Radon concentration varies from 0.5 to 643.9 Bql-1 with a median of 23.8 Bql-1. In bore well it varies with an average of 21.7 mBql-1 and 64.5 Bql-1 and in lake it is 18.42 mBql-1 and 29.4 Bql-1. Distribution of 226Ra and 222Rn activity concentration and the corresponding dose to the population at different hoblies of Mysore taluk is presented in table 1 and fig3. Statistical variation of 226Ra and 222Rn concentration in water samples is shown in table 2. 19% of the samples show less than permissible limit of 11.1 Bql-1, which is proposed by USEPA for radon concentration through water intake, only one sample shows concentration above the 400 Bql-1, which resulting an indoor radon concentration of 150 Bqm-3 for which remedial action is recommended by the USEPA. Low radon concentrations are observed in surface water due to lack of major contact with radon emanating mineral material and also aeration of radon gas to the atmosphere. Highest radon concentration of 643.9 Bql-1 is observed in the Mysore hobli (Bandipalya village located behind the Chamundi hill) which is rich in granite rocks. Previous studies on soil and rock samples at Chamundi hill show highest concentrations of radium and thorium radionuclides. When granite rock contains high radium concentrations, the ground water originating from granite formations is accompanied by leaching out of radionuclides with ground water (Kerur et al., 2010; Mose et al., 2010). Due to this reason, the highest radon concentrations in bore well water samples have been observed. Radium concentration of 20 mBql-1 and above are seen in few ground water of Yelwala hobli and in one lake at Mysore hobli (Kalkuare) shows 72.9 mBql-1, which result was attributed with the local geological region and the same was confirmed by the highest radon concentration. Activity concentration of 222Rn and 226Ra in bore well and lakes at different villages of Mysore Taluk is presented in table 3 and table 4 respectively and distribution of 226Ra and 222Rn in bore wells and lakes are presented in fig 4. The dose due to 222 Rn is divided into two parts, namely the dose from ingestion and the dose from inhalation. For the ingestion and inhalation part, 222Rn and its progeny in water impart a radiation dose to the stomach and lung respectively. Computing from the radium and radon activity concentrations in water samples, the committed effective ingestion dose vary from 15.57 to 56.98 µSvy-1 and inhalation dose due to radon pathway vary from 0.01 to 0.08 µSvy-1. Rajesh. B.M International Journal of Environmental Sciences Volume 4 No.4, 2014 561 Distribution of 226Ra and 222Rn in bore well and lake water of Mysore Taluk, Karnataka State, India According to WHO the dose received by population is below 100 µSvy-1 (Chandrashekara et al., 2012; Shashikumar et al., 2008; WHO, 2012). Table 1: 222Rn and 226Ra activity in water and the corresponding committed effective dose Mysore Taluk : Hoblies Yelawala Jayapura Mysore Mysore City Varuna Radon Conc. (Bq l-1) Radium Conc. (m Bq l-1) Inhalation dose due to 222Rn (µ Svy-1) Ingestion dose due to 222Rn and 226Ra (µ Svy-1) 25.52 30.5 42.7 20.1 18.3 23.78 0.064 0.076 0.011 34.66 40.83 56.98 Committed effective dose due to 226Ra and 222Rn (µ Svy-1) 34.72 40.91 57.09 18.27 5.68 0.046 23.92 23.97 12.02 1.84 0.032 15.54 15.57 5. Conclusion 222 Rn concentrations in 81% of the water samples are higher than the MCL 11.1 Bql-1 prescribed by the EPA. 226Ra activity concentration in Mysore city and the hoblies of Mysore taluk was very much less than the guidance value of 740 mBql-1 proposed by the USEPA. Consequently, the collective effective dose to the adult population was found to vary from 15.6 to be 57.1 µSvy-1, which is less than 100 µSvy-1 as recommended dose limits by WHO. The reason for higher radon concentration due to local geology of this region, which consists of different types of granites. Figure 3: Distribution of 226Ra and 222Rn activity concentration in Mysore taluk Rajesh. B.M International Journal of Environmental Sciences Volume 4 No.4, 2014 562 Distribution of 226Ra and 222Rn in bore well and lake water of Mysore Taluk, Karnataka State, India Table 2: Statistical variations of 226Ra and 222Rn in water samples Sl. No 1. 2. 3. 4. 5. 6. Statistical Variance Max Min Average GM Median SD Rn-222 (Bql-1) 643.90 BDL 53.12 22.83 23.80 101.50 Ra-226 (mBql-1) 72.90 BDL 20.48 13.39 17.90 16.00 Table 3: Activity concentration of 222Rn and 226Ra in bore well water samples at different villages of Mysore Taluk Sl. No Locations 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. Max Min Average Erappanakoppalu Seegalli Ankanahalli Gommata giri Ratnahalli Mallegowdana Koppalu Hulikere Naganahalli Hulikere Koorgalli Hosakote Sagarakatte Krishna Raja Sagara Kumarabidu Belagola Mandakalli Bandipalya Kumbara koppalu Manasagangothri T K Layout Jayanagara Lashkar Mohalla Vijaya Nagara Mahadevi Colony Dandikere Varuna Chatnahalli Puttegowdana Hundi Varkodu Chikkahalli Type Rn (BqL-1) Bore well Bore well Bore well Bore well Bore well Bore well Bore well Bore well Bore well Bore well Bore well Bore well Bore well Bore well Bore well Bore well Bore well Bore well Bore well Bore well Bore well Bore well Bore well Bore well Bore well Bore well Bore well Bore well Bore well Bore well 12.5 97.9 19.7 147.5 108.7 18 39.6 16.9 40 27.3 42 18.4 23.8 30.5 63 92.3 643.9 194 10.6 12.3 13.3 28 -27.2 7.3 19.5 33.8 7.5 57.2 19.3 643 0.5 64.5 Ra (m BqL1) 6.3 47.8 29.5 39.5 47 34.7 27.6 10.2 29 16.3 16 10.2 18.2 18.3 39 33.7 -21.7 1.73 1.2 12.8 15.51 1.17 -BDL -----47.8 BDL 21.7 Rajesh. B.M International Journal of Environmental Sciences Volume 4 No.4, 2014 563 Distribution of 226Ra and 222Rn in bore well and lake water of Mysore Taluk, Karnataka State, India Table 4: Activity concentration of 222Rn and 226Ra in lake water samples at different villages of Mysore Taluk Sl. No 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. Locations Nagavala Ratnahalli Nodehalli Halebeedu Belawadi Mandakalli lake Bandipalya Kal kuare Devikere Hebbal Kere Karanji kere Dalvai lake Marse Shettikere GiriBetta Max Min Average Type Lake Lake Lake Lake Lake Lake Lake Lake Lake Lake Lake Lake Lake Lake Lake Rn (BqL-1) 13.9 0.5 19.3 35.1 48 18.3 62.8 137.4 1.6 51.6 BDL 1.4 17.3 0.8 4.2 137.4 BDL 29.4 Ra (m BqL-1) 4.6 31.7 17.9 17.3 27.1 8.6 20.3 72.9 9.5 19.2 BDL 5 4.7 BDL 0.72 72.9 BDL 18.42 Figure 4: Distribution of 226Ra and 222Rn activity concentration in Bore wells and Lakes Rajesh. B.M International Journal of Environmental Sciences Volume 4 No.4, 2014 564 Distribution of 226Ra and 222Rn in bore well and lake water of Mysore Taluk, Karnataka State, India Acknowledgement This work had been carried out under the DAE, BRNS project. The authors thankful to the Board of Research in Nuclear Sciences, Department of Atomic Energy, Government of India for extending financial support for the present study. The authors sincerely thank Prof. P Venkataramaiah, former Vice-Chancellor, Kuvempu University, India for his constant guidance and encouragement. 6. References 1. Chandrashekara M.S., Veda S., Paramesh L., (2012), Studies on radiation dose due to radioactive elements present in ground water and soil samples around Mysore city, India. Radiation protection dosimetry ,149, pp 315-335. 2. 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B.M International Journal of Environmental Sciences Volume 4 No.4, 2014 565 Distribution of 226Ra and 222Rn in bore well and lake water of Mysore Taluk, Karnataka State, India 11. USEPA, (2000), Radionuclides notice of data availability: Technical support document, United States Environmental Protection Agency. 12. WHO, (2012),Uranium in Drinking-water: Background document for development of WHO Guidelines for Drinking-water Quality, World Health Organization. 13. Yu K.N., Guan Z.J., Stokes M.J., Young E.C.M., (1994), A preliminary study on the radon concentrations in water in Hong Kong and the associated health effects, Applied Radiation and Isotopes , 45, pp 809-810. Rajesh. B.M International Journal of Environmental Sciences Volume 4 No.4, 2014 566
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