Radiation Protection and Environment

ARTICLE
Year
: 2011  |  Volume : 34  |  Issue : 3  |  Page : 197--200

Concentration of 222 rn in drinking water along coastal kerala and evaluation of ingestion doses


Primal D'Cunha1, Y Narayana1, N Karunakara2, I Yashodhara2, Sudeep Kumara2,  
1 Department of Studies in Physics, Mangalore University, Mangalagangotri, India
2 University Science Instrumentation Center, Mangalore University, Mangalagangotri, India

Correspondence Address:
Y Narayana
Department of Studies in Physics, Mangalore University, Mangalagangotri
India

Abstract

In this study, the result of systematic measurement of activity concentration of 222 Rn in drinking water from sources of public water supply along the coastal regions of Kerala is discussed. The 222 Rn concentrations in water were measured using the emanometry method and it was found to vary from 0.03 to 1.31Bq l−1 . The associated effective doses were computed for the population of the region.



How to cite this article:
D'Cunha P, Narayana Y, Karunakara N, Yashodhara I, Kumara S. Concentration of 222 rn in drinking water along coastal kerala and evaluation of ingestion doses.Radiat Prot Environ 2011;34:197-200


How to cite this URL:
D'Cunha P, Narayana Y, Karunakara N, Yashodhara I, Kumara S. Concentration of 222 rn in drinking water along coastal kerala and evaluation of ingestion doses. Radiat Prot Environ [serial online] 2011 [cited 2021 Jan 23 ];34:197-200
Available from: https://www.rpe.org.in/text.asp?2011/34/3/197/101722


Full Text

 1. Introduction



Naturally occurring 222 Rn, belonging to the uranium-238( 238 U) decay series, is the most abundant and has the longest half-life among the noble gas radon naturalisotopes. It is produced after three alpha and two beta disintegrations following the initial 238 U alpha decay. 222 Rn is efficiently transferred from the solid matrix to the water-filled pore and fracture space by alpha recoil and associated effect. [1] The 222 Rn activity concentration in water sources depends not only on the concentration of uranium in certain types of rocks and soils, but also on the distribution of the parent radium-226 ( 226 Ra)inside the solid grain, degree of rock weathering, the disequilibrium state of the uranium series inside the solid grain, adsorption of radium in the rock grain andfracture surfaces, and on the effective rock surface exposed to ground water contact. [2]

Although 222 Rn may present in considerable activity concentration within the sources of water, most of the gas is lost before the water is consumed. As 222 Rn is more soluble in other gases than in water, it is easily transferred to the atmospheric air. Surface waters typically contain very low concentrations of 222 Rn [3] than ground waters. In recent years, concern has grown about the potentially hazardous effects of the continuous exposure of the general publicto low-level radioactivity environments. The 222 Rn in water can be ingested or inhaled during consumption of water and will result in exposure of human organs to radiation, primarily the lungs. Thus, assessing 222 Rn in water, in addition to that in air,is an important step in reducing the potential exposure to it.On the other hand, the use of water in dwellings may result in'enhanced' indoor concentration levels of 222 Rn.Suchan increase in the indoor levels of 222 Rn depends on the total consumption of water in the dwelling, the size of the dwelling, and the rate of air ventilation. [4] The present study was carried out to measure 222 Rn activities in several natural water samples from coastal Kerala which is known for high background radiation areas.

 2. Materials and Methods



2.1 Sample collection

Sampling stations were identified in selected locations for collecting drinking water. In the present study, all the drinking water samples were collected from open wells. The map showing the sampling stations is shown in [Figure 1]. About 1 L of water was collected from each sampling station in airtight bottles. The bottles were filled completely to minimize loss of 222 Rn during sample collection. The samples were brought to the laboratory with minimum delay and were analyzed immediately.{Figure 1}

2.2 Activity determination

The concentration of 222 Rn in aqueous samples was determined by the emanometry method. [5] In this method, about 50 mL of the water sample was transferred into the bubbler by the vacuum transfer technique. The dissolved 222 Rn in the water was transferred into a pre-evacuated and background-counted scintillation cell. The scintillation cell was stored for 180 minutes to allow 222 Rn to attain equilibrium with its daughters and then it was coupled to photomultiplier and alpha-counting assembly. The efficiency of the bubbler and scintillation cell was determined by using the standard samples of 226 Ra. The standard sample was digested employing a microwave digestion system and brought to solution form. The solution was transferred to the 222 Rn bubbler. The solution in the bubbler was allowed for build up of 222 Rn for 15 days and the built-in 222 Rn was transferred to the scintillation cell and the activity was counted. The overall efficiency of this setup was found to be 75%.

2.3 Assessment of effective dose

The effective dose for an individual via ingestion of drinking water is calculated using the formula D ing = C r× I f× E d [6] where, D ing is the annual effective dose for an individual due to ingestion of the radionuclide (Sv y−1 ), C r is the concentration of the radionuclide in ingested drinking water (Bq l−1 ), I f is the annual in takeof drinking water containing the radionuclide (ly−1 ), and Ed is the ingestion dose conversion factor for the radionuclide (Sv Bq−1 ).The effective dose due to the intake of 222 Rn was assessed using the measured activity of 222 Rn and dose per unit activity of radon ingested.

 3. Results and Discussion



3.1 Concentration of 222 Rn in water

The results of the concentration of 222 Rn in drinking water are presented in [Table 1] and [Figure 2]. The representative value of the level of 222 Rn for each sampling station is the average value of many measurements around the sampling station. The concentrations of radon in these water samples were found to vary in the range of 0.03-1.31 Bq l−1 with the mean value of 0.29 Bq l−1 . Comparatively higher activity was found in Kollam region.The 222 Rn concentrations in drinking water along coastal Kerala are comparable with the 222 Rn values reported for other regions [Table 2]. In Jordanian well water, the values reported were in the range 3.1-5.7 Bql -1 . [7] The concentration of 222 Rn in open well water in coastal Karnataka, India was found to vary in the range of 0.14-25.4 Bq l -1 . [8] Apart from this, the 222 Rn in drinking water in the public water supply around the world is also reported. Tayyeb [9] reported 0.92-2.12Bq l -1 values for tap water in Saudi Arabia and 0.019-0.041Bq l -1 for tap water in Istanbul, Turkey. [10] Xinwei has reported 8-18Bq l -1 in tap water in China. [11] Some researchers showed 222 Rn activity as high as 1.2×10 3 Bq l−1[12] and 50 Bq l−1 for wells in Finland. [13] The values of activity concentrations of 222 Rn obtained in the present study are within the proposed limit of 11 Bq l−1[14] of theUnited States Environmental Protection Agency.{Figure 2}{Table 1}{Table 2}

3.2 Dose due to dissolved 222 Rn

Using the measured concentration of 222 Rn in drinking water, the effective doses to the stomach, lung, and the whole body for the population of the region were estimated and are presented in [Table 1]. The conversion factor used for the calculation of effective dose for the stomach is 14.4 μSv Bq−1 . [15] The mean daily intake of wateris assumed to be a minimum of 2 L per person. [14]

The dissolved 222 Rn in water is one of the major sources of indoor level of radon and its contribution to the indoor air will depend on many factors such as rate of usage of water, the volume of indoor air and ventilation. It was estimated that 1Bqm−3 of 222 Rn in air with an equilibrium factor of 0.4 and an occupation factor of 0.8 results in an effective dose of 28μSvy−1 to the lung. [16] Considering the transfer factor of 222 Rn released from water to air to be 1×10−4,[17] the inhalation dose for the population of the region was estimated and the results are presented in [Table 1]. The effective dose received by the population of the region was found to vary from 0.25 to 9.53 μSv y−1 with a mean value of 2.15 μSv y−1 .

 4. Acknowledgments



One of the authors Ms. Primal D'cunha is grateful to the University Grant Commission Government of India for providing the financial support (RFSMS).[20]

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