Radiation Protection and Environment

ORIGINAL ARTICLE
Year
: 2018  |  Volume : 41  |  Issue : 2  |  Page : 84--87

Seasonal variation of radon concentration in water and assessment of whole-body dose to the public along South-west coast of Kerala, India


PV Divya, V Prakash 
 Department of Studies and Research in Physics, Payyanur College, Kannnur University, Kannur, Kerala, India

Correspondence Address:
Dr. V Prakash
Department of Studies and Research in Physics, Payyanur College, Kannur - 670 327, Kerala
India

Abstract

The South-west coast of Kerala is a well-reported high background radiation area. Hence, the radiological protection of the population in this region has great concern. In view of this, the study has been undertaken to understand the distribution of radon (222Rn) concentration in drinking water collected from the region. The seasonal variation of radon concentration in drinking water also forms part of the study. Emanometry method is used for the quantification of dissolved radon concentration in water collected from various open wells. The mean values of radon concentration obtained for pre- and post-monsoon were 0.95 Bq/l and 0.58 Bq/l, respectively. The whole-body dose ranges from 0.39 to 29.34 μSv/y for premonsoon and 1.33–18.76 μSv/y for postmonsoon. The average value of effective dose was below the recommended limit of 0.1 mSv/y suggested by WHO and EU council, and the water from the region can be safely consumed from the radiological protection point. All the results are presented and discussed in the manuscript.



How to cite this article:
Divya P V, Prakash V. Seasonal variation of radon concentration in water and assessment of whole-body dose to the public along South-west coast of Kerala, India.Radiat Prot Environ 2018;41:84-87


How to cite this URL:
Divya P V, Prakash V. Seasonal variation of radon concentration in water and assessment of whole-body dose to the public along South-west coast of Kerala, India. Radiat Prot Environ [serial online] 2018 [cited 2021 Sep 28 ];41:84-87
Available from: https://www.rpe.org.in/text.asp?2018/41/2/84/239680


Full Text

 Introduction



The larger fraction of natural radiation exposure to public comes from radon, a radioactive gas,[1] with half-life of 3.8 days. The radon emanating from rocks and soils tends to concentrate in enclosed spaces such as underground mines and dwellings and thereby significant contribution to human exposure. Radon is soluble in water [2] and the second leading cause of lung cancer [3] as per various reports.

Chavara-Neendakara at Kollam District in Kerala has got the second position in the ranking of high background radiation areas (HBRAs) in the world.[4] Hence, the objective of the study is to investigate whether radon concentration in drinking water at these HBRAs is within the permissible limits prescribed by WHO and other international scientific organizations.

 Materials and Methods



Sample collection

Sampling stations were identified in selected locations on the basis of radiation intensity (scintillometer UR 705) along South-west coast of Kerala; Kovalam (S1), Varkala (S2), Neendakara (S3), Chavara (S4), and Alappuzha (S5). Samples were collected and treated following standard procedure.[5] About one liter 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. In each region, three sets of samples and in total 15 samples were collected for the analysis.

Activity determination

The concentration of 222 Rn in aqueous samples was determined by the emanometry method.[6] In this method, about 50 ml of the water sample was transferred into the bubbler [Figure 1] by the vacuum transfer technique. The dissolved 222 Rn in the water was transferred into a preevacuated and background-counted scintillation cell or lucas cell [Figure 2]. The scintillation cell was stored for 180 min to allow 222 Rn to attain equilibrium with its daughters and then it was coupled to photomultiplier and alpha counting assembly for taking count. 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 into solution form and transferred to the 222 Rn bubbler. The solution in the bubbler was kept for a period of 15 days to build up 222 Rn, and the accumulated 222 Rn was transferred to the scintillation cell. Further, activity was counted, and concentration has been calculated using the equation below:{Figure 1}{Figure 2}

[INLINE:1]

Where, D is counts above background, V is volume of water, E is efficiency of the scintillation cell (75%), λ is decay constant for radon (2.098 × 10−6 s −1), T is counting delay after the sampling (in sec) and t is counting duration (in sec).

Assessment of effective dose

Ingestion and inhalation are two different pathways for radon to enter into the human body. The radon and its daughters in drinking water impart radiation dose to the stomach by means of ingestion. Considering two liters per day as an average consumption rate of open well water for a citizen of Kerala, the conversion factor used is D = 14.4 μSv/kBq.[8] The ingestion dose to the stomach is calculated by the following equation:

[INLINE:2]

Where, Cr is concentration of the radionuclide in ingested drinking water (Bq/l), If is annual intake of drinking water containing the radionuclide (l/y).

The dissolved radon is also a source for the indoor radon, and its contribution will depend on the usage rate, the volume of the indoor environment, and the air exchange rate. It was estimated that 1 Bq m -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 28 μSv/y to the lungs.[6] Considering the transfer factor of 222 Rn released from water to air to be 1 × 10−4.[6] Whole-body dose can be obtained by adding the doses to the lungs and stomach.

 Results



The concentration of radon in water samples collected along South-west coast of Kerala during pre- and post-monsoon seasons was measured by well-established emanometry method. The results of the study are tabulated in [Table 1]. Comparatively higher concentration of radon was found in the samples collected from Varkala and Chavara regions, and lower concentration was found in samples collected from the Alappuzha region. The results indicated that the radionuclide concentrations of the soil near to the sampling stations have influenced the activity of water samples. The higher activity observed in the samples collected from Varkala region may be attributed to the presence of colored granite in soil.[9] The presence of hot spring, which carry high amount of radium and its decay products to the surface, may also be influenced by the concentration of activity in the region.{Table 1}

Mary et al. (2012) have reported the presence of monazite in soil samples of Chavara region, and this may be the reason for comparative higher concentration of radon in this region. Comparison of radon concentration during pre- and post-monsoon is shown in [Figure 3].{Figure 3}

 Discussion



In premonsoon, radon concentration was high in all the water samples. It may be due to the reduced level of water column in the well. In postmonsoon, level of water column in the well raised due to heavy rainfall which reduces radon concentration in the water. Geological and geochemical conditions such as temperature, wind, pressure, degree of rock weathering, the disequilibrium state of the uranium series inside the solid grain, adsorption of radium in the rock grain and fracture surfaces and on the effective rock surface exposed to groundwater contact influence the quantity of radon in open well water. In premonsoon, degree of rock weathering is high due to high temperature about 40°C in southern Kerala coast. Weathered rock pieces have larger surface area and may enhance the radon concentration when subjected to water. The presence of monazite, a thorium-rich mineral, may be another reason for the enhanced level of radon concentration in water. The enhanced level of radon concentration in water in turn leads to radon exposure to the human beings. The whole-body doses (effective dose) during pre- and post-monsoon were found to vary in the range 0.39–29.34 μSv/y and 1.33–18.76 μSv/y, respectively. The 222 Rn concentrations in drinking water along southern coastal areas of Kerala were compared with the values reported for other environs [Table 2].{Table 2}

The concentrations of 222 Rn obtained in the present study were within the recommended limit of 11 Bq/l.[22] The results were also compared with the values recommended by the WHO and EU council.[23] It is found that the values from the present study were well within the permissible limit.

The seasonal variation of radon concentration is less significant in most of the samples collected along the region. However, a slightly higher concentration observed during premonsoon may be attributed to reduced water sources and prolonged period of absence of rain fall. This, in turn, leads to lowering of water table that concentrates radium and radon. The reduced level of radon concentration during postmonsoon may be associated to the increased rainfall and high water level of the well. Local geology and geochemical effect may be the reason for the lower concentration of radon in samples of Kovalam and Alappuzha in premonsoon. Comparison study indicated that the radon concentrations obtained in the present study were comparable with the reported values elsewhere. The observed values were well within the permissible limit recommended by the WHO and EU council, and the water from the region can be safely consumed from the radiological protection point.

Acknowledgments

The first author wishes to acknowledge the Kannur University for providing financial support in terms of research fellowship.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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