|Year : 2018 | Volume
| Issue : 3 | Page : 109-113
Seasonal variation of radon concentration in drinking water and assessment of whole-body dose to the public along coastal parts of Kerala, India
PV Divya, V Prakash
Department of Studies and Research in Physics, Payyanur College, Kannur University, Kannur, Kerala, India
|Date of Web Publication||27-Sep-2018|
Dr. V Prakash
Department of Studies and Research in Physics, Payyanur College, Kannur University, Kannur, Kerala
Source of Support: None, Conflict of Interest: None
Context: Some of the coastal parts of Kerala are well-reported high background radiation area. Hence, the radiological protection of the population in this region has of great concern. Aims: In view of this, a 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. Assessment of whole-body dose and excess lifetime cancer risk (ELCR) to the public were also done. Subjects and Methods: Emanometry method is followed for the quantification of dissolved radon concentration in water collected from various open wells. Results: Average value of ELCR at different locations is ranged from 0.009 × 10−3 to 0.123 × 10−3. Conclusion: The average value of effective dose was below the recommended limit of 0.1 mSv/y suggested by the WHO and the EU council. The present study indicates that water from the region can be safely consumed from the radiological protection point of view. All the results are presented and discussed in detail in the manuscript.
Keywords: Drinking water, excess lifetime cancer risk, emanometry, radon, seasonal variation
|How to cite this article:|
Divya P V, Prakash V. Seasonal variation of radon concentration in drinking water and assessment of whole-body dose to the public along coastal parts of Kerala, India. J Radiat Cancer Res 2018;9:109-13
|How to cite this URL:|
Divya P V, Prakash V. Seasonal variation of radon concentration in drinking water and assessment of whole-body dose to the public along coastal parts of Kerala, India. J Radiat Cancer Res [serial online] 2018 [cited 2019 Jan 16];9:109-13. Available from: http://www.journalrcr.org/text.asp?2018/9/3/109/242363
| Introduction|| |
The larger fraction of natural radiation exposure to public comes from radon, a radioactive gas with a half-life of 3.8 days. The radon, emanating from rocks, soils, etc., tends to concentrate in enclosed spaces such as underground mines and dwellings and thereby significant contribution to human exposure. Radon is soluble in water and the second leading cause of lung cancer 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 and also a significant position in the case of number of cancer patients. In the recent years, studies on the HBARs in the world have been of prime importance for risk estimation due to long-term low level whole-body exposure to the public. Hence, the objective of the study is radiological protection of the population in the selected region and to find the excess lifetime cancer risk (ELCR).
| Subjects and Methods|| |
Sampling stations were identified in selected locations along south-west coast of Kerala, namely, Kovalam (S1), Varkala (S2), Neendakara (S3), Chavara (S4), Alappuzha (S5), Cherai (S6), Chavakkad (S7), Padinjarekkara (S8), Kappad (S9), and Kannur (S10) on the basis of radiation intensity observed using scintillometer UR 705. Samples were collected and treated following standard procedure. About 1 l of water was collected from each sampling station in airtight bottles. The bottles were filled completely to minimize loss of 222Rn 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 30 samples were collected during each season for the analysis.
The concentration of 222Rn in aqueous samples was determined by the emanometry method. In this method, about 50 ml of the water sample was transferred into the bubbler [Figure 1] by the vacuum transfer technique. The dissolved 222Rn 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 222Rn 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 using the standard samples of 226Ra. The standard sample was digested employing a microwave digestion system and brought into solution form and transferred to the 222Rn bubbler. The solution in the bubbler was kept for a period of 15 days to build up 222Rn and the accumulated 222Rn was transferred to the scintillation cell. Further, activity was counted and concentration has been calculated using the equation below:
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), T is counting delay after the sampling (in seconds), and t is counting duration (in seconds).
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 2 L/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. The ingestion dose to the stomach is calculated by the following equation:
I = Cr × If × D (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 of 222Rn 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. Considering the transfer factor of 222Rn released from water to air to be 1 × 10−4. Whole-body dose can be obtained by adding the doses to the lungs and stomach.
Assessment of excess lifetime cancer risk
Potential carcinogenic effects are characterized by estimating the probability of cancer incidence in a population of individuals for a specific lifetime from projected intakes and chemical-specific dose-response data. The additional or extra risk of developing cancer due to exposure to a toxic substance incurred over the lifetime of an individual. ELCR is calculated following the equation.
ELCR = AEDE × DL × RF (3)
Where, AEDE is the annual effective dose equivalent or whole-body dose (μSv/y), DL is the duration of life (70 years), and RF is risk factor (0.05 S/v).
| Results|| |
The concentration of radon in water samples collected along coastal parts of Kerala during premonsoon, monsoon, and postmonsoon seasons was measured by well-established emanometry method. The results of the study are tabulated in [Table 1], [Table 2], [Table 3]. 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 Chavakkad region. The results indicate 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. The presence of hot spring, which carries high amount of radium and its decay products to the surface, may also be influenced the concentration of activity in the region. Lal et al. (1989) 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. Deviation of radon concentration during premonsoon, monsoon, and postmonsoon is shown in [Figure 3]. Variation of average value of ELCR parameter at different locations is shown in [Figure 4].
|Table 1: 222Rn concentration, doses to stomach and lungs, whole-body dose, and excess lifetime cancer risk parameter during premonsoon|
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|Table 2: 222Rn concentration, doses to stomach and lungs, whole-body dose, and excess lifetime cancer risk parameter during monsoon|
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|Table 3: 222Rn concentration, doses to stomach and lungs, whole-body dose, and excess lifetime cancer risk parameter during postmonsoon|
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|Figure 3: 222Rn concentration during premonsoon, monsoon, and postmonsoon|
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|Figure 4: Average value of excess life time cancer risk parameter at different locations|
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| Discussion|| |
Comparatively higher value of radon concentration is found in all water samples collected during postmonsoon. This may be due to the higher solubility of radon in water at low temperatures. Postmonsoon is the winter season and the temperature is comparatively low in Kerala coast. In premonsoon, radon concentration was high in all the water samples compared to monsoon season; however, it was less compared to postmonsoon. This may be attributed to the reduced level of water column in the well during postmonsoon. The level of water column in the well is raised due to heavy rainfall during monsoon, 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, and adsorption of radium in the rock grain and fracture surfaces and on the effective rock surface exposed to groundwater contact, etc., 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. Larger deposition of monazite has seen at Kerala coast during postmonsoon. 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 premonsoon, monsoon, and postmonsoon were found to vary in the range of 0.39–29.34 μSv/y, 1.33–18.76 μSv/y, and 1.59–57.90 μSv/y, respectively. The results were compared with the values recommended by the WHO and EU council. It is found that the values from the present study were well within the permissible limit. The average value of ELCR at Varkala and Chavara is comparable with the world average value of ELCR (0.29 × 10−3). According to Kerala state cancer profile, Kollam and Trivandrum Districts have the higher number of cancer patients which shows the significance of the area. According to Cancer and Allied Ailments Research Foundation (Kerala), Kerala has roughly 35,000 new cancer cases every year. There are 913 male and 974 female cancer patients per million in Kerala. A total of 100,000 cancer patients are in prevalence annually in the state. Among the above, 70%–90% of cancers are due to the environmental effects. Higher values of ELCR in the present study area may be involved in the above percentage of occurrence of cancer.
Recently, Forster et al. reported that the natural radioactivity in the study areas was associated with mitochondrial DNA mutations in the residents. Nair et al. reported that, in site-specific analysis, no cancer site was significantly related to cumulative radiation dose. Leukemia was not significantly related to HBRA, either. Although the statistical power of the study might not be adequate due to the low dose and their cancer incidence study, together with previously reported cancer mortality studies in the HBRA of Yangjiang, China, suggests it is unlikely that estimates of risk at low doses are substantially greater than currently believed. It is concluded that harmful radiation effects are posed to the public in the coastal parts of Kollam and Trivandrum Districts and the activity of radon in drinking water may be one of the reasons for such effects. Except Kollam and Trivandrum, other areas not possess significant cancer incidence.
| Conclusion|| |
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 postmonsoon may be due to the low temperature leads to the increase in solubility and large deposition of monazite sand along the regions, especially Varkala, Chavara, and Kovalam. In premonsoon, quantity of radon is significant may be attributed to reduced water sources and prolonged period of the absence of rainfall. This, in turn, leads to lowering of water table that concentrates radium and radon. The reduced level of radon concentration during monsoon may be associated with the increased rainfall and high water level of the well. Local geology and geochemical effect may be the reason for the lower or higher concentration of radon in each sample. 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.
The first author wishes to acknowledge the Kannur University for providing financial support in terms of Research Fellowship.
Financial support and sponsorship
There are no conflicts interests.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3]