Current World Environment

Introduction

Human beings are vulnerable to more than half of the dose exposure from natural radiation sources^1,2 ­­of the radon (²²²Rn) and its progeny, produced during the radioactive decay chain of uranium (²³⁸U) contributing approximately 55% of internal radiation exposure to human life.³ Radon coming on to contact with the land surface get mixed with the groundwater depending on various factors and its level depends on the radium concentration.

Groundwater can create a health risk while acting as a carrier of radon into domestic environment⁴ and the levels of radon in indoor dwellings can be enhanced partially by radon derived from water supply.^5,6 The exposure to high concentrations of radon can lead cancers of lung⁷ and stomach and gastrointestinal.⁸

Many researchers have conducted research all over the world for monitoring radon concentrations in different environments and efforts are on to find out the methods to reduce its adverse effects on the human beings^9-16 and on the other side simultaneously finding its applications.^17-19 In Uttarakhand various studies had been carried out in river waters of Garhwal and Shiwalik Himalayas and groundwater of the Doon valley where high radon concentrations have been reported.^20-22 In Shivalik Himalyas of Himachal Pradesh,²⁰ the radon concentration varied from 1.0 ± 0.3 to 653.5 ± 8.0 Bq L^-1 where as in Doon valley,²¹ in tube wells and hand pumps radon concentration varied from 25.4 ± 1.8 to 92.5 ± 3.4 Bq L^-1 with an average of 53.5 ± 2.6 Bq L^-1.

Keeping in view the above points, the present study is carried out in southern part of Roorkee area of Uttarakhand, India to investigate the radon levels in groundwater as it is widely used for drinking.

Study Area

Roorkee lies on the coordinates 29°52’ N latitude, 77°53’ E longitude and altitude 268m. Normal rainfall is 1156.4 mm and monthly average maximum temperature range observed between 20.4 - 39.2 and minimum temperature range varied between 10.6 -27.2²³.

Roorkee is a part of Gangetic alluvial plains and lithologically, the alluvium is formed of unconsolidated to semi-consolidated deposits of sand, silt, clay and kankar. The ground water conditions in alluvial parts are considerably influenced by the varying lithology of the subsurface formations which has been found in various studies of parts of Gangetic basin.^24-31

Methodology

9 representative groundwater samples from the hand pumps collected using standard methodology⁹ from the locations shown in table 1. The pH, EC and temperatures were recorded using hand held pH meter, EC meter and thermometer, respectively.

Radon concentrations in these samples were measured with RAD7 (Fig. 1), an electronic radon detector connected to a RAD-H₂O accessory (Durridge Co., USA), within 12 hours of sample collection.^9-10

Results and Discussion

Table 2 reveals that the varied values, due to different geological conditions,⁴ of ²²²Rn ranged between 0.55 ± 0.22 and 3.39 ± 0.28 Bq L^-1 with an average value of 2.16 ± 0.37 Bq L^-1, well within the EPA’s maximum contaminant level of 11.1 Bq L^-1and these values were correlated with EC, pH and temperature. There was a weak positive correlation of radon with EC and a moderate negative correlation of radon was found with pH and temperature (Table 3) means that there is a tendency of high radon scores to go with low pH and temperature scores. In arid regions of Rajasthan where the temperature is high, Mittal et al (2016)³³ reported radon concentration from 0.50 to 22 Bq L⁻¹ with the mean value of 4.42 Bq L⁻¹ in groundwater samples. However, EC values ranged between 240 – 550 µS/cm with an average value of 427 µS/cm; pH values ranged between 7.0-7.5 with an average value of 7.2 and temperature values ranged between 19.7 – 21.3^oC with an average value of 20.4 ^oC (Table 1). Akawwi (2014)³⁴ suggested radon concentration increases with temperature and similar results were also found by Garg et al.²² Some researchers have reported poor correlation of radon concentration with pH and TDS³⁵ due to inert nature of radon.

Table 1: Samples detail

Figure 1: RAD7 connected with RAD7H2O & accessories Click here to View figure

Table 2: EC, pH, temperature & concentration of radon in groundwater samples

Table 3: Correlation of concentration of radon v/s EC, pH, temperature (Dancey and Reidy's, 2004)³²

Conclusion

The values of natural radioactivity measured in groundwater in southern part of Roorkee area of Uttarakhand, India covered in the present survey is within the permissible limits prescribed by USEPA (1991)³⁶ but a regular monitoring is required. No significant correlation of radon values were found with other parameters viz. EC, pH & temperature and it was found that pH & temperature are moderately negatively correlated and a weak positive correlation was found with EC. However, some of the factors, such as precipitation, geologic and hydrologic variables are important and must be investigated.

Acknowledgment

Authors thank Director, National Institute of Hydrology, Roorkee for support and encouragement.

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