222Rn and 220Rn levels of Mansa and Muktsar district of Punjab, India

In this study 222Rn (Radon) measurement were performed in water and soil gas and also both 222Rn and 220Rn concentrations were determined in air of Mansa and Muktsar district of Punjab, India. The data then used for calculation of the annual effective dose for health risk assessment of public. Totally 35 locations have been selected for the measurements. All measurements (222Rn and 220Rn) were done with RAD7 detection system. The 222Rn concentration in the water of studied area varies from 0.4 ± 0.2 Bq l-1 to 17 ± 2.8 Bq l-1. The average value of 222Rn concentration in soil, 222Rn and 220Rn concentrations in indoor air are 8 ± 3 kBq m-3, 47 ± 21 Bq m-3 and 39 ± 19 Bq m-3, respectively. The total average annual effective dose for water samples is 13 μSv a- 1 and for indoor air samples is 2.3 mSv a-1. It has been observed that 222Rn concentration in water has increased with depth of groundwater.

Introduction 222 Rn is a radioactive inert gas that is a decay product of radium in the naturally occurring uranium series. The measurement of 222 Rn in the environment is of great interest due to its alpha emitting nature. A certain fraction of the 222 Rn escapes into the air, where in the outdoors; it is quickly diluted and is of no further concern. However, in confined spaces such as homes and office buildings, 222 Rn can accumulate to harmful levels. The main source of indoor 222 Rn and 220 Rn levels are the building material, soil and tap water. 222 Rn monitoring in soil involves either measuring 222 Rn in soil or measuring the 222 Rn flux from a soil, but the former measurement is more easy and quick by using the active technique of 222 Rn monitoring (Ruckerbauer and Winkler, 2001). 222 Rn is responsible for about half of the radiation dose received by the general population (UNSCEAR, 1994). The inhalation of 222 Rn and its progeny contributes more than 50% of the total dose from natural sources (UNSCEAR, 2000). A high value of the 222 Rn concentration in the particular geological area can be health hazard and will be the cause of lung Cancer for the residents of that area (Sevc et al., 1976;Khan, 2000). The 222 Rn from water contributes to the total inhalation risk associated with 222 Rn in indoor air. The high values of 222 Rn concentration in drinking water also lead to significant risk of stomach and gastrointestinal Cancer (Zhuo et al., 2001;Kendal and Smith, 2002).
As reported in earlier studies the concentration of Th, U, Pb, Cr, Ni, F and SO 4 are higher than the permissible limits in soil of South western Punjab (Kochhar et al., 2006;Mehra, 2009), so a study has been carried out in the Mansa and Muktsar area to make assessment of 222 Rn exposure for screening purpose and for investigating the geographical variation of the 222 Rn concentration as well as for the health-related hazards of the locality if any.The main objective of this work is to assess the indoor 222 Rn and 220 Rn Concentrations, soil gas concentration, 222 Rn concentration in water and the average annual effective dose to the population.

Geology
The scattered outcrops of the Aravali-Delhi Subgroup occur at Tosham (Haryana) just south of the study area i.e., Mansa and Muktsar districts as shown in Figure 1. The soil in the study area falls in the arid and moisture regime. The soils associated with alluvial planes shows better indurations and mature development of soil profile. They are composed of different layers of clay, sticky clay and fine to coarse grained micaceous sandstone (Kochhar et al., 2006).

Experimental Setup
An active technique RAD-7 in different modes has been used to measure the 222 Rn and 220 Rn concentration in air, water and soil of 35 locations in vicinity of Mansa and Muktsar districts of Punjab, India.

Rn and 220 Rn Measurement in Air
The measurement of 222 Rn and 220 Rn concentration in indoor air has been taken using RAD7 air accessories for continues 48 h protocol. EPA test protocols have been used for operating the RAD7 in indoor air (USEPA, 1993). The doors and windows of the houses were closed for at least 12 h before the measurement of 222 Rn and 220 Rn in air. The detector has an ability to distinguish alpha particles from 218 Po and 214 Po with energies of 6.0 and 7.9 MeV. RAD7 can measure the 222 Rn concentration > 0.4 Bq m −3 and < 750,000 Bq m −3 .

Rn Measurement in Water
The sampling locations of studied area have been chosen with great care and an attempt has been made to cover most of the area of study region. The in situ measurement of water samples was made using RAD-H 2 O accessories. The RAD-H 2 O uses a standard pre-calibrated degassing system and preset protocols, built into the RAD-7 which gives direct reading of 222 Rn concentration in water. A 250 ml vial has been used to collect the samples of water from various locations. A Wat-250 protocol and grab mode with 5 min cycle and four recycles have been used to run the instrument for the estimation of 222 Rn in Water. The water samples have been collected from each village by varying the depth of ground water, surface water and tap water.

Soil Gas Measurement
For analysis of 222 Rn concentration in soil gas the measurements were done in same 35 locations and four measurements were done at each location. The pilot rod has been hammered into the ground to the depth required for sampling. Once the rod has been successfully driven to the required depth, the pilot rod has been removed for the penetration of drive rod along with probe more easily to sampling site. The drive rod has been positioned inside the probe and continuously hammered the rods together into the sampling site. When drive rod along with probe has come to be required depth then removed the drive rod from the sampling site and connects the probe with RAD7 soil accessories for sucking the soil gas from deep soil. The soil gas sucked through the tube pipe into the measuring instrument for 5 min. The gab mode and sniff protocol were used for the soil gas sampling on the measuring instrument at each site. The measurement of 222 Rn and 220 Rn concentration in indoor air has been taken using RAD7 air accessories for continues 48 h protocol. EPA test protocols have been used for operating the RAD7 in indoor air (USEPA, 1993).
Where E WIg is the effective dose for ingestion, C RnW is 222 Rn concentration in water (kBq m −3 ) and C w is weighted estimate of water consumption (60 la −1 ), respectively and EDC is the effective dose coefficient for ingestion 3.5 nSv Bq −1 .
where E WIh is the effective dose for inhalation, R aW is the ratio of 222 Rn in air to 222 Rn in tap water (10 −4 ), F(Rn) is the equilibrium factor (0.4) between 222 Rn and its decay products, O is the average indoor occupancy time per person (7000 h y −1 ) and DCFR is the dose conversion factor for 222 Rn exposure 9 nSv h −1 (Bq m −3 ) −1 . The average annual effective dose for indoor 222 Rn is calculated by Equations (3) and (4) using parameters introduced in report by UNSCEAR (2008).
Where AEDR (mSva −1 ) is annual the effective dose for 222 Rn, 222 Rn air is the indoor 222 Rn concentration (Bq m −3 ) and remaining factors have been explained above.
Rn air or 220 Rn air = PAEC (WL) × 3700 F (Rn) or F (Th) (5)  , 1991). The measured values of 222 Rn in water of studied area are well within the safe limit of 4-40 Bq l −1 (UNSCEAR, 2008). The 222 Rn concentration in water is lower as compared to higher value of uranium content in the nearby region of the studied area (Kochhar et al., 2006). It may be because of the solubility of 222 Rn in water is relatively low and with its short radio-active half life much of it will decay before it has opportunity of release from the ground water. When 222 Rncontaining groundwater reaches the surface by natural or manmade forces, the 222 Rn will inevitably be out gassed into the atmosphere. In some villages, the samples of ground water have been collected from different depth of ground water and tap water. It has been observed that 222 Rn concentration in water has increased with depth of groundwater (Figure 2). The level of 222 Rn concentration in tab water has been found to be lower than the level of 222 Rn concentration in ground water. Tab water is actually stored ground water and 222 Rn gas escapes out when it stored. This may be due to the surface water typically containing very low concentrations of 222 Rn, with activities below 4 Bq l −1 (Hopke et al., 2000). However, concentrations of 222 Rn in ground water may be high, depending on the aquifer or hydrogeology of the region. In most of the cases the ground water concentration is higher than the tap water. The increase in the value of 222 Rn concentration in water with depth has been reported by many researchers as given in Table 2.

Results and Discussion
The 222 Rn in the drinking water is the main source of the radiation doses for stomach (Ingestion dose) and lungs (Inhalation dose). The ingestion and inhalation doses in the studied area vary from 0.1 µSva −1 to 3.6 µSv a −1 and 1.0 µSva −1 to 42.8 µSv a −1 and are less the worldwide average annual of Inhalation (1.26 mSv a −1 ) and Ingestion (0.29 mSv a −1 ) recommended by UNSCEAR (2008). The total average annual effective dose for 222 Rn in water is 13 µSva −1 . The annual effective dose of 0.1 mSv a −1 is the safe limit of drinking water from three radioisotopes viz. 222 Rn, 3 H, and 40 K recommended by European Commission and world health organization (European Commission, 1998;WHO, 2004).
It can be seen from Table 3 that the average Value of indoor 222 Rn and 220 Rn concentration in the vicinity of these districts are 47 ± 21 Bq m −3 and 39 ± 19 Bq m −3 , respectively. These values are within the range of intervention level (200-300 Bq m −3 ) recommended by International commission on Radiological    Table 2.
The ratio of PAEC of 220 Rn to that of 222 Rn is in the range of 0.06-0.46. Stranden and Dixon have reported measurements on a variety of underground mines and enclosures in Norway and UK (Dixon et al., 1985;Stranden, 1985). The estimated ratios of PAEC ( 220 Rn)/PAEC ( 222 Rn) are usually within the range of 0.1-1.0. The AEDR (mSv a −1 ) and AEDT (mSv a −1 ) in the studied area are varied from 0.4 mSv a −1 to 2.4 mSv a −1 and 0.3 mSv a −1 to 2.3 mSv a −1 , respectively. In all the villages studied, the average AEDR (mSv a −1 ) was 1.24 mSva −1 which is slightly less than the worldwide average annual dose (1.26 mSv a −1 ) recommended by UNSCEAR (2008). The 222 Rn concentration in soil of studied area has been varied from 3.2 kBq m −3 to 17.2 kBq m −3 . Figure 3 shows the correlation coefficient for measured 222 Rn concentration in air (Rn air ) and soil (Rn soil ). It has been found that a positive correlation (R 2 = 0.57) exits between 222 Rn concentration in air and soil gas. The value of 222 Rn concentration in soil is lower than the values reported in USA, Islamabad region of Pakistan and almost equivalent to china as given in Table 2. Using student's t-distribution with 95% confidence limit as shown in Equation (6).
Where σ is the standard deviation, m is arithmetic mean and (n -1) is degree of freedom. The calculated 95% confidence limits for 222 Rn and 220 Rn in indoor air is 33.3-4.2 Bq m −3 and 48.9-54.9 Bq m −3 , respectively. The calculated 95% confidence limits for 222 Rn in soil and water are 6.8-8.7 kBq m −3 and 3.8-5.6 Bq l −1 , respectively.

Conclusion
It has been seen that 222 Rn concentration in water samples are well below the recommended value. The total average annual effective dose for 222 Rn in water is lower than reference level (0.1 mSv a −1 ) recommended by EC and WHO organization (European Commission, 1998;WHO, 2004). It is observed that there is a positive correlation between 222 Rn concentration in air and soil, so the soil of the study area has significant contribution to the indoor 222 Rn concentration.