Introduction

Exposure of humans to radon gas is a cause of concern and many pooled as well as individual studies have been carried out to find the radiation levels and so the radiological health risk to the general public. About 90% of radiation exposure to humans is from natural sources like cosmic, terrestrial and internal (S Kansal et al. 2015). Among the various sources of natural ionizing radiations present on the earth, Rn-222 alone contributes to more than 50% of the total dose received by the general public(UNSCEAR, 2000; Parminder Singh et al., 2015)and is known to be the second largest cause of lung cancer after smoking (WHO, 2009; H. Al-Zabadi et al. 2015). Radon, a progeny of uranium, is an inert, colourless and odourless gas found in numerous kinds of rocks like granites, metamorphic rocks and sedimentary rocks containing phosphate (Errol Lowerence et al. 1991; Linda C.S. Gunderson et al. 1992; Fernando P. Carvalho et al., 2007). Radon gas is fifteen times more soluble than other noble gases like helium and neon in water and is dissolved and transported with the water when underground water moves through radium-rich soil and rocks. The existence of natural radioactivity in water is based on the local geological conditions of the source, soil or rocks (Fatima et al., 2007). Dissolved radon in water may enter into indoor air through de-emanation when water is used for showering, laundry (UNSCEAR, 2000).

A report by the National Research Council of the United States attributed 3,000 to 32,000 lung cancer deaths per year (with a mean of about 19,000 deaths annually) to Rn-222 and its short-lived progeny in indoor air (NCBI, 1999). Furthermore, there is a plethora of the literature suggesting that there is no safe level for stochastic (probabilistic) effects to occur (Tsoulfanidis et al. 2015). Several studies on radon and its correlation with geology have been attempted in different parts of the world (Choubey & Ramola, 1997; Ramola et al., 1989; Tanner, 1986). From various epidemiological combined investigation of seven North American case–control studies, it was established that radon in homes increases the risk of lung cancer to the local population (Lubin et al. 1995, 1997; D Krewski et al., 2005; Singla et al., 2021a). In a study by Henshaw, it was revealed that indoor radon concentration is related to leukaemia and certain different malignancies (Henshaw et al. 1990). According to USEPA, 1991, consumption of water causes 168 cancer deaths every year, 89% of lung cancer deaths were caused by breathing in radon released to the indoor air from water and 11% of stomach cancer deaths were caused by consuming water containing radon (USEPA, 1991; Rohit Mehra et al., 2015; Singla et al., 2021b). Radioactive contamination can lead to various life-threatening diseases like cancer and renal failures (Paivi Kurttio et al., 2006; K Skeppstorm et al. 2007; S Kansal et al., 2011). Radon progenies can also stick to aerosol particles thereby exposing indoor occupants to elevated radon exposure (Mishra et al. 2008). These progenies deliver most of the dose to tissues, thereby damaging the genetic material and leading to mutations. ICRP recommends a threshold exposure limit of 1 mSv per year for general public and 20 mSv per year for radiation workers for the total dose received for all sources (ICRP 2010). However, as per the United States Nuclear Regulatory Commission (US-NRC), exposure levels to individuals must be kept ‘as low as reasonably achievable’ (principle of ALARA). Besides acting as an indicator for uranium deposits, Rn-222 has some unique properties due to which it finds its use as a geophysical tracer for locating faults and geological structures (Tanner, 1986; Nazir et al., 2020a). However, the most important aspect of studying radon is the radiological hazard it poses to general public (Bajwa et al., 2005; Nazir et al., 2020b, c).

Water, being a basic component of all life forms, is essential for the survival of all living beings. It is therefore imperative to test water for such toxic and radiological components. Keeping in view the significance of the adverse health effects of radon, many studies have been carried out worldwide for quantifying radon in water. The present study in Barnala district of Punjab, India, has been carried out for the first time using Smart RnDuo to find the radiological risk assessment to the public. The ingestion and inhalation doses for various age groups like infants (1–2 year), children (8–12 year) and adults (above 17 year) have also been calculated. The data obtained in this study will add to the relevant scientific data pool for the radon mapping of the country.

Study area

Figure 1 shows the study area with latitude of 30°22′28.24″ North and longitude of 75°32′55.32″ East. The total geographical area of this district is 1410 km2. According to the Central Ground Water Board (2013) the hydrogeology of the area, is occupied by Indo Gangetic alluvial plain of quaternary age and falls in Ghaggar sub basin. The groundwater occurs in alluvium formations comprising fine to coarse sand which form potential aquifer. The rocks of the Aravalli- Delhi subgroup and the Malani igneous suite comprise grey-wacke, ortho-quartzites, carbonate-sediments, calcareous shale and slates and the high-heat-producing granites and felsites from the basement in region. There is no drainage system in the area except the Dhuala drain which intersects its territory. This drain carries flood water when heavy rainfall occurs in the catchment area. Abohar branch of Sirhind canal system passes in south-eastern part of the district. The groundwater is alkaline in nature (H.S. Virk, 2019). The main sources for drinking water in the study area comes from the canal and groundwater.

Fig. 1
figure 1

Map of study area (grid pattern), Barnala district, Punjab

Full size image

Methodology

The study area is divided into grid pattern of 6 × 6 km2 for uniform mapping. A total of 100 water samples were procured from 25 different villages with four samples (2 canal water, 2 underground water) from each village in each grid. The samples were collected in 60 mL airtight cleaned glass bottles. The samples were collected underwater by putting the sampling water bottles in the water container/ bucket (Fig. 2) so that radon could not escape during the sample collection. All sampling bottles were fully filled up to the top ensuring no bubble formation in the sample. The glass bottles have been preferred over other materials as it has more radon retention ability than other materials (P. Vesterbacka et al., 2010).

Fig. 2
figure 2

A schematic set up for water collection from source

Full size image

To measure Rn-222 concentration in the collected water samples in real time, a scintillation-based radon monitor, Smart RnDuo developed by Radiation Protection & Advisory Division (RP&AD) at Bhabha Atomic Research Centre (BARC), Mumbai, India (J.J. Gaware et al., 2011), has been used. A complete set up for radon monitoring is shown in Fig. 3. Prior to radon estimation, the inbuilt pump was turned on for 5 min to flush the air inside the detector in an open loop, and afterwards, sample bottle was connected with bubbler using rubber tubing. The pump was turned on in the closed loop for 5 min for extraction of radon from water. It has been done with the help of bubbler which is fixed on the top of sampling bottle. One end of the tube is connected with air inside the detector, and other end is put inside water bottle through the bubbler in such a way that when pump is in “ON” mode then air moves from detector to the water sample and bubbles are produced in it. The pump was turned off after 5 min and was given 5 min delay for thoron decay and to avoid the impact of the thoron on the radon estimation. The extracted radon (Cair) further flows towards detector volume and gathered in scintillation cell by passing through “progeny filters” and “thoron discriminator” eliminating radon/thoron progenies and thoron. The radon measurements in Smart RnDuo are based on the detection of alpha particles emitted from radon, and its decay products formed inside a cell volume which are continuously counted by the PMT and the associated counting electronics. The alpha counts obtained are processed by a microprocessor unit as per the developed algorithm the display the concentration of radon. The sample was analysed in continuous mode for 1 h of 15 min cycle each at constant temperature. Smart RnDuo attains an efficiency of 95% for radon within running time of 15 min. The instrument has minimum detection limit of 8 Bqm−3 at 1 sigma and 1 h counting cycle for radon, whereas the maximum detection limit is 10 MBqm−3 (Radon Hand Book developed by BARC, Mumbai, India; Nazir et al., 2020b). The device was calibrated using standard radon-thoron sources (Model RN-1025 & TH-1025) procured from Pylon Electronics Inc. Ottawa, Canada in a 0.5 m3 calibration chamber at laboratory facility of Bhabha Atomic Research Centre (BARC), Mumbai, India (B.K. Sahoo et al., 2013; Singh et al., 2020).The scintillation detector has two advantages, one is the least effect of humidity and another is that the counting error is less than the allowed limit of 10%(Jobbagy V et al. 2017).

Fig. 3
figure 3

A setup for measuring radon in water samples

Full size image

For statistical analysis of the data, OriginLab 8.5, IBM-SPSS and Microsoft Excel 2010 were used (Nazir, 2020).

Calculations

(i) Calculation for radon in water

The following formula is used to estimate the radon concentration in liquid (Cliq) from the measured concentration of radon in air (Cair) in water samples is given by Smart RnDuo (J.J.Gaware et al., 2011):

$$C_{{{\text{liq}}}} = C_{{{\text{air}}}} (k + \frac{{V_{{{\text{air}}}} }}{{V_{w} }})$$
(1)

where Cair is concentration of radon in air (Bqm−3),Cliqis concentration of radon in water (Bqm−3),

Vair and Vw are the air and water volumes, and k (= 0.25) is partition coefficient between air and water.

(ii) Estimation of annual effective dose due to ingestion and inhalation

The dose exposure due to ingestion and inhalation from the Radon in water has been calculated by the parameters given in UNSCEAR report (2000).

(a) The ingestion dose due to radon concentration in water is given by UNSCEAR, 2000:

$$I_{D} = C_{{{\text{liq}}}} \times A_{{{\text{DWI}}}} \times 365 \times {\text{DF}}$$
(2)

where ID is the ingestion dose per year (µSvy−1), Cliq is the radon concentration in water, ADWI is the age-wise daily water intake (for infants (0–2 year)(0.8 L), for children (8–12 year)(2.5 L) and for adult (above 17 years) (3L) (WHO, 2004).

and DF is the dose conversion factor for radon (3.5 nSvBq−1) for adults, (5.9nSvBq−1) for children and (23 nSvBq−1) for infants (UNSCEAR, 2000).

(b) The inhalation dose due to consumption of radon in drinking water is given by UNSCEAR, 2000:

$${\text{Inh}}_{D} = C_{{{\text{liq}}}} \times R_{w}^{a} \times \phi _{{Rn_{{222}} }} \times o \times {\text{DF}}$$
(3)

where InhD is the inhalation dose per year (µSvy-1), Cliq is the radon concentration in water,

\(R_{w}^{a}\) is the ratio of radon in air and water/ transfer coefficient (10–4), \(\phi _{{Rn_{{222}} }}\) is the equilibrium factor between radon and its progeny (0.4), (equilibrium factor is when radon is secular equilibrium with its progeny). \(o\) is the time of individual average indoor occupancy (7000 hy−1), (ICRP assumes 80% annual indoor occupancy (ICRP 1993) and DF is the dose conversion factor for inhalation of radon (33nSv (Bq h m−3)−1) for infants, (31.4 nSv (Bq h m−3)−1) for children and (28.3 nSv (Bq h m−3)−1) for adults (Brudecki et al., 2014).

Results and discussion

Table 1 shows the measured radon concentration in all 100 water samples. The concentration varies from a minimum value of 0.17 ± 0.01 BqL−1 (Sehra, canal water) to maximum value of 9.84 ± 0.59 BqL−1 (Dhanula, canal water) with a mean value of 3.01 ± 0.29 BqL−1. These values are lower than the safe limit of 11 BqL−1 as recommended by USEPA (1991), 100 BqL−1 by WHO (2004) and 4–40 BqL−1 by UNSCEAR (2008). The average value in the studied area is slightly more than the 2.72 BqL−1 in Bathinda district, India (Mehra et al., 2015) but less than 3.63 BqL−1 in Faridkot district, 4.7 BqL−1in Mansa and Muktsar district (Mehra et al., 2015). Figure 4 shows a frequency distribution graph for radon concentration. It has been observed that concentration in 31% of the samples lies between 0–2 BqL−1, in 32% samples it lies between 2-4BqL−1, and in 37% samples, it lies between 4–10 BqL−1.

Table 1 Radon concentration and annual effective dose due to ingestion and inhalation for various age groups
Full size table
Fig. 4
figure 4

Frequency distribution of radon concentration in all 100 water samples

Full size image

Table 1 also shows the annual effective dose due to ingestion and inhalation of radon in drinking water for various age groups. The annual effective dose due to ingestion for infants (0–2 year) lies in the range of 1.54 ± 0.09 to 90.89 ± 5.41 µSvy−1 with a mean value of 31.13 ± 2.68 µSvy−1, for children (8–12 year) it lies in the range of 1.47 ± 0.09 to 86.48 ± 5.15 µSvy−1 with a mean value of 29.62 ± 2.53 µSvy−1, and for adults (above 17 years), it lies in the range of 1.32 ± 0.08 to 77.94 ± 4.64 µSvy−1 with a mean value of 26.69 ± 2.3 µSvy−1. The annual inhalation dose varies from 1.12 ± 0.07 to 66.17 ± 3.93 µSvy−1 with a mean value of 22.66 ± 1.95 µSvy−1 for infants, 0.9 ± 0.05 to 52.95 ± 3.15 µSvy−1 with a mean value of 18.14 ± 1.56 µSvy−1 for children and 0.64 ± 0.04 to 37.7 ± 2.24 µSvy−1 with a mean value of 12.91 ± 1.11 µSvy−1 for adults. The calculated dose values are well below the annual effective dose of 100 µSvy−1 recommended by WHO (2004, 2008).

From the measured values, a weak correlation (R2 = 0.06) has been found for the radon concentration in groundwater samples with the depth of well (24–153 m) as shown in Fig. 5. Table 2 shows the descriptive statistics using SPSS, from which it has been found that the underground water sources have higher levels for Rn-222 than canal water sources and the same is shown in Fig. 6. This may be because of the reason that underground water directly encounters U-238 rich rocks that release Rn-222in water and cannot escape to atmosphere (Skeppstorm et al. 2007; A.N. Voronov et al. 2004). Also, radon levels are generally higher in underground water as compared to canal water because of the presence of granite, sand and gravel in the bedrock (Stojkovic et al. 2015). In contrast, Rn-222 in canal water samples can easily escape to atmosphere due to aeration and agitation in water. The variation in Rn-222 concentration in canal water and underground water depends upon geological factors and topography (Fonollosa E et al. 2016). The results show that the average Rn-222 concentration in underground water samples is 4.39 ± 0.33 BqL−1 which is higher than the average concentration of Rn-222in canal water sources is 2.29 ± 0.26 BqL−1.

Fig. 5
figure 5

Correlation between depth and radon concentration in underground water samples

Full size image
Table 2 Descriptive statistics using SPSS for samples collected from canal water and underground water
Full size table
Fig. 6
figure 6

Intercomparison between canal and underground water samples

Full size image

Using data from table no.1, the whisker plot has been drawn as shown in Fig. 7, in which minimum and maximum value of radon concentration are represented by lower and upper whiskers, respectively, while solid part in the box shows the mean concentration. The upper and lower lines in the whisker box plot represent the third and first quartile, whereas the line in the middle in the box shows second quartile or median.

Fig. 7
figure 7

Box whisker plot for radon concentration

Full size image

A normality test using Origin Lab 8.5, at a significance level of 0.01, revealed that the canal water data were not significantly drawn from a normally distributed population, while the groundwater data were significantly drawn from a normally distributed population. Table 2 shows a comparative descriptive statistical analysis of drinking water from canal and underground water (50 samples each) using IBM-SPSS. The minimum and maximum radon-222 concentration in canal and groundwater ranged from 0.17 – 9.84 Bqm−3 and 1.40 – 9.54 Bqm−3, respectively, with a standard deviation of 1.94 Bqm−3 and 2.06 Bqm−3, respectively. The mean (± SE) for canal and groundwater was found to be 2.29 ± 0.27 Bqm−3 and 4.39 ± 0.29 Bqm−3, respectively. For canal water, a positive value of 1.66 for skewness shows that the distribution is highly skewed and a high kurtosis value of 4.03 shows that the distribution is leptokurtic. Compared to a normal distribution, its tails are longer and fatter and often its central peak is higher and sharper. Similarly, for groundwater, a value of 0.57 for skewness shows that the data are moderately skewed, while as a negative value of kurtosis indicates that a distribution is platykurtic, that is, the distribution is flat and has thin tails.

Table 3 shows the comparison of measured Rn-222 concentration in water samples in the studied area with worldwide values and has been found to be lesser than these values.

Table 3 Worldwide comparison of radon (Rn-222) concentration in water samples
Full size table

Conclusion

  • The measured values of Rn-222 concentration have been found to be below the recommended limit of 100 BqL−1 by WHO (2004), 11 BqL−1 by USEPA, 1991 and 4–40 BqL−1 by UNSCEAR, 2008.

  • The annual effective dose due to ingestion and inhalation for infants has been found to be higher than the dose received by children and adults. While overall dose is far well below the safe limit of100 μSvy−1 recommended by WHO (2008).

  • The underground water samples have slightly higher values of radon concentration than in canal water because the radon easily escapes from canals, while underground water retains.

  • A weak positive correlation of radon in underground water with depth has been found.

  • As the measured values in the studied area are below the recommended safe limits, so it can be concluded that radon in water may not pose any significant radiological risk to the public.