Radioactivity of naturally occurring (226Ra, 232Th and 40K) and anthropogenic (137Cs) radioactive nuclides was measured in 29 potable ground and surface water samples of Punjab, Pakistan. The results showed average activity concentrations for 226Ra, 232Th, 40K and 137Cs as 1.09, 0.55, 16.17 and 0.40 Bql−1, respectively. 137Cs was detected in only a few samples. The obtained results showed that, in general, activity concentrations of radionuclides (232Th and 137Cs) in drinking water samples did not exceed WHO recommendations. 226Ra in the majority of samples exceeded WHO drinking water guidelines. The estimated committed effective dose due to intake of the water for three age-groups considered (<1 y, 2–7 y and ≥17 y) was below the ICRP permissible limit (0.1 mSvy−1) except for 226Ra and 40K.

INTRODUCTION

Daily consumption of water has made it an important subject to study because water can transport pollutants more rapidly through water supplies. The occurrence of radioactivity in potable water may pose a risk to human health on ingestion. Radionuclides in drinking water may cause human internal exposure by the decay of radionuclides in the body. Several naturally occurring radionuclides such as 40K, 226Ra, 228Ra and others are frequently dissolved in domestic water supplies and their concentrations vary over an extremely wide range, mainly depending upon the amount of radioelements present in the bedrock and soil with which the water comes in contact (Watson & Mitsch 1987; Malanca et al. 1998; Ajayi & Owolabi 2008). In addition, human activities such as mining, milling and processing of uranium ores and mineral sands, manufacture of fertilizers and oil drilling, and transportation, processing and burning of fossil fuels have enhanced the naturally occurring radioactive material concentrations in the environment (Pujol & Sanchez-Cabeza 2000).

The 238U isotope decay series includes 226Ra, with chemical properties similar to calcium and which acts as a major contributor to gamma emission in water and food. Its long half-life of 1620 years enables it to accumulate in the human body for a long time (Higuchi 1981; Cevik et al. 2006; Ajayi & Owolabi 2008). The US National Committee on Radiation Protection (NCRP 1954) and World Health Organization guidelines for drinking (WHO 2011) in terms of radiological aspects gave the same recommendations for activity concentration or maximum permissible concentration of 226Ra in drinking water as 0.1 Bql−1. The radium content of surface water is usually very low and water treatment methods are available to remove it. Approximately 20% is absorbed into the bloodstream when ingested and this is further distributed to soft tissues and bone, but its retention is mainly in growing bone (EPA 1991; ICRP 1993).

137Cs and 40K are important radionuclides for public health because of their long half-life (half-life in years: 137Cs = 30.07, 40K = 1.28 × 109) and health effects. Although, the major source for their occurrence in the body is from eating foods that contain radiocaesium or radiopotassium that are subsequently absorbed into different organs (Fujita et al. 1996), their effect in drinking water cannot be neglected. About 90%–100% of 40K and 137Cs are absorbed from the diet into the tissues of the body. Due to identical chemical and metabolic properties, the distribution patterns of both radionuclides in muscles is the same (Gustafson & Miller 1969; ICRP 1991).

Evaluation of dose and correct concentration of radionuclides received in dietary intake is vital because of the different pathways (ingestion, inhalation and absorption) by which radionuclides enter the human food chain (Cevik et al. 2006). According to the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), during everyday consumption of food and water, an average radiation dose of 0.29 mSvy−1 is received worldwide via ingestion of natural radionuclides of the 40K and 238U and 232Th series (UNSCEAR 2000).

There is evidence from both human and animal studies that radiation exposure at low to moderate doses may increase the long-term incidence of cancer and genetic malformations. Measurements of natural radioactivity in drinking water have been performed in many parts of the world, mostly for assessment of the doses and risk resulting from consuming water (Malanca et al. 1998).

Since the baseline concentration of natural radioactivity in groundwater in Punjab, Pakistan is not known, the levels of 40K, 226Ra, 228Ra, 232Th and 137Cs were investigated in representative drinking water to assess the radiological risk resulting from the consumption of groundwater. As the doses from pathways are strongly related to the amount of radionuclides present, an important objective from the point of view of the radioecological protection of the population is the accurate evaluation of the amounts received in dietary intake.

MATERIALS AND METHOD

Study area

In total, 29 deep groundwater samples, surface water samples and tap water samples were collected from 13 cities of Punjab, namely: Attock, Taxila, Rawat, Rawalpindi, Islamabad, Gujar Khan, Deena, Jehlum, Gujrat, Lahore, Gujranwala, Faisalabad and Mianwali (Figure 1). For the collection of water samples, a uniform site-selection criterion was adopted, i.e., one sample was collected from small cities while two to five samples were from medium/big cities. Water samples were collected in sealed leak-tight/lined-cap plastic bottles of 5 l capacities. Before collecting the samples, the bottles were washed properly and rinsed thoroughly several times first with water and then with distilled water.
Figure 1

Water sample locations in Punjab, Pakistan.

Figure 1

Water sample locations in Punjab, Pakistan.

Sample preparation and measurement of radioactivity

Water samples were filtered immediately with filter paper (Whatman™) of pore size 0.45 mm after collection. Water samples were first acidified with concentrated nitric acid in order to avoid precipitation of radionuclides onto the container walls. Water samples containing naturally occurring radionuclides were pre-concentrated by evaporation (Cazala et al. 2003; Parekh et al. 2003). Concentration of water samples is necessary in order to obtain sufficient measurement of radionuclides. The amount of water for concentration was approximately 2–5 l, which was concentrated ten times (10×). The evaporation process was carried out at 70–80°C. For radioactivity measurement, water samples were analyzed with a gamma spectrometer consisting of a GMX60P4-95-A end-window type coaxial high-purity germanium (HPGe) detector coupled with ORTEC TRUMP-PCI-Multi-channel analyzer. Detector photopeak relative efficiency was 60% with energy resolution (FWHM) of 2.3 KeV at 1.33 MeV 60Co. The spectroscopy amplifier was an ORTEC model 672. Recorded spectra were evaluated with the GammaVision 6.2 software package. To reduce gamma-ray background, the detector was shielded by a 14-cm-thick lead wall with a fixed bottom and sliding cover. The lead shield contained an inner lining of 0.5 cm copper to absorb lead X-rays.

226Ra concentration was determined by analyzing its peaks at transition energy 185.9 KeV, which has gamma abundance of 3.28%. 232Th activity was determined by its daughter products in the decay series of 228Ac at 911 keV with an emission probability of 29%. Peaks obtained at the energy values of 1460 and 661.66 keV were analyzed for the determination of 40K and 137Cs activity, respectively. Measurements were performed with identical geometries as those of the standard reference sources that were also used for energy and efficiency calibration of the gamma spectrometer. Both standard and sample jars were placed on top of the detector and analyzed for 64,800 seconds (18 hours). Efficiency for the specified geometry at the particular energy was calculated as described by Saat (2004) and Saat et al. (2010) while the radionuclide activity in the collected water sample was calculated as directed by Hamzah et al. (2012). Counting statistics of the test samples and detector background and the efficiency were taken into account as sources of uncertainty for the evaluation of overall uncertainties. Results are presented in Bql−1 for all the samples.

Annual dose estimation

In order to evaluate potential health hazards, total annual estimated dose for 226Ra, 40K, 232Th, and 137Cs was calculated for three different age groups. For this study, the annual average intake of drinking water was taken as 250, 350, and 730 l for the age groups<1 y, 2–7 y and ≥17 y, respectively (Ajayi & Owolabi 2008; WHO 2011). The annual committed effective doses for the three age groups of the population were calculated using the following formula (El-Mageed et al. 2013): 
formula
1
where DRw is effective dose (mSvy1), Aw is radionuclide activity (Bql−1) in drinking water (Table 1), IRw is the intake of water (per person y−1) and IDf is the equivalent conversion factor as mentioned by the International Commission on Radiological Protection (ICRP 1996) and provided in Table 2 as specific for age groups mentioned in present study.
Table 1

Activity concentrations (Bql−1) of 226Ra, 232Th, 40K, and 137Cs in drinking water of selected areas of Punjab, Pakistan

Sample codeLocation226Ra232Th40K137Cs
R1 H-10 sector, Islamabad 1.42 0.25 14.14 0.13 
R2 H-11 sector, Islamabad 1.23 0.13 18.12 0.09 
R3 G-10 sector, Islamabad 0.74 0.45 11.65 BDL 
R4 G-9 sector, Islamabad 2.11 0.87 24.23 BDL 
R5 I-9 sector, Islamabad 1.11 0.27 17.28 BDL 
R6 Chak Shehzad sector, Islamabad 1.19 0.92 17.24 BDL 
R7 Harley Street, Rawalpindi 1.22 21.16 BDL 
R8 Khanna, Rawalpindi 1.22 0.26 10.23 0.06 
R9 Westridge, Rawalpindi 1.32 0.73 16.23 BDL 
R10 Adiala Road, Rawalpindi 0.08 0.18 16.78 BDL 
R11 Khanpur Dam, Hazara 2.16 0.11 17.34 BDL 
R12 Rawal Dam, Rawalpindi 1.5 0.62 13.21 BDL 
R13 Simli Dam, Islamabad 0.11 0.32 21.12 BDL 
R14 Faisalabad 1 1.32 0.34 24.11 BDL 
R15 Faisalabad 2 1.14 0.12 20.01 BDL 
R16 Faisalabad 3 1.23 0.23 13.72 BDL 
R17 Lahore 1 1.18 0.78 13.22 0.08 
R18 Lahore 2 0.34 14.61 BDL 
R19 Lahore 3 2.12 0.56 15.23 BDL 
R20 Gujranwala 1 0.07 0.43 10.34 0.09 
R21 Gujranwala 2 0.08 1.12 16.23 BDL 
R22 Taxila 1.12 0.43 9.82 BDL 
R23 Chashma 1.25 0.42 18.99 BDL 
R24 Rawat, Rawalpindi 1.14 0.25 12.62 BDL 
R25 Gujjar khan 0.05 1.26 17.88 1.02 
R26 Jehlum 1.19 1.1 16.13 BDL 
R27 Deena 0.08 1.2 14.11 1.01 
R28 Gujrat 0.16 0.42 16.23 BDL 
R29 Attock 2.17 0.56 15.12 BDL 
 Minimum 0.05 0.11 9.82 0.06 
 Maximum 2.17 1.26 24.23 1.02 
 Average 1.09 0.55 16.17 0.40 
Sample codeLocation226Ra232Th40K137Cs
R1 H-10 sector, Islamabad 1.42 0.25 14.14 0.13 
R2 H-11 sector, Islamabad 1.23 0.13 18.12 0.09 
R3 G-10 sector, Islamabad 0.74 0.45 11.65 BDL 
R4 G-9 sector, Islamabad 2.11 0.87 24.23 BDL 
R5 I-9 sector, Islamabad 1.11 0.27 17.28 BDL 
R6 Chak Shehzad sector, Islamabad 1.19 0.92 17.24 BDL 
R7 Harley Street, Rawalpindi 1.22 21.16 BDL 
R8 Khanna, Rawalpindi 1.22 0.26 10.23 0.06 
R9 Westridge, Rawalpindi 1.32 0.73 16.23 BDL 
R10 Adiala Road, Rawalpindi 0.08 0.18 16.78 BDL 
R11 Khanpur Dam, Hazara 2.16 0.11 17.34 BDL 
R12 Rawal Dam, Rawalpindi 1.5 0.62 13.21 BDL 
R13 Simli Dam, Islamabad 0.11 0.32 21.12 BDL 
R14 Faisalabad 1 1.32 0.34 24.11 BDL 
R15 Faisalabad 2 1.14 0.12 20.01 BDL 
R16 Faisalabad 3 1.23 0.23 13.72 BDL 
R17 Lahore 1 1.18 0.78 13.22 0.08 
R18 Lahore 2 0.34 14.61 BDL 
R19 Lahore 3 2.12 0.56 15.23 BDL 
R20 Gujranwala 1 0.07 0.43 10.34 0.09 
R21 Gujranwala 2 0.08 1.12 16.23 BDL 
R22 Taxila 1.12 0.43 9.82 BDL 
R23 Chashma 1.25 0.42 18.99 BDL 
R24 Rawat, Rawalpindi 1.14 0.25 12.62 BDL 
R25 Gujjar khan 0.05 1.26 17.88 1.02 
R26 Jehlum 1.19 1.1 16.13 BDL 
R27 Deena 0.08 1.2 14.11 1.01 
R28 Gujrat 0.16 0.42 16.23 BDL 
R29 Attock 2.17 0.56 15.12 BDL 
 Minimum 0.05 0.11 9.82 0.06 
 Maximum 2.17 1.26 24.23 1.02 
 Average 1.09 0.55 16.17 0.40 

BDL = below detection limit.

Table 2

The annual estimated doses for three age groups of the population (mSvy−1) (infants, children and adults)

226Ra
40K
232Th
137Cs
Sample code< 1 y2–7 yAdult< 1 y2–7 yAdult< 1 y2–7 yAdult< 1 y2–7 yAdult
R1 2.02 3.08 0.29 0.18 0.10 0.06 0.10 0.03 0.04 0.0004 0.0004 0.0012 
R2 1.75 2.67 0.25 0.24 0.13 0.08 0.05 0.02 0.02 0.0002 0.0003 0.0009 
R3 1.05 1.61 0.15 0.15 0.09 0.05 0.18 0.06 0.08    
R4 3.01 4.58 0.43 0.31 0.18 0.11 0.35 0.11 0.15    
R5 1.58 2.41 0.23 0.22 0.13 0.08 0.11 0.03 0.05    
R6 1.70 2.58 0.24 0.22 0.13 0.08 0.37 0.11 0.15    
R7 1.74 2.65 0.25 0.28 0.16 0.10 0.40 0.12 0.17    
R8 1.74 2.65 0.25 0.13 0.08 0.05 0.10 0.03 0.04 0.0002 0.0002 0.0006 
R9 1.88 2.86 0.27 0.21 0.12 0.07 0.29 0.09 0.12    
R10 0.11 0.17 0.02 0.22 0.12 0.08 0.07 0.02 0.03    
R11 3.08 4.69 0.44 0.23 0.13 0.08 0.04 0.01 0.02    
R12 2.14 3.26 0.31 0.17 0.10 0.06 0.25 0.08 0.10    
R13 0.16 0.24 0.02 0.27 0.16 0.10 0.13 0.04 0.05    
R14 1.88 2.86 0.27 0.31 0.18 0.11 0.14 0.04 0.06    
R15 1.62 2.47 0.23 0.26 0.15 0.09 0.05 0.01 0.02    
R16 1.75 2.67 0.25 0.18 0.10 0.06 0.09 0.03 0.04    
R17 1.68 2.56 0.24 0.17 0.10 0.06 0.31 0.10 0.13 0.0002 0.0003 0.0008 
R18 2.85 4.34 0.41 0.19 0.11 0.07 0.14 0.04 0.06    
R19 3.02 4.60 0.43 0.20 0.11 0.07 0.22 0.07 0.09    
R20 0.10 0.15 0.01 0.13 0.08 0.05 0.17 0.05 0.07 0.0002 0.0003 0.0009 
R21 0.11 0.17 0.02 0.21 0.12 0.07 0.45 0.14 0.19    
R22 1.60 2.43 0.23 0.13 0.07 0.04 0.17 0.05 0.07    
R23 1.78 2.71 0.26 0.25 0.14 0.09 0.17 0.05 0.07    
R24 1.62 2.47 0.23 0.16 0.09 0.06 0.10 0.03 0.04    
R25 0.07 0.11 0.01 0.23 0.13 0.08 0.50 0.15 0.21 0.0028 0.0034 0.0097 
R26 1.70 2.58 0.24 0.21 0.12 0.07 0.44 0.13 0.18    
R27 0.11 0.17 0.02 0.18 0.10 0.06 0.48 0.15 0.20 0.0028 0.0034 0.0096 
R28 0.23 0.35 0.03 0.21 0.12 0.07 0.17 0.05 0.07    
R29 3.09 4.71 0.44 0.20 0.11 0.07 0.22 0.07 0.09    
226Ra
40K
232Th
137Cs
Sample code< 1 y2–7 yAdult< 1 y2–7 yAdult< 1 y2–7 yAdult< 1 y2–7 yAdult
R1 2.02 3.08 0.29 0.18 0.10 0.06 0.10 0.03 0.04 0.0004 0.0004 0.0012 
R2 1.75 2.67 0.25 0.24 0.13 0.08 0.05 0.02 0.02 0.0002 0.0003 0.0009 
R3 1.05 1.61 0.15 0.15 0.09 0.05 0.18 0.06 0.08    
R4 3.01 4.58 0.43 0.31 0.18 0.11 0.35 0.11 0.15    
R5 1.58 2.41 0.23 0.22 0.13 0.08 0.11 0.03 0.05    
R6 1.70 2.58 0.24 0.22 0.13 0.08 0.37 0.11 0.15    
R7 1.74 2.65 0.25 0.28 0.16 0.10 0.40 0.12 0.17    
R8 1.74 2.65 0.25 0.13 0.08 0.05 0.10 0.03 0.04 0.0002 0.0002 0.0006 
R9 1.88 2.86 0.27 0.21 0.12 0.07 0.29 0.09 0.12    
R10 0.11 0.17 0.02 0.22 0.12 0.08 0.07 0.02 0.03    
R11 3.08 4.69 0.44 0.23 0.13 0.08 0.04 0.01 0.02    
R12 2.14 3.26 0.31 0.17 0.10 0.06 0.25 0.08 0.10    
R13 0.16 0.24 0.02 0.27 0.16 0.10 0.13 0.04 0.05    
R14 1.88 2.86 0.27 0.31 0.18 0.11 0.14 0.04 0.06    
R15 1.62 2.47 0.23 0.26 0.15 0.09 0.05 0.01 0.02    
R16 1.75 2.67 0.25 0.18 0.10 0.06 0.09 0.03 0.04    
R17 1.68 2.56 0.24 0.17 0.10 0.06 0.31 0.10 0.13 0.0002 0.0003 0.0008 
R18 2.85 4.34 0.41 0.19 0.11 0.07 0.14 0.04 0.06    
R19 3.02 4.60 0.43 0.20 0.11 0.07 0.22 0.07 0.09    
R20 0.10 0.15 0.01 0.13 0.08 0.05 0.17 0.05 0.07 0.0002 0.0003 0.0009 
R21 0.11 0.17 0.02 0.21 0.12 0.07 0.45 0.14 0.19    
R22 1.60 2.43 0.23 0.13 0.07 0.04 0.17 0.05 0.07    
R23 1.78 2.71 0.26 0.25 0.14 0.09 0.17 0.05 0.07    
R24 1.62 2.47 0.23 0.16 0.09 0.06 0.10 0.03 0.04    
R25 0.07 0.11 0.01 0.23 0.13 0.08 0.50 0.15 0.21 0.0028 0.0034 0.0097 
R26 1.70 2.58 0.24 0.21 0.12 0.07 0.44 0.13 0.18    
R27 0.11 0.17 0.02 0.18 0.10 0.06 0.48 0.15 0.20 0.0028 0.0034 0.0096 
R28 0.23 0.35 0.03 0.21 0.12 0.07 0.17 0.05 0.07    
R29 3.09 4.71 0.44 0.20 0.11 0.07 0.22 0.07 0.09    

RESULT AND DISCUSSION

Radioactivity of 226Ra, 232Th, 40K and 137Cs in drinking water

Table 1 summarizes the specific activity of the natural radionuclides 232Th, 226Ra, 40K and 137Cs in water samples. The specific activity of naturally occurring radionuclides 226Ra, 232Th, and 40K varied in the ranges 0.05–2.17 Bql−1 with an average of 1.09 Bql−1, 0.11–1.26 with an average of 0.55 Bql−1 and 9.82–24.23 Bql−1 with an average of 16.17 Bql−1 respectively. The specific activity concentration of anthropogenic 137Cs in the drinking water samples ranged from 0.06 to 1.02 Bql−1 with an average of 0.40 Bql−1.

The results obtained show that the measured activity concentrations of 226Ra in nine samples are above the recommended limits of 0.1 Bql−1 (WHO 2008). Compared to several sets of data for 226Ra levels in different types of drinking water in other countries, the present results lie within the range reported in many countries, e.g., Saudi Arabia, Asia and the Far East including India and Japan (Iyengar 1990; Ahmed 2004; Jia & Torri 2007; Vengosh et al. 2009) and are found to be greater than the values reported by Cevik et al. (2006) for some parts of the world including the USA, France, Germany, Italy, Poland, Turkey and Spain. Geological variation between these areas is the main cause for such a wide range of 226Ra content found in the underground water. The high activity concentrations for 226Ra in the majority of water samples from the studied areas can be a good indicator for the high radioactivity levels in the aquifer rocks because radionuclide concentrations in groundwaters depend on the minerals derived from aquifer rocks (El-Mageed et al. 2013).

232Th activity concentration in all the samples including surface- and groundwater was low except for sample R21 and sample R25 which were not within the WHO (2008) permissible limits (0.1 Bql−1). In all the sites studied, concentrations of 226Ra were higher than that of 232Th, which reflects the fact that radium is more soluble in groundwater than its thorium precursors, and its solubility is enhanced by the common-ion effect (when dissolved solids are high), an oxygen-poor environment, and the fragmentation of uranium-bearing minerals (Kitto & Sook Kim 2005).

40K concentration in the drinking water samples of the present study is found to be greater than the values reported from some parts of the world (Cevik et al. 2006). However, Yu & Mao (1994) observed 40K activity of 0.11 Bql−1 in Hong Kong, which is lower than the activity recorded in our study but agrees with the findings of El-Mageed et al. (2013). The high 40K concentration in the present study may be due to local environmental conditions and the geomorphology of the surrounding area; there may be a high input of 40K from agricultural fields involving the use of potassium fertilizers which may have been transported into the groundwater, given that 40K is a highly soluble element.

Activity concentrations of 226Ra, 232Th and 40K in the Rawalpindi and Islamabad water samples of our study are much lower than reported natural radioactivity of these radionuclides in different brands of commonly sold bottled drinking water in Islamabad and Rawalpindi (Ahmed 2004; Fatima et al. 2007).

137Cs was detected in six out of 29 samples. In the rest of the water samples 137Cs was below the detection limit (<0.03 Bql−1). Its activity was below WHO recommended limits of 10 Bql−1 (WHO 2008). Hansen & Aarkrog (1990) observed 137Cs in the range of 0.31 to 1.6 Bql−1 in drinking water in Denmark; our observed values are far less than those in Hansen and Aarkrog's study.

Annual effective dose in water

The calculated annual committed effective doses for three age groups of the population are presented in Table 3 and Figure 2, calculated by applying Equation (1). It was inferred from the results that the annual committed effective doses (also known as total doses) for all the analysed drinking water are in the range of 0.51–9.73 mSvy−1 with an average of 4.95 mSvy−1, all of them well below the reference level of the committed effective dose (100 mSvy−1) recommended by WHO. For each radionuclide, the dose contributions (mSvy−1) for various age groups are different for each radionuclide (Table 3). The observed dose order in the three groups for each radionuclide is as follows:

  • 226Ra, children (2.38) > infants (1.56) > adults (0.22)

  • 40K, infants (0.21) > children (0.12) > adults (0.11)

  • 232Th, children (1.61) > adults (1.31) > infants (0.01)

  • 137Cs, adults (0.004) > children (0.0013) > infants (0.001)

Figure 2

Age-dependent annual effective dose (mSvy−1) percentage received by three age groups due to the intake of natural radionuclides of 226Ra, 232Th, and 40K and artificial 137Cs from drinking water.

Figure 2

Age-dependent annual effective dose (mSvy−1) percentage received by three age groups due to the intake of natural radionuclides of 226Ra, 232Th, and 40K and artificial 137Cs from drinking water.

Table 3

Age-dependent annual effective dose (mSvy−1) due to the intake of natural radionuclides of 226Ra, 232Th, 40K and artificial 137Cs from drinking water

Age groups
Radionuclides< 1 y2–7 y≥ 17 y
226Ra 
 Min 0.07 0.11 0.01 
 Max 3.09 4.71 0.44 
 Average 1.56 2.38 0.22 
40
 Min 0.13 0.07 0.04 
 Max 0.31 0.18 0.11 
 Average 0.21 0.12 0.12 
232Th 
 Min 0.04 0.01 0.02 
 Max 0.50 0.15 0.21 
 Average 0.22 0.07 0.09 
137Cs 
 Min 0.0002 0.0002 0.0006 
 Max 0.0028 0.0034 0.01 
 Average 0.0011 0.0013 0.004 
Age groups
Radionuclides< 1 y2–7 y≥ 17 y
226Ra 
 Min 0.07 0.11 0.01 
 Max 3.09 4.71 0.44 
 Average 1.56 2.38 0.22 
40
 Min 0.13 0.07 0.04 
 Max 0.31 0.18 0.11 
 Average 0.21 0.12 0.12 
232Th 
 Min 0.04 0.01 0.02 
 Max 0.50 0.15 0.21 
 Average 0.22 0.07 0.09 
137Cs 
 Min 0.0002 0.0002 0.0006 
 Max 0.0028 0.0034 0.01 
 Average 0.0011 0.0013 0.004 

The above mentioned values are calculated by the contribution of equivalent conversion factors that are specific for the studied age groups mentioned by ICRP (1996). The size of dose of radioactivity is dependent on the accumulation of radionuclides in different organs (ICRP 2012). The above mentioned results can be justified by mentioning that adults consume plenty of potable water that wash out their organs rapidly whereas in the other two groups, this process is slow and radionuclides remain accumulating for longer times.

Accumulation also depends upon the individual response as radiosensitivity can vary within a group of people that is homogeneous by nationality, race, age, gender, and physiology. It has been observed that the accumulation rate of 137Cs in people with Rh positive blood factor in their bodies is higher than in people with Rh negative (Yarmonenko 1988).

These findings are in agreement with other published data (Alam et al. 1999; Ajayi & Owolabi 2008; Altıkulac et al. 2015).

226Ra annual effective doses

Drinking water sources can be major contributors to human exposure to 226Ra. From the intake of 226Ra, the effective annual dose varies from 0.07 to 3.09 mSvy−1 with an average of 1.56 mSvy−1 for the age group <1 y, 0.11– 4.71 mSvy−1 with an average of 2.378 mSvy−1 for 2–7 y, and 0.01–0.44 mSvy−1 with an average of 0.22 mSvy−1 for adults. Most of the samples contained concentrations within permissible limits except for two samples (from Faisalabad and Mianwali). It may be due to the geology of the area which may have uranium-rich rocks. Most of the groundwater reacts with the bed rock and releases quantities of dissolved components that depend on the mineralogical and geochemical composition of the soil and rock. 226Ra is a highly radiotoxic radionuclide. As shown in Table 3, the 226Ra average annual effective doses of 1.56 and 2.37 mSvy−1 for the age groups of <1 y and 2–7y (children) was higher than the average annual effective doses for adults, indicating that the children are more vulnerable and comparatively at risk because of the intensive bone growth during their growth period. When humans ingest radium, ∼20% is absorbed into the blood stream. The absorbed radium is initially distributed to soft tissues and bones, but its retention is mainly in growing bones (El-Arabi et al. 2006). From Table 3 it can also be seen that the 226Ra contribution towards annual effective dose is also higher than that of the other radionuclides (232Th, 40K, 137Cs) against all age groups. Rožmarić et al. (2012) reported that the daily intake of 226Ra from drinking water sources contributes in the range of 0.001–0.0118 mSvy−1; our investigated values are higher than the reported values of other similar studies made in European countries (Desideri et al. 2007; Chau & Michalec 2009; Beyermann et al. 2010), and all of the assessed doses are well below the dose limit of 0.1 mSvy−1.

40K annual effective doses

The effective annual dose due to the intake of 40K varies from 0.13 to 0.31 mSvy−1 with an average of 0.21 mSvy−1, 0.07 to 0.18 mSvy−1 with an average of 0.12 mSvy−1, and 0.04 to 0.11 mSvy−1 with an average of 0.12 mSvy−1 for the age groups of <1 y, 2–7 y and adults, respectively. Infants are more exposed to the radionuclide present in water because they consume twice as much water per unit of their body weight as adults (infant formula, cereals mixed in water). For example an infant depending solely on formula milk consumes about one-seventh of its body weight of water daily, which would correspond to about 3 gallons of water for a 155-pound adult man (WHO 1986). Akhter et al. (2007) are in agreement with the present study along with countries having the same reported values like Indonesia, Asia, Japan, and Turkey, but on the other hand they mentioned South Korea, Spain, Iran and Finland receiving relatively higher annual doses of 40K.

232Th annual effective doses

The effective annual dose due to the intake of 232Th varies from 0.04 to 0.50 mSvy−1 with an average of 0.22 mSvy−1, 0.01 to 0.15 mSvy−1 with an average of 0.07 mSvy−1, and 0.02–0.21 mSvy−1 with an average of 0.09 mSvy−1 for the age groups of <1 y, 2–7 y and adults, respectively. Fewer data are available on 232Th intake with the diet, and few countries have conducted representative national surveys (UNSCEAR 2000). The results shows that infants are more at risk in these areas for 232Th ingestion as compared with adults and children. Similar findings have also been reported by Akhter et al. (2007) for Ukraine, Japan, the Philippines and for Pakistan, but for countries like Bangladesh and China the reported values are much higher than in the present study.

137Cs annual effective doses

The effective annual dose due to the intake of 137Cs varies from 0.0002 to 0.0028 mSvy−1 with an average of 0.0011 mSvy−1, 0.0002 to 0.0034 mSvy−1 with an average of 0.0013 mSvy−1, and 0.006 to 0.0097 mSvy−1 with an average of 0.0038 mSvy−1 for the age groups of <1 y, 2–7 y and adults, respectively. 137Cs is an artificial radionuclide and is carcinogenic. Its presence in water is proven to be fatal. Our results for 137Cs are in agreement with Altıkulac et al. (2015), who also observed a much lower annual effective dose for 137Cs and reported it as insignificant and negligible.

From the results, it was observed that the effective dose due to the intake of drinking water from natural radionuclides exceeded the recommended reference levels of 0.26, 0.2 and 0.1 mSvy−1 that have been recommended by WHO (1996), IAEA (2002) and UNSCEAR (2000), respectively. Estimated doses of 226Ra and 40K were higher than the permissible limit in all the three groups and in infants (<1 y), respectively.

CONCLUSION

Natural, anthropogenic and accidental exposure of water to pollutants may alter water quality, which can create several health risks for the population. Therefore drinking water quality must be monitored from the resource to the tap. Radioactivity concentration of 226Ra, 232Th, 40K, and 137Cs in water samples collected from different locations in Punjab, Pakistan ranged from 0.05 to 2.17 Bql−1, 0.11 to 1.26 Bql−1, 9.82 to 24.23Bql−1 and 0.03 to 1.02 Bql−1 respectively. These values showed that only 40K is above the tolerable limit. 137Cs was only found in some samples. On comparison of these values with those already reported in the literature it is found that there is no uniform trend for the values of radionuclides, as concentration depends upon many factors including varying topography and anthropogenic activities; however, our study area lies well within the reported range for other countries of the world. The solubility of the radionuclides in general, decreasing in the order 40K >226Ra >232Th >137Cs, shows that radionuclides did not show a constant trend and the results were area-dependent. The estimated committed effective dose due to intake of the water of selected areas of Punjab for the three age groups considered were below the ICRP permissible limit (0.1 mSvy−1) except for 226Ra and 40K, which were above the tolerable limit. 226Ra was above the limit in all the age groups while 40K was observed to be high in infants. The high activity concentrations for 226Ra and 40K measured in water samples explain the relationship between the groundwater and bedrocks in these areas along with the environmental pollution. It is, therefore, suggested that the drinking water of some areas is not acceptable for the targeted communities. For the sake of environmental and water supply safety, monitoring should be done on a regular basis and there should be rapid decision-making. Municipalities should consider this analyzed data as preliminary data for addressing the potential risk of water quality failure.

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