Abstract

Natural radioactivity and radon concentration were studied in drinking water samples from Baling area, Kedah, Malaysia, using HPGe and RAD-7 detectors, respectively. Average concentrations obtained for 226Ra, 232Th, 40K and 222Rn were 44.2 ± 3.9, 38.1 ± 5.0, 140.9 ± 10.6 mBq l−1 and 5.7 ± 0.68 Bq l−1, respectively. Cumulative annual effective doses due to ingestion of 226Ra, 232Th, 40K and 222Rn for infants, children and adults were estimated to be 13.77, 2.857 and 2.581 μSv y−1, respectively. Average annual effective doses due to inhalation of radon released in the air during consumption and ingestion of drinking water were separately estimated to be 15.2 and 1.2 μSv y−1, respectively. A positive correlation (R2 = 0.87) was observed between 222Rn and 226Ra determined by RAD-7 and HPGe detectors, respectively. In this study, the estimated annual effective doses due to ingestion of 226Ra, 232Th, 40K and 222Rn for infants, children and adults were found to be below the World Health Organization (WHO) recommended limits of 0.1 mSv y−1.

INTRODUCTION

Measurement of naturally occurring radioactive materials in drinking water is an important subject for public health studies, which permits the estimation of public exposure to radiation by using drinking water (Salih et al. 2002). Drinking water contaminated with natural radionuclides is one of the main causes of the health hazard to the population due to internal exposure of the absorbed radionuclide's decay inside the human body. Inhalation or ingestion of small amounts of radionuclides can become a serious health risk. It is estimated in an UNSCEAR report that due to ingestion of 226Ra, 232Th, and 40K, an average effective dose of 0.29 mSv y−1 is received worldwide (UNSCEAR 2000b). Polluted drinking water is one of the sources of many diseases in developed and developing countries of the world. The determination of natural radioactivity in drinking water is very helpful to estimate the public exposure to ionizing radiation due to ingestion of residential water consumption because the doses from these pathways are strongly connected to the amount of existing radionuclides. Radionuclides 226Ra, 222Rn, 234U from the decay series of 238U, 228Ra, and 232Th are most commonly found in water.

Like other radionuclides, 222Rn is most toxic and hazardous due to its solubility in water and can easily pass through underground water sources. Radon enters into the human body through ingestion from drinking water and inhalation from the air. Ionizing beta and gamma radiations emitted by radon and its progenies may cause cancers in human organs (USEPA 1994; Lee & Kim 2006). It is reported by USEPA (2010) that lung cancer due to inhalation of radon released from consumption of water in dwellings and stomach cancer from ingestion of radon in dwellings are the primary health risks. After inhalation or ingestion of radon, the alpha particles emitted during the decay of radon can interact with biological tissues leading to DNA damage (WHO 2009). Keeping in view all these reasons, this study was conducted to obtain the levels of radon, natural radioactivity and the corresponding effective doses for the population of Baling, Kedah, Malaysia.

Baling is located at latitude 5° 40′0″N and longitude 100° 55′0″E and lies to the south-east of Kedah, approximately 56 km from Sungai Petani and close to the border of Thailand. It has a total area of 1,530 km2 (590 square miles) with a population (2009) of 204,300.

MATERIALS AND METHODS

Drinking water samples, three from each site, were collected from 17 locations in Baling, Kedah, Malaysia. The geographic sites of sampling locations are given in Table 1. The population of the study area uses tap and well water for drinking purpose. Before collection of drinking water samples, bottles were washed according to the IAEA standard with 15% nitric acid and with double de-ionized water three times. Water samples from wells were collected after purging for 10 minutes to ensure the quality of water and tap water was taken directly from the tap. After labeling the samples with code and time, 20 ml HNO3 was added to each sample to avoid increase of organic materials and ionic changes (Ahmad et al. 2015). Before measurement of natural radioactivity and radon concentration, all samples were analyzed for pH using a pH meter (Elico, model LI 671). Each sample of volume 1 litre was sealed in a pre-washed Marinelli beaker for one month to achieve equilibrium and was analyzed for natural radioactivity using a high purity germanium detector shielded with 10 cm thick Pb, with an inner lining of Al, Cu, and Perspex. Each sample was counted for 36,000 sec. The background measured under the same conditions was tripped from the water spectra. The system was calibrated for efficiency using reference material (soil-375) obtained from the IAEA. 226Ra activities were assessed from the gamma-ray peaks of 214Pb (351.9 keV) and 214Bi (609.3 keV) while those of 232Th were assessed from the gamma-ray peaks of 212Pb (338.0 keV) and 228Ac (911.1 keV). 40K activities were assessed using the 1,460 keV photo peak (Alam et al. 1999; El Arabi et al. 2006). Equation (1) was used to calculate the activities of 226Ra, 232Th and 40K:  
formula
(1)
where A (Bq l−1) is activity concentration, c is counts per second after tripping of background and E is efficiency of the detector.
Table 1

Geographic sites of water sampling locations

Kampung Kaki Bukit, Batu BW1 Well 05° 41′8.20″N 100° 56′8.89″E 
Kampung Kaki Bukit, Batu BW2 Well 05° 41′8.61″N 100° 56′9.49″E 
Kampung Janjung Merbau BW3 Well 05° 39′6.88″N 100° 52′6.78″E 
Kampung Pantai Pulai BW4 Well 05° 40′6.61″N 100° 54′8.86″E 
Kampung Bangan Wang BW5 Well 05° 42′29.9″N 100° 53′31.7″E 
Kampung Batu BW6 Well 05° 42′14.1″N 100° 54′57″E 
Kampung Kupang BW7 Well 05° 37′54.1″N 100° 52′14.9″E 
Kampung Rambong BW8 Tap 05° 37′54.1″N 100° 52′14.9″E 
Kampung Baru BW9 Tap 05° 44′32″N 100° 53′36.9″E 
Kampung Landad hilir BW10 Tap 05° 38′10.2″N 100° 49′33.4″E 
Kampung Jenalik BW11 Tap 05° 41′48.8″N 100° 54′50.8″E 
Kampung Bukit Terbak BW12 Tap 05° 38′32.8″N 100° 51′0.37″E 
Kampung Limau Sungai Dalam BW13 Tap 05° 40′09.1″N 100° 51′47.9″E 
Kampung Padang Che Mas BW14 Tap 05° 41′42.7″N 100° 53′06.7″E 
Kampung Nering BW15 Tap 05° 41′58.5″N 100° 54′57.3″E 
Kampung Bukit Pusu BW16 Tap 05° 35′37.5″N 100° 55′029″E 
Kampung Teluk Teduri BW17 Tap 05° 38′47.9″N 100° 54′44.7″E 
Kampung Kaki Bukit, Batu BW1 Well 05° 41′8.20″N 100° 56′8.89″E 
Kampung Kaki Bukit, Batu BW2 Well 05° 41′8.61″N 100° 56′9.49″E 
Kampung Janjung Merbau BW3 Well 05° 39′6.88″N 100° 52′6.78″E 
Kampung Pantai Pulai BW4 Well 05° 40′6.61″N 100° 54′8.86″E 
Kampung Bangan Wang BW5 Well 05° 42′29.9″N 100° 53′31.7″E 
Kampung Batu BW6 Well 05° 42′14.1″N 100° 54′57″E 
Kampung Kupang BW7 Well 05° 37′54.1″N 100° 52′14.9″E 
Kampung Rambong BW8 Tap 05° 37′54.1″N 100° 52′14.9″E 
Kampung Baru BW9 Tap 05° 44′32″N 100° 53′36.9″E 
Kampung Landad hilir BW10 Tap 05° 38′10.2″N 100° 49′33.4″E 
Kampung Jenalik BW11 Tap 05° 41′48.8″N 100° 54′50.8″E 
Kampung Bukit Terbak BW12 Tap 05° 38′32.8″N 100° 51′0.37″E 
Kampung Limau Sungai Dalam BW13 Tap 05° 40′09.1″N 100° 51′47.9″E 
Kampung Padang Che Mas BW14 Tap 05° 41′42.7″N 100° 53′06.7″E 
Kampung Nering BW15 Tap 05° 41′58.5″N 100° 54′57.3″E 
Kampung Bukit Pusu BW16 Tap 05° 35′37.5″N 100° 55′029″E 
Kampung Teluk Teduri BW17 Tap 05° 38′47.9″N 100° 54′44.7″E 

A calibrated alpha spectrometer RAD-7 was used to measure the concentration of radon in drinking water according to the method used by Ahmad et al. (2015).

Annual effective dose equivalent (AEDE) due to ingestion of 226Ra, 232Th and 40K in drinking water was assessed using Equation (2) (Alam et al. 1999):  
formula
(2)
where Aw (Bq l−1) is natural radioactivity in water, IA (l y−1) is the annual intake of drinking water and E (Sv Bq−1) is ingested effective dose conversion factor for natural radioactivity. The value of the dose conversion factor is different for different radionuclides and the age of the individual. The values of dose conversion factor E were taken from EC Directive 96/29 and are 4.7 × 10−6 (infants), 6.2 × 10−7 (children) and 2.8 × 10−7 mSv y−1 (adults) for 226Ra and 6.2 × 10−8 (infants), 2.1 × 10−8 (children) and 6.2 × 10−9 mSv y−1 (adults) for 40K. For 232Th these values are 7.4 × 10−9 (infants), 1.4 × 10−9 (children) and 4.3 × 10−10 mSv y−1 (adults) (ECD 1996).
AEDE for radon inhalation was calculated using Equation (3):  
formula
(3)
where Rw (Bq l−1) is concentration of radon in drinking water, Awc (10−4) is water concentration ratio in air, O (7,000 hrs y−1) is indoor occupancy, EF (0.4) is equilibrium factor between radon and its daughters, and Dcf (9 nSv/Bqm−3h) is dose conversion factor of radon (UNSCEAR 2000a).
AEDE for radon ingestion was calculated using Equation (4):  
formula
(4)
where Rw is concentration of radon in water, 60 (l y−1) is estimated consumption of water and 3.5 (nSv Bq−1) is coefficient of effective dose for ingestion (UNSCEAR 2000a).

According to an UNSCEAR report in 2000, the ingestion of drinking water was estimated in the UNSCEAR (1993) report to be 100, 75, and 50 l y−1 for infants, children, and adults, respectively. Assuming the proportion of these groups in the population to be 0.05, 0.3 and 0.65, the estimated weight of consumption was determined as 60 l y−1 (UNSCEAR 2000a).

RESULTS AND DISCUSSION

Table 2 shows the activity concentrations of 226Ra, 232Th, and 40K as well as the pH of each sample of drinking water. The activity concentration of 226Ra ranged from 16.1 ± 2.4 to 85.8 ± 5.2 mBq l−1 with an average value of 44.2 ± 3.9 mBq l−1 while that of 232Th ranged from 10.1 ± 4.0 to 88.26 ± 6.7 mBq l−1 with an average of 38.1 ± 5.0 mBq l−1. For 40K the activity concentrations ranged from 90.2 ± 8.5 to 195.7 ± 12.36 mBq l−1 with an average of 140.9 ± 10.6 mBq l−1. The activity concentrations of all these three nuclides were found to be higher in well water and lower in tap water. The activity concentrations of 226Ra in this study were found to be less than the reported values in water from Italy (0.2–1,200 mBq l−1), Germany (1–1,800 mBq l−1), Spain (20–4,000 mBq l−1), Finland (10–49,000 mBq l−1) and France (7–700 mBq l−1) (Çevik et al. 2006). The results reveal that the activity concentrations of 226Ra in all samples are below the permissible limits of 100 Bq l−1 (IAEA) and 185 mBq l−1 (Fredj et al. 2005; Ajayi & Owolabi 2007). The average value of activity concentration of 232Th was found to be less than the reported concentrations of 51.43 and 190 mBq l−1 in drinking water from Upper Egypt (Ahmed 2004) and Bangladesh (Alam et al. 1999), respectively, while that of 40K was found to be less than the reported concentrations of 24,000 and 4,160 mBq l−1 in drinking water from Jordon (Saqan et al. 2001) and Bangladesh (Alam et al. 1999), respectively.

Table 2

Natural radionuclide concentration (mBq l−1) and pH in drinking water

Site codeSource of waterRadiumThoriumPotassiumpH
BW1 Well 66.2 ± 2.7 45.1 ± 2.9 195.7 ± 12.36 
BW2 Well 85.8 ± 5.2 56.4 ± 6.2 181.3 ± 10.5 7.1 
BW3 Well 76.6 ± 4.3 88.26 ± 6.7 165.3 ± 8.6 7.2 
BW4 Well 56.4 ± 4.5 46.5 ± 5.2 148.0 ± 12.4 7.1 
BW5 Well 62.4 ± 2.8 74.5 ± 8.1 172.3 ± 8.2 7.2 
BW6 Well 67.9 ± 3.0 66.9 ± 2.7 155.9 ± 4.2 
BW7 Well 52.7 ± 7.6 40.4 ± 4.7 144.1 ± 12.6 7.1 
BW8 Tap 24.2 ± 4.5 14.3 ± 4.8 117.6 ± 7.8 7.5 
BW9 Tap 34.5 ± 3.8 41.8 ± 3.0 153.9 ± 13.9 7.1 
BW10 Tap 24.4 ± 3.5 13.0 ± 4.3 112.5 ± 11.3 7.4 
BW11 Tap 21.3 ± 2.2 19.8 ± 4.4 97.5 ± 15.7 7.2 
BW12 Tap 37.7 ± 5.0 49.2 ± 5.7 125.7 ± 11.7 7.3 
BW13 Tap 16.1 ± 2.4 10.6 ± 7.4 117.4 ± 10.5 7.3 
BW14 Tap 23.9 ± 3.3 10.1 ± 4.0 90.2 ± 8.5 7.2 
BW15 Tap 33.5 ± 4.6 13.4 ± 6.3 137.1 ± 8.7 7.3 
BW16 Tap 41.2 ± 3.5 22.6 ± 3.2 158.2 ± 14.1 7.3 
BW17 Tap 26.7 ± 4.4 34.9 ± 5.9 122.7 ± 10.3 7.2 
Average   44.2 ± 3.9 38.1 ± 5.0 140.9 ± 10.6 7.2 
Site codeSource of waterRadiumThoriumPotassiumpH
BW1 Well 66.2 ± 2.7 45.1 ± 2.9 195.7 ± 12.36 
BW2 Well 85.8 ± 5.2 56.4 ± 6.2 181.3 ± 10.5 7.1 
BW3 Well 76.6 ± 4.3 88.26 ± 6.7 165.3 ± 8.6 7.2 
BW4 Well 56.4 ± 4.5 46.5 ± 5.2 148.0 ± 12.4 7.1 
BW5 Well 62.4 ± 2.8 74.5 ± 8.1 172.3 ± 8.2 7.2 
BW6 Well 67.9 ± 3.0 66.9 ± 2.7 155.9 ± 4.2 
BW7 Well 52.7 ± 7.6 40.4 ± 4.7 144.1 ± 12.6 7.1 
BW8 Tap 24.2 ± 4.5 14.3 ± 4.8 117.6 ± 7.8 7.5 
BW9 Tap 34.5 ± 3.8 41.8 ± 3.0 153.9 ± 13.9 7.1 
BW10 Tap 24.4 ± 3.5 13.0 ± 4.3 112.5 ± 11.3 7.4 
BW11 Tap 21.3 ± 2.2 19.8 ± 4.4 97.5 ± 15.7 7.2 
BW12 Tap 37.7 ± 5.0 49.2 ± 5.7 125.7 ± 11.7 7.3 
BW13 Tap 16.1 ± 2.4 10.6 ± 7.4 117.4 ± 10.5 7.3 
BW14 Tap 23.9 ± 3.3 10.1 ± 4.0 90.2 ± 8.5 7.2 
BW15 Tap 33.5 ± 4.6 13.4 ± 6.3 137.1 ± 8.7 7.3 
BW16 Tap 41.2 ± 3.5 22.6 ± 3.2 158.2 ± 14.1 7.3 
BW17 Tap 26.7 ± 4.4 34.9 ± 5.9 122.7 ± 10.3 7.2 
Average   44.2 ± 3.9 38.1 ± 5.0 140.9 ± 10.6 7.2 

Negative correlation between 226Ra, 232Th and 40K and pH shown in Figure 1(a)1(c) revealed that activity concentrations of 226Ra, 232Th and 40K decrease with the increase of pH. The literature shows the same trend (El Arabi et al. 2006).

Figure 1

The relation between pH and activity concentration of (a) 226Ra, (b) 232Th and (c) 40K.

Figure 1

The relation between pH and activity concentration of (a) 226Ra, (b) 232Th and (c) 40K.

As shown in Table 3 the activity concentrations of 222Rn in drinking water ranged between the minimum and maximum values 1.9 ± 0.31 and 11.9 ± 1.1 Bq l−1 with an average value of 5.7 ± 0.68 Bq l−1. The maximum value was found in well water due to the depth of the well, as the activity of radon in ground water is higher than in surface water (Ahmad et al. 2015). The average value of radon activity in drinking water was found to be below the EPA permissible limit of 11 Bq l−1 (Barnett et al. 1995; Ahmad et al. 2015). Figure 2 shows a positive correlation between radium and radon concentration for drinking water samples.

Table 3

Activity concentrations of radon and AEDE from drinking water

Site codeSource of waterRadon concentration Bq l−1AEDE μSv y−1
InhalationIngestionTotal
BW1 Well 10.7 ± 0.99 26.9 ± 2.49 2.2 ± 0.20 29.2 ± 2.70 
BW2 Well 11.9 ± 1.1 29.9 ± 2.77 2.4 ± 0.23 32.4 ± 3.00 
BW3 Well 11.0 ± 1.05 27.7 ± 2.64 2.3 ± 0.22 30.0 ± 2.86 
BW4 Well 7.7 ± 0.92 19.4 ± 2.31 1.6 ± 0.19 21.0 ± 2.51 
BW5 Well 7.9 ± 0.80 19.9 ± 2.01 1.6 ± 0.16 21.5 ± 2.18 
BW6 Well 6.8 ± 0.85 17.1 ± 2.14 1.4 ± 0.17 18.5 ± 2.32 
BW7 Well 9.6 ± 0.89 24.1 ± 2.24 2.0 ± 0.18 26.2 ± 2.42 
BW8 Tap 4.0 ± 0.56 10.0 ± 1.41 0.84 ± 0.11 10.9 ± 1.52 
BW9 Tap 5.7 ± 0.67 14.3 ± 1.68 1.2 ± 0.14 15.5 ± 1.82 
BW10 Tap 2.4 ± 0.38 6.0 ± 0.95 0.50 ± 0.07 6.5 ± 1.03 
BW11 Tap 2.8 ± 0.45 7.0 ± 1.13 0.58 ± 0.09 7.6 ± 1.22 
BW12 Tap 3.6 ± 0.48 9.0 ± 1.20 0.75 ± 0.10 9.8 ± 1.31 
BW13 Tap 1.9 ± 0.31 4.7 ± 0.78 0.39 ± 0.06 5.1 ± 0.84 
BW14 Tap 2.6 ± 0.47 6.5 ± 1.18 0.54 ± 0.09 7.0 ± 1.28 
BW15 Tap 4.4 ± 0.49 11.0 ± 1.23 0.92 ± 0.10 12.0 ± 1.33 
BW16 Tap 6.8 ± 0.80 17.1 ± 2.01 1.4 ± 0.16 18.5 ± 2.18 
BW17 Tap 3.0 ± 0.35 7.5 ± 0.88 0.63 ± 0.07 8.19 ± 0.95 
Average 5.7 ±0.68 15.2 ±1.7 1.2 ±0.14 16.5 ± 1.9 
Site codeSource of waterRadon concentration Bq l−1AEDE μSv y−1
InhalationIngestionTotal
BW1 Well 10.7 ± 0.99 26.9 ± 2.49 2.2 ± 0.20 29.2 ± 2.70 
BW2 Well 11.9 ± 1.1 29.9 ± 2.77 2.4 ± 0.23 32.4 ± 3.00 
BW3 Well 11.0 ± 1.05 27.7 ± 2.64 2.3 ± 0.22 30.0 ± 2.86 
BW4 Well 7.7 ± 0.92 19.4 ± 2.31 1.6 ± 0.19 21.0 ± 2.51 
BW5 Well 7.9 ± 0.80 19.9 ± 2.01 1.6 ± 0.16 21.5 ± 2.18 
BW6 Well 6.8 ± 0.85 17.1 ± 2.14 1.4 ± 0.17 18.5 ± 2.32 
BW7 Well 9.6 ± 0.89 24.1 ± 2.24 2.0 ± 0.18 26.2 ± 2.42 
BW8 Tap 4.0 ± 0.56 10.0 ± 1.41 0.84 ± 0.11 10.9 ± 1.52 
BW9 Tap 5.7 ± 0.67 14.3 ± 1.68 1.2 ± 0.14 15.5 ± 1.82 
BW10 Tap 2.4 ± 0.38 6.0 ± 0.95 0.50 ± 0.07 6.5 ± 1.03 
BW11 Tap 2.8 ± 0.45 7.0 ± 1.13 0.58 ± 0.09 7.6 ± 1.22 
BW12 Tap 3.6 ± 0.48 9.0 ± 1.20 0.75 ± 0.10 9.8 ± 1.31 
BW13 Tap 1.9 ± 0.31 4.7 ± 0.78 0.39 ± 0.06 5.1 ± 0.84 
BW14 Tap 2.6 ± 0.47 6.5 ± 1.18 0.54 ± 0.09 7.0 ± 1.28 
BW15 Tap 4.4 ± 0.49 11.0 ± 1.23 0.92 ± 0.10 12.0 ± 1.33 
BW16 Tap 6.8 ± 0.80 17.1 ± 2.01 1.4 ± 0.16 18.5 ± 2.18 
BW17 Tap 3.0 ± 0.35 7.5 ± 0.88 0.63 ± 0.07 8.19 ± 0.95 
Average 5.7 ±0.68 15.2 ±1.7 1.2 ±0.14 16.5 ± 1.9 
Figure 2

Relation between radium and radon concentrations for drinking water samples.

Figure 2

Relation between radium and radon concentrations for drinking water samples.

Based on measured activity concentrations of 222Rn, AEDE for inhalation, ingestion and total were calculated as shown in Table 3. The AEDE from radon ranged between minimum and maximum values 4.7 ± 0.78 and 29.9 ± 2.7 μSv y−1 with an average value of 15.2 ± 1.7 μSv y−1 for inhalation and 0.39 ± 0.06 and 2.4 ± 0.23 μSv y−1 with an average of 1.2 ± 0.34 μSv y−1 for ingestion. A total average effective dose was found of 16.5 ± 1.9 μSv y−1.

In addition, for exposure to radon from ingestion, annual effective doses from 226Ra, 232Th and 40K and 222Rn were separately calculated for infants, children and adults using Equations (2), (3), and (4) respectively. Figure 3(a)3(c) show annual effective doses from 222Rn, 226Ra, 232Th and 40K while Table 4 shows minimum, maximum and average values of 222Rn, 226Ra, 232Th and 40K. Owing to the intake of 222Rn, the annual effective dose ranged from 0.66 to 4.1 μSv y−1 with an average of 2.1 μSv y−1, 0.49 to 3.1 μSv y−1 with an average of 1.5 μSv y−1 and 0.33 to 2 μSv y−1 with an average of 1.05 μSv y−1 for infants (0–1 y), children (2–7 y) and adults (>17 y), respectively. Annual effective dose due to intake of 226Ra ranged from 18.99 to 101.2 μSv y−1 with an average of 52.14 μSv y−1, 3.49 to 18.6 μSv y−1 with an average of 9.59 μSv y−1 and 3.30 to 17.6 μSv y−1 with an average of 9.06 μSv y−1 for infants (0–1 y), children (2–7 y) and adults (>17 y), respectively.

Table 4

Age-dependent annual effective dose due to ingestion of radon and natural radionuclides of 226Ra, 232Th and 40K from drinking water

NuclidesInfants (0–1 y) (μSv y−1)Children (2–7 y) (μSv y−1)Adults (>17 y) (μSv y−1)
222Rn 
 Minimum 0.66 0.49 0.33 
 Maximum 4.1 3.10 2.00 
 Average 2.1 1.50 1.05 
226Ra 
 Minimum 18.99 3.49 3.30 
 Maximum 101.2 18.6 17.6 
 Average 52.14 9.59 9.06 
232Th 
 Minimum 0.157 0.074 0.045 
 Maximum 1.37 0.648 0.400 
 Average 0.591 0.280 0.173 
40
 Minimum 0.167 0.044 0.028 
 Maximum 0.362 0.095 0.061 
 Average 0.261 0.060 0.044 
Cumulative average 13.77 2.857 2.581 
NuclidesInfants (0–1 y) (μSv y−1)Children (2–7 y) (μSv y−1)Adults (>17 y) (μSv y−1)
222Rn 
 Minimum 0.66 0.49 0.33 
 Maximum 4.1 3.10 2.00 
 Average 2.1 1.50 1.05 
226Ra 
 Minimum 18.99 3.49 3.30 
 Maximum 101.2 18.6 17.6 
 Average 52.14 9.59 9.06 
232Th 
 Minimum 0.157 0.074 0.045 
 Maximum 1.37 0.648 0.400 
 Average 0.591 0.280 0.173 
40
 Minimum 0.167 0.044 0.028 
 Maximum 0.362 0.095 0.061 
 Average 0.261 0.060 0.044 
Cumulative average 13.77 2.857 2.581 
Figure 3

Age-dependent annual effective dose due to intake of 226Ra, 222Rn, 232Th, and 40K from drinking water.

Figure 3

Age-dependent annual effective dose due to intake of 226Ra, 222Rn, 232Th, and 40K from drinking water.

Annual effective dose due to intake of 232Th ranged from 0.157 to 1.37 μSv y−1 with an average of 0.591 μSv y−1, 0.074 to 0.648 μSv y−1 with an average of 0.280 μSv y−1 and 0.045 to 0.400 μSv y−1 with an average of 0.173 μSv y−1 for infants (0–1 y), children (2–7 y) and adults (>17 y), respectively. Similarly, the annual effective dose due to intake of 40K ranged from 0.167 to 0.362 μSv y−1 with an average of 0.261 μSv y−1, 0.044 to 0.095 μSv y−1 with an average of 0.060 μSv y−1 and 0.028 to 0.061 μSv y−1 with an average of 0.044 μSv y−1 for infants (0–1 y), children (2–7 y) and adults (>17 y), respectively. The age-dependent annual effective doses due to ingestion of 226Ra, 222Rn 232Th and 40K were found to be below the WHO permissible limit of 0.1 mSv y−1 for all ages (WHO 1993).

The cumulative annual effective doses due to the contribution of 222Rn, 226Ra, 232Th and 40K were 13.77 μSv y−1, 2.857 μSv y−1 and 2.581 μSv y−1 for infants, children and adults respectively. It is estimated that the most radiotoxic radionuclide is radium because 20% of ingested radium is absorbed into the bloodstream and then distributed to bones and soft tissues, but its retention is in growing bones (El Arabi et al. 2006). Table 4 shows that average annual effective dose due to the intake of 226Ra is higher for infants than children and adults (infants > children > adults). This study shows that infants are more vulnerable and comparatively at risk due to the intensive growth of bone.

CONCLUSIONS

To conclude, for the current study the average activity concentrations of 226Ra, 232Th and 40K in drinking water were found to be 44.2 ± 3.9, 38.1 ± 5.0 and 140.9 ± 10.6 mBq l−1, respectively. The activity concentrations of these three radionuclides were found to be below most of those in studies conducted by different researchers worldwide. A reasonable correlation between pH and 226Ra, 232Th and 40K shows the activity concentration of these radionuclides decreases with the increase of pH. The average activity concentration of radon was found to be below the permissible limit of EPA. The age-dependent annual effective doses due to ingestion of 226Ra, 222Rn 232Th and 40K were found to be below the permissible limit of WHO.

The results show that 226Ra is the main contributor/donor radioactive element to the annual effective dose for ingestion and infants and children are in danger compared with adults due to their intensive growth of bone. Limited data regarding natural radioactivity and radon concentration in drinking water is found in the literature and therefore further study is suggested to investigate drinking water for natural radioactivity and radon concentrations.

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