Radioactivity Measurements and Radiation Dose Assessments in Ground Water of Al-Baha Region, Saudi Arabia

Amal Hussain Al-Ghamdi

Department of Physics, Faculty of Science, University of Jeddah, Jeddah, KSA.

DOI: 10.4236/gep.2019.710009                

Abstract

Twenty samples of ground water were collected from different wells in Al-Baha region which is located at south-east of Saudi Arabia. Gamma spectrometer based on HPGe crystal was applied to determine activity concentrations in Bq·L^-1 of the natural radio nuclides: Radium-226 and Thorium-232 series also Potassium-40. The measured results indicate that the average concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K in the studied samples were 0.85, 0.43, and 2.84 Bq·L^-1, respectively. The average annual estimated effective dose was found to be 0.058 mSv/y which is lower than the annual limit of the dose allowed by WHO Thus, it has no harmful effects on health.

Keywords

Drilled Well Water, Natural Radioactivity, Doses, Hpge, Gamma Spectroscopy

1. Introduction

Natural radioactivity in groundwater arises from ²³⁸U, ²³²Th, ⁴⁰K and their decay products which are produced as a result of the interactions between rocks and water ( Todorović et al., 2012 ; Kraemer & Genereux, 1998 ). Consequently these radionuclides transported in ground water can enter the food chain through irrigation waters and the water source through ground water wells ( Malanca et al., 1998 ). Thus, the ingestion of radionuclides in drinking water causes human internal exposure ( Degerlier & Karahan, 2010 ). The estimated exposure of natural radioactivity sources contributes dose was 2.4 mSv y⁻¹ (cosmic ray 0.4, terrestrial gamma ray 0.5, radon 1.2, and food and drinking water 0.3) ( UNSCEAR, 2000 ). So, determinations of natural radioactivity concentrations in bedrock wells were important to estimate the dose in the water samples ( Salih et al., 2002 ). In the south-west of Saudi Arabia (Al-Baha region), there are no rivers, lakes, and springs. Therefore, people depend on the underground water especially those coming from wells. These wells must be safe and of good quality. Concentration levels of ²²⁶Ra, ²³²Th and ⁴⁰K in ground water used in this region and the radiological impacts of the consumed drinking water have not been reported in literature previously. So, the aim of this work is to determine the concentration values of natural radionuclides present in the well water samples collected from different location in Al-Baha region and estimate the corresponding radiation doses for people consuming these waters. This work is necessary due to the demands of having the database available on the waters and is highly required to keep human drinking water standards. The obtained data in this study may afford baseline levels of natural radioactivity in such water and provide background information for future research on drinking water for radiological protection of the human.

2. Materials and Method

2.1. Study Area

In order to determine the natural radioactivity in ground water, twenty water samples were collected from most frequently used wells spread in different locations of Al-Baha region. It is located in the south-east of Saudi Arabia (20˚0'0"N, 41˚30'0"E), as shown in Figure 1. The sampling locations were chosen mostly based on population density and accessibility. Al-Baha region is an agricultural area, the main agro products, are wheat, vegetables and fruits. This region was chosen based on the active usage of ground water for drinking and for irrigation purposes made by locals of the area which can also be a source of radionuclides in foods.

2.2. Samples Collection, Preparation and Measuring

The collected water samples were acidified with nitric acid to avoid the collection of organic materials, then each sample was filled into 500 ml capacity polyethylene Marinelli beakers ( IAEA, 1989 ). Before use the containers were washed

Figure 1. The study area (Al-Baha region—Saudi Arabia).

with dilute HCl and rinsed with distilled water. The Marinelli beakers were sealed and stored for more than 4 weeks before counting to reach the secular equilibrium between ²²⁶Ra nuclides and ²³²Th nuclides and their daughters for gamma ray measurements ( Abbady, 2004 ). Detection and measurements of the sample concentrations were carried out using a coaxial high-purity germanium (HPGe) detector with relative efficiency of 25% and FWHM 2.0 keV at 1332 keV, of ⁶⁰Co. The detector was housed inside a thick lead shield to reduce the background of the system. Genie 2000 basic spectroscopic software was installed in the computer for data acquisition and analysis. The system was calibrated for energy and efficiency on a regular basis in ( IAEA, 1989 ). Each sample after equilibrium was kept on the top of the HPGe detector and counted for 36,000 s. The background was measured every week under the same conditions of sample measurement.

2.3. Calculations of the Activity Concentration

The activity of ²²⁶Ra was determined based on the gamma ray energies of 351.9 keV from ²¹⁴Pb and 609.3, 1120.3 and 1764.5 keV (from ²¹⁴Bi). The activity concentration of ²³²Th was determined based on gamma ray energies of 338.8, 911.2 and 968.97 keV from ²²⁸Ac and 583.0 keV from ²⁰⁸Tl. ⁴⁰K was determined directly by its emission energy of 1461.8 keV gamma-ray line. The activity concentrations A_w of the natural radionuclides in the measured samples were calculated using the equation ( UNSCEAR, 2000 ):

$A_w\left(\text{Bq}\cdot {\text{L}}^{-1}\right)=Ca/\text{ε}P\text{γ}m$ (1)

where: Ca is the net gamma counting rate (counts per second), ε the detector efficiency of the specific γ-ray, Pγ the absolute transition probability of Gamma-decay and m the mass of the sample (kg).

3. Results and Discussion

3.1. Activity Concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K

The concentrations in Bq∙L⁻¹ of radionuclides ²²⁶Ra, ²³²Th, and ⁴⁰K measured in the water samples were listed in Table 1. As shown, in this table, ²²⁶Ra activities It ranged from 0.24 Bq∙L⁻¹ (w17) to 1.54 Bq∙L⁻¹ (w11). It was not detected in four samples (w3, w9, w18 and w20) and the measured samples (w5, w6, w7, w10 and w13) were higher than the recommended limits of 1.0 Bq∙L⁻¹ ( WHO, 2006 ). ²³²Th series were detected in eight samples only, the lowest value was 0.15 Bq∙L⁻¹ (sample 15) and the highest value was 0.81 Bq∙L⁻¹ (w16). The results show that the concentration values of ²²⁶Ra were higher than those of ²³²Th. This may because of the radium being more soluble in water ( Kitto & Kim, 2005 ). ⁴⁰K activities ranged from 0.66 Bq∙L⁻¹ (w7) to 5.64 Bq∙L⁻¹ (w4), all samples concentration were below the recommended limit 10.0 Bq∙L⁻¹ of ⁴⁰K reported by WHO 2006 ( WHO, 2006 ). The obtained average concentrations of the three nuclides (²²⁶Ra, ²³²Th, and ⁴⁰K) were 0.85, 0.43 and 2.84 Bq∙L⁻¹, respectively. The average values

Table 1. Activity concentrations of ²²⁶Ra, ²³²Th, and ⁴⁰K of the ground water samples.

ND: not detected.

for ²²⁶Ra and ⁴⁰K do not exceed the WHOO 2006 recommended limit in drinking water, whereas, slightly higher for ²³²Th than the limit. It should be noted that, in the present results, ⁴⁰K is the most abundant concentration, about 76% of the total (²²⁶Ra + ²³²Th + ⁴⁰K). Potassium-40 is an isotope of an essential element which is under homeostatic control ( Jabir et al., 2007 ). The activity concentration of ²²⁶Ra, ²³²Th and ⁴⁰K in the studied ground water samples illustrated in Figure 2.

3.2. Radiation Dose Estimation

The annual effective dose equivalents from the consumption of drinking water due to ²²⁶Ra, ²³²Th, and ⁴⁰K were estimated by UNSCEAR (2000) and El-Gamal et al. (2019) as:

$D_w=A_w\times C_w\times F_w$ (2)

where D_w is the annual effective dose equivalent from consumption of drinking water (mSv/year), A_w is the activity concentration of radionuclides in the ingested water (Bq/L), C_w is the consumption rate of water (L/year). According to WHO (2003) , the dose was estimated by considering a consumption rate is 730 L/year for adults. The dose conversion factors F_w (Sv/Bq) for adults were (2.8 × 10⁻⁷, 2.3 × 10⁻⁷ and 6.2 × 10⁻⁹ Sv Bq⁻¹) for ²²⁶Ra, ²³²Th and ⁴⁰K, respectively, ( WHO, 2006 ).

The calculated total annual effective doses for adults ingested radionuclides ²²⁶Ra, ²³²Th and ⁴⁰K from the ground water samples were tabulated in Table 1. The highest value (0.237 mSv/y) of effective dose was calculated in sample w6 due to the radium high concentration. The range of effective doses due to intake of ²²⁶Ra, ²³²Th, and ⁴⁰K were from 0.004 to 0.237 mSv/y, with an average value of 0.058 mSv/y which is below the average limit (0.1 mSv/y) reported by WHO ( WHO, 2006 ). Consequently, we recommended that, the investigated waters are acceptable as drinking water for life-long human without any treatment to reduce the concentrations of radioactive contaminants. Figure 3, shows the effective dose for the ingestion of ²²⁶Ra, ²³²Th and ⁴⁰K by adults.

3.3. Lifetime Risk Assessment (R)

Lifetime risk assessment was calculated using the Eq ( EPA, 1999 ):

Figure 2. Activity concentration of ²²⁶Ra, ²³²Th and ⁴⁰K in ground water samples collected from Al-Baha region, Saudi Arabia.

Figure 3. A comparison of total annual effective dose (mSv/y) for adults ingested radionuclides ²²⁶Ra, ²³²Th and ⁴⁰K from the ground water samples.

$\text{Lifetimerisk}\left(R\right)=D_w\times D_L\times R_F$ (3)

where D_w is annual effective dose equivalent (Sv/y), D_L is duration of life (70 years) and R_F is risk factor (Sv⁻¹). For risk assessment, the nominal probability coefficient of 7.3 × 10⁻² Sv⁻¹ was adopted ( ICRP, 1996 ).

The risk levels from the direct ingestion of the natural radionuclides in ground water were estimated as shown in Table 1. The cancer risk R for the adults, i.e. corresponding to the total ingestion dose of 0.058 mSv/y is estimated as 0.299 × 10⁻³. This risk is much lower than the limit 8.4 × 10⁻³, if the total natural radiation dose of 2.4 mSv/y as given by UNSCEAR 2000 UNSCEAR (2000) .

3.4. Comparison of Results with Similar in Other Countries

Table 2 shows a comparison between the measured activity concentration values of the groundwater samples in present work and other samples obtained from different countries. Where, the average concentration of ²²⁶Ra (0.56 Bq∙L⁻¹) is acceptable with all countries except the maximum values for Yemen and Nigeria. ²³²Th average value (0.16 Bq∙L⁻¹) is almost matched with Saudi Arabia ( Alseroury et al., 2018 ), higher than Jordan ( Al-Shboul et al., 2017 ) and lower than other countries. The present results show that the average of ⁴⁰K concentration is nearly matching the value of Nigeria ( Ajayi & Owolabi, 2007 ), higher than Yemen ( Abdurabu et al., 2016 ) and Jordan ( Al-Shboul et al., 2017 ), while it is lower than the other observed values. Therefore, we can indicate that the obtained results are in agreement with the data obtained from various locations in the world, taking into account the data of the countries of different geographical locations differ regarding specific mineral.

4. Conclusion

The activities of ²²⁶Ra, ²³²Th and ⁴⁰K in the well water samples collected from Al-Baha region, south-east of Saudi Arabia were investigated in the present study. The obtained average concentrations of the three nuclides (²²⁶Ra, ²³²Th, and ⁴⁰K) were 0.85, 0.43 and 2.84 Bq∙L⁻¹, respectively. The results indicate that

Table 2. Activity concentration of natural radionuclides in ground water from different countries.

the natural radioactivity concentrations of these nuclides were below the WHO guidance levels and were within the values reported by the other researchers. The risk assessment data show that the investigated radionuclides in water were below limit values and pose no detrimental health effect.

Acknowledgements

A special thanks to Nada Alshehri for helping in proofreading and organizing the paper.

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	Abbady, A. G. (2004). Estimation of Radiation Hazard Indices from Sedimentary Rocks in Upper Egypt. Applied Radiation and Isotopes, 60, 111-114. https://doi.org/10.1016/j.apradiso.2003.09.012
[2]	Abdurabu, W. A., Saleh, M. A., Ramli, A. T., & Heryansyah, A. (2016). Occurrence of Natural Radioactivity and Corresponding Health Risk in Groundwater with an Elevated Radiation Background in Juban District, Yemen. Environmental Earth Sciences, 75, 1360. https://doi.org/10.1007/s12665-016-6142-z
[3]	Ajayi, O. S., & Owolabi, T. P. (2007). Determination of Natural Radioactivity in Drinking Water in Private Dug Wells in Akure, Southwestern Nigeria. Radiation Protection Dosimetry, 128, 477-484. https://doi.org/10.1093/rpd/ncm429
[4]	Alseroury, F. A., Almeelbi, T., Khan, A., Barakata, M. A., Al-Zahrani, J. H., & Alali, W. (2018). Estimation of Natural Radioactive and Heavy Metals Concentration in Underground Water. Journal of Radiation Research and Applied Sciences, 11, 373. https://doi.org/10.1016/j.jrras.2018.07.004
[5]	Al-Shboul, K. F., Alali, A. E., Batayneh, I. M., & Al-Khodire, H. Y. (2017). Radiation Hazards and Lifetime Risk Assessment of Tap Water Using Liquid Scintillation Counting and High-Resolution Gamma Spectrometry. Journal of Environmental Radioactivity, 178-179, 245-252. https://doi.org/10.1016/j.jenvrad.2017.09.005
[6]	Darko, G., Faanu, A., Akoto, O., Acheampong, A., Goode, E. J., & Gyamfi, O. (2015). Distribution of Natural and Artificial Radioactivity in Soils, Water and Tuber Crops. Environmental Monitoring and Assessment, 187, 339. https://doi.org/10.1007/s10661-015-4580-9
[7]	Degerlier, M., & Karahan, G. (2010). Natural Radioactivity in Various Surface Waters in Adana, Turkey. Desalination, 261, 126-130. https://doi.org/10.1016/j.desal.2010.05.020
[8]	El-Gamal, H., Sefelnasr, A., & Salaheldin, G. (2019). Determination of Natural Radionuclides for Water Resources on the West Bank of the Nile River, Assiut Governorate, Egypt. Water, 11, 311. https://doi.org/10.3390/w11020311
[9]	EPA (1999). Radon in Drinking Water Health Risk Reduction and Cost Analysis. Federal Register, 64, 9560-9599.
[10]	IAEA (International Atomic Energy Agency) (1989). Measurement of Radiation in Food and the Environment. Guidebook. Technical Report Series. Vienna: IAEA.
[11]	ICRP (1996). European Commission Directive. Laying down Basic Safety Standards for the Protection of the Health of Workers and the General Public against the Dangers Arising from Ionizing Radiation. EC Directive.
[12]	Jabir, N. N., Farad, I. P., & Alas, S. K. (2007). Activity Concentrations of 226Ra, 228Th, and 40K in Different Food Crops from a High Background Radiation Area in Bitschi, Joss Plateau, Nigeria. Radiation and Environmental Biophysics, 46, 53-59. https://doi.org/10.1007/s00411-006-0085-9
[13]	Kitto, M. E., & Kim, M. S. (2005). Naturally Occurring Radionuclides in Community Water Supplies of New York State. Health Physics, 88, 253-260. https://doi.org/10.1097/01.HP.0000149879.58455.1f
[14]	Kraemer, T. F., & Genereux, D. P. (1998). Applications of Uranium-and Thorium-Series Radionuclides in Catchment Hydrology Studies. In Isotope Tracers in Catchment Hydrology (pp. 679-722). Amsterdam: Elsevier. https://doi.org/10.1016/B978-0-444-81546-0.50027-6
[15]	Malanca, A., Repetti, M., & De Macedo, H. R. (1998). Gross Alpha- and Beta-Activities in Surface and Ground Water of Rio Grande do Norte, Brazil. Applied Radiation and Isotopes, 49, 893-898. https://doi.org/10.1016/S0969-8043(97)00298-4
[16]	Salih, M. M. I., Pettersson, H. B. L., & Lund, E. (2002). Uranium and Thorium Series Radionuclides in Drinking Water from Drilled Bedrock Wells: Correlation to Geology and Bedrock Radioactivity and Dose Estimation. Radiation Protection Dosimetry, 102, 249-258. https://doi.org/10.1093/oxfordjournals.rpd.a006093
[17]	Todorović, N., Nikolov, J., Tenjović, B., Bikit, I., & Veskovic, M. (2012). Establishment of a Method for Measurement of Gross Alpha/Beta Activities in Water from Vojvodina Region. Radiation Measurements, 47, 1053-1059. https://doi.org/10.1016/j.radmeas.2012.09.009
[18]	UNSCEAR (2000). The United Nations Scientific Committee on the Effects of Atomic Radiation (pp. 93+156). Report to General Assembly. New York: United Nations.
[19]	WHO (2003). World Health Organization, Guidelines for Drinking Water Quality (Vol. 3). Geneva, Switzerland: WHO.
[20]	WHO (2006). Guidelines for Drinking-Water Quality (Vol. 1, 3rd ed.). Geneva, Switzerland: WHO.