Spatial Distribution of the Natural Radioactivity of the Water and its Association with the Physico-Chemical Parameters: Abu Tig, Assiut, Egypt

The main naturally occurring radioactive isotopes in water are uranium isotopes, radium isotopes, and radon isotopes, these radionuclides are mainly soluble in water [3]. The production of these radionuclides in groundwater is mainly from rockwater interactions. The levels of radioactivity in groundwater depends on many factors such as the concentrations of these radionuclides in the aquifer rocks, geomorphology, and lithology other ecological conditions of aquifer [4,5], depending also on chemical reactions and the physical processes of decay along the water-rock interface. 226Ra is an alpha emitter with longest a half-life of 1602yr, it originates from the 238U decay series and its descendant 222Rn has a half-life of 3.8d. 228Ra is a beta emitter with a halflife of 5.75yr and it originates from 232Th series. 40K is also radioactive and has a half-life of 1.3x 109yr. Generally, radium concentrations in surface water range from 0.01 to 0.1Bql1 [6], while its concentration in groundwater can reach values up to 38Bql-1, depending on the factors mentioned previously. 222Rn is produced which is a gaseous radioisotope and diffuses into the pore water of rock formation. The 222Rn concentration in groundwater reaches to 183Bql-1 [7]. The recommended reference level of radon concentration in tap water is 150Bql-1 as considered by [8].


Introduction
Most environmental studies provide the best ways to preserve water and improve its quality for the necessity of human life. Water may be a factor for the transport of pollutants by human consumption. The radionuclides cause health hazard by ingestion and through the human food chain when these radionuclides are taken to the body [1]. So that it is necessary to achieve the minimum radiation exposure to the human body and not skipped the reference dose level (RDL) of the effective annual dose of drinking water consumption of 0.1mSvyr -1 reported by WHO [2].
The main naturally occurring radioactive isotopes in water are uranium isotopes, radium isotopes, and radon isotopes, these radionuclides are mainly soluble in water [3]. The production of these radionuclides in groundwater is mainly from rockwater interactions. The levels of radioactivity in groundwater depends on many factors such as the concentrations of these radionuclides in the aquifer rocks, geomorphology, and lithology other ecological conditions of aquifer [4,5], depending also on chemical reactions and the physical processes of decay along the water-rock interface. 226 Ra is an alpha emitter with longest a half-life of 1602yr, it originates from the 238 U decay series and its descendant 222 Rn has a half-life of 3.8d. 228 Ra is a beta emitter with a halflife of 5.75yr and it originates from 232 Th series. 40 K is also radioactive and has a half-life of 1.3x 109yr. Generally, radium concentrations in surface water range from 0.01 to 0.1Bql -1 [6], while its concentration in groundwater can reach values up to 38Bql -1 , depending on the factors mentioned previously. 222 Rn is produced which is a gaseous radioisotope and diffuses into the pore water of rock formation. The 222 Rn concentration in groundwater reaches to 183Bql -1 [7]. The recommended reference level of radon concentration in tap water is 150Bql -1 as considered by [8].
The levels of detection of radon in water research are explained by the sovereignty of granite rocks as well as the rocks of aquifers under investigation. Increased risk of many types of cancer is associated with exposure to radon and its progeny [9]. In addition, the high concentrations of 222 Rn in water samples indicate the presence of the radon's parent nuclide 226 Ra in the water-rock/soil system, which is known as the health hazard when ingestion during drinking water [10].

International Journal of Environmental Sciences & Natural Resources
The present study attempts to report the results of drinking water radium, thorium, potassium and radon survey in Abu Tig, Assiut Governorate, Egypt. The inhabitants of villages and rural areas in the study area are totally dependent on groundwater and on surface water of the Nile River for water supply.
The present work aims to understand the occurrence and classification of natural radionuclides 226 Ra, 232 Th, 40 K and 222 Rn in drinking water samples from study area and in a first approach to estimate natural radionuclides exposure levels for inhabitants of this region to estimate radiation doses for several ages due to water consumption by people living in this region. The results might provide some helpful information for management of drinking water use.

Description of study areas
Assiut Governorate is the most populated governorate in Upper Egypt with more than 5 million inhabitants. Abu Tig is a big district within Assiut Governorate that located on the western bank of the river Nile, between Latitudes 26 o 57' 56.

Sampling and sample preparation
A total of twenty-seven samples were collected from various locations from the study region and classified into three types; surface water, hand-dug wells and deep wells. Standard Polyethylene Marinelli beakers (1 liter) are used as measuring containers. Before utilizing, the containers are washed with HCl and swilled with distilled water. A tad bit of nitric acid, around 0.5ml HNO 3 per liter, was added to clear solution to forbid any loss of radium isotopes around the container walls, and to avert growth of microorganisms [11]. After filling up the beaker to the brim, a tight cap is pressed on to completely remove the air from it. The samples store for over thirty days to arrive secular equilibrium before a radiometric analysis. Each sample is counted for almost 172800 second relying on the radionuclide's concentrations.

Gamma spectrometry
Water samples were subjected to a gamma ray spectrometer with a detector had closed-end coaxial Gamma-ray crystal made of high purity germanium in a vertical configuration cooled with liquid nitrogen. The energy resolution of the detector reads approximately 2.000keV and ≤ 0.925keV at 1.33MeV and 122keV, respectively, while the relative efficiency is 40μ. The germanium crystal is existed inside a lead shield to decrease the environmental background. The shield consists of four layers with the following specifications: a low carbon steel of 9.5mm thick as an outer jacket, a bulk shield of lead of 10cm thickness, and graded linings to absorb low energy X-rays of 1.0mm tin and 1.6mm copper [12].
The spectrometer was energy-calibrated using radioactive standards of known energies such as 137 Cs (662keV) and 60 Co (1172 and 1332keV) and it was calibrated for efficiency using Canberra's ISOCS calibration utility instead of standard source [12]. 226 Ra concentration was determined using gamma-lines of 214 Bi and 214 Pb for different energy (609.31, 1120.29, and 1764.49KeV) and (295.22 and 351.93KeV) respectively. The concentration of 232 Th was measured using gamma lines of 228 Ac, 212 Pb and 208 Tl for different energy (911.2 and 968.97KeV), (238.63KeV) and (583.19 and 2614KeV) respectively. Finally, 40 K concentration was determined one peak at 1460.8KeV.

International Journal of Environmental Sciences & Natural Resources
respectively as reported by IAEA, ICRP, and WHO [14][15][16]. The dose was estimated by knowing consumption rate for adults, children and infants of 730, 350, and 150L/yr respectively.

Results
Activity concentrations of 226 Ra, 232 Th and 40 K for the drinking water samples collected from various locations in Abu Tig region are listed in Table 1 and shown in Figure 2.   According to the data, 226 Ra concentration in most drinking water samples is very higher than the maximum contaminant levels (MCL) of 0.185Bq/L proposed in the USA [9] for drinking water. In addition, the current work is compared to a number of researches in different regions of the world which have lower values, such as reported in Egypt [17], Sudan [18], Malaysia [19], Jordan [20] and Ghana [21], as well as those with higher values as reported in Yemen [22] and Nigeria [23]. Table 2 includes a comparison of 232 Th and 40 K concentrations with Different values around the world. There is no clear correlation between 226 Ra, 232 Th and 40 K in this study region, where a weak correlation can be found between ( 226 Ra and 232 Th), ( 226 Ra and 40 K) and ( 232 Th and 40 K) with a correlation coefficient of R 2 = 0.1156, 0.1551 and 0.1794, respectively.

International Journal of Environmental Sciences & Natural Resources
222 Rn activity concentration in drinking water samples fluctuated between 0.081 ± 0.05 to 0.789 ± 0.34Bq/L with an average value of 0.184 ± 0.11, All the samples are below the maximum contaminant level (MCL) of 11.1BqL -1 [24] and 11BqL -1 as proposed by the US Environmental Protection Agency [25] the concentration of radon changes depending on the zone resulting from its geological structure. as well as, the depth of the source of water, do not rule out climate change and geo-hydrological processes occurring in the region [26]. 222 Rn concentration in present work is greater than that reported in Egypt [27] and less than that reported from other countries, as Table 2.  Table  1. There is no correlation between them where the correlation coefficients R 2 =0.0009 as shown in Figure 3.

International Journal of Environmental Sciences & Natural Resources
Physico-chemical properties of drinking water samples in study region are listed in Table 1. TDS, pH-value and water temperature ranged from 0.09 to 0.98ppt, from 7.21 to 8.76 and from 18.2 to 26.6°C, respectively. There is no correlation between physico-chemical parameters and radionuclides 226 Ra, 232 Th, 40 K and 222 Rn where the correlation coefficients R 2 in all cases are less than 0.2 as shown in Figure 4, except a moderate correlation was observed between 226 Ra activity concentration and pH-value and TDS with correlation coefficient R 2 = 0.2159 and 0.2667 respectively. Also, between 222 Rn activity concentration and pHvalue with correlation coefficient R 2 =0.2527.

The Annual Effective Dose
The annual effective doses are given in Table 3 for various ages: adults, children and infants due to ingestion of 226 Ra, 232 Th and 40 K through drinking water from different areas in study region. The annual effective dose fluctuated between 10.49 to 76.25μSvyr −1 with an average value of 41.81μSvyr −1 , between 19.02 to 135.85μSvyr −1 with an average value of 74.75μSvyr −1 and between 15.87 to 114.50μSvyr −1 with an average value of 60.79μSvyr −1 for infants, children and adults respectively. Figure  5 shows that doses received by children were higher than that received by infants and adults; this is because children have small bodies. They are in the developmental stage, because their organs and bones are not yet complete. Therefore, the dose which they are exposed to is large compared to adults. In addition to being shorter than adults, they may get a higher dose of radioactive distributed in and deposited on the ground [28]. Figure 5: The annual effective doses (μSvyr -1 ) for infants, children and adults due to intake for drinking water in study region.

Conclusion
The present study is a contribution to study behavior and distribution of radioactivity levels of 226 Ra, 222 Rn, 232 Th and 40 K which measured in drinking water from densely populated area, which is Abu Tig city, Assiut Governorate, Egypt, using gamma-ray spectrometry technique using HPGe detector. The results clearly showed low concentrations of activity in the studied area. The presence of 40 K in groundwater is attributed to the anthropogenic activities represented by the application of the agricultural fertilizers. The results of this study include the assessment of annual effective dose for adults, children and infants. The results of doses which received by children are the highest. The average annual effective doses for all radionuclides of drinking water consumption per year is much less than the recommended reference level and consequentially, therefore recommend that, the water that has been investigated be acceptable for human consumption for life. There is no clear correlation between 226 Ra and 222 Rn, as well as, no correlation between physico-chemical parameters and radionuclides.