|Year : 2013 | Volume
| Issue : 1 | Page : 14-19
The Natural Radioactivity in groundwater from selected areas in Greater Accra region of Ghana by gross alpha and gross beta measurements
Eric Jilbert M Nguelem1, EO Darko2, MM Ndontchueng3, C Schandorf4, TT Akiti4, AP Muhulo4, E.K.P. Bam5
1 Graduate School of Nuclear and Allied Sciences, University of Ghana, Atomic-Campus, P.O. Box AE1, Atomic Energy, Legon, Ghana; Department of Physics, Faculty of Science, University of Douala, P.O. Box 24157, Douala, Cameroon
2 Graduate School of Nuclear and Allied Sciences, University of Ghana, Atomic-Campus, P.O. Box AE1, Atomic Energy; Radiation Protection Institute, GAEC, Box LG 80, Legon, Ghana
3 National Radiation Protection Agency of Cameroon, Box 33732, Yaounde; Department of Physics, Faculty of Science, University of Douala, P.O. Box 24157, Douala, Cameroon
4 Graduate School of Nuclear and Allied Sciences, University of Ghana, Atomic-Campus, P.O. Box AE1, Atomic Energy,Legon, Ghana
5 Nuclear Chemistry and Environmental Research Center, NNR I, GAEC, Box LG 80, Legon-Accra, Ghana
|Date of Web Publication||21-Nov-2013|
Eric Jilbert M Nguelem
Department of Physics, Faculty of Science, University of Douala, P.O. Box 24157
Source of Support: This work was supported by the IAEA through AFRA fellowship TC project RAF/0/031, Conflict of Interest: Natural radioactivity in groundwater.
Gross alpha and gross beta in 26 groundwater samples from Adentan to Abokobi areas in the Greater Accra Region of Ghana were determined using Alpha/Beta counting system (Canberra iMatic TM ). The average activity concentrations of gross alpha and gross beta were 0.034 and 0.501 Bq/L for Adentan, and 0.066 and 0.470 Bq/L for Abokobi, respectively. The results obtained are below the guideline levels of gross alpha (0.5 Bq/L) and gross beta (1.0 Bq/L) in drinking water established by the World Health Organisation. These results show that consumption of groundwater for the study areas may not pose any significant radiological health hazards through ingestion to the population.
Keywords: Activity concentration, gross alpha, gross beta, groundwater
|How to cite this article:|
Nguelem EM, Darko E O, Ndontchueng M M, Schandorf C, Akiti T T, Muhulo A P, Bam E. The Natural Radioactivity in groundwater from selected areas in Greater Accra region of Ghana by gross alpha and gross beta measurements. Radiat Prot Environ 2013;36:14-9
|How to cite this URL:|
Nguelem EM, Darko E O, Ndontchueng M M, Schandorf C, Akiti T T, Muhulo A P, Bam E. The Natural Radioactivity in groundwater from selected areas in Greater Accra region of Ghana by gross alpha and gross beta measurements. Radiat Prot Environ [serial online] 2013 [cited 2020 Jul 7];36:14-9. Available from: http://www.rpe.org.in/text.asp?2013/36/1/14/121814
| Introduction|| |
The measurement of natural radioactivity in our physical environment allows the determination and assessment of population exposure to radiation. The occurrence of natural radionuclides in water depends on the waters origin as well as humans activities in the area, such as fertilizers used in agriculture, where the water is located. These are known as such products which usually contain some trace elements like uranium and thorium decay series and non-series of potassium ( 40 K) which may increase the amounts of natural radionuclides in soil. Industrial activities (the extraction and processing of earth materials or their industrial products) may increase the incorporation of radionuclides into the hydrosphere through surface or/and ground water.  For groundwater (boreholes and wells), it depends on their presence and contents in lithologic of solids aquifers or surrounding rocks where groundwater is stored.  These solids aquifers or rocks known as geological materials usually contain some trace amounts of radioactive elements such as uranium, thorium decay series and non-series of 40 K, which may dissolve into groundwater system during water/rocks-soils interaction mechanism. 
Considering the presence of these natural radionuclides in the groundwater system and the radiotoxicity to human, consumption of groundwater with high amounts of natural radionuclides may rise to internal exposure caused by the decay of natural radionuclides taken into body through ingestion as well as inhalation.  During the decay process, they release several alpha and beta particles which are also responsible for a generally small fraction of the total radiation dose received from natural radioactivity as well as artificial. , Gross alpha in water is usually presented by 238 U series while gross beta is presented by non-series of 40 K as well as 232 Th series.  Determination of gross alpha and gross beta activity concentration levels in groundwater are of particular interest for routine monitoring of radioactivity levels in groundwater resources.
According to the world health organization (WHO),  the recommendations apply to routine operational limits of gross alpha and gross beta in exciting or new water supplies below which no further action is required are 0.5 Bq/L and 1.0 Bq/L respectively. These guidelines levels of gross alpha and gross beta established by the WHO have been adopted by many countries in the world in order to avoid high dose to radiation and enhance radiological health hazards due to consumption of groundwater. These are also been used by other developed and under developed countries to develop their own nation water quality standards on natural radioactivity level in drinking and domestic water.
In Ghana, there is no guideline for gross alpha and gross beta activity concentrations levels in drinking water. Most of the rural communities as well as urban areas in the Greater Accra Region of Ghana who do not receive public water supply used groundwater (boreholes and wells) for domestic purposes particularly and drinking water as well. According to literature of natural radioactivity in groundwater by gross alpha and gross beta measurement, only few studies have been done on radiological quality of drinking water in Ghana;  and sufficient information is not available. Estimation of gross alpha and gross beta activity concentration in groundwater resources is an important route for assessment of the radiological health hazards to ionizing radiation due to ingestion.
The aim of this study was to determine the activity concentrations of gross alpha and gross beta in groundwater (boreholes and wells) in the Greater Accra Region of Ghana using gross Alpha/Beta counting system. The investigations were performed in selected communities, namely; Adentan and Abokobi. Both study areas have relatively different geological structure. The geological structure of the investigated communities is grouped into two major geological formations found in abundance in the study areas, mainly Dahomeyan formations (with undifferentiated rocks mainly schists and gneisses) found in abundance in the area where Adentan is located, Togo formations (with undifferentiated mainly siliciclastics, high or low metamorphosed) as well as Dahomeyan are major rocks found in a zone where Abokobi is located. Each of these dominant geological formations found in the study areas consist of different lithologic of solids aquifers or rocks. ,,, [Figure 1] below shows the geology of the study areas. Groundwater available in both areas is boreholes and wells. The hydrogeology of groundwater system in both areas is relatively different since this is governed by the geological settings of the areas. 
| Experimental|| |
The nuclear analytical technique used to carry out this study was a low background Gass-less Automatic gross Alpha/Beta counting system (Canberra iMatic TM ) set-up at the Radiation Protection Institute of Ghana Atomic Energy Commission. The equipment is a firmware based instrument and does not require a computer to set up. The entire program of the instrument is stored in flash memory. It consists of solid state Passivated Implanted Planar Silicon detector position facing down for alpha and beta detection; can be operated continually for over 6 h with internal batteries and is totally self-contained.
In order to cover the study areas, a pre-field survey was done to know the number of boreholes and hand dup wells available in the areas and frequently used by the population at the time of sampling for domestic use, in particular and drinking water as well. The sampling campaigns were carried out between November 2011 and January 2012 and the weather conditions at the time of sampling were fairly stable. The places where samples were collected were marked by using a global positioning system. These are depicted in [Figure 1] with their sample ID ((ADW and ABW) for Adentan and Abokobi samples, respectively). A total of (26) groundwater samples were collected from boreholes and wells covering some communities in Adentan and Abokobi. In this way, (10) groundwater samples from Adentan site and (16) groundwater samples were from Abokobi site. The pH, salinity and total dissolved solids (TDS) of the water samples were measured on field using Metrolin model 691 pH-meter for the pH and a portable (HACH) conductivity for salinity and TDS of water samples.
Samples were obtained after allowing water to run fully at least 10 min before in order to remove stagnant water from the pump. Samples were then collected into 2 L of polyethylene gallons tightly sealed and labeled. A few drops of ultra-pure nitric acid (60%) were added to prevent adherence of radionuclides to the walls of the containers. The samples were then stored in the laboratory for preparation and analysis. The sample containers were carefully watched and rinsed three times with the distilled water before sampling.
Sample preparation and measurement
One litre of each collected groundwater sample was first filtered through filter paper of mm of diameter and transferred into 1 L beaker. Two millimeter of ultra-pure acid were added into 1L of filtered sample in order to maintain the radionuclides in the sample and to liberate dissolved metals from exchange sites on dissolved organic particles  and let stay overnight. Each of filtered water sample (300 ml) was transferred into 400 ml glass beaker and evaporated slowly to near dryness on the electrical hot plate placed in a fume chamber. The remaining water sample was transferred quantitatively in 47 mm stainless steel counting planchets. These were then heated to near dryness, stored into desiccators to allow them to cool into room temperature and to prevent them from absorbing moisture reading for counting in a low background Gas-less Automatic Gross Alpha/Beta counting system to determine the activity concentrations of gross alpha and gross beta present in each sample.
The samples were counted according to the procedure selected during calibration of the equipment. The calibration was done using two standards sources: 241 Am source for Alpha and 90 Sr for beta, respectively. The counting efficiencies of alpha and beta were then 36.25% ± 2.18% and 73.16% ± 4.39%, respectively. The selected procedure was to allow the samples to be counted for 100 min each. This was done twice for each water sample. The background reading of the detector for alpha and beta after counting three blank stainless steel planchets according to the procedure was 0.00148 Bq and 0.0026 Bq, respectively.
| Results and Discussions|| |
[Table 1]a and b show the locations, pH, TDS, and salinity of water samples from Adentan and Abokobi areas recorded during sampling campaign. The count rates and the calculated activity concentrations of gross alpha and gross beta in the groundwater samples in Adentan and Abokobi are given in [Table 2]a and b.
The activity concentrations of gross alpha in water samples from Adentan and Abokobi varied from <0.0049 (alpha detection limit value) to 0.086 Bq/L with an average value of 0.034 Bq/L and between <0.0049 (alpha detection limit value) and 0.155 Bq/L with an average value of 0.066 Bq/L, respectively. The gross beta radioactivity concentrations in water samples ranged from 0.026 to 1.867 Bq/L with an average value of 0.501 Bq/L for Adentan and between 0.046 and 2.720 Bq/L with an average value of 0.470 Bq/L for Abokobi. The highest values of the gross beta radioactivity concentrations were recorded in Abokobi in the sample referenced as ABW13 located at Oyarifa followed by the sample referenced as ADW3 at Ashiyie in Adentan site.
Since both study areas have slightly different geological formations, this slight variation in the activity concentrations of gross alpha and gross beta could be a result of the geological characteristics of the soils, the irregular distribution of the minerals in the surfaces of rocks or solids aquifers from which each groundwater has been in contact, the residence time of groundwater in contact with soil and bedrock system, their inhomogeneous distribution in multi-grain aggregates , as well as the pH of each groundwater sample. This variation could also be as a result of radionuclides content in soil and bedrock system. As it is known, the gross alpha activity is presented by 238 U series and gross beta activity is presented by 40 K as well as 232 Th series.  The main aquifers or rocks in Adentan are Dahomeyan Formations (with undifferentiated mainly schists and gneisses) and those in Abokobi are Togo Formations (with also undifferentiated mainly siliciclastics, un-or low metamorphosed) and some Dahomeyan rock types, and consist of different lithology of solid aquifers or rocks [Figure 1].
The activity concentrations of gross alpha and gross beta obtained in the present study were compared with those values recorded in various groundwaters in different parts of the world collected from the literature and presented in [Table 3]. The recorded activity concentrations of the gross alpha and gross beta in water samples from both Adentan and Abokobi areas varied within the validated results observed in other countries. This statistical variation of the gross alpha and gross beta activity concentrations in the water samples of the present study compared to those obtained in other countries could be a result of the different geological characteristics of the soils and rocks in Adentan and Abokobi areas and the geographical locations of the groundwater system.
|Table 3: Comparison of the calculated activity concentrations of gross alpha and gross beta with other values from different countries|
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Considering the guidelines values of the average activity concentrations of 0.5 Bq/L for gross alpha and 1.0 Bq/L for gross beta in drinking water established by the WHO,  the calculated average gross alpha and gross beta radioactivity concentrations in both Adentan and Abokobi areas are below that established guidelines values as shown in [Figure 2]. However, the activity concentrations of gross alpha and gross beta in all the samples from various locations in Adentan and Abokobi are below the guidelines values established by the WHO with the exception of the samples referenced ADW3 located at Ashiyie in Adentan with gross beta activity concentration of 1.867 Bq/L followed by a sample referenced ABW13 located at Oyarifa in Abokobi with gross beta value of 2.720 Bq/L. This higher value of gross beta activity concentration can be related to the higher abundance of 40 K in soil and feldspar minerals of the bedrock system as well as 232 Th and its daughter's radionuclides contents.
|Figure 2: Comparison of the average gross alpha and gross beta activity concentrations with the WHO guidelines values|
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The activity concentrations of the gross alpha and gross beta obtained in the present study was also compared with the salinity and the TDS as shown in [Figure 3]. These parameters are given in [Table 1]a and b. Each of the parameters such as the salinity, the total dissolved solid, and the gross alpha and gross beta radioactivity were normalized to unity and expressed as percentage index, P(%). The TDS known as water quality parameters are assumed to have some effects on the gross alpha and gross beta concentrations and hence radiological quality of the water.  Comparing the trends in the TDS and the salinity with the gross alpha and gross beta activity concentrations, neither gross alpha nor gross beta related to both TDS and salinity. This indicated that the radionuclide released to the liquid phase is dependent on parameters that are difficult or impossible to properly evaluate. These parameters include the extent of large minerals surfaces and irregular distribution of large minerals in the surfaces of the rocks. 
|Figure 3: Comparison of the gross alpha and gross beta activity concentrations with the TDS and the salinity for both sampling site. Each parameter was expressed as a percentage index, P(%)|
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| Conclusions|| |
Natural radioactivity by gross alpha and gross beta measurements in 26 groundwater samples (borehole and wells) from Adentan to Abokobi in the Greater Accra Region of Ghana have been investigated using a low background gas-less Automatic Alpha/Beta counting system (Canberra iMatic TM ).
The average activity concentrations of gross alpha and gross beta recorded in groundwater samples were 0.034 and 0.501 Bq/L for Adentan and 0.066 and 0.470 Bq/L for Abokobi, respectively. The observed variation in the results from this work compared with those from different origins may be attributed to geological factors including the geochemical characteristic of each groundwater. A long time study is necessary to investigate the dependence of gross alpha and gross beta activity concentrations on these parameters. Some particular groundwater samples referenced as ADW3 from Adentan and ABW13 from Abokobi recorded higher values of gross beta than the WHO guideline value. This higher value of gross beta can be attributed to the higher content of 40 K as well as 232 Th and its daughter's nuclides in both groundwater samples. The average activity concentrations of gross alpha and gross beta in the groundwater samples are below the guidelines values of 0.5 Bq/L for gross alpha and 1.0 Bq/L for gross beta activity concentrations in drinking water established by the WHO. This indicated that consumption of water from boreholes and wells in the study Areas may not cause any radiological health hazards to human due to ingestion and any action to reduce radioactivity might not be necessary.
The study covers only a limited area of the country. It is recommended that further studies should be extended to cover the whole country in order to obtain the national global picture of gross alpha and gross beta activity concentration in water, which should include the epidemiological survey of incidences of radiation-related health effects as well as the effects of geological factors and the geochemical characteristics of groundwater on the gross alpha and gross beta values.
| Acknowledgment|| |
This work was supported by the IAEA through AFRA fellowship TC project RAF/0/031. The authors are very grateful to the IAEA/AFRA members for the financial support. The Radiation Protection Institute of the Ghana Atomic Energy Commission is also commended for the use of laboratory facilities.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3]