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 Table of Contents 
ORIGINAL ARTICLE
Year : 2021  |  Volume : 44  |  Issue : 1  |  Page : 3-11  

Gross alpha and gross beta radioactivity measurements in groundwater from Nasarawa North district Nasarawa state Nigeria


1 Department of Physics, Nasarawa State University, Keffi, Nigeria
2 Department of Physics, Nasarawa State University, Keffi; Department of Radiological Safety, Nigerian Nuclear Regulatory Authority, Abuja, Nigeria
3 Centre for Energy Research and Training, Radiation Biophysics Section, Ahmadu Bello University, Zaria, Nigeria

Date of Submission15-May-2020
Date of Decision03-Jun-2020
Date of Acceptance26-Jan-2021
Date of Web Publication07-Jun-2021

Correspondence Address:
Samuel Odumu Ogana John
Department of Physics, Nasarawa State University, PMB 1022, Keffi
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/rpe.RPE_24_20

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  Abstract 


Gross alpha and gross beta radioactivity in 40 groundwater (borehole and well water) samples from Akwanga, Wamba and N/Eggon Areas of Nasarawa North District, Nasarawa State Nigeria was measured using the low background MPC2000B DP model Gross Alpha/Beta counter (ORTEC®-Protean Instrument Corporation). The values of gross alpha activity in this study were observed to be less than those of gross beta activity. The average activity values of gross alpha and gross beta obtained were 0.25 ± 0.04 Bq/L and 2.23 ± 0.09 Bq/L for Akwanga, 0.19 ± 0.03 Bq/L and 1.62 ± 0.08 Bq/L for Wamba and 0.30 ± 0.05 Bq/L and 3.00 ± 0.14 Bq/L for N/Eggon areas, respectively. The results are found to be below the World Health Organization guideline levels for drinking water quality of 0.5 Bq/L for gross alpha but 45% of the samples slightly exceeded the 1.0 Bq/L for gross beta. This implied that the groundwater in the study area is radiologically safe for consumption and may not pose any significant health hazards to humans by way of ingestion. The groundwater from the study area is also safe for drinking as the total dissolved solids average values were below the contamination limit for palatable drinking water guideline level of 1000 mg/L. However, a radionuclide-specific test and a regular monitoring program of the environment are hereby suggested.

Keywords: Gross alpha, gross beta, groundwater, radioactivity, total dissolved solids


How to cite this article:
John SO, Akpa TC, Onoja RA. Gross alpha and gross beta radioactivity measurements in groundwater from Nasarawa North district Nasarawa state Nigeria. Radiat Prot Environ 2021;44:3-11

How to cite this URL:
John SO, Akpa TC, Onoja RA. Gross alpha and gross beta radioactivity measurements in groundwater from Nasarawa North district Nasarawa state Nigeria. Radiat Prot Environ [serial online] 2021 [cited 2021 Sep 19];44:3-11. Available from: https://www.rpe.org.in/text.asp?2021/44/1/3/317946




  Introduction Top


Safe drinking water is essential to life as air, food, and sunlight. Humans consider water safe for consumption when both the physical, chemical, microbiological, and radiological properties are well defined. Various factors such as mining, milling, and processing of uranium ores and mineral sands, solid mineral drillings, industrial disposal of waste, and sewage into environment and rivers; use of fertilizer by farmers contributes to the contamination of safe drinking water due to human activities.[1],[2] The presence of naturally occurring radionuclides of terrestrial origin such as uranium and thorium decay series and potassium nondecay series in rocks, soils and groundwater, in variable concentrations, contaminates drinking water and lowers its quality. These radioactive materials are alpha and beta emitters, which can deposit large amount of energy into humans on ingestion through drinking water and accumulate for long time, cause radiation exposure.[3],[4],[5],[6] The principal health concern associated with regulated radionuclide in drinking water include: Radon gas increases the risk of lung cancer; uranium increases toxicity risk to the kidneys and radium increases ones risk of bone cancers and cancers of the head sinuses.[7],[8],[9]

The assessment of groundwater resources for radioactivity levels is performed by measuring gross alpha and gross beta activity concentrations for routine monitoring. In water, gross alpha emanates from 238U decay series whereas gross beta is from both 232Th decay series and 40K. For radiation safety and protection, the World Health Organization (WHO)[10] recommend that gross alpha and gross beta activity screening be first performed, thereafter, radionuclide-specific analysis be done only if measured gross values exceed guidelines for drinking water of 0.5 Bq/L and 1.0 Bq/L, respectively. Many countries of the world have adopted the established gross alpha and gross beta guideline levels by the WHO so that the consumption of groundwater would not result in exposure to high radiation dose.[2]

The purpose of this study is to evaluate the gross alpha and gross beta radioactivity concentration levels as the radiological component of safe drinking water in Nasarawa North District (NND), particularly Akwanga, Wamba, and N/Eggon areas, respectively, of Nasarawa State, Nigeria. Although several studies on radioactivity levels in groundwater have been reported in Nigeria,[1],[5],[6],[11] Nasarawa State tagged as “Home of Solid Minerals” has only few studies reported on environmental radioactivity, most of which are on background radiation. This study therefore, would provide baseline data and information on the radiological quality of drinking water in NND of Nasarawa State, Nigeria.


  Materials and Methods Top


In this study, the nuclear analytical technique used is the ISO 9696 and ISO 9697[12],[13] and Protean Instrument Corporation MPC2000B DP model desktop lightweight Gross alpha/beta counter, with serial number 08172140 by Ortec 800-251-9750 USA. A dual phosphor, gas flow proportional detector with 80 μg/cm3 entrance window and a 5.715 cm diameter, located at the Centre for Energy Research and Training, Ahmadu Bello University, Zaria Nigeria. The gas flow control uses two flow rates – low for rest mode and high for counting mode. An anti-coincident guard counter is incorporated into the counting system for eliminating the influence of high-energy cosmic radiation and part of the ambient gamma ray that could enter the measuring environment. Hence, the only contribution to the counting would be from impurities in the chamber construction material. The chamber is covered with 10 cm Lead and has inside dimensions of 48 cm × 28 cm × 10.5 cm. The counting modes are Alpha plus beta; Alpha only; Beta only. The detector is controlled through a keyboard and a liquid crystal display, which displays alpha and beta numeric and graphical information, thereby does not require computer for set up.

Sampling

The study area is the NND of Nasarawa state Nigeria, located on Longitudes 8° 25' 00“N to 9° 25' 00”N and Latitudes 8° 25' 00“E to 9°55' 00”E, covering a total area of about 3360 Km2 (comprising of Akwanga, Wamba and Nasarawa Eggon LGAs), as illustrated in [Figure 1]. It comprises of the Mada Younger Granite Ring Complex of Nigeria, from Akwanga Sheet 209NE and Wamba Sheet 210SW. The area composed of biotite granite, gneiss, older granite, and rhyolite among others.[14] The Mapped area was arbitrarily divided into 20 grids of 2 cm × 1.8 cm, each grid has according to scale an area of 1.5 Km2, as shown in [Figure 1]. A total of 40 sampling locations were earmarked by simple random process. The Global Positioning System (GPS), GARMIN GPSmap76CS (S/N 10R-022508) USA was used to note the location of sample in terms of geographical coordinate.
Figure 1: Map of Nasarawa North District showing sample location

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Forty samples of both borehole and well water were collected in 2 L polyethylene bottles, acidified by adding a few drops (~ 20 ml) of ultra-pure nitric acid (60%) to pH ~ 2 to minimize precipitation and absorption of radionuclide to walls of container and tightly sealed then labeled. The sample containers were initially rinsed thrice with distilled water and the water collected, to minimize contamination. The samples were kept in the laboratory for preparation and measurement.

Sample preparation and measurement

The 2 L water samples collected were slowly evaporated in an open 500 ml Pyrex beakers on an electric hot plate in the fume cupboard (at a temperature <100°C) without boiling until it reduces to about 50 ml in the beaker. It was then transferred into a weighed evaporating dish and placed under the infrared lamp to evaporate to dryness. The residues were placed in desiccators for cooling to room temperature while preventing from moisture absorbing. A known weighed residue of 0.077 g was transferred into a cleaned standard planchet of diameter approximately 5.1 cm (2 in) using a spatula. Few drops of organic solvent, Vinyl acetate was added to the residue on the planchet to avoid dispersing of the sample.

The total dissolved solid (TDS) was determined in milligrams per liter, by drying the sample at 180°C using Equation 1



Where WD is the weight of the empty evaporation dish, WD+S the weight of dish plus sample after evaporation, Vs is the volume in milliliters of filtered sample and 106 is a conversion factor.

The standards used for calibration were 239Pu alpha source and 90Sr beta source, of diameter 38 mm in disc and 3 mm thickness with product name EBSB20, manufactured and certified by CERCA and LEA Laboratories in France. Their respective certification numbers are CT001/1285/00/1920–1927 and CT1001/1271/00/1778–1783.239Pu alpha source had impurities varying from 0.74% to 0.82% with radioactive content range of 133.3–185.8 Bq at 2π-radians at the date of manufacture. 90Sr beta source had impurities <0.1% with radioactivity range of 105.1–117.7 Bq at 4π-radians. At the time of calibration for the analysis, the source activity was 79 Bq. The operational voltage of the detector used was 1200 V. The respective alpha and beta counting average efficiencies were 37.33% and 44.10%, computed and automatically generated by the device. The average background values for both alpha and beta modes of the detector acquired for 45 min for 10 cycles, were found to be 0.06 and 39.10 cpm respectively. The Beta-Alpha Crosstalk and Alpha-Beta Crosstalk were also determined as 0.1% and 0.09%.

The minimum detectable activity (MDA) for the Gas-Flow Proportional Alpha and Beta analysis was calculated from the calibration parameters using Equation 2[15] and the values obtained were 0.05 Bq/L for gross alpha activity and 0.83 Bq/L for gross beta activity. Calculations are presented in annexure 1.



Where Ro is the counts of background in t seconds, t is the sample and background count time (sec), and ε is the counting efficiency and V is the volume.

The counting equipment is automatic. The protocol involves entering preset time, counting voltage and number of counting cycles. Also to be entered are the counter characteristics (efficiency and background) volume of sample used and sampling efficiency. The equipment was loaded and counting was taken for 45 min in each case, with repeated count where the average was taken. Acquisition was made in alpha only mode, then beta only mode respectively and results are displayed as raw count, (count/minute). Equations 3-5 were used to determine the count rate, activity concentration (Bq/L) and the standard deviation Sc associated with the activity of the sample due to the statistical counting error.[13],[14],[15],[16] Calculations are presented in annexure 2.







Where: Rn is the sample count rate, corrected for background counts. εs is the fractional efficiency of counting of the specified radioactive standard. Rb is background count rate (cps), Rs is sample + background count rate (cps), Vs is the volume of sample, in liters, equivalent to the mass of solid on the planchet. to and tb– are the respective counting time of the sample and background.


  Results and Discussion Top


[Table 1], [Table 2], [Table 3] presents the calculated gross alpha and beta activity concentrations as well as the TDS in groundwater samples from Akwanga (1), Wamba (2) and Nassarawa-Eggon (3) in this study.
Table 1: Gross alpha and gross beta activity concentrations (Bq/L) and total dissolved solids (mg/L) from Akwanga (B=borehole sample; W=well sample)

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Table 2: Gross alpha and gross beta activity concentrations (Bq/L) and total dissolved solids (mg/L) from Wamba (B=borehole sample; W=well sample)

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Table 3: Gross alpha and gross beta activity concentrations (Bq/L) and total dissolved solids (mg/L) from N/Eggon (B=borehole sample; W=well sample)

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The activity concentration levels of gross alpha in both well and borehole water samples from Akwanga area varied from 0.08 ± 0.02 to 0.77 ± 0.07 Bq/L with an average value of 0.25 ± 0.04 Bq/L and standard deviation of 0.16. The gross beta activity concentrations ranged from 0.87 ± 0.05 to 6.76 ± 0.18 Bq/L with average value of 2.24 ± 0.09 Bq/L and standard deviation of 1.52. The highest values of gross alpha and beta activity concentrations in Akwanga area were both recorded in Rinze well water sample with reference as AK4W.

Wamba area has activity concentration levels of gross alpha in both well and borehole water samples varying from 0.09 ± 0.02 to 0.29 ± 0.04 Bq/L with an average value of 0.19 ± 0.03 Bq/L and standard deviation of 0.07. The gross beta activity concentrations ranged from 0.86 ± 0.04 to 2.98 ± 0.12 Bq/L with average value of 1.62 ± 0.08 Bq/L and standard deviation of 0.58. The highest values of gross alpha and beta activity concentrations in Wamba area were both recorded in Waiyo Mare with sample reference as WA5W, well water sample.

Nassarawa-Eggon area has activity concentration levels of gross alpha in both well and borehole water samples varying from <0.05 (gross alpha detection limit value) to 0.93 ± 0.17 Bq/L with an average value of 0.30 ± 0.05 Bq/L and standard deviation of 0.23. The gross beta activity ranged from <0.83 to 10.87 ± 0.50 Bq/L with average value of 3.00 ± 0.14 Bq/L and standard deviation of 2.92. The highest values of gross alpha and beta activity concentrations in Nassarawa-Eggon area were both recorded in GH N/Eggon, a borehole water sample of reference NE11B.

The values of the activity concentrations of both gross alpha and gross beta of the borehole and well water samples, in this study showed a slight variation; with well water samples recording higher values, though the highest gross beta activity observed in borehole sample, since the geological formation and characteristics of the study areas are slightly different. Other factors responsible could include nature of the mineral distribution in the aquifers in contact with the groundwater, the period in which groundwater was in contact with the soil and bedrock system as well as their inhomogeneous distribution in multigrain aggregates.[3],[17] In addition, the variation could be due to the content of radionuclides in the soils and bedrocks system; as explain by the fact that, 238U decay series are the source of gross alpha activity whereas the 232Th decay series and 40K give rise to gross beta activity.[3],[10] In Akwanga area, the main aquifers or rocks are the granitic sedimentary rocks of Benue Trough, Nasarawa Eggon of Mada Younger Ring Complex of Nigeria comprised of Gneiss and Schist while Wamba area comprised of south Mada hill of granitic basalt and Schist.[12],[18]

The TDS values determined in this study vary between 118 and 613 mg/L with average of 357 mg/L for Akwanga, 158–550 mg/L with average of 351 mg/L for Wamba and 100–680 mg/L with average of 337 mg/L for N/Eggon areas, respectively. A comparison of the various TDS of groundwater indicates that the respective mean values of 343 mg/L (well water samples) and 357 mg/L (borehole water samples) are below the recommended WHO palatable water of 600 mg/L. The range values of 107–680 mg/L (well samples) and 100.00–613 mg/L (borehole samples) showed that well samples recorded higher values than the borehole samples. In both cases including their maximum values were within the WHO considerations for which it was put that drinking water with TDS level of less than about 600 mg/L is generally considered to be good but becomes significantly and increasingly unpalatable at TDS level greater than about 1000 mg/L.[10]

From the results therefore, the maximum value 680 mg/L falls within the recommendations, hence groundwater from the sample areas is palatable for drinking with respect to TDS.

[Table 4] presents the comparison of the activity concentration of gross alpha and gross beta from present study and those values from various studies in different parts of the world obtained from literatures. The mean value of gross alpha varies between 0.06 and 0.25 Bq/L while gross beta is 0.08 and 2.29 Bq/L, all of which were within the WHO guidelines levels, except for the upper limit of gross beta. The combined values of activity concentrations of the gross alpha and gross beta in groundwater samples from NND (Akwanga, Wamba, and N/Eggon) areas showed variation within the validated results reported from other countries. These variations could be due to the differences in geological characteristics and locations of the soils and rocks as well as the groundwater aquifers from different parts of the world.
Table 4: Comparison of the activity concentrations of gross alpha and gross beta with other values from different countries.

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Based on the established guidelines for drinking-water quality by the WHO[10] of average activity concentrations of 0.5 Bq/L for gross alpha and 1.0 Bq/L for gross beta, Akwanga, Wamba, and N/Eggon areas, respectively, have activity concentration values below and within the established guidelines, showing only slight increase on few locations as shown in [Figure 2].
Figure 2: Comparison of the average activity concentration of gross alpha and gross beta with the World Health Organization guideline values

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The values of gross alpha activity concentrations in this study were observed to be less than those of gross beta activity concentrations, which correlates well with the set guidelines in relation to source radionuclides of 238U series for gross alpha as well as 232Th series and 40K for gross beta. A good linear relationship was observed between the gross alpha and gross beta activity concentrations in groundwater of the study area NND as illustrated in [Figure 3], with the value of correlation coefficient (R2) of 0.9145, which agrees well with the study reported by.[1],[6],[9]
Figure 3: Correlation of gross alpha and gross beta activity concentration in groundwater

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The comparison of activity concentration of the gross alpha and gross beta with the TDS in the present study is illustrated in [Figure 4]. The parameters-gross alpha and gross beta radioactivity and TDS, which are presented in [Table 1], [Table 2], [Table 3], are expressed in percentage index, P(%) after being normalized to unity. The radiological quality of water is affected by gross alpha and gross beta activity concentrations, which in turn is assumed to be influenced by TDS, a water quality parameter.[3],[22]
Figure 4: Comparison of the gross alpha and gross beta activity concentrations with the total dissolved solid. The parameters are expressed as a percentage index, P (%)

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A comparison of the variations in the gross alpha and gross beta with TDS presented correlation coefficients values of 0.3655 and 0.2788, respectively, implying a very weak or no significant relationship. It therefore suggests that the radionuclide that produced the activity in the groundwater does not depend on the TDS but on some other parameters whose evaluation could be hard or impossible to determine such as “the extent of large mineral surfaces and irregular distribution of large minerals in the surfaces of the rocks.”[3],[22]


  Conclusions Top


The natural radioactivity of 40 groundwater (borehole and well water) samples from Akwanga, Wamba and N/Eggon of NND, were measured by gross alpha and gross beta using the low background MPC2000B DPmodel Gross Alpha/Beta counter (ORTEC®-Protean Instrument Corporation).

The values of the gross alpha and gross beta average activity concentrations obtained in the groundwater samples were 0.25 ± 0.04 Bq/L and 2.23 ± 0.09 Bq/L for Akwanga, 0.19 ± 0.03 Bq/L and 1.62 ± 0.08 Bq/L for Wamba and 0.30 ± 0.05 Bq/L and 3.00 ± 0.14 Bq/L for N/Eggon areas respectively. The gross alpha and gross beta average activity concentration values in the groundwater samples in this study are found to be below and slightly above the WHO guidelines for drinking water quality. This implied that the groundwater (both borehole and well) in the study area are radiologically safe for consumption and may not pose any significant health hazards to humans by way of ingestion. However, a radionuclide specific test may be performed for the 45% samples with gross beta values exceeding guideline levels. The groundwater from the study area was also safe for drinking as the TDS average values were below the contamination limit for palatable drinking water guideline of 1000 mg/L. The variation in activity concentrations from this study compared to those from different locations as observed could be because of factors that are geological base, such as respective groundwater geochemical characteristics, which may further be investigated. In addition, the scope of study may be broadened to cover the entire Nasarawa state the home of solid minerals and to evaluate for monitoring and baseline data purposes, the radiological exposure parameters.

Acknowledgment

The authors would like to thank the Radiation Biophysics Section, Centre for Energy Research and Training, Ahmadu Bello University, Zaria, Nigeria, for their support in the analysis of samples, especially Mallam Bappa I. the Laboratory Scientist.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.


  Annexure Top


Annexure 1

Minimum detectable activity (MDA) (As per 2 formula of the text)

MDA = (2.71 + 4.65 Sqrt [Background counts, Ro])/(time × efficiency × Volume)

  1. Gross beta MDA


  2. MDA = (2.71 +× 4.65 Sqrt [39.1 × 45])/(2700 × 0.441 × 0.2 L) = 0.83 Bq/L.

    MDA = 0.83 Bq/L.

  3. Gross alpha MDA


MDA = (2.71 + 4.65 Sqrt [0.06 × 45])/(2700 × 0.3733 × 0.2 L) = 0.05 Bq/L.

MDA = 0.05 Bq/L.

Annexure 2

  1. Gross beta: (As per 3, 4, 5 formula of text)


  2. Sample counts (S) = 2133; Background counts = 39.1 × 45 = 1760; Net counts = 2133 − 1760 = 373.

    Activity = (Net counts × 100)/(time × eff % × Volume) Bq/L.

    Activity = (373 × 100)/(2700 × 44 × 0.2287) = 1.37 Bq/L.

    Error = Sqrt (2133 + 1760) = 62.39 = (62.39 × 100)/(2700 × 44 × 0.2287) = 0.23 Bq/L.

    ctivity = 1.37 ± 0.23 Bq/L.

  3. Gross alpha (As per 3, 4, 5 formula of text)


Sample counts (S) = 54; Background counts = 0.06 × 45 = 2.7; Net counts = 54 − 2.7 = 51.3.

Activity = (Net counts × 100)/(time × eff % × Volume) Bq/L.

Activity = (51.3 × 100)/(2700 × 37.3 × 0.2287) = 0.22 Bq/L.

Error = Sqrt (51.3 + 2.7) = 7.34 = (7.34 × 100)/(2700 × 37.3 × 0.2287) = 0.032 Bq/L.

Activity = 0.22 ± 0.032 Bq/L.



 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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