Basement data of the Terrestrial Radionuclide Level of Abuja Federal Capital Territory, (FCT), Nigeria

doi:10.4236/jep.2011.24039

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Journal of Environmental Protection, 2011, 2, 359-364

doi: 10.4236/jep.2011.24039 Published Online June 2011 (http://www.SciRP.org/journal/jep)

359

Basement Data of the Terrestrial Radionuclide

Level of Abuja Federal Capital Territory, (FCT),

Nigeria

Ayodeji Awodugba1, Adetayo Abioye1, Dauda Adekunle1, Omowumi Ologun1, Isiaka Oyekunle1, Ola-

tunde Oni1, Pascal Tchokossa2

1Department of Pure & Applied Physics, Ladoke Akintola University of Technology, Ogbomoso, Nigeria; 2Centre for Energy Re-

search and Development, Obafemi Awolowo University, Ile-Ife, Nigeria.

Email: [email protected]

Received October 18th, 2010; revised January 18th, 2011; accepted March 16th, 2011.

ABSTRACT

A total of 30 samples were collected from six different locations from of Abuja Federal Capital Territory (FCT), the

administrative capital of Nigeria which is situated in the central part of the country. The samples which were thor-

oughly prepared following known dosimetry procedures were analyzed for 40K, 238U and 232Th by the meth od of Gamm a

ray spectrometry using NaI(TL) detector coupled to a multichannel analyzer. The activity concen tra tions in the top so ils

in these locatio ns for 40K, 238U and 232Th range from 301 ± 26.52 to 928.84 ± 80.57, Not detectable (ND) value to 27.68

± 8.21 and 4.65 ± 1.46 to 22.48 ± 5.26 respectively. The average absorbed dose rate and the annual effective dose

equivalent were found to be 40.33 nGyh–1 and 49.46 µSv respectively. The value of annual effective dose equivalent is

low compared to the world average of 70 µSv specified by UNSCEAR for an outdoor effective dose, hence the chances

of radiological hazards to the health of the populace are generally low.

Keywords: Gamma Ray Spectrometry, Soil, Radionuclide s , Abuja FCT, Nigeria

1. Introduction

The occurrence of natural radionuclide in soil depends

primarily on the geological and geographical conditions,

and appears at different levels in the soil of each region

in the world [1-5]. For example, higher levels of radia-

tion are associated with igneous rock such as granite and

lower levels with sedimentary rocks. However, some

shales and phosphate rocks have relative high content of

those radionuclides [6-7]. The composition of these soils

and rocks in which the natural radionuclides which are

primarily 238U, 232Th and 40K are contained are the major

source of the terrestrial component of the natural back-

ground radiation and contributes significantly to the total

dose from natural sources.

Abuja, the federal capital city of Nigeria which is

home to about 800,000 people with ever increasing rural

to urban migration rate is located between latitude 8o34′N,

longitude 7o10′E and latitude 9o14′N, longitude 7o34′E

and has a land area of 713 km2 and density of 1091.9 km–2.

The city is also witnessing aggressive construction

works to provide houses for this influx of people. ome

papers have been published on the radioactivity level in

some regions of Nigeria like [8-12] and more recently on

the neutron activation analysis of soil and leaf samples

from different parts of Abuja Metropolis [13-14] there is,

however, no data is available for radionuclides content in

soil samples in this city from the survey of literature and

authors’ knowledge. This work therefore focuses on the

measurement of decay products of the 238U and 232Th

series as well as of the primordial radionuclide 40K. The

baseline data of this type will certainly be of importance

in making estimations of population exposures.

The map of Abuja FCT showing the locations from

where the soil samples were collected is shown in Figure

1 below.

2. Materials and Method

30 samples from the six districts of the Abuja Federal

Capital territory were collected from top soil up to a

depth of about 15 cm. The description of the samples is as

below; 1-Municipal area council, 2-Kwali area council,

-Abaji area council, 4-Kuje area council, 5-Gwagwal- 3

Basement Data of the Terrestrial Radionuclide Level of Abuja Federal Capital Territory, (FCT), Nigeria

360

Figure 1. Sampling locations in the municipal council areas of Abuja city.

ada area council and 6-Bwari area council for the six area

councils while S1a-FCDA, S1b-NCC, S1c-National As-

sembly, S1d-Aso-rock Villa, S1e-Area 10 Garki, S2a-

Bako, S2b-Danduma, S2c-Darfa, S2d-Tunga Tofa, S2e-

Kwali, S3a-Dapara, S3b-Sabo Gida, S3c-Abaji, S3d-

Lafia-Yaba, S3e-Alampa, S4a-Gana, S4b-Koma, S4c-

Lugbe, S4d-Kuje, S4e-Dafara, S5a-Dobi, S5b-Abuja

airport, S5c-Iddo, S5d-University of Abuja, S5e-Jalita,

S6a-Katampe, S6b-Aya Asokoro, S6c-Yanyan, S6d-

Mpape, S6e-Zuba are the samples collected from the exact

locations in the six area councils. Grass and pieces of

wood were physically eliminated from the samples while

pebbles and other unwanted sediments were sieved witha

2 mm mesh and store in plastic bags pending analysis.

All soil samples were dried at 100˚C for 1.5 hours and

kept in air-tight containers of 3 cm in diameter and 8 cm

in height for about 28 days in plastic containers previ-

ously washed and rinsed with diluted sulfuric acid before

analysis with the gamma-spectrometer [15] to ensure

secular equilibrium between 227Ra and 228Th with their

Basement Data of the Terrestrial Radionuclide Level of Abuja Federal Capital Territory, (FCT), Nigeria361

daughter products. Measurements on soil samples were

carried out with a NaI(TL) detector which was connected

to a multichannel analyzer. The same geometry was used

for each sample, which was counted in sealed containers

for 10 hrs (36,000 s). For calibration, a 500 cc sand stan-

dard radionuclide source was prepared using 0.07721 g

measured gravimetrically from a master radionuclide

solution source which was calibrated using a NaI(TL)

gamma spectrometer system. The gamma spectroscopy

analysis was based on a computer program which matched

gamma energy at various energy levels to a library of

possible isotopes. 232Th concentration in soil was deter-

mined by the 911 keV gamma lines of 228Ac while the

238U concentrations were determined by the 609 keV

gamma lines of 214Bi. The activity concentration of 40K

was determined from the peak areas at 1460 keV.

The total absorbed dose rate in air, D (nGyh–1) due to a

partial evaluation of the radiological hazard posed by the

exposure to these estimated radioactivity concentrations

at 0.1 m above the ground was estimated using the em-

pirical formula [16].

D = 0.042Ak + 0.428Au + 0.666ATh

where Ak, Au, and ATh are the specific activity concentra-

tion for K, U and Th respectively.

Also, using an outdoor occupancy factor of 0.20 and

the conversion factor of 0.70 SvGy–1 (UNSCEAR, 1988),

the annual effective dose equivalent (AEDE) from the

calculated outdoor terrestrial gamma radiation at 1 m

above the ground in Abuja FCT were calculated using

the relation

EDEADRA DCFOF T





where T is 8760 h.

3. Results

3.1. Radionuclide Levels of Soil Samples

Table 1 shows the dry-weight activity concentrations of

Table 1. Radioactivity concentrations of 40K, 238U series, and 232Th series in Abuja soil samples.

Municipal Area

Council Samples collected

In location

40K

(BqKg–1)

238U (226U)

(BqKg–1)

232Th (228Th)

(BqKg–1)

S1a 412.10 ± 36.06 15.93 ± 2.79 18.83 ± 3.98

S1b 503.18 ± 43.88 24.10 ± 4.56 22.48 ± 5.26

S1 S1c 801.56 ± 69.59 8.91 ± 2.11 13.78 ± 3.80

S1d 432.73 ± 37.77 10.98 ± 2.41 4.90 ± 1.03

S1e 529.72 ± 46.12 7.72 ± 1.38 4.65 ± 1.46

S2a 760.69 ± 66.06 16.91 ± 4.06 13.49 ± 3.54

S2b 928.84 ± 80.57 13.07 ± 5.94 14.78 ± 2.61

S2 S2c 587.08 ± 51.09 5.63 ± 1.90 10.31 ± 2.68

S2d 645.15 ± 56.05 21.87 ± 5.17 12.77 ± 2.93

S2e 486.23 ± 42.37 17.28 ± 2.43 7.80 ± 1.58

S3a 462.61 ± 40.37 9.87 ± 2.27 17.32 ± 3.75

S3b 325.41 ± 28.65 17.02 ± 2.86 19.38 ± 4.20

S3 S3c 794.44 ± 68.98 17.16 ± 4.86 21.86 ± 4.10

S3d 800.78 ± 69.49 19.81 ± 4.91 19.99 ± 5.43

S3e 409.48 ± 35.77 11.85 ± 2.76 9.56 ± 2.06

S4a 622.86 ± 54.17 24.46 ± 5.73 21.43 ± 3.09

S4b 375.72 ± 32.92 20.55 ± 4.98 11.35 ± 1.90

S4 S4c 499.54 ± 43.58 10.28 ± 2.97 13.28 ± 3.55

S4d 301.87 ± 26.52 ND 8.13 ± 1.77

S4e 661.71 ± 57.48 3.07 ± 0.17 12.22 ± 3.54

S5a 908.17 ± 78.80 8.28 ± 1.42 16.46 ± 4.03

S5b 923.57 ± 80.12 18.92 ± 4.85 19.96 ± 2.86

S5 S5c 739.56 ± 64.24 27.68 ± 8.21 6.33 ± 1.29

S5d 709 ± 61.66 22.89 ± 5.72 9.25 ± 2.32

S5e 494.34 ± 43.06 18.04 ± 4.61 9.45 ± 1.06

S6a 450.64 ± 39.35 10.43 ± 2.33 12.28 ± 2.54

S6b 492.60 ± 42.96 10.57 ± 3.51 18.66 ± 2.60

S6 S6c 491.47 ± 42.87 18.47 ± 4.92 22.33 ± 3.74

S6d 714.61 ± 62.05 24.92 ± 6.19 7.84 ± 1.87

S6e 587.41 ± 39.92 8.44 ± 2.17 9.92 ± 2.42

Basement Data of the Terrestrial Radionuclide Level of Abuja Federal Capital Territory, (FCT), Nigeria

362

the main gamma-emitting radionuclides of the K, U, and

Th series in the soil samples. For 40K concentration, Dan-

duma in Kwali area council has the highest value of

(928.84 ± 80.57) Bqkg–1 while the lowest value of 301.87

± 26.52 is found in Kuje in Kuje area council. 238U has its

highest and lowest values of 27.68 ± 8.21 and ND at Iddo

(Gwagwalada area council) and Kuje (Kuje area council)

respectively.

NCC has the highest value of 232Th of 22.48 ± 5.26

while the lowest value of 4.65 ± 1.46 is found in Garki

area 10 all in the municipal area council. The mean activ-

ity concentrations of 40K, 238U and 232Th in Abuja FCT sur-

face soil samples area are 596.92, 14.84 and 13.36 Bqkg–1,

respectively.

3.2. Absorbed Dose Rate in Air (ADRA)

The results of the total absorbed dose rate at 1.0 m above

the soil are summarized in Table 2. It varies between

18.09 - 60.20 nGyh–1 with an average of 40.33 nGyh–1.

The highest dose rate was recorded at location 22 with

absorbed dose rate of 60.20 nGyh–1 which also revealed

the overall highest contribution in activity concentration

for all the radionuclides identified.

3.3. Annual Effective Dose Equivalent (AEDE)

Arising from this, the AEDE were found to be between

22.19 and 73.82 µSv for Kuje and airport respectively

while the average AEDE of 49.46 µSv is recorded.

Table 2. Radioactivity concentrations of 40K, 238U series, and 232Th series in Abuja soil samples, the absorbed dose rates from

gamma radiation and the annual effective dose equivalent.

S/N Sample 40K (BqKg–1) 238U (BqKg–1) 232Th (BqKg–1) Absorbed Dose Rate in

air nGyh–1) Annual effective dose

equivalent (µSv)

1 S1a 412.12 ± 36.66 15.93 ± 2.79 18.83 ± 3.98 36.68 44.98

2 S1b 503.18 ± 43.38 24.10 ± 4.56 22.48 ± 5.26 34.98 42.90

3 S1c 801.56 ± 69.59 8.91 ± 2.11 13.78 ± 3.50 40.99 50.27

4 S1d 432.73 ± 37.77 10.98 ± 2.47 4.90 ± 1.03 26.15 32.07

5 S1e 529.72 ± 46.12 7.72 ± 1.38 4.65 ± 1.46 25.94 31.81

6 S2a 760.69 ± 66.06 16.91 ± 4.06 13.49 ± 3.54 48.18 59.09

7 S2b 928.84 ± 80.57 13.07 ± 5.94 14.78 ± 2.61 54.46 66.79

8 S2c 587.08 ± 51.09 5.63 ± 1.90 10.31 ± 2.68 21.02 25.78

9 S2d 645.15 ± 56.05 21.87 ± 5.17 12.77 ± 2.93 44.98 55.16

10 S2e 486.23 ± 42.37 17.28 ± 2.43 7.80 ± 1.58 22.52 27.62

11 S3a 462.21 ± 40.37 9.87 ± 2.27 17.32 ± 3.75 35.18 43.14

12 S3b 325.41 ± 28.65 17.02 ± 2.86 19.32 ± 4.20 33.84 41.50

13 S3c 794.44 ± 68.98 19.81 ± 4.91 21.86 ± 4.10 55.27 67.78

14 S3d 800.78 ± 69.49 11.85 ± 2.76 19.99 ± 5.43 55.44 67.99

15 S3e 409.48 ± 35.77 24.46 ± 5.23 9.56 ± 2.06 28.65 35.14

16 S4a 622.86 ± 54.17 20.55 ± 4.98 21.43 ± 3.09 50.93 62.46

17 S4b 375.72 ± 32.92 10.28 ± 2.97 11.35 ± 1.90 32.16 39.44

18 S4c 499.54 ± 43.58 10.28 ± 2.97 13.28 ± 3.55 34.24 41.99

19 S4d 301.87 ± 26.52 ND 8.13 ± 1.77 18.09 22.19

20 S4e 661.71 ± 57.48 3.07 ± 0.17 12.22 ± 3.54 37.25 45.68

21 S5a 908.17 ± 78.80 8.28 ± 1.42 16.46 ± 4.03 52.66 64.58

22 S5b 923.57 ± 80.12 18.92 ± 4.85 19.96 ± 2.86 60.20 73.82

23 S5c 739.56 ± 64.24 27.68 ± 8.21 6.33 ± 1.29 47.15 57.82

24 S5d 709.98 ± 61.66 22.89 ± 5.72 9.25 ± 2.32 45.80 56.17

25 S5e 494.34 ± 43.06 18.04 ± 4.61 9.45 ± 1.06 34.79 42.67

26 S6a 450.64 ± 39.35 10.43 ± 2.33 12.28 ± 2.54 31.58 38.73

27 S6b 492.60 ± 42.96 10.57 ± 3.51 18.66 ± 2.60 37.65 46.17

28 S6c 491.47 ± 42.87 18.47 ± 4.92 22.33 ± 3.74 43.44 53.27

29 S6d 714.61±62.05 24.92± 6.19 7.84 ± 1.87 45.93 56.33

30 S6e 587.41±39.92 8.44 ± 2.17 9.92 ± 2.42 34.90 42.80

Average 5 9 6 .92 ± 51.42 14.84 ± 3.61 13.36 ± 2.90 40.33 49.46

Basement Data of the Terrestrial Radionuclide Level of Abuja Federal Capital Territory, (FCT), Nigeria363

4. Discussion of Results

Figure 2 shows the activity concentrations of 40K, 238U

and 232Th in the 30 samples collected. The activity con-

centration of the collected soil samples compare rea-

sonably well with the worldwide average concentrations

of 400, 40, 40 Bqkg–1, respectively [17] as reported by

UNSCEAR. Also, these values for U and Th values are

less than the world average while the soil in Abuja has

higher concentrations of K, perhaps due to the geological

features of the city.

Figure 3 shows the AEDE values which were found to

be between 22.19 and 73.82 µSv for Kuje and airport

respectively while the average AEDE of 49.46 µSv is

recorded. This value represents about 70.7% of the world

average of 70 µSv (UNSCEAR, 1988). However, this

value is just about 4.9% of the 1.0 mSv recommend by

the International Commission on Radiological Protection

(ICRP, 1992) [18] as the maximum permissible AEDE

for members of the public. This value clearly establishes

the fact that there is no potential danger to the health of

the citizenry of the Abuja Federal Capital Territory (FCT)

due to radiological hazards.

Figure 2. Pictorial representation of the 40K, 238U and 232Th in the samples.

Figure 3. Pictorial representation of the Annual Effective Dose Equivale nt (AEDE).

Basement Data of the Terrestrial Radionuclide Level of Abuja Federal Capital Territory, (FCT), Nigeria

364

5. Conclusion

A total of 30 measurements were made covering the

sampling stations in Abuja FCT comprising six area

councils. The concentration of the radionuclides 40K, 238U,

and 232Th in soil samples were measured. The absorbed

dose rate and annual effective dose equivalent were also

calculated. The value of the annual effective dose equiva-

lent of 40.33 nGyh–1 is low compared to the world aver-

age of 70 µSv specified by UNSCEAR for an outdoor

effective dose, hence the chances of radiological hazards

to the health of the populace is generally low. However,

it may be necessary to determine the radioactivity con-

centrations in soils of other adjoining states bordering

Abuja city to be able to draw better conclusions on the

radioactivity levels in the central part of Nigeria. Also,

the results may be useful as reference data for monitoring

possible radioactivity pollutions in the future.

6. Acknowledgements

The technical support of the Center for Energy Devel-

opment of the Obafemi Awolowo University, Ile-Ife,

Nigeria is appreciated. Mrs. Awodugba C.S. efforts at

proof-reading the manuscript is also equally valued.

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