Ionizing Radiation emitted from radionuclide has an adverse effect on human health. A continuing population exposure to naturally occurring radioactive materials (NORMS) found in our environment is one of the major scientific subjects that attract public attention. The assessment of radionuclide content of shore sediments of river Benue-North Central Nigeria was carried out using gamma-ray spectrometry. The activity concentrations of U-238, Th-232 and K-40 were found to have an average concentration of 1.17, 3.31 and 405.95 Bq ·kg -1 respectively. The values gotten from present study were compared with the world average values. World average values of U-238, Th-232 and K-40 are 50 Bq ·kg -1, 50 Bq ·kg -1 and 500 Bq ·kg -1 respectively. The mean concentration of daughter radionuclides generated from U-238, Th-232 was 4.32, 10.37, 5.24, 3.86, 11.87, and 6.52 for Bi-212, Pb-212, Bi-214, Pb-214, Ra-226 and Ac-228, respectively. The mean of the absorbed dose, Annual effective dose equivalent, for radium equivalent activity, and external hazard index, were evaluated to be 19.45 nGy ·h -1, 23.82 μSv ·y -1, 37.16 Bq ·kg -1, 0.10 mSv ·y 1, below the permissible limit of 57 nGy ·h -1, 70 μSv ·y -1, 370 Bq ·kg -1 and 1 mSv ·y -1 respectively. These shore sediments from river Benue are therefore, radiologically safe for construction and other domestic and industrial purposes.
Trace numbers of radionuclides such as U-238, U-235 and Th-232 occur in the soil, earth crust, water, air and vegetable [
Exposure to ionizing radiation may be as a result of rays generated from the outer space and from the solar system and also naturally occurring radionuclides present in the environment, such as radionuclides from sediment, crusts from the rock, building material, air, in our food and also human body [
Particulate matter such as dust particles, pollen grains, tiny particle of sand, etc., which can be transported from one place to another, by river or ocean flow is known as sediments. This can be deposited as solid particles on the coastline, river bank or to the environments [
Radiation emitted from our terrestrial environment has been substantially investigated in different locations of the world. However, little has been done in this regards in North Central Nigeria. High radiation emitted from some part of the North Central Nigeria, especially in the Akwanga area, may be as a result of the geology and geographical altitude of the area [
This research work focuses on three regions along the coastline of river Benue within Makurdi Metropolis. The Benue State capital, Makurdi is located between latitudes 7˚35˚-7˚53N and longitude 8˚24-8˚42E. Its covers a land area of 800 km2 and has a population of 300,000 people (2006 census data). The city is around the flood plan of Benue river, which bisects the city into the northern and southern parts [
River sediment samples were collected at three locations of river Benue within Makurdi Metropolis, namely around (NBRB), New Garage Riverbank (NGRB) and Wadata Market Riverbank (WMRB). This location was selected based on the high level of human activities such as fishing, vegetable farming, extraction of sand and gravel etc. Hand auger was used to collect the samples, at distance of 1 - 2 metre away from the river edge and the middle of the river. These samples were packed in small plastic bags and sealed to prevent Rn-222 and Rn-220 from escaping out of the samples. The residual moisture in the samples was removed by placing them in an oven, and was heated to maintain a temperature of about 110˚C for 24 hours, a gamma spectrometric assembly with a high purity germanium detector (HPGe). Located at Namibia University of Science and Technology Postgraduate laboratory was then used to count the sample for 28800 seconds (8 hours). The detector contains 70% efficiency and a resolution of 1.8 keV at the 1.3 MeV of Cobalt-60 source. The HPGe detector was calibrated using standards of known concentration of radioisotopes for energy and efficiency before measurements were taken. The background was monitored and subsequently subtracted from the spectrum of gamma radiation from each sample to obtain net counts for the samples. The spectrum of each standard was later used to obtain energy calibration.
The absorbed dose rate (D), Annual effective Dose equivalent (AEDE), Radium equivalent activity (Raeq), and External hazard index (Hex) were estimated using Equations (1)-(4) respectively [
D ( nGy ⋅ h − 1 ) = 0.462 A Ra + 0.604 A Th + 0.0417 A K (1)
where D represent the absorbed dose rate, ARa, ATh and AK represent the concentration of Ra-226 (U-238), Th-232 and K-40, respectively.
AEDE ( μSv ⋅ y − 1 ) = D ( nGy ⋅ h − 1 ) × 8760 h × 0.2 × 0.7 Sv ⋅ Gy − 1 × 10 − 3 (2)
where the conversion coefficient is represented as 0.7 Sv∙Gy−1 and 0.2 is the outdoor occupancy factor.
R a e q ( Bq ⋅ kg − 1 ) = A Ra + 1.43 A Th + 0.077 A K (3)
where ARa, ATh and AK are the activity concentration of Ra-226, Th-232 and K-40 in Bq∙kg−1, respectively.
H E X = ( A Ra 370 ) + ( A Th 259 ) + ( A K 4810 ) ≤ 1 (4)
Values of the external hazard index must not be more than the required limit, this help to reduce the effect of radiation hazard from the environment. The maximum value of Hex equal to unity corresponds to the upper limit of radium equivalent activity 370 Bq∙kg−1 [
The activity concentration of U-238, Th-232 and K-40 were measured from all the sample collected along the river coastline within Makurdi municipal area. The mean concentration of the radionuclides for the three locations were calculated as presented in
Locations | Activity Concentration (Bq/kg) | ||
---|---|---|---|
U-238 | Th-232 | K-40 | |
NBRB | 2.01 | 3.17 | 571.91 |
NGRB | 0.52 | 2.78 | 571.94 |
WMRB | 0.98 | 3.99 | 73.98 |
Mean Standard Deviation | 1.17 ±0.62 | 3.31 ±0.50 | 405.94 ±234.86 |
Maximum | 2.01 | 3.99 | 571.94 |
Minimum | 0.52 | 2.78 | 73.98 |
The presence of daughter radionuclides from U-238 and Th-232 such as Bi-212, Bi-214, Pb-212, Pb-214, Ra-226 and Ac-228 were detected in all the samples as presented in
• Use NB
New Bridge River Bank “NBRB” Sediment Sample recorded the highest activity Concentration of U-238, Bi-214, Pb-214 and Ac-228 while Wadata Market River Bank “WMRB” Sediment Samples recorded the highest activity Concentration of Th-232, K-40 and Ra-226. The highest concentration of Bi-212 and Pb-212 were found in sediment samples from New Garage River Bank “NGRB” Site.
Location(RBM) | Activity Concentration (Bq/kg) | |||||
---|---|---|---|---|---|---|
Bi-212 | Pb-212 | Bi-214 | Pb-214 | Ra-226 | Ac-228 | |
NBRB | 5.73 | 9.84 | 6.57 | 5.55 | 18.30 | 11.22 |
NGRB | 7.05 | 15.82 | 3.87 | 3.44 | 8.46 | 5.12 |
WMRB | 0.17 | 5.44 | 5.28 | 2.60 | 8.86 | 5.12 |
Mean Standard Deviation | 4.32 ±2.98 | 10.37 ±4.25 | 5.24 ±1.10 | 3.86 ±1.24 | 11.87 ±4.55 | 6.52 ±2.94 |
Maximum | 7.05 | 15.82 | 6.57 | 5.55 | 18.30 | 11.22 |
Minimum | 0.17 | 5.44 | 3.87 | 2.60 | 8.46 | 3.21 |
The absorbed dose (D), Annual effective dose equivalent (AEDE), Radium equivalent activity (Raeq) and Hazard index from river Benue Sediments were found to be 19.45 nGy∙h−1, 23.82 μSv∙y−1, 37.16 Bq∙kg−1 and 0.1 mSv∙y−1 respectively as shown in
Locations | Activity Concentration (Bq/kg) | Reference | ||
---|---|---|---|---|
U-238 | Th-232 | K-40 | ||
River Benue, Makurdi | 1.17 | 3.31 | 405.94 | Present study |
Osun River, Nigeria | 24.00 | 35.70 | 162.38 | Oyebanjo et al., 2012 |
Charfassion Island, Bhola Banglandesh | 16.82 | 32.84 | 743.52 | Nizam et al., 2013 |
Coastline of Erongo Region Namibia | 173 | 37.77 | 441.78 | Onjefu et al., 2016 |
Location(RBM) | D (nGy∙h−1) | AEDE (µSv∙y−1) | Raeq (Bq∙kg−1) | Hex |
---|---|---|---|---|
NBRB | 26.57 | 32.59 | 50.58 | 0.14 |
NGRB | 25.77 | 31.60 | 48.53 | 0.13 |
WMRB | 5.95 | 7.30 | 12.38 | 0.03 |
Mean | 19.42 | 23.82 | 37.16 | 0.10 |
Maximum | 26.57 | 32.59 | 50.58 | 0.14 |
Minimum | 5.95 | 7.30 | 12.38 | 0.03 |
Location(RBM) | D (nGy∙h−1) | AEDE (µSv∙y−1) | Raeq (Bq∙kg−1) | Hex | Reference |
---|---|---|---|---|---|
River Benue Makurdi | 19.42 | 23.82 | 37.16 | 0.10 | Present study |
Charfassion Island, Bhola, Banglandes | 58.61 | 0.07 | 120.93 | - | Nizam et al., 2013 |
Coastline of Erongo Region Namibia | 114.41 | 339.36 | - | - | Onjefu et al., 2016 |
Worldwide Average | 57 | 70 | <370 | <1 | UNSCEAR, 2000 |
respective permissible levels of 57 nGy∙h−1 [
The following natural radionuclides U-238, Th-232, K-40 and their progenies, Bi-212, Pb-214, Pb-214 Ra-226 and Ac-228 were detected in the shore sediments of River Benue along Makurdi municipality area. Their activity concentration and calculated radiological parameter (Absorbed dose D, Annual effective dose equivalent AEDE, Radium equivalent Raeq, and External hazard index Hex) were found to be below their respectively permissible safety limits.
This research study was carried out along the bank of River Benue, Makurdi, Nigeria. Future research studies on Activity Concentration of Radionuclide, can also be carried out in the industrial area of the City of Makurdi, where human activities are of high increase. This will help investigate and monitor the amount of ionizing radiation emitted to the environment.
We sincerely appreciate Namibia University of Science and Technology for assisting us during gamma spectrometry analysis.
Sombo, T., Emmanuel, E. and Ugwuanyi, J. (2017) Assessment of Radionuclide Content of Shore Sediments Collected from the Bank of River Benue, North-Central Nigeria. Journal of Geoscience and Environment Protection, 5, 57-65. https://doi.org/10.4236/gep.2017.512004