Journal of Environmental Protection, 2011, 2, 418-423
doi: 10.4236/jep.2011.24047 Published Online June 2011 (http://www.SciRP.org/journal/jep)
Natural Radionuclide Concentrations and
Radiological Impact Assessment of River
Sediments of the Coastal Areas of Nigeria
Olatunde Michael Oni1, Idowu Peter Farai2, Ayodeji Oladiran Awodugba1
1Department of Pure and Applied Physics, Ladoke Akintola University of Technology, Ogbomoso, Nigeria; 2Department of Physics,
University of Ibadan, Ibadan, Nigeria.
Received November 13th, 2010; revised February 8th, 2011; accepted March 16th, 2011.
ABSTRACT
This work was carried out to measure the radioactivity level in the coastal areas of Nigeria by gamma counting of river
sediment samples and assess the radiological impact associated with the use of the river sediments as building material.
The method of gamma spectrometry with a 7.6 cm by 7.6 cm NaI (Tl) detector was employed in determining 40K, 238U
and 232Th levels in 95 and 38 sediment samples respectively collected from representative sites in the oil producing and
non oil producing coastal areas of Nigeria. Results of the samples assayed showed that the radioactivity concentrations
of 40K, 226Ra and 228Ra in the sediment samples of oil producing areas range from 95.4 to 160.0; 7.6 to 31.0 and 9.5 to
41.6 Bqkg–1, respectively. The respective means were calculated as 122.39 ± 47.49; 18.93 ± 12.53 and 29.31 ± 18.67
Bqkg–1. In the sediment samples from the non oil producing areas, the respective mean values are 88.48 ± 8.22, 14.87
± 3.51 and (16.37 ± 3.87) Bqkg–1. Statistical analysis of the results showed that there is no significant difference be-
tween the radionuclide concentration of the sediment samples from different rivers in the oil producing and non oil
producing coastal areas, except for 40K. The values of the natural radionuclide concentrations however translate to the
determination of the radiological impact assessment values. The values of the radiological assessment indices obtained
were observed to be lower than limits internationally reported and recommended for building materials. It could there-
fore be reported that the operations of the oil companies in the coastline, involving use of radioactive materials have
not contributed adversely to the radioactivity level of the river sediments and that the use of river sediments as building
material in the coastal areas of Nigeria poses no radiological risk.
Keywords: Radiological Risk Indices, River Sediments In Coastal Area, Gamma Spectrometery
1. Introduction
Ionising radiations in any environment is traceable to
either natural or artificial sources. The artificial sources
are largely due to medical and industrial activities. In the
coastal areas of Nigeria, the dominating industry is the
oil production and exploration. Apart from medical ex-
posure, the petroleum industry is the largest importer and
consumer of radioactive materials. The uses of radioac-
tive sources in the industry cover both upstream and
downstream operations such as well-logging, automated
ionizing radiation gauge, radiography and application of
radiotracers in oil well management, reservoir studies
and leak detection in pipelines.
Despite conscious efforts and measures to ensure safety,
there is a possibility, based on accident, mishandling of
equipment, improper discharge, loss and theft, that ra-
dioactive materials of natural and artificial sources may
pollute the terrestrial and the aquatic environment of the
coastal areas which are mainly networks of rivers and
creeks. Following different pathways such as erosion
run-off and rainfall, large amount of these radioactive
materials end up in the aquatic environment. Due to
gravitational settling and other depositional phenomena,
the highest proportion of the radioactive materials is
mainly found in the sed iment compartment of the aqu atic
ecosystem.
The exposure of man to gamma radiation from these
radionuclides in the aqu atic environment is not limited to
the internal exposure due to ingestion through the con-
sumption of contaminated aquatic foods. The use of river
sediments as a constituent of building materials for floor-

Natural Radionuclide Concentrations and Radiological Impact Assessment of River Sediments 419
of the Coastal Areas of Nigeria
ing, plastering and in moulding bricks in the coastal areas
of Nigeria has the probability of increasing the external
exposure level to man if such sediments have high con-
centratio n of radionu clides.
In other parts of the world, research activities have been
done in recent time on the contribution to radiation ex-
posure from building materials [1-4]. Reports on related
work on building materials are few and scanty in Nigeria .
Among the reported few are [5] and [6]. In 2009, the
radiological safety assessment of surface-water dam sedi-
ments in the south west ern Nigeria was performe d by [ 7].
In the building, it has been pointed ou t that the highest
concentrations of radionuclides are found in mineral-
based materials such as stone, sand, bricks, cement and
sediments [8].Though these radionuclides are known to
be widely distributed in the environment, their concen-
trations have been found and reported [9] to depend on
the geological setting of a particular environment, and
such they vary from place to place.
The objective of this work however is to determine th e
radioactivity level of naturally occurring 40K, 238U and
232Th in river sediments across the oil producing coastal
areas of Nigeria. The measured radioactivity concentra-
tion would thereafter translate to the calculation of the
impact indices in order to assess the radiological implica-
tion of the use of sediments as a constituent of building
materials in the area, which for over four decades have
been witnessing the use of v arious types and strengths of
radionuclide by the oil companies [10] being accused of
polluting the environment of the coastal area in various
ways and degrees.
2. Materials and Methods
Sediment samples were collected at different points along
twenty major rivers in the oil producing coastal area
while seven locations were samples for the non oil pro-
ducing area. The spacing of the points, which vary be-
tween 100 and 500 metres was determined largely by
accessibility. Conscious efforts were made to sample
around operational sites of the oil companies at lo cations
not exceeding 1 km from the operational sites. In all, a
total of 133 sediment samples were collected. The map
of the areas of sample collection with oil facilities pre-
sent is shown in Figure 1.
At each sampling location, divers were provided with
grab samplers to collect the river sedim ents which consi st
Figure 1. Map of study area showing locations where samples were collected.

Natural Radionuclide Concentrations and Radiological Impact Assessment of River Sediments 420 of the Coastal Areas of Nigeria
of particulate organic and inorganic matter. After drain-
ing off water, each sample was bagged and labeled. The
samples were oven dried at a temperature of 105˚C be-
fore pulverization [11] and [12]. The dried samples were
then packed 200 g by mass in labeled cylindrical plastic
containers of uniform base diameter of 5.0 cm which
could sit on the 7.6 cm by 7.6 cm NaI (Tl) detector.
The plastic containers were tightly covered, sealed and
left for 28 days prior to counting, for attainment of secu-
lar equilibrium between 238U and 232Th and their respec-
tive progenies [11,13,14].
The radionuclide concentration in the sediment sam-
ples was measured with a well calibrated [7] low level
gamma counting spectrometer consisting of a 7.6 cm by
7.6 cm NaI (Tl) detector (Model 802 series) manufac-
tured by Canberra Inc. The detector was coupled to a
Canberra series 10 plus multi-channel analyzer (MCA)
through a preamplifier base. The photopeak regions of
40K (1.46 MeV); 214Bi (1.76 MeV) and 208Tl (2.165) re-
spectively were used for the analysis 40K, 238U and 232Th
in the samples. A region of interest was created around
the 0.662 MeV to detect and measure any trace of 137Cs
as an index of artificial radionuclides. All samples were
counted at a constant geometry and for a constant time of
10 hours.
3. Radiological Indicators
Following the measurement of the radionuclide concen-
trations in the samples, the radium equivalent activity
(Raeq), external hazard index (Hex) and internal hazard
index (Hin) were used as radiological indicators to esti-
mate the radiological implications of the use of the sedi-
ment samples as building materials. Assuming secular
equilibrium between 40K, 232Th and 238U and their proge-
nies, Raeq, the most frequently used indicators for the
assessment of the gamma-ray radiation hazard to humans
from environmental samples is defined [15] as
10 10
130 7
eqKTh Ra
RaCC C (1)
where CK, CTh and CRa are th e respective activity con cen-
trations of 40K, 232Th and 226Ra, measured in Bqkg–1 of
the dry weight.
The external hazard index, Hex, commonly used to
evaluate the indoor radiation dose rate due to external
exposure to gamma radiation from natural radionuclides
in building materials can be calculated from the expres-
sion of [16] presented as
1
4810259 370
Th Ra K
ex
CC C
H
(2)
where CK, CTh and CRa are the activities concentrations of
40K, 232Th and 226Ra (in Bq/kg) respectively. This expres-
sion indicates that the value of this index must be less
than unity in order to keep the radiation hazard to be
insignificant. Thus, the maximum values of Hex equal
to unity correspond to the upper limit of Raeq being
370 Bq/kg.
Considering the hazardous nature of internal exposure
to 222Rn and its decay products to the lungs and other
respiratory organ, and the fact that reducing the 226Ra to
half of its maximum acceptable limit for external expo-
sure only will make Hin, the internal hazard index less
than unity. Thus Hin is usually estimated as
4810259 185
Th Ra K
in
CC C
H (3)
Furthermore, following the definition of the absorbed
dose rate in indoor air D (nGyh–1) given by [17,18] and
[19] from natural radionuclides inside a standard room of
dimensions 4 m × 5 m × 2.8 m, and following the as-
sumption [20] that the wall thickness is 20 cm and the
density of the aggregates is 2.35 × 103 kgm–3, the frac-
tional contribution to the absorbed dose rate in air from
the activity concentrations of the three radionucl ides yields


1
.0.080 1.10.92

K
Th Ra
DnGyhCCC (4)
The absorbed dose rate in air however translates to the
annual effective dose rate indoors for individuals using
the values of the absorbed dose rate in indoor air, D
(nGyh–1), the indoor occupancy time and the absorbed
dose to the effective dose conversion factor(0.7 SvGy–1).
Assuming an indoor occupancy factor of 0.8, the annual
occupancy time is approximately 7000 hy–1. Hence the
effective dose rate is estimated using:





11
16
..7000 .
0.7 .10
E

1
H
mSvyDnGy hhy
Sv Gy





(5)
4. Results and Discussion
The range for the activity concentration due to 40K was
95.4 to 160.0 Bqkg–1 while those for 238U and 232Th were
respectively 7.6 to 31.0 and 9.5 to 41.6 Bqkg–1. These
ranges, belonging to the same population has been rep-
resented by a single mean. To establish this, variation in
the radionuclide concentration levels among the twenty
(20) sampled rivers in the oil producing area were sub-
jected to statistical test using analysis of variance
(ANOVA) at 95% confidence level. The result (Fcalculated
= 0.90 < Ftable = 1.86, p = 0.58 at df = 19) showed that
there is no significant difference between the radionu-
clide concentration of the sediment samples from the
different rivers in the oil producing coastal areas. Simi-

Natural Radionuclide Concentrations and Radiological Impact Assessment of River Sediments 421
of the Coastal Areas of Nigeria
larly, for the non oil pro ducin g coastal areas, the result of
the ANOVA (Fcalculated = 1.56 < Ftable = 2.99, p = 0.24 at
df = 6) also revealed a non significant difference. Based
on these findings, the representative means of the spe-
cific activities of the natural radionuclides in river sedi-
ments of the oil producing and non oil producing coastal
areas grouped into different states of the country, Nigeria
is presented in Table 1.
The errors presen ted with the means of the radioactiv-
ity concentrations of 40K, 238U and 232Th in the sediment
samples are the standard deviations in the values ob-
tained at different points along each river.
However, since no significant difference exists among
all the samples, the grouped mean of the samples from
each of the two areas are determined and tested for pos-
sible difference based on the area of collection using t-
test at 0.05 level of significance. Results of the test pre-
sented in Table 2 shows that there exits a significant
difference between the means of 40K in the sediment
samples from oil producing coastal areas and those from
the non oil producing areas, while 238U and 232Th were
observed not to be significantly different at 0.05 level of
significance. This observed difference in the 40K level
may be explainable from the geological composition of
the sediment which have been reported to be more sedi-
mentary in the Niger Delta region of the coastal areas
[21].
The radium equivalent and the results of other radio-
logical indices as shown in Table 3 revealed that despite
sediment samples from Cross River having the maximum
level of radium equivalent activity, based on the maxi-
mum acceptable external dose level of 1.5 mGy, corre-
sponding to radium equivalent of 370 Bqkg–1 for build-
ing materials [22], the values of the mean radium
equivalent activity for the sediments from the coastal
areas are all below the recommended limit.
Similarly, the observed results of other radiological
indicators show that external hazard index, internal haz-
ard index and the annual effective dose rate are all less
than unity, hence they are below the recommended lim-
its.
The absorbed dose rate in each of the states of the
coastal area of Nigeria is below the worldwide mean of
84 nGyh–1 for soil matrix as reported in [23].
Table 1. Mean concentrations of the radionuclides in the sediment samples.
Mean concentrations (Bqkg–1)
State No. of rivers No of sediment
collected 40K 238U 232Th
Oil producing
Delta 8 39 132.80 ± 15.89 22.37 ± 6.9 23.04 ± 1.64
Bayelsa 5 23 122.69 ± 14.77 15.82 ± 1.91 21.01 ± 2.45
Rivers 4 18 109.37 ± 12.03 16.26 ± 2.45 21.19 ± 1.94
Cross Rivers 1 5 99.74 ± 11.86 30.09 ± 1.26 41.55 ± 1.78
Akwa Ibom 2 10 147.38 ± 12.94 10.12 ± 1.02 39.76 ± 1.86
Non oil Producing
Ogun 2 10 79.65 ± 11.81 16.46 ± 1.97 16.93 ± 1.38
Lagos 5 28 97.31 ± 16.41 13.28 ± 2.54 39.76 ± 1.86
Table 2. Statistics of test of significance between radioactivity concentrations in sediments from oil producing and non oil
producing coastal areas.
N
40K (Bqkg–1) 238U (Bqkg–1) 232Th (Bqkg–1)
Oil producing 20 122.39 ± 47.49 18.93 ± 12.53 29.31 ± 18.67
Non-oil producing 7 88.48 ± 8.22 14.87 ± 3.51 16.37 ± 3.87
tcalculated 3.28 0.93 1.66
ttable (α = 0.05, df = 25) 1.71 1.71 1.71
p value 0.001 0.180 0.054

Natural Radionuclide Concentrations and Radiological Impact Assessment of River Sediments 422 of the Coastal Areas of Nigeria
Table 3. Values of the radiological indices.
State Raeq H
ex(Bqkg–1) Hin(Bqkg–1) D(nGyh–1) HE(mSvy–1)
Oil producing
Delta 65.49 0.177 0.237 56.54 0.277
Bayelsa 55.27 0.149 0.192 47.48 0.232
Rivers 54.94 0.148 0.192 47.01 0.230
Cross Rivers 97.11 0.262 0.343 81.36 0.398
Akwa Ibom 78.25 0.211 0.238 64.83 0.317
Non oil producing
Ogun 46.77 0.126 0.170 40.13 0.196
Lagos 43.35 0.117 0.153 37.39 0.183
5. Conclusions
The natural radioactivity concentrations of a total of 133
samples of sediment collected from twenty-seven(27) ma-
jor rivers in the coastal areas of Nigeria have been deter-
mined.
Statistical analysis of the results showed that there is
no significant difference between the radionuclide con-
centration of the sediment samples from different rivers
in the oil producing and non oil producing coastal areas
except for 40K. The values of these natural radionuclide
concentrations however translate to the determination of
the radiological impact assessment values. The values of
the radiological assessment indices obtained were ob-
served to be lower than limits international ly reported and
recommended for building materials. It could therefore
be reported that the oper ations of the oil companies in the
coastline, involving use of radioactive mater ials have not
contributed adversely to the radioactivity level of the
river sediments and that the use of river sediments as
building material in the coastal areas of Nigeria poses no
radiological risk. As no artificial radionuclide is observed
in the samples assayed, the results presented in this work
may thus serve as yardstick for future work in this
coastal area.
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