Vol.5, No.11, 1145-1153 (2013) Natural Science
http://dx.doi.org/10.4236/ns.2013.511141
Natural background radiation dose rate levels and
incidences of reproductive abnormalities in high
radiation area in Abeoku ta, Southwestern Nigeria
Nnamdi Norbert Jibiri*, John Bamidele Famodimu
Radiation and Health Physics Research Laboratory, Department of Physics, University of Ibadan, Ibadan, Nigeria;
*Corresponding Author: *[e-mail], *
Received 23 July 2013; revised 23 August 2013; accepted 30 August 2013
Copyright © 2013 Nnamdi Norbert Jibiri, John Bamidele Famodimu. This is an open access article distributed under the Creative
Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original
work is properly cited.
ABSTRACT
A 10 y (1999-2008) birth records from two pu-
blic and most accessible maternity hospitals
locally in the city of Abeokuta, Nigeria were used
to investigate the possible association of high
outdoor gamma radiation exposure on repro-
ductive abnormalities in the city. From the de-
livery record of 11,923 births in the period under
study, a total number of 485 incidences of re-
productive abnormalities were recoded. These
incidences comprise 228 multiple births, 190
still births and, 67 premature births. Using the
available terrestrial gamma radiation exposure
data for the city and different reproductive ab-
normalities, regression assessment was carried
out using the Pearson Product Moment (PPM)
correlation statistics. The correlation showed
that the incidences of reproductive abnormali-
ties and the radiation dose levels were nega-
tively correlated and correlation coefficient val-
ues were very low for each of the reproductive
abnormalities considered. Factors such as so-
cio-economic potentials of patients, dietary and
other environmental factors may have substan-
tial influence on the reproductive defects in the
area other than radiation. However, the present
study has added to the radiometric information
needed in understanding the relationship be-
tween natural outdoor radiation exposure and
occurrences of reproductive abnormalities in
areas of high radiation in the country.
Keyw ords: High Background Radiation; Gamma
Radiation Dose Rates; Reproductive Ab normalities;
Abeokuta Nigeria
1. INTRODUCTION
Assessment of impact of natural radioactivity on hu-
mans is very important because it will help in evolving
national average for human environments, which can
serve as a bench mark for introducing new technologies
and lifestyles, thus helping to improve the state of health
of man in areas with essentially high natural radiations.
Due to the nature of the environment, man is continu-
ously exposed to varying amount of ionizing radiation
doses. It has been established that out of the total radia-
tion dose received by man on the earth, about 96.1% is
from natural sources while the remaining percentage is
by man-made sources [1]. The main components of
natural background radiations are extraterrestrial cosmic
rays and the radiation due to the radioactivity of some
primordial elements in the earth principally from decay-
series elements, which are 238U, 232Th and non-decay 40K.
Apart from the inevitable natural background radiation
sources, the radiation exposure to man in his environ-
ment can also arise from activities such as mining, ra-
diological accidents and nuclear weapon testing. It has
been a global interest to carry out the study of naturally
occurring radiation and environmental radioactivity, and
the results from such studies are being used to assess the
radiation hazard of the exposed population. For example
in Iran, studies [2,3] conducted on inhabitant of Ramsar
which is an area with high level of natural radiation
showed that there were no significant differences in the
frequencies of any mental and physical disabilities as
well as malignancies between residents of normal and
high background radiation areas. Their results showed no
significant increase in the frequency of death, abortion
and mental depression among inhabitants in high back-
ground radiation area. Between August 1995 and June
2004, a clinical and cytogenetical observation of mal-

N. N. Jibiri, J. B. Famodimu / Natural Science 5 (2013) 1145-1153
1146
formation as well as a comprehensive health audit survey
was carried out in Kerala, India [4,5]. Out of the total
number of 92,689 babies, the overall incidences of still-
births and malformation recorded were 0.5% and 2.03%
respectively. Multiple logistic regression analysis of the
congenital malformations and stillbirths did not suggest
any correlation with the radiation levels in this area.
Furthermore, a study in Russia [6] also in high natural
background radiation area did not have effect on the ex-
posed population but altered the immune systems rather
than inducing radiation disorders. Other similar studies
have been carried out in Brazil and Egypt [7,8]. These
assessments conducted in different parts of the world
have been used to determine the impact of natural back-
ground radiation on birth defects, haematologic problems
and other radiation induced diseases of the exposed
population. While natural sources of radiation could be
considered as low level exposure delivering low doses,
high doses of ionizing radiation can lead to effects such
as skin burns, hair loss, birth defects, illness, cancer, and
death, depending on the dose and the period of time over
which it is received [9]. Acute doses such as resulting
from a serious accident involving nuclear materials can
result in damage to the blood-forming organs, gastroin-
testinal tract, and central nervous system [5,6]. In Nigeria,
the risks associated with environmental radioactivity
have been carried to determine regional risks across the
country [9,10]. The study showed that population in the
northern part of Nigeria is associated with high radiation
risks than that in the southwestern and Eastern regions
[11]. In 2003, Obioha et al. [12] carried out assessment
of incidences of reproductive defects due to natural ra-
diations in two major towns, Enugu and Owerri, from the
Southeastern part of the country. After the realization of
Abeokuta as an area with high natural background radia-
tion [10] principally due to its geological formation
which is majorly a basement complex formation consist-
ing of essentially granites [13] (Figure 1), various meas-
urements and studies have been extensively carried out
on the natural radioactivity levels of Abeokuta [14-16].
The natural radiation dose level in Abeokuta is more than
four times higher than the world average value of 70
µSv·y−1 and as such it has been classified as one of the
high radiation areas in Nigeria [11]. However, no attempt
has been made to use the data provided from the results
of these various natural radioactivity level measurements
to determine if the radiation dose rate levels from this
area contribute to the incidences of reproductive abnor-
malities in the city. This present study is therefore being
carried out to evaluate the incidences of reproductive
abnormalities and the contribution of natural radiation
dose levels to report cases in the city known for high
radiations. Results are expected to add to the radiometric
data on environmental radioactivity in the country and
may equally be useful information to the Nigerian Nu-
clear Regulatory Authority (NNRA) in environmental
radiation protection policy formulation and implementa-
tion initiatives.
2. PHYSIOGRAPHY AND GEOLOGY OF
STUDY AREA
The study area Abeokuta is located in the sub-humid
tropical region of Southwestern Nigeria situated at coor-
dinates: 7˚9'39"N, 3˚20'54"E and 7˚9'39"N, 3˚20'54"E
latitudes and longitudes. As at 2005, Abeokuta and the
surrounding area had a population of 593,140. The city
enjoys a tropical climate with distinct wet and dry sea-
sons with dry period of about 130 days. The mean annual
rainfall and temperature are about 1270 mm and 28˚C
respectively while the estimated mean annual potential
evaporation is 1100 mm. The city is underlain by crystal-
line pre-Cambrian basement complex of igneous and
metamorphic origin noted for their rather poor ground-
water bearing properties and high contents of natural
radioactive elements [13,17]. The area is known for scat-
tered grey masses of granite and the city is drained
mainly by River Ogun which passes through and divides
the city into two, and the drainage pattern is dendritic.
The geological map of the study area is shown in Figure
1.
3. MATERIALS AND METHODS
3.1. Collection of Birth Records
Two hospitals selected for the study were the most
popular local medical care centers for the local popula-
tion. They are Oba Ademola Maternity hospital and Ijaye
State hospital. These two hospitals represent the most
accessible and affordable medical care centers by low
and medium income earners of the population and would
therefore give records of patients who have been resident
in the area for the past 25 years and whose livelihood
equally revolves around the area. The people who live in
areas of high natural radiation levels are of particular
interest because they have been exposed abnormally to
radiation over generations. As such there is a general
perception that birth defects among the population in the
high level natural radiation areas such as in Kerala are
more than those in areas of normal background radiation
[5]. The cases of incidences of reproductive abnormali-
ties were obtained from the patient’s admission registra-
tion records from the maternity ward of the hospitals.
The registration numbers of the patients were then used
to locate the case file to obtain all relevant and necessary
information such as: occupation, level of education,
place of birth, residential area, religion, age and the type
of reproductive abnormality. The cases considered in-
cluded multiple birth, stillbirth, premature birth, con-

N. N. Jibiri, J. B. Famodimu / Natural Science 5 (2013) 1145-1153 1147
Figure 1. Geological map of Ogun State, showing Abeokuta city and its geological formation.
genital malformation and spontaneous abortion. A 10
years data of these birth defect records from each hospi-
tal was extracted for the study. The records of incidences
per year per residential areas of the patients are presented
in Table 1.
3.2. Analyt ical T e chniques
A simple statistical treatment of the data was em-
ployed. The correlation between the annual effective
dose and the birth defects observed from each location
was determined using the Pearson Product Moment Cor-
relation statistical method. For the purposes of definition
birth defects are physical or physiological abnormalities
that exist at the time of birth. In this work we have de-
fined birth abnormality to represent incidences pertaining
to births that are deviant from single and normal live
births. Hence birth defects do not represent congenital
abnormalities (teratogenic effects). In order to achieve
the aim of this study the following hypotheses were
tested:
1) H0: The natural radiation dose level in Abeokuta
does not contribute to the reproductive abnormalities
incidences in the selected hospitals (Null hypothesis).
2) H02: The natural radiation dose level in Abeokuta
contributes to the reproductive abnormalities incidences
in the selected hospitals (Alternative hypothesis).
4. RESULTS AND DISCUSSIONS
A total number of 178 birth defects were recorded out
of a total number of 4453 deliveries taken at Oba Ade-
mola Maternity hospital within the period of years con-
sidered while at Ijaye State hospital a total number of
307 birth defects were recorded out of a total number of
6470 delivery cases considered. The summary of distri-
butions of the incidences of the birth defects from the
two hospitals is summarized in Tab l e 2 while Figure 2
shows the yearly distribution of the incidences.
The result of the survey presented above was related to

N. N. Jibiri, J. B. Famodimu / Natural Science 5 (2013) 1145-1153
1148
Table 1. The 10-year reproductive abnormalities incidences at different locations of Abeokuta per the hospital record.
Locations/Abnormality Type Number of incidences of abnormality per year
1999 2000 2001 200220032004 2005 2006 2007 2008 Total
Obantoko M.B 2 1 0 2 1 0 1 1 0 1 20
S.B 1 1 0 0 2 0 1 1 0 2
P.B 0 0 1 0 0 1 1 0 0 0
FCE Osiele M.B 0 0 2 0 0 0 1 1 1 0 11
S.B 0 0 1 0 1 0 1 1 0 0
P.B 1 0 0 0 0 0 1 0 0 0
Asero Estate M.B 1 2 1 2 2 1 0 1 1 2 32
S.B 1 1 1 1 1 1 2 2 1 0
P.B 0 0 1 0 0 1 1 0 1 1
Ake M.B 1 1 1 1 0 1 2 1 0 1 20
S.B 0 1
1 1 1 2 0 1 1 0
P.B 1 0 0 2 0 0 0 0 0 0
Olorunsogo M.B 2 0 1 1 1 1 2 3 1 2 27
S.B 0 1 1 0 1 1 1 2 2 2
P.B 0 1 1 0 0 0 0 1 0 0
Idi Aba M.B 1 1 0 2 1 1 0 1 0 0 14
S.B 0 1 1 0 0 1 1 1 0 1
P.B 0 0 1 0 0 0 1 0 0 0
Oke Sokori M.B 0 0 1 2 1 0 0 1 0 1 13
S.B 1 0 1 0 2 0 0 0 1 0
P.B 0 1 0 0 0 1 0 0 0 0
Kuto M.B 0 1 2 2 0 1 2 4 5 3 41
S.B 1 1 3 1 0 1 2 2 2 3
P.B 0 0 1 1 1 0 1 0 0 0
Oke Saje M.B 0 1 0 1 0 1 1 2 1 1 18
S.B 0 0 0 1 2 1 1 1 1 1
P.B 1 0 0 1 0 0 0 1 0 0
Aro M.B 0 0 0 2 1 0 2 1 2 3 23
S.B 0 0 1 1 1 1 1 1 2 1
P.B 0 1 0 1 0 0 0 0 0 1
Ago Oko M.B 0 0 0 1 0 1 0 2 1 0 16
S.B 1 0 1 2 1 0 0 1 1 0
P.B 0 0 0 0 0 1 0 0 1 0
UNAAB M.C. M.B 0 0 1 1 0 1 1 2 2 2 22
S.B 0 0 0 2 1 0 2 1 2 1

N. N. Jibiri, J. B. Famodimu / Natural Science 5 (2013) 1145-1153 1149
Continued
P.B 1 0 0 0 0 0 0 1 0 0
Isabo M.B 0 0 1 2 1 0 0 1 3 1 17
S.B 0 1 0 0 0 1 0 2 1 3
P.B 0 0 0 1 0 0 0 0 0 1
Onikolobo M.B 0 0 0 1 1 1 1 1 3 1 20
S.B 0 1 0 2 1 0 1 1 1 1
P.B 0 0 0 0 0 0 1 1 1 0
Oke Sabo M.B 0 0 1 1 0 1 0 2 0 1 29
S.B 1 0 0 2 0 1 1 3 3 1
P.B 0 0 0 1 0 0 0 1 1 0
GRA Ibara M.B 0 0 0 1 1 0 1 2 1 2 18
S.B 0 0 1 0 0 1 0 3 1 2
P.B 0 0 0 1 0 0 0 1 0 0
Mokola M.B 1 1 1 0 0 1 1 1 1 0 14
S.B 0 0 0 1 0 0 0 2 1 1
P.B 0 0 0 0 0 0 0 1 0 1
Ijeun Titun M.B 0 1 1 0 0 0 3 2 3 4 30
S.B 0 0 1 0 0 1 2 3 4 1
P.B 0 1 1 1 0 0 0 0 0 1
Ijaye M.B 0 0 0 0 0 0 2 3 3 3 23
S.B 0 1 0 0 0 1 1 1 2
P.B 0 0 1 0 0 0
1 0 0 1
Llafenwa M.B 1 1 0 0 0 1 1 3 2 2 24
S.B 0 0 0 1 0 1 2 2 1 2
P.B 0 1 0 0 1 0 2 0 0 0
Iberekodo M.B 0 1 2 1 0 1 1 3 1 2 26
S.B 1 0 1 0 0 0 1 3 2 2
P.B 0 0 0 0 0 1 1 2 0 0
EHS Asero M.B 0 1 1 0 1 1 2 5 1 1 27
S.B 0 0 0 0 0 0 1 4 3 3
P.B 0 1 0 0 0 0 1 1 0 0
Total 20 28 37 47 27 33 58 100 65 70 485
M.B—Multiple birth, S.B—Still birth, P.B—Premature births.
the data available on radiation dose levels measured in
the city of Abeokuta by Farai and Vincent [15]. The re-
sult of the measurement done by Farai and Vincent [15]
showed that the estimated average value of the annual
effective dose in Abeokuta is 0.45 ± 0.27 mSv/y, this
value was in agreement with the estimated average value
of 0.40 ± 0.26 mSv/y obtained in the earlier reports
[14,16]. Using the patient records in Table 2 the data
collected from the hospitals were regrouped and correla-
tion analysis was carried out. The correlation coefficient
values obtained for each reproductive abnormality and
the radiation dose levels is presented in Table 3 while the

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1150
Table 2. Reproductive abnormalities at the locations and corresponding annual effective dose rates.
Locations Annual Effective Dose (mSv) [11,15] Multiple births Still births Premature births Total abnormality
Obantoko 1.64 9 8 3 20
FCE Osiele 0.96 5 4 2 11
Asero Estate 0.35 15 13 4 32
Ake 0.30 9 8 3 20
Olorunsogo 0.39 13 11 3 27
Idi Aba 0.39 7 5 2 14
Oke Sokori 0.37 6 5 2 13
Kuto 0.23 20 16 5 41
Oke Saje 0.58 8 7 3 18
Aro 0.75 11 9 3 23
Ago Oko 0.49 5 6 2 16
UNAAB M C 0.33 10 9 3 22
Isabo 0.31 8 7 2 17
Onikolobo 0.53 9 8 3 20
Oke Sabo 0.19 14 11 4 29
GRA Ibara 0.51 8 7 3 18
Mokola 0.20 7 5 2 14
Ijeun Titun 0.41 14 12 4 30
Ijaye 0.40 11 9 3 23
Lafenwa 0.27 11 9 4 24
Iberekodo 0.50 12 10 4 26
EHS Asero 0.29 13 11 3 27
Figure 2. The annual distribution of birth defects in the se-
lected hospital in Abeokuta.
correlation matrix is presented in Table 4.
Figures 3-5 showed the scatter diagrams for each cor-
relation between the variables considered. The corre-
Table 3. The correlation between the annual effective dose and
reproductive abnormalities.
Reproductive abnormalitiesCorrelation coefficient (r)r2
Multiple birth −0.069 0.00480
Still birth −0.061 0.00370
Premature birth −0.026 0.00068
Total −0.049 0.00240
lation coefficient value for each of the reproductive ab-
normality was very low and the values of r2 were less
than 10%. This is an indication of poor correlation be-
tween the radiation dose and the reproductive abnormali-
ties. As could be seen from the correlation analysis no
strong correlation was established hence an indication
that no obvious relationship between the incidence of
reproductive abnormality with radiation dose levels.
From the observations, the null hypotheses formulated

N. N. Jibiri, J. B. Famodimu / Natural Science 5 (2013) 1145-1153 1151
Table 4. Correlation matrix.
Effective
Dose
Multiple
Birth Still Birth Premature Birth
Total Birth
Defect
Effective
dose 1
Multiple
Birth −0.29231 1
Still Birth −0.25944 0.980874 1
Premature
Birth −0.17328 0.893024 0.890928 1
Total Birth
Defect −0.26977 0.994902 0.992796 0.917821 1
Figure 3. The correlation of effctive dose and multiple births in
the city.
Figure 4. The correlation of effctive dose and still births in the
city.
Figure 5. The correlation of effctive dose and premature births
in the city.
are set aside as follows:
H02: The natural radiation dose level from Abeokuta
contributes to the reproductive abnormalities incidences
observed is hereby rejected on the ground that there is no
correlation between the radiation dose and reproductive
abnormalities observed.
H01: The natural radiation dose level from Abeokuta
does not contribute to the reproductive abnormalities
incidences observed, is hereby accepted on the same
ground.
This study did not specifically show differences based
on socio-economic parameters but according to a similar
study by Obioha et al. [12] it is arguable that there are no
valid demographic indications for demarcation of our
population into various socio-economic classes. However,
how a person lives is determined largely by where he
lives and greatly influences his disposition and accessi-
bility to medical care. The frequency of reproductive
defects was found almost doubled in the low to medium
income groups as low income mothers are usually multi-
gravidae and therefore more prone to reproductive de-
fects. Indeed there is a large population of low income
mothers who do not frequently visit the hospitals except
when reproductive difficulties arise. However, it has
been now shown that there are no excess stillbirths or
birth defects among the newborns in the HLNRA of Ker-
ala [18]. According to studies [18,19], there is no scien-
tific evidence to show that population groups exposed to
low level radiation may suffer any harmful effect. The
congenital anomalies in newborns found in high level
natural radiation areas (HLNRA) is not different from or
their frequency higher than those found in any other part
where the radiation level is normal.

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1152
Some of the anomalies are lower in HLNRA probably
because of higher literacy, health awareness, and prac-
tices in the study population. A similar trend could be
seen in this study following Table 2, higher incidences of
these abnormalities were found to occur in the areas with
low level radiation dose rates (Kuto, Asero, Ijeun Titun,
Oke sabo) than in the high dose rate areas (Obantoko,
FCE Osiele and Aro). This present study is therefore in
agreement with the findings of other research on soil
radioactivity and incidences of cancer [10] and those of
natural radiation and birth abnormalities in Eastern cities
in Nigeria [12]. These studies [10-12] showed no star-
tling differences on background gamma radiation levels
and incidences of cancer and birth defects. Within the
limitations of this present study, it has added information
on the radiometric knowledge needed in understanding
the relationship between natural outdoor radiation expo-
sure and occurrences of cancer and reproductive abnor-
malities in areas of high radiation in the country. Impor-
tantly this study will help set a basis for future research
efforts in this direction.
5. CONCLUSION
The importance of an adequate knowledge of the
natural background radiation in an environment is highly
essential for correct assessment of the radiological effect
of the natural radiation dose levels on the exposed popu-
lation. A 10 years hospital based data on the incidences
of reproductive defects in Abeokuta city known for high
radiations have been used to investigate the contributions
of natural background radiation to reproductive abnor-
malities in the city. The records of data were classified
into different reproductive abnormalities and were re-
lated to the available data on terrestrial radiation dose
rate levels in the city. The correlation of the two sets of
data showed that the natural radiation dose levels in the
city played no glaring role on incidences of reproductive
defects within the study area and the period considered.
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