Natural background radiation dose rate levels and incidences of reproductive abnormalities in high radiation area in Abeokuta, Southwestern Nigeria

doi:10.4236/ns.2013.511141

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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: *[email protected], *[email protected]

Received 23 July 2013; revised 23 August 2013; accepted 30 August 2013

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

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.

OPEN ACCESS

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

N. N. Jibiri, J. B. Famodimu / Natural Science 5 (2013) 1145-1153

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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.

N. N. Jibiri, J. B. Famodimu / Natural Science 5 (2013) 1145-1153

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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