Applied Radiation and Isotopes 191 (2023) 110534
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Review
Radiological indices estimation from radon concentration in selected
groundwater supplies in Abeokuta, south western Nigeria
Idowu Peter Farai a, Abubakar Adekunle Muritala a, *, Olatunde Micheal Oni b, Tunde
Daniel Samuel a, Aremu Abraham b
a
b
Department of Physics, University of Ibadan, Ibadan, Nigeria
Department of Physics, Ladoke Akintola University of Technology, Ogbomoso, Nigeria
A R T I C L E I N F O
A B S T R A C T
Keywords:
Radon concentration
Groundwater
RAD 7 solid state detector
Annual effective dose
Inhalation and ingestion
Abeokuta
Lung cancer has been linked to long-term exposures to radon through food or water consumption, inhalation in
caves or closed chambers, or exposure to radon-saturated open air. In Abeokuta, Nigeria, 58 samples of drinking
water were tested for radon. 25 samples from a hand-dug well and 33 samples from a borehole of water used for
drinking and other domestic purposes were each taken from different locations in Abeokuta. For this study, the
RAD7 Radon Monitor system was employed. The water samples were taken using a 250 mL radon-tight bottle. A
bubbling kit was included with the radon detector. Radon measurements were performed using the WAT 250
technique and grab mode on the water samples. On each sample, a total of two cycles were performed. The
findings revealed that the mean value for radon concentration in borehole drinking water samples is 18.8 Bq/L,
with a range of 10.65–29.5 Bq/L. In contrast, the measured samples from hand-dug wells range from 1.41 to
20.02 Bq/L, with a mean value of 9.7 Bq/L. 100% of borehole water samples and 48% of hand-dug well water
samples showed radon concentrations over 11 Bq/L, the maximum contamination limit advised by the US
Environmental Protection Agency (EPA). Furthermore, water samples from boreholes range between 0.037 and
0.081 mSv per year with an average mean of 0.051 mSv per year, while the total annual effective dose of radon
concentration due to ingestion and inhalation from hand-dug well samples ranges between 0.0038 and 0.055
mSv per year with a mean of 0.027 mSv per year. No samples from hand-dug wells or boreholes have cumulative
yearly effective doses of radon that are higher than the maximum contaminant level advised, which is 0.1 mSv/y.
1. Introduction
In the early 1900s, Dorn discovered the radioactive gas radon. Radon
has an atomic weight of 222 and an atomic number of 86. Natural radon
gas is an odourless, colourless gas that dissolves in water. Since it is a
noble gas, it has the remarkable potential to move around freely in the
soil, the air, etc. (Matiullah et al., 1993a). Three separate radioactive
decay processes, beginning with Uranium-238 (238U), Thorium-232
(232Th), and Uranium-235 (235U), produce the three natural isotopes
of radon. The half-life of radon (222Rn), which is part of the 238U decay
series, is 3.82 days (Samuel et al., 2022). When assessing risk factors
from radon exposure, radon, as it is often known, is typically regarded to
be a health danger. Radon daughters (Polonium-218 and
Polonium-214), which are alpha particles and make up over 90% of the
overall radiation dosage from radon exposure, are created after radon
gas is inhaled or consumed (Gruber et al., 2009). The water molecule
and this alpha particle engage, causing DNA damage. Lung cancer is
caused by the result of DNA damage (Farai, 1989).
More than half of the annual effective dosage from natural sources of
radiation for the average person comes from indoor radon exposure
(UNSCEAR, 2000). Lung cancer brought on by inhaling radon is the
greatest health risk (WHO, 2011). However, because the gas readily
disperses from the liquid and adds to the overall concentration in an
indoor environment, radon in water may pose a health risk.
Radon is regarded as the second leading cause of cancer after
smoking because when it is inhaled or consumed, the - particles released
by 218Po, 214Po, and other solid daughter particles cause radiation en­
ergy to be transferred directly to the tissues of the lungs and stomach
(UNSCEAR, 2000). Additional internal exposure from radon disinte­
gration offspring has been assessed and reported to be the cause of in­
stances of cancer in other internal organs, primarily the gastrointestinal
tract (Knutsson and Olofsson, 2002). According to epidemiological
* Corresponding author.
E-mail address: muritalaabubakr@gmail.com (A.A. Muritala).
https://doi.org/10.1016/j.apradiso.2022.110534
Received 28 August 2022; Received in revised form 19 October 2022; Accepted 25 October 2022
Available online 29 October 2022
0969-8043/© 2022 Elsevier Ltd. All rights reserved.
I.P. Farai et al.
Applied Radiation and Isotopes 191 (2023) 110534
studies, occupational exposure carries a higher risk than residential
exposure (Samet, 1989).
In the southwest of Nigeria, hand-dug wells and boreholes are the
primary sources of drinking water. For many villages, they are the only
supply of freshwater. Drilled wells or boreholes can be used to extract
groundwater from bedrock, or a soil aquifer can be used (dug well).
To supply water to specific residences that are not connected to the
main water supply, private wells are frequently drilled or excavated.
Because of the various radon concentrations in the soil and water, the
amount of radon that people are exposed to varies greatly from place to
location (UNSCEAR, 1988). According to the EPA Environmental Pro­
tection Agency (2003), the amount of radon in indoor air is greatly
influenced by the amount of radon in water. This is because when
household water is used, dissolved Rn-222 is released. It is vital to
communicate our findings to the general public as proof of the presence
of Rn-222, which is most prevalent in groundwater.
In Nigeria, insufficient attention has been paid to radon gas and its
radioactive isotopes. Several work on radon level in ground water for the
south west region exist in literature (Oni et al., 2014; Oni et al., 2014;
Ademola and Ojeniran, 2017; Oni and Adagunodo, 2019; Oni et al.,
2014) as a result, information on the degree of exposure brought on by
radon in groundwater is limited. Therefore, one of the goals of this study
is to ascertain the radon concentration in a few carefully chosen
groundwater sources in Abeokuta, Ogun State.
quantity of a material that is permitted in public water systems.
The maximum contamination level is not a line between safe and
harmful, but rather the point at which radon mitigation measures are
typically justified.
The amount of a contaminant that can be present without having a
negative impact on health is first determined by the EPA before setting a
Maximum Contaminant Level for it.
1.3. Study area
Abeokuta lies between 7◦ 5′ N and 7◦ 20′ N and Longitudes 3◦ 17′ E to
3 27′ E (see Fig. 1). The granite, granitic gneiss, and pegmatite meta­
morphic rocks of the basement complex are characterized by a variety of
folds, structures with varied degrees of complexity, faults, and foliation.
The researched locations are dominated by crystalline rock formations
and high background radiation levels (Jibiri and Famodimu, 2013;
Samuel et al., 2022)
◦
2. Material and method
Radon and its decay products can be measured using a variety of
techniques and equipment, each of which has advantages and disad­
vantages depending on the situation. The type of measurement to be
employed is specifically determined by the quantity to be measured and
the length of the measurement. The amount that needs to be measured is
groundwater. The materials collected for this study were analysed using
the RAD7 detector. The DURRIDGE RAD7 uses a solid state alpha de­
tector. A solid state detector, constructed of a semiconductor material,
converts alpha radiation directly into an electrical signal (often silicon).
The RAD7 works by electrostatically collecting decay products. It con­
tains a chamber where air is pushed or diffused into a desiccant to
remove water vapour. With the use of a solid state detector, the energy
of alpha particles is determined. A very high voltage is provided to the
detector to capture the charged radon decay products as they form.
Alpha particles from the decay products will go into the solid state de­
tector in part for counting (Durridge Company Inc, 2010).
The water samples have been taken directly from the source using a
250 mL radon-tight bottle. The radon detector and a bubbling kit were
used to determine the radon levels in water samples. The radon levels in
the water samples were measured using the WAT 250 technique and
grab mode. To aerate the sample and send the degassed radon to the
RAD7 measuring chamber, the RAD7’s built-in pump initially runs
automatically for 5 min. After this amount of time, the pump shuts off
automatically, and the system waits another 5 min before counting
again. Each sample will undergo a total of two cycles.
Samples of groundwater from hand-dug wells and boreholes were
collected in Abeokuta, Ogun State, Nigeria. Fig. 2 shows the schematic
diagram of RAD7 assembly.
1.1. Annual effective doses of drinking water samples due to ingestion
Drinking water contaminated with radon can expose one to the gas,
and using water can release radon into the air, which can expose anyone
to it as well. According to the UNSCEAR 2000 Report, new-borns,
children, and adults absorb ground water at rates of 50, 75, and 100
Ly-1, respectively. The weighted estimate of consumption is 60 Ly-1
assuming that these groups make up 0.65, 0.30, and 0.05 of the popu­
lation, respectively. Utilizing the guidelines set forth in UNSCEAR, the
yearly mean effective doses of drinking water samples owing to inges­
tion were determined by:
Ew.Ig (nSvyˉ1) = CRnw × Cw × (EDC)
where EwIg is the effective dose for ingestion, CRnw is the radon con­
centration in water (kBq m− 3), Cw is the weighted estimated of water
consumption (60 Lyˉ1), (EDC) is the Effective Dose Coefficient for
ingestion 3.5 nSv Bq− 1.
1.2. Annual effective doses of drinking water samples due to inhalation
When water is utilized, radon that has been dissolved in it may deemit into the indoor air. The amount of radon presents in water used
for drinking, bathing, laundry, etc. determines how much water is
contributed to the water supply.
Using the criteria outlined in UNSCEAR (2000), the yearly mean
effective doses of drinking water samples due to inhalation were
calculated:
3. Results and discussion
The measured value of radon concentration in 58 drinking water
samples collected from different areas of Abeokuta are tabulated in
Table 1 and Table 2. 33 water samples were taken from boreholes and 25
hand-dug wells both having depths ranging from 50 to 600 feet.
From Table 1, the results from borehole shows that radon concen­
tration in drinking water samples varies from 10.647 Bq/L to 29.501 Bq/
L with the mean value of 18.8 Bq/L.
Similarly, from Table 2, the results from hand-dug wells, the radon
concentration in drinking water samples varies from 1.408 Bq/L to
20.017 Bq/L with the mean value of 9.7 Bq/L.
Ew.Ih (μSvyˉ1) = CRnw × Ra.w × F × O × (DCF)
where Ew.Ih is the effective dose for inhalation, CRn.w is the radon con­
centration in water (KBq m− 3), Ra.w is the ratio of radon in air to radon in
tap water (10− 4), F is the equilibrium factor between radon and its decay
products (0.4), O is the average indoor occupancy time per person
(7000 h y− 1) and DCF is the Dose Conversion Factor for radon exposure
9 nSvh− 1(Bqm− 3)− 1.
The United States Environmental Protection Agency (EPA) and other
regulatory agencies for the quality of drinking water subjected the re­
sults to various rules and standards. The name of this standard is
Maximum Contaminant Level (MCL). The Safe Drinking Water Act’s
Maximum Contaminant Level (MCL) is the legal upper limit on the
3.1. Summary of the estimate of annual mean effective dose of radon gas
due to ingestion and inhalation
The annual mean effective dose of intake from a borehole source is
2
I.P. Farai et al.
Applied Radiation and Isotopes 191 (2023) 110534
Fig. 1. Geological map of Abeokuta (Source: Samuel et al., 2022).
Fig. 2. Experimental set-up of RAD7 detector.
3
I.P. Farai et al.
Applied Radiation and Isotopes 191 (2023) 110534
Table 1
Radon Concentration in 25 samples of hand-dug well.
Table 2
Radon Concentration in 33 samples of Borehole.
Sample Type: Hand-dug Well
S/
N
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
Location
Adatan
Olomoore
Panseke
Ita Oshin
Ita Eko
Onikolobo
Aro
Oke Itoku
Oke Olumo
Idi Araba
Olorunsogo
Iparo
Ibere Kodo
Igbore
Saje
Akomoje
Osiele
Camp
Obantoko
Aregbe
Agbetu
Idera
Eleweran
Arinlese
Arakanga
Sample Type: Borehole
Air
Temp
Radon Conc.
In Water
Annual Mean Effective Dose (μ
(0C)
Bq/L
Ingestion
Inhalation
Total
33.5
32.9
32.6
32.9
32.9
32.9
32.9
32.9
32.9
32.9
32.9
32.6
32.6
32.6
32.2
31.9
25.8
26.2
26.5
26.8
26.8
27.1
32.7
32.5
28.5
1.4
3.3
5.6
9.4
13.1
14.3
12.8
14.4
15.0
14.7
14.3
15.2
15.4
15.1
17.7
20.01
1.4
2.7
3.6
3.6
6.2
7.8
4.3
7.9
4.8
0.29
0.69
1.18
1.97
2.75
3.00
2.69
3.02
3.15
3.09
3.00
3.19
3.23
3.17
3.72
4.2
0.29
0.57
0.63
0.76
1.3
1.64
0.9
1.06
1.01
3.53
8.32
14.11
23.69
33.01
36.04
32.26
36.29
37.8
37.04
36.04
38.3
38.81
38.05
44.60
50.43
3.53
6.8
7.56
9.07
15.62
19.66
10.84
19.91
12.09
3.82
9.01
15.29
25.66
35.76
39.04
34.95
39.31
40.95
40.13
39.04
42.21
42.04
41.22
48.32
54.63
3.82
7.37
8.19
9.83
16.92
21.3
11.74
21.57
13.11
S/
N
Svȳ1)
Location
Air Temp.
(0C)
Radon Conc. In
Water
Annual Mean
Effective Dose (μ
Svȳ1)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Apena
Alogi
Somorin
Elega
Erunwon
Abule Lukosi
Asero
Osiele
Ita Itolorin
Ilugun
Ita Eko
Olomore
Odeda
Agberu
Stadium Road
Adigbe
Ita Eko
(Orisun)
Ewaals
Obada Road
Surulere
Oluwo29.2
Mango
Funaab Camp
Itamola
Ita Oshin
Isale Ake
Alogi
Oke Ido
Ago Ika
Ikija
Quarry
Ikere
Agbeloba
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
higher than that from a hand-dug well, as shown in Fig. 3. When
compared to a hand-dug well, the annual mean effective dosage of
inhalation from a borehole source is greater. In general, a borehole’s
total mean effective dose for ingestion and inhalation is higher than a
hand-dug well’s total mean effective dose for the same.
3.2. Comparing radon concentration in borehole and hand-dug well with
theMaximum contaminant level
In Fig. 4, the blue bars in the borehole represent the concentration of
radon, whereas the yellow bars in the hand-dug well show the
concentration.
According to the findings, from Table 3. Rn-222 concentrations can
range from 1.41 Bq/L to 29.50 Bq/L. The concentration of Rn-222 in
water samples from various sources varied steadily over time. The water
from borehole sources was determined to have the highest concentra­
tion. However, some well water exhibited higher radon concentrations
than borehole water, particularly from samples taken in Akomoje with
20.01 Bq/L. This observation might be related to the well’s depth
because of the nearby rocky formation.
The Standards Organisation of Nigeria (SON, 2007) presented the
maximum contamination level (0.1 Bq/L) for radioactive concentration
in drinking water in Nigeria, and it was discovered that the concentra­
tion of radon in all the water tests was over this level.
The MCL of 11.1 Bq/L for radon was found to be exceeded in US
states without a radon monitoring strategy or an upgraded indoor air
program in all borehole-sourced water.
Bq/
L
Ingestion
Inhalation
Total
32.2
27.1
27.4
27.4
32.5
31.6
31.6
31.6
31.6
31.1
31.3
31.3
31.3
31.0
30.1
30.1
30.1
19.4
20.3
22.3
19.1
27.4
14.6
16.8
13.1
10.6
4.6
28.9
29.5
27.0
25.3
22.2
15.9
15.9
4.07
4.26
4.68
4.01
5.75
3.07
3.53
2.75
2.23
3.07
6.07
6.19
5.67
5.31
4.66
3.34
3.34
48.89
51.16
56.19
48.13
69.05
36.79
42.34
33.01
26.71
36.79
72.83
74.34
68.04
63.76
55.94
40.07
40.07
52.96
55.42
60.88
52.14
74.8
39.86
45.87
35.76
28.94
39.86
78.9
80.53
73.71
69.07
60.6
43.41
43.41
30.1
29.8
29.5
16.2
29.5
29.5
27.4
27.4
27.7
28.0
28.3
28.6
28.9
28.9
28.6
28.6
14.2
16.5
16.0
3.40
16.2
15.3
14.8
14.6
19.1
18.0
14.7
18.5
17.7
15.6
20.9
29.5
2.98
3.47
3.36
40.82
3.40
3.21
3.9
3.07
4.01
3.78
3.09
3.89
3.72
3.28
4.39
6.19
35.78
41.58
40.32
44.22
40.82
38.56
37.29
36.79
48.13
45.36
37.04
46.62
44.6
39.31
52.67
74.34
38.76
45.05
43.68
44.22
41.77
41.25
39.86
52.14
49.14
40.13
50.51
48.32
42.59
57.06
80.5
Fig. 3. Plot of annual mean Effective dose of Ingestion and Inhalation.
3.4. Comparison between radon concentration in borehole water samples
and hand-dug well water samples using statistical tool
Using the t-value equation given as:
3.3. Comparison between existing research on radon and the result
obtained
t=
Table 4 shows the correlation of previous work and the present
investigation.
Oni M. O., et al. (2014) recorded 0.95 Bq/L as the lowest and 112
Bq/L as the highest Radon concentration compared to the present
investigation whose values falls within this range.
x1 − x2
√̅̅̅̅̅̅̅̅̅̅̅̅
1
+ n12
n1
σx1 x2
σ x1 x2 =
4
√̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅
(n1 − 1)σ 2x1 + (n2 − 1)σ 2x2
n1 + n2 − 2
I.P. Farai et al.
Applied Radiation and Isotopes 191 (2023) 110534
concentration. The EPA’s recommended Radon concentration in water
for human consumption is 11 Bq/L, yet 75.9% of the water samples
tested had readings that were higher.
None of the measurements reached the European Union’s recom­
mended measurement threshold of 100 Bq/L, which justifies taking
corrective action into consideration.
No sample in the current investigation, however, has surpassed the
alternative maximum contamination limit of 148 Bq/L recommended by
EPA. The total yearly effective dosage of radon and the measured radon
concentration in all drinking water samples from the Abeokuta districts
analysed are substantially below the safe limit (0.1mSv/y) recom­
mended by UNSCEAR (2008), WHO (2011), and EU council (1998)
35
RADON CONC. (BQ/L)
30
25
20
15
11.1 Bq/L
10
5
0
W W W W W W W W B W W B W B W B W B B B W B W B B B B B B
NO. OF WATER SAMPLES
Borehole
CRediT authorship contribution statement
Hand-dug well
Fig. 4. The Radon Concentration in Borehole and Hand-dug well (sorted
increasingly).
Idowu Peter Farai: Writing – review & editing, Supervision, Project
administration. Abubakar Adekunle Muritala: Writing – original draft,
Methodology, Investigation, Formal analysis, Data curation. Olatunde
Micheal Oni: Writing – review & editing, Methodology, Investigation.
Tunde Daniel Samuel: Writing – review & editing, Methodology,
Investigation, Data curation. Aremu Abraham: Supervision, Formal
analysis, Data curation.
Table 3
Radon-222 Concentrations in Nigeria and different part of the World.
222
Region
Sources of Water
Abeokuta
Abeokuta
Hand-dug well
Borehole & Hand-dug
well
Hand-dug well
Hand-dug well
Public water supply
3.05–90.80
0.95–112.00
Rabiu J.A. et al. (2017)
Oni M. O. et al. (2014)
0.02–112.5
0.670–1.45
6.44–8.36
Public water supply
Borehole & Hand-dug
well
0.91–12.58
1.41–29.50
Bonotto (2014)
Nasir and Shah (2012)
Shivakumara et al.,
2014
Tarim et al. (2012)
Present Investigation
Brazil
Pakistan
India
Turkey
Abeokuta
L)
Rn Conc.(Bq/
Reference
Declaration of competing interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
Data availability
Data will be made available on request.
Acknowledgement
Table 4
T-value of concentration of radon gas in borehole water samples and hand-dug
well water samples.
Type of water
sample
No
Mean
(Bq/L)
SD
(σ)
Df
Calculated tvalue
Critical
value
Borehole
Hand-dug well
33
25
18.8
9.7
0.009
0.036
56
13.06
2.01
I appreciate Prof. M. O. Oni’s assistance and consistent supply of
Rad7 Equipment during the fieldwork.
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Where df = n1 + n2 − 2 (degree of freedom), t-value = calculated T-test
value, x1 and x2 are mean radon concentration for borehole water and
hand-dug well water respectively σx1 and σ x2 = standard deviations for
borehole water and hand-dug well water respectively, n1 and n2 =
number of samples for borehole water and hand-dug well water
respectively.
Hypothesis. There is no significant difference between concentration
of radon gas in borehole water samples and hand-dug well water
samples.
Since σ x1 ∕
= σx2 and n1 ∕
= n2 , therefore df at 0.05 level of significant tcritical is 2.01. From Table 4, the t-calculated value (13.06) is greater
than the t-table (2.01) which rejects the hypothesis, i.e there is signifi­
cant difference between concentrations of radon gas in borehole water
samples than the hand-dug well water samples.
4. Conclusions
According to the study’s findings, the concentration of Rn-222 in
several water samples taken from Abeokuta and its environs is equiva­
lent to that found in a previous study done in the same area. This finding
demonstrates that the radon concentration in Abeokuta’s public drink­
ing water samples is 24.1% below the EPA-required safety limit of 11
Bq/L for both borehole and hand-dug well recorded Rn-222
5
I.P. Farai et al.
Applied Radiation and Isotopes 191 (2023) 110534
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