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Radiation Effects and Defects in Solids
Incorporating Plasma Science and Plasma Technology
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RESRAD-ONSITE simulation to evaluate the effect
of contamination thickness in determining the
dose and excess lifetime cancer risk due to tin
mining activities in Nigeria
Abdu Nasiru Muhammad, Aznan Fazli Ismail & Nuraddeen Nasiru Garba
To cite this article: Abdu Nasiru Muhammad, Aznan Fazli Ismail & Nuraddeen Nasiru Garba
(08 Feb 2024): RESRAD-ONSITE simulation to evaluate the effect of contamination thickness
in determining the dose and excess lifetime cancer risk due to tin mining activities in Nigeria,
Radiation Effects and Defects in Solids, DOI: 10.1080/10420150.2024.2313574
To link to this article: https://doi.org/10.1080/10420150.2024.2313574
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RADIATION EFFECTS & DEFECTS IN SOLIDS
https://doi.org/10.1080/10420150.2024.2313574
RESRAD-ONSITE simulation to evaluate the effect of
contamination thickness in determining the dose and excess
lifetime cancer risk due to tin mining activities in Nigeria
Abdu Nasiru Muhammad a,b, Aznan Fazli Ismail a,cand
Nuraddeen Nasiru Garba d
aNuclear Science Program, Faculty of Science and Technology, University Kebangsaan Malaysia (UKM), Bangi,
Malaysia; bNigerian Nuclear Regulatory Authority (NNRA), Abuja, Nigeria; cNuclear Technology Research
Centre, Faculty of Science and Technology, University Kebangsaan Malaysia (UKM), Bangi, Malaysia;
dDepartment of Physics, Ahmadu Bello University, Zaria, Nigeria
ABSTRACT
Soil excavation in search of mineral ores provides a means of liveli-
hood to many families in Nigeria. However, the practice was found to
be associated with many radiological health concerns that were not
known to the miners and people living within the mining vicinities.
In an effort to provide such useful information, the activity concen-
trations of 40K, 226 Ra, and 232Th from tin mining areas in Zainabi,
Kano, Nigeria, were analyzed using a high-purity germanium detec-
tor. The results obtained show activity concentrations of 40K, 226 Ra,
and 232Th higher than their corresponding world average values.
A RESRAD-ONSITE software code was further used to evaluate the
dose and cancer risk using a variable contamination thickness. The
results obtained show an annual effective dose value greater than
the maximum acceptable limit of 1 mSv/yr for non-radiation workers
in Nigeria. The evaluated excess lifetime cancer risk also exceeded
the United States Environmental Protection Agency threshold and
the word average values of 1.45 ×10−3and 1.06 ×10−4, respec-
tively. Therefore, sustainable mining practices should be imple-
mented in the areas to avert the perceived radiation-related
problems.
ARTICLE HISTORY
Received 12 October 2023
Accepted 29 January 2024
KEYWORDS
Tin tailings; Zainabi; excess
lifetime Cancer risk;
RESRAD-ONSITE
1. Introduction
Despite its benefit in providing the daily needs of workers, their families and providing a rev-
enue to the government, mining of metal ores and its associated activities such as milling,
and smelting has been regarded as one of the major routes of exposure to natural radiation
due to irradiation by Naturally Occurring Radioactive Materials (NORMS) (1,2).
Naturally, in most cases, the concentration of NORMs in any material in the environment
is negligible, but disposal of large quantities of soil in the processes of mining of ores can
enhance the concentration of NORMs in the affected environment (3,4). This is because
CONTACT Abdu Nasiru Muhammad abdu.muhammed@nnra.gov.ng; Aznan Fazli Ismail aznan@ukm.edu.my
© 2024 Informa UK Limited, trading as Taylor & FrancisGroup
2A. N. MUHAMMAD ET AL.
tailings were found to contain a significant concentration of 40K and other radionuclides
in the decay series of 232Th and 238 U from the earth crust, which, when purged into the sur-
face of the earth, can result in the radionuclide concentrations becoming elevated in the
affected environment (5).
The miners brought soil and stones rich in tin and other minerals to the surface for pro-
cessing. The tailings generated are exposed to wind, runoff water, and other prevailing
weather conditions, resulting in the transportation of the particles containing radionuclides
to uncontaminated areas (6).
As such, miners, farmers, and members of the public living nearby the mining concession
may also be exposed to radiation above ambient level during the extraction, processing,
and transportation of the tin ores. They may also experience internal radiation exposures
from radon and its short-lived decay products, which are airborne or ingestible dust from
their environment (7,8).
Members of the public within the mining localities are also exposed to an increased radi-
ation dose due to the presence of suspended particulates of radionuclides that are carried
away by wind, directly ingested when washed and deposited into the water bodies, uptake
via the food chain, or when the tailing is used for building purposes (9,10).
AccordingtoICRP(11), in underground mining, the dose received by the mining work-
ers is directly related to the concentrations of the radionuclides, the mining type, and the
degree of ventilation.
In Nigeria, tin is mined mostly by illegal miners who normally resides in or near the min-
ing communities. Currently, active tin mining activities can be found in various parts of the
country particularly in Jos Plateau, Kano, Bauchi, Kaduna, and other state in Southern part of
the country. Despite this, there is inadequate information on the radiological effects asso-
ciated with tin mining activities in Nigeria. The available ones mostly reported on the dose
and risk burden using only generic methods (12–16).
Hence, this study will provide baseline information on the radiological effect of tin min-
ing using the commonly used method and RESRAD simulation approaches as it related to
contamination thickness. The findings will be useful to the regulatory agencies for proper
monitoring, legislation, and sustainable mining not only in Nigeria but in other places with
a similar scenario.
2. Materials and method
2.1. The study area
Geographically, Zainabi tin mining areas lie within longitude 8.520E and latitude 11.740
N. It is located about 202 km from the ancient city of Kano, Nigeria. The area is covered
with younger granite rock, which consists mainly of ash fall tuffs, pre-caldera agglomer-
ate, basalts, biotite granite, and biotite micro-granite. Currently, mining activities in the
areas are illegal, unregulated, and characterized by using rudimentary tools such as axes,
hoes, buckets, diggers, and pans with no skills or expertise to take precautionary mea-
sures against metals and radiation exposure toxicities (17). Cassiterite (SnO2) is the main tin
mineral that is mined in the study areas because of its significant commercial importance.
Figure 1shows the study area on the geological map of Nigeria.
RADIATION EFFECTS & DEFECTS IN SOLIDS 3
Figure 1. Geological Map of Nigeria showing the study area.
2.2. Collection and preparation of samples
Fifty-four (54) samples were selected randomly to allow for equal chances of selection. The
samples were taken within the concession of the active mine using a hand shovel at a depth
of 5–20 cm. At each point of sampling, four (4) samples were collected at an interval of
100 cm ×100 cm. To have a single representative sample, the collected samples were then
mixed and transferred into a polythene bag, sealed, and labeled. The sampling point’s coor-
dinates were recorded using a geographic positioning system (ATOMtex model l0), and
the corresponding background radiation was recorded at 1 m above the ground using a
radionuclide identifier device (NG-Variant, manufactured by FLIR, USA).
The samples collected were then prepared according to the standard procedure
described in (18) and transported to the University Kebangsaan Malaysia’s Nuclear Science
Program Laboratory for gamma-ray analysis. At the laboratory, the samples were then trans-
ferred to a Marinelli container in a replica of two (A and B) each, sealed with an adhesive
gum, weighted, and kept untampered for more than four weeks to allow for the attainment
of secular equilibrium. The prepared samples were analyzed with a high-purity germanium
detector (HPGe).
2.3. Gamma ray spectroscopic analysis
The lead shielding reduces unwanted ambient background interference to a shallow level,
The detector is equipped with a high-purity germanium detector (crystal height of 50 mm
and a diameter of 59 mm). The energy resolution of the detector was 1.8 keV (FWHM) of a
4A. N. MUHAMMAD ET AL.
60Co γ-ray peak of 1332.5 keV, coupled with an efficiency of 30% (19). The detector capsule
was arranged vertically in a cylindrical Canberra-747 model shield of approximately 1 cm
thick lead coating lined with 1.6 and 1.0 mm 1.0 – and 1.6-mm copper and tin, respectively.
Thus, enhancing the counting time and detection limit. The copper lining decreased the
characteristic lead X-ray (73.9 keV) generated due to interaction with the external radiation.
The detector was placed into a vacuum chamber of liquid nitrogen (LN2)at−196 OC (77
K) with the room temperature around the detector of 16–20 OC. A high-voltage power sup-
ply of 4000 V gives the detector a working-biased voltage. The HPGe detector output was
coupled to an AFT 2025 model amplifier with a pulse shaping time of 4 μs and a computer-
based MCA (Accuspec B) for data acquisition and peak fitting (20). The spectral analysis and
display of γ-rays were executed using Genie 2000 software (CANBERRA).
The energy and absolute photo-peak efficiency calibrations were performed prior to
sample measurement using an epoxy standard reference (EG-ML-7603) manufactured by
Eckert and Ziegler (Valencia, USA) containing an isotope of 109Cd, 60 Co, 85Sr, 57 Co, 88Y,
139Ce, 203 Hg, 241Am, 113 Sn, and 137Cs in the energy range of 60–1836.06 keV.
A time 12 h (43600 s) was chosen as the counting time for the background, the standard
soil (IAEA Soil-375), and the prepared samples. The corresponding gamma radiation peak
of potassium (40K) at 1461 keV was used for the analysis of (40K), 1764keV (214 Bi) was used
for (226Ra), and 2615 keV (208 Tl) was used for (232Th) both in the samples, standard, and
background measurements. These energies, 1764 keV (214Bi), 1461 keV (40K), and 2615 keV
(208Tl), have an emission probability of 15.3, 10.8, and 9.7%, respectively.
In order to observe the radiation fluctuations in the detector environment and to avoid
tempering with the actual counts of the prepared samples, a background count that
involved counting an empty container with a similar geometry to the sample containers
was measured at every three-day interval. The peak energy (total) efficiency was estimated
using Eq. 1, the limit of detection of the detector used (DL), and the minimal detectable
activity of the detector (MDA), which depends on factors like counting time, were obtained
from Curie’s formulas in Eqs. 2 and 3, respectively (18).
ε=N
νAB (1)
DL =2.71 +4.66√BN (2)
MDA =DL
νε BM (3)
Where N(count/sec) =net count; Éč =time (sec), A(Bq) =activity, B=the ratio of
branching, BN (count/sec) =background counts, M(kg) =sample/standard mass.
The total energy of the photo-peaks efficiency of 1764, 2615, 1461 keV are 0.02, 0.005
and 0.06, respectively. The detection limit DL is 67 ±0.5, 86 ±4 and 112 ±2 Bq/kg, while
the MDA of the detector is 6.2 ±0.1, 5.3 ±0.1, and 22.1 ±0.2 Bq/kg for 226Ra, 232 Th and 40K,
respectively.
During this study, the International Atomic Energy Agency’s prepared Soil-375 is used
for quality control and quality assurance of the detector. The 375-Soil can also be used as
a tool for quality control in other laboratory analytical work (21). The quality control of the
detector was performed by preparing the reference material (Soil-375) in two replicas and
counting several times for 12 h before counting the background and the prepared samples.
RADIATION EFFECTS & DEFECTS IN SOLIDS 5
Tab le 1 . Activity concentrations of 226Ra, 232 Th, and 40 K in IAEA Soil-375 and their corresponding values
in the reference material’s certificate (Based on dry weight).
Activity concentration (Bqkg−1)
Radionuclides Mean (375-Soil) Reference material certificate
226Ra 19.54 ±0.4 20
232Th 20.59 ±0.6 21
40K 418.84 ±0.5 424
The obtained mean activity concentrations of 232Th, 226 Ra, and 40K herein are presented
in columns 2 of Table 1, while the activity concentrations of the reference material given in
the reference material’s certificate are shown in column 3. It is observed that the percent-
age uncertainty between the mean activity concentration of 226Ra, 232Th, and 40Kinthe
prepared 375-Soil herein (Column 2) and the activity concentrations given in the reference
material’s certificate (Column 3) for 226Ra, 232 Th, and 40K is 2%, 2%, and 1%, respectively.
The observed variations, from the counting results to the readings in the reference material
certificate, are all within the 5% acceptable error (uncertainty) range.
The net counts/second obtained, which correspond to the energy photo-peak of a par-
ticular radionuclide in soil-375, background, and the samples were then substituted into
Eq. (4) (22).
Cs=MstdXNs
Ms×Nestd
XCstd (4)
Where, Cs=sample’s concentration (Bq/kg), Cstd =reference material’s concentrations
(Bq/kg).Mstd =mass of the reference (Soil-375) material (kg), Ms=mass of the soil sample
(kg) Nestd =Net count of reference material, Ns=net count of the soil sample.
2.4. The internal and external hazard index, excess lifetime cancer risk and the
annual eective dose using the generic mode
The obtained concentrations of 226Ra,40 K, and 232Th were further used to determine the
internal and external hazard index, excess lifetime cancer risk, and annual effective doses.
2.4.1. External and internal hazard index
The external and internal hazard indices are evaluated with the prime objective of assess-
ing the radiation risk, which is related to the emitted gamma radiation from the measured
radionuclides and their decay products, as well as when the mining residues are used as
building materials. It is measured using Equations 5 and 6, respectively (23–25).
Hex =CRa
370 +ATh
259 +AK
4810 (5)
Hin =CRa
185 +Ath
259 +Ak
4810 (6)
2.4.2. Internal and external dose rate
The air external dose rate (absorbed) at 1 m above the soil surface due to the contributions
of the primordial radionuclides was calculated in accordance with the international recom-
mendations using equation 8. The factors taken were 0.0417 for 40K, 0.599 for 232Th and
6A. N. MUHAMMAD ET AL.
0.436 for 226Ra. The indoor dose rate was calculated based on the factors of 1.1, 0.92, and
0.081 for 232Th, 226 Ra, and 40K, respectively, as depicted in equation 7 (26–28).
Din =1.1Cth +0.92CRa +0.081CK(nGyh−1)(7)
Dout =0.436CRa +0.599Cth +0.0417CK(nGyh−1)(8)
Where, CK,CRaandCth are the mean activity values of 40 K, 226Ra, and 232 Th, respectively.
2.4.3. Indoor and outdoor annual effective dose
The annual effective dose (indoors and outdoors) was calculated using equations 9 and 10.
A conversion factor from the effective dose of air to the absorbed dose DCF (0.7 Sv/Gy) was
used. The occupancy factor (outdoor) OF of 0.4 was adopted in this study to reflect the typ-
ical lifestyle of most Nigerian peasant farmers who spent at least 10 h working on the farm
per day. While OF (0.6) was considered the indoor occupancy factor, T(8760) represents the
number of hours in a year (2).
EDin =Din(nGyh−1)×DCF ×OF ×T(9)
EDout =Dout(nGyh−1)×DCF ×OF ×T(10)
The EDin and EDout represent the respective indoor and outdoor effective doses. The total
(indoor and outdoor) annual effective dose was evaluated using the equation 11.
EDtotal =EDin +EDin (11)
2.4.4. Generic estimation of excess lifetime cancer risk
The excess lifetime cancer risk is evaluated using the ICRP model (29). The indoor and out-
door effective dose were used to determine the indoor and outdoor excess lifetime cancer
risk in equations 12 and 13, respectively.
ELCRindoor =Eindoor×LE ×RF (11)
ELCRoutdoor =Eoutdoor×LE ×RF (12)
Where by, ELCRindoor and ELCRoutdoor are the indoor and outdoor cancer risk, Eindoor and
Eoutdoor are the indoor and outdoor effective doses,LE is the life expectancy time, 61.7years
is considered as the average life expectancy of a typical Nigerian while the RF is the cancer
risk factor (0.05)as per the ICRP (29–31).
2.5. Annual eective dose and excess cancer risk using the RESRAD Software
The mean concentrations of 226Ra,232 Th, and 40K in tailings (Table 3) were used during
the RESRAD simulation to assess the annual effective dose and cancer risk to onsite recep-
tors/miners. To reduce hypoethical errors, some modifications were made to some default
values of the software prior to the simulation, as presented in Table 2. This helps in reflecting
the true situation of the studied environment (32,33).
The RESRAD-ONSITE-ONSITE 7.2 code is used in evaluating the dose and cancer risk to
the onsite miner. The code carries out calculations by utilizing well-published and verifi-
able radiation protection reports that involve dose conversion factors and cancer slope
RADIATION EFFECTS & DEFECTS IN SOLIDS 7
Tab le 2 . Modification made on the RESRAD ONSITE default values.
S/N Modification made Value Reference
1 Dose limit mSv/yr (Nigerian public) 1.0 (37)
2 Contaminated zone density (g/m3) 1.440 (38)
3 Hydraulic conductivity (m/year) 1090 (35)
4 Speed of wind (m/s) 4.10 (39)
5 Rate of precipitation (m/year) 1.0 (34)
6 Factor of occupancy (outdoor/indoor) 0.3/0.5 (34)
9 Irrigation 0
10 Soil ingestion rate (g/year) 37.0 (40)
11 Coefficient (Runoff) 0.65 (35)
Figure 2. Schematic diagram of radiation exposure pathways in mining environment.
factors. Resrad codes are currently being used by different agencies, among which are the
US Nuclear Regulatory Commission, the US Environmental Protection Agency, the military,
universities and research centers, radiation protection, and nuclear regulatory bodies (34).
The studied areas are considered a cluster, with multiple mine concessions dispersed in
different locations within the areas, and the simulation was carried out by opening all nine
(9) pathways where an active miner could possibly be exposed to radiation, as depicted in
Figure 2. The pathways are external gamma irradiation, radon (water-independent), plant
ingestion, inhalation, meat ingestion, aquatic foods, milk ingestion, drinking water, and soil
ingestion.
An active miner residing on contaminated sites may be exposed to direct external
gamma radiation emanating from NORMS and their decay daughters. Inhalation is mainly
concerned with the radiation doses received when suspended radionuclides in the air are
accidently or intentionally inhaled and find their way into the respiratory system, which
adds to the internal irradiation.
8A. N. MUHAMMAD ET AL.
An active miner could also receive additional radiation when he drinks water that is
radioactively contaminated with radionuclides. He may also receive radiation doses when
he eats the meat of animals that have grazed in contaminated areas or when their milk is
taken as food.
The radon pathway (water-independent) is a pathway whereby radon nuclides emit their
powerful gamma radiation, which adds to the exposure burden of miners. Soil particles
could be swallowed accidentally or not accidentally together with water, dust, or food, and
when they contain radionuclides, it adds to the exposure burden of a miner (35).
The onsite mining worker is considered to be a male adult with a life working period of
30 years, a weight of 70 kg, and a height of 1.7 m. In accordance with the typical Nigerian
farmer/miner working strategy, it is estimated that, each year, a miner works with an out-
door and indoor fraction time of 0.3 and 0.5, respectively (34). Other parameters that are
changed from the default values of the code that are used in this simulation are listed in
Table 2.
Aside from the modified parameters listed in Table 2, other modifications made to the
default values of the code during this simulation include the adjustment of the ‘storage
time before use’ for meat, fish, and milk to three (3) days and seven (7) days for leafy veg-
etables and water due to the poor electricity connection and supply in most Nigerian rural
areas (6).
The code uses the dose conversion factor (DCF-PAK 3.02 mortality/morbidity) as their
default library, which provides the dose conversion, transfer factor, and bioaccumulation. It
utilizes attributes of a reference person’s receptor features, as described in the US-DOE tech-
nical standard reports (36). The codes model exposure scenarios by integrating all possible
exposure pathways, as depicted in Figure 2.
3. Result and discussion
3.1. Soil activity concentration of 40K, 226Ra, and 232Th
The summary of the activity of 226Ra, 232 Th, and 40K is presented in Table 3. The con-
centration of 226Ra ranged from 19 to 410 with an average value of 80 Bq/kg, while the
concentration of 232Th ranged from 21 to 570 Bq/kg with an average value of 108 Bq/kg. The
activity concentrations of 40K varied from 113 to 1193, with an average value of 461 Bq/kg.
The average values of 40K, 226 Ra, and 232Th obtained are higher than their corresponding
world average values of 420, 32, and 45 Bq/kg in soil (2).
Even though the average values of 226Ra, 232Th, and 40K obtained in this study are higher
when compared with their corresponding world mean values, exponentially higher values
of 1347.5 and 12138.3 Bq/kg, as the values of 238U and 232Th, respectively, were reported
Tab le 3 . Activity concentration of the 40K, 226Ra, and 232Th.
Activity Bqkg−1
Parameter 40 K226Ra 232 Th
Minimum 113 19 21
Maximum 1193 410 570
Mean +SD 461 ±14 80 ±9 108 ±11
World average 400 30 35
RADIATION EFFECTS & DEFECTS IN SOLIDS 9
Tab le 4 . Activity values of 40 K, 226Ra, and 232 Th from some selected tin mining areas in Nigeria.
Radionuclides Concentration (Bq/Kg)
226Ra 232 Th 40K Sample used Location Reference
115 143 705 Tailings Tin mining areas, Ririwai, Kano (6)
3779 8175.2 NA Soil Tin mining areas, Jos Plateau. (41)
772 1680 NA Tailings Tin Mining area, Jos Plateau (43)
776 2.72 35.4 Soil Tin Mine Bukuru, Jos Plateau (44)
13 30 NA Tailings Tin Mining areas of Bisichi, Jos (45)
163 451 466 Farm soil Bisichi Tin Mining areas, Jos Plateau (9)
1110 1967 NA Tailings Tin processing areas, Malaysia (22)
1–4 6–170 NA Tailings Bukuru, Bisichi and Kuru (14)
BDL-27420 500–35800 30–670 Tailings Bisichi, Bukuru and Kuru Jos Plateau (46)
38.78 105.77 491.89 Soil Toro Tin Mining areas, Bauchi (47)
53–96 73–176 177–271 Soil Bisichi old Tin mining site, Jos Plat (48)
80 108 461 Tailings Zainabi Tin mining areas This study
na =not available.
in the tailings soil of the Jos tin mining areas by (41). Additionally, (13) reported a higher
value of 226Ra and 232 Th that correspond to 772 and 1680 Bq/kg, respectively, around the
tin mining areas in Jos Plateau, Nigeria.
Higher than our obtained values of 226Ra and 232 Th are also reported in the sediment of
a tin processing plant in Malaysia by (22). The values of 232Th, and 226 Ra in the sediment at
the discharging point of treated water are 1966.6 and 1110.5 Bg/kg, respectively.
The mean activity concentrations of 232Th,226 Ra, and 40K recorded in this study corrob-
orated well with a related study carried out in neighboring tin mining areas in Riruwai by
the same authors (6) and other tin mining areas in Nigeria, as depicted in Table 4. However,
the values are much below the recommended exempt values of 1000 Bq/kg for 226Ra and
232Th and 10,000 Bq/kg for 40 K mentioned in the Basic Safety Standard (BSS) (42).
3.2. Estimation of hazard indices, annual eective dose and cancer risk using the
generic method
The calculated mean values of internal and external hazard indices are 0.95 and 0.73, respec-
tively. These values are lower than the maximum recommended value of 1, as prescribed
by (2). However, 37% of the samples show values of the internal hazard index higher than
the maximum recommended value of 1, as depicted in Figure 3. This signifies a greater
radiation risk when the tailings are used in buildings, as practiced in the study areas (41).
The outdoor and indoor annual effective doses were found to be 0.29 and 0.84 mSv/yr,
respectively. The calculated value of the indoor dose is about two (2) times higher than the
world average of 0.41 mSv/year, while the calculated value of the outdoor annual effec-
tive dose is also four (4) times higher than the corresponding world average value of 0.07
mSv/year (2).
The total annual effective dose is 1.13 mSv/yr, which exceeds both the world average
value of 0.52 mSv/yr (2) and the 1 mSv/yr as a dose limit for the Nigerian non-radiation
workers set by the Nigerian Nuclear Regulatory Authority (37). The higher values of dose
recorded could be attributable to the higher activity concentrations of the measured
radionuclides. The obtained value of the annual effective dose in the present study was
in good agreement with that obtained in Ririwai tin mining areas by the same authors (6).
10 A. N. MUHAMMAD ET AL.
Figure 3. Internal and external hazard indices of individual sample.
However, the mean value of the annual effective dose recorded here is lower than the 9.1
mSv/y reported by (41) in a tin mining area of the Jos Plateau, Nigeria, and the 22 mSv/y
reported by (49) from Brazilian underground mines.
The excess lifetime cancer risk for indoors and outdoors were found to be 2.8 ×10−3and
0.9 ×10−3, respectively. The total excess lifetime cancer risk was found to be 3.7 ×10−3.
The total value exceeded 1.45 ×10−3and 1.06 ×10−4as the world average values and
the US-EPA recommended threshold values, respectively (50). The obtained results demon-
strated a relatively higher risk of cancer development due to the stochastic radiation effect,
especially among the mining workers who spend considerable amounts of their time in the
mining concession.
3.3. Estimation of annual eective dose and cancer risk RESRAD-ONSITE
The annual effective dose and the risk for cancer due to the exposure to ionizing radiation
emanating from the 226Ra, 232Th, and 40K and their decay progenies in tailings for the onsite
receptor were performed using the RESRAD-ONSITE 7.2 software code.
In the study areas, miners deposited tailings of various heights and thicknesses around
the mining concession after extracting the tin ore, the simulation was carried out using a
variable thickness of the contaminant (0.25–20) meters to evaluate the effect of thickness
contamination with respect to dose and cancer risk.
AsdepictedinTable5, the radiation dose received by miners and the risk of developing
lifetime cancer increase with an increase in thickness. As the thickness increases, the annual
effective dose and risk of developing lifetime cancer also increase, as shown in Figure 4.
Even though there is an insignificant increment in dose as the thickness reaches 3 meters,
at this thickness (3 m), the total dose increases exponentially over a period of 100 years, as
shown in Figure 5.
At the lowest thickness (0.25 m), the dose incurred by miners from all the possible path-
ways is less than the threshold value of 1 mSv/y for non-radiation workers. But as the
RADIATION EFFECTS & DEFECTS IN SOLIDS 11
Tab le 5 . Contribution of pathways to total dose and cancer risk.
Pathways contribution to dose (mSv/y)
Water-independent
Contamination
thickness (m)
Total annual
effective dose
(mSv/y)
Cancer risk
(×10−3) External Inhalation Ingestion Radon Plant Meat Milk
0.5 0.91 2.51 0.2032 0.0008 0.0029 0.4924 0.1721 0.0285 0.0150
1.0 1.19 3.38 0.2103 0.0008 0.0029 0.5779 0.3194 0.0530 0.0270
1.5 1.22 3.62 0.2125 0.0008 0.0029 0.6038 0.3225 0.0542 0.0275
2.0 1.23 3.74 0.2136 0.0008 0.0029 0.6131 0.3240 0.0549 0.0278
3.0 1.24 3.86 0.2148 0.0008 0.0029 0.6179 0.3256 0.0555 0.0280
4.0 1.24 3.92 0.2154 0.0008 0.0029 0.6188 0.3264 0.0558 0.0280
5.0 1.24 3.96 0.2157 0.0008 0.0029 0.6192 0.3268 0.0561 0.0282
7.0 1.25 4.01 0.2158 0.0008 0.0029 0.6193 0.3278 0.0564 0.0283
10 1.25 4.04 0.2164 0.0008 0.0029 0.6196 0.3281 0.0565 0.0584
15 1.25 4.04 0.2166 0.0008 0.0029 0.6198 0.3283 0.0561 0.0585
20 1.25 4.08 0.2167 0.0008 0.0029 0.6199 0.2384 0.0563 0.0586
Figure 4. Excess lifetime cancer risk versus thickness of contamination.
thickness increases to 1 m and above, the dose received by miners exceeds the maximum
allowable dose limit for members of the public in Nigeria (37). Irrespective of the thickness,
the perceived dose mainly originates from the 226Ra and its decay daughters, as shown in
Figure 6.
As shown in Table 5, among the pathways, the major contributors to dose and can-
cer incursion are external radiation, radon, and plant ingestion (water-independent), while
inhalation, soil ingestion, meat, and milk ingestion pathways contributed negligibly to the
total dose. Drinking water and aquatic foods’ manifestation in dose contributions only
arises after a period of thirty (30) years.
The significant contribution to dose from the radon (water-independent) pathway is due
to the fact that the study areas are hot and windy in nature, which allows the radon gas to
diffuse freely and become accessible for inhalation by mining workers.
12 A. N. MUHAMMAD ET AL.
Figure 5. Annual effective dose over time.
Figure 6. Dose contributions (%) of the measured radionuclides.
As the contamination increases to 3 m and above, the contribution to dose from the
radon pathway increases negligibly, and even when the thickness increases to 20 m, a little
increment in dose from the radon pathway is observed. This could be due to the efficient
shielding of radon gas by the topsoil, and this trend was previously reported by (6,51).
The radon emanation rate was also found to be affected by soil porosity and soil mois-
ture. As the thickness of contaminated soil increases, the rate at which the button soil
retains moisture also increases. This could help slow down the radon diffusion rate from
the bottom soil (52).
Another pathway that contributed significantly to the observed dose is external gamma
radiation. As the thickness increases, the dose contribution from external irradiation
increases due to the increase in scattering of radiation from the NORMS and their decay
products, as well as the build-up factor. However, at a thickness above 3 m, the dose
contribution from the external irradiation pathway increases negligibly. This is because
the emitted radiation from the NORMS in the bottom soil will be properly shielded by
RADIATION EFFECTS & DEFECTS IN SOLIDS 13
the topsoil. This observation is in good agreement with (53), who reported an excellent
gamma-shielding efficacy of soil.
The inhalation and soil ingestion pathways cause insignificant radiation exposure to the
onsite receptors. Even with an increase in contamination thickness, the contributions from
these pathways remain unchanged. This is due to the fact that the inhalation pathway takes
into account only the dose from 3H, 14CO2gas, and 14 C radionuclides that have a low con-
centration in the most common environment (6). In addition to the physical half-life, the
ingested radionuclides have a biological half-life that can facilitate their removal from the
human body (54).
As the dose increases with an increase in the thickness of contamination, so does the risk
of developing cancer, as depicted in Figure 4. At a thickness of 0.25 m, the risk of developing
lifetime cancer is within the acceptable limit of the cancer threshold value set by the US-
EPA (50). As the thickness increases to 3 m, the risk increases to 3.8 ×10−3.Thisvalueis
significantly higher than the maximum recommended cancer risk value of 2.4 ×10−4by
UNSCEAR (2).
As such, to minimize the identified dose and cancer risk in the studied areas, it is rec-
ommended that the thickness of mining residues (tailings) be kept as thin as possible. This
could help in the faster spread of radon gas and external gamma radiation. In addition,
personnel protective equipment could protect miners from the direct radiation emitted by
NORMS in tailings.
Upon detailed monitoring of the studied mining areas, comprehensive soil remedia-
tion may be needed to avert the perceived radiological hazards. It is recommended that
future work evaluate the dose and cancer risk based on the actual lifestyle of miners and
the geological nature of the mining areas.
4. Conclusion
The activity concentrations of 40K, 226 Ra, and 232Th in the tailings around the Zainabi tin
mining areas in Kano, Nigeria, were evaluated using the HPGe detector. The evaluated
mean activity concentrations of 40K, 226 Ra, and 232Th obtained in this study are higher
than their corresponding world average but corroborated well with related studies car-
ried out in other tin mining areas in Nigeria and other parts of the world. Irrespective of
the method, the dose and cancer risk obtained in this study exceeded the Nigerian and
other international threshold values of 1 mSv/yr and 4.3 ×10−3respectively. This shows
a greater risk of developing radiation-related complications, especially for mining workers.
Albeit, it is imperative to note that the actual dose may be lower than the one reported here
because both methods take into account the dose from 40K that the human body regulates
via homeostasis. Finally, sustainable mining, less stay time in the mining concession, and
personnel protective clothing could help reduce the observed risk.
Acknowledgement
A section of this research was financially supported by the National University of Malaysia (UKM)
under research grant number DIP-2020-039. Abdu Nasiru Muhammad thanks the management of
the Nigerian Nuclear Regulatory Authority (NNRA) for the PhD fellowship.
14 A. N. MUHAMMAD ET AL.
Availability of data and materials
Additional data/materials related to this work can be made available upon reasonable
request from the corresponding author.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Funding
This work was supported by Universiti Kebangsaan Malaysia: [grant no DIP-2020-039].
Notes on contributors
Mr. Abdu Nasiru Muhammad is a nuclear regulator; he works with the Nigerian Nuclear Regulatory
Authority (NNRA). Currently, he is a PhD student at the University Kebangsaan Malaysia (UKM). He
works on the environmental and radiological impact assessment of mining activities in Nigeria.
Dr. Aznan Fazli Ismail is an associate professor at the University Kebangsaan Malaysia (UKM) depart-
ment of applied physics (Nuclear Science Program). He holds a Bachelor of Science in Nuclear Science
from the University of Kebangsaan Malaysia and a Doctor of Philosophy degree in Nuclear and Quan-
tum Engineering from the Korean Advance Institute of Science and Technology (KAIST). He has
published more than 70 articles in reputable journals, and his research interests include environ-
mental radioactivity, radiological impact assessment, radiation protection, radiation detection, and
uranium and thorium extraction.
Dr. Nuraddeen Nasiru Garba is a senior lecturer and researcher at the Department of Physics at
Ahmadu Bello University. He has obtained a B.Sc. (Hons.) degree in Physics from Bayero University
Kano, an M.Sc. in Radiation Biophysics from Ahmadu Bello University Zaria, and a Ph.D. in Physics
(Radiological Health and Safety) from Universiti Teknologi Malaysia. He has supervised many MSc
and PhD students and has held many administrative responsibilities. He has participated in so many
projects, notably the production of the radiological map of Malaysia between 2013 and 2014. He has
attended many conferences and workshops and has published 81 articles in peer-reviewed journals.
He is a member of the Nigerian Institute of Physics, the Nigerian Young Academy, and the Health
Physics Society, and currently he is the publicity secretary of the Nigerian Young Academy (NYA). His
research focuses on environmental radiation monitoring and protection.
ORCID
Abdu Nasiru Muhammad http://orcid.org/0000-0002-7676-8214
Aznan Fazli Ismail http://orcid.org/0000-0001-7733-2888
Nuraddeen Nasiru Garba http://orcid.org/0000-0002-1620-4214
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