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Assessment of 39K, 232Th, and 238U isotopes in soil samples with ICP-
MS in El-Obied, Sudan
Amar Belly1,2, Abdelrazig M. Abdelbagi3,4Abdelaziz A.M. El Shokali13, Ahmed Elfaki1
1Physics Department, College of Science, Sudan University for Science and Technology, Khartoum, Sudan
2University of Sennar, Physics Department, Education College, Sennar, Sudan
3Physics Department, College of Science and Humanities, Al-Dawadmi, Shaqra University, Riyadh, KSA
4Omdurman Islamic University, Faculty of Science, Omdurman, Sudan
DOI: https://doi.org/10.51583/IJLTEMAS.2025.1410000120
Received: 02 November 2025; Accepted: 08 November 2025; Published: 17 November 2025
Abstract: The main objective of the present study was to determine the concentrations of the radioisotopes potassium-39K, thorium-
232Th, and uranium-238U in soil samples collected from selected areas around El-Obeid City, Sudan. Inductively Coupled Plasma
Mass Spectroscopy (ICP-MS) analysis was employed to quantify these isotopes. Soil samples were obtained from five locations
surrounding El-Obeid, specifically from two regions in the southern and western parts of the city within North Kordofan State, in
areas located away from residential zones. High correlation coefficients between 232Th and 238U indicate that these isotopes likely
originate from the same source. Principal component and factor analyses further confirm that 232Th and 238U share common sources
in the soil samples collected from various locations around El-Obeid City. In addition, the measured concentrations of 238U and 39K
are in reasonable agreement with values reported in the literature. The concentration of 232Th observed in this study is relatively
high compared to values reported from other regions worldwide, suggesting possible local geological or anthropogenic influences.
Keyword: Radioactive elements, Potassium; Thorium; Uranium; ICP_MS spectrometer, Data Analysis, Elobied, Sudan
I. Introduction:
Natural terrestrial background radiation in the environment originates from various sources, including gamma, alpha, and beta
radiation emitted by naturally occurring radionuclides found in soil, rocks, water, and air. The natural terrestrial background
radiation primarily comes from naturally occurring radionuclides in the Earth's crust, soil, and atmosphere (1). These originate from
radioactive elements present in the soil, rocks, and building materials (2). The level of environmental radiation pollution provides
essential radiological information on radiation levels in soils, building materials, water, food, and air. Uranium is the most abundant
naturally occurring element, which is primordially radioactive and decays until it reaches a stable nucleus (3).
Moreover, uranium in the earth's crust is mainly found in soil, beach sand, and rocks, with the highest concentration in phosphate
rocks, which represent an estimated abundance of 0.5 to 5 ppm. A significant natural radionuclide found in the Earth's crust is the
uranium isotope (4). After decaying into thirteen radioactive daughter isotopes and emitting alpha radiation, the parent atom 238U
eventually becomes stable lead (206Pb). Uranium-238 is the most abundant of the three natural uranium origins in the Earth's crust
and is an important radionuclide since Earth's formation, continuously emitting alpha radiation (5). Uranium can be leached from
source rocks and redeposited in reducing environments such as sandstones, clays, and organic-rich layers. Concentrations are
usually lower unless secondary enrichment occurs. Two isotopes of uranium, uranium-238U, are found (6). The province under
study, located within the uranium province district, aligns with the geological features typical of sub-Saharan African countries
where uranium ore has been discovered. The natural presence of uranium in soil and human activities are the main sources of trace
levels of uranium in the human environment. Both natural and external sources of irradiation emit gamma radiation (7). Terrestrial
environmental radiation, which originates from naturally occurring radioactive elements in the Earth's crust, can indeed have
negative impacts on both the environment and human health (8). An essential step in assessing the radiation dose exposure to
individuals in the area, as a basis for the environmental pollution from 39K, 232Th, and 238U radioactive sources, is determining the
natural radioactivity of the elements in the soil in the study district (9). Potassium is an abundant element essential to life, and 39K
is found in the Earth's crustal rock in three isotopes: 39K, 40K, and 41K. Potassium-39 (K-39) is a stable isotope that naturally occurs
in soil, typically at concentrations ranging from 1 to 2 milligrams per kilogram (ppm) (10). This isotope contributes to the overall
potassium content in geological materials but is not radiogenic. The stable isotope 39K constitutes 93.258% of the total of potassium
isotopes in nature. (Steno Wang; Morgan et al., 2018).
In the Earth's crust, thorium is frequently found in the thorium-phosphate minerals, which can contain up to 12% thorium oxide,
ThO₂. Since thorium is likewise radioactive, the parent isotope's typical decay cycle results, and many of the daughters are gamma
emitters. The predominant isotope, thorium-232, is a naturally occurring radioactive metal that is concentrated mainly in acidic
igneous rocks such as granites. Also, the average thorium concentration is 16.19 ppm (11).
Assessing the natural radioactivity in the soil of the study area is a critical step in evaluating the potential radiation dose to human
exposure. This assessment provides a scientific basis for understanding the extent of environmental pollution arising from naturally
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occurring radioactive materials, particularly 39K, ³²Th, and ²³⁸U. Monitoring naturally occurring radionuclides in the environment
is essential for accurate radiological risk evaluation and effective long-term environmental health management (12).
Study Area:
El-Obeid, located in central-western Sudan, is the capital of North Kordofan State. Its approximate geographical coordinates are
13°11′ N, the latitude, and 30°13′ E. El-Obeid is situated within the semi-arid Sahel region, not far from the border between North
and South Kordofan, and is distinct from Sudan’s Eastern Desert, which lies much farther east (9). The western and southern regions
of El Obeid are primarily composed of sand and sediment. A total of thirty-seven (37) soil samples were collected from various
locations throughout the province, including sites near residential. The Eastern Desert lies to the east of the Nile, while El Obeid is
well to the west, in the Sahelian belt of central-western Sudan. The region around El Obeid experiences a semi-arid. In terms of
natural resources, five zones have been identified in the area for their sample collections. The surrounding area shows extensive
agricultural cultivation and animal husbandry, highlighting the city's deep connection to the land. These activities are crucial not
only for subsistence and the local economy but also serve as a fundamental aspect of the native cultural identity within the region.
The zones' qualitative analysis of samples from selected locations indicated promising elemental signatures, suggesting the potential
radioactive enrichment that warrants further investigation. The qualitative analyses of samples from chosen locations revealed
encouraging elemental signatures, indicating the potential radioactive enrichment, which requires further examination.
Experimental and Methods:
Soil samples were collected from five sites located around El-Obied City in western Sudan. These sites were selected to evaluate
trace elements in the local environment. Due to the nature of the samples, soil extracted from the underground area at a depth of
0.5 meters can be analyzed with minimal or no pretreatment. Inductively Coupled Plasma Mass Spectrometry ICP-MS is a highly
sensitive and precise technique for detecting trace and ultra-trace elements across a wide range of scientific fields (13). The
capability to measure both concentrations and low detection limits makes it a go-to method in environmental and nuclear sciences.
In this study, the concentration of trace elements in soil samples was measured using ICP-MS at the Atomic Energy Authority
Nuclear Research Center, Center Laboratory for Elemental and Isotopic Analysis, Cairo, Egypt. Inductively Coupled Plasma Mass
Spectrometry was employed for precise concentration measurements, aiding in the exploration of the isotopic analysis of elements.
In this study, the analysis focused on the radioactive elements Potassium (39K), Uranium (238U), and Thorium (232Th).
II. Results and Discussion:
The preliminary outcomes of the study highlighted the value of using ICP-MS to detect potassium, thorium, and uranium, as well
as for assessing the spatial distribution of other elements in the area. The resulting data were subjected to various assessment
methods and statistical analyses to ensure accuracy, reliability, and meaningful interpretation of the elemental concentrations.
Samples are typically prepared in a soluble form for accurate analysis. Qualitative analysis of the soil samples indicated the presence
of 39K, 232Th, and 238U, with the corresponding peak concentrations presented in Figure 1. Distribution patterns, particularly of
uranium multiplied by 1000 at the value, appear in the graph of the soil samples collected from the Elobied, Sudan. Figure 2 displays
the factor analysis distribution of nuclear isotope concentration values, indicating that 232Th and 238U varied across all samples and
were different from 39K. The factors of variable concentration in one part of the graph, and the factors of variable 232Th and 238U
from similar sources in all sites.
Area-1 Area-2 Area-3 Area-4 Area-5
0
1000
2000
3000
4000
5000
6000
7000
8000
C
on
ce
nt
ra
tio
n
(p
pm
)
Area around Elobied city
K39
Th232
U238X1000
Fig. 1 Average radionuclide element concentration in Elobied.
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Table 1: Correlation is significant at the 0.01 level.
Isotopes 39K 232Th 238U
39K 1 .401 .319
232Th .401 1 .983**
238U .319 .983** 1
Projection of the variables on the factor-plane ( 1 x 2)
Active
39K
23Th
238U
-1.0 -0.5 0.0 0.5 1.0
Factor 1 : 73.32%
-1.0
-0.5
0.0
0.5
1.0
F
a
c
to
r
2
:
2
6
.2
6
%
Figure 2: The Factor Analysis Distribution of Nuclear Isotope Concentration Values.
Table 2: t-test of the location
Element
Area-1 Area-2
Area-3
Area-4
Area-5
Isotope t T t t t
39K 5.601 4.251 10.369 7.148 4.064
232Th 6.185 8.142 5.323 7.556 10.425
238U 5.595 7.584 4.524 7.561 13.499
Table 3: Factor Analysis
Extraction Method: Principal Component Analysis
Location east
ELobied
Location south
Elobied
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Isotopes elements
Communalities
Extraction
Component Matrix a
Communalities
Extraction
Component Matrix a
39K .013 .113 .317 .563
232Th .918 .958 .853 .924
238U .920 .959 .873 .935
Table 4. International reference data on the soil.
Region Th(ppm) U(ppm) K (%) Reference
IAEA-326-soil-
Reference
9.71 2.38 1.91 Bajanowki-2001
United state 8.9±4.2 3.0± 2.5 - Myrick et al 1983
Amman, Jordan 7.1 4.6 1.7 Ahmed et al(1997)
Istanbul, Turkey 9.1 1.7 1.1 Karahan and Bayulken-
(2000)
Coastal area, Greece 17.5±6.2 7.5± 3.5 2.9 ± 1.2 Florouand Kritidis
(1992)
Taiwan 10.8 2.4 1.4 Yu.Ming et al (1987)
Italy 18-21 4.6- 5.7 1.9 – 2.5 Bellia et al (1997)
Spain 3.2-20.9 1.6-57.6 1.0-2.3 Martinez-Aguirre and
Garcia-Leon. 1992)
Rajasthan India 10.6- 26.1 2.4-6.3 0.2-0.5 Nageswara et al (1996)
Worldwide average 7.4 2.8 1.3 UNSCEAR report (2000)
El Obied, Sudan 1572.2-6331.47 0.1499-0.6741 0.0581- 0.7723 Present study
III. Discussion
The results of the soil analysis from the collected samples in the province under study, conducted using an ICP-MS spectrometer,
are presented in the accompanying graph. Among the samples, the soil from El-obeid shows the highest concentrations of 232Th
and 39K. The graphical representation highlights factors contributing to concentration variability, with 232Th and 238U displaying
similar distribution patterns, suggesting a common source is based on their relative percentage variations across all sampling sites.
Table 1 shows the correlation coefficients among the element concentrations of these isotopes across the different sampling
locations. The observed data suggest a direct relationship between 232Th and 238U concentrations, whereas 39K shows notable
variations among the study areas, reflecting differences in soil composition or mineral content (14). The results are summarized in
Table 2, which presents the t-test values for the elements ³⁹K, ²³²Th, and ²³⁸U in soil samples collected from the five study sites,
indicating identical values for ²³²Th and ²³⁸U. Table 3 presents the results of the principal component analysis (PCA), including the
communalities extraction and component matrix for the isotopes ³⁹K, ²³²Th, and ²³⁸U in soil samples collected from two locations,
the western and southern sites of El-Obied. The communalities extraction and component matrix values for 232Th and 238U show
almost identical results across the sites, with noticeable differences observed for 39K in the area (15). Table 4 presents international
reference data on soil alongside the average results from this study, which were obtained from locations characterized by lower
238U concentrations, 39K values within a similar percentage range, and higher 232Th levels.
IV. Conclusion:
This study presents the first evaluation of the concentrations of the radioactive isotopes 39K, 232Th, and 238U in soil samples collected
from various locations around Elobied, Sudan. The investigation detected the isotopes in a province surrounding Elobied city,
located in North Kordofan State, Sudan, in areas situated away from residential zones. A significant difference in the concentrations
of thorium 232Th and uranium 238U was observed; however, statistical analyses, including principal component analysis (PCA) and
factor analysis, indicated that a considerable portion of the data exhibited nearly constant values. The uranium 238U concentration
obtained in this study was lower than the international reference values presented in Table 4 and those reported by UNSCEAR
(2000). In contrast, the concentration of 232Th was relatively high in all 37 soil samples collected from the five study areas, compared
with international reference data. Furthermore, the 39K concentration exceeded the optimum level; however, the total potassium
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values remained within acceptable limits when compared to global reference data from previous studies (Table 4). Moreover, the
findings of this study provide a valuable baseline for future environmental monitoring and research in the region. These results,
particularly the elevated levels of thorium, highlight the critical importance of establishing local guidelines and regulatory policies
to accurately assess and mitigate the risks associated with heavy metal exposure.
Acknowledgment: The author(s) gratefully acknowledge the Atomic Energy Authority Nuclear Research Center, Center
Laboratory for Elemental and Isotopic Analysis, Cairo, Egypt, which provided the ICP_MS facilities and equipment. support for
this research.
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