https://orcid.org/0000-0001-8972-3384
Figures
Abstract
Soil can pose significant radiation hazard in areas with elevated radioactivity levels from geological or anthropogenic sources, potentially contributing to human exposure through the food chain and atmosphere. However, industrial activities can alter radionuclides distribution by releasing residues or effluents, leading to their accumulation in the environment. In general, soil provides clear insights into geological characteristics and heavy metal exploration, in addition to assessing the risks of radiation exposure. This study investigates the distribution of NORMs and assesses radiological hazards in twenty soil samples collected from two major industrial zones in the Chattogram City of Bangladesh: the Bayazid Industrial Area and the Kalurghat Heavy Industry Area. The activity concentrations of 226Ra, 232Th, and 40K in the analyzed soil samples range from 8 ± 1–18 ± 1, 15 ± 1–35 ± 3, and 192 ± 17–420 ± 35 Bq/kg, respectively, remaining below the global average for soil. The radiological hazard indices indicate negligible health risks to the public or environment, suggesting that the industrial activities are not releasing any radiotoxic elements in the surrounding environment. Statistical analysis identified 40K and 232Th as the primary contributors to radiological hazards, supported by strong correlations and significant principal component loadings. Additionally, this study provides baseline data for monitoring environmental radioactivity levels, particularly in light of the upcoming commissioning of the Rooppur Nuclear Power Plant in 2025.
Citation: Siraz MM, Islam S, Shelley A, Alam MS, Mahmud A, Rashid MB, et al. (2025) Radioactivity distribution and concomitant hazards evaluation of industrial zones soils from Chattogram, Bangladesh: A multivariate statistical analysis. PLoS One 20(7): e0328356. https://doi.org/10.1371/journal.pone.0328356
Editor: Hesham M.H. Zakaly, Ural Federal University named after the first President of Russia B N Yeltsin Institute of Physics and Technology: Ural'skij federal'nyj universitet imeni pervogo Prezidenta Rossii B N El'cina Fiziko-tehnologiceskij institut, RUSSIAN FEDERATION
Received: April 10, 2025; Accepted: June 30, 2025; Published: July 16, 2025
Copyright: © 2025 Siraz et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: All relevant data are within the manuscript.
Funding: The author(s) received no specific funding for this work.
Competing interests: The authors have declared that no competing interests exist.
1. Introduction
Natural radioactivity is characterized by the spontaneous decay of unstable atomic nuclei and is a ubiquitous environmental phenomenon [1]. Natural radiation exposure to humans is widespread and diverse, resulting from a range of notable sources, including terrestrial (such as building materials, water, air and foodstuffs), extra-terrestrial (e.g., cosmic radiation), and internal radiation (such as 40K) [2]. The main external source of human irradiation is terrestrial background radiation, which is mostly sourced from naturally occurring radioactive materials (NORM) such as 40K and the decay products of 238U and 232Th series. Nearly 85% of the annual radiation dose that humans receive comes from natural radionuclides, which include both terrestrial and cosmogenic sources. Overall, natural radiation sources comprise about 80% of total human radiation exposure, with artificial sources accounting for the remaining 20% [3].
Radiation exposure has significant and dose-dependent biological effects. While both acute and chronic exposures have been epidemiologically associated to a variety of malignancies, including different kinds of leukemia and organ-specific tumors, as well as those affecting the thyroid, breasts, and lungs, high levels have the potential to cause cellular death [4]. Research has shown that higher radiation exposure levels are linked to a higher risk of developing cancer, suggesting that exposure over the average of natural background radiation worldwide is linked to a higher chance of developing cancer [4,5]. This connection emphasizes how crucial it is to track and control radiation exposures, both natural and man-made, in order to reduce any possible health hazards. Natural radiation makes up the majority of human exposure patterns, which emphasizes how important it is to comprehend and measure background radiation levels for both public health evaluation and efficient radiation protection.
Depending upon the variation in the geology, the NORM activity concentration in earth crust can greatly show a discrepancy from region to region [6–8]. The primary sources of natural radioactivity in earth crust are 226Ra, 232Th, and 40K. Due to the non-uniformity of the distribution of these radionuclides in the environs, it is important to measure and analyze their activity concentrations in various locations. While 226Ra, 232Th, and 40K are major natural contributors, total radiation inventory also includes cosmic rays from space, radon gas in the atmosphere, and human-made sources [9,10]. These artificial sources include nuclear power plants, medical procedures, and industrial activities. The industrial sector is particularly important, as in most manufacturing processes, radioactive materials could be generated, or the existing ones could be concentrated during operations [1], leading to products and waste materials that have higher levels of radioactivity than the original raw materials [11]. These concentrated materials are known as technologically enhanced naturally occurring radioactive materials (TENORM). The term “technologically enhanced” is used to highlight that these naturally occurring radionuclides have been concentrated through industrial activities. When industrial waste is dumped into nearby low-lying areas without adequate treatment, it can significantly contaminate the soil by increasing levels of TENORM [5]. This untreated waste presents serious risks, damaging the ecosystem’s macrophytes and soil fauna, while also posing potential health threats to human populations. Several major industrial sectors have been identified as primary sources of TENORM [6]. Industries such as fossil fuel energy production, phosphate processing, textile manufacturing, fabric and knit production, footwear manufacturing, medical disposable products, and oil and gas extraction, all contribute to the release of radioactive waste into the environment [12]. This situation necessitates stringent environmental management protocols to mitigate potential risks to ecosystems and human health. With rising public awareness and concern regarding environmental quality, it has become increasingly crucial to assess the impacts of radioactive waste discharge, even when it involves NORMs. Consequently, thorough monitoring and management strategies are vital to ensure both environmental and public safety.
A survey of literature shows that a thorough investigations into natural radionuclides in industrial soil matrices have been carried out in various geographical locations, including studies in Bangladesh [5,13–18] and other regions worldwide [19–29]. A study carried out in China has reported higher levels of 232Th and 40K in industrial areas [30]. Similarly, research in Bangladesh has shown increased concentrations of 226Ra, 232Th, and 40K in soil samples near industrial sites [5,17,18]. Investigations carried out in Spain [28], Russia [29], and Saudi Arabia [31] have revealed the presence of 137Cs contamination in soils near industrial areas, highlighting the uneven distribution of radionuclides linked to industrial activities across various regions. A prior study in Chattogram [32] noted the presence of 137Cs along with increased levels of 232Th in soil samples. Despite these important findings, there is still a considerable gap in our understanding of how NORMs are distributed within the industrial zones of Chattogram.
Chattogram, Bangladesh’s principal port city, encompasses strategically positioned industrial zones in Kalurghat, Bayezid, and Nasirabad. This comprehensive radiological assessment establishes a crucial baseline through precise documentation of current NORM concentrations in Chattogram, thereby facilitating the detection of temporal variations in radiation levels, particularly within industrially impacted zones. In this regard, our investigation focused on determining the distribution of NORMs in soil matrices proximate to Chattogram’s industrial zones. The findings may contribute to the development of targeted mitigation strategies aimed at reducing radiological hazards to ensure the protection of local populations and natural resources. Further, this research work may contribute to and be an excellent reference for radiological assessments at other important sites, like the Rooppur Nuclear Power Plant, and for the betterment of overall knowledge regarding radiological risk management and environmental sustainability related to industrial areas.
2. Methodology
2.1 Study area
The present research area (Fig 1) is situated in the Folded Flank Tectonic Element of Bengal Basin [34]. The area is composed of recent coastal plain sediments along the west of the eastern coast (Cliff coast) backed by the hilly terrain which is composed of Miocene to Plio-Pleistocene sediments. Piedmont plain deposits are present in front of hilly terrains. Coastal plain sediments are enriched of silty clay and slight sand mixed with piedmont sediments, whereas the hilly terrain consists of inter-layered shale, sandstone, claystone, siltstone, silty shale, etc. The major portion of the area consists of recent fluvio-tidal plain and the sediments of the plain are mainly silty clay and clayey silt. Rashid et al. (2023) [35] noted that the recent sediments were deposited under tidal conditions and fluvial influences. These sediments originate from felsic-dominated metamorphic rock sources associated with the tectonic environment of continental island arcs, active continental margins, and oceanic islands. The sediments are categorized as shale, Fe-rich shale, and wake, respectively.
2.2 Sampling and preparation procedure
Twenty soil sampling was conducted across two distinct industrial zones: Kalurghat and Bayazid. The soil sampling procedure involved delineating a 1.0 m × 1.0 m quadrat at each sampling point, followed by surface clearing. Multiple soil samples were collected randomly within each quadrat at a depth of 05–10 cm and thoroughly homogenized to ensure representative sampling. To minimize analytical interference, the samples underwent preliminary processing to remove extraneous materials including stones, plant materials, glass fragments, organic debris, and lithic components. Each processed sample was subsequently stored in labeled polyethylene bags to prevent cross-contamination. Sample labels documented essential metadata including geographical location, unique sample identifier, and collection date. The samples were subsequently sent to the Health Physics Division of the Atomic Energy Centre Dhaka (AECD) for further processing. Initially, the samples were sun-dried naturally, followed by oven-drying at 105°C to 110°C at AECD. The samples were dried to a constant mass, pulverized, and standardized using a 2-mm mesh sieve. Approximately 500 g of each processed sample was placed in a plastic beaker, which was then sealed with PVC tape to prevent the escape of the gaseous radioisotopes [36]. The sealed samples were stored for 40 days to ensure secular equilibrium between 222Rn and its short-lived daughter nuclei prior to gamma spectroscopic analysis [37,38].
2.3 Measurement procedures and data analysis
A high-resolution HPGe detector was used to measure the amount of gamma-ray-emitting radionuclides present in the samples. To shield the detector from outside radiation, a Pb tube-shaped structure was placed over it. This construction had a fixed bottom and a sliding cover at the top. To calibrate the detector’s energy response, point sources of 22Na, 133Ba, 57Co, 60Co, 137Cs, and 152Eu, each with an activity of 1 microcurie, were used. The detector’s efficiency for soil samples was evaluated using a known activity of 152Eu in an Al2O3 matrix, prepared in containers identical to those used for the actual samples [39]. Additional information regarding the fitting process and efficiency calibration has been detailed elsewhere [40]. The energy and efficiency calibration curves of the HPGe detector are presented in Figs 2 and 3.
The following equation (1) has been used to determine the activity concentration for each radionuclide [41–46]:
Here Ai (Bqkg-1) = the specific activity, = the net count rate per second (sample – background),
= HPGe detector’s efficiency, ργ = γ-ray emission probability, and w = mass of the sample (kg).
The mathematical expression for estimating the uncertainty of the determined radioactivity, as described in [47,48] is provided in Eq. (2).
The sample counts, sample mass, counting time, γ-ray ray emission probability, and counting efficiency are represented by the symbols N, w, T, ργ, and ε, respectively.
2.4 Radiological hazard parameters
2.4.1 Radium equivalent activity (Raeq).
The expression of the overall radioactivity of the soil samples with respect to the hazardous radium is called radium equivalent activity. Equation (3) has been used to determine the radium equivalent activity in the samples [49,50].
The mean activities of 226Ra, 232Th, and 40K are represented by SRa, STh, and SK in Bq/kg, respectively.
2.4.2 The absorbed dose rate.
It is assumed that human being is always receiving exposure to gamma radiation emitted from the radionuclides available in the soil. It means the presence of radionuclides in the soil possesses a relationship with the radiation exposure and possible health hazards. This relation has been characterized by a quantity called outdoor absorbed dose rate (Dout). The outdoor absorbed dose rate from gamma-ray exposure at one meter above the ground was calculated using Equation (4) [51,52]:
By using the Dout value, it is also possible to calculate indoor exposure, [44].
2.4.3 The annual effective dose.
The measured exposures outside and indoors, respectively, can be used to compute the annual effective doses. Therefore, using Eqs. (6) and (7), the yearly effective doses Ein (mSv/y) and Eout (mSv/y) were calculated [3,53].
Globally, the average annual effective dose of all terrestrial radiation, both indoors and outdoors, is 0.48 mSv/y [3]. In situations involving public exposure, various organizations advocate a yearly effective dose limit of 1 mSv/y [3,54–60].
2.4.4 Hazard indices.
Assessing radiological risks associated with radioactivity depends essentially on some fundamental risk indices that present quantifiable parameters of the potential health risks from radionuclides. These indices help to establish rules and regulations concerning the safe applications of studied materials. The external hazard index, Hex, which helps in the overall assessment of external radiation exposure is evaluated using equation (8) [61].
Equation (9) yields the internal hazard index (Hin) [62].
3. Results and discussion
Twenty soil samples were collected from two industrial zones in the Chattogram City of Bangladesh: the Bayazid Industrial Area and the Kalurghat Heavy Industrial Area. The activity concentrations measured in these soil samples are presented in Table 1.
The measured activity concentrations of 226Ra, 232Th, and 40K in the soil samples collected from the Bayazid and Kalurghat Heavy Industrial Area remain below the global average values of 30, 35, and 400 Bq/kg, respectively, as reported in the literature [3]. Furthermore, the absence of 137Cs activity in the samples eliminates the possibility of contamination from nuclear fallout, such as the Chernobyl or Fukushima incidents. The radionuclides exhibit a distinct hierarchy of activity concentrations, with 40K being the highest, followed by 232Th and 226Ra. This pattern reflects the geochemical characteristics and natural prevalence of these radionuclides, with 40K levels being higher due to the abundance of potassium in rocks and minerals. The higher activity of 232Th compared to 226Ra aligns with the known crustal abundance of thorium, which is approximately 1.5 times that of uranium [12].
While industrial zones are often associated with elevated radioactivity [65,66] due to anthropogenic and natural factors, the absence of specific conditions in the studied locations explains the relatively low activity levels. Industries such as oil and gas, mining, or phosphate fertilizer production, which bring NORMs to the surface, are not present in the Bayazid and Kalurghat industrial areas. Similarly, activities involving the use of radioactive isotopes, such as in nuclear power plants or medical facilities, are absent in these regions. Improper disposal of industrial waste, a common contributor to elevated radioactivity, is not evident in the study area, and no waste containing radioactive byproducts, such as fly ash, has been identified. Additionally, the natural geology of the studied regions does not indicate the presence of uranium- or thorium-rich minerals that could contribute to high radioactivity levels.
The geochemical properties of the radionuclides further influence their distribution. The relatively low 226Ra concentrations are likely due to the limited interaction between the soil and uranium-bearing minerals. Similarly, the low 232Th levels suggest the non-abundance of thorium-rich minerals such as monazite in the local geology. Minor variations in radionuclide distribution across soil samples may be attributed to differences in geological and topographical characteristics within the area [4,6,51,62,67–72]. These findings indicate that the Bayazid and Kalurghat industrial zones do not exhibit the conditions typically associated with high radiological hazards, making them safer in comparison to regions with significant industrial or geological contributions to elevated radioactivity.
The following Table 2 compares the activity concentration of soil samples from industrial areas in various countries worldwide with the findings of the current study, based on previously published literature.
A comparative analysis of radionuclide activity concentrations in industrial soils across various countries reveals significant variations, primarily influenced by geological characteristics, industrial activities, and waste disposal practices. The highest activity concentration of 226Ra was observed in Port Said, Egypt, with values between 18.03 and 398.66 Bq/kg; the authors [13] propose that the elevated radium levels are likely due to the site’s proximity to areas with heavy industrial activities, such as fertilizer production, chemical factories, and a paint manufacturing plant. Other notable locations with high ²²⁶Ra levels include Odiel and Tinto River, Spain (66.0–225 Bq/kg), where chemical plants for phosphoric acid and phosphate fertilizer production contribute to radionuclide accumulation. The highest ²³²Th activity concentration was observed in the Industrial District of Abuja, Nigeria, with values ranging from 71.1 to 107.3 Bq/kg [78]. This is likely due to the presence of natural thorium-bearing minerals in the soil, combined with industrial waste discharge from agro-allied and household item production industries. Other areas with high ²³²Th levels include the Odiel and Tinto River in Spain (19.9–58.1 Bq/kg) [28] and the Industrial Park of Northwest China (56.5–79.8 Bq/kg) [30], both of which have industries that process raw materials containing thorium-rich minerals. The highest ⁴⁰K concentration was recorded in Port Said, Egypt, with a range of 583.12 to 3237.88 Bq/kg [2]. This high value is likely due to the accumulation of potassium-rich fertilizers and industrial byproducts. The highest ¹³⁷Cs activity concentration was found in Severodvinsk, Russia, with values ranging from 1.4 to 188.6 Bq/kg [29]. This can be attributed to the presence of a radioactive waste storage facility and historical nuclear activities in the area. In contrast, other industrial regions showed minimal or undetectable levels of ¹³⁷Cs, suggesting that artificial radioactivity contamination is not widespread in non-nuclear industrial areas.
The activity concentrations of 226Ra, 232Th, and 40K in industrial soil across different region in Bangladesh vary significantly, depending on the type of industry and environmental factors. The highest levels were recorded in the Karnaphuli river sediment, Chattogram (22.28–132.42 Bq/kg) [80], likely due to municipal and industrial waste disposal. In comparison, the Savar Industrial Area exhibited moderate levels (24.75–39.84 Bq/kg) [79], while the current study area had lower values (8–18 Bq/kg). The Turag River industrial zone reported the highest ²³²Th concentrations in Bangladesh (59.76–140.22 Bq/kg) [17], possibly due to industrial effluents containing thorium-rich minerals. In contrast, the present study recorded lower levels (15–35 Bq/kg), indicating a relatively lesser influence of industrial thorium contamination. The highest ⁴⁰K concentration in Bangladesh was found in the Karnaphuli river sediment (370.07–1207.40 Bq/kg) [80], likely due to potassium-rich industrial waste. In contrast, the current study area showed relatively moderate values (192–420 Bq/kg). Overall, the radionuclide concentrations observed in the present study are lower than those found in contaminated regions of Bangladesh, such as the Turag River and Karnaphuli River sediments, as well as in other parts of the world.
The calculated values of various hazard parameters for the soil samples are provided in Table 3, with the spatial distribution of total effective dose is depicted in Fig 4.
The comprehensive evaluation of radiation hazard parameters, as detailed in Table 3 and illustrated in Fig 4, demonstrates that the radiation hazard values associated with the soil samples are well within the safety thresholds established by several reputable international organizations [83,84]. This analysis collectively indicates that the radiation levels in the soil samples from the industrial areas of Chattogram, Bangladesh do not pose any significant immediate risk to public health or the environment. Consequently, the results provide reassurance that the soil from these areas does not require any special precautions or remediation. Given the absence of notable radiation hazards, all the examined soil samples are considered suitable for practical uses such as agricultural activities or construction purposes. This finding is especially important for promoting sustainable development in the region, as it ensures that the land can be safely utilized without compromising the well-being of the local population or the surrounding environment.
4. Statistical analysis
4.1 Descriptive statistics
Researchers typically employ both univariate and multivariate statistical techniques to comprehensively analyze the relationships between various radiological parameters when evaluating natural radiation levels in environmental matrices such as soil, sand, and water. This study performed a thorough investigation into the concentrations of radioisotopes (226Ra, 232Th, and 40K) and assessed the potential radiological hazards associated with them. The analysis involved a detailed examination of a standardized dataset (Table 4) using various quantitative measures namely mean, median, mode, standard deviation, kurtosis, and skewness, as well as dendrogram hierarchical cluster analysis. The close alignment between the mean and median values for each NORM indicates a robust normal distribution.
Skewness measures the asymmetry in data, indicating deviation from a normal distribution. A distribution can exhibit either positive or negative skewness. Positive skewness signifies that the distribution leans to the right, with the mean surpassing both the mode and median. In contrast, negative skewness means the distribution tilts to the left, with the mode exceeding the mean and median. The positive skewness observed in 232Th and 40K shows that 232Th has the highest skewness values. Figs 5(a), 5(b), and 5(c) display the frequency distribution histograms for 226Ra, 232Th, and 40K respectively. These histograms support our findings regarding the distribution of these NORMs in the soils from the sampling area at Chattogram.
Kurtosis quantifies the extent of peakedness in a frequency distribution by analyzing the shape of its curve. Kurtosis is classified into three categories: A curve with a relatively sharp peak is referred to as leptokurtic, while a curve with a flat-topped peak is termed as platykurtic [85]. A normal distribution curve is known as mesokurtic. The positive kurtosis values observed for 232Th, and 40K indicate a leptokurtic distribution, characterized by a sharp peak (kurt 0). In contrast, the negative kurtosis values for 226Ra suggest a platykurtic distribution, with a flatter peak (kurt
0).
4.2 Pearson’s correlations study
The Pearson correlation coefficient (r) was employed to quantify the strength of the linear association between the NORMs and related radioactive variables. The correlation coefficients are visualized in Fig 6, where positive correlations (the correlation plot) are shown in red and negative correlations in blue, with the intensity reflecting the strength of the correlation. Significant correlations are marked based on their p-values (*p 0.05, **p
0.01, ***p
0.001). The positive correlation coefficient (r > 0.75, p
0.001) between 232Th and 40K reflects a strong relationship, implying that their concentrations in soil are probably derived from similar origins and factors [86]. There was a weak correlation observed between 226Ra and 232Th (0.63
r
0.75), 40K (0.30
r
0.75), indicating that 226Ra has a different source or influence in the study samples. The radionuclides 232Th and 40K showed a strong positive correlation with all radiological factors (r = 0.85
0.75), indicates that the levels of K and Th are closely related to and influence the radiological hazards. In contrast, 226Ra exhibited a weak correlation with radiological hazard parameters, suggesting that 226Ra possess minimal impact on radiological risks. Radiological hazard parameters, including hazard indices (Hin and Hex), dose rates (Din and Dout), gamma radiation index (Iγ), effective dose (E) showed strong correlations with 226Ra, 232Th and Raeq (r > 0.9, p
0.001) reinforcing their interdependence in assessing gamma radiation hazards.
4.3 Hierarchical Cluster Analysis (HCA)
Hierarchical cluster analysis is a clustering method that organizes objects into a tree-like structure based on their similar characteristics. The goal of cluster analysis is to illustrate the hierarchical relationships among objects, ensuring that the clusters are distinctly different from each other [87]. Clusters can be created from a standardized dataset and are effectively visualized and analyzed with a dendrogram. This study employed hierarchical clustering with Ward’s method, utilizing the same variables as in the Pearson correlation analysis. Figs 7(c) and 7(d) shows two statistically significant clusters of radiological parameters and sampling locations based on Euclidean similarity. Cluster II include the 40K and 232Th radioisotopes, as well as all key radiological hazard variables, which show a strong similarity. This highlights that the increased levels of E, Hin, Hex Iγ, Din, Dout, ELCR and overall soil radioactivity are primarily due to the concentrations of 232Th compared to 40K. Cluster I consist only of 226Ra, suggesting that the health risks from radioactive decay are unaffected by the amount of 226Ra present in the sand. These findings closely align with the outcomes of the Pearson correlation analysis. Investigating these discrepancies could offer important insights into the mechanisms driving the formation and differentiation of these clusters.
4.4 Principal Component Analysis (PCA)
Principal Component Analysis (PCA) is a widely recognized multivariate statistical technique used to emphasize variations and identify significant patterns in a dataset, simplifying its analysis and interpretation. In this study, 3D PCA loading plot and 2D biplot was conducted with varimax rotation and employing Kaiser normalization [88]. The explained variance for PC1, PC2 and PC3 are reported in Table 5. The first principal component (PC1), explaining the majority (93.54%) of the total variance, is predominantly influenced by 226Ra, 232Th, hazard indices (Hin, Hex) and ELCR, indicating their strong interdependence and contribution to radiological hazards. while PC2 (5.78% of variance) accounts for minor variations. In contrast PC2 explains 5.78% of the variance, captures minor variations with 40K, exhibiting a distinct loading that indicates its weaker association with these parameters. Fig 5(a) illustrates the 3D loading plot, highlighting the contributions of each radiological parameter to the principal components (PCs), while Fig 5(b) displays the 2D biplot, mapping sampling locations alongside radiological parameters. Sampling locations cluster are grouped based on their radiological characteristics, through certain outliers (e.g., locations 1 and 15) showing unique properties likely influenced by environmental or anthropogenic factors. This analysis highlights the dominant roles of 226Ra, 232Th and related hazard parameters in contributing to radiological risks while demonstrating the variability in sampling locations, influenced by geochemical and environmental heterogeneity.
4.5 Analysis of variance for zonal disparities
In ANOVA (Analysis of Variance), a significance level of 0.05 meaning there is a chance of incorrectly rejecting the null hypothesis. The F-value indicates the probability of differences among group means, while the F-critical value, based on the F-distribution, acts as the cutoff point. When the F-value surpasses the F-critical value, it implies the presence of significant group differences. In this study, a one-way ANOVA was conducted (Table 6) to examine the zonal disparities in radionuclide levels across the industrial sites (Kalurghat and Bayazid) in Chattogram. In ANOVA, box plots are commonly used to visually compare the distribution of data across different groups. The horizontal line inside each box represents the median of the dataset displayed in Figs 8(a), 8(b), 8(c). Differences in the position of the boxes, median lines, and spread suggest variations in concentration levels between the two industrial sites. For the radionuclides 226Ra, 232Th and 40K, the F-values were found to be less than the critical F-value, and the P-values exceeded the significance level of 0.05. This indicates that the null hypothesis could not be rejected in any of the cases, suggesting that there is no statistically significant variation among the groups for any of the radionuclides.
5. Conclusion
This study presents a comprehensive assessment of NORM in twenty soil samples collected from two major industrial zones in Chattogram, Bangladesh, using a high-resolution high-purity germanium (HPGe) detector. The measured average activity concentrations of radionuclides—namely 226Ra (13 ± 1 Bq/kg), 232Th (22 ± 2 Bq/kg), and 40K (296 ± 25 Bq/kg)-were all found to be below the worldwide average values reported by UNSCEAR. Furthermore, no traces of artificial radioactivity, such as 137Cs, were detected, affirming the natural origin of the observed radionuclides and indicating an absence of nuclear contamination in the sampled areas. The analysis of radiological hazard indices-including radium equivalent activity, hazard indices, absorbed gamma dose rate, and annual effective dose-confirmed that all values were within internationally recommended safety limits. This suggests that, under current conditions, the investigated areas do not pose any significant radiological health risk to the public or to the surrounding environment. Beyond mere quantification, the study applied rigorous statistical and multivariate analyses-including Pearson’s correlation, hierarchical cluster analysis (HCA), and principal component analysis (PCA)-to explore the interrelationships and potential sources of these radionuclides. These methods collectively revealed that 40K and 232Th are the primary contributors to radiological hazards in the area. This finding is substantiated by their strong positive correlations with hazard indices, their tendency to cluster together, and their significant loadings on the principal components, suggesting similar geochemical behaviors or shared natural sources. Importantly, this is the first study of its kind conducted in the industrial regions of Chattogram. As such, it offers crucial baseline data that will be invaluable for future environmental monitoring, especially in light of Bangladesh’s growing industrialization and the upcoming commissioning of the Rooppur Nuclear Power Plant in 2025. Establishing this reference point is essential for detecting any future changes in environmental radioactivity that may arise from anthropogenic or natural factors. This research underscores the necessity of expanding such monitoring efforts to include other industrial areas, especially those adjacent to residential neighborhoods. Continuous surveillance is vital to preemptively identify any radiological threats and to protect public health as industrial activities intensify. Future studies should also consider seasonal and depth-wise variations in radionuclide distribution to develop a more dynamic and long-term understanding of environmental radioactivity inventory in Bangladesh.
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