Radiological assessment of natural radionuclides (238 U, 232 Th, and 40 K) in soil and sugar samples from the Arjo-Didessa Sugar Factory, Ethiopia

Introduction

Natural radioactivity in agricultural soils and food products is an important environmental and public health concern in Ethiopia, particularly in regions with intensive agro-industrial activities such as sugar production. The Ethiopian sugar industry plays a strategic role in the country’s economic development under the Ten-Year Development Plan (2021–2030) and the Growth and Transformation Programme, contributing significantly to export earnings and rural employment. Naturally occurring radionuclides (²³⁸U, ²³²Th, and ⁴⁰K) present in Ethiopian soils can be transferred to crops and processed products, potentially contributing to internal radiation exposure of local populations and consumers. Although the Ethiopian Technology Authority (ETA) has established national guidelines for radiation safety, site-specific baseline data on natural radioactivity in major agro-industrial zones remain scarce. Recent studies conducted in sugar-producing regions across Africa, the Middle East, and Asia have reported activity concentrations of these radionuclides in soils and sugar products that are generally below internationally recommended safety limits, although localized elevations associated with geological conditions and industrial activities have been observed (Alhous et al., 2020; Ali, 2025; Melquiades and Appoloni, 2004; Odumu et al., 2025; Wahab and Morsy, 2006; Gad, 2019; Hiwa et al., 2025; Karthikayini, et al., 2025). Radiological risk indicators, including absorbed dose rate, annual effective dose, and excess lifetime cancer risk, are typically within permissible limits, suggesting low radiological health risks from both agricultural soil exposure and sugar consumption (Elsaman et al., n.d.; Odumu et al., 2025).

Recent studies focusing on environmental radioactivity across Africa have highlighted varying radionuclide distributions. While investigations in Nigerian regions (Mbonu and Ben, 2021; Oladejo et al., 2025) and the Egyptian Nile Delta (Delta and Gad, 2022) have provided valuable data on agro-industrial exposures, baseline site-specific data within Ethiopia remains heavily focused on limited locales. Recent Ethiopian assessments in Bambasi, Dejen, and the Addis Ababa peri-urban areas reported activity concentrations that generally aligned with global limits; however, no published data exist for the Arjo-Didessa Sugar Factory, one of the most extensive estates in the region (Gizachew and Cherie, 2023; Kidane et al., 2024). This knowledge gap is particularly critical given the factory’s location in the Didessa Valley, its extensive irrigation network, and the widespread domestic and export consumption of its sugar (Gad, 2019; Joel et al., 2019; Senthilkumar and Narayanaswamy, 2016).

The main aim of this research work is to determine the activity concentrations of naturally occurring radionuclides (²³⁸U, ²³²Th, and ⁴⁰K) in soil and sugar samples collected from the area of Arjo-Didessa Sugar Factory. Moreover, for the assessment of possible health hazards associated with environmental exposure and sugar ingestion, important radiological risk indices such as radium equivalent activity, absorbed dose rate, annual effective dose, and Excess Lifetime Cancer Risk (ELCR), internal and external hazard indices are calculated. The findings support continued efforts to guarantee environmental and food safety standards in Ethiopia and offer baseline radiation data for the region. Furthermore, comprehensive environmental monitoring requires evaluating primordial radionuclide measurements and elemental concentrations in soil, as well as assessing soil radon activity concentrations. These parameters are critical drivers of localized radiological health risks, influencing both external gamma exposure and internal inhalation hazards in agricultural settings (Azeez et al., 2024; Jafir et al., 2025). Addressing these factors provides a holistic understanding of the radioecological dynamics affecting both crop uptake and occupational safety.

Materials and methods

Study area description

The Arjo-Didessa Sugar Estate is in the Arjo-Didessa Rift Valley, within the Oromia National Regional State of Ethiopia, spanning the East Wollega, Illubabor, and Jimma Administrative Zones (Table 1). The estate lies at an average elevation of 1350 m above sea level, between latitudes 8°30′–8°40′ N and longitudes 36°22′–36°43′ E, approximately 395 km from Addis Ababa.

Sample collection and preparation

Soil samples were collected from five specific command locations within the 2,545-ha estate (Table 1). At each command, five discrete sampling points were established using a rectangular design with a central point. Using an auger, soil was extracted from a depth of 30 cm. Plant material and rocks were removed, and the five sub-samples were mixed firmly before applying the quartering method (discarding two opposite quarters) to yield a highly representative 1 kg composite sample per command. Sugar samples were collected randomly by extracting 1 kg from each of five 5 kg sacks. At the Ethiopian Technology Authority (ETA) laboratory, samples were crushed, homogenized, and passed through a 200-mesh sieve to optimize enrichment of heavy material. Samples were then transferred into 500 mL polyethylene Marinelli beakers and sealed completely for 4 weeks. This period is essential for achieving secular equilibrium, ensuring that the decay rate of the daughter products equals that of the parent nuclides and preventing the escape of confined radon gas (Rejah et al., 2021; Singh et al., 2018; Tamiru Bayissa Hundie, 2024). The same procedures were applied to five sugar samples collected from the factory. These prepared samples were then analyzed for natural radioactivity and radiological hazard parameters. The geographic distribution and specific sampling sites within the Arjo–Didessa Sugar Factory district are illustrated in Figure 1. Soil-to-sugar transfer factors (TF) were calculated as the ratio of the activity concentration in sugar (Bq/kg dry weight) to that in the corresponding soil sample (Bq/kg dry weight) from the same command area.

Representative workflow of sample collection and preparation

The step-by-step workflow for soil and sugar sample collection, field preparation, and laboratory sealing in Marinelli beakers is illustrated in Figure 2.

Gamma spectrometry and quality control

Gamma spectrometric measurements were performed using a High-Purity Germanium (HPGe) detector (Code: B13010) with a relative efficiency of 70 % and energy resolution of 1.90 keV (FWHM) at 1332.5 keV. To achieve high peak counting statistics and minimize relative counting uncertainties (< 5 %), each composite sample was counted once for an extended duration of 57 , 600 s (16 h), while environmental background was measured for 201 , 600 s (56 h) to facilitate accurate background subtraction. The specific activity concentrations (A in Bq/kg) for each identified radionuclide were calculated using the standard Equation 1:where N s and N b represents net counts of the sample and background, t s and t b represent their respective counting times, I γ is the gamma emission probability, ϵ E i is the peak efficiency, and M s is the sample mass. Detector calibration and QA/QC were maintained via proficiency testing (PT) provided biannually by the IAEA. System calibration and measurement traceability were validated using certified reference materials (IAEA-375 soil matrix standard and IAEA-152 milk powder standard) provided by the International Atomic Energy Agency (IAEA), along with routine participation in the IAEA biannual proficiency testing programs. Measured activity values for certified reference materials were within ± 4.5 % of certified reference values.

A = N s / t s − N b / t b ϵ E i . I γ . M s (1)

Excess lifetime cancer risk (ELCR)

To quantify the long-term ingestion risk, the Annual Effective Ingestion Dose (AEID) and ELCR were calculated. The AEID for individual radionuclides was derived using Equation 2:where C i is the activity concentration, I a n n u a l is the adult dietary sugar consumption rate (30.7 kg/year), and D C F i is the dose conversion factor for ingestion. The total ELCR was then calculated by combining the total AEID with the standard life expectancy (DL = 70 years) and the risk factor (RF = 0.05 Sv^-1):

A E I D i = C i × I a n n u a l × D C F i (2)

E L C R = A E I D i × D l × R F

Determination of radiological dose and risk assessment parameters

Activity concentrations of ²³⁸U, ²³²Th, and ⁴⁰K were measured using gamma spectrometry.

Radium equivalent activity (Raeq)

Radium equivalent activity (Raeq) is a widely used index that allows the radiological effects or activity concentrations of materials containing ²³⁸U, ²³²Th, and ⁴⁰K to be compared using a single value. This index is important for assessing the potential radiation hazards of materials and for establishing safety guidelines for the public in areas under investigation (Angjeleska et al., 2020; Caridi et al., 2022; Eke et al., 2024). Raeq is calculated based on the assumption that 1 Bq/kg of ²³⁸U, 0.7 Bq/kg of ²³²Th, and 13 Bq/kg of ⁴⁰K produce the same gamma radiation dose rate. The Raeq value is a weighted sum of the activity concentrations of these radionuclides, typically expressed as Equation 3:where C U , C Th and C K are the average activity concentrations in the sample in Bq/kg of ²³⁸U, ²³²Th, and ⁴⁰K, respectively (Kareem and Tawfiq, 2023; Lemlem and Chaubey, 2022; Zubair, 2020). This formula enables a direct comparison of the radiological hazard posed by different materials, regardless of the varying proportions of these radionuclides. A Raeq value of 370 Bq/kg is generally considered the upper safety limit for building materials, as it corresponds to an external gamma dose of 1.5 mGy/year, which is the recommended maximum for the public (Angjeleska et al., 2020; Caridi et al., 2022; Lewicka et al., 2022).

R α e q = C U + 1.43 C Th + 0.077 C K (3)

Absorbed dose rate (D)

The absorbed dose rate in air (D) is a key metric for assessing the impact of environmental gamma radioactivity from natural radionuclides such as ²³⁸U, ²³²Th, and ⁴⁰K. It quantifies the gamma radiation energy absorbed per unit time at a height of 1 m above ground, providing a direct measure of external exposure risk to humans (Doyi et al., 2017; Hassan et al., 2018; Jilbert et al., 2016). D is typically calculated using the activity concentrations (in Bq/kg) of ²³⁸U, ²³²Th, and ⁴⁰K in soil, applying dose conversion factors recommended by UNSCEAR (2000) The widely accepted formula is expressed in Equation 4:where:

D n G y h − 1 = 0.462 × A U + 0.604 × A Th + 0.0417 × A K (4)

• A_U = activity concentration of ²³⁸U (Bq/kg)
• A_Th = activity concentration of ²³²Th (Bq/kg)
• A_K = activity concentration of ⁴⁰K (Bq/kg)

These coefficients (0.462, 0.604, 0.0417) represent the conversion factors that translate radionuclide concentrations into absorbed dose rates, as established by UNSCEAR (Mekonnen and Deressu, 2020; UNSCEAR, 2000). This approach is widely used in environmental radioactivity studies to estimate the external gamma dose rate at 1 m above ground, which is considered representative of human exposure. The calculated dose rates are compared to global averages to assess radiological safety and inform public health guidelines.

Annual effective dose equivalent (AEDE)

The annual effective dose equivalent (AEDE) estimates the radiation dose an individual receives from environmental gamma radiation over a year. AEDE is calculated from the absorbed dose rate in air (D) using a dose conversion factor of 0.7 Sv/Gy and occupancy factors of 0.2 for outdoor and 0.8 for indoor exposure, reflecting the average time people spend in each environment (Equation 5) (Jilbert et al., 2016; Onjefu et al., 2016).

AEDEmSv / y = D nGy / h × 0.2 × 0.7 Sv / Gy × 8760 h / y (5)

The external and internal hazard index (H_ex &H_in)

The external (H_ex) and internal (H_in) hazard indices are used to assess the potential radiological risks from gamma radiation in soil due to natural radionuclides (²³⁸U, ²³²Th, and ⁴⁰K). Both indices must be less than one to ensure negligible radiation risk for human health and safe use of materials (Dina et al., 2022; MD. Samiul ehsan, et al., 2019). where:

• External Hazard Index (Hex):

Hex = A U / 370 + A Th / 259 + A K / 4810

• Internal Hazard Index (Hex):

Hin = A U / 185 + A Th / 259 + A K / 4810

• A_U = activity concentration of ²³⁸U (Bq/kg)
• A_Th = activity concentration of ²³²Th (Bq/kg)
• A_K = activity concentration of ⁴⁰K (Bq/kg)

A H_ex or H_in value below unity signifies that the radiation risk is within globally recognized safety parameters, correlating to a maximum radium equivalent activity (Raeq) of 370 Bq/kg (Al-Ghamdi, 2019). All calculations followed internationally recognized protocols for environmental radioactivity assessment.

Results and discussion

The activity concentrations of the naturally occurring radionuclides ²³⁸U, ²³²Th, and ⁴⁰K in sugar and soil samples collected from the Arjo-Didessa Sugar Factory are summarized in Tables 2, 3 and illustrated graphically in Figures 3, 4. The associated radiological hazard parameters, including radium equivalent activity (R a e q), internal and external hazard indices (H i n and H e x), absorbed dose rate (D), and annual effective dose equivalent (AEDE), are presented in Tables 4 and 5, with their corresponding variations shown in Figures 5–8 for sugar and soil samples, respectively. Together, these tables and figures provide a comprehensive evaluation of radionuclide distribution and the resulting radiological impact in both environmental and food samples from the study area.

TABLE 1. Samples were gathered from multiple points in the Arjo-Didessa Sugar estate, and their specific GPS coordinates are summarized.

TABLE 2. Radioactivity concentration of ²³⁸ U, ²³²Th, and ⁴⁰K in Sugar samples Bq/kg.

TABLE 3. Radioactivity concentration of ²³⁸U, ²³²Th and ⁴⁰K in Soil samples Bq/kg.

Tables 2, 3, For individual sample rows, ± values represent the combined standard measurement uncertainty (k = 1). For the Average row, ± values represent the sample standard deviation (S D, n = 5). World average baseline values for soil (35 Bq / kg for U x ` 238, 40 Bq / kg for Th 232, 420 Bq / kg for K 40) represent terrestrial crustal reference levels for environmental gamma exposure (UNSCEAR, 2000).

TABLE 4. Radiological hazard parameters for sugar samples, including R a e q, H i n, H e x, absorbed dose rate, and AEDE.

TABLE 5. Radiological hazard parameters for soil samples, including R a e q, H i n, H e x, absorbed dose rate, and AEDE.

Annual Effective Ingestion Dose and ELCR.

Activity concentrations in sugar samples

The activity concentrations of ²³⁸U, ²³²Th, and ⁴⁰K measured in the sugar samples are presented in Table 2 and Figure 2. The ²³⁸U concentrations ranged from 2.86 ± 0.52 to 6.98 ± 0.62 Bq/kg, with an average of 4.78 ± 0.60 Bq/kg, substantially below the global reference value of 35 Bq/kg. For ²³²Th, concentrations ranged from 21.75 ± 2.14 to 26.20 ± 1.92 Bq/kg, with an average of 23.23 ± 1.56 Bq/kg. All ²³²Th measurements were also below the permissible concentration of 40 Bq/kg.

The ⁴⁰K activity concentration ranged from 228.90 ± 15.50 to 308.74 ± 17.30 Bq/kg, with an average of 274.93 ± 14.53 Bq/kg, well below the global mean value of 420 Bq/kg. These results demonstrate that radionuclide concentrations in processed sugar are very low and within internationally accepted limits, confirming that the final product is radiologically safe for consumption.

Activity concentrations in soil samples

The measured radionuclide concentrations in soil samples (Table 3) and (Figure 4) show that ²³⁸U levels ranged from 20.25 ± 1.90 to 24.30 ± 0.52 Bq/kg (average 22.44 ± 1.56 Bq/kg), while ²³²Th varied from 20.95 ± 6.23 to 42.86 ± 3.52 Bq/kg, with an average of 34.98 ± 3.64 Bq/kg. Both radionuclides fall below global reference values, indicating that the soil does not present an elevated radiological burden.

The average activity concentration of ⁴⁰K in soil (482.95 ± 23.73 Bq/kg) slightly exceeds the UNSCEAR global terrestrial average of 420 Bq / kg While detailed soil chemical analysis and fertilizer application records were outside the scope of this study, this elevation is tentatively attributed to the combined influence of local potassium-rich volcanic geology and historical agricultural practices, such as the use of Nitrogen-Phosphorus-Potassium (NPK) fertilizer.

Radiological hazard indices

The potential radiological hazard to humans was evaluated using several parameters, as shown in Tables 4, 5. where A c is the activity concentration of the specific radionuclide in the sugar sample (Bq / kg), I w is the annual per capita consumption rate of sugar (kg / y), and D C F is the standard dose conversion factor for ingestion. Based on ICRP guidelines, the D C F values applied were 4.5 × 10 − 8 Sv / Bq for U 238, 2.3 × 10 − 7 Sv / Bq for Th 232, and 6.2 × 10 − 9 Sv / Bq for K 40.

• Radium Equivalent Activity (R a e q): for sugar samples, the average R a e q was 59.17 Bq/kg, ranging from 52.23 to 65.50 Bq/kg. For soil samples, the average R a e q was 109.64 Bq/kg, ranging from 74.73 to 124.05 Bq/kg. All computed results fell far short of the internationally acceptable threshold of 370 Bq/kg.
• Hazard Indices (H i n and H e x): The internal hazard index (H i n) averaged 0.17 (0.14–0.19) for sugar and 0.36 (0.26–0.43) for soil. The external hazard index (H e x) averaged 0.16 (0.14–0.17) for sugar and 0.32 (0.19–0.48) for soil. In every sample of both sugar and soil, both (H i n and H e x) were less than unity (1), indicating that the substance was not dangerous to human health.
• Absorbed Dose rate (D): The averaged absorbed dose rate was 28.33 nGy/h, ranging from 28.33 nGy/h for sugar samples and 51.63 nGy/h, ranging from 35.15 to 59.57 nGy/h, for soil samples. The average absorbed dose rate for sugar samples is less than half of the global average value of 60 nGy/h, while the absorbed dose rate for soil samples remains slightly below this global reference level.
• Annual Effective Dose Equivalent (AEDE-External Exposure): The average AEDE for sugar was 0.03 mSv/y, ranging from 0.031 to 0.039 mSv/y, and for soil was 0.06 mSv/y, ranging from 0.04 to 0.08 mSv/y. Both average values are significantly less than the 1 mSv/y annual dose limit. These findings clearly indicate that sugar consumption does not pose any harmful radiological exposure. Overall, both external and internal radiation hazards linked to the soil in the study area are minimal, and the environment can be considered radiologically safe for workers and the surrounding community.
• Annual Effective Dose from Ingestion A E D i n g − I n t e r n a l D i e t a r y E x p o s u r e: To assess the radiological risk to consumers, the Annual Effective Dose due to the ingestion of radionuclides in refined sugar (A E D i n g, in Sv / y) was calculated using the following Equation 6:

A E D i n g = ∑ A c · I w · D C F (6)

Across all samples, the activity concentrations of ²³⁸U and ²³²Th were consistently below global averages, while ⁴⁰K in soil showed natural variability attributable to geological and agricultural factors. All calculated radioactive hazard parameters for both soil and sugar comply with international safety standards, demonstrating that environmental exposure and food consumption from the Arjo-Didessa region do not pose radiation health risks.

Annual effective ingestion dose and ELCR

The calculated total Annual Effective Ingestion Dose (AEID) resulting from sugar consumption averaged 222.96 μSv/yr (2.23 × 10⁻⁴ Sv/yr), based on the global standard adult intake. The associated Excess Lifetime Cancer Risk (ELCR) values for sugar ranged from 7.10 × 10⁻⁴ to 8.40 × 10⁻⁴, with an average of 7.8 × 10⁻⁴. For soil exposure, the total AEID ranged up to 4.19 × 10⁻⁴ Sv/yr, translating to a maximum ELCR of 1.47 × 10⁻³. These findings clearly indicate that the probability of developing cancer over a lifetime due to the ingestion of Arjo-Didessa sugar or long-term environmental exposure to the estate’s soil is negligible and well within safe operational limits.

The daily radionuclide intake, annual committed effective dose (C E D), and excess lifetime cancer risk (E L C R) resulting from sugar consumption are summarized in Table 6. The mean daily intakes of U 238, Th 232, and K 40 were 0.402 Bq / day, 1.954 Bq / day, and 23.124 Bq / day, respectively. The overall annual committed effective dose averaged 222.96 μ Sv / y (2.23 × 10 − 4 Sv / y), based on the standard adult ingestion rate of 30.7 kg / year. The corresponding E L C R values ranged from 7.10 × 10 − 4 to 8.40 × 10 − 4 (mean: 7.80 × 10 − 4). Because the total C E D is far below the international public limit of 1.0 mSv / y, sugar produced at the Arjo-Didessa facility presents negligible dietary radiation risk.

TABLE 6. Daily radionuclide intake (D I), annual committed effective dose (C E D), and excess lifetime cancer risk (E L C R) for sugar samples.

D I (Daily Intake) is based on a standard adult sugar consumption rate of 84.11 g / day (30.7 kg / year). C E D (Committed Effective Dose) is calculated using ICRP 119 ingestion dose conversion factors (0.045 μ Sv / Bq for U 238, 0.230 μ Sv / Bq for Th 232, and 0.0062 μ Sv / Bq for K 40). E L C R (Excess Lifetime Cancer Risk) is calculated using an average life expectancy (D L) of 70 years and a cancer risk factor (R F) of 0.05 Sv − 1. The international annual dose limit for public exposure is 1.0 mSv / year (1000 μ Sv / year).

For the soil samples, the calculated ELCR values ranged from 8.22 × 10⁻⁴ to 1.47 × 10⁻³ (Table 7), reflecting the natural baseline radioactivity of the agricultural environment. Although these values are slightly higher than those for the refined sugar, the lifetime excess cancer risk associated with long-term environmental exposure to these soils remains very low, indicating that the site is radiologically safe for agricultural workers.

TABLE 7. Total Annual Effective Ingestion Dose (AEID) and Excess Lifetime Cancer Risk (ELCR) in Soil samples.

Soil-to-sugar transfer factors (TF)

The soil-to-sugar Transfer Factors (TF), defined as the ratio of activity concentration in sugar to that in the corresponding soil, were calculated for each paired sample from the five command areas. The mean TF values were 0.21 ± 0.07 (range: 0.12–0.29) for ²³⁸U, 0.70 ± 0.20 (range:0.51–1.04) for ²³²Th, and 0.61 ± 0.22 (range: 0.49–1.00) for ⁴⁰K (Table 8). These values indicate limited transfer of uranium and thorium, and moderate transfer of potassium from soil into the processed sugar. The calculated Soil-to-Sugar transfer factors (TF) indicate the net retention of radionuclides after processing. Because the refinement process from raw sugarcane to crystallized sugar involves rigorous physical and chemical clarification that precipitates heavy minerals from the juice, the low observed TF values accurately reflect limited biological uptake, compounded by heavy mineral removal during industrial processing.

TABLE 8. Soil-to-sugar transfer factors (TF) of ²³⁸U, ²³²Th, and ⁴⁰K for the five paired samples.

The calculated soil-to-sugar transfer factors provide further insight into radionuclide mobility in the Arjo-Didessa agro-industrial system. The mean TF values of 0.21 for ²³⁸U and 0.70 for ²³²Th are relatively low, consistent with the strong binding of these radionuclides to soil particles in tropical agricultural soils, which limits root uptake. The higher TF for ⁴⁰K (0.61) is expected, as potassium is an essential plant nutrient readily taken up by sugarcane. These TF values align with those reported for other crops and sugar products in tropical and subtropical regions, where transfer of uranium and thorium is typically below 1. Importantly, the moderate TF for ⁴⁰K, combined with the low sugar activity levels, confirms that fertilizer practices and factory processing do not result in significant radiological accumulation in the final product.

The mean activity concentrations measured in the soils of the Arjo-Didessa Sugar Factory (²³⁸U = 22.4 Bq/kg, ²³²Th = 35.0 Bq/kg, and ⁴⁰K = 482.95 Bq/kg) fall within the range reported for many regions worldwide (Table 9). The ²³⁸U and ²³²Th levels are comparable to those observed in Turkey’s Marmara Region and in soils from Owerri, Nigeria, and remain below the higher values reported in Guangdong (China), and the Iperindo mining area of Nigeria. The ⁴⁰K concentration at Arjo-Didessa is slightly above the UNSCEAR, global average (420 Bq/kg) and is like values from Turkey (Ardahan), India (Kalpakkam), and China (Guangdong). Compared with other Ethiopian data, Arjo-Didessa shows lower uranium and thorium but higher potassium than the Bambasi region. Overall, the radionuclide concentrations in Arjo-Didessa soils are moderate and align with typical global ranges, indicating no unusual radiological burden.

TABLE 9. Comparison of the mean activity concentration of ²³⁸U, ²³²Th, and ⁴⁰K within Argo-Didessa factory soils in Ethiopia with other countries.

The mean activity concentrations of natural radionuclides measured in sugar samples from Arjo-Didessa (²³⁸U = 4.78 ± 0.60 Bq/kg, ²³²Th = 23.23 ± 1.56 Bq/kg, and ⁴⁰K = 274.93 ± 14.53 Bq/kg) are within the range reported internationally (Table 10). The uranium concentration is considerably lower than the worldwide average value of 22 Bq/kg and is comparable to values reported for South Africa. The thorium activity is higher than that reported in South Africa, Iraq, and Brazil, but remains close to the global reference level of 15 Bq/kg. The potassium-40 concentration is below the worldwide average value of 420 Bq/kg and comparable to values reported for South African sugar samples. Overall, the results indicate that sugar produced at Arjo-Didessa does not pose a radiological health risk and is consistent with global observations for foodstuffs.

TABLE 10. Comparison of mean specific activity concentration of ²³⁸U, ²³²Th, and ⁴⁰K (Bq/kg) in sugar samples from Ethiopia and other countries worldwide.

Daily radionuclide intake and ingestion dose assessment

To evaluate dietary radiation exposure, the daily intake of natural radionuclides and the resulting Committed Effective Dose (C E D) were calculated for sugar samples (Table 6). The average daily intake rates of U 238, Th 232, and K 40 were 0.402 Bq / day, 1.954 Bq / day, and 23.124 Bq / day, respectively. The resulting mean annual C E D values were 6.60 μ Sv / y (U 238), 164.03 μ Sv / y (Th 232), and 52.33 μ Sv / y (K 40), yielding a total annual committed effective dose of 222.96 μ Sv / y (0.223 mSv / y). This total ingestion dose is well below the internationally recommended public exposure limit of 1.0 mSv / y (ICRP, 1991; UNSCEAR, 2000), confirming that sugar produced at the Arjo-Didessa factory is radiologically safe for consumption.

Limitations of the study

This preliminary baseline study provides valuable initial data, but several methodological boundaries should be noted:

• Spatial Sample Size: Sampling was limited to five composite soil and sugar samples (n = 5 per matrix) across five command zones due to resource constraints, limiting spatial resolution across the full 2,545-ha estate.
• Replicate Analysis: Samples underwent single long-duration counting runs (57 , 600 s) rather than intra-sample counting replicates.
• Statistical Scope: Comparisons are descriptive (mean values vs. regulatory limits); formal inferential statistical hypothesis testing was not conducted due to the sample size.
• Matrix Selection: Analysis was restricted to agricultural soil and refined sugar. Intermediate stages (raw sugarcane, cane juice, press mud, and irrigation water) were not sampled, precluding a step-by-step mapping of radionuclide reduction during processing.

Conclusion

This study provides a preliminary baseline assessment of natural radioactivity levels and associated radiological hazards in soil and sugar samples from the Arjo-Didessa Sugar Factory. Activity concentrations of ²³⁸U and ²³²Th were within or below global reference values, whereas ⁴⁰K in soil exhibited moderate elevation attributable to local geological characteristics and agricultural practices. Crucially, the soil-to-sugar transfer factors remained low to moderate, confirming minimal radionuclide translocation into the final refined product. All evaluated radiological hazard parameters, including radium equivalent activity (Raeq), external and internal hazard indices (H i n and H e x), absorbed gamma dose rate (D), and annual effective dose equivalent (AEDE), were substantially below internationally accepted safety limits, confirming negligible risk from both environmental exposure and sugar consumption. Furthermore, the newly integrated Excess Lifetime Cancer Risk (ELCR) values for both dietary sugar consumption and environmental soil exposure demonstrate a negligible risk, confirming that long-term exposure poses no significant radiological threat to human health.

In the Ethiopian socio-economic context, these findings are highly timely and relevant. As the Arjo-Didessa Sugar Factory plays an essential role in national sugar production, domestic supply optimization, and export earnings under the country’s Ten-Year Development Plan (2021–2030), verifying food safety is paramount. The Ethiopian Technology Authority’s (ETA) national food safety regulations and radiation protection standards are fully complied with, as evidenced by the low radioactive load found in this study. Consistent with global literature, the measured radionuclide levels in the Didessa Valley are comparable to or lower than those of other prominent agricultural areas, reinforcing the radiological safety of the region’s agro-industrial operations. This confirms that intense sugarcane agriculture in this area does not present an increased radiation hazard.

While this investigation was logistically constrained to five primary sampling sites, which limit its ability to provide a complete spatial representation across the entire estate, it successfully establishes an indispensable, high-precision baseline for the region. To address this spatial limitation and build a holistic radiological profile, future investigations must expand sampling systematically across all eleven command zones of the estate. Additionally, tracking the programmatic transition of radionuclides by evaluating alternative environmental matrices, such as irrigation water and raw sugarcane juice, will provide deeper insights into the environmental dynamics within the valley. Overall, this study confirms that refined sugar from Arjo-Didessa is radiologically safe for public consumption and that the operational environment is safe for the workforce and surrounding communities, thereby contributing significantly to Ethiopia’s radiation monitoring framework and sustainable agro-industrial development.

Recommendations

This study covered only five of the eleven operational zones of the Arjo-Didessa Sugar Factory due to budget constraints. Future researchers or institutions are encouraged to extend this work by including all operational areas to obtain a more comprehensive radiological assessment. The present findings can serve as a valuable baseline for further monitoring and expanded investigations.

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Footnotes

Edited by: Antonije Onjia, University of Belgrade, Serbia

Reviewed by: Hussein M. Elmehdi, University of Sharjah, United Arab Emirates

Hawbash Karim, Koya University, Iraq

Said Khadour, Universite Moulay Ismail Departement de Physique, Morocco

Ahmed Mahmood, Directorate General of Education in Kirkuk, Iraq