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J. Radiat. Prot. Res > Volume 48(2); 2023 > Article
Coulibaly, Kpeglo, and Darko: Assessment of Radiological Hazards in Some Foods Products Consumed by the Malian Population Using Gamma Spectrometry

Abstract

Background

Food consumption is one of the most important routes for radionuclide intake for the public; therefore, there is the need to have a comprehensive understanding of the amount of radioactivity in food products. Consumption of radionuclide-contaminated food could increase potential health risks associated with exposure to radiation such as cancers. The present study aims to determine radioactivity levels in some food products (milk, rice, sugar, and wheat flour) consumed in Mali and to evaluate the radiological effect on the public health from these radionuclides.

Materials and Methods

The health impact due to ingestion of radionuclides from these foods was evaluated by the determination of activity concentration of radionuclides 238U, 232Th, 40K, and 137Cs using gamma spectrometry system with high-purity germanium detector and radiological hazards index in 16 samples collected in some markets, mall, and shops of Bamako-Mali.

Results and Discussion

The average activity concentrations were 9.8±0.6 Bq/kg for 238U, 8.7± 0.5 Bq/kg for 232Th, 162.9±7.9 Bq/kg for 40K, and 0.0035±0.0005 Bq/kg for 137Cs. The mean values of radiological hazard parameters such as annual committed effective dose, internal hazard index, and risk assessment from this work were within the dose criteria limits given by international organizations (International Commission on Radiological Protection and United Nations Scientific Committee on the Effects of Atomic Radiation) and national standards.

Conclusion

The results show low public exposure to radioactivity and associated radiological impact on public health. Nevertheless, this study stipulates vital data for future research and regulatory authorities in Mali.

Introduction

Natural radioactivity is mostly caused by the primordial radionuclides, namely 40K, and 238U-232Th decay series, which are present in earth formations. It is important to understand the concentrations and distributions of naturally occurring radioactive materials (NORM) since it gives helpful information to monitor environmental radioactivity. Artificial radionuclides such as 137Cs which are occasioned by anthropogenic activities also contribute to environmental monitoring [1].
Several human activities enhance the level of NORM in the environment. For example, there are the burning of fossil fuels and the unrestrained mining processes, etc. These radionuclides accumulated in the soil can reach foods or plants through metabolic processes and ultimately can be transferred to animals and subsequently to humans when they consume contaminated foods. The level of risk to human health is dependent on the type, amount of radionuclide, and the exposure time. Radiation exposure to humans differs from one place to another depending on the geographical and geological conditions [2, 3].
The key objective of this study is to calculate the activity concentration of radionuclides and evaluate the radiological hazards in some food products consumed by the Malian population using gamma spectrometry.
This study will offer a basis for more assessment of exposures to radionuclides in food products and useful data for the Malian regulatory body Agence Malienne de Radioprotection (AMARAP) and other relevant authorities.

Materials and Methods

1. Sample Collection, Preparations, and Measurement

Mali is the second largest importing country in West Africa. Around 13.91% of agricultural products are imported and 13.45% of this value is foods only [4]. Based on the collected data from Direction Généraledu Commerce, de la Consommation et de la Concurrence (DGCCC) and Office des Produits Agricoles du Mali (OPAM), four different kinds of the most consumed foods by the Malian population (powdered milk, rice, sugar, and wheat flour) were selected for sampling. Thirteen samples were collected: three from powdered milk, three from sugar, three from rice, and four from wheat flour from different markets, malls, and shops around Bamako city (Mali), between them, five samples were made in Mali (one rice, one sugar, and three wheat flour samples).
Sixteen samples were prepared and stored for almost 1 month for secular equilibrium between the U-Th series and their daughters to be reached. The activity concentration of samples was obtained using a gamma spectrometry system with a high-purity germanium (HPGe) detector at the Ghana Research Reactor-1 (GHARR-1) of the Ghana Atomic Energy Commission (GAEC). The gamma spectrometry system was made up of an HPGe detector connected to a computer-based multi-channel analyzer. The detector has a relative efficiency of 40% with an energy resolution of 2.0 keV at gamma-ray energy of 1,332 keV of 60Co. The individual radionuclides were identified by their characteristic gamma-ray energies and the quantitative analysis of radionuclides was done with the Genie 2000 gamma acquisition and analysis software (Mirion).

2. Calculations of Activity Concentration and Annual Committed Effective Dose

1) Activity concentration

After the secular equilibrium time, all the samples were read for 10 hours, the activity concentrations of 238U and 232Th were assessed by averaging the peaks of different daughters for the U-Th series, 40K and 137Cs were calculated using the photopeak in the spectrum. The activity concentrations of 238U were obtained by using the gamma-ray energies and the respective gamma-intensity of 214Bi at 609.3 keV (44.8%) and 214Pb at 351.9 keV (35.8%). That of 232Th was obtained using gamma energies of 228Ac at 911 keV (26.6%), 212Pb at 238.6 keV (43.3%), and 208Tl at 583 keV (30.1%), and 2,614.7 keV (35.3%) considering a branching ratio of 33.7% from 212Bi towards 208Tl. For 40K, it was estimated from its energy line at 1,460.8 keV (10.7%) while the 137Cs were calculated from the gamma energy line at 661.67 keV (85.1%). All the energies and yields of the various radionuclides were from a standard library.
Therefore, the activity concentration (AE,i) in Bq/kg, for a radionuclide i with a photopeak at energy E, was calculated as:
(1)
AE,i=NE,iɛE·t·γd·M
where NE,i is the net peak-area of i radionuclide at energy E, εE is efficiency at energy E, t is counting time (s), γd is the gamma emission probability, and M is the mass (kg).

2) Annual committed effective dose

The annual committed effective dose (AED) (Sv/yr) was calculated using the activity concentration of all radionuclides detected and analyzed in the samples as:
(2)
AED=e(g)j·Aj·Uj
where e(g)j is the effective dose conversion factor for ingestion of nuclide j (Sv/Bq), Aj is the activity concentration of nuclide j (Bq/kg) and Uj is the consumption rate of food (kg/yr). In this study, the international values of annual consumption rate were used [5].

3) Internal hazard index

The internal exposure to radon and its short-lived daughters is also dangerous to the respiratory organs. To account for this threat the internal hazard index (Hin) was quantified using the activity concentration of 40K, 238U, and 232Th. It should be below one to provide safe levels for the respiratory organs of individuals. The internal exposure from the daughters of 238U, 232Th, and 40K, was calculated using Equation (3) [6]:
(3)
Hin=AU185+ATH259+AK4810
where AU is activity concentration of 238U (Bq/kg), ATh is activity concentration of 232Th (Bq/kg), and AK is activity concentration of 40K (Bq/kg).

4) Risk assessment calculation

Risk is estimated by the assumption that a linear dose-effect relationship has no threshold according to the International Commission on Radiological Protection (ICRP) [7]. Lower doses have a fatal cancer risk factor (RF) of 0.05 Sv−1 reported by International Atomic Energy Agency (IAEA) [7]. This RF determines the likelihood of an individual dying of cancer by a 5% increase of 1 Sv dose received throughout his entire life.
The AED (Sv/yr) in food is estimated to determine the cancer risk of an adult using Equation (4).
(4)
Riskassessment(RA)=AED·LE·RF
with where LE is life expectancy in Mali which is 59.3 years [8] and RF is 0.05 Sv−1 [7] for low doses.

Results and Discussion

1. Results

1) Activity concentration

In the present study, 16 food samples were analyzed. Table 1 shows the activity concentrations of 238U, 232Th,40K, and 137Cs. The minimum detection activity obtained for 238U, 232Th,40K, and 137Cs were 0.038, 0.044, 0.31, and 10−3 Bq/kg, respectively.

2. Radiological Hazard Indices

1) Annual committed effective dose

Owing to the unavailability of updated and reliable national consumption rate values of foods in Mali, the AED was calculated using international consumption rate values reported by United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) in 2008 [5] as presented in Table 2.

2) Internal hazard index

The Hin was determined in the various samples of powdered milk, rice, sugar, and wheat flour as presented in Table 3.

3) Risk assessment

The RA was calculated using Equation (4) above and the results are shown in Table 4.

3. Discussion

The range of activity concentrations for 238U varies from 1.1±0.1 to 32.8±2.3 Bq/kg, for 232Th from 0.01±0.001 to 33.9±2.2 Bq/kg, for 40K from 3.2±0.2 to 382.2±19.5 Bq/kg, and for 137Cs from 0.0025±0.0004 to 0.0044±0.0006 Bq/kg. The peaks of 40K and 137Cs for most of the rice, wheat flour, and sugar samples were below the detection limit as indicated in Table 1.
The result of samples showed that S-01, S-03, R-01, WF-04 represented the lowest activities concentrations level of 238U, 232Th, 40K, and 137Cs, respectively; M-01, WF-02, M-03, and R-03 represented the highest values of 238U, 232Th, 40K, and 137Cs, respectively. The results proved that the samples of powdered milk contained the maximum values of activity concentrations of NORM; the R-03 contains the maximum value of 137Cs. All of which are imported from Europe and Asia. Special or more investigation must be carried out on the milk because they are more consumed by infants and children.
The activity concentrations of measured radionuclides in the food samples are much lower than the Malian standard 1,000 Bq/kg for 238U and 232Th, 10,000 Bq/kg for 137Cs, and 100,000 Bq/kg for 40K and in comparison, to other works as shown in Table 5 [1, 913].
The AED from ingestion is calculated for various age groups (from infant to adult). The range of values for AED (μSv/yr) of samples was; for powdered milk 248.8 (M-03) to 2,201.3 (M-03), for rice 2.2 (R-01) to 432.6 (RF-03), for sugar 0.2 (S-03) to 25.1 (S-02), and for wheat flour 9.2 (WF-04) to 1,155.9 (WF-02), as shown in Table 2. The highest values of AED were reported again in powdered milk. The AED’s mean value for the consumption of these foods was around 0.33 mSv/yr. This compared well with the UNSCEAR worldwide average annual dose due to the ingestion of foodstuffs of 0.29 mSv/yr.
Based on the calculated values (Hin<1), the obtained values of this index due to the ingestion of these food products were below one. For consumption of these foods products, the calculated Hin means good safe levels for the respiratory organs due to internal exposure to radon and its short-lived progenies as in Table 3.
The RA was calculated for different ages from 1 year to more than 17 years, the range of RA varied from 7.07×10−4 (for 1 to 2 years) to 1.5×10−3 (for 2 to 7 years). It is 4 to 8.5 times less than the risk (6.0×10−3) from all natural radiation sources based on the global average annual radiation dose which is 2.4 mSv/yr to man [5]. The mean value of RA is 9.28×10−4, which is 6.5 times less than the risk 6.0×10−3 as mentioned above as shown in Table 4.
The cancer risk is based on an annual dose limit of 1 mSv for the public, which gives an annual death probability of 10−5, i.e., 1 in 100,000 reported by ICRP in 1990 [14]. That means the death probability by cancer due to the ingestion of these food products is much lower than the estimated value reported by ICRP in 1990 [14].

Conclusion

Natural and artificial radionuclides (137Cs) in selected foods were studied for their radiological hazards. The radionuclides of 238U, 232Th (through their daughters) and 40K, and 137Cs were the main radionuclides detected in the food samples in this research. The analysis revealed that the results of activity concentrations of the 238U, 232Th, 40K, and 137Cs in samples were generally lower than the national standard and global reference. The calculated AED values were less than the authorized limit for the public which is 1 mSv/yr. The mean radiological parameters such as AED, Hin, and RA were below the dose criteria limits given by international organizations (ICRP and UNSCEAR) and national standards.
The results of this study proved that these foods are safe for human consumption even if the risk (stochastic effect) associated with internal exposure due to low dose intakes exists. Based on obtained values, the probability of someone dying of cancer due to the ingestion of these foods is less than 10−5 in the Malian population.

Acknowledgements

I am very grateful to the supervisors and the staff Radiation Protection Institute (RPI) particularly the staff of gamma spectrometry of Ghana Atomic Energy Commission (GAEC). I am also grateful to my organization: Malian Regulatory Body (AMARAP) through its General Director and the staff of the regulatory analysis laboratory of DCST.

Notes

Conflict of Interest

No potential conflict of interest relevant to this article was reported.

Ethical Statement

The study was conducted in accordance with the Declaration of Helsinki, and the protocol was approved by the Ethics Committee of Department of Radiation Protection of School Nuclear and Allied (SNAS) of University of Ghana (UG) (IRB approval no. 10751253). Written informed consent by the patients was waived due to a retrospective nature of our study.

Author Contribution

Conceptualization: Coulibaly A, Kpeglo DO, Darko EO. Methodology: Coulibaly A, Kpeglo DO, Darko EO. Formal analysis: Coulibaly A. Supervision: Kpeglo DO, Darko EO. Funding acquisition: Coulibaly A. Project administration: Coulibaly A. Investigation: Coulibaly A, Kpeglo DO, Darko EO. Visualization: Kpeglo DO, Darko EO. Validation: Coulibaly A, Kpeglo DO, Darko EO. Writing - original draft: Coulibaly A. Writing - review & editing: Coulibaly A. Approval of final manuscript: all authors.

References

1. Awudu A, Faanu A, Darko E, Emi-Reynolds G, Adukpo O, Kpeglo D, et al. Preliminary studies on 226Ra, 228Ra, 228Th and 40K concentrations in foodstuffs consumed by inhabitants of Accra metropolitan area, Ghana. J Radioanal Nucl Chem. 2012;291(3):635-641.
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2. Adjirackor T, Darko EO, Emi-Reynolds G, Kpeglo DO, Awudu R, Owusu Banahene J. Radiological study of soil, fertilizer and foodstuffs in some selected farming communities in the greater Accra region, Ghana. Elixir Nuclear Radiation Phys. 2014;77:29112-29118.

3. Melqiades FL, Appoloni CR. Natural radiation levels in powdered milk samples. Food Sci Technol. 2004;24(4):501-504.
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4. World Perspective. Mali, imports and exports [Internet]. World Perspective; 2015 [cited 2023 Jun 1]. Available from: https://perspective.usherbrooke.ca/bilan/servlet/BMImportExportPays?codePays=MLI

5. United Nations Scientific Committee on the Effects of Atomic Radiation. Sources and effects of ionizing radiation [Internet]. UNSCEAR; 2008 [cited 2023 Jun 1]. Available from: https://www.unscear.org/docs/reports/2008/11-80076_Report_2008_Annex_D.pdf

6. Ahmed SNEM. Radioactivity analysis of local and imported cement in Sudan [dissertation]. University of Khartoum. 2006.

7. Karim K. Modelling radionuclides transport and dose assessment in a groundwater system in Somita-Taparko Goldmine in Burkina Faso [dissertation]. University of Ghana. 2015.

8. United Nations Development Programme. Human Development Reports. Human development report 2020. The next frontier: human development and anthropocene [Internet]. UNDP; 2020 [cited 2023 Jun 23]. Available from: https://hdr.undp.org/content/human-development-report-2020

9. Décret N°2014-0931/P-RM du 31 décembre 2014: Fixant les Règles Relatives à la Protection contre les Rayonnements Ionisants à la Sûreté et la Sécurité des Sources de Rayonnements Ionisants. Fixing relatives rules to protection against ionizing radiation, safety and security of ionizing radiation sources in Mali. J Off Mali. 2015;4:131-160. (French).

10. Hamdan AM. Radioactivity of flour, wheat, bread improvers and dose estimates in Sudan [dissertation]. University of Kordofan. 2004.

11. Abojassim AA, Al-Gazaly HH, Kadhim SH. Estimated the radiation hazard indices and ingestion effective dose in wheat flour samples of Iraq markets. Int J Food Contam. 2014;1:6.
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12. Najam LA, Tawfiq NF, Kitha FH. Measuring radioactivity level in various types of rice using NaI (Tl) detector. Am J Eng Res. 2015;4(3):126-132.

13. Ababneh ZQ, Alyassin AM, Aljarrah KM, Ababneh AM. Measurement of natural and artificial radioactivity in powdered milk consumed in Jordan and estimates of the corresponding annual effective dose. Radiat Prot Dosimetry. 2010;138(3):278-283.
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14. International Commission on Radiological Protection. 1990 Recommendations of the international commission on radiological protection. ICRP Publication 60. Ann ICRP. 1991;21(1–3):1-201.

Table 1
Activities Concentration of Radionuclide in Some Imported and Locally Consumed Food Products by the Malian Population (Bq/kg Dried Weight) Compared with the National Standard by the Regulatory Authority in Mali [9]
Sample type Sample code Activity concentration (Bq/kg)

238U 232Th 40K 137Cs
Milk M-01 32.8±2.3 10.3±0.6 117.9±6.0 <0.001
M-02 <0.038 14.3±0.8 228.2±14.7 <0.001
M-03 <0.038 <0.044 382.2±19.5 0.0026±0.0004
Average±SD 32.8±2.3 12.3±1.0 242.8±6.8 0.0026±0.0004

Rice R-01 <0.038 <0.044 3.2±0.2 <0.001
R-02 <0.038 7.9±0.5 <0.31 <0.001
R-03 1.7±0.1 8.5±0.5 <0.31 0.0044±0.0006
RF-01 6.3±0.3 11.5±0.6 <0.31 <0.001
RF-02 <0.038 3.3±0.2 <0.31 <0.001
RF-03 11.3±0.7 11.2±0.9 <0.31 <0.001
Average±SD 6.3±0.3 8.5±0.3 3.2±0.2 0.0044±0.0006

Sugar S-01 1.1±0.1 <0.044 <0.31 0.0025±0.0004
S-02 <0.038 0.8±0.05 <0.31 <0.001
S-03 <0.038 0.01±0.001 <0.31 <0.001
Average±SD 1.1±0.1 0.4±0.04 <0.31 0.0025±0.0004

Wheat flour WF-01 2.8±2.0 8.7±0.5 <0.31 0.0043±0.0006
WF-02 10.1±0.6 33.9±2.2 <0.31 0.0039±0.0006
WF-03 1.9±0.1 6.4±0.4 <0.31 <0.001
WF-04 <0.038 0.6±0.03 <0.31 <0.001
Average±SD 5.0±0.2 12.4±1.0 <0.31 0.0041±0.0006

Mean 9.8±0.6 8.7±0.5 162.9±7.9 0.0035±0.0005

Malian standard [9] 1,000 1,000 100,000 10,000

SD, standard deviation.

Table 2
Annual Committed Effective Dose of Radionuclide in the Samples
Sample code Activity concentration (Bq/kg) Annual committed effective dose, AED (μSv/yr)


238U 232Th 40K 137Cs Age 1–2 yr Age 2–7 yr Age 7–12 yr Age 12–17 yr Age >17 yr
M-01 32.8 10.3 117.9 <0.001 1,708.0 1,044.9 810.2 623.7 480.6

M-02 <0.038 14.3 228.2 <0.001 2,086.9 1,175.8 853.7 584.1 494.0

M-03 <0.038 <0.04 382.2 0.0026 2,201.3 963.1 596.2 319.5 248.8

R-01 <0.038 <0.04 3.2 <0.001 7.0 3.1 3.8 2.2 2.8

R-02 <0.038 7.9 <0.31 <0.001 159.3 123.9 205.3 177.0 253.3

R-03 1.7 8.5 <0.31 0.0044 179.3 138.7 230.1 199.2 282.4

RF-01 6.3 11.5 <0.31 <0.001 266.7 203.6 338.4 296.5 409.6

RF-02 <0.038 3.3 <0.31 <0.001 66.7 51.9 85.9 74.1 106.0

RF-03 11.3 11.2 <0.31 <0.001 288.3 217.5 362.1 320.2 432.6

S-01 1.1 <0.04 <0.31 0.0025 5.8 3.8 6.5 6.4 6.7

S-02 <0.038 0.8 <0.31 <0.001 15.8 12.3 20.4 17.6 25.1

S-03 <0.038 0.01 <0.31 <0.001 0.3 0.2 0.3 0.3 0.4

WF-01 2.8 8.7 <0.31 0.0043 190.2 146.3 242.9 211.5 296.2

WF-02 10.1 33.9 <0.31 0.0039 741.5 570.6 947.2 824.2 1,155.9

WF-03 1.9 6.4 <0.31 <0.001 140.3 107.1 179.3 156.0 218.8

WF-04 <0.038 0.6 <0.31 <0.001 11.9 9.2 15.3 13.2 18.8

Mean 504.3 298.3 306.1 239.1 277.0
326.0 (~0.33 mSv/yr)
Table 3
Internal Hazard Index (Hin) Values
Sample Radionuclide activity concentrations (Bq/kg) Hin
238U 232Th 40K
Powder milk 32.8 12.3 242.8 0.3
Rice 6.3 8.5 3.2 0.1
Sugar 1.1 0.4 <0.3 0.01
Wheat flour 5.0 12.4 <0.3 0.1
Table 4
Risk Assessment Values
Variable Age range (yr)
1–2 2–7 7–12 12–17 >17
AED (Sv/yr) 5.04×10−4 2.98×10−4 3.06×10−4 2.39×10−4 2.77×10−4
RA 1.50×10−3 7.07×10−4 9.08×10−4 7.09×10−4 8.21×10−4
Mean value of RA 9.28×10−4

AED, annual committed effective dose; RA, risk assessment.

Table 5
Evaluation of the Average Activity Concentration (Bq/kg) of 238U, 232Th, 40K, and 137Cs in Foods in the Present Study and Other Published Data around the World
Country Sample 238U 232Th 40K 137Cs Reference
India Rice - - 120.8±2.1 - [1]
Ghana Rice - - 104.36±10.22 - [1]
USA Rice - 13.67 231.87 - [12]
New-Zealand Powder milk - - 349.86±36.45 0.7±0.62 [13]
Europe Powder milk - - 337.6±19.83 0.43±0.05 [13]
Iraq Wheat flour 6.60±3.72 1.95±1.33 133.10±67.04 - [11]
Sudan Wheat flour 2.83±0.95 3.19±2.03 11.87±7.12 - [10]
Mali Powder milk 32.8±2.3 12.3±1.0 242.8±6.8 0.0026±0.0004 Present study
Mali Rice 6.3±0.3 8.5±0.3 3.2±0.2 0.0044±0.0006 Present study
Mali Sugar 1.1±0.1 0.4±0.04 - 0.0025±0.0004 Present study
Mali Wheat flour 5.0±0.2 12.4±1.0 - 0.0041±0.0006 Present study
Malian standard 1,000 1,000 100,000 10,000 [9]

Values are presented as mean±standard deviation.

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