|Ahead of print publication
Estimation of cancer risk due to radiation exposure for some daily consumption of foods
Akbar Abbasi1, Vali Bashiry2
1 Department of Engineering, University of Kyrenia, Girne, Mersin 10; Department of Engineering, Near East University, Nicosia, Northern Cyprus, Mersin 10, Turkey
2 Faculty of Art and Sciences, Cyprus International University, Nicosia, Northern Cyprus, Mersin 10, Turkey
Department of Engineering, University of Kyrenia, Girne, TRNC, Mersin 10
Source of Support: None, Conflict of Interest: None
Aims: Considering the increasing concern about the cancer risk caused by environmental radiological effects related to the food consumption, the study was carried out evaluate the activity concentrations and cancer risk assessments of 226 Ra,232 Th, and 40 K in 72 food samples collected from different suppliers in Tehran Province of Iran.
Subjects and Methods: The specific activity concentration was determined by means of a high-resolution high-purity germanium gamma-spectroscopy system. The collected various sample groups were wheat, rice, meat, milk, and mushroom.
Results: The maximum concentration of 226 Ra and 232 Th was found in the wheat sample, equal to 0.7862 Bq/kg and 0.968 Bq/kg, respectively, whereas for 40 K, it was 598.35 Bq/kg in the milk sample. The annual effective dose rate ranged from 2.47 μSv/y in mushroom to 64.66 μSv/y in rice. The average excess lifetime cancer risk (ELCR) was varied from 1.60 × 10–5 for mushroom to 4.20 × 10–4 for milk, with the total ELCR value from main daily diets 1.37 × 10–3, which was a little more than the acceptable ELCR limit of 10–3.
Conclusions: The ELCR due to five main daily diets was a little more than the acceptable ELCR limit of 10–3 for radiological risk in general.
Keywords: Activity concentration, cancer risk, effective dose, food
| > Introduction|| |
Natural radioactivity is the main sources of both internal and external radiation exposures in humans. The initial radionuclides such as 238 U,232 Th and their decay series products, and singly occurring 40 K present in the earth's crust contribute to the background radiation of a particular region. In some places, such as Tapire in the Brazilian coast and Kerala in India, the natural background radiation level is one or two orders of magnitude greater than in other places. Concentrations of naturally occurring radionuclides in foods vary widely because of the differing background levels, climate, and agricultural conditions that prevail. The reference values were reported for the concentrations of uranium and thorium series radionuclides in foods. Furthermore, the radioactivity concentration in food has been studied in many countries of the world.,,,, In Iran, the research on the radioactivity concentration in some imported foods was reported. The mean annual effective dose due to the consumption of foodstuff was estimated to be at least one-eighth of the total from natural radiation sources. Public radiation exposure from natural sources, especially of 238 U and 232 Th series, occurs mainly because they are dissolved in water and transfered to surface water reservoirs, leading to the possibility to enter foodstuffs, following soil-to-plant transfer as well as getting into the human body. The purpose of this study was to calculate the amount of radiation exposure of 226 Ra,232 Th, and 40 K, annual dose levels, and lifetime cancer risk in various kinds of national food samples representing the daily main diet of Tehran Province residents. The reason for the selection of 226 Ra,232 Th, and 40 K was because these radionuclides are the main radioactivity sources in food., Although IAEA has specified guideline levels for the natural radioactive elements in foodstuffs moving in international trade, there are no guidelines for the local foodstuffs.
| > Subjects and Methods|| |
Sample collection and preparation
A total of 72 locally widely consumed foodstuff samples were collected from different markets and farms in the Tehran Province, Iran. The main food selection was based on a survey questionnaire of the diets of 60 residents. The major food groups including wheat, rice, cow meat, cow milk, and mushroom were selected.
All food samples were prepared according to the recommendations given by IAEA. Beef and milk samples were weighed and freeze-dried with a SJIA-10N freeze-drier. After drying, the samples were homogenized, and due to indirect measurement of 226 Ra and 232 Th, each sample was packed in a standard Marinelli beaker (500 g) and sealed for four weeks to reach the radioactivity equilibrium between parents and their daughter radionuclides. After grinding and weighing, the wheat, rice, and mushroom samples were ashed in a muffle in 250°C. The ash samples were ground to fine powder and then sealed in cylindrical polyethylene beaker of 250 ml volume.
The gamma-ray spectra analytical techniques were used to determine the natural radionuclides 226 Ra,232 Th, and 40 K. This measurement system inclusive a typical high-resolution gamma-spectrometer based on a coaxial P-type shielded high-purity germanium detector, with the energy resolution of 1.80 keV full width at half maximum for the 1332 keV gamma-ray line of 60Co. The relative photopeak efficiency of detector is 80%, which coupled to a high count-rate Multi-Task 16k multichannel analyzer card.,, Commercial software Gamma-2000 from Selena, Italy, was used for data analysis.
According to the photopeak line energy, the 232 Th activities were measured by taking the mean activity of photopeaks of the daughter nuclides 228 Ac (338.40, 911.07, and 968.90 keV) and 212 Pb (238.63 keV).226 Ra activities were calculated by 609.30 keV, line energy of 214 Bi. Activities of 40 K were determined directly from its gamma-emission at 1460.83 keV. The counting time for each sample was 80,000 s.
The activity concentrations of samples were calculated from the net area of a certain peak, according to the following equation that already used by few authors:,,
where is the activity concentration of the radionuclide in the sample, Cn, is the count rate under the corresponding peak, C0, is the count rate of background, ξ is the detector efficiency at the specific γ-ray energy, Py is the probability of gamma emission and Ms is the mass of the sample.
For the lower limit of detection (LLD), 96% confidence was calculated using the relation:
Where Fc is the Compton background in the region of the selected gamma-ray spectrum.
Effective dose due to ingestion
The effective dose is a parameter to provide a single number proportional to the radiobiological “detriment” from an inhomogeneous radiation exposure, with detriment representing a balance between carcinogenesis, life-shortening, and hereditary effects. Estimates of the radiation exposure induced health effects associated with intake of radionuclides in the various organs. The effective dose due to ingestion is given by:
where HE is effective dose (Sv/y), i denotes a food group, Ui and are the mean annual consumption (kg/y) and activity concentration of the radionuclide (Bq/kg), respectively and gE is the dose coefficient for intake by ingestion of radionuclide (Sv/Bq). The values of gE in (Sv/Bq) are 2.8 × 10−7 for 226 Ra, 2.3 × 10−7 for 232 Th, and 6.2 × 10−9 for 40 K.
| > Results and Discussion|| |
[Table 1] summarizes the activity concentration of the 226 Ra,232 Th, and 40 K measured on each of the group samples. The activity concentrations are calculated in Bq/kg (dry weight). The highest radionuclide concentrations are due to 40 K in all the food samples measured. Similar results have been reported by Tuo et al.40 K concentration value in rice was higher than other foodstuffs. The highest concentration level of 226 Ra and 232 Th radionuclides were rice and wheat, respectively. The lowest 226 Ra and 232 Th activity concentration values were found in the mushroom and cow milk, respectively. The mean concentrations of 226 Ra in rice and wheat are 0.040 Bq/kg and 0.032 Bq/kg, respectively. For rice, it is lower than the rice product in India, 3.070 Bq/kg, similar to that of rice product in the North Iran, 0.033 Bq/kg, while the activity concentration of 226 Ra in grain products (wheat and rice) was lower than the UNSCEAR reference values 0.08 Bq/kg.
|Table 1: Activity concentration (dry weight) of 226Ra, 232Th, and 40K measured in collected food samples|
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The 226 Ra,232 Th, and 40 K contamination source of the rice, wheat, and mushroom is due to root absorption of soil to plant and irrigation water through the root. Indeed, the farm of rice and wheat irrigation is different from the mushroom during the ripening period. Furthermore, the wheat and mushroom irrigation period is less than that of wheat and rice. Therefore, soil-to-plant absorption in mushroom is than in rice and wheat. The mean activity concentration of 226 Ra,232 Th, and 40 K in the cow milk was 0.014 Bq/kg, 0.022 Bq/kg, and 43 Bq/kg, respectively.
The activity concentration of 226 Ra,232 Th, and 40 K in cow meat was ranged from 0.016 Bq/kg to 0.025 Bq/kg with a mean of 0.019 Bq/kg, 0.020 Bq/kg to 0.035 Bq/kg with a mean of 0.024 Bq/kg, and 44 Bq/kg to 73 Bq/kg with a mean of 69 Bq/kg, respectively. Whereas, the mean activity concentration in cow meat was obtained 0.019 Bq/kg for 226 Ra, 0.024 Bq/kg for 232 Th, and 69 Bq/kg for 40 K, comparable with the results presented by Tuo et al. and Hosseini et al.,
The mean annual consumption amount of five type foods and annual effective dose intake are presented in [Table 2]. The mean annual consumption amount was estimated by questionnaire form. The minimum and maximum estimated values of total effective dose due to the intake of radionuclides were in mushroom and rice, respectively. This value is from 2.47 μSv/y in mushroom to 64.66 μSv/y in rice.
|Table 2: The mean annual consumption values kg per person estimated by questionnaire form, effective dose rate, and excess lifetime cancer risk by consumption of main daily diet|
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Excess lifetime cancer risk
In today's world, cancer is a major disease for communities. One of the cancer reasons is the radiation effect on biological cell.,, That is why an effort was made to assess the excess lifetime cancer risk (ELCR) due to the consumption of daily food using the procedure proposed by EPA. The following equation was used to calculate the mortality cancer risk and presented in [Table 2].
ELCR = Air× AIS× Rc (4)
Where ELCR, Air, AIS and Rc are the ELCR, annual intake of radionuclide (Bq), average span of life (70 years), and mortality risk coefficient (Bq −1) for the ingestion of food, respectively. The ingestion mortality cancer risk coefficients in (Bq −1) are 9.56 × 10−9 for 226 Ra, 2.45 × 10−9 for 232 Th, and 5.89 × 10−10 for 40 K. The average ELCR was varied from 1.60 × 10−5 for mushroom to 4.20 × 10−4 for milk, with the total ELCR value from main daily diets 1.37 × 10−3, which was a little more than the acceptable ELCR limit of 10−3 for radiological risk in general [Table 2]. The histogram of ELCR in five main daily diets and total ELCR with world average is shown in [Figure 1].
|Figure 1: Comparison of excess lifetime cancer risk in five main daily diets with world average|
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| > Conclusions|| |
Because of an increase in digestive cancer disease over the past years, this investigation is the first systematic study on natural radioactivity concentration in some foodstuffs based on the national production local diets in Tehran. Measurements of 226 Ra,232 Th, and 40 K concentration in samples were by the gamma-spectrometry system. The results of this study can be concluded as follows:
The content of 226 Ra in grain products (wheat and rice) was higher than that in other food groups and it is half of UNSCEAR reference values. The 232 Th concentration value in all food groups was higher than UNSCEAR reference values. The concentrations of 40 K in the study foodstuff were less than or comparable with those from other countries.
- The effective dose value has the highest contribution dose rate in cow's milk. According to the UNSECAR reports, the annual effective dose level by ingestion is 290 μSv/y, averagely. Therefore, our results were comparable with UNSECAR report value. It is recommended to milk production resources should be investigated further.
- The ELCR due to five main daily diets was a little more than the acceptable ELCR limit of 10−3 for radiological risk in general.
The authors are grateful to the Nuclear Science and Technology, Institute of Iran, for granting access to the gamma-spectrometry system used in this study.
Financial support and sponsorship
This study was financially supported by the University of Kyrenia.
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2]