|Year : 2015 | Volume
| Issue : 1 | Page : 29-34
226Ra, 228Ra, and 40K activity concentration in some vegetables consumed in Jordan, and resultant annual ingestion effective dose
Eman Al-Absi1, Tariq Al-Abdullah2, Hayel Shehadeh3, Jamal AI-Jundi4
1 Department of Coastal Environment, Faculty of Marine Sciences, University of Jordan, Aqaba, Jordan
2 Department of Physics, Hashemite University, Zarqa, Jordan
3 Department of Physics and Material Sciences, American University of Madaba, Jordan
4 Department of Physics, Islamic University in Madinah, Medina, Saudi Arabia
|Date of Web Publication||14-Aug-2015|
Department of Physics, Islamic University in Madinah, Medina
Source of Support: Nil., Conflict of Interest: None
The activity concentrations of the naturally occurring nuclides 226Ra, 228Ra, and 40K were determined in vegetable crops largely consumed by people in Jordan. Samples of potatoes, tomatoes, cucumber, radish, spinach, and cabbage were collected from several markets in the capital Amman. The activity concentrations in Bq/kg of 226Ra, 228Ra and 40K were measured by the gamma-ray spectroscopy using the high purity germanium detector. The ranges of the activity concentration of 226Ra, 228Ra and 40K in the chosen vegetables were found to be 7.1–11.7 Bq/kg, nondetectable - 3.3 Bq/kg, and 201–684 Bq/kg, respectively. The daily intake of 40K was the highest among the radioisotopes measured, but it was lower than the intake in other countries. The estimated total annual effective dose resulting from the ingestion of the above-mentioned vegetable samples is 51.56 µSv/y according to the measured activity concentration of 226Ra, 228Ra, and 40K. 226Ra was the highest contributor to the total annual effective dose (23.98 μSv/y).
Keywords: Effective dose, Jordan, natural radioactivity, radium, vegetables
|How to cite this article:|
Al-Absi E, Al-Abdullah T, Shehadeh H, AI-Jundi J. 226Ra, 228Ra, and 40K activity concentration in some vegetables consumed in Jordan, and resultant annual ingestion effective dose. Radiat Prot Environ 2015;38:29-34
|How to cite this URL:|
Al-Absi E, Al-Abdullah T, Shehadeh H, AI-Jundi J. 226Ra, 228Ra, and 40K activity concentration in some vegetables consumed in Jordan, and resultant annual ingestion effective dose. Radiat Prot Environ [serial online] 2015 [cited 2019 Jun 25];38:29-34. Available from: http://www.rpe.org.in/text.asp?2015/38/1/29/162819
| Introduction|| |
The long-lived radioisotopes uranium( 238U) (t1/2 = 447×107 y), 232Th (t1/2 = 1.4×107 y), and 40K (t1/2 = 1.25×107 y) and their daughter nuclides do present naturally in all ground formations. Nuclear technologies and industrial products and by-products may add more to the terrestrial radiations, making the earth a source of background radiations where all living creatures are exposed to and subject to their absorption consequences. It is an established fact that radioactivity might be transferred to human beings through the food chain., Detailed knowledge of the presence of radioactivity in soil, building materials, food, and vegetation is, therefore, highly desirable.,,,,,,,,,,, In addition, a large portion of the annual effective dose due to natural sources is caused by the intake of foods. Plants are the primary recipients of radioactive contamination in a food chain. Vegetation may be subject to direct and indirect contamination. The direct contamination of terrestrial vegetation refers to the deposition of radioactive materials from the atmosphere onto the parts of plants above ground., Indirect contamination refers to the absorption of radionuclides from the soil by the root system of plants. The variation of the activity concentration of 226Ra, 228Ra, and 40K in different vegetables and between the same type of vegetables from different sites if affected by several reasons such as activity concentration of these radionuclides in soil, the radionuclide transfer factor, climate, and finally time of harvest.. The concentration of naturally occurring radionuclides in the vegetables (leafy vegetables, fruit, root, bean, and rice) and derived products (sugar, coffee, etc.) consumed mostly by the adult inhabitants of Rio de Janeiro City, Brazil was studied. They reported that cucumber, potato, and tomato were among the main contributors to intake and consequent internal dose. They concluded that about 70% of the ingestion of 226Ra, 228Ra arises from the consumption of vegetable products. Concentration of 40K activity was found to be much higher than the activity concentration of 226Ra, 228Ra in different food crops and vegetables grown in high level natural radioactive area in south-west India. Therefore, it is necessary to determine the activity concentrations of radionuclides in vegetables that were highly consumed by people in Jordan. 238U activity concentration was studied because its series decay products represent the main external source of radiation. Since radium ( 226Ra, 228Ra) is a member of alkaline earth metal group in the periodic table and its chemical behavior is similar to that of calcium in the body. Furthermore, radium has been known for a long time as one of the most radiotoxic radionuclide. Moreover, radium is among the daughter of 238U series, which present on phosphate areas and hence in about 70% of Jordan surface area., In addition, potassium (40K) is an essential constituent of the cellular tissue; hence, 40K is one of the most important natural radionuclides. Therefore, in this study, we will determine the activity concentration of the natural radionuclides ( 226Ra, 228Ra, and 40K) in most popular types of vegetables consumed by Jordanian people, and then estimate the annual effective dose from the consumption of such vegetables.
| Materials and methods|| |
Vegetable types were chosen carefully to represent three different plant categories namely: Leafy, root, and stem vegetables, and from major vegetable types consumed by the majority of the Jordanian people. Leafy types are very prone to external contamination during their growing season. Other vegetables types, including root vegetables, may also become contaminated. Therefore, it is important to obtain representative vegetables samples for this study. Our vegetables were purchased from local markets in the capital Amman. The minimum time gap between two successive samples taken of the same type was about 1-month. The time between bringing the crops to the market and collecting the samples was between 1 and 3 days with the exception of potatoes, which are normally stored for a longer period of time. Nearly 2–3 kg of each fresh sample type was collected for every measurement. After collection, the samples were properly stored in zip-plastic bags to avoid contamination.
Samples were cleaned by water to remove sands and/or soil, dried in air, and weighed to determine the corresponding fresh mass. Samples were then oven-dried at approximately 80°C until a constant weight is reached. The dried samples were then crushed, homogenized and sieved through a 2 mm mesh. A portion of each dried sample was then taken at random, weighed, sealed, and stored into a special cylindrical plastic container (55 mm diameter, and 35 mm height), the geometrical dimensions of the samples were kept identical to that of the reference material. The approximate dry weight of the samples used ranged between 66 g (for potato) to 50 g (for tomato). Thereafter, these containers were left for a period of approximately 1-month to establish a state of secular radioactive equilibrium between 226Ra and 228Ra with their short-lived decay products.
The activity concentrations in the dried samples were analyzed in radiation laboratory by gamma-ray spectroscopy using hyper purity germanium detector, of 20% relative efficiency and a resolution of 2 keV at 1.33 MeV. (Canberra Company). The detector was enclosed in a 10 cm thick lead shield, internally lined with 2 mm copper foil. The detector connected to a multi-channel analyzer with (8000 channels), and interfaced to a computer system for data acquisition and analysis. Software (Aptec, Canada) was used for data collection and analysis. Energy and efficiency were calibrated using a certified multi-gamma ray standard source-5 supplied by Canberra, USA, covering gamma rays in the range of 60 keV ( 155Eu) to 1461 keV (40K). Quality control procedures were carried out using standard reference material International Atomic Energy Agency (IAEA)-321 and IAEA-330. The samples were counted for about 20 h for both the vegetable samples and the standard source. The background spectra measured under the same conditions for both the samples and the standard source. The activity of 226Ra, 228Ra and 40K were determined according to secular equilibrium between 226Ra and 228Ra with their daughters. The determination of 226Ra activity is based upon the detection of 351.9 keV gamma rays emitted by 214Bi and the detection of 295 keV gamma rays emitted by 214Pb. The determination of 228Ra activity is found by the detection of 238.6 keV gamma rays from 212Pb, 911.2 and 969 keV from 228Ac, while the detection of 1460.8 keV gamma rays was taken for 40K activity calculations. The net area under each photopeak, after background corrections, was used to calculate the activity concentration of each radionuclide in the food samples. The minimum detectable values observed for 40K, 228Ra, and 226Ra were 4.4, 0.56, and 0.96 Bq/kg, respectively.
| Results and Discussions|| |
The concentrations activities of 226Ra, 228Ra and 40K of the dried vegetable samples ranged between 7.1 ± 1.1 Bq/kg and 11.7 ± 3.4 Bq/kg, nondetectable (N.D.), and 3.3 ± 1.8 Bq/kg, and between 201 ± 10 Bq/kg and 684 ± 15 Bq/kg, respectively as shown in [Table 1]. It is obvious that the activity concentration of 40K was the highest in all vegetable samples, followed by 226Ra, whereas 228Ra exhibited the lowest activity concentration. Plants absorb potassium from soil in different amounts, according to their metabolism, in addition, the levels of potassium in soil from which vegetables were cultivated might vary geographically from one place to another. Consequently, it is expected that the concentrations of potassium were much higher than those of 238U in plants. Furthermore, the activity concentration of 40K and other natural radionuclides in food crops in an area of high background radiation in Nigeria was measured. They found that 40K was the highest activity concentration among other natural radionuclides measured in their work. They ascribed the reason to the use of fertilizers by farmers to improve crop yields. In contrast, the variation of 226Ra activity concentration in the vegetable samples was not significant. The obtained activity concentrations of 226Ra in this study (7.1 ± 1.1 and 11.7 ± 3.4) Bq/kg were found to be lower than those obtained by other reported study, who showed that the 226Ra activity concentration ranged between 15.96 ± 1.91 Bq/kg and 52.80 ± 513 Bq/kg in dry weight collected from agricultural fields, in Gediz River Basin of Turkey. The activity concentration of 226Ra in potatoes, spinach, cabbage, cucumber, and tomato were found to be 19.2 Bq/kg, 26.4 Bq/kg, 14.7 Bq/kg, 8.66 Bq/kg, and 8.76 Bq/kg, respectively. Several studies have reported that 226Ra activity concentration in plants ranged from 0.5 Bq/kg to 410 Bq/kg in dry weight, depending on the type of contaminated soil and 226Ra concentration., The range of the activity concentration of 228Ra in this study ranged from N.D. to 3.3 ± 1.8 Bq/kg. In all vegetable analyzed samples, the activity concentration ratios of ( 226Ra/ 228Ra) were found to be >1. Hence, the levels of 226Ra in Jordanian soil are higher than those of 228Ra agrees with previous studies. The activity concentrations of 226Ra and 228Ra in this study are higher than those of vegetable samples from the Northern Jordan Rift Valley. They reported a higher 40K activity concentration.
|Table 1: Mean activity concentrations (in Bq/kg, dry weight) for some types of vegetables samples|
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Daily intakes of radioactivity
The radionuclide intakes can be calculated from the annual consumption rate and from the measured concentration of radionuclides in foodstuffs. [Table 2] shows the annual consumption rate and dried weight to fresh weight ratio of most popular Jordanian vegetables. The radionuclide intakes can be calculated from the measured concentration of radionuclides in vegetables (Bq/kg fresh) and from the daily consumption rate of vegetables (kg/y). The radionuclide intakes from each type of vegetables are shown in [Table 3]. The radioisotope with the highest intake from fresh vegetables (of 2.766 Bq) was 40K. The daily intakes of 40K ranged from 0.0848 Bq to 2.766 Bq. Due to the high consumptions of potatoes and tomatoes, they are the most contributors to 40K and 226Ra intakes. [Table 3] also shows a comparison between 226Ra, 228Ra, and 40K daily intake in the present study and other countries. 226Ra daily intakes from potato and tomato were higher than those from other vegetables, although radish is from the same vegetable group of potato; it gives the lowest 226Ra daily intake. This might be due to the higher daily consumption rate of potatoes than radish. Furthermore, [Table 3] shows the daily intake of 226Ra, 228Ra, and 40K in various types of vegetables consumed in Jordan is relatively lower than those reported in other studies which illustrated. Both 40K and 226Ra daily intakes give the same trend. [Table 3] also shows that the highest daily intake of 226Ra from potato is followed by tomato, cucumber, spinach, cabbage, while the lowest is from radish.
|Table 2: Annual consumption rate and dried weight/fresh weight ratio of some vegetables in Jordan|
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|Table 3: Daily intake of 226Ra, 228Ra, and 40K (Bq) in the present study and other countries|
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Effective dose is a useful concept which enables the radiation doses from different radionuclides and from different types and sources of radioactivity to be added. It is based on the risks of radiation-induced health effects and the use of the International Commission on Radiological Protection metabolic model that provides relevant conversion coefficient to calculate effective doses from the total activity concentrations of radionuclides measured in foods., Estimates of the radiation-induced health effects associated with intake of radionuclides in the body are proportional to the total dose delivered by the radionuclides while resident in the various organs. Ingested radiation doses are obtained by measuring radionuclide activities in foodstuffs (Bq/kg) and multiplying these by the masses of food consumed over a period of time (kg/y). A dose conversion coefficient (Sv/Bq) can then be applied to give an estimate of ingestion dose. Thus, according to Shanthi, et al.  and Samavat, et al. the annual effective doses (HT, r) due to ingestion are calculated by:
where, idenotes a food group, the coefficients Ui and Cirdenote the consumption rate/year (kg) and activity concentration of the radionuclide (Bq), respectively, and gT, r is the dose coefficient for intake by ingestion of radionuclide r (Sv/Bq). hi is the ratio of dried to fresh vegetable. The values of gT, r for 40K, 226Ra, and 228Ra are 6.2 × 10-9 Sv/Bq, 2.8 × 10-7 Sv/Bq, and 6.9 × 10-7 Sv/Bq, respectively, for adult members of the public., The annual consumption rate of vegetables by adults in Jordan was reported from Department of Statistics in Jordan. Applying the annual consumption rate of vegetables by adults and the above conversion coefficients, into the above formula, the annual effective dose (μSv/y) was calculated. These results are shown in [Table 4]. The largest ingestion dose was from potatoes whereas the lowest ingestion dose was from radish. Jordanians consumed large amounts of potatoes 27.9 kg/y and small amounts of radish 1.1 kg/y as given in [Table 2]. The total annual effective dose due to ingestion of naturally occurring radioisotopes 40K, 226Ra, and 228Ra in six vegetables is 51.56 μSv/y. The annual effective dose due to the ingestion of potatoes and tomatoes are found to be 31.1 μSv/y and 13.3 μSv/y respectively. 55.6% and 43.1% of the total ingestion annual effective dose of tomatoes and potatoes are from 226Ra. The intake of 226Ra contributes to about 47% from the total annual effective dose rises from the ingestion of the vegetables in this study. The contribution of 226Ra from different types of vegetables is shown in [Figure 1]. The total annual effective dose obtained in this study (51.56 μSv/y) due to daily intake of 40K, 226Ra, and 228Ra, via those vegetables included in this study is much comparable to those values reported in United Nations Scientific Committee on the Effects of Atomic Radiation.
|Figure 1: Contribution of 226Ra in various types of vegetables to annual effective dose|
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|Table 4: Annual consumption rate, and estimated annual effective dose by ingestion of some vegetables in Jordan|
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| Conclusions|| |
The activity concentrations of 226Ra, 228Ra, and 40K in dry samples were varied from 7.1–11.7 Bq/kg, from N.D. to 3.3 Bq/kg, and from 201 Bq/kg to 684 Bq/kg. The activity concentration of 40K in all vegetables under investigation was the highest and this could be due in part to the use of fertilizer by farmers to improve crop yields. The estimated value of the total annual effective dose by ingestion of all six vegetables was calculated to be 51.56 μSv/y which is in the worldwide range.
| Acknowledgments|| |
The authors sincerely thank Prof. A. Al-Wriekat and others from JAEC for their assistance. They also wish to express appreciation for the technical support received from the Hashemite University.
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[Table 1], [Table 2], [Table 3], [Table 4]