Radiation Protection and Environment

ORIGINAL ARTICLE
Year
: 2020  |  Volume : 43  |  Issue : 3  |  Page : 140--147

Ingestion dose due to 226Ra, 228Ra, and 40K in the plant origin food materials grown around BARC, Visakhapatnam


P Padma Savitri1, T Samba Murty1, J Sudhakar1, NS Krishna1, SK Sahoo2, Anil Gupta2, A Vinod Kumar1,  
1 Environmental Monitoring and Assessment Division, BARC, Visakhapatnam, Andra Pradesh, India
2 Health Physics Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India

Correspondence Address:
P Padma Savitri
Environmental Monitoring and Assessment Division, BARC, Visakhapatnam, Andra Pradesh
India

Abstract

Naturally occurring radionuclides of uranium, thorium series, and potassium are significant contributors of ingestion dose. Radioactive concentrations of 226Ra, 228Ra, and 40K in plant origin food cultivated around BARC, Visakhapatnam, were determined and the assessment of the ingestion dose through food consumption to different groups of population was estimated. Radionuclides in the samples analyzed were measured by high purity germanium gamma spectrometry system. The estimated annual effective dose from the ingestion of cereals, pulses, vegetables, fruits, and leafy vegetables due to 226Ra, 228Ra, and 40K radionuclides is 0.32 mSv. In this paper the estimated annual effective dose in the study area is compared to the ingestion dose due to intake of different food materials by various natural radionuclides reported in various parts of India and world. The data generated will be a useful baseline studies for the upcoming BARC facilities at Visakhapatnam, India.



How to cite this article:
Savitri P P, Murty T S, Sudhakar J, Krishna N S, Sahoo S K, Gupta A, Kumar A V. Ingestion dose due to 226Ra, 228Ra, and 40K in the plant origin food materials grown around BARC, Visakhapatnam.Radiat Prot Environ 2020;43:140-147


How to cite this URL:
Savitri P P, Murty T S, Sudhakar J, Krishna N S, Sahoo S K, Gupta A, Kumar A V. Ingestion dose due to 226Ra, 228Ra, and 40K in the plant origin food materials grown around BARC, Visakhapatnam. Radiat Prot Environ [serial online] 2020 [cited 2021 Jan 21 ];43:140-147
Available from: https://www.rpe.org.in/text.asp?2020/43/3/140/306279


Full Text



 Introduction



Thorium, uranium along with progenies and radioactive potassium (K40) are the long-lived naturally occurring radionuclides present in the earth's crust. Public radiation exposure from these natural radioactive decay series occurs mainly based on its dissolution in water and migration to surface water reservoirs.[1],[2] Plants are the main recipients of the radionuclides from soil.[2] Uranium, thorium series, and radioactive potassium can get transferred into plants along with the nutrients during mineral uptake and accumulate in various parts and even reach human body through consumption of edible portions. The use of fertilizers leads to the elevation of uranium series nuclides in food crops.[3] Typical concentrations of uranium in phosphate rock range between 30 and 260 ppm.[4] The manufacture and use of phosphates can lead to the contamination of agricultural land during cultivation, as well as contamination of the air and water supplies. Knowledge of radioactivity levels in human diet is of particular concern for the estimation of possible radiological intake to human health. When inhaled or ingested, these elements accumulate and get distributed in human body and deliver radiation doses. It has been estimated that at least one-eighth of the mean annual effective dose due to natural sources is caused by the consumption of foodstuff and consumption of drinking water.[5]

The distribution of radionuclides in different parts of the plant depends on the chemical characteristics and several parameters of the plant and soil. The presence of radioactivity in different parts of the plant has been reviewed by various reports.[6],[7] Worldwide average annual effective dose due to natural sources is 2.4 mSv[1] and ingestion dose due to the natural radioactivity in food and water is reported as 0.29 mSvy-1.[1] 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. The major contributing radionuclide to the dose is potassium, which is an essential nutrient. The amount of potassium in the body is nearly constant. As compared to uranium and thorium, the potassium has the higher transfer factor.[8] Potassium is essential to grow plants to adapt the environmental stresses. 40K is ingested through many foods that humans eat and is critically important element for proper functioning of the human body. 40K content in the body of an adult person with body weight 70 kg ranges from 4000 to 5000 Bq.[9],[10] In this study, radioactivity measurements in food crops cultivated in the fields of villages located around upcoming BARC facilities, Visakhapatnam, was performed. The radioactive concentrations of 226Ra, 228Ra, and 40K in food crops cultivated in the fields were determined using gamma spectrometry. The assessment of the ingestion dose through food consumption by different groups of population in the area was made. The study focused mainly on plant origin food materials that are commonly cultivated and consumed in the study area. This study will provide a baseline report of the natural radioactivity concentration in food of the area.

 Materials and Methods



Samples of 25 kinds of food materials of plant origin from various categories such as cereals (wheat and rice), pulses (cowpea, red gram, black gram, gingerly seeds, green gram, horse gram, peanut, millet, and chia-seeds), green leafy vegetables (GLV) (spinach and sorrel leaves), vegetables (brinjal, cucumber, ridge gourd, lady's finger, banana, bitter gourd, papaya, and stem of banana), and fruit (papaya, coconut) were collected from local farming fields around BARC, Visakhapatnam up to a distance of 30 km in different directions. These food categories are as per the daily diet in the study area.[11] Samples were collected from different fields at different times and mixed to get representative samples. From the samples collected the edible parts were taken and its net wet weight was noted. The edible parts were subjected to volume reduction by thermal heating and the residual ash was transferred to standard geometry. The plastic container was sealed and kept for 30 days to ensure radioactive equilibrium between 226Ra, 228Ra and its daughter products.

Food samples after processing were analyzed using high resolution gamma spectrometry system consisting of p-type high purity germanium detector, with a relative efficiency of 50%, coupled to a PC-based spectrum stabilized 8 K MCA along with other electronic accessories. The energy resolution measured in terms of full width at half maximum is 1.8 keV at 1332.5 keV of 60Co gamma energy at 25 cm from the top of the detector. The detector is shielded by 10 cm lead rings with graded shielding to reduce the background radiation contribution from surrounding and cosmic origin. The certified reference materials IAEA RGU and RGTh have been used for the energy and efficiency calibration of the system in the energy range 46.5–2614.5 keV. IAEA reference materials IAEA-321 and IAEA-156 standards were used for quality assurance of vegetation samples analysis. For other gamma energies, efficiency is estimated from self-attenuation correction method. The spectra were acquired for 100,000 s and the photo peaks were evaluated using gamma spectrum analysis software.

Activity of the sample was calculated using the following formula:

[INLINE:1]

Where, B is the background counts,

N is the gross counts (sample + background),

T is the counting time(s),

γ is the gamma emission probability,

e is the absolute efficiency of the detector at particular gamma energy,

w is the fresh edible sample weight (kg).

When density of the sample and standard were different, required self-attenuation corrections were carried as per the standard protocol (IAEA-289). The samples are sealed for 1 month to allow secular equilibrium of two primordial radionuclides 226Ra and 228Ra with their corresponding decay products. Weighted average activity of 226Ra and 228Ra was calculated using the mentioned gamma energy peaks and their respective intensities. 226Ra activity was calculated through gamma emissions 295 keV, 351 keV of 214Pb and 609 keV, 1764 keV of 214Bi which are daughter products of uranium-238 series. The intensities of gamma emissions 295 keV, 351 keV, 609 keV, and 1764 keV are around 19%, 36%, 47%, and 17%, respectively. For the estimation of 228Ra in the sample gamma energies 338 keV with 11% intensity and 911 keV with intensity 25% of 228Ac and 583 keV with intensity 30% of 208Tl and 238keV of 212Pb (43%) were used. 40K was estimated using the gamma energy 1460 keV with 11% intensity. The combined standard uncertainty has been estimated by considering the errors due to counting statistics, gamma emission probability and absolute efficiency. Minimum detectable activity (MDA) is defined as the minimum concentration of radionuclide present in a particular sample which can be detected with 95% specified degree of confidence. MDA for vegetation samples are calculated for a sample size of 5 kg fresh weight and for counting time of 100,000s for 250 ml standard geometry.

MDA (95% degree of confidence) were estimated using the following formula:

[INLINE:2]

Where, B is the background counts,

T is the counting time(s),

γis the gamma emission probability,

e is the absolute efficiency of the detector at particular gamma energy,

w is the sample weight (kg).

Estimation of age dependent effective dose

Food intake varies for different groups of population. Daily consumption rates provided by the National Nutrition Monitoring Board[11] for different categories of foods based on the age, gender, and physiological conditions of general public is considered in the present study. The annual effective dose was estimated using the following relation:

[INLINE:3]

Where, E is annual effective dose through ingestion of food to member of population given in μSvy-1, If is the daily intake of food material in gd-1, Cf is activity of natural radionuclide in fresh food material given in Bqkg-1, e is dose coefficient for particular isotope given in μSv Bq-1, 365 and 1000 are conversion from d-1 and gram to y-1 and kg, respectively.

 Results and Discussions



Activity concentration in food materials

[Table 1] shows the activity concentration of 226Ra, 228Ra, and 40K in different food materials analyzed. The activity concentration is given for fresh weight of food materials after removing nonedible parts whenever applicable and measurement of error is shown representing one sigma uncertainty. The activity concentration of 40K is high in all the samples compared to 226Ra and 228Ra. The activity concentration of 226Ra was observed to be in the range of <0.06–0.8 Bq kg-1. Finger millets from pulses category was observed to have highest 226Ra activity concentration of the measured samples. Concentration of 40K radioactivity in different foods as reported[12] to be in the range of 45.9–649.0 Bq kg-1; 226Ra in the range of 0.01–1.16 Bq kg-1; and that of 228Ra in the range of 0.02–1.26 Bq/kg. The activity concentration of 226Ra in the present study is observed to be lower than the earlier reported values for Indian foodstuffs.[12],[13] 226Ra concentrations reported by[13] are in the range of 0.03 ± 0.01–7.52 ± 0.5 Bq kg-1 for vegetation from south India. The activity concentration of 228Ra was observed to be in the range of <0.03–2.1 Bq kg-1 in Gingerly seeds which is highest among all. 228Ra concentration of 2 Bq kg-1 was observed in finger millets. 228Ra concentration in some of the food materials studied was slightly higher than 226Ra, possibly due to the high abundance of 232Th in soil as reported by.[14] The 40K activity concentration in the present study was observed to vary from 44 ± 1 in Papaya fruit to 660 ± 15 Bq kg-1 in green gram. Activity concentration of 40K was reported as 29.7 ± 9.1–482.7 ± 19.2 Bqkg-1[13] for south Indian food crops. This verifies 40K is nearly in the same range as reported by[12] for Indian food material and by[13] for south Indian food crops.{Table 1}

Annual radionuclide intake from normally consumed food materials

Daily intake of radionuclides was calculated based on mean value of activity concentration for different food categories. Mean intake of the particular food category for the age groups of 1–3 years, 4–6 years, 7–9 years, 10–12 years boys and girls, 13–15 years boys and girls, 16–18 years boys and girls, >18 years females, pregnant and lactating women[11] are shown in [Table 2]. For the samples which have below the detection limit activity concentration, MDA value of respective sample was considered for the evaluation of mean intake. Estimated annual intake from daily intake of 226Ra, 228Ra, and 40K for various population groups from different food categories in the study area is presented in [Table 3]. The estimated total daily intake of 226Ra, 228Ra, and 40K through food for different population groups varied from 0.01 to 0.04Bqd-1, 0.01–0.04 Bqd-1 and 33.4–107Bqd-1, respectively. Minimum intake for all food items is for children of age 1–3 years and maximum is for men adults. Intake of women/girls for different food items studied is either equal or less than men/boys by 5%–20%. The estimated mean daily intake of 226Ra, 228Ra, and 40K is 0.03, 0.03, and 78.6 Bqd-1, respectively, of all age groups and genders considered. The radionuclide with highest daily intake is 40K through cereals which ranges from 22.7Bqd-1 for children of 1–3 years age to 77.1 Bqd-1 for adult males. Cereals contribute highest daily intake of all the radionuclides measured. The radionuclide with lowest daily intake is 226Ra for all the food categories. The total activity concentration of all the radionuclides is lowest in food category of vegetables. Total intake of all the radionuclides is lowest through GLV among all the food categories. Daily intake of radionuclide through food is compared with those reported from other places. The present study values are lower than that observed in south Indian food,[13] whereas the same is higher when compared to Korean intake through food.[15] The reason could be due to less intake of vegetarian food in Korea. The percentage distribution of total daily intake of radionuclides through different food categories for various population groups is shown in [Figure 1]. Around 70% of total daily intake of radionuclides measured in the study is due to cereals. The second highest contributor is pulses and is around 15% for different age groups of population. This variation can be explained with regard to consumption rates of different food categories. [Figure 2] shows the percentage intake of each radionuclide studied. There is significant variation in percentage intake of radionuclides through food with different population groups. More than 99% intake of the radionuclides measured is due to 40K. Daily intake of 228Ra from all food categories varies from 0.036% to 0.043% and for 226Ra is around 0.035% for different population groups. These values are consistent with the data reported in the reference.[13]{Table 2}{Table 3}{Figure 1}{Figure 2}

Annual effective dose

International commission on radiological protection provides age dependent dose conversion factors for the radionuclides.[16],[17] Age ranges considered for the calculation of dose in this study are 1–2 years, 2–7 years, 7–12 years, 12–17 years, and >17 years (adults) as per ICRP-72.[16] Age-specific dose conversion factors for the radionuclides are shown in [Table 4]. Appropriate age groups are considered from estimated annual intake presented in [Table 3] for boys and adults for the calculation of annual effective dose. As intake is around 5%–20%[11] lower for girls compared to boys of the same age group as per [Table 2] and [Table 3] by considering intake of boys/men total effective dose estimated is conservative. The age-weighted dose assumes a fractional population distribution of 0.05, 0.3, and 0.65, respectively for infants, children and adults as per.[1] Annual weighted average effective dose was evaluated using 0.65 for adults and 0.35 to other age groups considered in this study. Annual effective dose to the members of population due to intake of 226Ra, 228Ra, and 40K through different food categories grown around BARC, Visakhapatnam, is presented in [Table 5]. The total annual effective dose received by different population groups due to intake of 226Ra, 228Ra, and 40K varies between 3.9 μSv (adults) and 19.6 μSv (1–2 y), 10.2 (adults) to 73.1 μSv (1–2 y) and 242.8 (adults) to 512.5 μSv (1–2 y), respectively by consumption of all the food categories studied. The total annual effective dose received by different population groups due to consumption of cereals, pulses, GLV, vegetables, and fruit varies from 180.2 to 358.3 μSv, 41.8–107.8 μSv, 6.9–13.7 μSv, 15.1–26.4 μSv, and 13–39.6 μSv, respectively, by intake of 226Ra, 228Ra, and 40K. Maximum annual effective dose among the entire population group when considered either by intake of radionuclide or by consumption of food category is received by children of 1–2 years of age group. This is due to the higher radio sensitivity of the children. The minimum annual effective dose due to intake of 226Ra, 228Ra, and 40K is received by population group of adults. Variation in weighted mean effective dose received by all population groups due to consumption of different food categories is between 9.1 (GLV) to 215.0 (cereals) μSv y-1. Similarly, weighted mean of effective dose received by all population groups due to intake of different radionuclides studied is 5.6 μSv y-1 due to 226Ra, 21.5 μSv y-1 due to 228Ra and 291.5 μSvy-1 due to 40K. [Figure 3] shows the percentage of annual effective dose received due to intake of different radionuclides through all the food categories for all the population groups. Around 92% of effective dose through food pathway to various population groups is from intake of 40K, 1.8% from 226Ra and around 6.2% from 228Ra measured. Minimum annual effective dose by ingestion of food is received by adults is 257 μSv and maximum 546 μSv is received by children of 1–2 years of age. Although intake of various food items is higher in adults dose conversion co-efficients are 10 times higher to infants and children compared to adults. Hence, the dose received by children is higher compared to other age groups of the population. [Figure 4] shows fractional mean effective dose to different age groups due to consumption of different food categories by intake of the radionuclides studied for all the population groups. [Figure 5] presents fractional mean effective dose due to different types of food materials for the total population. Maximum contribution 66% to the effective dose due to ingestion of food is by cereals which is staple food of south India. Mean contribution of pulses to the total effective dose by ingestion of food for members of population is around 20%. The total estimated annual effective dose due to intake of radionuclide through all the food materials studied and for all age groups is 0.32 mSv.{Figure 3}{Figure 4}{Figure 5}{Table 4}{Table 5}

Comparison with other studies

Comparison of the annual effective dose determined in the present study with others is shown in [Table 6]. As per the reference,[13] total annual effective dose due to intake of all natural radionuclides through ingestion of food varieties considered in their study from south India was 1.79 mSv to the population of south India where as it was 1.7 mSv by considering only plant origin food. In the same way by considering only plant origin food around Kalpakkam, India,[18] annual effective ingestion dose due to 40K was 0.08 mSv. From the values given in Table 6 of different studies done at various parts of the world the annual effective dose due to some or all natural radionuclides in different foods is in the range 0.09 mSv due to potassium[18] to 1.8 mSv[13] due to 226Ra, 228Ra, 228Th, 40K. With reference to[22] average annual effective dose to adult population in eight Asian countries from daily dietary intake of 238U and 232Th and were reported as 0.20 μSv and 0.34 μSv, respectively. In the present study, from only plant food annual dose due to 226Ra and 228Ra estimated is 5.6 μSv and 21.5 μSv, respectively for all age groups. From the estimates of ingestion dose in the present study, it may be concluded that the dose imparted by the food materials cultivated from the local environment falls under the range of other studies mentioned in Table 6. The total annual effective dose obtained in this study is 0.32 mSv/y due to intake of 226Ra, 228Ra, and 40K through those food materials included in this study. Average worldwide total ingestion exposure due to uranium series, thorium series, and 40K due to all food materials and drinking water reported by UNSCEAR 2000[1] is 0.29 mSv/y.{Table 6}

 Conclusions



Activity concentration of 226Ra, 228Ra, and 40K was measured in various plant origin food materials that are commonly cultivated around upcoming BARC facilities, Visakhapatnam, India. Daily intake of radionuclides was estimated based on consumption of different category of food by various population groups. The highest activity concentration of those measured radionuclides was observed for 40K and food with the highest concentration was green gram. Cereals contribute maximum to the daily intake of radionuclides studied due to its higher consumption by study population. The estimated annual effective dose due to intake of 226Ra, 228Ra, and 40K by consumption of plant origin food studied for different population groups varied from 3.85 to 19.6 μSv with mean of 5.6 μSv, 10.2–73.1 μSv with mean of 21.5 μSv, and 292.8–512.5 μSv with a mean of 291.5 μSv, respectively. The total estimated annual effective dose due to intake of radionuclide through all the food materials that were studied varied between 257 and 546 μSv with mean of 0.32 mSv of which 92% is due to intake of 40K. Total annual effective dose due to all the radionuclides studied through food pathway from plant origin food in the present study ranged between 0.26 mSv (adults) and 0.55 mSv (Children 1–2 years age group) for different population groups weighted average being 0.32 mSv. The present study estimates are only for the contribution of ingestion dose due some of the locally grown food items. The data generated will serve as a baseline data for upcoming BARC facilities at Visakhapatnam, India.

Acknowledgments

The authors would like to acknowledge Shri Venkateswarulu, Project Director, BARC, Visakhapatnam and Shri M. Venkata Ratnam, Head, ESSV, BARCF Visakhapatnam, for their help in logistics.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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