Introduction

238U, 232Th, and 40K are the naturally occurring radionuclides (NORMs) which are present in all compartments of environment. The average activities of 40K, 238U, and 232Th permissible in soil are 400, 35, and 30 Bq kg−1, respectively (UNSCEAR 2000). These radionuclides get incorporated into vegetation either through activity interception by external plant surfaces, i.e., through foliar uptake of suspended materials from the atmosphere or through soil to plant transfer via root system. Although soil acts as a natural buffer system, controlling the transport of chemical elements and substances into various components of biosphere (Yadav et al. 2017; Smuc et al. 2012), plants may uptake toxic substances including radionuclides along with nutrients which may subsequently get transferred to the food chain (Rattan et al. 2005). The mobility of bio-available fraction of radionuclides from rhizospheric soil to plants is influenced by several factors (Ravi et al. 2014) such as climatic conditions, physico-chemical properties of soil, degree of plants maturity at harvesting, chelating ions outside plant roots and sub-cellular compartmentalization, controlled influx through plasma membranes, binding of ions to cell walls, and selective uptake by plant.

Accumulation of radionuclides in soils and their uptake by crop plants followed by their subsequent movement in food chain are a matter of concern for radio-ecologists. Higher concentrations of radionuclides in crop grains may cause toxicity to human beings or other living species feeding on them (Alloway and Ayres 1997). Agricultural soil to plant transfer of contaminants can be an important pathway of human exposure assessment, as the soil is an imperative resource that is used for food production (Al-Kharouf et al. 2008). A number of studies have been conducted in the preceding two decades to explore the transfer factor of radionuclides from soil to crops. Site-specific baseline values of radioactivity concentration in different matrices are important information to understand the status of NORMs in a typical location and to assess the impact of anthropogenic activities.

Baseline studies are mandatorily carried out at all proposed nuclear facility sites. Radionuclides activity varied from 0.002–10.6 Bq kg−1 (238U), 0.002–2.8 Bq kg−1 (232Th), 0.1–7.2 Bq kg−1 (226Ra), 3.0–110.8 Bq kg−1 (40K), and 0.03 to 3.0 Bq kg−1 (137Cs) in different food matrices collected from vicinity of proposed nuclear facilities, near Vizag, India (Patra et al. 2014). The activity concentrations of 40K, 228Ra, and 226Ra were quantified in pulses, cereals, and vegetables cultivated around Kudankulam, India (Ross et al. 2013). Mean 40K, 228Ra, and 226Ra activities in pulses were 294.3, 1.07, 0.15 Bq kg−1, while 70.78, 0.47, and 0.09 Bq kg−1, respectively, in cereals. Reported activity concentrations were higher in pulses as compared to other studied food categories. The concentrations of 232Th, 238U, 226Ra, and 40K were determined in staple cereals (rice and wheat), pulses, and drinking water consumed by the population residing around high background radiation area located in Chhatrapur, Odisha, India (Lenka et al. 2013). 232Th, 238U, 226Ra, and 40K activities in the collected samples were in the range of 0.3–2.0, 0.3–32.0, 0.4–28.2, and 14.3–957 Bq kg−1, respectively. Kumar et al. (2009) analyzed uranium content in food samples including wheat and Brassica grains from different areas of the district Bathinda, Punjab. The uranium content was 0.38 Bq kg−1 in Brassica grains and 4.60 Bq kg−1 in wheat grains.

Nuclear power Corporation of India (NPCIL), India has proposed a nuclear power plant (2800 MW capacity, 700 × 4) at Village Gorakhpur, Fatehabad district, Haryana, India. Uranium concentration in water has been reported for urban and rural areas of the district (Singh et al. 2014a, b). Wheat is the staple food and major crop cultivated in this area in rabi season. Keeping this in view, this study was conducted to quantify 40K, 232Th, and 226Ra radioactivity in agricultural field soil, wheat crop grains, their transfer factor (TF), and natural internal dose imparted from consumption of wheat grown within 30-km radius area of the proposed site. These basic radiometric data generated in the study might be useful especially with regard to food policy and other administrative functions.

Materials and Methods

Study Area

This study has been conducted within 30-km radius area of the proposed Gorakhpur Haryana Anu Vidyut Pariyojana (GHAVP), and the study area stretches into Fatehabad and Hisar districts of Haryana, India.

Climate of the area is tropical with significant variations in ambient temperature from 47 °C in summer to 2 °C in winter. The area receives an annual average rainfall of 395.6 mm of which about two third is received during the short southwest monsoon period from July to September. Study area is an alluvial plain of Indo-Gangetic basin having flat plain topography with an average elevation 215 m, gently sloping from northeast to southwest. A total of 23 sampling locations were established in the study (Fig. 1). All sampling locations were geo-referenced using Global Positioning System (Table 1).

Fig. 1
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Map of the study area showing different wheat grain sampling locations

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Table 1 Sampling locations detail in the study area
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Sampling and Sample Processing

A total of 46 agricultural field soil and 46 wheat grain samples (≈1.0 kg each) from identified sampling stations were collected during wheat harvesting season (April–May) for two years, i.e., 2011 and 2012. Soil samples from wheat crop-cultivated agricultural fields were collected with the help of a wooden spade from a sub-surface depth level of 5–10 cm. To obtain a representative sample, four sub-samples of soil from rectangular grid of 0.5 m2 area were collected and then mixed together to have a composite sample. After dehusking the wheat grains and removing debris from the soil samples, they were packed in plastic containers and transported to the laboratory.

Soil samples after removing foreign materials, pebbles, etc. were first air dried and then kept in oven to achieve a constant sample weight, ground and passed through a 2.0 mm sieve and stored in cylindrical plastic containers. Grain samples were dried in drying oven at 110 °C until constant weight was attained. Dried sub-samples were ashed in muffle furnace at ≈350 °C till the ash was completely white. The ashed samples after being homogenized were kept in cylindrical plastic containers, tightly sealed with adhesive tape. Both grain and soil samples packed in cylindrical vials were left for a minimum of 28 days for secular equilibrium to be established between 226Ra and its short-lived daughters before gamma spectrometry measurements (Singh et al. 2005).

Radionuclides’ Quantification

40K, 226Ra, and 232Th were quantified using High-purity Germanium detector (HPGe, Baltic scientific instruments, Latvia) in ashed wheat grains and dried soil samples. Co-axial p-type HPGe detector was connected to preamplifier, amplifier, ADC converter, and acquisition interface module (Orion, Itech Instruments). A cylindrical-shaped special heavy-lead shield (210Pb < 50 Bq kg−1) of about 100 mm thickness with outer jacket of 1.5 mm of low Carbon steel, inner diameter (with copper lining) of 200 mm, and inner height (with copper lining) of 330 mm surrounded the detector to minimize the background radiation. Characteristic X-rays from lead were reduced using a 9.0-mm-thick layer of copper lined with 1.0-mm tin. Detector output was connected to an Amplifier (Model GCD 50 190). To maintain measurement quality, energy and efficiency calibration of the spectrometer were carried out using a standard mixed multi-nuclide source, traceable to the U. S. National Institute of Standard and Technology (NIST) standard. The standards and samples were prepared with a uniform geometry and counted for a period of 80,000 s in order to get sufficient counts at desired peaks. The activity of 40K was evaluated using the photo peak of its characteristics gamma line at 1460 keV. However, the activities of 232Th and 226Ra (238U) can be determined using their short-lived decay products, i.e., of 232Th from 583 keV gamma-ray of 208Tl and 226Ra from 609 keV γ-ray of 214Bi (Mehra 2009). The instrument had energy resolution (FWHM) of 0.90 keV for energy 122 keV(Co-57) and 2.0 keV for energy 1332 keV(Co-60), and relative efficiency (w.r.t. 3″ × 3″ NaI detector and Co-60 source mounted 25 cm above the detector) at 1332 keV γ-photon is ≥50%. Qualitative and quantitative analyses of gamma spectra were processed using INTERWINNER 7.0 program. Detector was attached with cryocan of liquid nitrogen of 30 L capacity to keep it cool continuously for avoiding any change in crystal structure.

Transfer Factor Analysis

Transfer factor of NORMs from soil to wheat grains was calculated using Eq. 1 (Singh et al. 2014c).

$$TF = \frac{{C_{\text{Grain}} }}{{C_{\text{Soil}} }},$$
(1)

where C grain and C soil are the radioactivity concentration of radionuclides in grains and respective agricultural field soils, respectively, expressed in Bq kg−1 (On dry weight basis).

Annual Effective Dose

Annual effective dose (AED) received by the adult population due to ingestion of 40K, 232Th, and 226Ra through dietary intake of wheat grains cultivated in the vicinity study area were calculated using Eq. 2 (Patra et al. 2014).

$${\text{AED}} \left( {\text{Sv}} \right) = {\text{CR}} \times {\text{FI }} \times {\text{DCF,}}$$
(2)

where CR is the activity of radionuclide in wheat grains (Bq kg−1); FI is the food ingestion rate (0.295 kg day−1 for wheat grains) for an adult person living in the study area; DCF is the dose conversion factors (ICRP 2012) for calculations of effective dose due to 40K, 232Th, and 226Ra, which were 6.2E−09, 2.3E−07, and 2.8E−07 Sv Bq−1, respectively.

Results and Discussion

40K, 232Th, and 226Ra Activity in Soil Samples of Wheat Fields

Activity concentration of naturally occuring radionuclides in the soils of wheat fields was detectable in all the samples and varied from 445.4–708.7 Bq kg−1 for 40K, 31.9–50.9 Bq kg−1 for 226Ra, and 24.2–39.0 Bq kg−1 for 232Th (Table 2). 226Ra, 232Th, and 40K activities in the soil of the study are comparable to the global average concentrations of these radionuclides in soils reported by United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR 2000). Geometric mean activity concentrations of NORMs (Bq kg−1) in the soil samples of wheat fields were in the following order: 40K (544.7 ± 14.6 Bq kg−1) > 226Ra (41 ± 1.6 Bq kg−1) > 232Th (32.3 ± 1.2 Bq kg−1). Activity concentrations of NORMs in different types of soils from Indian subcontinent have been reported by several authors. Pulhani et al. (2005) reported 226Ra, 238U, 232Th, and 40K activities from two morphologically different regions, viz., Punjab and Mahabaleshwar, India. 226Ra, 238U, 232Th, and 40K activities were in the range of 45.2–53.6 Bq kg−1, 11.2–46.2 Bq kg−1, 46.5–78.5 Bq kg−1, and 394–579 Bq kg−1 respectively in Punjab and in the range of 16.01–20.9 Bq kg−1, 9.4–20.5 Bq kg−1, 10.4–19.6 Bq kg−1, and 32–52 Bq kg−1 respectively in Mahabaleshwar. Authors concluded that the activity of radionuclides is higher in cultivated soils, which may be due to mineral inputs from regular irrigation and fertilizer application. In the soils of Kaiga region, Karnataka, India, 40K and 210Pb activities were in the range of 57.8–227.2 Bq kg−1 and 10.4–75.9 Bq kg−1, respectively (Karunakara et al. 2013). In one another study, 226Ra activity in the soils of Kaiga region has been reported in the range of 5.1–51.6 Bq kg−1 (James-Joshy et al. 2011). 40K, 226Ra, and 232Th activities in soil and beach sand samples of Kalpakkam, India were in the range of 38–760 Bq kg−1, 7.0–81 Bq kg−1, and 14–160 Bq kg−1, respectively (Kannan et al. 2002). 40K, 238U, and 232Th in the soil of Agastheeswaram taluk, Kanyakumari district, India were in the range of BDL–613.24 Bq kg−1, BDL–229.86 Bq kg−1, and 32.03–567.76 Bq kg−1, respectively (Khanna et al. 2005). The activity concentrations of 226Ra, 232Th, and 40K have been reported to be in the range of 18.2–90.3 Bq kg−1, 34.8–124.7 Bq kg−1, and 80.4–181.4 Bq kg−1 from some areas of Punjab and Himachal Pradesh, India (Singh et al. 2005). 40K, 232Th, and 238U activities in the soils of Kotagiri Taluk, Nilgiri biosphere, India were 229.2, 102 Bq kg−1, and 41.4 Bq kg−1, respectively, (Selvasekarapandian et al. 2002). A comparison of these studies showed that activity of NORMs in the soil is variable at different regions. This variation may be attributed to soil origin, soil type, landuse pattern, agronomic practices used by the farmers, etc.

Table 2 Naturally occurring radionuclides’ activity (Bq kg−1 DW) in wheat fields’ soil around GHAVP site during 2011 and 2012
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40K, 232Th, and 226Ra Activity in Wheat Grain Samples

All the collected wheat grain samples were quantified for 40K, 226Ra, and 232Th. 40K activity was detectable in all the samples and ranged from 111.3 to 245.7 Bq kg−1 with a geometric mean of 202 ± 3.7 Bq kg−1. 226Ra and 232Th activities were detectable in most of the wheat grain samples and ranged from <0.04 to 0.37 Bq kg−1 and <0.015 to 0.11 Bq kg−1 with geometric mean values of 0.12 ± 0.05 Bq kg−1 and 0.04 ± 0.03 Bq kg−1, respectively (Table 3).

Table 3 Naturally occurring radionuclides’ activity (Bq kg−1 DW) in wheat grains grown around GHAVP site during 2011 and 2012
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Activity of NORMs reported in various types of grains by various authors from different parts of the world is given in Table 4. The activity concentration in wheat flour samples collected from the local markets in Iraq ranged from 1.08 to 12.53 Bq kg−1 with an average 6.60 Bq kg−1 for 238U, 0.12–4.30 Bq kg−1 with an average 1.95 Bq kg−1 for 232Th, and 41.84 to 264.73 Bq kg−1 with an average 133 Bq kg−1 for 40K (Abojassim et al. 2014). This study concluded that consumption of wheat flour as foodstuff is safe for target population. Changizi et al. (2013) quantified 226Ra, 232Th, and 40K activities in wheat and corn grains collected from Iran. Mean activities of 226Ra, 232Th, and 40K were 1.67 Bq kg−1, 0.5 Bq kg−1, and 91.73 Bq kg−1 respectively, in wheat grains and 0.81 Bq kg−1, 0.85 Bq kg−1, and 101.5 Bq kg−1 respectively, in corn grains. Other studies have reported higher activity concentrations of 226Ra and 232Th and lower activity concentration of 40K in both the matrices compared to the present study. Organically and conventionally grown winter wheat from Belgium was monitored for the distribution of natural radionuclides, and no significant difference between two were observed (Lindahl et al. 2011). Overall average activity concentrations in wheat grains obtained for 40K, 226Ra, 228Ra, and 228Th were 115 ± 22 Bq kg−1, 0.10 ± 0.05 Bq kg−1, 0.15 ± 0.05 Bq kg−1, and 0.04 ± 0.03 Bq kg−1, respectively.

Table 4 Globally measured naturally occurring radionuclides’ activity in different food and grain matrices
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Pulhani et al. (2005) measured 226Ra, 238U, 232Th, and 40K activity in wheat grain samples collected from two geographically different provinces (Punjab and Maharashtra) in India. 226Ra, 238U, 232Th, and 40K activities in wheat grain samples collected from Punjab were in the range of 0.4–0.8 Bq kg−1, 0.02–0.06 Bq kg−1, 0.6–1.2 Bq kg−1, and 79.1–110 Bq kg−1, respectively. 226Ra, 238U, 232Th, and 40K activities in wheat grain samples collected from Mahabaleshwar, Maharashtra were in the range of <0.2 Bq kg−1, 0.03–0.04 Bq kg−1, 0.1–0.2 Bq kg−1 and 116–130 Bq kg−1, respectively. 226Ra, 232Th, and 40K were higher in wheat grains in the present study than those from Punjab, while reported 226Ra and 40K activities were lower and 232Th activity was higher in wheat grains from Maharashtra.

Transfer Factor of 40K, 232Th, and 226Ra from Soil to Wheat Grains

The mobility of NORMs from rhizospheric zone of soils to the harvestable, edible part of the wheat plant, i.e., grains, was evaluated in terms of transfer factors (Fig. 2a, b). Transfer factors of 226Ra and 232Th were not countable for some of the wheat grain samples as radionuclides activity in one of the matrices was below detection limit (BDL). Soil to wheat grains TF of 40K, 226Ra, and 232Th were in the range of 0.19–0.48, BDL–0.01, and BDL–0.004, respectively. The geometric mean TF of studied NORMs was in the following order: 40K (0.37) > 226Ra (0.003) > 232Th (0.001). The soil to plant transfer factor is one of the important parameters to estimate the probable uptake and subsequent ingestion of radiation dose from radionuclides through food (IAEA 1982, 1994). Factors likely to affect radionuclide transfer from soil to plants may include soil characteristics, soil management practices, climatic conditions, type of plants, parts of the plant concerned, physico-chemical form of the radionuclides, and the effect of the competitive species (Bettencourt et al. 1988).

Fig. 2
figure 2figure 2

a Transfer factors of 40K from soil to wheat grains collected from GHAVP vicinity. b Transfer factors of 226Ra and 232Th from soil to wheat grains collected from GHAVP vicinity

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Transfer factors of radionuclides in the crops cultivated in different soil types may vary up to one or two orders of magnitude, and this variability may be attributed to genetic variability intrinsic in plants and distinctiveness among species besides the soil characteristics affecting the mobility of nutrients. 40K shows maximum transfer factor due to its monovalent nature and higher solubility resulting in higher mobility and uptake. Also, K is an essential nutrient, and therefore plant will seek K according to its requirement. In addition to stable K, 40K is also taken up by the plants. Radium is divalent and also has good solubility, but can be retarded by adsorption on hydroxides or by competition with calcium which will be in large excess in the soil. So, its uptake is less than potassium or 40K. Thorium is highly insoluble in soil water and so has minimum uptake.

In different agricultural systems, fecundity of the plant cultivated soil and crop cultivation techniques like soil processing; application of agrochemicals, including pesticides and fertilizers, enhanced irrigation in drought affected areas, and water drainage from marshy territories may results in redistribution of radionuclides in the rhizospheric zone, consequently altering the radionuclide uptake by crops (IAEA 2006). Speciation of the radionuclides and their bio-available fraction present in rhizospheric soil may also influence radionuclide transfer within the same plant (IAEA 2009).

Radionuclide concentration in phosphate fertilizers, field soil, and their uptake by wheat grains grown at Faisalabad, Pakistan was determined by Tufail et al. (2010). Soil to wheat grain transfer factor of 40K (0.12 ± 0.02) was lower, while that of 226Ra (0.02 ± 0.004) and 232Th (0.04 ± 0.007) were higher than that of the present study. Akhter et al. (2007) reported that soil to grain transfer factors of 40K were the highest and that of 226Ra were the lowest in wheat grown at agricultural farms in two districts in Pakistan. Transfer factors of natural radionuclides in wheat grains grown under natural field conditions on two morphologically different soils, from India varied from 6.0 × 10−3 to 2.4 × 10−2 for 232Th, 4.0 × 10−4 to 2.1 × 10−3 for 238U, 9.0 × 10−3 to 1.6 × 10−2 for 226Ra, and 0.14 to 3.1 for 40K (Pulhani et al. 2005). About 54–75% of total 238U, 232Th, and 226Ra activity was concentrated in the roots of the wheat plants and only 1–2% was found distributed in grains. On the other hand, 57% of 40K activity accumulated in the shoots and 16% in the grains.

Effect of Soil Parameters on Transfer Factor of Natural Radionuclides

Uptake of elements from the soil is influenced by physico-chemical properties of soil in the agricultural field, age and part of the bio-available concentration, and nature of the species (Sharma et al. 2007). Therefore, different soil properties of collected soil samples were determined. Transfer factors were calculated per soil group and evaluation of dependency of transfer factor on specific soil properties was performed, following correlation analysis and principal component analysis (PCA). Wheat grain TF of 40K was negatively correlated with available K (r = −0.47**, p ≤ 0.01) and total Ca content (r = −0.35*, p ≤ 0.05) of soil. Decreased uptake of 40K may be attributed to increased Ca content of the soil, as the cation contributes greatly to cation potential of the soil and may interfere with ion uptake by plants leading to their decreased transfer factor (Anke et al. 2004). Transfer factors of 40K, 226Ra, and 232Th were positively correlated with total organic carbon content (r = 0.49**, p ≤ 0.01; r = 0.32*, p ≤ 0.05; r = 0.36*, p ≤ 0.05) of soil. Increased transfer factor of these radionuclides with increasing organic carbon content of the soil may be due to their higher bio-available fraction present in soil solution at higher TOC. Higher the TOC content of the soil, more will be the retention of different ions on its surface against the leaching, and thus greater the uptake by plants. On the contrary, Hunsen and Huntington (1969) suggested that the mobility of thorium in soil is strongly affected by soil organic matter as the radionuclide may get strongly complexed with soil organic matter. Transfer factor of 232Th in wheat grains were positively correlated with CEC (r = 0.35*, p ≤ 0.05) content of the soils of corresponding fields.TF of 226Ra of wheat grain was positively correlated with the TF of 40K (r = 0.32*, p ≤ 0.05) and TF of 232Th (r = 0.59**, p ≤ 0.01) (Table 5).

Table 5 Correlation among transfer factor of NORMs in wheat grains and parameters of rhizospheric soils of the corresponding fields
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Principal component analysis with Varimax normalization (PCA-V) was applied for qualitative evaluation of correlation matrix results. Three factors loaded with TF of different NORMs in wheat grains and corresponding fields’ soil physico-chemical parameters, explaining a total variance 66.1%, were obtained. Factor-1 contributed 26.57% to the total variance, a high loading on K (r = 0.83) and Ca (r = 0.64) supporting correlation between two soil cations. With high loading on TF- 232Th (r = 0.75), TF- 226Ra (r = 0.67), and CEC (r = 0.61), Factor-2 contributed 20.22% to the total variance. Factor-3 accounting for 19.29% of the total variance was highly loaded with different soil properties, supporting associations among them (Fig. 3).

Fig. 3
figure 3

Principal component plot in rotated space (PCA) for transfer factor of NORMs in wheat grains and physico-chemical parameters of the soil of the corresponding fields

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Annual Effective Dose from the Ingestion of 40K, 232Th, and 226Ra Via Dietary Intake of Wheat Grains Grown in the Study Area

Radionuclide exposure in foodstuffs depends upon their uptake by specific plants and consumption level of specific foodstuffs, soil type, and soil physico-chemical characteristics. Calculated annual effective dose rates due to ingestion of 40K, 232Th, and 226Ra through dietary intake of wheat grains grown in the vicinity of proposed site are given in Table 6. The annual effective dose incorporated due to ingestion of 40K via dietary intake of wheat grains to the residents of study area varied from a minimum of 0.0743 mSv year−1 at Dhani majra-1 location to a maximum of 0.164 mSv year−1 at Sabarwas-1 location. The spatial variation in radioactivity dose from 40K was low with arithmetic and geometric mean doses of 0.137 and 0.135 mSv year−1, respectively.

Table 6 Annual effective dose of NORMs from consumption of wheat grains cultivated in the vicinity of proposed GHAVP site, Haryana, India
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The annual effective dose incorporated due to ingestion of 226Ra via dietary intake of wheat grains to residents of study area varied from minimum of <1.21E−03 mSv year−1 at Nangthla-1 location to a maximum of 1.12E−02 mSv year−1 at Dhani majra-2 location. The spatial variation in radioactivity dose from 226Ra was moderate with arithmetic and geometric mean dose values of 4.14E−03 and 3.51E−03 mSv year−1, respectively.

The annual effective dose incorporated due to ingestion of 232Th via dietary intake of wheat grains to residents of study area varied from a minimum of <4.95E−04 mSv year−1 at Kumharia-1 location to a maximum of 2.83E−03 mSv year−1 at Dhanimajra-2 location. The spatial variation in radioactivity dose from 232Th was moderate with arithmetic and geometric mean dose values of 1.10E−03 and 9.75E−04 mSv year−1, respectively. The annual ingestion dose incorporated due to studied radionuclides varied by one order of magnitude. The intake of radionuclides by consumption of wheat grains from the cultivated in study area contribute a small fraction of the total annual ingestion dose received by man due to naturally existing radioactivity in the environment.

The total cumulative annual effective dose from the ingestion of 40K, 232Th and 226Ra through dietary intake of wheat grains varied from 0.07 to 0.17 mSv year−1. Total radioactivity dose from ingestion of 40K, 232Th and 226Ra via ingestion of wheat grains in present study was found to be in magnitude order of 10−2 to 10−1 mSv year−1; well under the global average permissible limits for general public (UNSCEAR 2000). At this magnitude order, the dose to general public is negligible to be effective.

Lenka et al. (2013) estimated the annual effective dose from the ingestion of 232Th, 238U, 226Ra, 40K, and 137Cs in staple cereal (rice and wheat) grains, pulses, and drinking water in high background radiation area located in Chhatrapur, Odisha, India. The annual effective doses from cereals, pulses, and drinking water varied in the range of 0.11–0.94, 0.10–0.31, and 0.005–0.003 mSv year−1, respectively with an estimated total average annual effective dose of 0.53 mSv year−1. The dose from the cereals was highest due to their higher consumption. Shanthi et al. (2010) estimated the annual effective dose with highest contribution of 0.66 mSv year−1 by 228Ra followed by 0.47 mSv year−1 by 228Th, 0.46 mSv year−1 by 40K and 0.20 mSv year−1 by 226Ra ingestion via consumption of south Indian foods with total annual effective dose of 1.79 mSv year−1. Akhter et al. (2007) measured the annual committed effective doses to be 0.008, 0.005 and 0.178 mSv year−1 for 232Th, 238U and 40K, respectively, through ingestion of daily diets to Pakistani population. The total annual committed effective dose impact of these radionuclides was 0.18 mSv year−1. Total annual effective dose due to 40K, 238U, and 232Th activity ingestion via different foodstuffs in tin mining area of Jos Plateau, Nigeria individuals was reported in the range of 0.0002 mSv year−1 in Sword beans to 0.22 µSv year−1 in Yam (Jibiri et al. 2007). Hosseini et al. (2006) reported annual effective dose of 2.88 × 10−2 μSv due to 238U and 2.15 μSv due to 226Ra ingestion via wheat grains intake collected from markets in Tehran. Mlwilo et al. (2007) reported total annual effective doses due to total 232Th and 238U activity ingestion via staple food grains (maize and rice) from various localities of Tanzania. Estimated total annual effective doses were 0.16 mSv year−1 for infants, 0.29 mSv year−1 for children, and 0.36 mSv year−1 for adults respectively.

Conclusion

In the present study, naturally occurring radioactive materials (40K, 226Ra, and 232Th) activities have been quantified in wheat grains, the major widely consumed foodstuff in North India. Dosimetry analysis revealed that ingestion of wheat grains cultivated in the study area is radiologically safe for general public. 40K is the main contributor to total cumulative annual effective dose, but the radionuclide is of limited interest in dose calculations because this is an essential isotope of the element remains under homeostatic control in the human cells. Therefore, 40K content in human body is regulated and determined largely by its physiological characteristics rather than its intake. Also, the measured activity concentrations of terrestrial radionuclides in the soils of wheat crop fields were comparable to the global averages. Correlation analysis revealed that total organic carbon is the major factor governing the transfer of radionuclides from soil to wheat grains. The study gives the baseline information of soil and wheat grains’ natural radioactivity contents and uptake under specific conditions around GAHVP site, which will be useful for assessing the impact of operations of nuclear power plant in future.