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ORIGINAL ARTICLE
Year : 2022  |  Volume : 45  |  Issue : 2  |  Page : 71-75  

Studies on transfer coefficient from grass to milk for 137Cs and 40K at Kakrapar Gujarat site, India


1 Environmental Survey Laboratory (Environmental Studies Section, Environmental Monitoring And Assessment Division, Bhabha Atomic Research Centre), Kakrapar Gujarat Site, P.O. Anumala, Surat District, Gujarat, India
2 Environmental Monitoring and Assessment Division, Bhabha Atomic Research Centre, Mumbai, India

Date of Submission06-Sep-2022
Date of Decision26-Sep-2022
Date of Acceptance08-Oct-2022
Date of Web Publication20-Dec-2022

Correspondence Address:
S S Wagh
Environmental Survey Laboratory (ESS, EMAD, BARC), Kakrapar Gujarat Site, P.O. Anumala, Surat - 394 651, Gujarat
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/rpe.rpe_25_22

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  Abstract 


Transfer coefficient from grass to milk (Fm) for 137Cs and 40K was computed based on the activity measurement data in the respective matrix at Kakrapar Gujarat site, India, during 2013 - 2019. The annual geometric mean value of 137Cs activity in grass and milk samples varied from 0.13 to 0.48 Bq/kg dry wt. and 0.03 to 0.14 Bq/l, respectively. Activity observed during the year 2013 - 2019 is comparable with preoperational baseline activity level, which indicated its fallout origin. The site-specific Fm has varied between 1.0E-02 to 3.71E-02 d/l with a GM of 2.22E-02 d/l (137Cs) and between 6.69E-03 to 1.54E-02 d/l with a GM of 9.63E-03 d/l (40K), respectively. The annual effective dose due to the ingestion of 137Cs and 40K through milk consumption was found to be 0.036 μSv/y and 16.94 μSv/y, respectively. The result is an useful input for the estimation of radiation dose to human beings in accidental conditions.

Keywords: 137Cs, 40K, ingestion dose, site-specific transfer coefficient


How to cite this article:
Wagh S S, Patra A K, Jaison T J, Saradhi I V, Kumar A V. Studies on transfer coefficient from grass to milk for 137Cs and 40K at Kakrapar Gujarat site, India. Radiat Prot Environ 2022;45:71-5

How to cite this URL:
Wagh S S, Patra A K, Jaison T J, Saradhi I V, Kumar A V. Studies on transfer coefficient from grass to milk for 137Cs and 40K at Kakrapar Gujarat site, India. Radiat Prot Environ [serial online] 2022 [cited 2023 Jan 28];45:71-5. Available from: https://www.rpe.org.in/text.asp?2022/45/2/71/364558




  Introduction Top


Studies on radiation levels and radionuclide distribution in the environment provide vital radiological baseline information. Such information is essential in understanding human exposure from natural and human-made sources of radiation and necessary in establishing rules and regulations relating to radiation protection.[1] Effective radiation protection of man and the environment requires improved knowledge and reliable methods for a better assessment, understanding, and evaluation of radiation risks from external and internal radiation exposure to a variety of natural and artificial sources. 137Cs is one of the most important contaminant from nuclear fallout because of its long radiological half-life, affinity for biological systems and its uptake to man through dietary intake.[2] Cesium behaves much like potassium because of its similar physical and chemical properties. 137Cs may also be released from nuclear power reactors. In order to assess the impact of nuclear power reactors on human beings, it is essential to have an assessment of levels of 137Cs in foodstuffs. One of the important ingestion pathways of 137Cs is grass to cow, cow to milk and exposure to man due to the consumption of milk. Therefore, it is necessary to measure the concentration of 137Cs in grass and milk samples and to calculate the dose to human being due to the consumption of milk.

Transfer coefficient is a measure of the transfer of radionuclides to animal-derived food products to describe the transfer of radiocesium from the diet to the milk of dairy cattle. To estimate the transfer coefficient, the dietary composition of the animal must be quantified. For agricultural animals, this varies according to feeding strategies (indoors or grazing), maintenance requirements, agricultural practices, and diet composition and characteristics such as dry matter digestibility. The relative proportion of grass, grain, and other dietary constituents is important in determining radionuclide intake by agricultural animals since grassy vegetation tends to be more highly contaminated. Typical dietary constituents for agricultural animals vary between and within countries, and with the season.[3] The transfer coefficient from grass or feed to cow milk, Fm at equilibrium (d/1) is defined as the ratio of radionuclide activity concentration in milk (Bq/1) to the daily dietary radionuclide intake (Bq/d). In other words, Fm is the fraction of animal's daily intake of the radionuclide that appears in each liter of milk at equilibrium.[4] The grass-to-milk transfer of 137Cs is influenced by the 40K activity concentration in the grass; higher transfer of 137Cs occurs when the 40K content is lower in the grass.[5]

This article presents the 137Cs and 40K activity in grass and milk samples collected around the Kakrapar Gujarat site and the respective site-specific transfer coefficients from grass to milk.


  Materials and Methods Top


Site description

The study was carried out at Kakrapar Gujarat site, situated on the southern bank of Moticher Lake, which is about 85 km by road from Surat city, the southern region of Gujarat State (Latitude-21° 14' N and longitude-73° 22' E). Kakrapar Gujarat site comprises three nuclear power reactors (PHWR type) of capacity 220 MWe each (KAPS-1 and 2) and 700 MWe (KAPP-3), which are operational. One unit (PHWR type) of capacity 700 MWe which is under advanced stage of construction (KAPP-4).

Sample collection and processing

Sampling, sample processing, counting, and evaluation of radionuclides were carried out as per standard procedures. Cow feed samples such as grass (66 nos.) and milk (84 nos.) were collected from the same location from the local farmers around the Kakrapar site during the year 2013 - 2019.

Gamma spectrometric analysis

High Purity Germanium (HPGe) detector, coaxial type having 100% relative efficiency, a resolution of 1.9 keV at the 1332 keV gamma energy of 60Co and coupled to 8 K MCA was used for sample analysis. 662 keV peak was used for 137Cs estimation and 1460 keV was used for 40K estimation. HPGe detector was calibrated by using primary reference standard solution containing 152Eu, 137Cs, and 60Co. The efficacy of the sample counting was verified by the analysis of certified reference materials such as IAEA-375 and IAEA-444.

Estimation of site-specific Fm

The grass-to-milk transfer coefficient (Fm) was estimated using the following relation.[4]

Fm = (Am) ÷ (Ag × Qm)----------------(1)

where,

Fm is the transfer coefficient (d/l)

Am is the radionuclide activity concentration in milk (Bq/l)

Ag is the radionuclide activity concentration in grass (Bq/kg dry wt.)

Qm is the daily intake of grass (kg/d on dry weight basis).

Representative daily intake value used was 8.3 kg dry wt. of grass per day.[5]


  Results and Discussion Top


137Cs and 40K activity in grass

[Table 1] shows the range and annual geometric mean values of activity of 137Cs and 40K in the grass samples. 137Cs activity in grass samples was found to vary from 0.03 to 3.2 Bq/kg dry wt. The annual geometric mean value of 137Cs activity in grass samples was found to vary from 0.13 to 0.48 Bq/kg dry wt. The values observed at this site are comparatively lower as compared to the Kaiga region, Karnataka.[5],[6] [Figure 1] shows the variation of 137Cs activity in grass and milk sample in the form of box whisker plot. [Figure 2] shows the frequency distribution of 137Cs activity in the grass sample. It is observed that the frequency distribution of 137Cs activity in grass samples follows lognormal distribution with ƛ2 value of 2.1 (P = 0.72). The mean 137Cs activity in the Austrian alpine varies between 70 and 1132 Bq/kg.[7] 40K activity in grass samples is also tabulated in [Table 1]. The annual geometric mean values of 40K activity in grass samples for the corresponding period vary from 260 to 701 Bq/kg dry wt. The values are comparable with the values of 305 to 443 Bq/kg dry wt. reported for the Kaiga region, India.[6]
Table 1: 137Cs and 40K activity in grass samples from Kakrapar Gujarat site

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Figure 1: Variation of 137Cs activity in Grass and milk sample along with Site-specific Fm values

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Figure 2: Frequency distribution of 137Cs activity in Grass sample

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137Cs and 40K activity in milk

[Table 2] shows the range and annual geometric mean with geometric standard deviation values of activity of 137Cs and 40K in the milk samples. 137Cs activity in milk samples varied from ≤0.03 to 0.14 Bq/l. Most of the values are Below Detectable Limit (≤0.03 Bq/l) of our HPGe system. The values were comparable with the preoperational baseline level.
Table 2: 137Cs and 40K activity in milk samples from Kakrapar Gujarat site

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The 137Cs activity in milk in Mumbai (Maharashtra state) and the tropical region of Kaiga (Karnataka State) ranged from 0.007 to 0.442 Bq/l during the period 1965–1990 and 0.07 to 0.33 Bq/l during the period 2000 - 2009.[6],[8] The annual geometric mean of 137Cs activity in milk ranged from 12 Bq/l in 1986 to 0.02 Bq/l in 2014 in Czeck region.[9] It was also reported that in alpine regions, Austria, 137Cs activity in milk varied from 3.5 to 162 Bq/l and in vegetation ranging from 14 to 2595 Bq/kg.[7] 137Cs activity in milk collected around the Kakrapar Gujarat Site is comparable to those reported for other sites in India and lower than that reported for other countries. The values observed in the present study are comparable to 33 to 66 Bq/l and 14.9 to 22 Bq/l for 40K reported for Mumbai and Kaiga region,[6],[8] respectively.

Transfer coefficient of 137Cs and 40K from grass to milk (Fm)

The transfer coefficients from grass to milk (Fm) for 137Cs and 40K, were calculated based on the mean activity concentration of radionuclide present in the grass and milk by using Eq. 1. and is summarized in [Table 3]. The Fm of 137Cs and 40K was found to vary from 1.00E-02 to 3.71E-02 d/l with GM 2.22E-02 d/l and from 6.69E-03 to 1.54E-02 d/l with GM 9.63E-03 d/l, respectively. [Figure 1] shows the site-specific variation of Fm for 137Cs from grass-to-milk transfer in the form of box whisker plot. It is observed that Fm value of 40K is comparatively lower than that of 137Cs value. It is reported that the factors influencing the transfer coefficients are grass intake, assumption of equilibrium, physicochemical form affects transfer to tissue, age/body weight, and stable element.[3]
Table 3: Site-specific transfer coefficient (Fm) for 137Cs and 40K at Kakrapar Gujarat site

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Radiocesium Fm values of Japan after the Fukushima Daiichi nuclear power plant accident were reported to be 0.0027 and 0.0064 d/l,[10],[11],[12],[13],[14] after 2 months of this accident, the Fm value was reported to be 0.0029 d/l.[15] After Chernobyl nuclear power plant accident, the radiocesium Fm value in the milk was found to be 0.005 d/l.[16] Transfer coefficients of 137Cs reported from various locations are compared with Kakrapar site values and tabulated in [Table 4]. Fm value estimated during this study is comparable with other reported values. Fm value for 137Cs reported in the IAEA report ranges from 6.0E-04 to 6.8E-02 with a mean of 4.6E-03 d/l.[4] It was reported to vary from 3.9E-03 to 8.0E-03, with a mean of 5.5E-03 d/l in Sweden.[17]
Table 4: Comparison of site-specific transfer coefficient values (Fm) with other location

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In Kaiga region, Fm value for 137Cs and 40K were 6.43E-03 to 1.09E-02 with the mean 8.00E-03 d/l and 3.06E-03 to 3.48E-03 with the mean 3.26E-03 d/l, respectively.[6] In Tarapur and Narora site, the mean Fm value for 137Cs is 4.50E-03 and 1.15E-03 d/l,[18],[19] Fm for 40K varied from 6.92E-03 to 8.01E-03 d/l with a geometric mean value of 7.45E-03 d/l at Narora Site.[19]

Estimation of radiation dose to the public due to the intake of 137Cs and 40K through milk consumption

The annual effective dose due to the ingestion of radionuclides through milk was estimated using the following equation,[20]

Eing, p = Cp, i × Hp × DFing---------(3)

where,

Eing, p is the annual effective dose from consumption of radionuclide in foodstuff p (Sv/y).

Cpi is the concentration of the radionuclide i in foodstuff p at the time of consumption (Bq/kg).

HP is the consumption rate for foodstuff p (kg/y).

DFing is the dose coefficient for ingestion of radionuclide i (Sv/Bq).

The average milk consumption rate of the Kakrapar region by an adult was 73 l/y. The dose coefficients for an adult used for the estimation of the internal doses for 137Cs and 40K were 1.3 × 10−8 Sv/Bq and 6.2 × 10−9 Sv/Bq, respectively. The internal dose for 137Cs and 40K due to milk ingestion for the adult population were found to be 0.036 μSv/y and 16.94 μSv/y, respectively. This is comparable to the annual effective dose of 0.05 μSv/y due to the ingestion of 137Cs through milk consumption in the Kaiga region.[5]


  Conclusions Top


Systematic investigation on 137Cs and 40K activity in grass and milk samples was carried out for the Kakrapar Gujarat site. Activity observed during the year 2013 - 2019 is comparable with preoperational baseline activity level. Based on activity concentration, the site-specific transfer factor Fm was calculated and was found to vary in the range of 1.0E-02 - 3.71E-03 d/l with GM of 2.22E-02 d/l (137Cs) and 6.69E-03 - 1.54E-02 d/l with GM of 9.63E-03 d/l (40K), respectively. The annual effective dose due to the ingestion of 137Cs and 40K through milk consumption was found to be 0.036 μSv/y and 16.94 μSv/y, respectively. The results provide an useful input for the estimation of radiation dose to human beings in accidental conditions and in providing the guidelines for regulatory bodies during routine release from Nuclear Power Plants.[21]

Acknowledgments

The authors would like to thank Site Director, Kakrapar Site, Station Director, KAPS-1&2 and ACE (E&US), for their keen interest and encouragement. The assistance rendered by Shri M. K Chaudhary, Smt. Padma Chaudhary, Shri. J. J. Chaudhary, and all other ESL staff is thankfully acknowledged.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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