Radiation Protection and Environment

ARTICLE
Year
: 2011  |  Volume : 34  |  Issue : 3  |  Page : 210--212

Estimation of grass to milk transfer coefficient for cesium for emergency situations


P Ujwal1, N Karunakara1, I Yashodhara1, Chetan Rao1, Sudeep Kumara1, BN Dileep2, PD Nayak2, PM Ravi3,  
1 University Science Instrumentation Centre, Mangalore University, Mangalagangothri, Mangalore, India
2 Environmental Survey Laboratory, Kaiga Generating Station, Kaiga, India
3 Heath Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai, India

Correspondence Address:
N Karunakara
University Science Instrumentation Centre, Mangalore University, Mangalagangothri, Mangalore
India

Abstract

The grass to milk transfer coefficient is usually represented as F m values. This paper reports the results of grass to cow milk transfer coefficients (F m ) for Cesium for emergency situation. An experimental grass field was developed in Kaiga region and two cows were adopted for collecting milk samples regularly. Grass was cut from the field and spiked with very low concentration of Cs (in the form of CsCl or CsI), to simulate a sudden deposition of Cs on grass and fed to the adopted cows. The milk samples were collected during normal milking periods (morning and evening) for several days and analyzed. The peak concentration of Cs in milk was observed during time period 24-36 hrs after the intake of spiked grass. Three spike experiments were carried out and values of F m were found to be 7.8 × 10 -3 d L -1 , 3.5×10 -3 d L -1 and 2.4×10 -3 d L -1 . The grass to milk transfer coefficient values observed under spiked conditions were an order of magnitude lower when compared to the equilibrium transfer coefficient for Kaiga region, which highlights the importance of studies aimed at generating site-specific database on F m for simulated emergency situation.



How to cite this article:
Ujwal P, Karunakara N, Yashodhara I, Rao C, Kumara S, Dileep B N, Nayak P D, Ravi P M. Estimation of grass to milk transfer coefficient for cesium for emergency situations.Radiat Prot Environ 2011;34:210-212


How to cite this URL:
Ujwal P, Karunakara N, Yashodhara I, Rao C, Kumara S, Dileep B N, Nayak P D, Ravi P M. Estimation of grass to milk transfer coefficient for cesium for emergency situations. Radiat Prot Environ [serial online] 2011 [cited 2021 Jan 17 ];34:210-212
Available from: https://www.rpe.org.in/text.asp?2011/34/3/210/101727


Full Text

 1. Introduction



Several studies have been reported on the soil to grass transfer factors (F v ) and grass to cow's milk transfer coefficients (F m ) for 137 Cs for equilibrium conditions for the environs of different nuclear power stations of both India and other parts of the world. In such studies, the activity concentration of 137 Cs was measured in grass collected from different places and Cow milk samples collected from nearby localities or from milk dairies and the F m values were estimated. In situations where 137 Cs is not present in measurable activity concentrations, its stable counterpart (Cs) is measured for the estimation of F m values. But, it should be noted that F m values obtained for equilibrium conditions may not be applicable for use in dose estimation to the public for an emergency situation.

Studies aimed at evaluating transfer coefficient of 137 Cs for emergency situations are sparse. Nuclear power plants do not release 137 Cs during normal operating conditions and therefore sudden deposition of this radionuclide on grass does not happen. However, generation of site-specific database on F m for emergency situations is very essential because such database would help in quick assessment of environmental contamination, decision making and to take specific counter measures.

We have carried a detailed study to estimate site specific data on F m for Kaiga region. A grass field was developed specifically for this study and grass grown in the field was cut and spiked with very low concentration of stable Cs (Cs taken in the form of either CsCl or CsI) and fed to the adopted cows. The variation of Cs concentration in the cow milk was monitored and the F m values were estimated. The results of these studies are presented and discussed in detail in this paper.

 2. Materials and Methods



2.1 Development of experimental grass field

An experimental grass field was developed on a land of an area 30×20 m, in Kuchegar village (14°52′2.5″N, 74°22′41.1″E), located at a distance of about 8 km north west from the Kaiga Generating Station (KGS). The land used for developing the experimental field was an open land, used previously for growing rice and vegetables. Grass species Pennisetum purpureum, Schum, commonly known as Napier grass and used as fodder grass in the milk dairies in the region, was planted in the field and was allowed to grow normally with no external application of fertilizers. The soil in experimental grass field was silt loam with very low clay content.

2.2 Cows for collecting milk samples

Milk samples were collected from two cows adopted for this study. The adopted cows were local breed variety called "Malnad Gidda", which is a dominant breed in the West Coast region of India including Kaiga. The Malnad Gidda cows are small to medium built, graze in hilly areas and resistant to pest and diseases. The milk yields of these cows vary significantly but the maximum milk yield is about 4 L d -1 (Survey report, 2007), [1] with majority of the cows yield much less milk. The two cows adopted in the present study had maximum milk yields of 1.9 and 2.2 L d -1 respectively. The milk yield is low but it is very thick when compared that of the diary farm cows. Necessary prior approval was obtained from the University Animal Ethics Committee, which is approved by the University Grants Commission, New Delhi to adopt the cows in Kaiga region.

2.3 Spiking of grass with stable Cs

To simulate a sudden deposition of caesium isotopes on grass, the grass from the experimental field was cut and sprayed with very low concentration of Cs (in the form of CsCl or CsI) and fed to the adopted cows. The milk samples were collected during normal milking periods (morning and evening) for several days for analyses. Three spike experiments were carried out and the spiked grass fed to the cow were 0.15, 0.2 and 0.18 kg (dry weight) respectively for experiment 1, 2 and 3. Cows were fed with the spiked grass only once and then it was allowed to feed on normal grass. The study involved the use of very low concentration of stable Cs and no radioactive isotopes were used.

2.4 Estimation of stable Cs concentration in grass and milk samples

The samples were processed following standard method. [2] For the determination of stable Cs concentration in grass and milk samples, the ashed samples were digested in a closed vessel Microwave Digestion System (Milestone, Italy) to get clear solutions. The concentration of Cs in the digested samples was determined using an Atomic Absorption Spectrometer (GBC, Australia). The instrument was calibrated using AAS standards procured from MERCK (Germany). High purity water (obtained used Milli Q, Millipore system) was used for sample preparation and dilution.

 3. Results and Discussions



In the first two spike experiments Cs was spiked onto grass in the form of CsCl. In the case of emergency situation radioisotopes of Cs from the nuclear facilities may also be released in the form of CsI and therefore for one of the spike experiment stable Cs was taken as CsI. After feeding the spiked grass to the cow, milk samples were collected at regular milking intervals upto 6 days and analyzed.

[Figure 1] and [Figure 2] shows the variation of Cs concentration in milk with time when Cs was fed in the form of CsCl and CsI respectively. The concentration of Cs in milk increased with time initially, reached a maximum, and then decreased with the time. Peak concentration of Cs in milk appeared between 24-36 hrs duration after ingestion of the spiked grass. It may be noted that mean value of inherent stable Cs concentration in grass was found to be 1.0 mg kg -1 , which is negligible when compared to the concentration fed through spiked grass, and that in milk was 0.11 mg L -1 . The daily intake of grass by the adopted cow was found to be 8.3 kg d -1 and the total daily intake of inherent Cs through grass was negligible when compared to one time intake through spiked grass. {Figure 1}{Figure 2}

From the results of concentration of Cs in grass and milk the F m value was estimated as under (IAEA, 2010): [3]

[INLINE:1]

Where, F m is transfer coefficient (d.L -1 )

A m is the Cs concentration in milk (mg l -1 fresh weight)A g is the Cs concentration in grass (mg kg -1 dry weight)S m is the intake of spiked grass by cow (kg d -1 dry matter)

The value of A m was obtained from the area under the curve of time verses Cs concentration in milk [Figure 1] and [Figure 2]. The area under the curve was divided by the total time to get the average concentration of Cs in milk. The F m values thus calculated were found to be 7.8×10 -3 d L -1 and 3.5×10 -3 d L -1 when Cs was fed in the form of CsCl and 2.4×10 - 3 d L -1 when it was fed in the form of CsI and the mean value of all the three spiking experiments was 4.6×10 -3 d L -1 . This value is an order of magnitude lower when compared to the equilibrium F m value (2.9×10 -2 d L -1 ) obtained from a detailed study for Kaiga region. [4] Equilibrium transfer coefficients were established by analyzing more than 60 grass and equal number of milk samples and for these studies samples were collected from (i) experimental grass field and adopted cows, (ii) Nine common grazing areas around Kaiga region and cows of local farmers which graze in common grazing areas and (iii) dairy farm in Kaiga. For establishing the equilibrium F m value both 137 Cs and stable Cs were studied and these studies did not involve spiking of grass.

IAEA has compiled data on F m values of both stable and radioactive Cs isotopes reported in literature for different parts of the world and the values varied in the range 6.0×10 -4 - 6.8×10 -2 d L -1[] with a mean value of 4.6×10 -3 d L -1 (IAEA, 2010). [3] Green and Woodman [5] have extensively reviewed the literatures published on F m values for cesium and summarized that the F m values vary in the range 7.5 ×10 -4 - 6.82×10 -2 d L -1 with an overall mean of 5.65×10 -3 d L -1 . The results summarized by Green and Woodman (2003) included studies conducted on different conditions such as radiocesium added to feed, orally administered to cow, continuous fallout, Chernobyl fallout and post Chernobyl fallout and the mean value of F m for radiocesium added to feed trials was found to be 5.0 × 10 -3 d L -1 and that for orally administered trials it was 8.4 × 10 -3 d.L -1 . The F m value obtained in the present study, in which stable Cs was added to the feed, was very much comparable with the mean value reported by Green and Woodman [5] for similar studies. They have also concluded that the highest and lowest values reported were only about one order of magnitude different from the mean, regardless of the type of experiment, diet, milk yield or age of cow. Field experiment gave a wider range of transfer values than did feeding trails and this was attributed to the fact that in field experiments control over the animals diet would be less.

 4. Conclusion



The F m value obtained in the present study by feeding the cow with grass spiked with stable Cs is comparable to those reported in the literature. The F m values generated in the present study would help to predict ingestion dose to the general public due to the intake of Cs radioisotopes through cow milk in case of an emergency situation. The mean value of F m value obtained from spike experiments was an order of magnitude lower when compared to that observed for equilibrium conditions for Kaiga region.

 5. Acknowledgments



The authors would like to thank the Nuclear Power Corporation of India Ltd. (NPCIL) for providing financial support for the study. The support received from the Board for Research in Nuclear Science (BRNS), DAE is gratefully acknowledged. Thanks are due to Sri S G Ghadge, Director, Safety, NPCIL, Sri P K Malhotra, Associate Director, RSA, NPCIL and Sri M Kansal, Chief Engineer, RSA, NPCIL for many useful comments. Thanks are also due to Sri J P Guptha, Site Director, NPCIL, Kaiga, Dr Joshi P James, Mrs. Selvi, Mr. Raghu M Joshi and other scientific staff of ESL, Kaiga for their help and suggestions during sample collection and analyses.

References

1Survey report, Govt. of Karnataka. Biodiversity conservation and management in coastal districts of Karnataka-part 2. Karnataka Biodiversity Board 59-76; 2007.
2BARC (Bhabha Atomic Research Centre), Standard Protocol for evaluation of environmental transfer factors around NPP sites. In: Hegde AG, Verma PC, Rao DD, editors. Mumbai: BARC; 2008.
3IAEA. Handbook of Parameter Values for the Prediction of Radionuclide Transfer in Terrestrial and Freshwater Environments. International Atomic Energy Agency, Vienna, Technical Reports Series No. 472, 2010.
4Ujwal P, Karunakara N, Yashodhara I, Rao C, Kumara S, Dileep BN, et al. Studies on soil - grass- cow milk transfer of 137 Cs in Kaiga region. Book of Abstracts. 30 th IARP Conference on Radiological Protection and Safety in Nuclear Reactors and Radiation Installations. India: Mangalore University; 2012.
5Green N, Woodman RF. Recommended transfer factors from feed to animal products. National Radiological Protection Board, NRPB-W 40, 2003.