The transfer of 137Cs and 90Sr to dairy cattle fed fresh herbage collected 3.5 km from the Chernobyl nuclear power plant

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Abstract

A study conducted during summer 1993 to determine the bioavailability and transfer of 137Cs and 90Sr to dairy cattle from herbage collected from a pasture contaminated by particulate fallout is described. The study pasture was located 3.5 km from the Chernobyl nuclear power plant. The true absorption coefficient (At) determined for 137Cs (0.23) was considerably lower than previous estimates for radiocaesium incorporated into vegetation by root uptake. It is likely that the low dry matter digestibility of the diet and the potential presence of 137Cs associated with adherent soil-associated fuel particles contributed to this low bioavailability. The At value determined for 90Sr (0.27) did not indicate a reduced bioavailability. It is suggested that the current and previous calcium status of the animals was the controlling influence on the transfer of 90Sr from the diet to milk.

Introduction

A number of studies following the Chernobyl accident have demonstrated the importance of the form in which radiocaesium is ingested by grazing animals in determining absorption across the gut and the subsequent activity concentrations in milk and meat (Beresford et al., 1992; Cooke et al., 1996; Mayes, Beresford, Howard, Vandecasteele & Stakelum, 1996). These studies have been concerned with artificially contaminated or environmentally contaminated sources from western Europe. Radiocaesium deposited in western Europe from the Chernobyl accident was predominantly in the form of aerosols. Closer to the Chernobyl nuclear power plant (NPP) large areas were contaminated with particulate material (hot particles) ejected into the atmosphere as the result of the explosion. Animals grazing in such areas may ingest radioactivity associated with these particles if they are resuspended onto vegetation surfaces; the availability for transfer to meat and milk of radionuclides associated with such ingested particles is unknown. We describe a study to measure the transfer of 137Cs and 90Sr to dairy cattle conducted within the Ukrainian Chernobyl exclusion zone at a site contaminated by particulate fallout.

Section snippets

Experimental animals and study site

The six experimental cows were of a local dairy breed with a mean (±SE) live-weight of 410±15 kg. The animals were in their second to fourth month of lactation and had a mean milk yield of 9.1±0.84 kg d−1; individual yields ranged from 7.2 to 11.9 kg d−1.

The cattle were moved to experimental housing 20 d prior to the start of the experiment. The housing consisted of open-sided stalls with concrete flooring at the edge of ca. 0.15 km2 pasture (standing biomass approximately 900 kg dry matter (DM) ha−1

Results

The activity concentrations of 137Cs and 90Sr in the daily cuts of herbage fed over the final week of the study are shown in Fig. 1. Daily variation in the activity concentration of herbage was low for both radionuclides with the exception of results for 137Cs in samples collected on 27/7/93. Mean activity concentrations (±SE; n=21) over the week were 41.9±1.44 kBq kg−1 DM for 90Sr and 28.4±1.55 kBq kg−1 for 137Cs. The ratio of 134Cs : 137Cs in herbage was 0.048±0.0005 (x̄±SE;n=21). The 134Cs and

Animal performance

The dry matter intakes of the cattle met the requirements advised by the National Research Council (NRC) (1989) for cows with such a live-weight and milk yield. However, the dry matter digestibility of the complete diet was low (51%) and is likely to have limited dry matter intake and hence possibly milk production rate (NRC, 1989). The milk yields of the animals were low considering that they were in early lactation when production should have been close to maximum. If we assume that the dry

Conclusion

These results suggest that the radiocaesium present in vegetation close to the Chernobyl NPP was poorly absorbed by lactating cattle. The transfer of both radiocaesium and radiostrontium to milk was probably influenced by the poor quality of the diet, increasing plasma-to-milk transfer of radiocaesium and reducing the transfer of radiostrontium to milk. Derived parameters for the transfer of 90Sr to milk are likely to have been influenced by the animals’ calcium intake prior to the study.

Acknowledgements

The authors would like to thank those members of staff of the Department of Radiology and Land Reclaiming (RIA Pripyat) who took part in this study, and also Cath Barnett (ITE), Dave Benham (ITE), Beverley Dodd (ITE), Stuart Lamb (MLURI), Arthur Sanchez (ITE), the staff of the Chernobyl Central Laboratory, and members of the Analytical Chemistry Section at ITE Merlewood for their assistance during experimental planning and sample analyses. We also acknowledge the support of Michael Sedov

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