FACTORS AFFECTING THE TRANSFER OF RADIONUCLIDES TO SHEEP GRAZING ON PASTURES RECLAIMED FROM THE SEA

The ingestion of soil by sheep grazing on pasture reclaimed from the s ea has been studied. Seasonal variation of soil intake was small compa red to that found in a parallel study at an inland farm, but this coul d be explained by the husbandry, specifically the provision of supplem entary feed during the winter months, and the quality of the pasture. The quantity of soil ingested, expressed as a percentage of the dry ma tter intake, was typically about 2%, much lower than values normally u sed in models used to assess the impact of radionuclides in the enviro nment. These results have been combined with relevant data from earlie r studies at this same site in order to quantify the factors affecting intakes of various radionuclides by; sheep and their onward transfer along the foodchain. Strontium-90 and Tc-99 have relatively, high soil :grass transfer factors and ingestion of soil-associated activity was not an important contributor to intakes. For Cs-137, the relative cont ributions to intake from activity incorporated into foliage and from t hat associated with soil were about equal. However, after ingestion mo st of the soil-associated Cs-137 activity would be unavailable for upt ake by the animal, and so soil:grass transfer was the most important c ontributor, to the subsequent transfer to animal products. For Pu-239, Pu-240 and Am-241, inadvertent ingestion of soil-associated activity. This process was also the most important contributor to uptake even th ough only about 5% of the soil-associated activity, was soluble in rum en fluid. The implications of these results for radiological assessmen ts are discussed.