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 sea has been studied. Seasonal variation of soil intake was small compared to that found in a parallel study at an inland farm, but this could be explained by the husbandry, specifically the provision of supplementary feed during the winter months, and the quality of the pasture. The quantity of soil ingested, expressed as a percentage of the dry matter intake, was typically about 2%, much lower than values normally used in models used to assess the impact of radionuclides in the environment. These results have been combined with relevant data from earlier 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 contributions to intake from activity incorporated into foliage and from that associated with soil were about equal. However, after ingestion most of the soil-associated Cs-137 activity would be unavailable for uptake by the animal, and so soil:grass transfer was the most important contributor, 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 though only about 5% of the soil-associated activity, was soluble in rumen fluid. The implications of these results for radiological assessments are discussed.