THE IMPORTANCE OF SOIL ADHERED TO VEGETATION AS A SOURCE OF RADIONUCLIDES INGESTED BY GRAZING ANIMALS

Soil ingestion has been identified as a potentially important source of radionuclides to grazing animals. Seasonal patterns of soil adherence to vegetation and its implications for the radionuclide intake of grazing animals were measured at two west Cumbrian sites. Soil adhesion to vegetation was highly seasonal, being highest in autumn and winter. At Site 1 (a lowland pasture close to the British Nuclear Fuels plc Sellafield Reprocessing Plant, Cumbria, UK), vegetation samples were found to consist of up to 46% soil (by dry weight). Therefore, the importance of soil as a potential source of radionuclides to grazing animals was also seasonal; soil comprised up to 92% of the Cs-137 and potentially all of the PU-239/Pu-240 of vegetation samples at Site 1 and up to 62% of the Cs-137 at Site 2 (an upland farm contaminated following the Chernobyl accident). Analyses of sheep faecal samples confirmed the seasonal importance of soil as a potential source of radionuclides. The importance of soil adhering to vegetation, as a source of contaminant Cs-137, increased with time after the Chernobyl accident. Calculations of soil ingestion must be made when the intake of radionuclides by grazing animals is being studied. In some circumstances, present radioecological models may considerably underestimate the importance of soil ingestion.