DEVELOPMENT OF AN IN-VITRO METHOD TO ASSESS THE AVAILABILITY OF SOIL-ASSOCIATED RADIONUCLIDES FOR UPTAKE BY RUMINANTS

A simple in-vitro method has been developed to estimate the availabili ty of soil-associated radionuclides for uptake by grazing ruminants. T he radio-nuclides of principal interest were Cs-137, (239)/240Pu, and Am-241. A range of soils was incubated with freshly-collected rumen li quor over a 24 h period under simulated in-vivo conditions. The mixtur es were then separated into liquid and solid phases, and the distribut ion of each radionuclide between the two phases was determined. The pe rcentage of the activity found in the liquid phase was generally low a nd for the radionuclides of principal interest was never moi re than 2 0%. All of the radionuclides were found to be most readily extracted f rom poorly developed organic soils. The effect of pH on radionuclide e xtractability was evaluated for two soils, an alluvial gley and a peat y ranker. For both soils, radiocaesium extractability was constant acr oss the range of pH likely to be encountered in the rumen, and was in good agreement with values derived from in-vivo studies in the literat ure, In contrast, actinides were found to be move readily extracted at pH 6.5 than 5.5 from the peaty ranker. For all of the soils studied, estimates of actinide availability based on this technique were low an d comparable with those derived from the limited