A NEW METHOD FOR PREDICTION OF RADIOCESIUM LEVELS IN VEGETATION - EVIDENCE FROM IRISH UPLANDS

Vegetation and soil samples from three upland areas in the Republic of Ireland were collected and analysed for radiocaesium. The data were used to investigate temporal trends in vegetation and to examine the relationships among radiocaesium concentrations in soils and various plant species. Radionuclide concentrations in Calluna vulgaris were compared with those in Erica cinerea, Erica tetralix and Juncus squarrosus and a consistent pattern emerged on all three study sites. No marked seasonal variations in concentrations were observed in these species. Clearly defined seasonal behaviour was, however, observed in Scirpus caespitosus. Concentrations were highest in Calluna vulgaris and Scirpus caespitosus, reaching peak activities of approximately 2000 Bq kg-1 dry weight. Concentrations in the other species were considerably less. A plant-to-plant ratio system is proposed as a new method for prediction of radionuclide concentrations in plants. Values calculated for plant-to-plant ratios are compared to traditional soil-to-plant ratio values and field data are used to test the performance of these ratios. Replication of both ratio systems gave consistent results when the experiments were repeated. The data demonstrate that the plant-to-plant ratio system can produce predictions as accurately as the soil-to-plant system. Results further suggest that the two systems are intrinsically related and that ratio values tend to be site specific but are of some value for between site predictions.