Das Projekt "Verhalten von Cs und Sr in natuerlichen Oekosystemen und potenzielle Strahlungsexposition bei ihrer extensiven Nutzung" wird vom Umweltbundesamt gefördert und von Bundesamt für Strahlenschutz durchgeführt. Objective: The Chernobyl accident led to an enormous amount of measurements of 134Cs and 137Cs activities in, for example, wild berries and mushrooms. These data, which vary widely, are helpful for evaluating actual radiation exposure to man, but they are of no help in understanding the behaviour of radionuclides in forest ecosystems. The project Cycling of Radiocaesium and Strontium in Natural Ecosystems, investigates the fate of radiocaesium and strontium 90 in natural ecosystems in Belgium, Germany, Sweden and Italy, in order to improve the knowledge of the cycling mechanisms and the understanding of their short and long term behaviour. General Information: Seven laboratories from Belgium, Italy, Sweden and Germany are involved in this research project. The investigations take place in different forests sites in their countries. For joint investigations, boreal forests in Sweden and beech forests in the Italian Alps have been chosen. The experimental strategy is focusing on the fate of radiocaesium and strontium 90 after their deposition in forest ecosystems. One major point is the uptake of caesium and strontium from soil to plants. Until now it is not completely understood why the uptake rates of caesium in natural ecosystems are significantly higher than on agriculturally used areas. Natural ecosystems are characterized by undisturbed soils with organic and mineral horizons. In a first step, the distribution of radiocaesium and strontium 90 within the different layers are measured. To improve the knowledge of the plant availability, soil parameters like nutrient concentration, exchange capacity, kd values, etc. are determined. Additionally, plant parameters such as mycelium and rooting depths, potassium and calcium distribution within the plants are analyzed. The importance of various parameters on the transfer of caesium and strontium will be analyzed by statistical methods. The plant and herbivore interactions are analyzed by a special programme on moose. Moose meat contributes to about 5 per cent to 10 per cent of the average meat consumption in Sweden and is therefore of radiological interest. To obtain the radionuclide intake rate, the migration of single moose is observed during the year as well as their seasonal consumption habits. Later they are shot and caesium 134 and 137 activities in meat are measured. The correlation of radiocaesium and potassium intake rates will be tested. For long term considerations, the loss of radionuclides from the ecosystems by migration and runoff is analyzed. Further studies are concerned with the distribution of caesium and strontium within the ecosystems, the antagonisms of caesium and potassium as well as strontium and calcium, etc. ... Prime Contractor: Bundesamt für Strahlenschutz, Fachbereich Strahlenschutz, Institut für Strahlenhygiene; Oberschleißheim; Germany.