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In southern German spruce forests on different geological substrates the depth distributions of the activity inventories of 134 Cs and ,37 Cs radionuclides from Chernobyl and nuclear weapons testing fallout and the corresponding activity concentrations in the dry mass of different plants were measured. Using a compartment model based on first order kinetics, the vertical residence half-times and migration rates of 137 Cs were calculated. Migration rates decrease with increasing soil depth and retention time of the 137 Cs radionuclides in the soil. The aggregated soil to plant transfer factors [m 2 /kg] on the other hand, are comparatively high: Up to 1.1 m 2 /kg for fern, and smaller values for bilberry and raspberry. It is suggested that a fixation of cesium radionuclides in the organic matter of the litter debris occurs and that the transfer to plants is mediated by carrier substances produced by microorganisms responsible for the degradation of the litter.

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