CS-134/137 CONTAMINATION AND ROOT UPTAKE OF DIFFERENT FOREST TREES BEFORE AND AFTER THE CHERNOBYL ACCIDENT

The Cs-134/137 activities were measured from different tree organs of spruce, larch and sycamore maple. Two locations in South Bavaria were monitored during a period of 2.5 years following the Chernobyl accident. Samples taken in 1985 allow to determine the Cs-137 contamination before the accident. Increasing Cs-137 activities from older to younger needle years of Picea abies caused by root-uptake of the global weapons' fallout are due to the high phloem mobility of this element and the remaining of the needles at the tree for about 6-7 years. In contrast, the Cs-137 activity was much smaller in leaves of larch and sycamore maple. After the Chernobyl accident, the higher contamination of spruce > larch > sycamore maple is dependent on the roughness of bark, absolute bark surface and the existence of leaves during the deposition of Chernobyl-derived radioactivity. The Cs-134/137 activity (Bq/kg d.w.) was about 25-times higher in bark compared to wood of Picea abies and 1.5-4.7 times higher in directly contaminated twig-axes than in leaves. Till the end of the investigation the major contamination of the shoots was due to direct deposition of cesium on the trees. A maximum of 5-15% of the total activity of the directly contaminated branches of the plants was calculated to be part of root-uptake, depending on the amount of initial retention. 20% of the translocated cesium into new leaves of larch and about 50% into sycamore maple resulted from root-uptake 2.5 years after the accident.