NONLETHAL DEFOLIATION TO IMPAIR THE FOLIAR UPTAKE OF FALLOUT RADIONUCLIDES BY FOREST TREES

The foliar uptake of fallout radionuclides is the most important way o f contamination of plant species. The Chernobyl accident showed that t he mangement of contaminated forest is not an easy task. Studies on co untermeasures after a nuclear accident performed within the European R ESSAC programme (Rehabilitation of Soils and Surfaces after an Acciden t) were undertaken to impair the internal contamination of woody parts of forest trees as well as perennial cultures like vine or orchards. The first non-lethal defoliation experiments were to examine the selec tion of appropriate defoliants. The five compounds experimented are no n-toxic to man and wildlife. Some which give good results are normally used to chemically dress vine without adverse effect on plant health and are expected to be non-lethal defoliants. Parallel laboratory expe riments on the translocation kinetics of soluble labelled caesium and strontium deposited on the leaves proved that only 2% of the deposited activity is translocated into the stem of poplar and oak after 200 h. These kinetics compared to those of defoliants may suggest that this countermeasure would be efficient in impairing the contamination of wo ody parts of forest trees.