TIME-DEPENDENCE OF THE TRANSFER-FACTOR OF CS-137 FROM SURFACE SOIL TOPLANTS

The time dependence of the availability of Cs-137 in soil for root upt ake by plants was studied. This was accomplished by taking advantage o f the prolonged drought in Greece during the years 1986-1990 in order to simulate the chemical evolution of caesium in soil. Several measure ments of the soil to plant transfer factor were performed on a lake bo ttom, exposed due to the drought since 1986. The transfer factor for c aesium to vegetation growing on recently exposed lake bottoms was foun d to be three to five times higher than the transfer factor to vegetat ion growing on areas that had dried up for more than 2 years. These re sults support the premise that with the passage of time radiocaesium f rom nuclear fallout is trapped in surface soil and thus becomes less, available for uptake by vegetation.