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

The time dependence of the availability of Cs-137 in soil for root uptake by plants was studied. This was accomplished by taking advantage of the prolonged drought in Greece during the years 1986-1990 in order to simulate the chemical evolution of caesium in soil. Several measurements of the soil to plant transfer factor were performed on a lake bottom, exposed due to the drought since 1986. The transfer factor for caesium to vegetation growing on recently exposed lake bottoms was found to be three to five times higher than the transfer factor to vegetation growing on areas that had dried up for more than 2 years. These results support the premise that with the passage of time radiocaesium from nuclear fallout is trapped in surface soil and thus becomes less, available for uptake by vegetation.