Influence of zeolite on the availability of radiocaesium in soil to plants.

Plant availability of radiocaesium is usually high immediately after incorporation in a soil. However, for some Swedish soils, e.g, peat soils, a high radiocaesium uptake in plants has also been observed during a second growth period after contamination. For these soils the reduction in the plant availability of the nuclide seems to be a slow process. In the last two years the mineral zeolite has become of interest and has been tested as a caesium binding agent in both animal and in soil-plant systems. The aim of this study was to evaluate the time dependency and the effect of zeolite on the plant availability of radiocaesium in a peat soil-plant system. The pot experiments designed for this purpose were carried out in a climate chamber, using winter wheat as the test crop. A significant reduction of the uptake of 134Cs was obtained in wheat when increasing amounts of zeolite were added. This reduction in plant uptake, up to a factor of 8, might depend on two factors. One is that zeolite has reduced the activity concentration of radiocaesium in the soil solution available to the plant roots. The other is that the potassium added with the natural zeolite increased the degree of dilution of caesium in the soil solution. Also, increasing equilibration time for caesium in soil before sowing brought about an effective reduction in the caesium uptake.