AVAILABILITY OF RADIOCESIUM IN SOILS - A NEW METHODOLOGY

Two issues are addressed in this paper: (a) the partitioning of radioc aesium between the micaceous specific site pool and the reversible ion exchange pool in mineral soils characterized by relatively low conten ts of organic matter; (b) the presentation of a new methodology for me asuring radiocaesium availability in soils. The partitioning of radioc aesium between specific sites and reversible ion exchange sites is pre dicted on the basis of soil characterization: specific sites and overa ll ion exchange capacity. It is predicted that, in mineral soils, only very small fractions of radiocaesium can be expected to be present in readily reversible ion exchange sites. Such predictions are confirmed by an experimental screening study on radiocaesium desorption in a sa ndy, loamy sand, loam and clay soil, using a variety of desorption age nts. A new methodology is presented for measuring radiocaesium availab ility, using an infinite bath scenario. The method is illustrated by a series of radiocaesium desorption protocols on humic acid, a referenc e illite clay, a sand loam, loam and clay soil and a set of podzolic s oils, including samples from the Chernobyl 30-km zone. It is demonstra ted that the (Ca + Mg)/K ratio in soils may play a key role in acceler ating the radiocaesium fixation process in the specfic sites. The impl ications of the positive effect of a high Ca-Mg status in the soil on its fixation potential are discussed in terms of the long-term effects of possible countermeasures.