Availability of radiocaesium in soils : a new methodology

Two issues are addressed in this paper: (a) the partitioning of radiocaesium between the micaceous specific site pool and the reversible ion exchange pool in mineral soils characterized by relatively low contents of organic matter; (b) the presentation of a new methodology for measuring radiocaesium availability in soils. The partitioning of radiocaesium between specific sites and reversible ion exchange sites is predicted on the basis of soil characterization: specific sites and overall 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 sandy, loamy sand, loam and clay soil, using a variety of desorption agents. A new methodology is presented for measuring radiocaesium availability, using an infinite bath scenario. The method is illustrated by a series of radiocaesium desorption protocols on humic acid, a reference illite clay, a sand loam, loam and clay soil and a set of podzolic soils, including samples from the Chernobyl 30-km zone. It is demonstrated that the (Ca + Mg)/K ratio in soils may play a key role in accelerating the radiocaesium fixation process in the specific sites. The implications 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.