Effect of soil K-status and bentonite additions on radiocaesium transfer

The influence of bentonite additions and soil K status on radiocaesium transfer to ryegrass was investigated in a potted soil experiment. A sandy soil was contaminated with I M Cs and amended with K salts (0-97 mM kg") and K bentonite (0-2 %). After 4 weeks incubation of the mixtures, ryegrass was grown for 18 weeks and trimmed at 7 occasions. During subsequent harvests, the radiocaesium transfer factor (TF) decreased up to 2.7 fold in soils amended with more than 0.25 % bentonite whereas they increased 3.0 to 14,4 fold in unamended soils or at the lowest bentonite application (0.25 %). Different trends are related to the formation of specific sorption sites and the depletion in soil K which was more pronounced in soils with <0.25 % K-bentonite added. Radiocaesium Interception Potential (RIP) and percentage K bentonite added were positively correlated. 10-40 fold higher RIP values at 1 to 2 % supply compared to unamended soils were obtained. Built-up of RIP following subsequent cycles of partial drying and rewetting during plant growth is reflected in a loss in exchangeable K and the quantitative reduction of the TF. The potential role of K-bentonite as countermeasure for Cs contaminated soils is discussed.