The use of sapropels as amendments in radiocaesium and radiostrontium contaminated soils

Two issues are addressed in this paper: the solid/liquid distribution behaviour of radiocaesium (¹³⁷Cs and ¹³⁴Cs) and radiostrontium (⁹⁰Sr) in sapropels, and the potential effectiveness of sapropels as amendments to remediate soils contaminated with these radionuclides. It is shown that the solid/liquid partitioning of radiocaesium and radiostrontium in sapropels is governed by the same processes as in soils. Experimental K(D) values measured in a representative solution vary between 300 and 5000 dm³ kg^-1 for radiocaesium and between 15 and 50 dm³ kg^-1 for radiostrontium. These K(D) values can be interpreted quantitatively on the basis of the main factors which govern the solid/liquid partitioning of these radionuclides. This quantitative approach also allows predictions to be made on the potential effectiveness of sapropel amendments in contaminated soils. These predictions agree very well with experimental results from simple laboratory experiments aimed at investigating the amendment effect. Addition of 1-4 wt.% doses of 2 sapropel samples with different radiocaesium retention characteristics had no significant effect on the radiocaesium distribution coefficient in sandy soils. It is therefore expected that the addition of such sapropels will not result in a decrease of the radiocaesium soil-to-plant transfer, at least not from the point of view of the increase of the radiocaesium retention in the amended soil. Addition of 1-4 wt.% doses of a high CEC sapropel to low CEC sandy soils increased the radiostrontium distribution coefficient up to 3.5 times. It can thus be expected that addition of such high CEC sapropel will increase the radiostrontium retention in the amended soil, and thus decrease the radiostrontium soil-to-plant transfer.