Total caesium-fixing potentials of acid organic soils

The persistent absence of immobilisation (fixation) of Chernobyl-derived radioactive caesium in soils of the upland areas of Britain has been attributed to their peaty nature and assumed lack of Cs-fixing clay minerals. In the present study of a number of the affected soils the Cs-fixing clay mineral illite was found to be present in all cases. However, the amount of illite, and possibly the total clay fraction, was reduced by hydrogen peroxide pretreatments, which are required to remove organic matter prior to mineralogical analysis, unless they were buffered at a value close to the natural pH of the soil. Determination of the total number of potential Cs-fixing sites, using a batch-equilibrium sorption method, was not possible for these acid organic soils, due to the occurrence of edge-interlayer trapping. To overcome this a new sequential sorption method was devised. The total number of potential Cs-fixing sites in the soils studied was found to exceed those present in lowland mineral soils. This may be due to a greater proportion of clay interlayer regions being in the expanded state in the organic soils compared to the mineral soils. It is noted, however, that although a soil may have the potential to fix Cs ions, conditions necessary for the realisation of this potential may not occur in the field.