The persistent absence of immobilisation (fixation) of Chernobyl-deriv
ed radioactive caesium in soils of the upland areas of Britain has bee
n 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 C
s-fixing clay mineral illite was found to be present in all cases. How
ever, the amount of illite, and passible the total clay fraction, was
reduced by hydrogen peroxide pretreatments, which are required to remo
ve organic matter prior to mineralogical analysis, unless they were bu
ffered at a value close to the natural pH of the soil. Determination o
f the total number of potential Cs-fixing sites, using a batch-equilib
rium sorption method, was not possible for these acid organic soils, d
ue to tire occurrence of edge-interlayer trapping. To overcome this a
new sequential sorption method was devised. Tire total number of poten
tial Cs-fixing sites in the soils studied was found to exceed those pr
esent in lowland mineral soils. This may be due to a greater proportio
n of clay interlayer regions being in the expanded slate in rite organ
ic soils compared to the mineral soils. It is noted, however, that alt
hough a soil may have the potential to fix Cs ions, conditions necessa
ry for the realisation of this potential may not occur in the field.