Radio‐caesium fixation dynamics: measurement in six Cumbrian soils

Five peat soils and a mineral soil were artificially contaminated with 137 Cs. Soil solution activity and radio-lability of 137 Cs were monitored over 709 days to quantify progressive 137 Cs fixation. The peat soils fixed large amounts of 137 Cs, but less than the mineral soil did. Distribution coefficients (K d , cm 3 g -1 ) ranged from 30 to 5000 at the end of equilibration. A labile 137 Cs distribution coefficient, K dl , was estimated by a method involving solid = solution equilibration in dilute solution. In a separate study several concentrations of KCl were added to soils in increasing concentration both before and after the addition of 137 Cs. Differences in apparent adsorption strength of radiocaesium indicated that K + induced the collapse of expanded mineral interlayers, thereby trapping ions. It seemed that 137 Cs adsorbs at sites in the small micaceous clay fraction of the peat soils. The different rates of 137 Cs adsorption and fixation in the peat and mineral soils, in which the rate of access of 137 Cs to fixation sites in peat soils is less, seems to have been caused partly by lack of K, and partly by the scarcity of fixation sites.