The influence of soil properties on the environmental mobility of caesium in Cumbria

The interaction of caesium isotopes with soil has been widely investigated and the influence of important soil properties studied. From the results of such work and a detailed knowledge of the physico-chemical properties of soils it is possible to classify Cumbrian soil according to its ability to immobilize caesium. The ‘immobilization capacity’ is a reflection principally of the clay mineral content and type, organic content, pH, ammonium content and potassium status. Although it is not quantifiable, the immobilization capacity permits ranking of the soils and indicates which areas may give rise to persistent caesium problems. Combination of the soil sensitivity classification with deposition data for Cumbria indicates that the mountainous region in the south-west of the county is the most vulnerable. This conclusion is supported by field evidence, since the area identified coincides closely with that where sheep movement and slaughter are restricted and where caesium remains persistently available to the plant-animal chain.