Fixation of 137Cs by soils and sediments in the Esk Estuary, Cumbria, UK

Abstract

Abstract Enhanced levels of 137Cs are observed on the Cumbrian coast (UK) due to the discharge of low level waste by BNFL (British Nuclear Fuels Ltd) at Sellafield. Sorption of this radionuclide onto estuarine sediments is of considerable strategic importance as these areas represent a secondary source of transfer to inland areas. The study reported here was undertaken to determine, both quantitatively and qualitatively, the characteristics of the sorption and fixation of 137Cs in sediments and soils sampled from within the Esk estuary. This was carried out by means of a detailed set of laboratory analyses on samples collected from the area. These involved a sequential solvent extraction to determine the relative proportions of 137Cs associated with exchangeable, reducible, oxidiseable and residual fractions of various substrates; a series of batch sorption experiments was also carried out to determine the sorption characteristics of a selection of the substrates sampled. To complement these investigations grain size determinations coupled with X-ray diffraction analyses were employed to determine the mechanical and mineralogical properties of each sample collected. 137Cs was most strongly associated with the residual phase as defined by the sequential leaching scheme. The more consolidated, clay rich substrates appeared to sorb the greatest quantities of 137Cs within the residual phase although there was no obvious correlation between the quantity of radiocaesium associated with this phase and the relative proportion of illite and