Radionuclide behaviour and transport in a coniferous woodland ecosystem: The distribution of radionuclides in soil and leaf litter

A coniferous woodland in the vicinity of the British Nuclear Fuels reprocessing plant at Sellafield, Cumbria, was used to examine the spatial, temporal and depth distribution of Cs-134, Cs-137, Pu-238, Pu239+240 and Am-241 in soil and leaf litter. All the radionuclides, with the exception of Cs-134, showed a consistent fall in accumulated soil and litter deposits with increasing distance from the woodland edge nearest to Sellafield. Cs-137 levels in soil declined from 53 to 28 kBq m(-2), Pu239+240 from 5.5 to 3.6 kBq m(-2) and Am-241 from 2.9 to 1.1 kBq m(-2) within 100 m of the forest edge. This decline is attributed to greater deposition occurring at the leading edge of the woodland. The uniform deposition pattern of Cs-134 in soil is consistent with the hypothesis that, at the time of sampling, these deposits derived largely from wet deposition during passage of the Chernobyl plume over Cumbria in May 1986. Results for the leaf litter indicate a similar spatial distribution to that: observed in soil. Radionuclide concentrations were also similar but this is not attributable to adventitious soil contamination because significant differences between isotopic ratios of Cs-134:Cs-137 and Pu-238: Pu239+240, imply that the contamination on leaf litter is of more recent origin than that in soils.