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 reproces sing plant at Sellafield, Cumbria, was used to examine the spatial, tempora l 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 incr easing 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. T his decline is attributed to greater deposition occurring at the leading ed ge of the woodland. The uniform deposition pattern of Cs-134 in soil is con sistent with the hypothesis that, at the time of sampling, these deposits d erived largely from wet deposition during passage of the Chernobyl plume ov er Cumbria in May 1986. Results for the leaf litter indicate a similar spat ial distribution to that: observed in soil. Radionuclide concentrations wer e also similar but this is not attributable to adventitious soil contaminat ion because significant differences between isotopic ratios of Cs-134:Cs-13 7 and Pu-238: Pu239+240, imply that the contamination on leaf litter is of more recent origin than that in soils.