Behaviour and transport of radionuclides in soil and vegetation of a sand dune ecosystem

Abstract

A sand dune ecosystem in the vicinity of the British Nuclear Fuels reprocessing plant at Sellafield, Cumbria, UK was used to examine the spatial, temporal and depth distributions of 134Cs, 137Cs, 238Pu, 239+240Pu and 241Am in soil and in two species of vegetation (Festuca rubra, Ammophilaarenaria). Core samples showed evidence of the accumulation of radionuclides derived mainly from sea-to-land transfer. Accumulated deposits of radioactivity (0–0.1 m) lie within the range: 1.1–3.4 Bq kg−1 (134Cs), 260–440 Bq kg−1 (137Cs), 31–40 Bq kg−1 (238Pu), 150–215 Bq kg−1 (239+240Pu) and 190–240 Bq kg−1 (241Am). Soil profiles showed greater activity concentrations in their deeper regions and this is attributed to leaching of radionuclides in percolating drainage water accentuated by the coarse texture, low organic matter and clay mineral content of coastal sands. Radionuclide activity concentrations in F. rubra and A. arenaria were similar, in the ranges 20–70 Bq kg−1 (137Cs), 1–5 Bq kg−1 (238Pu), 10–30 Bq kg−1 (239+240Pu) and 10–65 Bq kg−1 (241Am). Clear temporal and spatial variations were observed in both species of vegetation, reflecting the weather conditions antecedent to the sampling period and the influence of sea-to-land transfer. Concentration ratios (vegetation:soil) for activity concentrations in the two species were similar, in the ranges: 0.05–0.14 (137Cs), 0.025–0.097 (238Pu), 0.022–0.057 (239+240Pu) and 0.025–0.212 (241Am).