Uptake and retention of strontium, iodine and caesium in lowland pasture following continuous or short-term deposition

Abstract

Data from the extensive routine environmental monitoring programme around the nuclear reprocessing plant at Sellafield, West Cumbria, are analysed for soil to plant uptake of strontium, iodine and caesium. Relative to the top 10 cm of soil, dry weight concentration ratios derived for lowland pastures for strontium, caesium and iodine are 9, 3 and 2 respectively. Long-term trends indicate a ‘spring flush’ of activity in vegetation, although this is not statistically significant. Uptake of caesium and iodine is highest generally for mosses and lichen and lowest for grass. The vegetational field loss of these elements over the first 50 days following deposition, is described by: Sr: R eff (t) = 0.7e −1.15t + 0.25e −0.049t + 0.05e −0.011tI: R eff(t) = 0.7e −1.26t + 0.25e −0.17t + 0.05e −0.092tCs: R eff(t) = 0.6e −0.87t + 0.2e −0.20t + 0.16e −0.065t + 0.04e −0.011t where t is in days. The functions are consistent with the effects of washoff and grazing. Equilibrium plant:soil concentration ratios are established for caesium within about 8 months following short-term deposition. Soil distribution profiles for caesium imply a half-time for transfer through the surface layers of about 6 years.