137Cs, 239,240Pu and 241Am in boreal forest soil and their transfer into wild mushrooms and berries

Abstract

Profiles of podzolic soil from boreal forests were sampled from eight sites in Finland and the distribution of (137)Cs in the soil layers was determined. In addition, (239,240)Pu and (241)Am were determined from two soil profiles taken at one sampling site. Inventories of (137)Cs in the soil profiles varied between 1.7 kBq/m(2) and 42 kBq/m(2), reflecting known variation in (137)Cs fallout from the Chernobyl accident. The highest proportions of the radionuclides were found in the organic layer at a depth of less than 5 cm, which on average contained 47% of (137)Cs, 76% of (239,240)Pu and 79% of (241)Am. In the litter, clearly higher proportions of (137)Cs were found compared to (239,240)Pu and (241)Am, probably indicating its more effective recycling from the organic layer back to the surface. Only very minor proportions of (137)Cs were recorded below 20 cm. The concentration of (137)Cs in the soil profiles could be approximated with a declining logarithmic trend. The activity concentrations of (137)Cs were determined for six wild mushroom species and three wild berry species at two sites, as well as the aggregated transfer factors and the distribution of (137)Cs between their various parts. In addition, (239,240)Pu and (241)Am were determined in one mushroom and three berry species at one site. Very high concentrations of (137)Cs, up to 20 kBq/kg (d.w.), were found in mushrooms, and their transfer factors were between 0.1 m(2)/kg and 1.0 m(2)/kg. In berries, the transfer factors were an order of magnitude lower. (137)Cs accumulated more in the caps of mushrooms and in the fruits of berries than in other parts. Transfer factors for (239,240)Pu and (241)Am were two to three orders of magnitude lower than those of (137)Cs.