Fractionation of caesium (Cs) in coniferous forest soil in central Sweden

Sequential extraction procedure (SEP) was applied for fractionation of Chernobyl fallout ¹³⁷Cs bound onto soils of a coniferous forest ecosystem located in central Sweden. Results of sequentially extracted ¹³⁷Cs fractions demonstrated that 8% (mean value) of the total deposited ¹³⁷Cs was water soluble (F1) and 13% was NH₄OAc extractable (F2). Oxidation of F2 residuals by H₂O₂ led to a release of 15% of soil-bound ¹³⁷Cs (F3). Acid digestion of F3 residuals showed a possibility of releasing an extra amount of soil-bound ¹³⁷Cs, 22% of the total soil ¹³⁷Cs inventory (F4). These two fractions (F3 and F4) include strongly bound ¹³⁷Cs that seems to require longer biodegradation processes by soil microflora and microfauna before becoming available for uptake by plants and fungi. More than 37% of the total soil ¹³⁷Cs inventory was bound onto soil residuals in a non-extractable form that includes slowly degradable organic matter and other soil residual compartments. The distribution coefficient (K_d) was rather low and shows an inverse relation with the increase of percentage of soil organic matter, which indicates a week binding of ¹³⁷Cs onto forest soil. In contrast, chemical fractionation of soil bound ¹³⁷Cs showed a substantial fraction of ¹³⁷Cs was strongly bound onto soil as organically bound ¹³⁷Cs. Apparently, the binding processes of radiocaesium onto forest soil seems to be time dependent.     

Distribution of (210)Pb and (210)Po in boreal forest soil

Vertical distribution and activity contents of ²¹⁰Pb and ²¹⁰Po were investigated in forest soils of Scots pine-dominated (Pinus sylvestris L.) stands from seven different locations in Finland. The mean total inventory in the soil profile, up to 20 cm, of ²¹⁰Pb was 4.0 kBq m^− 2 (range 3.1-5.0 kBq m^− 2) and ²¹⁰Po 5.5 kBq m^− 2 (range 4.0-7.4 kBq m^− 2), the organic soil layer containing 45% of the total inventory of both nuclides. In both the organic and the mineral layers the ²¹⁰Po/²¹⁰Pb ratio was close to unity indicating a radioactive equilibrium between them. In the litter layer there was, however, a clear excess of ²¹⁰Po suggesting that polonium is recycled via root uptake from the root zone to the ground surface. The activity concentration (Bq kg^− 1) of ²¹⁰Pb clearly correlated with organic matter and the Fe, Al and Mn concentrations in soil indicating that radioactive lead is associated both with humic substances and the oxides of iron, aluminium and manganese. Radioactive lead was also seen to follow the behavior of stable lead. No systematic correlation between polonium and soil properties was seen.     

Vertical distribution of Th-isotope ratios, 210Pb, 226Ra and 137Cs in sediment cores from an estuary affected by anthropogenic releases

In an estuary system highly polluted by mining and industrial activities, the sections of sediment cores affected by anthropogenic inputs of U-series radionuclides (due to fertilizer plants releases) were determined through the vertical profiles of Th-isotopic ratio (230Th/232Th). Also, when possible, a modified version of the 210Pb dating method was applied in the uncontaminated sections of these cores. Using the information provided by the Th-isotopic ratio and 210Pb methods, we were able to establish confident chronologies, covering the last century, in several of the analysed sediment cores. These chronologies will be used in forthcoming research to study the time evolution of pollutant concentrations in the estuary. Additionally, and based on the established chronologies, we have found that sedimentation rates have drastically increased in some zones of the estuary since the commencement of several industrial activities in the surrounding environment and since the construction of two dikes in the area.     

Accumulation of potassium, rubidium and caesium (Cs and Cs) in various fractions of soil and fungi in a Swedish forest

Radiocaesium (¹³⁷Cs) was widely deposited over large areas of forest in Sweden as a result of the Chernobyl accident in 1986 and many people in Sweden eat wild fungi and game obtained from these contaminated forests. In terms of radioisotope accumulation in the food chain, it is well known that fungal sporocarps efficiently accumulate radiocaesium (¹³⁷Cs), as well as the alkali metals potassium (K), rubidium (Rb) and caesium (Cs). The fungi then enhance uptake of these elements into host plants. This study compared the accumulation of these three alkali metals in bulk soil, rhizosphere, soil-root interface, fungal mycelium and sporocarps of mycorrhizal fungi in a Swedish forest. The soil-root interface was found to be distinctly enriched in K and Rb compared with the bulk soil. Potassium concentrations increased in the order: bulk soil < rhizosphere < fungal mycelium < soil-root interface < fungal sporocarps; and Rb concentration in the order: bulk soil < rhizosphere < soil-root interface < fungal mycelium < fungal sporocarps. Caesium was more or less evenly distributed within the bulk soil, rhizosphere and soil-root interface fractions, but was actively accumulated by fungi. Fungi showed a greater preference for Rb and K than Cs, so the uptake of ¹³⁷Cs could be prevented by providing additional Rb or K at contaminated sites. The levels of K, Rb, and Cs found in sporocarps were at least one order of magnitude higher than those in fungal mycelium. These results provide new insights into the use of transfer factors or concentration ratios. The final step, the transfer of alkali metals from fungal mycelium to sporocarps, raised some specific questions about possible mechanisms.