Transfer of radiocaesium from soil to vegetation and to grazing lambs in a mountain area in northern Sweden

Radioecological studies on a mountain farm in the Chernobyl fallout area in the county of Jaemtland, Sweden, were carried out in 1990-1993. Activity analyses of soil samples, taken to 10 cm depth at nine sampling sites within a grazing area of about 10 km2 showed a mean deposition of 137Cs of 15.7 (range 14.1-17.6) kBq/m2. The mean ratios of 134Cs/137Cs in the upper 0-5 cm and 5-10 cm of the soil layer were 0.523 and 0.521, respectively. The average 137Cs concentration of the herbage cut at the various sites decreased with time from 1175 to 900 Bq/kg dry weight (when corrected for physical decay to August 1990). This gave an average transfer factor from soil to plant of 0.067 (range 0.074-0.057) m2/kg, which corresponds to an average transfer to the cut herbage of 0.86% of deposited 137Cs. The 137Cs concentration in single plant species decreased in the order: herbs>grasses>woody plants>trees and shrubs. The average 137Cs concentration in the abdomen wall muscle of lamb carcasses was 1087, 668, 513 and 597 Bq/kg wet weight in the years 1990-1993, respectively, indicating an effective ecological half-time of 3.4 years or 3.8 years when corrected for physical decay (ecological half-time). All carcasses exceeded the intervention level applied in Sweden, 300 Bq 137Cs/kg, and were thus discarded for human consumption. (Author)