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

Abstract

Radioecological studies on a mountain farm in the Chernobyl fallout area in the county of Jämtland, 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 10km 2 showed a mean deposition of 137Cs of 15.7 (range 14.1–17.6) kBq/m 2. 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) m 2/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. Transfer factors (plant to muscle) decreased from 0.93 kg dry weight/kg wet weight in 1990 to 0.61, 0.56 and 0.71 in the following years. Similarly, the aggregated transfer factor (soil to muscle) decreased over the years, from 0.062 to 0.047, 0.032 and 0.046 m 2/kg wet weight. The results show high availability and transfer of radiocaesium in the mountain grazing areas of Sweden 4–7 years after the Chernobyl fallout.