3.6. Radiocaesium Transfer to Grazing Sheep in Nordic Environments

Abstract Radiocaesium transfer in the soil-herbage-lamb food chain was assessed in a four-year trial conducted in sheep production locations of the Nordic countries. Radiocaesium contamination of the topsoil ranged from 3 to 30 kBq m −2 and was predominantly of Chernobyl origin in Finland, Norway, and Sweden, whereas in Iceland 137 Cs was primarily of nuclear weapons test origin, and in Denmark and the Faroe Island contamination was derived from both sources. Soil-to-herbage radiocaesium transfer factors were high on the organic and acidic soils of the Faroe Islands, Iceland, Norway, and Sweden, averaging 18–82 Bq 137 Cs kg −1 herbage on a soil deposition of 1 kBq 137 Cs m −2 , and much lower on the sandy soils of Denmark and clay soils in Finland (0.4–0.8). Herbage-to-lamb concentration factors were generally more homogeneous, with values ranging from 0.25–0.70, indicating that the absorption of radiocaesium from herbage was similar in each of the countries. A 137 Cs deposition of 1 kBq m −2 soil gave rise to much lower meat radiocaesium concentrations at the sites in Denmark, the Faroe Islands, and Finland (0.5–3.0 Bq kg −1 ) than in Iceland, Norway, and Sweden (20–47 Bq kg −1 ). Major factors which will determine the time-integrated dose of radiocaesium transferred to man are levels of consumption of lamb meat, aggregated transfer factors from soil to meat, and effective ecological halflives of 137 Cs in the production system. It is concluded that among the Nordic countries the soil-herbage-lamb pathway is clearly of greatest importance in Iceland and Norway, intermediate in the Faroe Islands, and of comparatively lesser importance in Denmark and Sweden.