Chernobyl radiocaesium in an upland sheep farm ecosystem

Following the deposition of radiocaesium from the Chernobyl accident the movement and slaughter of sheep in upland areas of west Cumbria, Scotland and Wales was restricted. Studies on the radioecology of Cs-137 and Cs-134 have been conducted at a farm within the affected area of west Cumbria since July 1986. The radiocaesium activity of upland sheep was found to decline when they were brought on to the farms' enclosed pastures and rise when they were returned to the open fell, where the radiocaesium content of vegetation has remained higher than on the pastures. The Cs-137 activity concentration of mixed grassland vegetation samples from the fell has declined over the study period, whereas the Cs-137 activity of ewes whilst grazing on the fell was higher in summer of 1987 than in autumn 1986. A number of factors which may have contributed to this discrepancy were investigated and are discussed. It is suggested that husbandry changes would be effective in reducing the number of lambs leaving the restricted area with radiocaesium activities over the limit (1000 Bq/kg fresh weight Cs-134 + Cs-137) set by the United Kingdom authorities.