The deposition of Chernobyl caesium-137 in heavy rain and its persistent uptake by grazing sheep

Abstract

Activity escaped from the wrecked reactor at Chernobyl for 10 days and spread over most of Europe. Part of the debris crossed Britain a week after it was emitted. Heavy thunderstorms and a northward-moving cold front washed out much of the radioactive iodine and caesium it carried, especially on to the upland areas of North Wales, northern England, SW Scotland and Ulster. Several lessons have been learnt, including information on the dry and wet removal rates. The deposition of Chernobyl debris was of transient importance to agriculture in lowland areas which are rich in clay minerals. There, levels of iodine-131 in milk in the 2 weeks following the debris' passage over the country were readily detected, even though the levels were well below Government limits, but fell to insignificance thereafter. In contrast, in upland sheep-rearing areas, the caesium has remained mobile in the acidic soils and levels in sheep have often exceeded Government limits, and have been decreasing only slowly since 1986.