Investigations on the caesium-137 household of Lake Lugano, Switzerland

Sediment samples were taken from different basins of Lake Lugano, and the caesium 137 inventory and vertical distribution was measured. In all samples, a distinct maximum at a depth of 5 to 10 cm can be attributed to the 1986 Chernobyl fallout. Relatively high specific activities of 500 to 1,000 Bq/kg can still be found in the top layer of the sediment. 5 step extraction experiments on sediment samples resulted in percentages of extracted caesium which are a factor of 2 to 8 higher than those of Lake Constance, where caesium is strongly bound to illites. The activity concentration of the water of 3 main tributaries, of the outflow and of the lake water was in the order of 5 to 10 mBq/l.