Caesium–137 Household of Lake Lugano INVESTIGATIONS ON THE CAESIUM–137 HOUSEHOLD OF LAKE LUGANO, SWITZERLAND J. DRISSNER, E. KLEMT*), T. KLENK, R. MILLER, G. ZIBOLD FH Ravensburg Weingarten, University of Applied Sciences, Center of Radioecology, P. O. Box 1261, D 88241 Weingarten, Germany M. BURGER, A. JAKOB GR, AC Laboratorium Spiez, Sektion Sicherheitsfragen, Zentrale Analytik und Radiochemie, CH 3700 Spiez, Switzerland *)
[email protected] SedimentCaesium–137J. Drissner, E. HouseholdKlemt, TH. of Klenk Lake et Lugano al. 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. 1 Introduction Lake Lugano with an area of 48.9 km2 and a mean depth of 134 m is one of the large drinking water reservoirs of southern Switzerland, in the foothills of the southern Alps. The initial fallout of Chernobyl caesium onto the lake was about 22,000 Bq/m2 [1], which is similar to the initial fallout of about 17, 000 Bq/m2 onto Lake Constance, which is located in the prealpine area of southern Germany (north of the Alps).