JOINT RUSSIAN-FINNISH STUDY OF RADIOACTIVE CONTAMINATION IN THE NW PART OF LAKE-LADOGA

In August 1992 a joint Russian-Finnish expedition was arranged to the NW part of Lake Ladoga to study radioactive contamination in the regio n. Special attention was paid to the area surrounding the Heinamaa Isl ands, where the wreck of the former mine carrier ship ''Kit'' had been lying about 30 years before it was moved to Novaya Zemlya in 1991. Du ring this period the wreck had been used as a store for radioactive wa ste containing principally Sr-90, Cs-137 and Pu-239,Pu-240. Lake water , bottom sediment and some biological samples were collected for stron tium, plutonium and gammaspectrometric analyses. In all the samples th e radioactivity concentrations were very low, indicating radioactive c ontamination of about the same level as caused by global fallout in th e 1960's and the Chernobyl fallout in the area. Only in two water samp les taken close to the former site of the wreck slightly elevated Pu-2 39,Pu-240 concentrations were detected. The great water volume of Lake Ladoga and effective water exchange at the wreck site may explain the very low levels of radioactive wastes detected in the aquatic environ ment.