Radiochemical contamination of bottom sediments of some natural and artificial lakes of Middle East Poland

An investigation of the presence of some radioactive isotopes in the bottom sediments of two lakes, Piaseczno and Masluchowskie (Middle East of Poland) has been performed. Similar measurements were done at the Zalew Zemborzycki artificial water reservoir, filled up few years after the most intensive period of atmospheric nuclear explosions. It was estimated, that the concentration of radionuclides, especially of artificial origin was much greater in natural lakes than in examined artificial one. That testifies for an accumulation of radioactive substances on the bottom of the water tanks. ?he confirmation of this thesis may be the fact, that 85% of Cs-137 detected in Zalew Zemborzycki comes from Chernobyl fallout while in natural lakes this isotope amounts only to 56-60%. Other isotopes, such as Pb-210, Ra-226 and Ra-224 were detected in significant amounts. The radioactivity of Pu-239,Pu-240 isotopes reaches 2.2-2.6 Bq/kg for the lakes and 0.7 for Zalew Zemborzycki. The Pu-238 to Pu-239,Pu-240 ratio suggests, that detected plutonium comes from world fallout.