The Radioactivity of Sediments in Danube Reservoirs in Austria before and after the Chernobyl Accident

Abstract

A major part of pollutants transported by rivers are normally adsorbed to the fine-grained particles in suspension. The coupling between pollutants and particles leads to an enrichment of radionuclides in sediments that settle in river reservoirs and lakes. The concentration of radionuclides is a function of grain-size distribution and of the mineralogical composition. In a survey, sediment samples from the lock area of each Danube reservoir were collected during the spring of 1985. Three grain-size fractions (<20 µm, 20–63 µm, 63–250 µm) were analyzed. On an average the estimated concentration of radionuclides is about 600 Bq/kg for K-40, 50 Bq/kg for Ra-226, and 40 Bq/kg for Th-232. A 17 m depth borehole has allowed us to trace the history of radionu-clide distribution for the past 25 years since the culmination and the end of atomic testing in the atmosphere, which coincides with the damming of the river Danube at Aschach. The content of Cs-137 in freshly deposited Danube sediments rose by two orders of magnitude following the accident at Chernobyl (i.e. up to 3000 Bq/kg).