Evidence of 99Tc in Ural river sediments

Sediments collected from the Techa River at Nadirov Bridge were analysed for 99Tc. The maximum concentration was found at a depth of 14–18 cm. This layer was sedimented around 1950, i.e. at a time when the maximum releases of waterborne radionuclides occurred to the river from the MAYAK plutonium production plant in the Urals. The vertical distribution of 99Tc in sediments followed that of 137Cs, and the mean ratio between 99Tc and 137Cs in the sediments at the time of discharge was 0.41 × 10−3. Laboratory experiments showed that 99Tc under anoxic conditions, e.g. when organic material is decomposing, will be retained by sediments.