PHYSICOCHEMICAL CHARACTERISTICS OF RADIONUCLIDES ASSOCIATED WITH SEDIMENT FROM A CONTAMINATED FRESH-WATER STREAM

The relationships between concentrations of Am-241, Cs-132 and Pu-239, Pu-240 and sediment particle size and geochemical species were examine d for sediments taken from a freshwater stream contaminated by radioac tive effluent from a low-level waste disposal site. Both Cs-132 and gr oss alpha concentrations were strongly correlated with the silt and cl ay content of the sediment, radionuclide concentrations following the order: clay>silt>sand. Positive correlations with organic content were also observed for both Cs-137 and gross alpha activity. These relatio nships, together with erosional and depositional characteristics obtai ned from streamflow data, largely explained the spatial variation in r adionuclide concentrations in streambed sediments. Sequential extracti on experiments showed that Cs-137 was mostly ''irreversibly'' bound to sediment particles, principally illitic clays, whereas Am-241 and Pu- 239,Pu-240 were associated primarily with organic and oxy-hydroxy spec ies within the sediments.