THE DISTRIBUTION OF RADIONUCLIDES BETWEEN THE DISSOLVED AND PARTICULATE PHASES OF A CONTAMINATED FRESH-WATER STREAM

Streamwater concentrations of the radionuclides Cs-137, 241Am and 239,240Pu from a contaminated freshwater stream showed significant relationships between total concentration and flow rate. When total concentrations were divided into their dissolved and particulate components 239,240Pu was shown to exist mainly (>80%) in the solute phase (<0.2mum), whereas Cs-137 and 241Am were distributed equally between the two phases. Cs-137 was most likely present either as the dissolved ion or as the specifically adsorbed ion on particulate sediments. Particle-associated 241Am and the small particulate component of 239,240Pu, were believed to be bound to sediment surface coatings, such as organic or oxide/hydroxides, rather than the truly adsorbed ion. Solute phase 239,240Pu was most likely associated with colloidal organic carbon species (such as humic or fulvic acids). This was also apparent, but to a lesser extent, for 241Am. Distribution coefficients were determined for a number of discrete sites and environmental conditions. The response of the stream to removal of its source of radioactivity (via a re-routing scheme) was both significant and rapid.