The distribution of radionuclides between the dissolved and particulate phases of a contaminated freshwater stream

Streamwater concentrations of the radionuclides 137Cs, 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 (<0.2 μm), whereas 137Cs and 241Am were distributed equally between the two phases. 137Cs 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. (author)