Effects of dissolved organic carbon on the adsorption properties of plutonium in natural waters

The colloidal organic carbon (COC) found in natural aquatic systems is shown to profoundly inhibit the adsorption of reduced plutonium (oxidation states III or IV) to suspended sediment particles. This effect can be described by a system of equilibria in which COC competes with the solid particles for Pu(III,IV). Pu(III,IV) forms both 1:1 and 1:2 complexes with COC. Low pH conditions suppress the formation of 1:2 complexes but not 1:1 complexes. When corrected for the influence of COC, the intrinsic adsorption coefficient (K/sub D/0) for plutonium(III,IV) falls in the range (0.5-3) x 106 for all the surface waters examined. On a weight basis, the COC and natural sediments have approximately equal affinities for plutonium