i9 dominate the solid phase of plutonium and controls the equilibrium between ursequestered species in natural waters. 3.4 Plutonium and Americium Distribution in Soil and Sedimentary tnvironm7*s, Andelman and Rozzell (1968, 1970, 1971) have presented a consider- able body of information concerning the sorption of aqueous plutonium onto silica. In these articles, they find that the relative amount of plutonium sorbed by silica varies with the ionic strength, pH, concentration, and distribution of the sizes of the colloids in solution. Sorption was found to be drastically reduced by the presence of 1072 Mbicarbonate jon in solution. The sorption of Pu (IV) onto silica was found to reach an apparent equilibrium after 12-15 days' sorption. Aging solutions of Pu (IV) for up to five days rrior to sorption resulted in progressively more sorption onto the silica, After five days aging, however, decreased sorption of plutonium occurred. Their results indicated that slow coagulation of the hydrolysis products of Su (IV) yields colloidal species whose size determines their sorbability onto stlica. They conclude that the sorbable species were of two types, and include positively charged ions (which are rapidly sorbed) and low molecular weight ce'loids. two steos. Desorption of plutonium from silica grains was found to proceed in Approximately one-third of the sorbed plutonium was found to be ‘rently bound and desorbed with a half time of 350 days, and two-thirds was released into a water bath of "infinite" volume (at pH 7) within hours. Cuursma and Parsi (1974) measured distribution coefficients between “<tterranean Sea sediments and sea water spiked with Pu (III), Pu (IV), and *- (1) under both oxic and anoxic conditions. They found distribution co- ei clents of about (10° te in each case, with half times for attaining an equili- '* cf from one to four days. This rate is not appreciably different from