i54 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



Th was 20 times as high as that for Pu(IV) when both elements were equilibrated with 

 montmorillonite clay. No valences were determined, but the concentration of ^^^Pu used 

 undoubtedly resulted in some initial disproportionation. 



This discussion is meant to illustrate that the adsorption of Pu to soils is more 

 complex than the simple distribution of a radioelement between a solid phase and a 

 solution. For Pu the problem of mixed-oxidation-state species is significant. Attempts to 

 delineate the soil/sediment chemistry of Pu must consider that more than one oxidation 

 state may be present in stock solutions or may be formed during the experiment. 

 Attempts to correlate Pu adsorption with soil type may be confounded by the complex 

 interplay between soil components and the stability of various Pu oxidation-state species. 

 Thus Glover, Miner, and Polzer (1976) and Polzer and Miner (1976) observed that the 

 adsorption of Am(III) by various soils was as great as or greater than that of Pu(IV). They 

 also noted that the variability in Am(III) sorption was much less than that in Pu. At the 

 Pu concentrations used (10~^ to \Q~^M), disproportionation may have been the cause 

 of this variability. A small proportion of Pu(V) or Pu(VI) with their correspondingly 

 lower sorption tendencies would provide erroneous sorption values for "Pu(IV)." 



Plutonium at Contaminated Sites 



General 



Contaminated field sites provide the best situations for studies to understand the behavior 

 of plutonium in environmental systems. Full appreciation of the behavior of Pu in these 

 sites requires knowledge of the initial character of the contaminating event(s). From this 

 information conclusions can be drawn regarding Pu behavior up to the time of samphng 

 and potential behavior extrapolated for different source terms. 



Nevada Test Site. One of the largest contaminated areas in the United States is the 

 Nevada Test Site (NTS), which serves as the test area for nuclear detonations. Within the 

 NTS several sites were used for safety shot evaluation; these sites, which have been 

 declassified, contain dispersed plutonium from a series of liigh-explosive detonations 

 simulating an accidental detonation of a subcritical atomic device. The detonation would 

 be expected to produce a wide range of particles. Since plutonium metal is relatively 

 reactive, the oxide form would be expected to be produced (Cunningham, 1954). 

 Although a size distribution as a function of distance from ground zero (GZ) might be 

 expected, this relationship is difficult to establish since considerable cleanup took place 

 after the test. Some indication of decreasing size with increasing distance from GZ has 

 been reported by Tamura (1975). Samples taken from 500 to 6700 ft from GZ showed 

 that at 500 ft the 125- to 50-jum soil-size fraction contained 25% of the activity; at 6700 

 ft this fraction contributed less than 2%. 



The solubility of plutonium oxides decreases with increasing ignition of the oxide 

 (Cunningham, 1954). The plutonium in the safety shot sites was not subjected to fission 

 temperatures but to explosion temperatures. The lower solubility of plutonium at NTS 

 has been reported by Tamura (1976), who subjected contaminated soils from NTS to 8Af 

 nitric acid extraction at room temperatures. Compared with samples from Oak Ridge 

 Nafional Laboratory (ORNL) and Mound Laboratory (ML), the NTS samples were only 

 one-fifth to one-eighth as soluble. 



Rocky Flats. The contamination at the Rocky Flats (RF) plant in Colorado was caused 

 by leaking barrels of Pu-contaminated cutfing oil (Krey and Hardy, 1971). Before 



