ASSOCIATIONS OF Pu AND OTHER ACTINIDES IN SOILS 159 



TABLE 4 Concentration Ratios for U, Th, and Pu 

 of Plants Grown on Contaminated Soil* 



*Values are ± standard errors of replicate analysis; for single samples, U and Th 

 analyses are typically ±10%; Pu analysis is ±50% (counting error). Data set represents 

 plants cleaned by washing. Edible tissues were peeled or cleaned as if being prepared 

 for cooking; several analyses (not included) showed high and similar CR's for three 

 elements, indicating soil contamination; in no case, however, was Th and/or Pu 

 significantly higher than LI. 



tMean ± standard deviation. 



found in the aqueous phase after uhracentrifugation (9000 x g for 1 hr). This 

 corresponds to a desorption Kj of 5 X 10^ ml/g. 



Extraction by Growing Plants. Like chemical extractants, plants grown on this 

 floodplain soil reveal that U is extracted more readily than Pu or Th. Table 4 illustrates 

 this for both whole plants and reproductive and storage organs. Both Th and Pu appear in 

 vegetative tissue in similar concentrations relative to 871/ nitric acid extractable soil values. 

 This observation suggests that the Pu is probably present in the III or IV oxidation state 

 rather than in the V or VI. The similarity to Th suggests that the IV state dominates. 



Conclusions on Chemical Associations of Pu in an Alluvial Soil 



Tamura (1976) concluded that the Pu in the tloodplain soil was most likely present in 

 monomer rather than polymer form. This conclusion was reached because the Pu was 

 highly extractable in citrate and leached in cold 8Af HNO3. The extraction of the Pu by 

 strong carbonate solution and the extractability with diethylenetriaminepentaacetic acid 

 also suggest that monomeric forms are present as do the isotopic-exchange results. 



The Pu associated with this soil appears to represent surface-sorbed associations, with 

 humic materials representing one, but not the only, site. About 7 to 11% of the Pu is 



