Physicochemical Associations of Plutonium 

 and Other Actinides in Soils 



E. A. BONDIETTI and T. TAMURA 



Soil physicochemical behavior of plutomum and other actinides is discussed with primary 

 emphasis on the behavior ofplutonium in acnial contaminated soil and the importance of 

 actinide speciation in interpreting laboratory results. The behavior of actinides in soil is 

 strongly influenced by physical form and/or oxidation state. The chemistry ofplutonium, 

 americium, curium, and neptunium is reviewed, particularly with respect to the oxidation 

 states likely to control their behavior in most soils. Several aspects of sorption to soils are 

 discussed, particularly those for plutonium. Tlie comparative behavior of plutoniwn, 

 thorium, and uranium in soil is also illustrated to provide a perspective for evaluating 

 long-term environmental behavior. The relative hazard associated with plutonium- 

 contaminated soil is evaluated and the importance of both physicochemical form of the 

 plutonium and the soil particle-size association is emphasized. 



The exposure of internal organs to ionizing radiation is tiie major potential hazard 

 associated with the production and release of actinide alpha emitters to the environment. 

 Two predominant pathways of exposure from this environmental contamination are 

 inhalation and ingestion. 



Inhalation of discrete radioactive particles (i.e.. PUO2) and carriers (i.e., contaminated 

 soil particles) can result in exposure of the lung and of other body organs following 

 transport of particles or ions through the lung to other organs. Ingestion of radionuclides 

 present in biologically assimilated fomis or as surface contamination also serves as a 

 source of possible exposure to critical organs. 



The relative importance of inhalation and ingestion as pathways for human exposure 

 depends on many environmental parameters exclusive of the physicochemical associations 

 of the radioelement in soils. However, the physicochemical properties of the radioelement 

 in soils strongly influence the pathway and magnitude of transport. This is illustrated by 

 the ~10^ greater assimilation by plants of plutonium added in monomeric fomi as 

 compared with PuOt microspheres (Adams et al., 1*^75). 



This chapter examines two aspects of the physicochemical associations ofplutonium 

 and other actinides in contaminated soils: (l)the case in which plutonium is 

 monomerically distributed in soil (i.e., the potentially most biologically available form) 

 and (2) the case in which plutonium exists or its origin is traced to a discrete particulate 

 source. However, it is also important to evaluate general principles of actinide— soil 

 interactions. For this purpose we also explore several aspects of sorption behavior to soil 

 colloids. 



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