SYNTHESIS OF THE RESEARCH LITERATURE 9 



the sediments. This loss was interpreted as a direct return to the water column rather than 

 physical redistribution of sediments. 



These studies indicate that sediments will be continually reworked by physical and 

 biological processes. New plutonium will be continually added to the Great Lakes and 

 coastal waters by wind erosion and transport of sediments down river. Because of the 

 dynamics of the system, the inventory and distribution of plutonium will continue to 

 change (Edgington and Robbins, 1975). 



Solubility and Chemistry 



Theoretical Considerations 



The transuranic elements, starting with neptunium (atomic number 93), are a subset of 

 the actinide series. This series is similar to the lanthanide series in that electrons are 

 added successively to the 5f orbitals in a manner similar to the filling of the 4f orbitals. 

 However, the shielding of the 5f electrons by outer electrons is less effective than that of 

 4f electrons; thus the chemical properties of the actinides are more complicated than 

 those of the lanthanides. Although the latter exist primarily in the III oxidation state and 

 exhibit ionic bonding, the actinides (through plutonium) can exist in multiple oxidation 



TABLE 4 Comparison of Oxidation States for the 

 Actinide Elements in Solution* 



f = 



7 



*The solid lines bound the most likely oxidation states 

 in aqueous solution. 



States (Table 4). Because of their extreme reactivity, the II and VII oxidation states are 

 not likely to be encountered in the environment. The oxidation— reduction behavior of 

 the triad U-Np— Pu is complicated, and multiple oxidation states can coexist in solution. 

 Actinides with atomic numbers exceeding that of plutonium behave similarly to the 

 lanthanides. 



The complex interactions between the various oxidation states of neptunium and 

 plutonium are partly governed by their total concentration in solution. When concentra- 

 tions are sufficient, disproportionation reactions between oxidation states are common. 

 However, such concentrations are unlikely to be found in the envirormient, and the stable 

 oxidation states will be a function of the chemical environment, e.g., the presence of 



