306 TRANS URANIC ELEMENTS IN THE ENVIRONMENT 



100 



LLI 



_l 

 03 

 D 

 _I 

 O 



00 



I- 



< 



10 



0.1 



0.03 



239pjj_DJPA (144 ^g/g) 



A 239p^_[3TPA (1 ^g/g) 



O 238pu_DTPA (0.6 Mg/g) 



H 238pu_pHrate (0.6 mq/q) 



□ 239p^J_p|trate (144 Mg/g) 



20 40 60 80 



INCUBATION TIME, days 



100 



120 



Fig. 2 Solubility of plutonium with time after addition to soil as the nitrate and the 

 DTPA complex. [From Wildung and Garland ( 1975).] 



the largely insoluble hydrated oxide. It is clear that organic ligands have a pronounced 

 effect on plutonium solubility in soil. The rate of decrease in the solubility of each 

 isotope added as the nitrate was similar. However, in contrast to the slightly lower 

 solubility of the ^^^Pu-DTPA compared with the ^^'^Pu-DTPA. ^^^Pu added as the 

 nitrate was a consistent factor of 2 to 3 times as soluble as ^■'^Pu initially added as the 

 nitrate. This difference probably resulted from the formation of larger hydrated oxide 

 particles at the higher plutonium concentration (^^^Pu), but it may also have reflected 

 the presence of soil components, such as organic ligands, which stabilized plutonium in 

 solution but were present in limited concentrations and became important only at lower 

 plutonium concentrations. 



The water solubility of ^■'^Pu, when incorporated in relatively large plutonium oxide 

 particles (>1 /jm), would be expected to be greater than the solubility of '^^^Pu oxide 

 particles of similar size as a result of crystal damage and radiolysis arising from the greater 

 specific activity of the ^^^Pu (an approximate factor of 270). However, the behavior of 

 the two isotopes in soil on solubilization of the oxide might be expected to follow a 

 course similar to that exhibited by the nitrates (Fig. 2). 



Equilibrium solubility after 6 days of incubation (Garland. Wildung, and Routson, 

 1976) of plutonium, added as Pu(N03)4, in soils of different properties occurred after 

 approximately 20 hr (Fig. 3). The quantities of plutonium soluble at equilibrium in water 



