20 TRANS URANIC ELEMENTS IN THE ENVIRONMENT 



Nelson and D. N. Edgington, Argonne National Laboratory, personal communication). A 

 few measurements have been made of the oxidation state of plutonium adsorbed on 

 particulate matter (Nelson and Lovett, 1978). Samples of surface sediment from the 

 Great Lakes and Miami River indicate that plutonium absorbed by sediment particles is 

 predominantly in the (III) and (IV) states. On reequilibration of sediment with water, it 

 has been shown that there is a conversion of Pu(III) + Pu(IV) back to Pu(V) or (VI) 

 (D. M. Nelson, Argonne National Laboratory, personal communication). 



TABLE 8 Values of the Distribution 

 Coefficients (Kp ) and Concentration Ratios 

 (CR) for Phytoplankton for the Actinide and 



Lanthanide Elements in Lake Michigan 



pCi/kg water 



Therefore the concentration of plutonium in many freshwater lakes and streams 

 apparently is controlled by an equilibrium between water and sediment. From the data it 

 is possible to calculate values of Kq for Pu(III) and Pu(IV) and Pu(VI). These values are 

 given in Table 8 and are compared with those for stable-element homologs, such as 

 La(III), Th(IV), and U(VI). As would be expected, results for ^^*Pu from U-pond and 

 ponds and canals in Miamisburg (Table 6) show little or no difference in behavior of the 

 plutonium owing to isotopic composition. 



Finally, leaching experiments with sediments have shown that a major fraction of 

 fallout plutonium can be removed with extractants, such as dilute acids or complexing 

 agents (Alberts, Muller, and Orlandini, 1976). Furthermore, studies of plutonium in 

 natural waters have shown low but measurable concentrations of plutonium in true 

 solution. In Lake Michigan the plutonium concentration was essentially constant over the 

 whole lake (Wahlgren and Nelson, 1975). The measured concentration of 0.5 fCi/liter of 

 239,240pjj corresponds to a chemical concentration of 3xlO"^'^A/, or 20,000 

 atoms/ml. Hence molecular collision theory implies that the formation of polymeric 

 plutonium species in the lake (i.e., many plutonium atoms linked as — Pu— Pu or as 

 — Pu— 0— Pu) is unlikely. Even the possibility of the formation of dimers is vanishingly 

 small. 



Marine Ecosystems. Studies of transuranic elements in marine and estuarine ecosystems 

 have encompassed a wide range of sources: worldwide fallout as a result of the testing of 

 nuclear weapons, lagoons in tropical atolls where many tests were performed, and direct 



