SYNTHESIS OF THE RESEARCH LITERATURE 29 



TABLE 1 2 Distribution Coefficients (Kd ) for Soil 



Sorption and Relative Plant Uptake of the 



Transuranic Elements 



Relative 

 Element Log Kj)* uptakef 



*Plutonium (Prout, 195 8); americium and neptunium 

 (Routson, Jansen, and Robinson, 1977); curium (Routson, 

 1978, personal communication). 



t^Ci/g barley per mCi/container (~0.1 mCi/container); 

 transuranic element may not have been uniformly 

 distributed in container (Schreckhise and Cline, this 

 volume). 



Plutonium is probably transported across biological membranes in the Pu(IV) state, 

 particularly in plant roots (Fig. 4). Plutonium(IV) has been identified in the plant xylem 

 of plants grown in a solution containing predominantly Pu(VI) (Delaney and Francis, 

 1978). 



Once in the root plutonium is probably translocated downward in the root and 

 upward in the xylem stream to shoot tissues as Pu(IV). Simple organic acids typical of 

 microbial and plant metabolites quantitatively reduce Pu(VI) to Pu(IV) (Wildung et al., 

 1977). Plutonium(IV) dominates in the plant xylem regardless of the oxidation state 

 supplied in nutrient solution (Delaney and Francis, 1978). The low solubility of Pu(IV) 

 limits translocation in plants unless complexed, and several anionic and cationic 

 complexes of plutonium have been identified in the xylem stream of plants supphed 

 Pu(IV) and Pu(VI) (Wildung et al, 1977). During growth a fraction of tlie plutonium is 

 lost from the root with other inorganic and organic exudates and by decomposition of 

 slouglied cells (Fig. 4). The plutonium associated with this material in the rhizosphere 

 may be subject torecychng into the plant, subsequent modification, leaching, and 

 diffusion. 



Translocation in plants can also serve as a primary factor governing entrance of 

 transuranic nuclides into foodstuffs. Plutonium was mobile in barley and soybeans but 

 was not unifomily distributed in the plant (Garland et al., 1974). In general, 

 concentrations of plutonium in the leaves of soybeans were 5 to 10 times as high as those 

 in stems. The lowest plutonium concentrations were observed in barley and soybean 

 seeds, which minimized the amount of plutonium ingested with these edible tissues. 



Animal Uptake. The gut absorption of plutonium by mammals requires the presence of 

 soluble forms, and solubility is governed by chemical reactions similar to those previously 

 discussed (hydrolysis and complexation). When large amounts of plutonium (>1 mg) are 

 introduced into the gut as Pu(VI) in the absence of foodstuffs (starved animals) and in 

 the presence of large excesses of a holding oxidant, Pu(VI) is absorbed in significant 

 quantities (Weeks et al., 1956). In Chicago plutonium is present largely as Pu(VI) in 

 chlorinated drinking water (Larsen and Oldham, 1978). However, the reducing potential 

 in the gut seems to be sufficient to reduce very low concentrations of Pu(VI) to Pu(lV), 

 which would limit uptake in the absence of the holding oxidant. This conversion would 



