328 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



For an aid in distinguishing soil sorption and plant root discrimination and for the 

 evaluation of the role of complexes in the plant uptake of plutonium, hydroponically 

 grown soybeans (Glycine max) were placed in micromolar level ^•^^Pu— DTPA solutions 

 and permitted to accumulate plutonium for up to 48 hr (T. R. Garland, D. A. Cataldo, 

 and R. E. Wildung, unpublished). Concentration ratios (microcuries per gram of plant per 

 microcuries per milliliter of nutrient solution) for shoot tissues were found to be 

 6x 10"^ and 0.3 after 1 and 24 hr, respectively. This would suggest that plants do 

 possess the potential to effectively accumulate plutonium, with much of the apparent 

 discrimination in soil— plant studies resulting from the effect of soil sorption in reducing 

 the quantity of plutonium available to the plant. In a preliminary effort to determine the 

 form of mobile plutonium in the plant, several plants were decapitated, xylem exudates 

 were collected in 1-ml aliquots at intervals over a 48-hr period, and the solutions were 

 subjected to thin-layer electrophoresis to resolve plutonium-containing components. The 

 electrophoretic mobilities of plutonium in the medium, in the control exudate spiked 

 with Pu(N03)4, and in the exudate collected from decapitated plants grown in 0.1/iM 

 Pu-DTPA solution over a 24-hr period are illustrated in Fig. 10. The plutonium- 

 containing components in the exudate from plants grown in the absence of Pu— DTP A 

 but spiked with Pu(IV) or Pu(Vl) indicated the presence of ligands capable of binding 

 plutonium and forming stable complexes. Similarly, several anionic and cationic 

 plutonium complexes were evident in exudates from plants grown in the presence of 

 Pu— DTPA. A major anionic component with an electrophoretic mobility similar to 

 Pu-DTPA reached maximum concentration in the second aliquot after decapitation and 

 then decreased in concentration with time. The application of several solvent systems to 

 separation subsequently indicated that this component was not the Pu-DTPA complex 

 suppHed in the growth media. These data suggest that plants do possess the ability to 

 effectively accumulate soluble plutonium and transport the plutonium to shoots in one or 

 more organic complexes. Furthermore, from the high concentration ratios for plutonium 

 supplied as Pu— DTPA and the lack of uptake of the complex, it can be concluded that 

 much of the apparent discrimination in soil-plant studies results from the effect of soil 

 sorption in reducing the quantity of soluble plutonium available to the plant. The form of 

 plutonium in alfalfa fed to animals was also characterized, and this provided insight into 

 observed differences in gastrointestinal absorption. 



Animals 



The accepted value for the gastrointestinal transfer ratio of plutonium from food to man 

 is 3 X 10~^ (U. S. Atomic Energy Commission, 1974). This value is based on the 

 gastrointestinal absorption of inorganic Pu(IV) in animals, administered by gavage (Weeks 

 et al., 1956), and the apparent assumption that foodstuffs would contain primarily 

 inorganic Pu(IV). However, the study demonstrated that gavaging Pu(VI) and complexed 

 forms of Pu(IV) resulted in higher absorption rates, e.g., 500 times as great as those for 

 Pu(VI). Until recently it was not possible to test the assumptions because plant tissues 

 with plutonium concentrations sufficient to measure uptake were not available. However, 

 studies with alfalfa indicated that tissues containing up to 400,000 d/min per gram could 

 be obtained under a sequential harvesting regime (T. R. Garland, D. A. Cataldo, and R. E. 

 Wildung, unpublished). These tissues, used in conjunction with a sensitive analytical 

 method (Wessman et al., 1971) for the measurement of plutonium at levels of <1 d/min, 

 allowed preHminary investigations of the availability to animals of plutonium in alfalfa 



