UPTAKE AND DISTRIBUTION OF Pu, Am, Cm, AND Np 365 



As illustrated in Fig. 1 , the relative uptake of either plutonium isotope was not 

 statistically different (a = 0.01) for the two soil concentrations used (approximately 0.03 

 and 0.3 juCi/g soil). Soil concentration did not appear to have any effect on the uptake of 

 ■^"^'Am or ^'^'*Cm, which were also added at the same two levels. Also, as shown in 

 Fig. 1, the relative uptake of ^^^Pu was not statistically different from ^•'^Pu (a = 0.01). 



Since soil concentration did not appear to affect phytoavailability or differences in 

 ^^^Pu vs. ^^^Pu, the relative plant-uptake data were combined for each element so that 

 further statistical comparisons could be made. Most interesting was a comparison of the 

 uptake values for the four different elements (Fig. 2). The relative uptake of ^^^Np 

 ranged from 2,200 to 45,000 times as great as that of plutonium, depending on the plant 

 part compared. Neptunium-237 was accumulated 35,000 and 45,000 times as great as 

 plutonium in barley and pea seeds, respectively, and averaged a factor of 4,700 more in 

 the remaining plant tissues. There was no significant difference (a = 0.01) in the uptakes 

 of ^'^^ Am and ^^'^Cm, which were both 10 to 20 times as great as plutonium. 



The relative uptakes of the transuranics by the four different plant species were 

 noticeably different. Generally, the legumes (peas and alfalfa) accumulated approxi- 

 mately 10 times as much as the grasses (cheatgrass and barley). Concentrations of 

 transuranics in various plant tissues examined were also different. The values were 

 considerably lower in the seeds than in other aboveground plant parts. The concentra- 

 tions in barley seed were lower by a factor of 30 to 50 than those in the entire combined 

 plant parts for plutonium, americium, and curium and about a factor of 5 lower for 

 neptunium. For peas the ratio of concentration in the seeds compared to the rest of the 

 plant was 230, 150, 70, and 30 for plutonium, americium, curium, and neptunium, 

 respectively. 



Discussion 



Our results showed soil concentration to have no observable effect on the uptake of 

 either plutonium isotope. This differs somewhat from results reported by Wildung and 

 Garland (1974). They observed an increase in the relative uptake of plutonium as the soil 

 concentration decreased. However, they noted little effect on uptake at soil concentra- 

 tions of 0.5 /iCi/g or less, which exceeded the maximum level used in this study (0.3 

 A/Ci/g). 



Plutonium-238 has been reported to be more available than ^^^Pu in a grassland 

 ecosystem (Little, 1976) and in the southeastern United States (McLendon et al., 1976). 

 As noted previously, this difference was not observed in this plant uptake study. 



The results of this study showed that the relative plant uptake of the four different 

 transuranium elements was Np > Cm ^ Am > Pu. These trends are consistent with data 

 reported by Price (1972) on the uptake of "^Pu, ^^'Am, ^^"^Cm, and ^^^Np by 

 cheatgrass and tumbleweeds (Salsola kali). The same differences in the relative uptake of 

 2"^^ Am and "^Pu have been reported by Cline (1968) and Schulz et al. (1976). A 

 significant aspect of this trend is that, if the CR of plutonium is approximately 0.0001 as 

 summarized by Price (1973) and ^^''Np was taken up into the entire plant some 3900 

 times as great as plutonium, one can infer that the CR value for neptunium would be 

 about 0.4; i.e., under usual agronomic conditions, the concentration of vegetation 

 growing on soil contaminated with ^^^Np in the upper 15 to 20 cm would be equal to 

 approximately one-half the soil concentration on a dry-weight basis. Likewise, the CR 

 values for ^'^^ Am and ^'^'^Cm would be expected to be about 0.002 since the relative 



