398 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



this atypical distribution was attributed to variable deposition of sediments over an initial 

 plutonium deposit rather than to plutonium cycling by leaching processes. 



Plutonium was not distributed uniformly between the silt and clay fractions of the 

 soil. Although 72% of the soil was silt, this fraction contained 60% of the plutonium, 

 whereas the 24% clay contained 40% of the plutonium. In this case the affinity of 

 plutonium for colloids, the clay fraction, may be responsible for plutonium enrichment in 

 clay. 



The results of various attempts to extract plutonium from the soil indicated that 

 more than 95% of the plutonium can be removed by hot 8M HNO3 ' milder HNO3 

 treatments removed smaller amounts of plutonium (Auerbach, 1975). These treatments 

 indicated that plutonium recovery from the floodplain soil did not require rigorous 

 treatment, such as HNO3— HF or carbonate fusion. Milder treatment with O.IM citric acid 

 removed 16 to 24% of the soil plutonium. Contact with a CHELEX resin removed 11%. 

 Humic acid solubilized by the presence of Na from a sodium-saturated CHELEX resin 

 contained 5% of the total plutonium after 4 weeks. The carbonate treatment removed 

 54% of the soil plutonium. Further analysis of the carbonate extract showed that at least 

 90% of the plutonium behaved as Pu(lV) (Bondietti and Sweeton, 1977; Bondietti, 

 Reynolds, and Shanks, 1976). 



General Discussion 



The various CR values for the agricultural vegetation at SRP are generally higher than 

 those obtained for indoor-grown plants. Schulz et al. (1976a; 1976b) obtained values for 

 barley on the order of 10~^ for vegetative material; grain was a factor of 20 to 100 

 lower. In wheat grain they obtained CR values ranging from 1.1 X 10~^ to 3.8 x 10~^. 

 Lipton and Goldin (1976) obtained CR values for pea plants on the order of 10"'*. 

 Natural plant species not subject to contamination from atmospheric releases or 

 resuspension were observed to have CR values on the order of 10~^ to 10"'' (Francis, 

 1973; Hanson, 1975), much lower tlian values obtained at SRP. However, in arid, windy 

 environments, dust and soil particles can become airborne and can be deposited and 

 retained in leaves, causing plutonium CR values to approach 10° (Romney et al., 1975). 

 Earher studies at SRP indicated that deposition on the surfaces of tlie leaves and stems 

 was the principal mechanism of plutonium contamination of natural vegetation (Adriano 

 and Pinder, 1977; McLendon et al., 1976). The plutonium concentrations of all 

 ecosystem components decreased as the distance from reprocessing plants increased 

 (McLendon, 1975; McLendon et al., 1976). Thus considerable external contamination of 

 plants from atmospheric releases and resuspension is a complicating factor in field data 

 interpretation. 



The CR values from the glasshouse studies at SRP are on the order of 10"'* to 10~^ 

 for the vegetative materials and, in general, are similar or sUghtly higher than the values 

 obtained by Schulz et al. (1976a; 1976b) and Lipton and Goldin (1976). Our glasshouse 

 results suggest that ^^^Pu is more available than ^'^^Pu, as indicated by relatively higher 



Pu percentage values in the vegetative samples than in the soil. The percent Pu 

 ranged from 33 ± 6 for soybeans to 55 ± 1 1 for corn. The soils used for growing these 

 crops had only 21% ^^^Pu. This difference in availability between the two radionuclides 

 has been observed also at the Trinity Site ecosystem, where changing ratios of 



