UPTAKE OF TRANSURANIC NUCLIDES FROM SOIL BY PLANTS 357 



TABLE 7 (Continued) 



Plant species 



Range of CR 



Conditions and comments 



Reference 



Pot culture 



Cheatgrass 

 Tumbleweed 



10 

 10 



Neptunium 



Cheatgrass and tumbleweed 

 grown in 1 kg of 

 soil spiked with 

 50nCi/gof ^"'Np 

 as NpCNOj)^ ; organics 

 tended to enhance 

 uptake. 



Price, 1973 



^_ _ radioactivity/g (plant ash) 



radioactivity/g (soil) 

 t Background level of activity. 



Summary 



Experiments on plant uptake of the transuranic nuclides conducted under controlled 

 environmental conditions using spiked soils from the Savannah River Plant and 

 contaminated soils from the Nevada Test Site revealed the following: 



1. In general, the uptake of '■*' Am by crop plants (Baliia grass and rice) grown on 

 soils from the humid southeastern United States was influenced by soil amendments and 

 indigenous soil factors. Lime generally immobilized ^"^^Am in the soil and decreased 

 uptake by Baliia grass. The DTPA chelate somewhat enlianced the uptake by other crops 

 tested in these acidic soils, but its greatest effect occurred where DTPA was supplied in 

 Hmed soils. 



The addition to soil of up to 5.0% OM appeared to demote ^^^ Am uptake in Bahia 

 grass, but its effect was not so great as that of lime alone. This was possibly caused by 

 temporary immobilization of ^"^'Am in microbial bio mass, by an increase in cation- 

 exchange capacity, or production of organic ligands from the OM. 



The addition of ^ "* ^ Am to soil resulted in almost no translocation of this radionuclide 

 to the rice grain. However, when ^^'Am was introduced in a chelated form to the 

 ponded water, it appeared that there was relatively more absorption and translocation to 

 the grain. 



2. Crop plants (barley, alfalfa, and soybeans) grown on Nevada Test Site soils had an 

 average CR of 10^"^ for plutonium in the vegetative parts. Americium appeared more 

 available than plutonium; the average americium/plutonium ratio was about 4 for barley, 

 10 for alfalfa, and 22 for soybeans. 



Of the various soil amendments (nitrogen, sulfur, OM, and DTPA) used, only DTPA 

 markedly and consistently increased both plutonium and americium uptake by plants; the 

 increase with barley and soybeans was usually more than one order of magnitude but 

 only a factor of 2 with alfalfa. 



Americium appeared to be more mobile for transport (70% greater) than plutonium 

 from shoots to fruits in soybeans. Concentrations of both plutonium and americium in 

 shoots were liighly correlated compared to those in fruits. The chelator DTPA did not 

 differentially influence the transport of plutonium and americium from shoots to fruits. 



