>48 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



ATMOSPHERIC 



ENVIRONMENTAL 

 CONDITIONS 



PLANT 

 PROPERTIES 



SOIL 

 PROCESSES 



SOIL 

 PROPERTIES 



SOURCE 



Fig. 1 Schematic diagram of various factors influencing the bioavailability of the 

 transuranic nuclides in the soil-plant system. 



Discussion 



Several factors influence the availability of the transuranic nuclides to plants. A 

 generalized outline is shown in Fig. 1. Plant uptake is influenced by soil pH, Eh 

 (oxidation state), cation exchange capacity, texture (particularly percent clay), fertilizers 

 and other amendments, and soil OM. 



Lime significantly suppressed ■^'^'Am uptake by crops grown in southeastern soils 

 owing either to a lower solubility of ^'*' Am at higher pH, an increased cation exchange 

 capacity caused by liming (Fiskell, 1970; Helyar and Anderson, 1974), or to 

 calcium— magnesium and ^'*' Am antagonism. The first two processes could have caused 

 high Kd* values. The latter could have resulted in Ca^^ and Mg^"" ions suppressing the 

 uptake of ^'^^ Am^'' ions. Chelates have been known to make insoluble cations available 

 to plants. Such chelates increase the diffusion and mass tlow of cations to roots by 

 replenishing those taken up by the plants. It has been shown that chelates, including 

 DTPA, decreased the Kd values of plutonium; i.e., less plutonium was retained by the soil 

 (Relyea and Brown, 1978). Wallace (1972a; 1972b) observed that ^^'Am-DTPA was 

 most stable at about pH 7.7, where plant uptake was greatest. 



*Kd (distribution coefficient) = 



concentrution ot" ^ "' Am/g (soil) 

 concentration of ^ " ' Am/ml (solution) 



