340 TRANS URANIC ELEMENTS IN THE ENVIRONMENT 



Results and Discussion 



Soils from the Humid Southeastern United States 



Current field conditions at tlie SRP do not provide an environment suitable for the study 

 of the incorporation of transuranic elements in plant tissues through root uptake because 

 of a confounding effect from deposition of particles on the foliage following resuspension 

 or stack emission from reprocessing operation. Thus studies were conducted in a 

 glasshouse to evaluate the influence of some common soil amendments on the uptake and 

 translocation of ^"^ * Am by Bahia grass (Paspahmi notatum) and rice (Oryza sativa). Bahia 

 grass is a common pasture crop grown extensively in the southeast. Rice was included 

 because it is one of the most important food crops in the world and is widely distributed 

 throughout the tropical, subtropical, and temperate zones of all continents (Adair, Miller, 

 and Beachell, 1962; Harlan, 1976). 



For brevity, only the CR* values are presented. In studies of this nature, the CR is a 

 convenient method of expressing the availability of an element from the soil and its 

 pattern of translocation to the plant parts. Since the soil '^^ ' Am concentrations are given 

 in the footnotes to the tables of results, the corresponding plant concentrations can be 

 calculated from the CR values. 



Bahia Grass Experiment. The effect of soil type on ^'*'Am uptake in Bahia grass 

 (Table 2) was not so pronounced as that in the bush bean and corn seedlings (Adriano 

 et al., 1977). Nevertheless, the most striking differences in uptake were caused by soil 

 type and lime. On the average, ^^ ' Am concentrations in plant tissues from the unlimed 

 Dothan soil (pH 4.2) were approximately twice as high as those from the unlimed Troup 

 soil (pH 5.0). This wide disparity between these two soils was minimized when both soils 

 were limed. Consequently liming of both soUs (pH 7.1 for Dothan soil and pH 6.6 for 

 Troup soil) significantly (p < 0.01) reduced ^'*' Am availability to Baliia grass. Across the 

 OM treatments, the plant tissues from unlimed Troup soil had 12.0pCi/g (dry-weight 

 basis), compared to only 1.0 pCi/g from limed soil, on the average. On the average plants 

 from unlimed Dothan soil had 35.3 pCi/g vs. pCi/g (below detection limit) from limed 

 Dothan soil. 



The clipping period affected the ■^'*'Am concentration pattern in Bahia grass, 

 particularly in unlimed soils (Table 2). In unlimed Dothan soil, the concentration 

 progressively declined with clipping time. The peak occurred on the first clipping (50th 

 day of growth) and the minimum occurred on the last cHpping (130th day of growth), 

 irrespective of OM rate. The concentrations in the first clipping were always significantly 

 higher than those from subsequent clippings. In unlimed Troup soil, the concentrations 

 generally peaked during the second clipping, although at the 1.25% OM rate they were 

 not significantly different from the other clippings. No meaningful pattern can be 

 deduced when either soil was limed, and, in some cases, hming caused plant ■^^'Am 

 concentrations to be equal to background level. 



The addition of OM affected ^^' Am plant concentrations to some extent. Plants in 

 unlimed Troup soil in wliich no OM had been added had the higliest concentrations. The 

 mean concentrations for all three chppings were 23.2, 9.5, and 5.6 pCi/g for 0.0, 1.25, 



^^ ^ radioactivity/g (plant tissue) 



*CR (concentration ratio) = —. — ; r- 



radioactivity/g (soil) 



