342 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



and 5.0% OM rates, respectively. Similarly, although less pronounced than in the Troup 

 soil, plant concentrations in the unlimed Dothan soil were highest at the 0% OM rate 

 (45.2pCi/g) and decreased to 36.9 and 14.5 pCi/g for the 1.25 and 5.0% OM rates, 

 respectively. In both unlimed soils, small differences in ^'''Am concentrations were 

 obtained from the 1.25% OM rate. However, the 5% OM rate decreased the ^"^'Am 

 concentrations in both unlimed soils somewhat substantially. 



The CR values in Table 2 for limed treatments, in general, are 10 times lower than 

 those for the unlimed treatments and, in some cases, as much as two orders of magnitude 

 lower. The effects of OM rate and clipping period on ^"^^ Am availability can also be 

 easily deduced from Table 2 and further elaborate the effects of these treatments on 

 ^^^ Am concentrations. The slight reduction in uptake with OM addition was possibly 

 caused by immobiUzation of ^^ ^ Am in the soil microbial biomass and the fixing capacity 

 of OM for metals. 



The CR values were calculated on the basis of the total soil mass in the pot. These 

 values can also be calculated by using only the amount of soil that was spiked, in which 

 case the present CR values should be multipUed by a constant factor of 0.25. 



Rice Experiment. Results (Table 3) indicate that, in some cases, americium applied in 

 water was detectable in the rice grain. However, these are low radioactivities compared 

 with other plant parts. No radioactivity was detected in the grain when americium was 

 applied to the soil. Americium increased in the following order: unshelled grain < green 



TABLE 3 Influence of Chelate DTPA, Time of Spiking, and 

 Method of Placement on ^ '* ' Am Concentration Ratios for Rice 

 Grown in a Southeastern U.S. Soil Under Flooded Conditions*t 



Unshelled 

 grain/soil 



Green blades/soil 



Old (dead) blades/soil 



Applied to water 



Period 1 



Period 2 



Period 3 

 Applied to soiH 



(1.1 ± 

 (1.0 ± 



0.36) X 

 0.18) X 



10-' 

 10-' 



With DTPAt 



(3.8 ± 1.4) X 10-' 

 (1.3 ±0.18)x 10-' 

 (1.7 ±0.40)x 10-' 

 (0.2 ± 0.85) X 10-' 



(2.7 ± 1.4) x 10-' 

 (6.5 ± 2.5) x 10-' 

 (1.6 ± 0.54) X 10° 

 (2.8 ± 0.27) X 10- 



Applied to water 



Period 1 



Period 2 



Period 3 

 Applied to soiH 



(6.8 ± 2.3) X 10" 



Without DTPA$ 



(5.3 ±2.8)x 10-' 

 (5.7 ± 1.3) X 10-' 

 (1.0 ± 0.80) X 10-' 

 (2.6 ± 0.80) X 10-' 



(4.6+ 1.3) X 10-' 

 (4.8 ± 3.7) X 10-' 

 (4.2 ± 3.4) X 10-' 

 (2.5 ± 0.22) X 10-' 



*Concentrations in plant materials can be calculated from the CR values and the 

 assumed concentrations (400 pCi/g dry soil) of the potted soil. 



t Values are means of five replicates ±1 standard error. 



^Chelated or nonchelated ''"Am (in 50 ml of 100 ppm DTPA as acid or water) was 

 added to the standing water when the rice plants were at booting (period 1), flowering 

 (period 2), and dough (period 3) stages. 



§ Activities were below the detection Umit. 



% Data taken from Table 4. 



