388 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



Results and Discussion 



Field Crops at SRP 



Wheat. Data for wheat are summarized in Table 1. The results for the South and North 

 fields are presented separately because of the differences in proximity to the stack and 

 hence the possibly different deposition patterns. There appears to be no significant 

 change in the plutonium concentrations of wheat foliage with time on either the South or 

 the North Field. The plutonium content of foliage or straw for both fields averaged 

 4 X 10"^ pCi/g(dry weight). 



The isotopic composition of the foliage, as indicated by the a % ^^^Pu, changed with 

 time (Table 1). In March the wheat plants were short, and the foliage was not yet dense. 

 At this stage contamination of the foliage appeared to originate primarily from the soil, as 

 in rain splash or resuspendible matter. As the plants grew taller and their foliage became 

 denser, they were able to intercept fallout particles from the stack more efficiently. Also, 

 the dense foliage minimized rainfall energy on impact with the ground. The foUage had 

 much higher ^'^^Pu values in April and June than in March. This discrepancy indicated 

 that contamination originated primarily from fallout particles from the emission stack 

 because the ^^^Pu values were closer to those of the deposifion particles than to those of 

 the soil samples (Dahlman and McLeod, 1977). The plutonium concentration of straw 

 was approximately 300 times greater than that of the laboratory-thrashed grain and 40 

 times greater than that of the field-combined grain. That the plutonium values for the 

 grain were lower than those for the straw indicates that the grain was possibly shielded 

 from atmospheric deposition. The plutonium concentrations in foliage, straw, and grain 

 samples were slightly higher in the South Field. 



The straw from the off-plant control site had only (8 ± 2) x lO"'* pCi/g (data not 

 shown), about two orders of magnitude lower than SRP field samples. The thrashed grain 

 from the control site, however, had the same plutonium contents as the SRP thrashed 

 samples. However, the high ^^*Pu percentage of 62 ± 15 for thrashed grain from the 

 control site, which is disparate from the straw value, should be noted. This liigh value 

 was apparently caused by contamination from thrashing of the SRP samples since all 

 tlirashed samples had similar plutonium values. 



The concentration ratios (CR) for the June straw were 5 X 10"^ and 1 X 10"^' for 

 the South and North fields, respectively. Similar values (1 X 10~') were obtained for 

 samples from the control site. The CR for the grain collected from the combine averaged 

 2 X 10~^ compared with an average of 2 X lO"""* for the thrashed grain from the two 

 fields. 



In Table 2 plutonium contents of field- and glasshouse-grown wheat plants are 

 compared. The glasshouse-grown plants had total plutonium contents one order of 

 magnitude lower than the plants from the South Field. The combined grain from the 

 fields was sifted with a soil screen to evaluate the effects of removing extraneous matter 

 on the plutonium content. Data from Tables 1 and 2 for the unsifted grain harvested with 

 a combine are remarkably similar. The sifted combined grain had a factor of 2 less total 

 plutonium content than the unsifted grain, which indicates that the extraneous matter 

 had higher plutonium contents than the grain. The extraneous matter included unshelled 

 grain and chopped straw. 



