392 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



TABLE 3 Comparison of Total Plutonium Contents of 



Vegetative Materials from Crops Grown on the South 



Field and in a Glasshouse at SRP* 



Plutonium contents, fCi/g 



(dry weight) 

 Vegetative contaniuiation,f 



External 

 tamin: 

 material South Field Glasshouse % 



Wheat straw 88.0 3.0 97 

 Soybeans, 



whole plants 52.2 5.6 89 



Corn leaves t 33.5 1.1 97 



*The soils used in the glasshouse were from the top layer of the 

 South Field. 



fCalculated from the equation: [(field content - glasshouse 

 content)/field content] x 100. 



t Fiberglass mats were placed on top of the soil in the corn pots in 

 the glasshouse to prevent plant contamination by resuspension. 



of particles from the soil surface to the air. (2) The floodplain soil moisture was 

 maintained continuously near field capacity owing to capillary conductivity from a 

 shallow water table. The cohesive force of a thin film of water surrounding the soil 

 prevented particles from becoming airborne. (3) Owing to protection provided by the 

 surrounding forest, the floodplain site was not exposed to wind, and particles did not 

 become airborne by aeoUan mechanisms. (4) The plastic mulch used for weed control 

 eliminated the need to cultivate; therefore airborne dust particles were not created by 

 mechanical operations. (5) The surrounding floodplain soil was covered by moist 

 decomposing litter and by a dense cover of herbaceous understory vegetation. The 

 boundary layer afforded by such conditions prevented soil-borne plutonium from 

 becoming airborne. These five factors reduced the likelihood that soil-borne plutonium 

 would become airborne and deposited on vegetation; indeed plutonium was not 

 detectable in 346-m^ air samples collected next to the test plot at 1-mheiglit. Attempts 

 to measure plutonium in air were unsuccessful because of liinited sample size over a 6- to 

 8-hr collection period, but the air concentration would be less than 0.3 X 10~^ pCi/m^ 

 on the basis of a minimum detectable level of 0.1 pCi per sample (Dahlman and McLeod, 

 1977). 



Concentrations of 239,240p^ -j^ foliage of bush beans, soybeans, tomatoes, lettuce, 

 radishes, and millet ranged from 0.01 to 0.33 pCi/g (dry weiglit) (Table 4). Concentra- 

 tions of plutonium in the fruit of these species were lower by at least an order of 

 magnitude tlian those in the foliage. Liinited observations on root crops (carrots, 

 potatoes, and beets) indicated that the plutonium concentrations of the edible portion 

 were similar to those of the foliage. 



The plutonium concentrations of foliage and fruit appeared to represent plutonium 

 assimilated by the root pathway because surface contamination was removed before 

 radiochemical analysis. Samples of bush beans, soybeans, and tomatoes were washed and 

 rinsed in a sonic bath. This procedure effectively removed surface-bound plutonium 



