250 TRANS URANIC ELEMENTS IN THE ENVIRONMENT 



is poorly defin-^d or nonuniform (Corley, Robertson, and Brauer, 1976; Krey et al., 

 1976b; Maxfield, 1974; Mishima, 1973; Mishima and Schwendiman, 1973; 1974; Nees 

 and Corley, 1975); hence the data cannot at present be analyzed to reflect resuspension 

 rates or resUspension factors for nonrespirable particles. 



Plutonium Concentration per Gram of Airborne Soil 



Airborne plutonium concentrations were normalized to the soil collected with the 

 airborne plutonium. Plutonium concentrations (in microcuries per gram) were determined 

 as a function of particle diameter as determined with both particle cascade impactors for 

 respirable particle diameters and sieve sizes for nonrespirable particles. Resuspended 

 plutonium is attached to nonrespirable as well as to respirable particles. Hence 

 nonrespirable soil particles may contribute significantly to downwind airborne plutonium 

 concentrations and represent one mechanism for transporting plutonium to surrounding 

 land. 



For Rocky Flats nonrespirable soil collected at 0.3 m above ground level was sieve 

 sized (Sehmel, 1976a) into twelve different size increments. Each size increment was 

 analyzed for '^^^Pu and ^^^Pu. Plutonium concentrations were normalized (micrograms 

 per gram) to the grams of soil collected within each size increment. Results are shown in 

 Fig. 11 for ^^^Pu as a function of particle size at sites A and AB. Plutonium-239 was 

 associated with all particle sizes. The maximum concentration was about 10""* /uCi/g for 

 particle sizes between 10 and 20 jum. For larger particle diameters up to 230 jum, 

 concentrations tended to decrease with an increase in particle diameter. Concentrations at 

 site A were greater than those at site AB. This is expected since site A was closer to the 

 original oil storage area at which plutonium leakage occurred. 



At each site plutonium concentrations (in microcuries per gram) indicate general 

 continuous relationships as a function of particle diameter, which might be used to infer 

 how plutonium is attached to airborne-soil particles. For nonrespirable particle diameter 

 ranges determined from sieve sizes, the data could be approximated by a straight Une 

 inversely proportional to particle diameter. The relationship is complicated by the 

 collection of both contaminated on-site and uncontaminated off-site nonrespirable 

 particles within the cowls. 



For respirable particles, the ^^^Pu microcuries per gram was nearly independent of 

 particle diameter. This independence might suggest that plutonium attachments are 

 volume phenomena for these respirable particles. In contrast, plutonium particle 

 attachment to soil particles is expected to be controlled by available soil particle surface 

 area for nonrespirable particles. Additional data are required to conclude how plutonium 

 particles are attached to airborne particles in both respirable and nonrespirable size 

 ranges. 



Plutonium-238 concentrations on airborne soil are shown in Fig. 12. In this case only 

 nonrespirable particle diameter ranges are shown. There was insufficient ^^^Pu collected 

 in the particle cascade impactor samples to yield positive results in respirable particle 

 diameter ranges. SimUar to ^^^Pu, '^■^^Pu nonrespirable concentrations were greater at 

 site A than at site B and also showed an inverse relationship with particle diameter. 

 However, there is fine structure showing deviation around any apparent inverse 

 relationship. This fine structure indicates that there is yet much to be learned about 

 plutonium resuspension and plutonium attachment to nonrespirable as well as to 

 respirable host particles. 



