260 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



One can only hypothesize as to why there should be a difference in ^^^Pu/^^^Pu 

 ratios at sites AB and A as compared with soil-surface samples. One difference is that the 

 surface activity level at site A is greater than that at site AB. As was shown in Table 1 , the 

 ground-soil-surface activity level at site A was 8 to 80 times as great as that at site AB. If 

 plutonium particles were attacked by microorganisms (Wildung and Garland, 1977) in the 

 soil, microorganism activity might be decreased by the increased activity level at site A. If 

 microorganisms preferentially attacked ^^^Pu at site AB, which had a lower plutonium 

 contamination, ■^■^^Pu on surface soils might become more readily available for 

 resuspension. Other possibilities for increased resuspendibility of surface ^^^Pu at site AB 

 might be differences in soil chemistry between sites A and AB or preferential ^^^Pu 

 ejection (Oksza-Chocimowski, 1976) from particles during decay. Many possibilities exist, 

 but the reasons for the elevated ^^^Pu/^^^Pu ratios at site AB are uncertain. Additional 

 research is needed to determine causes of elevated ^^^Pu/^^^Pu ratios at site AB. 



Estimation of Relative Plutonium Fluxes for Respirable 

 and Nonrespirable Particles 



Direct comparisons between airborne fluxes on respirable and nonrespirable particles 

 were not made since respirable and nonrespirable samples were sampled differently. 

 Respirable particles at Rocky Flats were sampled at a constant flow rate of 0.57 m'^/min, 

 and nonrespirable particles were collected by inertial collection within cowls. To calculate 

 the relative flux on respirable and nonrespirable particles, one needs to know (l)the 

 average wind speed to determine the average flux on respirable particles and (2) how 

 particles were collected within the cowl by inertial impaction. In this case inertial 

 impaction means that particles would enter the cowl as if cowl sampling were isokinetic. 

 Actually there is flow divergence around the cowl inlet. Consequently correction factors 

 are needed for calculating true airborne particle fluxes for nonisokinetic sampling. 

 However, nonisokinetic correction factors are not available. Even with these qualifica- 

 tions, one might still be interested in approximating the relative plutonium fluxes for 

 respirable and nonrespirable particles. Consequently a simple calculation was made using 

 the Rocky Flats data to illustrate the relative orders of magnitude for respirable and 

 nonrespirable plutonium fluxes. 



The horizontal plutonium flux can be estimated from airborne soil fluxes and 

 plutonium concentrations on airborne soil. Since soil fluxes are reported (Sehmel, 

 1976a), plutonium concentrations on airborne soil will be discussed before plutonium 

 fluxes. Plutonium concentrations of airborne respirable and nonrespirable soil are shown 

 in Table 5. This table summarizes both total plutonium concentrations per gram of soil 

 collected within cowls and respirable concentrations per gram for cases in which air was 

 sampled continuously with particle cascade impactors. Concentrations of ^^^Pu ranged 

 from 2 X 10~^ to 6.2 x 10"^ /nCi/gon respirable airborne soil. Concentrations of ^^^Pu on 

 respirable soil were less than radiochemical analytical limits. On nonrespirable soil ^^^Pu 

 concentrations ranged from 1 X 10~^ up to 3 x lO"'* /jCi/g, and ^^^Pu concentrations 

 ranged from 2 x 10~^ up to 5 x 10^^ A^Ci/g. Respirable and nonrespirable concentra- 

 tions were combined in the last two columns to estimate the average plutonium 

 concentration on airborne soil. For this calculation isokinetic sampling was assumed. This 

 assumption is discussed further in a later section. Total plutonium concentrations on 

 airborne soil ranged from 1 X 10~^ up to 1.9 x lO"'* ^Ci/g for ^^^Pu and from 

 2 X 10"' up to 3 x 10"^ juCi/g for "^Pu. 



