166 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



release (McLendon, 1975; McLendon et al., 1976). Soil concentrations were negligibly 

 affected by reprocessing facilities at distances exceeding 10 km from the point of release 

 (McLendon etal., 1976). Second, we anticipated that plutonium concentrations in soils 

 collected in close proximity (i.e., within 2 ni) to one another might vary greatly owing to 

 microtopographical heterogeneity in the deposition of plutonium particles. Tlie occur- 

 rence of a single large particle at a site could greatly elevate the soil plutonium 

 concentration. Soil concentrations could also be elevated by an accumulation of 

 resuspended plutonium particles due to some feature of terrain, vegetation, or surface 

 roughness. The third source of variation was termed "sampling error." This is the 

 variation in plutonium concentrations observed among aliquots of a well-mixed soil and 

 includes both errors introduced in taking an aliquot for analysis and the analytical errors 

 associated with determining plutonium concentration in the aliquot. 



Large plutonium particles may affect both the microtopographical heterogeneity and 

 the sampling error components of variation. If plutonium deposition from aerial releases 

 occurs as large particles that are resistant to weathering, the particle deposition will influ- 

 ence the sampling error term because the particle will occur in one aliquot and not in the 

 others. If, however, the deposition occurs as large particles that are easily weathered into 

 smaller independent particles which can be easily homogenized in the sample, then 

 aliquots of the soil will have similar concentrations. In that case, the effect of particulate 

 deposition would be expressed as large differences in concentrations among closely 

 spaced soils, i.e., as microtopographical heterogeneity. A mixture of particle sizes, or the 

 confounding effects of resuspension and redistribution of particles, may produce results 

 that are intermediate between the above two extremes. 



Methods 



To partition the total variation in soil plutonium concentration into components that are 

 due to distance from the source, microtopographical heterogeneity, and sampling error, 

 we collected three soils from each of five independent transects located from 183 to 

 436 m to the northwest of the point of release (a 62-m stack that exhausts filtered air 

 from the internal atmosphere of the reprocessing facility). Each transect was 2 m long, 

 and soil was collected at distances of 0, 1 and 2 m along the transect. Soil was obtained 

 from the upper 5 cm of the profile with a soil auger. For each point on each transect, we 

 homogenized the soil by vigorous, manual shaking in a cardboard ice-cream carton for 

 1 min and divided the soil into two samples of equal volume. The auger was cleaned 

 between sampling points, and a separate ice-cream carton was used at each point to 

 prevent cross-contamination. The samples were collected in the vicinity of H-area at the 

 SRP on a field that was being used for long-term studies of the transport and fate of 

 transuranic elements in agricultural ecosystems. The samples were collected before the 

 soil had been disturbed for agricultural purposes in November 1974. 



The concentrations of ^^^Pu and 2 3 9,2 4 op^^ ^q^q determined by alpha spectrometry 

 under the direction of A. L. Boni at the Savannah River Laboratory (operated by E. I. 

 du Pont de Nemours & Co.). Ten-gram aliquots of soil were ashed and leached with HCl. 

 A triisooctylamine, 200- to 800-mesh solid ion-exchange resin was used to remove the 

 plutonium from the leachate by liquid ion exchange. Plutonium was leached from the 

 resin with H2 SO3 , electroplated on platinum disks, and counted. Plutonium-236 was used 

 as an internal standard in estimating recoveries of plutonium from the soil. Large soil 

 particles (>3 mm in diameter) were removed from the samples before aliquots were 

 drawn. 



