516 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



Soil Plutonium Characteristics in the Canyon Ecosystem 



Concentrations of plutonium in alluvial soil from the canyon are strongly a function of 

 distance from the waste-effluent outfall (Hakonson and Bostick, 1975; Nyhan, Miera, and 

 Peters, 1976b). Highest concentrations, averaging about 250 pCi/g, occur near the outfall, 

 whereas successively lower concentrations are measured with increasing distance 

 downstream. Downstream transport of waste has occurred to about 3500 m below the 

 outfall where fallout levels of plutonium are measured. Stream-bank soils to 1 m either 

 side of the channel are contaminated to the same level as adjacent channel soils. 



Plutonium is rather uniformly distributed within the canyon soil profile to depths of 

 30 cm, wliich reflects the effect of turbulent mixing processes during storm runoff events. 

 The mixing of plutonium with depth has been rapid (<years) as inferred from the 

 distribution of ^^^Pu with depth (Hakonson and Bostick, 1975). 



Over 85% of the plutonium in canyon alluvium is associated with sand particles of 

 from 0.05 to 23 mm in diameter. About 14% of the plutonium inventory is present in the 

 silt— clay fraction (<0.05 mm), which comprises only 2% of the soil mass (Nyhan, Miera, 

 and Peters, 1976a). Significant correlations with solid-phase constituents (i.e., carbonates 

 and the colloidal exchange complex) suggest that plutonium is sorbed to particles and 

 minerals. 



Concentration Ratios 



The availability of soil plutonium to biota can be inferred from the concentration ratios 

 (CR's) in Table 3. The low CR's for biota at both sites demonstrate the small fraction of 

 plutonium that has moved from soil to biota. Vegetative components (root, litter, and 

 herbaceous species) most intimately associated with the soil exliibited the highest CR's at 

 both sites. Arborescent components generally exhibited the lowest CR's. The fact that all 

 CR's are less than 1 confirms that there is no evidence of biomagnification of plutonium 

 in these terrestrial ecosystems two to three decades after the environments were 

 contaminated. 



TABLE 3 Concentration and Inventory of Plutonium in Major Components of the Oak Ridge 

 Floodplain and the Los Alamos Mortandad Canyon 



*Concentrations and inventories averaged for the 3-ha floodplain. 



t Concentrations and inventories based on the 0- to 1500-m segment of Mortandad Canyon. 

 JCR = [PuJcomponent/lPulsoil- 



§1R = [Pu] receptor/(P") source- The IR's for all components except soil are based on soil as the plutonium source. 

 The soil IR represents the fraction of total plutonium of the ecosystem that is present in soil, 

 fl Weighted average for intensive study sites 1 and II. 



