TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



TABLE 3 Range in Inventory Ratios for Plutonium in 

 Major Ecosystem Compartments 



Compartment 



Range in 

 inventory ratio* 



Reference 



Soils 



0.998 to 0.986 



Romney and Wallace, 1977; 



Dahlman, Garten, and Hakonson, 



this volume; Little, this volume 

 Hanson, 1975; Romney et al., 1976; 



Dahlman, Garten, and Hakonson, 



this volume ; Little, this volume; 



Pinderetal., 1979 

 3 X 10~^ to 2 X 10"" Dahlman, Garten, and Hakonson, 



this volume; Little, this volume 

 7 X 10~^ to 6 X IC^' ' Dahlman, Garten, and Hakonson, 



this volume; Little, this volume 



Vegetation 2 x 10~^ to 3 x 10" 



Litter 



Animals 



*The proportion of the total plutonium in the ecosystem that is found in 

 each major compartment. 



More than 99% of the plutonium inventory is found in the soil compartment of most 

 ecosystems (Table 3), and most of the contamination occurs near the soil surface 

 (Francis, 1973; Little and Whicker, 1977). Notable exceptions occur in arctic systems 

 where lichens intercept and retain fallout for long periods of time and in ecosystems that 

 are still receiving aerial depositions from nuclear processing facilities. However, even in 

 these special cases soil will be the eventual repository after deposition ceases (Hanson, 

 this volume; Holm and Persson, 1975; Dahlman and McLeod, 1977). 



At some sites, a considerable amount of water has percolated into the soil since 

 the initial deposition (e.g.. Savannah River Plant), but still the major inventory of 

 plutonium is in the top few centimeters of soil. The concentration of plutonium is only 

 occasionally higher in the subsoils below 10 cm than in the surface materials (Essington et 

 al., 1976). Plutonium is found at depths greater than 20 cm but usually in very low 

 concentrations unless soil or sediment mixing is actively in progress. Such mixing can 

 occur in steep canyons and delta regions of running-water ecosystems (Nyhan, Miera, and 

 Peters, 1975) and in terrestrial sites where natural biotic or human activities have mixed 

 or buried the plutonium. 



Transuranic radionuclides can often be buried and remain immobile after deposition. 

 The exact distribution in the soil profile has an important influence on the availabiUty of 

 transuranic elements for resuspension and root uptake. 



The proportion of plutonium associated with biotic components of the ecosystem can 

 be as small as 0.1% (e.g., southeastern forests) (Dahlman, Garten, and Hakonson, this 

 volume). This fact reflects generally lower concentrations in biota but more importantly 

 the small mass of biota relative to soil. Even if transuranic elements were randomly 

 distributed among ecosystem components, the majority would still be associated with 

 soil. 



The amount of plutonium associated with vegetation is greater than that associated 

 with animals (Table 3) but ranges over five orders of magnitude. Inventory ratios for 

 animals range over eight orders of magnitude. Most of this variation is probably due to 

 the amount of surface contamination on samples and not to internal concentrations of 

 plutonium in plants and animals (Dahlman and McLeod, 1977). 



