ECOLOGICAL RELATIONSHIPS OF PLUTONIUM 411 



TABLE 5 Comparative Distribution of Plutonium in Surface Soil 

 (0 to 2.5 cm) Size Fractions at the Los Alamos and Trinity Study Areas 



*Size fraction data based on composite samples. 



tPu denotes primarily ^^'Pu in Mortandad Canyon and 2 3 9,2 4opjj .^^ all other study locations. 



Vegetation 



Plant- Soil Relationships. The concentrations of plutonium in the study area vegetation 

 were related to the levels of plutonium in associated soils (Fig. 2). The relationship 

 between plutonium concentrations in vegetation and in soils was predictable over a range 

 of five orders of magnitude in concentrations; this relationship is similar to relationships 

 that were observed in the Rocky Flats environs (Little, 1976). 



Plant -soil plutonium concentration ratios (CR = picocuries per gram of vegetation/ 

 picocuries per gram of soil) are a convenient means of estimating the plutonium levels in 

 vegetation growing on contaminated soils. Ratio estimates for native grasses in the Los 

 Alamos and Trinity Site study areas (Table 6) ranged from 0.05 to 1.2, whereas the values 

 for forbs ranged from 0.04 to 1.1. All these ratios are higli relative to those derived from 

 experimental studies where root uptake was the contamination mechanism (Romney and 

 Davis, 1972; Wilson and Cline, 1966), which indicates that either plutonium is much 

 more available to plants under field conditions or that mechanisms other than root 

 uptake are responsible for the plutonium measured in plant samples from the field. 



The relative amounts of plutonium associated with the internal and external portions 

 of the vegetation are difficult to assess under field conditions, although we contend that 



