ECOLOGICAL RELATIONSHIPS OF PLUTONIUM 413 



most of the plutonium in our study areas is externally deposited on plant surfaces. 

 Information supporting this conclusion includes: 



• The high plant /soil plutonium concentration ratios compared to greenhouse studies. 



• The obvious presence of soil in vegetation samples. 



In addition, other investigators have shown that some of the plutonium associated with 

 native vegetation samples can be removed by a wasli treatment (Alldredge, Arthur, and 

 Hiatt, 1977). 



Rodents 



Rodent-Soil Relationships. Plutonium in internal organs (i.e.. liver, bone, and muscle) 

 of rodents sampled within our study areas generally could not be measured. However, 

 concentrations of plutonium in pelt and Gl tract samples were readily measured and were 



TABLE 7 Inventory of Plutonium in Small 

 Mammal Tissues from Mortandad Canyon 



* Based on six pooled samples. 



directly correlated with levels in the study area soils (r^ = 0.90). Over 95% of the 

 plutonium body burdens in rodents was associated with these two tissues, as shown by 

 the data for Mortandad Canyon in Table 7. Thus we conclude that, in our study areas, 

 physical and biological processes (i.e., contamination of the pelt or ingestion of soil) 

 dominate in the transport of plutonium to rodents. 



Plutonium Inventories 



The fractional distribution of plutonium in Los Alamos and Trinity ecosystem 

 components (Table 8) is based on quantitative estimates of ecosystem component mass 

 (grams per square meter) and corresponding plutonium concentrations (picocuries per 

 square meter) in those compartments. The distribution of plutonium among five 

 components was generally quite similar between sites in that over 99% of the plutonium 

 was associated with soil and less than 1% with biota. Live vegetation contained 10"^ to 

 10~*% of the plutonium inventory. We conclude that very little of the environmental 

 plutonium present in our study areas has appeared in the biological components of the 

 ecosystem even after 30 yr of exposure. These results are essentially the same as those 

 observed at Rocky Flats and Oak Ridge (Little, 1976; Dahlman, Garten, and Hakonson, 

 this volume). 



