ECOLOGICAL RELATIONSHIPS OF PLUTONIUM 417 



although splash-up of soil by raindrops may be an important transport mechanism in 

 these arid, sparsely vegetated study locations. 



There was no evidence for a trophic-level increase of plutonium from soil to 

 vegetation to rodents. We believe that rodents come into contact with environmental 

 plutonium directly from the soil and to a lesser extent througli a food-web intermediary. 



Research Needs 



The importance of the soils component as a receptor of plutonium released to the Los 

 Alamos and Trinity Site study areas coupled with the direct role these soils play in 

 contamination of biota emphasizes the importance of understanding soil formation and 

 transport processes. Factors governing these processes will be instrumental in determining 

 plutonium distribution and transport as a function of time. Hydrologic and wind 

 transport processes discriminate against certain soil particle sizes; therefore studies on the 

 relationsliip of plutonium to soil separates will be useful in evaluating the potential 

 importance of a transport pathway and the resuhing hazard. We know, for example, that 

 wind transport of silt -clay material at Area GZ, Trinity Site, would represent a relatively 

 smaller inhalation hazard than corresponding transport at Area 21 simply because the 

 silt— clay fraction of Area GZ soil contains very little of the plutonium inventory. 



Factors affecting migration of plutonium into the soil profile require understanding 

 since depletion of plutonium from the soil surface will likely reduce the horizontal 

 transport potential and may alter the availability of the element to vegetation. 



Field studies should be conducted to quantify the relative importance of the root 

 pathway for contaminating vegetation to serve as a basis for judging changes in 

 physiological availability of environmental plutonium with time. As yet few field studies 

 have been able to show conclusively the relative importance of the two contamination 

 mechanisms. 



in our opinion studies should be continued on the availability of plutonium to native 

 animals in our study ecosystems; however, on the basis of present concentrations and the 

 high variability associated with these measurements, we believe that the frequency of 

 sampling should be drastically reduced. Perhaps sampling at intervals of 5 to 10 yr would 

 be adequate to judge whether significant changes in plutonium availability have occurred. 



Acknowledgments 



We wish to recognize the following individuals for their valuable contributions to this 

 research: J. L. Martinez, G. Trujillo, E. Trujillo, K. Bostick, T. Schofield, G. Martinez, 

 K. Baig, P. Baldwin, R. Peters, W. Schwietzer, and S. Lombard. We also wish to thank 

 R. 0. Gilbert, D. Adriano, J. Corey, and G. Matlack for their efforts in reviewing this 

 manuscript. This research was performed under U. S. Department of Energy contract No. 

 W-7405-ENG-36. 



References 



Alldredge, A. W., W. J. Arthur, and G. S. Hiatt, 1977, Mule Deer as a Plutonium Vector, in 

 Radioecology of Natural Systems. 15th Annual Progress Report Jor the Period August I. 

 1976-July 31, 1Q77, ERDA Report COO-11 5 6-89, Colorado State University, NTIS. 



