MODEL FOR ESTIMATING Pu TRANSPORT AND DOSE 461 



represent net transport via the pathways indicated. Arrows that cross the arbitrary 

 boundary represent net transport out of the system. 



The distribution of plutonium in the contaminated areas of principal interest at the 

 NTS has been described by Gilbert et al. (1975). Present levels of soil contamination in 

 the areas of interest range from about 1 .0 ^Ci/m^ to >6000 idCi/rn^ . Because these levels 

 of soil contamination resulted from nuclear safety tests carried out from 1954 through 

 1963 and because current worldwide fallout rates are insignificant compared with existing 

 levels of contamination, Fig. 1 shows no current plutonium input to the system. 



r 



ARBITRARY BOUNDARY 



Fig. 1 Principal pathways of plutonium transport to man. 



Under these conditions the plutonium concentration in soil is the principal factor 

 forcing the transport system. Air is contaminated by resuspension of plutonium-bearing 

 soil particles. Vegetation is contaminated internally by root uptake from soil and 

 externally by deposition of resuspended particles. Plutonium input to herbivores is due to 

 ingestion of soil and vegetation and to inhalation. Plutonium could reach man by 

 inhalation of contaminated air, by accidental ingestion of contaminated soil, by ingestion 

 of contaminated vegetation, and by ingestion of milk or meat (skeletal muscle or internal 

 organs) from animals raised in the contaminated area. Drinking water for herbivores and 

 man is assumed to come from deep wells or from sources outside the contaminated area 

 and to contribute nothing to plutonium intakes by herbivores or by man. Numerous 

 other pathways, most of them trivial and unsubstantiated, could be postulated, but we 

 have tried to limit our consideration to genuinely important pathways. 



If it is assumed that (1 ) the major ecosystem compartments and important transport 

 pathways are as indicated in Fig. 1,(2) the plutonium in each compartment is well mixed 

 with the other contents of the compartment, and (3) the net rate of transfer from one 

 compartment to another is the product of a transfer coefficient and the quantity of 

 plutonium in the transmitting compartment, then the intercompartmental flux of 



