MODEL FOR ESTIMATING Pu TRANSPORT AND DOSE 487 



For predictive purposes, Anspaugh (1974) has suggested the use of a mean 

 mass-loading factor of 100 jug soil/m^ air. We combine this factor with the further 

 assumption that the specific activity of plutonium in resuspended materials is the same as 

 that in the associated soil and estimate Am as follows: 



Am =BmLaCs= 0.002 Cs (28) 



where Am = plutonium inlialation rate for man (pCi/day) 

 Bm = respiration rate (20 m^/day) 

 La = mass-loading factor (100 ;Ug/m^) 



Cs = average concentration of plutonium (pCi/g) in the soil of the contaminated 

 area 



The observed mass-loading factor during cascade impactor runs at NTS was 70 Mg/m^ 

 (Anspaugh, 1974), and the specific activity of particles recovered from the impactors was 

 about one-third as high as that of surface-soil samples from the same locations (Phelps 

 and Anspaugh, 1974). Compared with these observations, the estimate of Am provided 

 by Eq. 28 may be conservatively high by a factor of about 4 under average conditions. 

 High winds or mechanical disturbances, such as vehicular traffic, plowing, etc., could 

 cause the mass-loading factor to increase temporarily to very higli levels. However, a 

 comparison of observed and predicted air concentrations based on La = 100 jug/m^ 

 showed very good agreement (Anspaugh et al., 1975). 



Ingestion Rate. The plutonium ingestion rate is defined as the sum of products of the 

 rates at which different kinds of contaminated materials are ingested and the 

 concentration of plutonium in each kind of material. The formula used for estimating a 

 probable ingestion rate for use in this study was 



n=6 



Hm = Cs L liDi (29) 



i=l 



where Hm is the plutonium ingestion rate for man (pCi/day), Ij is the ingestion rate for 

 substance i (g/day), and D, is the discrimination ratio (dimensionless) for substance i. 



The kinds of materials considered, their assumed ingestion rates (Ij), and associated 

 discrimination factors (Di) are Usted, together with their products and sum, in Table 5. 

 The methods, experimental data, and assumptions used to estimate the discrimination 

 factors (Dj) are explained in the following text. 



Soil. The assumption that the Standard Man of the model accidentally ingests soil at 

 an average rate of 0.01 g/day is purely speculative but not unreasonable considering the 

 amount of dust that can be raised in desert environments by activities that disturb the soil 

 surface. 



Vegetation. To estimate the plutonium concentration in native vegetation, we 

 assume an average vegetation/soil ratio of 0.1 . As explained earlier, this ratio should tend 

 to overestimate the concentration of plutonium growing in areas of relatively high soil 

 concentration at NTS. To distinguish between native vegetation and cultivated plants 



