where Cc. is the soil concentration (pCi/g)}) and 0.017 is the alfalfa/sot1 ratio which is assumed to be one~sixth the desert vegetation/soil ratio due to plowing and mixing of the soil to a depth of 30 cm. The equation for estimating the concentration in milk is Coriy = £1505)(3 x 107°) (0,007) cy 25 tt (27) from the same locations (Phelps and Anspaugh, 1974). Compared with these observations, the estimate of A_ provided by Equation (28) may be conservatively high by a factor of about four, 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 high levels. However, a comparison of observed and predicted air concentrations based on L_ = 100 ug/m3 showed very good agreement (Anspaugh et al., 1975). = Ingestion Rate = 1.37 x 1073 C, (pCi/kg). The Pu-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 Pu in each kind of material. The formula employed for estimating a probable ingestion rate for use in this study was where AMTLK = 1n(2)/0.75 (Figure 2). n=6 H, = Cs 2 1D, In the preceding discussion, we have considered the dynamics of the plutonium transport system (Figure 1) and attempted to establish mathematical relationships between compartments. Our present knowledge of the food chain kinetics of plutonium in contaminated areas at NTS is not adequate for modeling the dynamic aspects of all parts of the transport system. To simplify estimation of the plutonium inhalation and ingestion rates for herbivores (cattle), we assumed the system ta be in steady-state and the intake rates to be constant. We now apply the same simplifying assumptions to estimate potential plutonium inhalation and ingestion rates for the hypothetical Standard Man. Inhalation Rate The Pu-inhalacion rate (A_) is defined as the product of the respiration rate (B_) and the concentration of Pu in air. The concentration of Pu in air is, of course, quite variable; bue, since it is due to resuspension of contaminated soil, it can be related to the average concentration in surface soil (c,). For predictive purposes, Anspaugh (1974) has suggested the use of a mean mass loading factor of 100 ug (soil)/m? (air). We combine this factor with the further assumption that the specific activity of Pu in resuspended materials is the same as that in the assoctated soil, and estimate AN, as follows: An = a Lic. = 0.002 Cy (28) where, AL is the Pu-inhalation rate for man (pCi/day), BY is the respiration rate (20 m3/day), Le is the mass loading factor (100 we/m?), and C_ is the average concentration of Pu (pCi/g) in the soil of the contaminated area. The observed mass loading factor during cascade fmpactor runs at NTS was 70 ug/m? (Anspaugh, 1974) and the specific activity of particlea recovered from the impactors was about one-third as high as that of surface soil samples 654 (29) where H_ is the Pu-ingestion rate for man (pCi/day), I, is the ingestion rate for substance 1 (g/day), and D, is the discrimination ratio (dimensionless) for substance ft. The kinds of materials considered, their assumed ingestion rates (1,), and associated discrimination factors (D,) are listed, together with théir products and sum, in Table 5. The methods, experimental data, and assumptions used to estimate the discrimination factors (By) are explained below. 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 (alfalfa hay), we assumed a sixfold dilution of soil concentration due to plowing to a depth of 30 cm, i.e., the plant/sofl ratio for cultivated plants is 0.017 instead of 0.1. In preparing Table 1, we assumed that 90 percent of the external contamination of "leafy vegetables" and that 99 percent of the contamination associated with "other food plants" would be In removed by washing, peeling, etc., during preparation for consumption. spite of this assumed reduction, leafy vegetables and other food plants account for 90 percent of Standard Man's estimated plutonium ingestion rate (Table 5).