examined with respect to ingestion was the ingestion to inhalation ratio (H_/Am). The ingestion model takes the form (Martin and Bloom, 1976; 1977); HL = ©, 2 1, D, (24) I. is the ingestion rate for substance i (g/day) where D. is the discrimination factor which is the ratio of concentration of 23%Pu in substance i to the concentration of 239Pu in soil. The principal item to note from Equation (24) is that H_ is directly ANALYSIS OF THE EFFECTS OF VARIATIONS The simplified model given by Fquations (19) through (24) allows us to examine the effects of variations in the significant parameters in a relatively easy manner. The parameters subject to the most variation are (a) the average soil concentration: (C_), (b) the mass loading factor (L_), (c) the various fractions and biological half-times involved in the lung model (Equations (20) and (21)), (d) the ingestion to inhalation ratio (Hm/Am) » and (e) the biological elimination rate for bone OA, = in(2)/T>) and fraction from blood to bone. Statistical summaries of soil inventory data by Gilbert et al. (1975) show large variations of soil concentration within a particular area. This variation is compounded by uncertainties as to the proper size and boundaries to assign to the ecosystem model. The mass ltoading factor is also quite variable and depends on wind velocities and frequencies as well as the size of soil particles and whether the soil has been mechanically disturbed (e.g., plowed). The various fractions and half-times in the lung model are subject to considerable uncertainty because we are generally ignorant of the particle size which affects the initial deposition fractions (D,, Dis and D.) as well as the chemical and physical form of the plutonium (which affects the translocation class). The ingestion to inhalation ratio is uncertain because of the potential variation in the parameters of the ecosystem model that predicts ingestion as well as uncertainties in L, and C_. The biological elimination rate (or half-time) of bone and the fraction from blood to bone can be significant because bone does not reach equilibrium within the time period of interest (50~70 years) and because a range of values has been proposed for these two parameters (ICRP 19, 1972). 525 SF Ane Ace RO AO SOI, lA enti proportional to C.> but varies with respect to the composition of the diet.