MODEL FOR ESTIMATING Pit TRANSPORT AND DOSE 483 



where r^v is the rate at which ingested plutonium reaches the blood (pCi/day) and fgb is 

 the fraction transferred from the gastrointestinal tract to blood. Since this cow was left in 

 the inner compound of Area 13 for 177 days before sacrifice (Smith, 1977), the total 

 ^ ^^Pu expected to have entered the blood via ingestion would be 3000 pCi. 



The transter of inhaled plutonium to blood is considerably more complicated than 

 indicated by Fig. 2. Assuming resuspended particles to have an activity median 

 aerodynamic diameter (AMAD) of 0.5 jum and applying the Task Group on Lung 

 Dynamics model (Fig. 4 and Table 1 1) to the cow, we obtain the following expression for 

 the rate at which inhaled plutonium would be expected to enter the blood: 



rba =0.0021 la + 0.0833 Xiyi +X2y2 +3 X 10"^ yj (22) 



dy, 



dt 



dy2 



- = 0.18I, -Xiyi (23) 



dt 



dya 

 dt 



0.225 Xiyi -X2y2 (24) 



0.75 lio.2079 +-y^U 0.667 Xiyi (25) 



where r^g = rate (pCi/day) at which inhaled plutonium enters the blood 



0.0021 = fraction of inhaled plutonium transferred directly to blood from 



the upper respiratory tract 

 0.0833 = fraction of plutonium deposited in the lungs and then transferred 

 to blood 

 yi = amount (pCi) present in the lung at time t 

 Xi = In (2)/ 500 days = the lung clearance rate 



y2 = amount (pCi) present in the lymph at time t 

 X2 - In (2)/ 1000 days = the lymph clearance rate 



ya = amount (pCi) present in the gastrointestinal tract at time t 

 0.18 = fraction deposited in the lungs and cleared with a 500-day 

 half-life 

 0.225 = fraction transferred from lung to lymph and then cleared to 

 blood with a 1000-day half-hfe 

 0.75 (day ) = average residence time of plutonium in the gastrointestinal tract 

 0.2079 = fraction transferred directly from the upper respiratory tract to 

 the gastrointestinal tract 

 0.12 = fraction cleared from lungs to the gastrointestinal tract with a 

 1-day half-hfe 

 Xo =ln(2)/l day 

 0.667 = fraction cleared from lungs to the gastrointestinal tract with a 

 500-day half-life 



Note that Eq. 22 consists of four terms. These terms represent transfers of inhaled 

 plutonium to blood from the upper respiratory tract, the lungs, the pulmonary lymph, 

 and the gastrointestinal tract, respectively. Equations 23, 24, and 25 are the differential 



