MODEL FOR ESTIMATING Pu TRANSPORT AND DOSE 489 



Discussion. Models for calculating organ burdens and cumulative organ doses due to 

 ingestion and inhalation of ^^^Pu are discussed in considerable detail later in this chapter. 

 On the basis of the ICRP-II model for ingestion and the Task Group on Lung Dynamics 

 model for inhalation, radiation doses to the respiratory system would be entirely due to 

 inhalation, and doses to the gastrointestinal tract would be primarily due to ingestion. 

 Doses to organs receiving the radionuclide from blood (bone, liver, kidney, etc.) would be 

 due to both ingestion and inhalation. The relative importance of inhalation vs. ingestion 

 can be compared by comparing the two components of organ burden after a period of 

 chronic exposure. Such a comparison is provided in Table 6. 



TABLE 6 Fractions of " ^ ^Pu in Bone, Liver, 



or Kidney Due to Chronic Ingestion and Inhalation 



for a Period of 50 yr* 



*Estimated burdens based on ICRP Publications 2 and 

 19 (International Commission on Radiological Protection, 

 1959; 1972). 



On the basis of our estimates for the hypothetical Standard Man at NTS 

 [inhalation = 0.002 C^ (pCi/day) and ingestion = 0.2 C^ (pCi/day)] , the ingestion/ 

 inhalation ratio would' be 100, and ingestion would contribute about 5% of the 50-yr 

 bone burden. As indicated by Table 6, the relative importance of ingestion vs. inhalation 

 increases as the ingestion/inhalation ratio increases. Any factor tending to increase the 

 transfer from the gastrointestinal tract to blood would have the same effect as an increase 

 in the ingestion/inhalation ratio. A factor tending to decrease the inhalation rate would 

 also increase the ingestion/inhalation ratio. The point of Table 6 is that, to have a 

 significant effect on internal organ burden, dose, or dose commitment, the ingestion rate 

 must exceed the inhalation rate by a factor of 100 or more. 



Dose-Estimation Models 



Plutonium reaches man by ingestion of contaminated food and water or by inhalation of 

 contaminated air. Part of this plutonium is distributed througliout the body where it may 

 remain for some time. While it remains within the body, organs that retain the plutonium 

 will receive a radiation dose that depends on the weight of the organ, the amount of 

 plutonium retained, and the time that the plutonium is retained. The several models we 

 have used to estimate plutonium distribution in man are discussed in this section. 



