A computational study of the urinary excretion rates for 239Pu using new ICRP internal dosimetry models

A computational study of the urinary excretion rates for 239 Pu has been carried out using a methodology which involved the solution of a complete compartmental model describing the biokinetic behaviour of inhaled plutonium aerosols in the human body. The methodology, after proper validation, was applied to investigate the dependence of urinary excretion rates for 239 Pu on the transfer rates given in the complete compartmental model. For this purpose, the default values of the transfer/absorption rates were modified by factors of 2 and 4 and urinary excretion rates were computed on 1, 10, 100, 1000 and 10.000 d post-intake. The percentage variations in the urinary excretion rates as a result of the modified transfer rates were computed for exposures to Type M and S aerosols of 239 Pu. These results facilitated the identification of parameters significantly affecting the short-term and long-term urinary excretion rates. In addition, time variations of the predicted ratios of 239 Pu activity in daily urine to that in blood (excretion ratios) were studied for the three biokinetic models of plutonium: the ICRP 67 model, the modified ICRP 67 model with the compartment ST1 to urinary bladder removed and Luciani and Polig's model. All the computational results are presented and discussed in this paper.