Plutonium Biokinetics in Human Body A. Luciani - Kit-Bibliothek - FZK

Percentage daily urinary excretion [%d -1 ]
1E+0
1E-1
1E-2
1E-3
1E-4
1 10 100 1000 10000 100000
Days post injection
Figure 3.1.15 Reference data set and ICRP 67 original and modified versions predictions for
percentage daily urinary excretion of Plutonium.
According to Figure 3.1.8 any additional improvement of urinary excretion at long
times after intake should inevitably consider the organs and tissues that affect the biokinetics
at this time range, i.e. liver and skeleton. Firstly attempts for improving model predictions of
Plutonium urinary excretion by considering liver transfer rates were carried out. However it
turned out that the necessary variations of liver transfer rates should be so large to generate
values for skeleton to liver partitioning ratios far from the findings in autopsy studies. The
latter range from about 0.60 to 0.73 [158, 159, 160, 161]. Therefore a modification of Polig’s
skeletal model, up to now implemented into the ICRP 67 model without any adjustment, was
considered.
As previously carried out in the phase of analyzing the ICRP67 model, skeletal time
depending transfer rates were considered. The general rule of ICRP 70, based on
physiological studies, for the age-related variation of bone turnover rates was adopted: The
bone turnover rates suggested by Polig were used up to the age of 35 and from then onwards
were linearly increased up to the doubled value at age 60. The trend of the skeletal transfer
rates versus the age of the subjects is similar to those shown in Figure 3.1.5 even if now the
values are those provided from Polig’s study. It was found that introducing time-dependent
skeletal turnover rates (Model-b) effects a lifting of the urinary excretion beyond about 10
years post injection. At the same time the transfers of the liver compartments (arrows 3 in
Figure 3.1.12) and the fecal excretion parameters (arrows 4 in Figure 3.1.12) were changed in
order to achieve a correct estimate of the skeleton to liver partitioning and the fecal excretion,
respectively. The modification of these parameters was obtained by a “qualitative” fitting to
the few available measurements.
The model’s predictions for the urinary excretion of Plutonium are shown in Figure
3.1.16 (Model-b) together with the reference data set, Model-a, ICRP 67 model and its
105
experimental data
Khokhryakov (1994)
ICRP67
ICRP67-a
Model-a