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

The structure of Polig’s skeleton model is characterized by an initial deposition on
both surface and volume bone compartments and not only on cortical surface as assumed in
ICRP 67 model. Furthermore a transfer of activity from volume to surface compartments
(dashed arrows in Figure 3.1.9) is theoretically introduced to achieve maximum generality in
skeleton modelling by considering a possible local recirculation too. As presently there is no
experimental evidence of such process, it was not longer considered in this skeleton model.
The two models differ in the transfer rates values too, as given in Table 3.1.6.
Table 3.1.6 Transfer rates of the skeletal models in ICRP 67 and Polig [157].
Parameter
99
Value [d -1 ].
ICRP 67 Polig
Blood compartment to Trabecular surface 0.1941 0.226
Blood compartment to Trabecular volume N.A. 0.0716
Blood compartment to Cortical surface 0.1294 0.0952
Blood compartment to Cortical volume N.A. 0.00448
Trabecular surface to marrow 0.000493 0.00159
Trabecular volume to marrow 0.000493 0.00159
Trabecular surface to volume 0.000247 N.A.
Cortical surface to marrow 0.0000821 0.000156
Cortical volume to marrow 0.0000821 0.0000822
Cortical surface to volume 0.0000411 N.A.
Trabecular/Cortical marrow to blood compartment 0.0076 0.0076
By comparing the transfer rates for the two skeletal models it can be pointed out that
Polig’s model is characterized by a higher transfer of activity to the trabecular bone (+53%)
and slightly smaller (-23%) to the cortical bone. The final effect is a generally higher activity
transfer to the whole skeleton. Furthermore the skeletal transfer rates of Polig’s model are
generally higher then those ones of ICRP 67 model. On the basis of such preliminary
considerations two aspects will characterize Polig’s model in comparison to ICRP 67 one:
• initial higher deposition into the skeleton;
• a lower retention in the skeleton at long time with a higher transfer of activity to the blood
compartment.
These considerations are confirmed by analyzing the biokinetics of Plutonium in a
study compartmental model composed by just a transfer (blood) compartment connected to
the skeletal model (Polig or ICRP67). The activity retention in skeleton and blood
compartments was calculated and is presented in Figure 3.1.10 for both skeletal models. As
preliminarily argued on the basis of the transfer rates in Table 3.1.6, the initial amount
retained in the skeleton is slightly higher if Polig’s model is adopted. More significantly at
intermediate and long time Polig’s skeletal model predicts a lower Plutonium retention than
ICRP 67 and, consequently, the blood compartment contains a higher amount of activity. For
example at 1,000 days post intake the use of Polig’s skeletal model yields skeleton and blood