Plutonium Biokinetics in Human Body A. Luciani - Kit-Bibliothek - FZK
Plutonium Biokinetics in Human Body A. Luciani - Kit-Bibliothek - FZK
Plutonium Biokinetics in Human Body A. Luciani - Kit-Bibliothek - FZK
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excretion that is one of the ma<strong>in</strong> issue of the present work. For such reasons it was not more<br />
analyzed here. It should be just mentioned that two extreme approaches were briefly<br />
considered for the systemic behaviour of Americium <strong>in</strong>growth: one based on the same<br />
systemic behaviour of <strong>Plutonium</strong> and a second one on Americium own systemic model. The<br />
results showed that <strong>in</strong> the first case a pretty good agreement of model’s predictions for the<br />
Americium fecal excretion was found; <strong>in</strong> the second case the model’s predictions don't fit<br />
anymore the measurements for this bioassay but significantly improve their agreement with<br />
the measurements for Americium blood content. Similar effects were observed if bone and<br />
liver burden of Americium are considered. This seems to confirm the idea that the Americium<br />
<strong>in</strong>growth is characetrized by a biok<strong>in</strong>etics that is <strong>in</strong> between the two possible extreme<br />
assumptions, i.e. its own biok<strong>in</strong>etics and the father <strong>Plutonium</strong> biok<strong>in</strong>etics.<br />
3.2.5 PLUTONIUM URINARY EXCRETION ENHANCEMENT<br />
In the frame of the analysis of the reliable measurements group, a deviation of model’s<br />
predictions from experimental f<strong>in</strong>d<strong>in</strong>gs for the ur<strong>in</strong>ary excretion of <strong>Plutonium</strong> was po<strong>in</strong>ted out<br />
after 2,000 days post <strong>in</strong>take. In fact the ur<strong>in</strong>ary excretion of the studied subject is<br />
characterized by a cont<strong>in</strong>uous enhancement of the ur<strong>in</strong>ary excretion of <strong>Plutonium</strong> that is<br />
gett<strong>in</strong>g more and more significant with time. This phenomenon was already observed by<br />
previous measurements campaigns and it is confirmed by the last measurements, carried out<br />
at about 6,000 days post <strong>in</strong>take <strong>in</strong> occasion of the present work (Table 2.4.1). The ur<strong>in</strong>ary<br />
excretion of <strong>Plutonium</strong> for the studied subject resulted to be higher by up to about a factor 6<br />
and by about an average factor 3.5 <strong>in</strong> comparison to the ur<strong>in</strong>ary excretion observed at about<br />
1,000 days post <strong>in</strong>take.<br />
A similar excretion enhancement seems to be present, at a lesser extent, even for the<br />
<strong>Plutonium</strong> fecal excretion (Figure 3.2.8).<br />
Such enhancement of the ur<strong>in</strong>ary excretion of <strong>Plutonium</strong> was recently also observed <strong>in</strong><br />
other subjects [122] too that were accidentally contam<strong>in</strong>ated long time ago (ten years ago or<br />
more). However the enhancement of <strong>Plutonium</strong> ur<strong>in</strong>ary excretion observed <strong>in</strong> those subjects<br />
is less significant than what was observed for the subject <strong>in</strong>vestigated here.<br />
3.2.5.1 The effect of the uncerta<strong>in</strong>ty of the transfer rates<br />
The hypothesis of further <strong>in</strong>ternal contam<strong>in</strong>ation events that could expla<strong>in</strong> the<br />
enhancement of <strong>Plutonium</strong> ur<strong>in</strong>ary excretion can be neglected on the basis of the typology of<br />
work<strong>in</strong>g activity <strong>in</strong> which the subject was engaged after the ma<strong>in</strong> contam<strong>in</strong>ation event<br />
occurred <strong>in</strong> 1983. Such enhancement can't be described by the available biok<strong>in</strong>etic models for<br />
the <strong>Plutonium</strong> metabolism <strong>in</strong> humans. Accord<strong>in</strong>g to the optimized model (Model-b), that can<br />
be reasonably considered now the most recent updated model for <strong>Plutonium</strong> biok<strong>in</strong>etics, the<br />
ur<strong>in</strong>ary excretion of <strong>Plutonium</strong> from 1000 days to 6000 days post <strong>in</strong>take should decrease by a<br />
factor 1.5. ICRP 67 model for <strong>Plutonium</strong> metabolism would predict even a more significant<br />
decrease (a factor 2.6) <strong>in</strong> the same time period, therefore more <strong>in</strong> disagreement with the<br />
experimental f<strong>in</strong>d<strong>in</strong>gs that, on the contrary, po<strong>in</strong>ted out for this subject an enhancement by an<br />
average factor 3.5.<br />
The biok<strong>in</strong>etic model developed here, as all the biok<strong>in</strong>etic models generally used <strong>in</strong><br />
radiation protection dosimetry, describe the metabolism of a radionuclide for a standard<br />
subject, represent<strong>in</strong>g the average of the morphometric and physiological characteristics of the<br />
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