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

Recent technologic developments in Plutonium isotopes production made available
amounts of 237 Pu with increasing levels of isotopes purity. Metabolism of Plutonium was
investigated following intravenous injection of 237 Pu as Pu(IV) citrate in two healthy male
volunteers [98, 99]. Excreta and blood samples were collected at intervals during the first 21
days and measurements of their Plutonium content were carried out. The patterns of hepatic
and skeletal uptake too were monitored up to 153 days after injection with an external
scintillation counter located close to liver, sacrum, knees and skull. Yet, these measurements
provided only a limited information on organs uptake because of the difficulties in
discriminating the contributions from activity in adjacent tissues and blood.
Following the same experimental methodology, ten further volunteers were
intravenously injected with 237 Pu(IV) [100]. Larger amounts of Plutonium were administered
in order to detect it in bioassays for a longer time after injection. Moreover six women were
included in the studied groups of volunteers and sex-related differences in Plutonium
metabolism, particularly in the excreta, were investigated and considerations were extended
also to other actinides [101]. Samples of urine, feces and blood were collected and measured
at intervals for the first 21 days after injection. Further samples were collected and analyzed at
around 40 and 90 days post injection. Measurements of hepatic uptake and gonads deposition
were also carried out [102, 103].
2.1.2 EMPIRICAL CURVES
The original data set from Langham’s subjects has been used and re-evaluated
numerous times over the years by various researchers. This confirms the importance and
originality of these first experiments that were for different decades the only source of direct
knowledge about Plutonium biokinetics. One of the first modifications of Langham’s urinary
excretion curve was proposed by Beach and Dolphin [104] to distinguish two phases in the
Plutonium excretion: an initial rapid excretion of the injected Plutonium in the citrate form
and the lower excretion rate of metabolized plutonium. This approach yielded a nonintegrable
equation for which a graphical solution was provided.
As a result of the developments in computer programming slight discrepancies were
observed between Langham’s function and the functions calculated by minimization routine
with computer. On this basis the following function for the percentage daily urinary excretion
was calculated by Robertson and Cohn [105] with the Brookhaven Merlin computer:
eu(t) = 0.193t −0.721
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equation 2.1.4
Yet the most important and interesting re-evaluation of Langham’s subjects data set
was carried out at the beginning of seventies by Durbin [106]. A meticulous re-examination
of the original data was carried out particularly considering the physiological and health status
of the investigated subjects and integrating the available data with occupational exposure and
laboratory animals’ data. The need of a Plutonium urinary excretion curve representative of
an adult human being in good health was pointed out. Therefore only the data from those
subjects without abnormal kidney function or abnormal plasma Plutonium binding due to
anaemic status were considered, because irregular Plutonium urinary excretion rates were
observed for subjects characterized by such pathologies. Moreover differences in biokinetics
of Pu(IV) and Pu(VI) were pointed out, particularly for the early urinary excretion. As the
Pu(IV) oxidation state was deemed likely to be the chemical form of Plutonium commonly