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

The expression (equation 2.1.1) for the urinary excretion through 138 days was then
adjusted by including data collected in the frame of the monitoring control of occupational
exposure in Los Alamos Laboratory. Three subjects were considered. They accumulated
significant amounts of Plutonium during wartime operations and Plutonium measurements in
urine were available up to about five years (1750 days) after their last possible exposure. This
last set of data is not analogous to the previous data from volunteers because the individuals
received unknown amounts of Plutonium over an indefinite time period and via likely
inhalation route. However Langham and co-workers made an attempt to use these data: they
approximated a chronic variable intake in term of an effective single intake occurred at a
certain effective time between the probable limits of exposure. This was carried out using the
aforementioned urinary excretion function on the short time urinary excretion data. Then the
experimental urinary excretion curve was fitted again extending it to 1750 days. The resulting
expression for the percentage urinary excretion was:
35
equation 2.1.3
Two subjects of Langham’s study, a male and a female patient (HP-3 and HP-6),
survived to their illness. Therefore further data on Plutonium biokinetics at long time after
injection became available. Samples of urine, feces and blood were collected at about 10,000
days (around 27 years) after the injection [88, 89, 90, 91, 92,]. A review of the original
injection experimental records was later carried out and additional data were found [93]. In
this work it was evident that the data reported by Langham’s group were not corrected for
chemical recovery losses. Starting from this observation all the original data for the urinary
excretion rate of Plutonium from Langham’s study (Chi-3 and from HP-1 to HP12) were
reviewed [94]. Through a literary research recovery correction factors of 90% for samples
collected at 0-526 days post injection and of 67.4% at 1610-1648 days were adopted. No
correction factors were necessary for samples collected at later time.
2.1.1.2 Further experimental investigations
eu = 0.20t −0.74
In the last decade further studies were carried out in order to investigate Plutonium
biokinetics in humans. New experiments based on intravenous injection of Plutonium isotopes
into healthy volunteers were designed. Yet, 239 Pu, the most important isotope in the radiation
protection practice from Plutonium exposure, would have delivered a prohibitive radiation
dose if injected into healthy subjects in the amount required for such studies. Therefore the
use of other Plutonium isotopes was considered. 237 Pu resulted as one of the best candidates.
Studies in rats and beagles showed 237 Pu can be a suitable metabolic tracer for other
Plutonium isotopes with longer half time [95, 96]. 237 Pu, with 45.3 d half life and radioactive
decay mainly due to electron capture (>99.99 %), delivers an effective dose significantly
smaller than 239 Pu, limiting the radiotoxicological effects for the same administered amounts.
For instance in case of ingestion of 237 Pu with any f 1 values the effective dose per unit of
intake is from 90 up to 2500 times smaller then 239 Pu [97]. Moreover the x rays emitted during
its decays would allow to study the patterns of organ uptake with direct measurement
techniques. Even though all these characteristics, making 237 Pu a suitable tracer for biokinetics
studies, were known since long time, it was not previously used because of difficulties in
producing it sufficiently free of other Plutonium isotopes potentially delivering much larger
effective doses.