239py and 236Ra, but 7 32u, 233y, 9%S5r, and “Sca,* Figure 1 from her paper is
reproduced herewith as Figure 3.
The greater effectiveness of 233pu on a
Others have calculated the relative
uCi/kg injected dose basis is very clear.
radiation doses and while the ratios change somewhat, the basic relationships
between plutonium and radium are the same on either an administered dose or
calculated radiation dose basis.
In Figure 4 (Dr. Finkel's Figure 2), the
comparative lethality is shown using radium-226 as the baseline.
It was this information which, more than anything else, influenced the decision
in 1950 to consider plutonium-239 as at least five times as effective as
radium-226 in producing osteogenic sarcoma (Langham, et al., 1973).
We are now accustomed, particularly in considering environmental exposures to
plutonium, to regard inhalation as the most likely route of entry. Nearly all
of the above toxicity studies involved intravenous injection. Was there
anything in the early work pertinent to our present concerns regarding the
production of lung cancer by plutonium?
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INHALATION STUDIES
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RBE RELATIVE TO 778pg
These toxicity studies led directly to the founding of the beagle dog experiment
at the University of Utah.
After all, there was still a large gulf in probable
effective doses, lifespan, tumor susceptibility, etc., between the CFl female
mouse and man.
The beagle experiment was a much needed intermediate step.
But while its inception date might fit the caption of "early work," the results
have been coming to full flower only recently.
Suffice it to say here that
the basic relationships seen in the mouse have appeared also and held in the
dog.
Also, the addition of 228Th to the Utah experiment helped to sustain the
suspicion, based on earlier radiochemical data, that plutonium and thorium
might have more in common than plutonium and radium-226.
A brief glimpse at
some of the Utah results on comparative toxicity is shown in Figure 5, taken
from Dougherty and Mays (1969}.
Admittedly, inhalation studies were slower in coming about because of the
large technical difficulties of preparing and administering controlled aerosols
of radioactive materials.
There were some rather crude inhalation experiments
performed using hot wires to produce the aerosols.
But the primary early
information was obtained by the technique of intratracheal intubation. We now
know that this direct instillation of material is not a satisfactory substitute
for true inhalation experiments.
But the results were useful in giving first
approximations regarding pulmonary retention and clearance, even effects.
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’The fact that 2320 and 2330 were employed in this work has only recently been
fully appreciated.
The relationships shown here are entering into current
thinking about uranium standards.
Figure 3.
Bone tumor induction in the CFl female mouse.
9
From Finkel (1953).