minutes
of the meeting, Stone provided
the following information on the toxici-
ty of plutonium:
Alpha emitter and is expected to be
stored in bones. With Ra, 1 to 2
micrograms sometimes fatal. Pu
perhaps less dangerous by factor
of 50. Not proven as yet to be ac-
cumulative. Radium in body can
be identified by radon in exhaled
breath or by Geiger counter explo-
ration around body. These meth-
ods do not help for Pu.
Compton added:
For moment should consider Pu as
potentially extremely poisonous.
Investigation necessary. Factor of
50 probably represents worst case
and [corresponds to] a tolerance
level of stored material of about 5
micrograms.
Stone’s discussion of the “poisonous
nature” of plutonium at the meeting re-
sulted in two actions. In the absence of
plutonium metabolic data, the manage-
ment of the Plutonium Project adopted
Stone’s recommendation of a 5-micro-
gram tolerance limit for plutonium re-
tained in the body. Also, Compton,
with Oppenheimer’s concurrence, au-
thorized a shipment of scarce plutonium
to Hamilton at Berkeley. Ten mil-
ligrams of the scheduled February 1
production of reactor plutonium from
the Clinton site were to be allocated for
metabolism tests in animals at the
Berkeley lab.
Early in February, Los Alamos received
copies of the minutes of Met Lab infor-
mation meetings, thereby making per-
sonnel at Los Alamos aware of Chica-
go’s concerns about working with
plutonium, the proposed tolerance limit,
and the current suggestion of using the
analysis of urine to monitor the uptake
of plutonium relative to the 5-micro-
gram limit. The documents mentioned
Hamilton’s belief that the “dust hazard
was far more serious than oral intake.”
Based on the known behavior of metal-
lic zirconium, he felt that fifty per cent
of inhaled plutonium dust might be re-
tained in the lungs.
Also recorded in the minutes, Cecil
Watson, Associate Director of the Met
Lab’s Health Division, said:
Twenty to 30 micrograms [of plu-
tonium] may possibly be a lethal
dose. Present laboratory floor sur-
faces, desk tops, ventilation, labo-
ratory service [are] inadequate to
cope with this. May decide to han-
dle under hoods, like Ra. Should
plan so that all Pu can be recov-
ered quantitatively if accidentally
lost.
The minutes also mentioned an accident
in which an individual had spilled plu-
tonium on his hand. His stools and
urine were being examined at the Met
Lab for evidence of plutonium that
might have passed through the skin into
his body.
Learning about the proposed 5-micro-
gram tolerance limit in February,
Hempelmann traveled to Boston with
other Met Lab personnel to study meth-
ods used by the radium industry for
handling radium. Meanwhile, Kennedy
(who’d been processing cyclotron-pro-
duced plutonium at Berkeley the previ-
ous year but was now head of the
Chemistry and Metallurgy Division at
Los Alamos) was anticipating delivery
of gram amounts of plutonium from the
Clinton site and requested information
from Hempelmann about the danger to
personnel from inhaled or ingested dry
plutonium materials. Hempelmann’s
response (in an undated memo) said
that the risk of biological damage from
plutonium would be local in character,
a result of energy absorbed by tissues
from plutonium’s alpha particles. He
calculated that the energy absorbed in
10 grams of lung tissue from the alpha
particles of a 1-microgram plutonium-
239 dust particle would result in a radi-
ation dose that exceeded the daily toler-
ance limit of radiation for a single
organ. In the case of ingestion, he said
that 100 to 500 micrograms would con-
stitute a lethal dose, assuming that ab-
sorption from the intestinal tract and
subsequent metabolism was the same as
radium (and applying the estimated fac-
tor of 50 difference between the radio-
logical toxicity of the two metals).
Thus, people throughout the Manhattan
Project were aware of the potential dan-
gers of plutonium. But their thinking
involved the various assumptions about
plutonium’s biological behavior and
toxicity. Because the number of people
working with plutonium was increasing
rapidly, the people responsible for their
health were forced to develop safe pro-
cedures and detection techniques based
on best guesses, estimates from the
properties of other metals, or whatever
useful information could be gleaned
from the initial animal studies at Berke-
ley and, later, Chicago.
Working With Plutonium
The first shipment of cyclotron-pro-
duced plutonium sent to Los Alamos
arrived in October 1943—650 micro-
grams of plutonium-239 shipped from
Berkeley as a semi-purified, partially
decontaminated plutonium salt.* Op-
penheimer immediately informed his
staff that “purification of the 650 [mi-
crograms] of Pu, at least to the point
where the material is suitable for physi-
cal work, should be carried out with
maximum speed.” Several 100-micro-
gram allotments of this plutonium were
committed to study the isotope’s nu-
clear properties. The remainder was as-
signed to Kennedy’s Chemistry and
Metallurgy Division for research on re-
moval of light-element contaminates.
The first reactor-produced plutonium-
239 was shipped from the pilot reactor
in Clinton, Tennessee, in January 1944
The Human Plutonium Injection Experiments
Number 23 1995 Los Alamos Science
185
*In July 1943, 165 micrograms of cyclotron-pro-
duced plutonium-239 were lent to Los Alamos
from the Met Lab for the study of its fission
properties. The plutonium was returned later that
same month.