The Human Plutonium Injection Experiments

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.

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