The Human Plutonium Injection Experiments

two kinds of experimental results.  The

first were the results of Met Lab toxici-

ty experiments with animals in which

the ability of plutonium and radium to

create recognizable and measurable in-

jury, such as death in a certain number

of days, was compared.  The results of

these studies did not agree with the as-

sumption, based on alpha energy de-

posited in tissue, that plutonium should

be about 50 times less toxic than radi-

um.  When radium or plutonium were

injected in amounts capable of causing

death in 30 days, they were essentially

equal in toxicity.  As the dose was low-

ered so that the number of days to

death increased, plutonium did become

less toxic than radium, but the ratio was

typically more like 4 than 50.  

The second type of experimental result

that lead to the reduction in the toler-

ance limit were autoradiographic stud-

ies of bone samples that showed how

plutonium and radium were deposited.

Much of both ended up in the bone, but

radium appeared to be distributed

throughout the volume of calcified

bone, whereas plutonium concentrated

on bone surfaces, especially those sur-

faces throughout the more biologically

active portions of the bone, such as the

bone surfaces where the marrow is lo-

cated (Figure 3).

In a report on the May 14 and 15 con-

ference on plutonium, issued July 23 by

the Met Lab, it was postulated that plu-

tonium had a higher level of acute toxi-

city than expected in relation to radium

because of the differences in deposi-

tion.  A large proportion of the radium

buried itself “deep in bony structures

where it is relatively innocuous from

the standpoint of acute toxicity.”  On

the other hand, plutonium concentrated

“in the endosteal layers of bone close to

the marrow and (at least to a greater

extent than radium) in soft tissues.”  In

fact, these same studies found that an-

other heavy-metal radioisotope, poloni-

um-210, was about 2 to 10 times “as

toxic as plutonium per unit of alpha-ray

energy dissipated in the body,” most

likely a result of the fact that polonium

concentrated in “highly radio-sensitive

soft tissues, such as the hematopoietic

and lymphatic tissues themselves.”

The Los Alamos Health Handbook.

On August 17, 1945, Los Alamos is-

sued the Chemistry and Metallurgy

Health Handbook of Radioactive Mate-

rials, outlining the hazards and safety

procedures for radioactive materials.

This handbook put into practice for plu-

tonium what had been learned from the

recent animal and human injection stud-

ies.  The introduction stated:

It was deemed essential to indicate

to the reader the intensive effort

being made to eliminate radiation

health hazards: hence, the detailed

description of monitoring instru-

ments and, as an example, the

chemical assay for 49 [plutonium]

and polonium in the urine. . . . The

worker exposed to nuclear radia-

tions is emphatically urged to fol-

low the two basic rules:  (1) know

all the possible radiation hazards

in a given job, and, (2) see that

proper protective procedures are

followed in the job.

The handbook included a discussion of

“tolerance” dose, stating that this

“means an upper limit to the radiation

energy absorbed per day indefinitely

which will be ‘absolutely safe,’ i.e.

which will produce no observable im-

pairment of any function of a large

number of healthy humans.”  The hand-

book went on to discuss the fact that a

“safety factor” was built into the toler-

ance limit, but that this factor could

vary from individual to individual.  

If the average individual stays

within the tolerance limits he can

be practically certain of suffering

no impairment of any of his func-

tions.  If he exceeds the tolerance

limits one cannot always predict

what the results will be.  In gener-

al, however if the tolerance limits

are not greatly exceeded, the indi-

vidual need not be considered a

“dead duck,” for in all probability

only minor disability may result.

The level established for plutonium was

The Human Plutonium Injection Experiments

200

Los Alamos Science Number 23  1995

Figure 3.  Deposition of Plutonium in the Bone

A neutron-induced autoradiograph (magnified 190 times) of portions of trabecular bone

(B) in dog, showing fission tracks from particles of plutonium deposited on the bone

surface (S).  Radium, in contrast, deposits throughout the bone volume (B).  (In 

 

Radio-

biology of Plutonium.  1972.  Betsy J. Stover and Webster S. S. Jee, editors.  (Universi-

ty of Utah/Salt Lake City: J.W. Press).)

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a body burden of one microgram.  If a

level of more than one microgram was

indicated by urine tests, the worker was

to be “removed from further contact

with the material.”  This level was es-

tablished by “a persistent excretion of 7

or more counts per minute per 24 hour

sample” (which corresponds to a 1-mi-

crogram body burden at an 0.01-per-

cent daily excretion rate and a 50-per-

cent counting efficiency).

In relation to plutonium, the handbook

added:

For materials such as 49, for

which there is not a large experi-

ence of long-period human expo-

sure, the tolerance amounts are

necessarily set with a conservative

view, thus affording the possibility

of additional safety factor.  Lethal

and chronic effects of 49 and Po

are being studied extensively in 

animals.  The rate of elimination

and the manner of deposition of 49

and Po in tissues of humans is also

being studied.  At some later time

the results of experimentation and

experience may lead to an upward

revision of the specified tolerance

amounts.  At present it is safe for

the worker to proceed with the

presently accepted tolerance 

values, keeping in his favor any

safety factors that may result from

conservatism in specifying the 

tolerances.

One of the safety factors was the fact

that it took several weeks for the 0.01

per cent excretion rate to be reached.

For a recent exposure, 7 counts per

minute in urine would correspond to a

body burden lower than 1 microgram.

Thus, there needed to be a “persistent

excretion” at that rate before a person

was actually removed from work with

plutonium.

The handbook also discussed most of

what was known about the relative dan-

gers of plutonium and radium, the dif-

ferences in deposition in the body for

these two metals, details of the testing

process (both obtaining the urine sam-

ples and analyzing them), the various

ways plutonium might enter the body

and the relative dangers of each path-

way, and the fact that plutonium “tends

to be deposited on the surface of the

bone in close approximation to the ra-

diosensitive cells of the bone marrow.”  

Hempelmann and his group obviously

wanted the people working with pluto-

nium to be as up-to-date as possible

about the material and its hazards and

to understand what was being done to

protect them.

Further Human Plutonium

Injection Experiments

By late summer 1945, there were still

serious concerns about the Health

Group’s ability to monitor the plutoni-

um workers adequately and about the

type of exposures they were receiving.

Hempelmann documented the situation

in a memo to Kennedy.

This is to confirm our telephone

conversation of 22 June 1945 dur-

ing which we discussed the recent

high exposure of personnel in the

[Plutonium] Recovery Group.  At-

tached is a list of all urine counts

of the people in this group and of

high nose counts during the past

month.  This indicates, I think, that

the situation seems to be getting

completely out of hand.

The main concern was the fact that, de-

spite “steps to improve their chemical

operations,” it was “a grave medical

problem.”  At Kennedy’s request,

Hempelmann reported these facts to

Oppenheimer in a memo on June 26,

stating that “as soon as we have evi-

dence that the men have reached toler-

ance, I shall . . . advise [Kennedy] that

they are to be removed from their

work.”  

Also troubling was the fact that the

urine assays and nose-swipe counts did

not correlate well.  It was expected that

in some cases, the urine assays would

rise.  But this would depend on whether

a high nose-swipe reading was due to

hand contamination or an actual inhala-

tion exposure and then, further, on

whether the form of the plutonium was

soluble or insoluble.

Likewise, there were questions about

the data from the first three studies.

The excretion data for CAL-1 appeared

consistently lower than the others; HP-

12’s data were in doubt because of his

abnormal kidney function; it was far

from certain at what value the excretion

rate leveled off, or even if it did; and

no autopsy tissue samples had been ob-

tained (CHI-1 would die early in Octo-

ber from his diagnosed cancer).  More

research was needed—such as a care-

fully controlled study using about 10

patients in which excretion samples

were obtained daily for about three

weeks.

On September 5, 1945, Langham and

Warren met in Rochester with others of

the Rochester group to complete the

overall plan for such a series of plutoni-

um injection experiments in humans.  A

summary of the plan written by Lang-

ham states that over three six-week pe-

riods, ten patients would be admitted to

the metabolism ward at Rochester for

the purpose of plutonium injections.

The first two weeks of each six-week

period would be a control period used

to “determine the degree of normalcy

of the metabolism of the subject, collect

blank feces, get the subject on a stan-

dard diet, and get ward attendants and

subjects in the habit of collecting all

urine and feces.”  One of the purposes

of the control period would be to estab-

lish “the normal radioactivity content”

of the patient due to elements such as

uranium, thorium, and radium that are

normally ingested in food.

At the end of the control period, each

subject would “be given five micro-

grams of product in a single intra-

venous injection.  For the next 24 days

The Human Plutonium Injection Experiments

Number 23  1995  Los Alamos Science  

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