The Human Plutonium Injection Experiments

as

plutonium

nitrate.  One-and-a-half milligrams of

plutonium went to the Chicago Met

Lab on January 6, and six 

milligrams went to Los Alamos on Jan-

uary 17.  The quantity shipped to Los

Alamos was ten times larger than the

previous 650 micrograms and was large

enough, in its

glass vial, for Weisskopf to remark in

his memoirs: “I held on the palm of my

hand the first little grain any of us had

ever seen.  (I should not have done it, I

suppose, because of its radioactivity,

but it was such a tiny quantity that it

didn’t have any detrimental effect.)”*

Increasing 

amounts of plutonium followed in sub-

sequent months. 

At the Met Lab, they implemented safe-

guards for plutonium work by putting

linoleum on all the floors and having

their people use filter masks, rubber

gloves, and outer protection cloth-

ing.  Eating in the laboratories was

stopped.  Methods were developed

to monitor the air in the labs for

evidence of plutonium dust conta-

mination.  Similar safety proce-

dures were adopted at Los Alamos

at the beginning of March 1944.

Nose swipes.  By the end of

April, the Met Lab proposed a

plutonium air tolerance limit of

5

3

10

2

10

micrograms per cubic

centimeter of air (arrived at by

estimating the build-up of pluto-

nium in the lungs over a two-

year period for a worker

breathing the air 300 days a

year).  A procedure to detect

the inhalation of plutonium

dust using nose swipes had al-

ready been initiated.  A moist

filter-paper swab was inserted

into the nostril and rotated,

then the swab was spread

out, dried, and read in an

alpha detector.  A reading of

100 counts per minute or

higher 

was considered evidence of

an exposure.  

It was realized early with

this procedure that the

nose-swipe could easily be

contaminated with plutoni-

um from the worker’s

hand.  Steps were included to help

eliminate such contamination, and the

procedure was changed so that individ-

ual counts were taken from each nostril

to serve as a check.  (Nose swipes are

still used for plutonium workers.  Nose-

swipe counts and air monitoring are the

criteria used to decide when medical

treatment for the worker, including

prompt collection of urine samples and

the initiation of chelation therapy, is

necessary.)

The new procedure quickly bore re-

sults, because on May 30, the Los

Alamos Safety Committee informed

Kennedy that Ted Magel, one of the

The Human Plutonium Injection Experiments

186

Los Alamos Science Number 23  1995

*Victor Weisskopf.  1991.  The Joy of Insight:

Passions of a Physicist.  BasicBooks.

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workers making the first plutonium

metal-reduction runs, had a nose swipe

of 11,372 alpha counts per minute.

They felt it was apparent that safety

rules had been violated, and Magel was

instructed to follow those rules in the

future.  Apparently, in his desire to

make sure that a metal-reduction exper-

iment was being set up correctly, Magel

had lifted the lid of a crucible contain-

ing plutonium without first putting on

his respirator and so exposed himself to

plutonium dust particles.  Magel contin-

ued to work with plutonium until he

left Los Alamos a couple of months

later in August 1944.  (A positive urine

assay of a sample obtained from Magel

in 1945 confirmed the nose-swipe evi-

dence of exposure.)

By the end of August, Los Alamos had

received 51 grams of plutonium, and

scientists had used the material in over

2,500 different experiments.  In a

memo to Groves, Oppenheimer stated

that “the overall loss per experiment

has been about 1 per cent,” and that 36

grams remained.  One group at the

Laboratory was dedicated solely to re-

covery (and repurification) of the pre-

cious metal both from laboratory acci-

dents and from completed experiments.

Because they could never be sure what

substances or chemicals the plutonium

would be mixed with (for example, as-

phalt floor tiles in a laboratory spill or a

mass of burned material from a furnace

in a metal-reduction experiment), they

had worked out a flow chart for sepa-

rating plutonium from every other ele-

ment in the periodic table.  In his

memo, Oppenheimer continued:  “We

are now in a position to carry through

the operations necessary for final fabri-

cation with a very high yield (99%) and

to recover almost all that is not includ-

ed in the yield.”  He felt that the loss of

15 grams of plutonium “will be paid for

many times over by the effectiveness

with which we can deal with produc-

tion lots when they become available.”

There was, of course, great concern

about the lost material.  In September,

Kennedy wrote a memo expressing that

concern to the people in his division

working with plutonium.  Among other

things, he said, “the suspicion that sev-

eral grams of 49 are scattered some-

where in building D is not pleasant.  In

addition to its great value, this material

constitutes a definite hazard to health.”

He went on to describe efforts to im-

prove handling and recovery.

Plutonium Animal Studies

The quickest way to obtain more realis-

tic information about the toxicity of

plutonium was with animal studies.  It

was hoped that such studies would an-

swer a lengthy series of questions, in-

cluding how the amount of plutonium

taken into the body would depend on

the exposure mode (for example, oral

ingestion, inhalation, or absorption

through the skin), how retention would

depend on the chemical, physical, or

valence state of the plutonium, and how

much of the plutonium that had become

internal would be excreted and how

rapidly.  It was also unknown what

fraction of internal plutonium would

become “fixed” in tissue in the body

(see Figure 1) and how it would be dis-

tributed among the various organs.

When Hamilton started his series of an-

imal experiments, his guess was that a

plutonium tolerance dose of even 10

micrograms was “very conservative.”

His reasoning was most likely based on

the known excretion behavior of radi-

um, which was very high at first (more

than 20 per cent of radium administered

as a soluble salt was eliminated in hu-

mans the first day) but eventually be-

came very low (less than 1 per cent by

the tenth day and less than 0.3 per cent

by the twenty-first day).  It was thought

that the high elimination rate occurred

The Human Plutonium Injection Experiments

Number 23  1995  Los Alamos Science  

187

Figure 1.  Daily Urinary Excretion for an Internal Exposure

When a person or animal gets a quantity of a metal compound, such as those of pluto-

nium, radium, or zirconium, into their blood, the material may initially circulate in a rela-

tively “free” form.  Eventually, however, material that isn’t rapidly excreted—within a

few minutes, hours, or days—may deposit and become “fixed” in the tissue of various

organs and be less available to the blood stream.  As a result, a lesser amount will be

filtered out by the kidneys and excreted.  The two phases (the initial-intake phase and

the metabolized phase) will be evident in urine excretion curves as regions with differ-

ent slopes.  The duration and excretion rate of the two phases for a given element will

depend on that element’s chemical nature and biochemical affinities.  The figure shows

a theoretical excretion curve.

Days after injection

Fraction excreted

Metal free in blood

Metal fixed in tissue

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