The Human Plutonium Injection Experiments

which meant the assumptions about

rapid initial elimination and slow “fix-

ing” of plutonium in the tissue were not

accurate.  After roughly 20 to 30 days,

the excretion rate appeared to become

constant, but again, at much lower rates

(about 0.01 per cent in urine).  The

total excretion rate (urinary and fecal)

at 21 days was about 10 times less than

that of radium.

The discovery that absorption of solu-

ble compounds of plutonium through

the gastrointestinal tract was very low

and essentially no absorption occurred

through the skin meant that the main

routes to internal deposition were ab-

sorption from contaminated wounds or

inhalation of dust particles.  Such con-

siderations led Hamilton, on May 5,

1944, to suggest treatment for puncture

wounds.

Hamilton informed Stone that in acci-

dents involving intramuscular injec-

tion—such as might occur if closed

systems at high temperatures exploded

and shards punctured the worker’s

skin—absorption of plutonium would

be slow.  Hamilton felt that “only a few

percent [of soluble product] would be

expected to be taken up within a matter

of an hour or so.”  He realized “that

analogies are frequently dangerous for

the purposes of comparison, but the su-

perficial similarities . . . to snake bite

come to mind.”  As a result, he sug-

gested a treatment that included, when

possible, the use of a tourniquet, which

“facilitates the washing out of the mate-

rial by bleeding and at the same time

retards absorption.”

Acute effects. By the end of 1945,

studies with rodents and dogs had

shown that the acute radiation effects of

plutonium were less “toxic” than highly

toxic chemicals (such as curare, strych-

nine, and botulinus toxin) but far ex-

ceeded any known chemical hazard of

heavy metals.  The clinical picture of

acute plutonium toxicity in dogs was,

superficially at least, quite similar to the

effect of a single lethal dose of total-

body x rays.  Although the initial vom-

iting and depression seen with x rays

were absent, weight loss and refusal of

food and water in the first days were

followed, around the tenth day, by the

final “shock” phase that included a rise

in body temperature, pulse rate, labored

breathing, and various hemorrhages.

Changes occurred in the blood as well,

including drops in white and red cell

counts.  However, other animal species

showed certain dissimilarities between

acute plutonium toxicity and total-body

x rays.  

The acute lethal dose for animals ap-

peared to be somewhere in the range

from 400 to 4000 micrograms of pluto-

nium per kilogram of body weight, de

pending on the species and, to a lesser

extent, on the chemical form of the plu-

tonium.  Damage tended to occur more

specifically in the liver, kidneys, and

spleen and to red blood-cell production

in the bone marrow.  In rats, about 

60 per cent of the retained plutonium

ended up in the skeleton and 18 per

cent in the liver.

At that time, very little of the experi-

mental work extended over a period of

more than six or seven months, so the

picture of chronic plutonium toxicity

was essentially a guess.  A few bone

tumors and one instance of bone thin-

ning had been observed in rats and

mice.  It was not at all certain whether

the various effects, including those to

the blood, were progressive or whether

they could be extrapolated to lower

doses.

Certainly, extrapolating the results of

animal studies to humans had to be

done with caution.  Experiments with

other toxic substances had shown in-

stances of dramatic differences between

animals and humans.  Rats, for exam-

ple, will tolerate quantities of deposited

radium per unit of body weight that

would be lethal to humans, and various

inbred mice are capable of surviving

huge doses of external gamma radiation

compared to humans.  Likewise, any

study involving skin was particularly

suspect because of the very great differ-

ences between human skin and those of

animals.  Thus, the animal studies

could only be suggestive of what was

expected to happen in humans.

The Human Plutonium Injection Experiments

Number 23  1995  Los Alamos Science  

189

Table 1.  The Metabolic Behavior of Radium and Plutonium in Animals

Property

Radium

Plutonium

Initial excretion (rats)

urinary (first day)

~15 %

~0.7 %

fecal (first day)

~16 %

~2.3 %

Total excretion in 25 days (rats)

urinary

~23 %

~2.5 %

fecal

~32 %

~25.0 %

Overall deposition

bone

99 %

~50 %

liver

—

~30 %(at first)

Bone deposition

within the 

surface of

mineralized bone

“active” bone

---

Planning for the Human

Injection Studies

By August 1944, despite the efforts of

a full-time chemist at Los Alamos and

another at Chicago, no satisfactory

method of analyzing excreta that could

consistently detect 1-microgram body

burdens had yet been devised (assum-

ing the 0.01-per-cent urinary excretion

rate suggested by the animal experi-

ments).  An ion-exchange method de-

veloped by the Met Lab was satisfacto-

ry at the 5-microgram level, but

Hempelmann was convinced it was im-

portant to achieve even lower levels of

detectablility (see “Detection of Internal

Plutonium”).

People in the Chemistry Division at

Los Alamos were concerned “about the

inability of the Medical Group to detect

dangerous amounts of plutonium in the

body.”  They had already had instances

of significant inhalation exposures and

one accident in which a chemist inad-

vertently swallowed an unknown, but

small amount of plutonium solution

(see “A Swallow of Plutonium”).  In

addition, there had been five accidents

involving wound exposures.  They

could not afford to continue using

guesswork as the basis for transferring

skilled workers who had experienced

plutonium exposures away from priority

work.  

As a result, on August 16, 1944,

Hempelmann proposed a new research

program to Oppenheimer.  The first

order of business would be “develop-

ment of methods of detection of pluto-

nium in the excreta.”  Hempelmann

also stressed the importance of deter-

mining “the factor by which the amount

of plutonium in the excreta must be

multiplied to ascertain the amount in

the body” and of developing “methods

of detection of plutonium in the lung.”  

Oppenheimer authorized work on the

detection of plutonium in both excreta

and lungs, but he was concerned about

balancing priorities.  He said, “in view

of the many urgent problems facing the

laboratory, it should be carried out with

as small an investment of personnel as

possible . . . fewer than ten people.”  In

the same vein, he continued: “As for

the biological sides of the work, which

may involve animal or even human ex-

perimentation . . . it is desirable if these

can in any way be handled elsewhere

not to undertake them here.”  Los

Alamos lacked the appropriate medical

research facilities, and Oppenheimer

suggested that Hempelmann and he

“discuss the biological questions with

Colonel Warren at a very early date.”

Warren, of course, had by now been in

charge of the medical programs for the

Manhattan Project for over a year.  It

was logical that biological research

should be carried out at a site, such as

Rochester, which housed the appropri-

ate staff and facilities.

A three-part plan. Groves, informed

of the plutonium exposure problems,

apparently made sure that Warren was

in Los Alamos about a week later.  On

August 29, Hempelmann summarized

The Human Plutonium Injection Experiments

190

Los Alamos Science Number 23  1995

A Swallow of Plutonium

On August 1, 1944, a sealed tube containing plutonium chloride solution

ejected part of its contents while being opened.*  Gases had built up, most

likely from the dissociation of water by the alpha radiation, and some of the

solution shot through the narrow tube out against the wall when the pres-

sure was released and the gases “boiled.”  Don Mastick, the young chemist

working with the plutonium, realized from the taste of acid in his mouth that

part of the solution must have bounced off the wall into his mouth.  

It was estimated that about 10 milligrams of the material was lost, mostly on

the walls of the room, with some on Mastick’s face and some swallowed.

Although his face was thoroughly scrubbed, the skin remained contaminated

with about a microgram of plutonium.  His mouth was also thoroughly

washed, but for many days afterwards, he could blow at an open-faced ion-

ization chamber across the room and cause the needle to go off-scale—the

level of contamination estimated to be about 10 micrograms.  (This last fact

suggests that the plutonium solution may have had other radioactive conta-

minants in it since it was later found not to be possible to detect plutonium

deposited in the lungs through ionized air molecules.)

Hempelmann pumped out Mastick’s stomach to retrieve much of what had

been swallowed (analysis of the contents for plutonium registered 4098

counts per minute, which corresponds to only about 60 nanograms).  Since

very little would have been absorbed through his gastrointestinal tract, Ma-

stick ended up with only a barely measurable body burden.  His initial 24-

hour urine assays, when the excretion rate was highest, were only 5 to 7

counts per minute, which translates to well below a 1-microgram body bur-

den.  Some plutonium was absorbed, of course, and improved assay meth-

ods available in the early seventies were able to detect small amounts of

plutonium in his urine thirty years later (hundredths of counts per minute).

*The 10 milligrams that were ejected in the accident were not “Los Alamos’ entire supply of pluto-

nium,” as reported elsewhere (for example, by Eileen Welsome in her 1993 articles in the

 

Albu-

querque Tribune  and in the October 1995 Final Report  of the President’s Advisory Committee on

Human Radiation Experiments).  In March the first 1-gram reduction of plutonium to metal had

been performed at Los Alamos, and by the end of August, the Laboratory was working with over

50 grams of plutonium (5000 times more than the amount sprayed at the wall).

---