The Human Plutonium Injection Experiments

where Y is the amount of plutonium

(expressed as a per cent of injected

dose) excreted in a single day, X is the

time of observation in days after the in-

jection, and a and b are constants de-

rived from the observable data by the

method of least squares.”  This equa-

tion was what they had been striving

for—a general formula describing the

amount excreted as a function of time

that could be extrapolated back to the

amount originally taken in by the

body—and it became known as the

Langham power-function model.

They were able to fit the mean daily

excretion data from fifteen patients to

this type of expression for 138 days

after the injection (see Figure 4).  How-

ever, if only the first ten days of data

were used, the best fit gave a different

exponent (-1.0 rather than -0.77).  They

felt that “this difference . . . may be

due to the clearance of the injected plu-

tonium from the blood during this early

period after injection.”  Thus, if a

worker was receiving chronic but vari-

able exposures to plutonium, an initial

screening assay could be used to deter-

mine if he should be removed from fur-

ther exposures, but a precise value for

the body burden could only be deter-

mined from later assays, after the first

ten days.  At that time, the initially

higher excretion rates for any recent ex-

posures would no longer be masking

the lower excretion rates of the less re-

cent exposures, and the assays would

reflect the actual amount accumulated

in the body.

Beyond 138 days, extrapolation of the

Langham power function “introduces

increasing uncertainty with increasing

values of X,” which made it difficult to

determine a “biological half-life” for

plutonium.  For those reasons, they had

felt it “important to supplement the

urine excretion data beyond 138 days 

to the greatest possible extent.”  As a

result, they had obtained additional

urine samples from two of the

Rochester patients (four consecutive

daily urine samples from HP-6 a year-

and-a-half after the injection, and four

consecutive daily urine samples from

both HP-6 and HP-3 four-and-a-half

years after the injection).  Those

longer-term data showed an excretion

rate consistent with that predicted from

the power-function model derived from

the 138-day data, which gave Langham

confidence that a one-term power-func-

tion model was a satisfactory way to

treat even long-term data.  

Los Alamos workers.  The plutonium

workers at Los Alamos were another

source of long-term urinary excretion

data.  Between 1944 and 1950, over

6000 urine analyses were made on

workers, and of these men, 27 excreted

measurable amounts of plutonium.  For

this latter group, the exposures had all

occurred in the early work between

1944 and 1946, and the records showed

one or more instances of high nose-

swipe counts in each case.  (Four of

these men had been removed from fur-

ther exposure to the substance in 1945;

twenty-two of the twenty-seven left Los

Alamos after 1946; and only a couple

remained working with plutonium after

1946).  Body burdens were estimated

for the 27 workers using the 0.01-per-

cent excretion model, and the values

ranged from 0.1 to 1.2 micrograms.

(These men are referred to as the UPPU

club—see “On the Front Lines.”  A

study of their health has been conduct-

ed from 1952 to the present, first by

Langham and Hempelmann and, later,

by George Voelz.)

One of the sources of concern to

Hempelmann and Langham was the

fact that, for some of the men, there

was a poor correlation between an ap-

parent inhalation exposure, as indicated

by a high nose-swipe count, and subse-

quent positive urine assays.  The poor

correlation could have been due to hand

contamination of the nose or the result

of an exposure to insoluble plutonium

particles that took awhile to be ab-

sorbed into the circulatory system and,

thus, detectable in the urine.  They con-

cluded that the nose-swipe data should

be treated as supplementary information

to the urine assays and moved ahead

The Human Plutonium Injection Experiments

Number 23  1995  Los Alamos Science  

211

Figure 4.  Plutonium Excretion for 138 Days

These excretion data for the human injection experiments, as presented in the original

Los Alamos Scientific Laboratory Report LA-1151 and reproduced in a 1980 

Health

Physics article, represent the observed means for the excretion data of the injected pa-

tients.  A power-function fit is given for urinary (squares), fecal (triangles), and total

excretion (circles).

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with their analysis, not knowing in

many cases the date of the primary ex-

posure to the worker.  

Although the plutonium body burden in

a given worker was the result of multi-

ple unknown doses that had built up

over an indefinite period rather than a

single, measured exposure, the chronic

exposure could be treated in terms of

an effective single dose given at some

effective time during the period the

worker was exposed in 1945.  The 138-

day power-function model was used

with the urinary excretion data of three

workers to calculate their body burdens

(two measurements separated enough to

be significantly different, and with no

exposures in between, were used in the

calculation).  Then the data of the

workers were combined with the addi-

tional long-term data of the injectees to

produce a longer excretion curve (Fig-

ure 5).  The urinary-excretion equation

derived from these data through 1750

days (almost 5 years) was:

Y

u

5

0.20 X

2

0.74

.

A similar equation was obtained for

fecal excretion, but it was based only

on data from the patients through 138

days.  This expression, plus a few ob-

servations of fecal excretion at later

times, indicated that roughly equal

amounts of plutonium are excreted in

the urine and the feces over the first

month.  By the end of a year, however,

although both excretion rates have

dropped in absolute terms, there is

about four times as much in the urine

as in the feces.  The equation for total

excretion of plutonium was obtained by

adding the separate expressions for uri-

nary and fecal excretion.  

By integrating the expression for total

excretion of plutonium, it was deter-

mined that only about 8.7 per cent of a

single plutonium dose is excreted in the

urine and feces over a five-year period

and 12.7 per cent in 20 years.  This

very slow rate of elimination led the

authors to conclude that it would take

about 118 years for the body to elimi-

nate half of the plutonium (the biologi-

cal half-life).  Futhermore, there was

“no practical significance . . . in permit-

ting the return to work of an individual

who has reached the maximum permis-

sible body burden.”  In other words,

“once a worker is retired from work

with plutonium . . . it must be assumed

that he is retired . . . for the balance of

his lifetime.”

What happened to the injectees? Of

the 18 people in Table 2 who were in-

jected with plutonium, 11 died less than

10 years later, before any long-term ef-

fects should have been seen.  Eight of

those 11 died within two years of the

injection; a ninth died about 2.5 years

after the injection.  The 8 people who

lived much longer survived for times

ranging from 10.9 years to 38.2 years.

HP-6 lived the longest, dying when he

was 82 years old.  In fact, four of the

patients lived into their eighties and

two into their seventies.

There is no evidence that any of the pa-

tients died for reasons that could be at-

tributed to the plutonium injections

(one cause of death is unknown).  Ten

of the patients died from the disease for

which they were admitted to the hospi-

tal prior to their injection (or from com-

plications related to that disease).  Of

the others, there is evidence that several

of them benefited from their stay in the

hospital.  For example, the patient with

Addison’s Disease (HP-6), the result of

insufficient steroid hormones, had ac-

cess in the clinic to steriods and the

close observation needed to achieve

proper regulation of a hormone-supple-

ment regime.  A woman patient (HP-3)

suffering from an unexplained weight

loss was thought to have some undiag-

nosed chronic disease; however, the

close medical scrutiny permitted the

physicians to recognize that she was in-

stead suffering from severe depression.

The increased attention she received at

the hospital may have helped her be-

cause she apparently recovered and

lived another 37 years.

On the other hand, with the end of the

war in 1945, many of the health

physics researchers throughout the

Manhattan Project moved on to other

jobs and organizations or became in-

The Human Plutonium Injection Experiments

212

Los Alamos Science Number 23  1995

Figure 5.  Plutonium Excretion for 1750 Days

These plutonium excretion data, as presented in the original Los Alamos Scientific Lab-

oratory Report LA-1151 and reproduced in a 1980 

Health Physics article, include the

additional long-term points for the plutonium injectees HP-3 and HP-6 (circles) and data

for three Los Alamos plutonium workers (triangles).  The top curve represents total

(urinary plus fecal) excretion; the lower curve, urinary excretion.

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