The Human Plutonium Injection Experiments

later microscopic examination of the

tumor revealed no evidence of cancer

and indicated that the diagnosis was in-

correct.  After another year or so in

which no other cancer appeared, the

physicians became completely con-

vinced that CAL-1 had had a benign

gastric ulcer.

CAL-1 lived for almost another 21

years and died in 1966 from heart dis-

ease at the age of 79.  Although CAL-1

lived much longer after the injection

than expected (based on the original di-

agnosis), his treatment, including the

operation in 1945, was independent of

the injection and was not altered be-

cause of the plutonium experiment.

The plutonium given to CAL-1 was ac-

tually a mixture of plutonium-239 (0.75

micrograms) and plutonium-238 (0.2

micrograms).  As noted earlier, Hamil-

ton had proposed using plutonium-238

in metabolic studies because the higher

activity of plutonium-238 made it easier

to analyze samples.  For the sake of

comparison, if plutonium were retained

in the body, say, at the one-microgram

level, urine samples would yield thou-

sands of counts per minute for plutoni-

um-238 compared to 7 counts per

minute for plutonium-239.  

At the same time, of course, the addi-

tional activity of the plutonium-238 in-

creased the radiation dose to the tissue

The Human Plutonium Injection Experiments

198

Los Alamos Science Number 23  1995

Figure 2.  The First Plutonium Urinary Excretion Curves

These urinary excretion curves for the first three injection patients, HP-12, CHI-1, and CAL-1, based on the data as originally ana-

lyzed in 1945, illustrate the main features of urinary excretion: a rapid initial rate, but at values much lower than what had been ob-

served for radium, and an apparent leveling off, after about 20 days, at a daily rate somewhere between 0.02 and 0.005 per cent.

The curves also illustrate various problems.  The initial excretion rate was relatively low for HP-12 (0.1 per cent), which might have

been due to his abnormal kidney function.  The curve for CAL-1 appears to be consistently lower than the other two; this could

have been due to errors in the injected dose (a possible factor of 2), differences in analytical techniques, or differences in the chem-

ical form of the plutonium.  It may have also been an indication that the excretion rate varied significantly from person to person.

There are instances of unexpected variations in the excretion rate, such as the high values for HP-12 after day 50.  As it turns out,

the latter values for HP-12 were obtained when researchers at Los Alamos were attempting to improve their analytical procedure

and not all the experiments were successful or the results reliable.  (Also, after day 42 there were errors in the days-after-injection

values—these samples were obtained from HP-12 later than shown, going out as far as day 89).  Finally, the long-term data for the

CHI-1 and CAL-1 patients suggested that the urinary excretion rate actually continued to fall slowly rather than to stabilize at an

0.01-per-cent daily rate.

 

20

 

40

 

60

 

80

 

100

 

120

 

140

Days after injection

0.001

0.01

0.02

0.05

0.1

1.0

Per cent of injected dose excreted

HP-12

CAL-1

CHI-1

*Recalculated in 1976 by Patricia Durbin

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for each mass unit of retained plutoni-

um (the total activity of the CAL-1 in-

jection was 3.55 microcuries;* the ac-

tivity of the HP-12 injection was about

0.3 microcuries).  As it turned out, be-

cause CAL-1 lived almost 21 more

years, he received the highest total radi-

ation dose of the eighteen patients in-

jected with plutonium.  His total effec-

tive dose-equivalent was 6400 rem,

which corresponds to about 309 rem

per year, or 858 times what the normal

U.S. citizen receives on average every

year from natural and manmade radia-

tion sources (0.36 rem).

The urinary excretion rate for CAL-1

started at 0.5 per cent, assumed about

the same rate as for the other two pa-

tients for the next 12 days, but then

reached a constant rate at or below an

0.01 per cent daily rate from about 15

days onward.  When data for all three

patients were viewed beyond 50 to 60

days after the injection, it appeared as

if the “constant” excretion rate actually

continued to fall off gradually.  For ex-

ample, by 100 days, the CHI-1 patient

had dropped below a daily excretion

rate of 0.015 per cent and, between

days 130 and 155, was averaging 0.008

per cent.  

Hamilton and his group, in a report re-

leased a year later on May 31, 1946,

stated: “The retention of plutonium in

this subject is so great that the loss of

this material can be considered negligi-

ble.  The half time of plutonium excre-

tion is probably greater than fifty

years.”

The May 31 report also stated that four

days after the injection, in the course of

the planned surgery, “specimens of rib,

blood, spleen, tumor, omentum, and

subcutaneous tissue were taken from the

patient.”  Analysis of the bone sample

showed that “the major portion of pluto-

nium deposited in the skeleton is to be

found in the bone marrow and trabecu-

lar [fibrous or spongy] bone.”  It was

also estimated that “87.2% of the pluto-

nium administered was deposited in the

skeleton, provided the rib sample is rep-

resentative of the skeleton generally.”

What were some of the main conclu-

sions of the initial injection studies?

An August 29, 1946, report of the

Chicago work (written by E. R. Russell

and J. J. Nickson) stated that:

The urinary rate of excretion of

plutonium in humans is exceedingly

low.  The best evidence available

at this time would indicate that the

“chronic” (150th day) excretion

rate does not exceed 0.01 percent

per day of the amount fixed in the

body.

In regard to fecal excretion, the report

stated:

The fecal rate of excretion of pluto-

nium fixed in the body is lower

than the urinary rate by a factor of

approximately three.  What evi-

dence we have would indicate that

the rate of fecal excretion does not

exceed 0.003 percent per day of

the amount in the body.

The May 31 report of Hamilton’s group

concluded:

This high degree of prolonged re-

tention, together with the tendency

of plutonium to become deposited

adjacent to the bone marrow in the

endosteal and trabecular regions,

makes the problem of chronic plu-

tonium poisoning a matter of seri-

ous concern for those who come in

contact with this material.

Reduction of tolerance limit. On May

14 and 15, 1945, before the results of

the third injection experiment (CAL-1)

were available, most of the people in-

volved in this work met at a conference

in Chicago to discuss the results of the

first two human experiments.  They still

could not reach a definite conclusion as

to what the tolerance limit for plutoni-

um should be.  

In a May 21, 1945, letter to Friedell,

Wright Langham stated that Los Alam-

os should “adopt a conservative arbi-

trary limit [of one microgram] for the

maximum tolerance dose and remove

all people from further contact with

material when they have reached that

limit.”  He agreed with Friedell that

“this is probably much too low.”  Nev-

ertheless, “the urgent need . . . for a

working basis and the failure of the

Chicago Meeting to establish a limit

seems to make it imperative that we

adopt a conservative value and go

ahead.”  He thought “it quite likely that

further work on the part of other groups

will eventually establish a legal toler-

ance limit of at least one microgram,”

but in the meantime, the practice of

consistently retiring workers below that

limit would take care of “the medico-

legal aspect” and, “of still greater im-

portance, [reduce the chance of] poi-

soning someone in case the material

proves to be more toxic than one would

normally expect.”

Langham also suggested that they “con-

tinue to collect 24-hour urine samples

from [HP-12]—collecting on every

third day as long as he is available.”

He wanted to test extrapolations of the

excretion time curve and to have actual

samples “with which to try to develop a

simpler method of assaying.”  Because

HP-12’s kidney function had shown

some abnormalities, he also suggested

repeating “our human study carefully

on an individual whose kidney function

has been established as normal beyond

question.”  

Toward the end of June 1945, after data

from the first three human-injection ex-

periments were available, the Manhat-

tan District Medical Office lowered the

provisional allowable body tolerance

for plutonium to 1 microgram.  (The

Hanford site, because of their operating

conditions, such as their new remote-

handling facility, was able to adopt an

even lower provisional limit of 0.5 mi-

crogram.)  The rationale for this reduc-

tion by a factor of five was based on

The Human Plutonium Injection Experiments

Number 23  1995  Los Alamos Science  

199

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