The Human Plutonium Injection Experiments

 

In 1944, not only were there uncer-

tainties in the animal data, but meth-

ods for measuring the amount of plu-

tonium retained in the bodies of

workers were not well defined.  Peo-

ple realized that because plutonium

was an alpha emitter, the radiation

was readily absorbed by the sur-

rounding material, and analysis of

excreta for plutonium activity offered

the most promising route for estimat-

ing body burdens of internal plutoni-

um.  However, the low excretion

rates predicted from animal experi-

ments would make analysis difficult.

On the first day after injection, when

the fecal and urinary excretion rates

were at their highest, the total amount

excreted in the urine in 24 hours was

less than 10 per cent of the amount

injected, and similarly with feces.

The excretion rates then dropped

rapidly for several weeks, finally lev-

eling off, for urine, at only 0.01 per

cent of the injected plutonium.  

Although large doses could be inject-

ed into animals to insure good analyt-

ical results, the same could not be

done with humans.  If an 0.01-per-

cent daily urinary excretion rate was

true for humans, a 24-hour urine

sample from a subject with 5 micro-

grams of retained plutonium would

contain only 0.5 nanograms (nano =

10

-9

) of plutonium (see “Estimates of

the Detection Regime”).  

Excreta samples also had the problem

that most of the alpha radiation

would be absorbed by the sample

mass.  Thus, analytical techniques

had to be developed to reduce the

mass of other material and to concen-

trate the plutonium by dissolving,

evaporating, or ashing the sample and

by extracting, precipitating, or plating

the plutonium for measurement of

alpha activity.

 

Ion-exchange.  That summer, the

Met Lab’s Health Division developed

a urinalysis procedure for isolating

and detecting tenths of nanograms of

plutonium in urine.  The method was

based on direct isolation of the pluto-

nium by passing an acidified 100-mil-

liliter urine sample through a cation-

exchange resin.  After the resin had

captured the plutonium, the concen-

trated metal was eluted from the col-

umn and transferred to a counting

plate where the alpha activity was

measured.

In July 1944, Hempelmann was in-

formed of the Met Lab urinalysis

procedure and of the apparent con-

stant 0.01 per cent urinary excretion

rate derived from animal studies.

Several items—such as his calcula-

tion for the dose to the lungs from a

1-microgram plutonium dust particle,

early results from the animal experi-

ments, and a difference of opinion of

a factor of 10 about what constituted

a “safe” alpha radiation dose for tis-

sue cells—were beginning to make

him think that detection methods

needed to be sensitive to lower levels

than the proposed 5-microgram toler-

ance limit.  Also, the Met Lab had

determined that blood counts gave

evidence of over-dosage but not until

a relatively late stage following depo-

sition of the plutonium in the bone.

Thus, Hempelmann informed Oppen-

heimer that analysis of excreta sam-

ples in the early stages following ex-

posure, when the excretion rates were

highest, was the only method for

early detection of overexposure. 

Hempelmann assigned a biochemist,

Anne Perley, to investigate if the

Chicago procedure was suitable for

detecting 1-microgram body burdens.

By the end of the month, she in-

formed him that the combination of

the Met Lab procedure and the Los

Alamos alpha counters were inade-

quate for detection of plutonium lev-

els consistent with 1-microgram body

burdens.  In fact, attempts to use the

The Human Plutonium Injection Experiments

Number 23  1995  

 

Los Alamos Science  

191

 

Detection of Internal Plutonium

the program that he, Warren, Kennedy,

and Oppenheimer had decided upon.

Los Alamos would develop “chemical

methods of determining plutonium in

the excreta and in tissues and of ioniza-

tion methods of detecting plutonium in

the lungs.”  Experiments at Los Alamos

with animals would be used to check

the detection methods.  The third part

of the program would involve “tracer

experiments on humans to determine

the percentage of plutonium excreted

daily.”  

It was stated that “when satisfactory an-

alytical methods have been developed

in this laboratory the problem of carry-

ing out further metabolic studies will be

turned over to another medical group,

presumably the Rochester group.”  Ini-

tially, Rochester would determine the

lethal dose in animals using plutonium

supplied by Los Alamos.

The excretion rate. By February

1945, Los Alamos, the Met Lab, and

the Berkeley groups all had analytical

methods they felt were adequate for the

analysis of plutonium in excreta (see

“Detection of Internal Plutonium”).

They could thus turn to the next puzzle,

the ratio of excreted to retained plutoni-

um.  Much of the animal data showed

that a constant daily urinary excretion

rate occurred within two or three weeks

that was 0.01 per cent of the initial in-

jection.  By March, urine samples from

Los Alamos workers were indicating,

based on the 0.01-per-cent rate, that

some of the workers were approaching

or had exceeded a body burden of one

microgram.  Concern about this situa-

tion was mounting.

There were other discrepancies and

concerns.  Numerous workers with high

nose-swipe counts had no definite sign

of plutonium in their urine.  Was this

due to hand contamination of the nose,

insoluble plutonium particles that had

not reached the circulatory sytem, or

large particles still lodged in the upper

bronchi and nasal passages?  The large

variations in the animal data for the uri-

continued on page 194

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