The Human Plutonium Injection Experiments

Changes in production methods be-

tween Kelley’s first and second stints as

a plutonium worker had considerably

increased the ratio of plutonium-238 to

plutonium-239 in the material being

handled.  This fact, coupled with the

record of nose counts and exposures,

allowed them to distinquish somewhat

the “early” from the “late” plutonium

and, thus, to trace qualitatively the

movement of plutonium from the lungs

to other organs.  An article discussing

the findings stated:

[The] observations suggest (a) a

relatively rapid clearance rate for

plutonium in the lungs, compared

to that in bone and lymph nodes;

and (b) that a relatively small per-

centage of the material deposited

in the lungs must migrate to the

latter tissues. . . . [Also,] the rate

of clearance from the lungs to the

liver must be relatively fast and the

retention time in the liver must be

longer than in the lungs. 

The body burden. Equally important,

of course, was checking the reliability

of estimating a plutonium body burden

from urinary excretion data when the

exposure had been primarily through

inhalation.  Using a computer program

developed by James N. P. Lawrence of

the Los Alamos Health Physics Group

(see “A Computer Analysis of Plutoni-

um Excretion”), a body burden was cal-

culated for Kelley of 19 nanocuries

(equivalent to 0.30 micrograms of plu-

tonium-239).  This value was extremely

close to the autopsy estimate of 18

nanocuries (or 16 nanocuries if the 10

per cent in the lungs was subtracted).

In the discussion, Foreman, Langham,

and Moss concluded that “the . . .

agreement between body burden from

tissue analyses and estimated burden

from urine assays is so very satisfactory

that it is undoubtedly fortuitous.”  Nev-

ertheless, the agreement was a very

strong indication that the execretion

modeling approach was, indeed, close

to the mark.

Changes in the Maximum 

Permissible Body Burden

We have already discussed the fact that

in July 1945 the provisional tolerance

limit for plutonium was lowered from 5

micrograms to 1 microgram because of

the results of acute toxicity experiments

with animals and because of the deposi-

tion pattern of plutonium in bone and

soft tissue.  In September 1949 at the

Tripartite Permissible Dose Conference

at Chalk River, Canada, Austin Brues

presented the results of experiments on

rats and mice on the comparative

chronic toxicity of plutonium and radi-

um.  His results indicated that plutoni-

um was 15 times as damaging as radi-

um-226 when both were injected in

microcurie amounts.

Those results prompted the Conference

to recommend lowering the maximum

permissible body burden to 0.1 micro-

gram.  Langham later reported that

“this value placed an extremely strin-

gent restraint on air tolerance in such

facilities as Los Alamos.”  The Labora-

tory’s plutonium work would have been

seriously delayed.  The same month as

the Conference, Truman had announced

the Russians’ first test of an atomic

bomb, and arguments were building for

development of the hydrogen bomb,

which would need plutonium for its

“fission-bomb trigger.”  

After the conference at Chalk River,

Brues pointed out two mitigating fac-

tors.  First, the 15 to 1 toxicity ratio for

plutonium versus radium was based on

injected amounts.  However, about 75

per cent of the plutonium was retained

in rodents versus only about 25 per cent

for radium, which meant the ratio in

terms of retained dose should be a fac-

tor of 3 less.  Second, fifty per cent of

the radon from radium decay was re-

tained in man versus only 15 to 20 per

cent in rodents, which meant the ratio

should be reduced by at least another

factor of 2.  The combined factor of 6

meant that the fixed body-burden limit

for humans should be set at 0.6 micro-

gram rather than 0.1 microgram.

On the other hand, Langham’s analysis

had shown that only 8.7 per cent of a

plutonium body burden was excreted

after 5 years and 12.7 per cent after 20

years.  Those results supported the ac-

ceptance of a lower tolerance dose for

plutonium.  

Early in 1950, the Atomic Energy

Commission authorized an official max-

imum permissible body burden of 0.5

microgram (32 nanocuries) for plutoni-

um-239.  In 1951, the International

Committee on Radiological Protection

(ICRP) recommended 0.6 microgram

(40 nanocuries), and by 1953, both na-

tional and international committees

were recommending this limit.  The

main doubts about this limit concerned

use of the maximum permissible body

burden for radium-226 as the corner-

stone for calculating the plutonium bur-

den.  Although the critical organ for ra-

dium was the skeleton, that might not

be the case for plutonium—especially

when the main exposure route for

workers was chronic inhalation.  That

type of exposure appeared to result in

higher concentrations in the respiratory

lymph nodes, lung tissue, and liver than

in the skeleton.

In 1962, Langham, Lawrence, Jean Mc-

Clelland, and Hempelmann published

data on the analysis of autopsy samples

from eight Los Alamos plutonium

workers who had died of natural caus-

es, as well as the samples from Kelley.

The body burdens estimated from urine

data using Lawrence’s PUQFUA code

ranged from 0 to 20 nanocuries (0.0 to

0.3 microgram of plutonium-239), and

in fact, the three workers with the high-

est estimated body burdens also had the

highest concentrations of plutonium in

their tissue.  Calculation of body bur-

den from the tissue samples was not

done; in some cases, only a few sam-

ples had been obtained.  

In regard to distribution of plutonium in

the body, the tissue samples, ranked in

The Human Plutonium Injection Experiments

216

Los Alamos Science Number 23  1995

continued from page 213

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