Ne AALS
(On
we
because the bulk of all initially inhaled insoluble matertal is sooner or later deposited in the
intestines, where it remains for longer periods before being eliminated,''
;
It ahould be emphasized that these deductions and experimental results in the laboratory
were obtained with insoluble radioactive particulate materials. If the radioactive fall-out ma- tertals had contained a high percentage of soluble and therefore absorbable substances, the
dangers from inhalation could be greater fromthe physiological standpoint, However, the
same physical factors would apply aa in the case of insoluble air-borne particles, with the exception that a considerable fraction of the largor particles, trapped in the upper respiratory
passages, would be absorbed into the general circulation rather than removed and subsequently
it seems apropos, in view of the repeatedly expressed concern'?:'.' over the potential hazard
from retaining a single particle of high activity in thy lung and its possible relation to subsequent lung cancer, to reiterate the results of some data, previously published only in UCLA
quarterly reports (Reports UCLA-175, 195, 216, and 238), which are pertinent to this problem
and also to the long-term {tnhalation hazard.
.
First, a controlled expertment was made in {00 rats to investigate possible carcinogenic
effects of large-particte retention, Five particles of pure silica, each measuring approximatety 1000 yp, were implanted in the left lung through a 15-gauge needle. The next week radioactive
particles of similar size and chemical composition (obtained fromthe site of Trinity shot)
were iniplanted by the same techniques in the right lung of the same animals. The radioactive
particles had reached a plateau regarding radtoactive decay and were water insoluble, The
radioactivity per five particles averaged 25 d‘min of alpha rays and 75 d/sec of beta-gamma
rays. At monthly intervals beginning 3 months after implantation, groups of 10 rats were
sacrificed, and attempts were madeto identify the particles on each side, Localization was
not possible in nearly 60 per cent; however, in these cases the entire thorax was ashed and
counted, and the original amount of beta-gamma radio .ctivity was still present, In a few
instances of this type, particles were identified in the pleural space at the base of the lung,
The important findings were that ({) there was no evidence, in microscopic sections tmmediately surrounding the position of the embedded particles, of malignant cellular change and (2)
the same foreign body reaction surrounded both radioactive and nonradioactive particles,
It 19 estimated that the amount of radiation received in the first {5 yp around each particle
during the {2-month period was approximately 80 rem, due primarily to alpha radiation. In
the next few millimeters the beta dose was estimated at 340 rep, The conclusions from this
{-year study were that the amount of radioactivity used waa too little and the time of exposure
was too short to induce neuplastic changes in surrounding lung tissue.
:
yes
- ce ote ot
-T
weer rk.
stbe
-“- wae
~
oy cs~*At peat
materials in the lungs over long periods of time. The present investigations have been limited
to short-term experiments designed to study only the acute or short-term aspects of the overall inhalation problem.
Although the primary objective of this project was to evaluate the acute inhalation hazard,
--: om ey emma
amounts of Isotopes such as Sr’*, Pu??, Ca", etc., in the bones or accumulatton of particulate
oe
>
aaaDe Na . widgetAD
well be considerable danger from repeated long-term (months to years) inhalation and concurrent ingestion exposures to radioactive air-borne particles. Under such conditions one is
dealing with long-lived isotopes and must consider the absorption and deposition of microcurie
et
urinary excretion, The danger from inhalation would not be from radiation to the lungs or intestines but rather to the bone marrow and possibly to the kidneys. But again, from physical
reasons alone, the danger from external radiation exposure to fall-out of soluble materials
also would far exceed that from all the inhaled and the subsequently swallowed particles combined if no protective measures were employed,
This discussion has been limited to an evaluation of the acute inhalation hazard from
radioactive fall-out materials under actual field conditions in Nevada and from data obtained
in the laboratory, where field conditions were simulated. The authors realize that there may
Vere!
=
aS
ological-safety factor with inhaled soluble particulate materials would be rapid and effective
ie “dé‘,
areas of the lungs would be negligible because of the extreme rapidity of absorption from such
surfaces, Likewise, the duration of exposure to the mucous-membrane surfaces of the respiratory passages and mucosal lining of the intestines would be relatively short. The main physt-
vin} wy
excreted in the feces. With soluble particulate materials the local radiation danger to alveolar