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CHAPTER 1
INTRODUCTION
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OBJECTIVES
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1.2
BACKGROUND
Various dusts have been studied in this laboratory to determine their pulmonary absorption, distribution, and clearance, following single and/or repeated controlled inhalation exposures of rats and rabbits. The materials tested have included soluble agents, such as peni-
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at two test sites along the estimated midline of the fall-out path following a tower detonation
and, second, to measure the pulmonary uptake and clearance in rabbits following controlled inhalation exposures (UCLA dust chamber) to 0- to 5.0-p size particulate material ui .igh-level
radioactivity obtained from the Nevada Test Site,
cillin,' and insoluble particulate materials, such as P**-labeled 8. subtilis spores,* barium
sulfate,’ colloidal prodigiosin dusts,‘ and micropulverized radioactive siliceous material®’
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The purposes of this project were, first, to determine the pulmonary uptake of soluble and
insoluble particulate radioactive fall-out material in rabbits from acute inhalation exposures
from the Nevada Test Site having beta-gammaradioactivity of 1 x 10° a/min/g. The latter material was collected from Area 3 near Ground Zero 5 days after a tower detonation in the Upshot-Knothole series, spring 1953.
Results have demonstrated the importance.of particle size® in initial penetration and retention in the lungs vs the gastrointestinal tract (see Table 1.1), the relation of concentration
of dust particles* to the rate of pulmonary clearance (see Tables 1.1 and 1.2), and the relation
between duration of exposure’ In hours to the amountof insoluble material initially deposited
in the lungs (see Table 1.3). Most important, pulmonary clearance studies’ have shown that
insoluble dusts are removed rapidly upward from the lungs (exponential decline of pulmonary
content) and finally leave the body through the gastrointestinal tract (see Table 1.4). Furthermore, insoluble materials are cleared from the lungs morerapidly and efficiently in radiated
animals’ than in control animals owing to increased mucous secretions and phagocytic factors
(see Table 1.2). Soluble dusts, such as penicillin, are absorbed within a few hours from mu-
cous membranesof the entire respiratory tract and enter the blood stream.' Inhaled sodium
penicillin is absorbed and removed from the body at rates similar to those following intramuscular injection’ of this same material.
The tevels of radioactivity over the thyroid gland and in blood and urine samples in human
subjects following oral administration of I"*!-labeled Nal have been reported.” Preliminary
studies in rabbits have shown agreement with the humandata.
The operations of this field project were designed to gain information concerning the biological fate of short-half-lived soluble and insoluble isotopes, especially yt following|acute
inhalation exposures to fresh radioactive fall-out materials.
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