RETENTION OF SUB-MICRON AEROSOLS IN THE HUMAN
RESPIRATORY TRACT’
By J. N. Stanwarn and P. E. Morrow
University of Rochester, Rochester, New York
Since the 1930’s there has been a steady
growth in our appreciation of the parameters
which govern the deposition of dust in the
respiratory tract of man and laboratory animals. Particle size, shape, density, and the
anatomical and physiological characteristics of
the respiratory system all play 4 part. Of
cardinal importance in these is particle size.
A summary of our knowledge of the role of
the particle size, or was until recently, virtually
a summary of our knowledge of the deposition
process. In Figure 1 is a graphic summary of
some key studies on this subject. This is
reproduced from a very timely and informative
survey by Hultqvist [1].
As indicated in the legend, curves 1-5 are
derived from theoretical considerations.
They
relate to ideal particles in model lungs, in
postulated gravitational and centrifugal fields.
Curves 6-12 are based on experimental data.
Differences between the experimental curves
are due in part to differences in the respiratory
characteristics and methodology in the various
experiments.
Note that the graphs refer to total retention
in the respiratory tract, i. ¢., retention in the
upper respiratory tract as well as the alveoli.
If the percentage lower respiratory tract reten-
(This paper was not originally intended as more than a 16-15 minute
summary of some current experimental work being done by one of us
(P. EB. Morrow}, However, in view of the rathor extensive reviews presented on other phases of the fatlout problem at this symposium, the
Paper wus expanded somewhat to fit a more general considezation of
possible inhalation hazards in a fallout field. The experimental work
appeated a8 an abstract in the American Journal of Physiology, £87; 618,
1956, and in a University of Rochester Atomic Energy Project report
(OR-604). The carmplete manuscript has beenaccepted for publication:
in the A. M. A. Arctilves of Industria! Health, ‘This betng the casa, the
Manuscript was revised somewhat In proof to omit experimental details
which can now be found elsewhere.
448029 O--G8—~—14
tion were plotted the relationship would be
similar excepta distinct maximumwould appear
at about 1-2 x diameter. This occurs because
particles above 5 ,» seldom reach the lower
respiratorytract.
The results show considerable variation in
detail, but agree in showing two things:
(1) less percentage deposition at sizes between 2 » and 0.2 » than at either larger or
smaller-sizes. (This does not supply a minimum in total mass deposition.)
(2) almost complete lack of experimental
information and no notable unanimity of
theoretical opinion in the submicroscopic size
range (i. «., <(0.1 4) where particles are relatively unaffected by gravity or the usual
inertial forces.
From the standpoint of the hazard from inhaled fallout material, other things being equal,
it will make a great deal of difference whether
the radioactivity is:
(a) Predominantly on particles so large
they will not be respired.
(6) Predominantly on particles in the size
range which will deposit in the upper respiratory tract.
(ec) Predominantly on small particles which
will be retained largely in the deeper portion
of the respiratory (ree.
Data on the particle size distribution as re-
lated to the activity distribution are not generally available for fallout activi
Obviously at earlytimes the activity distribu-
tion will presumably involve a wide range of
particle sizes. Later as settling or aggregation,
ete., occur the bulk of airborne activity may be
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