THE SHORTER-TERM BIOLOGICAL HAZARDS OF A FALLOUT FIELD
nique is about 63 percent“efficient” [11]. This
implies that particles under 1,000 A are primar-
fallout field may or may not be the same as the
distribution of particle sizes.
More informa-
tion on this point is needed from field tests.
bility that much of the activity at later times
ily involved with the 87 percent remainder.
U. 5. A., is in large measure tropospheric may
be a basis for the apparent preponderance of
radioactivity on “larger” particles. So one
able on the retention of the smaller size particles
hy the human.
must presume that the persistent atmospheric
radiation is in a colloidal state and that, provided not more than 10°~10' of these particles
occur/ml ofair, they arc likely to remain aloft
subject only to radio decay and washout due
to precipitation.
Animal experiments
(particularly on rat,
mouse, etc.) will probably underestimate the
risk of these smaller particles due to the extraor-
dinary surface to volume ratio of their nasalpharynx. On the other hand, man’s anatomy
and physiology appear to predispose him to
the deposition of these particles in amounts
uniquely higher than in most experimental
animals (with a few exceptions).
The above discussion should make it clear
that while the role of particle size has been
examined and discussed more than any other
factor, manystudies, including the present one,
point out that the physiology of respiration can
influence dust deposition as profoundly as particle size,
Direct application of the above experimental
data to quantitative prediction of how the
retention of fallout particles in the human
lung will be related to particle size is obviously
not poasible nor intended.
However,
it is
hoped that it will serve to emphasize some
points not usually appreciated and aid in the
planning of future field experiments.
ges. Physiol. 261, 219, 1955).
(Particularly number distribution vs. mass
distribution.) However, there is a real possimay be resident on smaller particles, and rela-
Thepossibility that “fallout,” as studied in the
indications that deposition of particles smaller than
0.1 # may be higher than predicted by theory was
published by Dautrehande, et al. (A. M. A. Arch. Ind.
Health 16, 179, W457) and an indication of the same
tendency was found in a paper by Veradr, ef al. (Arch.
tively little experimental information is avail-
(3) Samples collected by settling techniques
may or may not showthe activity of greatest
importance as an inhalation hazard.
(4) Preliminary experiments in humans with
a sub-micron size sodium chloride aerosol show
deposition (retention) to be somewhat higher
than predicted by theory, and to be related to
the breathing pattern of the individual. The
former is important since much of the radioactivity may be on relatively small particle
sizes. The latter indicates that, though the
primary physiologic factors have not been
isolated, there can be little doubt that the
manner in which an individual respires may
influence the deposition process quite significantly.
(5) While not immediately pertinent to the
short-term effects of a fallout field because of the
over-riding importance of external radiation
hazards, and the relative radioresistance of
the lung in an acute sense, these considerations
canbe of importancein the assay of the possible
damage from particles which may be present
in such a field—-and possibly inhaled under
conditions where the external hazard would
be minimized.
Obviously, they are pertinent
to evaluation of the longer-term hazards.
ADDENDUM
Since the date of the fallout meeting, two reports
pertinent to the distribution of radioactivity as a
REFERENCES
. Hutravist, B., Studies on naturally ocurring
jonizing radiations, Kungl. Svenska Vetenskapsakademiens Handlingar, Fjiirde Serien. Band
6. Nr. 3, 1-125, 1956.
2. Finversen, W., Uber das Absetzen kleiner, in der
Luft suspendierter Teilchen in der mensehlichen
Lunge bei der Atmung. Pfliigers Arch. fiir das
ges. Phystol., 236: 367-79, 1935.
3. Lanpant, H. D., Removal of air-borne droplets
by the humanrespiratory tract. The Lung.,
Bull, Math, Biophys. 12: 43-56, 1950.
4, ——ee, TRACEWELL, T. N., Lassen, W.
=
On the
Williamson (USNROL TR 152, 1957) and by Farlow
and Schell (USNRDL-TR 170, 1957), Also other
in the human lung. JI. Arch. Indusir. Hyg., 8:
359-66, 1951.
- Wiuson, J. A., La Mer, V. K., Retentionof aerosol
particles in the human respiratory tract as a
195
10. Vow Smonuciowskr, M., Versuch einer matrematischen Theorie der Koagulationskinctik Kolloider Josingen, Zietschr. phys. Chem. 20:
492-95, 1917.
11, Exsensup, M. and J. H. Haruzy, Radioactive
fall-out through September 1955, Science 124:
251-55, 1956.
12. Morxen, D, A. and P, FE. Morsow, The control
and measuring systems of an apparatus for the
study of respiratory tract retention, University
of Rochester Atomic Energy Project Report,
UR-415, 1956.
13. Monnow, P. E., FE. Menrnor, L, J. Casanerr,
D, A. Morxen, A study of the deposition of a
subinieronie aerosol in buman subjects, University of Rochester Atomic Energy Project
Report. UR-504, 1957,
14. Monrow, P. E., E. Menanor, L. J. Casarerr,
D, A. Morken, An experimental study of
aerosol deposition in human subjects, A. M.A.
Arch. Industr, Health (in press).
DISCUSSION
H., On the retention of air-borne particulates
a
cles under 1,000 A (0.1 ») diameter.
other hand, assay of fallout concentrations by
sedimentation (with possibly a small amountof
impaction and Brownian motion deposition) of
airborne radicactivity onto adhesive surfaces
iscommonly employed. Presumably, this tech-
These are by
J. N. Stannard and P. E. Morrow
function of particle radius, 7, Industr. Hyg. 30:
Dr. Lancuam. Thank you, Dr. Stannard.
Because of the time we are not going to be able
. Brown, J. H., Coox, K. M., Ney, F. G., Harcn,
much, purcly because the particle problem in
265, 1948.
a
ponderance of radioactivity (>90%) on parti-
CONCLUSIONS
(1) Particle size is a cardinal parameter
in respiratory tract. deposition.
(2) The distribution of radioactivity in a
T., Influence of particle size upon the retention
of particulate matter in the lung, Am. J. Pub.
Health, 40: 450, 1950.
7. Vaw Wu, A. M.. Parrerson, H. 8. The per-
centage of particles of different sizes removed
from dust-laden sir by breathing, J. Industr.
Hyg, 22: 31-35, 1940.
. Witkenine, M. H., Natural radioactivity as 8
tracer in the sorting of aerosols according to
mobility, Her. Sci. Inst. 28: 13-16, 1952.
. Murcer, T. T., A study of some physical properties
of an aerosol in relation to airborne decay products of radon, UR-~474, 1957; and Charging
and precipitation characteristics of sub-micron
particles in the Rohmann electrostatic particle
separator, UR-475, University of Rochester
Atomic Energy Project, 1957.
a
the work of Wilkening and others have indicated that in nature, one does encounter a pre-
RETENTION OF SUB-MICRON AEROSOLS IN HUMAN RESPIRATORY TRACT
function of particle size have appeared.
co)
194
to discuss this.
However, I would like very
this whole business has been that which is
always thrown at you when you are trying to
assess the hazards associated with inhalation of
radioactive materials.
Every time you make
a statement there is always some fedlow who
brings up the idea that this all depends on
particle size.
When he says that it is supposed
to stop you cold just like a doctor is supposed
to stop you when he says you have a virus
infection. So I think anything that can be
doneto get this particle size problem on a basis
of where you can say what specifically does
this mean to our problem, then I think we are
getting somewhere.