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.