230 DISCUSSION ON TOPIC ¥ THE SHORTER-TERM BIOLOGICAL HAZARDS OF A FALLOUT FIELD book, one. will find a very arbitrary decision posed to be on immerliatefallout, it was obvious deposited up to age 20 and maintained at the made on the disposition of radioactive particles in the lung, made primarily to enable us to go abead and calculate the maximum permissible air concentrations based on lung retention. One nation, Here our ignoranec beeomes even greater, though reading as muchof the informa- normal background from cosmic rays and radium. , of that which is inhaled or of those particles ean’tfeel that we are in any serious trouble. we are considering that for somatic changes; since strontium does not concentrate in the will find thal we arbitrarily say that 25 percent which are inhaled comeright back out without setling down on the mucous Hnings of the respiratory tract. We say 50 percent deposit in the upper bronchial tree. Twenty-five pereent of these particles gel on down into the alveolar sacs. This might be true for a specific particle size distribution. To think it would be true for all 17 of these conditions that 1 mentioned on which lung retention is dependent is asking for quite a bit, But anyway, in order to have » basis for calculation, we must assume this 25 pereent tums around and comes right back out, 50 percent deposits in the upper bronchial tree, 25 percent gets in the alveolar sacs. Of that which deposits in the upper bronchial tree wesayit is all essentially removed with a biological half time that is strictly a guess. We say of that which goes into the alveolar sacs, if the particle is insoluble, twelve and one-half percent of it turns around and comes up in the bronchial tree, and eventually ends up in the gut. T think Dr. Morgan said this morning that 61 percent ends up in the gut. I hope he meant 62.5 percent, because his pencil can pick up those differences. The biologists cannot tell the difference plus or minus a factor of 10. Of that 12% percent which remains in the alveolar spaces, all is assumed to be eventually absorbed and contributed to the body burden. Thatis a mode] on which our present concepts are based. To test this model in animals of various Lypes and especially in the humanis certainly one of the great needs and 1 think one of those things for which the biologists will éventually collect the data if they live long enough, and receive enough support from the various agencies, Lastly, something that has dominated this meeting entirely is this concern for the fallout problem. Even though this meeting was sup- the thinking was on long-term chronicfallout, such as may be involved in worldwide contamition from Operation Sunshine that one ean, T I think it is true that we in all probability may have the strontium content in children by 1970 up to maybe 1/100th or maybe 2/100ths of the maximumpermissible body burden for large populations, that being set at 0.1 micro- curie for strontium. As far as I can see all of the excitement. that we have just had over this problem, is hardly justified. There is hardly any doubt that we are dropping radioactivity on people, and we have, in keeping with the urgency of the Public Health Service, been pursuing this as a problem in order that we will know whatthe status of it is, and what to do with it before it ever becomes a problem, we hope. Let us merely question this 0.1 micro- curie for worldwide populations. Long term chronic studics are needed to really determine whether 0.1 microcurie of strontium is a maximum permissible level in the humansubject, one that we can live with and feel confident of. [would say thatit is probably a conservative one. If one calculates the radiation delivered to the bone from natural sources over a 70 year period under normal radium content soils and building materials, he comes up with the idea that the bone mayreceive about 8.5 rom per 70-yearlifetime. In high radium areas, it may be as much as 3 Limes that, or 4 times, which would be up to around 30 or 36 remper 70-year lifelime. If one takes one-tenth microcurie of strontium and assumes that this remains in the bone throughout a 70-year lifetime one comes up with about 18.5 rem per 70yearlifetime. . This is taking the pessimistic view, because we knowthat a major part of this strontium is laid downby age 20, and that in all probability maybe equilibrium will be maintained by ex- change. Maybe it won't. If one considers a factor of decay from age 20 on, then one would say that a tenth of a microgram of strontium normal radioactive decay rate to age 70 would deliver a dose to the bone that is about equal to This is cutting the numberpretty fine when gonads, we are considering thal we can only double the natural background. But until we do know where we are going,it is obviously wise to walk with caution. T might say still more fundamental and trou- 231 Ts the radiation partially delivered to an organ worse than to the whole body? I think the importanceof this can be seen when yousee Dr. Morgannow calculating maximum permis- sible levels on the basis of the radiation of a small arnountof thelarge howel. Is to irradiate the large bowel with 0.3 rem a week as bad as radiating the whole body? It may be that irradiating the large bowel is just as important because the large bowel may be a very sensitive organ. This T have said in summary of the sym- especially the second one. This formulais based posium here because it is my understanding that the Chairman has theprivilege of getting up and making broad sweeping statements and 0.3 of a rem to the whole body. sion. blesome in this whole problemof internal emitters is the formula that we gave earlier and on the concept that it is equally bad to give to an organ 0.3 of a rem per week asit is to give closing the mecting, which does not. allow his sweeping statements to be a subject of discus-