THE SHORTER-TERM BIOLOGICAL HAZARDS OF A FALLOUT FIELD 4 O 319 jLO]LOlLO LO] Lal to}Lopio 100 500 1000 16900 2000 07 0.0 O58 0.3 0.2 Fraure f--Vhyroid upinke of 1-181 as influeneed by trradiation. (MPC), == maximum permissible concentra. tion in water(uc/¢.c.) “ rsx effective half-life (days) J,=frection inhaled that arrives in critical body organ fe=fiaction ingested that arrives in critical body organ t==period of exposure (days) The basis of our present calculations for the maximum permissible burden of internal emitters goes back to either of Gwe concepts that are themselves based on human experience. We have had enough experionce with X-rays and gamma. rays to feel that 0.3 roentgen per week will not do appreciable damage to a personif taken throughout a workinglifetime. On the basis of 0.8 reentgen per week, then, the Subcommittees on Internal Tolerance or Internal Maximum Permissible Levels have chosen to relate the dose of the internal emitter to that amountof the internal emitter which will deliver the equivalent of 0.3 of a roentgen per week to a critical organ, usually the organ which shows the highest concentration of the matorial. We find that q, the maximum permissible amount in microcuries, is equal to a constant times the mass of the critical organ ‘times the 0.3 rem per week. The biologist. cannot even tell Dr. Morgan with certainty what the mass of thecritical organis. Obviously this is the fault of biological variability and not the biologists. This factor is divided by the fraction of the material in the total body that concentrates in the critical organ, that is, f;, Dr. Morgan gets these f, values from any animal experimentation that he can or anywhere he can find thei. Manyof us do only service to him by calling an occasional number fo his attention, But for that matter, no one is really certain in every case of every isotope what the fraction of that in the total bodyis concentrated in the critical organ. Especially is this trne of humans. This then is multiplied by the sum of all the energies - this of course can be gotten from physical date~-weighted for some or all the energies for each disintegration, weighted for the relative biological effectiveness of each. Now we really have him in the land of uncertainty. RBE is supposedly thateffect. of the radiation when compared to a similar effect of X-ray on an energy to energy basis. In other words, it is surprising to find that we do not agree to this day whether or not 100 ergs of energy delivered from an alpha particle is 1 or 20 times as effective as 100 ergs of energy delivered from X- or gamma ray. So obviously, RBE is an area of uncertainiy, and one which will probably remain uncertain for a great length of lime, because it seems now that RBE may be specific or may be different for every biological effect and every biological system thai one wishes to test. Then the factor N, which is the distribution factor, and in some cases is called the ignorance factor. It is into N that we can lump all of those uncertainties, including the uncertainty as regards the homogeneous distribution of the material in the critical organ. There, then, we can sec that there is plenty of room for improvement in the various numbers that go into the basic formula of calculating maximum permis- sible levels. Taking advantage of another human experience, it is customaryto relate the maximum per- missible level of internal emitters of bone seek- ers to 0.1 microcurie of radium, and the first formula I gave previously expresses this rela- tion. In other words, q now the microcuries of the unknownsubstance whichis the bone seeker DISCUSSION ON TOPIC V is equal to 16 divided again by the f;, the fraction of that in the total body which is concentrated in the eritieal organ, times the suimma~ Gion of the cnergies of all the disintegrations, each one weighted for its RBE and forits distribution and energy deposition in the critical organ. We cansee for that mattor that there is absolutely an area of uncertainty in whether or not a tenth of a microgram of radiumis a (rue base line in humans on which to base these data. But until better data are available, this thenis the best we can do. When wecalculate maxi- mum permissible concentrations of air and water we find that the MPC equal to a constant times q, the q which was derived in some manner as specified earlier, times the fraction of the material in the total body that is in the critical organ, divided by another biological uncertainty, and that is the fraction of that which is inhaled which ends up in the critical organ, times the effective half time, and the effective half timein this caseis the radiological half time times the biological half time divided by the sum of the two, all of that times one minus e raised to the 0.693 power times t, the time of exposure that we intend to let the individual receive in order (0 come to equilibrium, divided again by the effective half time. We see here, then, many places where the data could be improved by experimental data on humans or primates or for that matter even better animal data. For example, the biologi- cal half time of many of these substances has never been determined in animals. The fraction of that which is inhaled, which goes to the critical tissue, is very closely tied in with the problem Dr. Stannard was discussing this 229 factor, | would like to mention our own work which involves whole body human counting in which by means of the whole human body Cechniques (ihe Hquid senitillator at our place, and the crystal spectrometer at the Argonne), wefind it is possible to give as litle as 1/100th of the rem maximum permissible burden to a human and get biological turnover times by merely counting the individual at intervals. We have started through the periodic table using every good gamma emitter to iy to correlute biological turnover time in mice, rats, dogs, monkeys and man. Here we inject the material info the animal and merely count him in the whole body counter periodically to get the retention curves, Going through the periodic (able is a slow process. In fact, as I said at the Health Physies Society meeting, if we report on one sub-family each year, then we are assured of getting to attend the mecting for the next 18 years, We find that we are not quite keeping up with the schedule. You camot get through one subfamily of the periodie table in that length of time. Such interesting relationships are already starting to come out as trying to correlate the weight of the animal with the biological turnover time. Wefind that for sodium and potassium, if one plots the log of the weight of the animal species versus the biological half time one gets a nice straight line. When one gets to rubidium and cesium. up through the dog and monkey, one seems to get a straight line. Whenone gets to man, man no longer fits on the curve, The biological half time determined by whole body counting of cesium is of the tors reported in the literature, which are supposed to affect hing retention. order of 110 days in man; for rubidium it is of the order of 85 days. We hope by going through the periodic table and picking gamma emitters and giving (hem te human volunteers of we still have 16 others to go. We can then see a great degree of uncertainty that may exist where more information or more nuclides in humans especially, and primates, are sorely needed, even such a simple thing as a biological retention times, Another point 1 would like to mention, of course, is his very idea of retention of particulate matter in the hmg. Lf one looks in the International Commission handbook, and 1 am morning. size. Obviously this depends on particle Particle size is only 1 of 17 different fac- After we get the particle problem taken care turnover time. In regard to that particular we can eventually get more data on biological sure in the newversion of the National hand-