ATTACHMENT 21 LAB-H-4 January 20, 1950 Dr. Shields Warren, Director Division of Biology and Medicine U.S. Atomic Energy Commission Washington, D.C. SUBJECT: RADIATION TOLERANCES PROPOSED BY THE CHALK RIVER PERMISSIBLE DOSE CONFERENCE OF SEPTEMBER 29-30, 1949 Dear Dr. Warren: The Technical Director of the Los Alamos Scientific Laboratory has asked the Laboratory's Health Division to prepare evidence to support the request that the tentative tolerances proposed at the Chalk River conference be carefully re-examined before any move is taken to adopt them as official AEC operating tolerance values. His move resulted from the fact that, if accepted officially, the extremely conservative tolerances proposed at the conference may have a drastic effect on the efficiency and productivity of the Los Alamos Laboratory. Their official adoption will undoubtedly force major alteration in both present and future laboratory facilities and may add millions of dollars to the cost of construction of the permanent building program now in the planning phases. In making his request for reconsideration of the Chalk River values, the Director stated emphatically that the operations of the Los Alamos Laboratory would be curtailed or stopped if such action were necessary to the reasonable and sensible protection of the personnel. The seriousness of this action, however, seems to be adequate reason for requesting that official adoption of the tolerances by the AEC be postponed until they have been carefully reviews in order to make certain that the values are not unnecessarily conservative. The tolerances which are of greatest concern to this Laboratory are those for plutonium, polonium and uranium. Los Alamos is primarily concerned with U235 containing 1-4 per cent of U234. No tolerance was proposed at Chalk River for this material, however, if values are chosen that are consistent with those proposed for plutonium, natural uranium, and U233, another very important Los Alamos operation will be seriously affected. Since the chalk river meeting, I have talked to and corresponded with a number of persons regarding the conference proposals and many of them agreed that re-examination of the values would seem to be highly desirable. I will try to point out in the following pages some of the reasons why reconsideration of the tolerances seems to be in order. The discussion will be confined to the body and air tolerances for those substances that are of primary concern to the Los Alamos Scientific Laboratory. 1 CONFIDENTIAL 236-39-19 FOR OFFICIAL USE ONLY REPOSITORY LANL/RC COLLECTION TR 6704 BOOK No. 236, G-3 FOLDER 39 VERIFIED UNCLASSIFIED JA BROWN FSS-1b 10/10K1 COPIED FOR HSPT PUBLICLY RELEASABLE LANL Classification Group William W. Hirsch 8/12/"illegible" "illegible" "illegible" 9/15/"illegible" COPIED DOE CONFIDENTIAL 236-39-20 FOR OFFICIAL USE ONLY COPIED/DOE LANL RC Dr. Shields Warren In order to emphasize the fact that the members of the Los Alamos Scientific Laboratory are not the only group who feel that values recommended at the Chalk River conference are open to question, I am including photostatic copies of letters I have received from D. K. Z. Morgan and Dr. Robley Evans. I have also included for your information a preliminary draft of a report covering the experience of the Los Alamos Scientific Laboratory with the plutonium health problem. Sincerely yours, Wright H. Langham WHL/ea:s Encls. 2 CONFIDENTIAL 236-39-21 FOR OFFICIAL USE ONLY COPIED/DOE LANL RC I. Plutonium A. Body Tolerance Dose for Plant Personnel -- The Chalk River Permissible Dose Conference tentatively proposed 0.1 ug. of plutonium as the tolerance dose for plant personnel. They arrived at this value by the following reasoning: 1.0 ug. of radium was accepted as the known or estimated fixed minimal damaging dose. The amount of plutonium equivalent to 1.0 ug. of radium was calculated merely by taking the ratio of their half lives -- 1 x 24,000 years over 1600 years = 15 ug. plutonium. Acute toxicological experiments in rats were then cited which seemed to show that plutonium on a microcurie basis was 5 to 15 times as toxic as radium. On the basis of this information, the committee chose to introduce a biological toxicity factor of 15 into the previous calculation which gave a 1 to 1 ratio between plutonium and radium (on the weight basis), resulting in an estimated fixed minimal dose of 1.0 ug. of plutonium. By continued analogy with radium, the estimated safe dose fixed in the body for plant personnel became 0.1 ug. It is the opinion of some of us that this tolerance is unnecessarily low. Some four reasons for believing this are as follows: 1. There is little justification for introducing the biological toxicity factor of 15 since some of the prominent persons in the field believe that acute toxicity experiments have little or no relation to the establishment of a chronic tolerance dose. (See paragraph 2, page 3 of accompanying letter from Dr. Robley Evans). 2. The choice of the biological toxicity factor may be drastically dependent upon the time after injection at which one considers the results. As an example, the accompanying graph taken from the Rochester Report, UR-44, showing the relative acute toxicity of radium, plutonium and polonium shows 1 FOR REFERENCE SEE (11bb06.gif) 2 CONFIDENTIAL 236-39-23 FOR OFFICIAL USE ONLY COPIED/DOE LANL RC that the relative toxicity of these various substances approach unity with increasing time. If one chooses to use the mean survival time at about twelve days after injection as a criterion of the relative biological toxicity, plutonium may be about 35 times as toxic as radium. According to this graph the relative toxicity at about 350 days should be essentially 1 to 1. In fact, the two curves may actually cross after 350 days at which time, according to this reasoning,m the toxicity of plutonium may actually be less than radium. It is therefore, our belief that the biological toxicity factor of 15 has no more foundation in actual experimental observation than does any other number from 0.1 to 35 that one may care to select. 2. The method of deriving the plutonium tolerance proposed at Chalk River did not take into consideration the retention of fifty per cent of the daughter products of radium decay. This consideration will make a difference of approximately a factor of 3 in the energy ratio between radium and plutonium. The calculation should be as follows: FOR REFERENCE SEE (11bb07.gif) As can be seen from the above calculation, the relative ratios of the energy delivered to the tissues by radium and plutonium should be approximately 45 to 1 instead of 15 to 1, thereby making a difference of a factor of 3 in the calculation of an estimated fixed minimal damaging dose of plutonium from that of radium. 4. The calculation of the estimated safe dose of plutonium from other considerations gives little support to the necessity of choosing a tolerance value as low as that proposed at the Chalk River meeting. If one considers the tolerance value of plutonium from the accepted beta-gamma tolerance of 3 FOR REFERENCE SEE (11bb08.gif) 4 FOR REFERENCE SEE (11bb09.gif) 5 FOR REFERENCE SEE (11bb10.gif) 6 FOR REFERENCE SEE (11bb11.gif) 7 II. Uranium A. Body Tolerance Dose for Plant Personnel --- 1. Natural uranium -- Two different values for minimal damaging amounts of natural uranium were suggested at the Chalk River conference. For soluble salts, 120 ug. was proposed as the "minimal damaging dose" based on chemical toxicity to the kidney. For insoluble compounds, 150 mg. was proposed as the "minimal damaging amount" on the basis of irradiation danger to the lung. It must be assumed from the philosphy of the meeting that the maximum permissible dose of natural uranium for plant personnel should be a factor of 10 below the above values (soluble salts, 12 ug., insoluble salts, 15 mg.). The question immediately arises as to whether the 120 ug. value for soluble salts of natural uranium was not meant to be the maximum permissible dose for plant personnel. Howland (Ntl. Nuclear Energy Series, VI, 1 pages 993-1017) has summarized and discussed the literature on human exposure to uranium compounds. The information that was presented does not indicate the necessity of such conservatism. In fact, numerous workers were reported as excreting as much as 400 ug. per day in the urine. The body content in these cases must have been higher than 400 ug. and no symptoms of kidney damage, even of a transitory nature, were observed. Six human tracer studies conducted by Bassett, et al 'UR-37) failed to show any kidney symptoms until the dose was increased to 3910 ug. (70.9 ug/Kg body wt) of uranium as +6 acetate. Even at this dosage the symptoms were a transitory elevation in urinary protein and catalase. This dose was 33 times the minimum damaging dose proposed at Chalk River and 330 times the proposed maximum permissible limit for plant personnel. Neither do toxicological studies on animals bear out the necessity of such a low minimum damaging dose. 8 CONFIDENTIAL 236-39-29 FOR OFFICIAL USE ONLY COPIED/DOE LANL RC FOR REFERENCE SEE (11bb12.gif) the potential hazard to the bone and to the kidney created by this material seems to be of the same order of magnitude. B. Uranium Air Tolerance 1. Natural uranium - The maximum permissible air content of natural uranium was considerably confused in the various reports of the Chalk River Conference. The value appearing in the first and second versions gave 9 FOR REFERENCE SEE (11bb14.gif) 10 CONFIDENTIAL 236-39-31 FOR OFFICIAL USE ONLY COPIED/DOE LANL RC If the maximum permissible dose of plutonium can be increased by a factor of 10, then by analogy the air tolerance for soluble salts of U233 would become 6 x 8-8 ug/cc. The proposed maximum air concentration for insoluble salts of U233 required to deliver 0.3 rem/wk to 100 grams of lung tissue assuming 25 per cent retention and no elimination, exposure of 24 hours/day and 365 days/year for a working time of twenty years. Practically every conservative step possible has been introduced into this calculation including the use of the RBE factor of 20 for alpha particles. Such conservation seems unnecessary and can serve only to work hardship on any large scale process handling U233 or U235 + 2% U234. 3. U235 + 2% U234 -- the maximum permissible air levels corresponding to the Chalk River values for U233 may be obtained merely by multiplying the values for the latter material by the ratios of their specific activities, as follows: 6 x 10-9 ug/cc x 9.4 x 10-3 uc/ug=4.2 x 107 ug/cc for soluble salts ___________ 1.34 x 10-4 uc/ug 2.5 x 10-11ug/ccx9.4x10-3 uc/ug=1.75 x 10-9 ug/cc for insoluble salts ___________ 1.3 x 10-4 uc/ug The Los Alamos Laboratory has never made any distinction between soluble and insoluble materials. The maximum permissible air level now in use is 1.3 x 10-6 ug/uc (1.8 x 10-10 uc/cc). The average of all air measurements made in all U235 operating areas of the laboratory during the past eight months was 3.1 x 10-7 ug/cc. This is a factor of about 175 times the value calculated from the Chalk River proposal for insoluble salts. The adoption of these tolerances would undoubtedly force the U235 metal production and fabrication operations to close down. III. Polonium A. Body Tolerance Dose for Plan Personnel -- the maximum amount of 11 CONFIDENTIAL 236-39-32 FOR OFFICIAL USE ONLY COPIED/DOE LANL RC polonium permissible in the body of plant personnel was determined at the Chalk River conference by relating polonium to radium by essentially the same reasoning as was employed in the case of plutonium. Mention was then made of acute lethal studies in rats which compared the toxicity of radium and polonium on a microcurie basis. These studies indicated polonium was twenty times as toxic as radium, therefore, the maximum permissible dose of the latter substance was given as 0.1 uc x 1/20 = 0.005 uc. The Rochester report, UR-44 by Hursh and Stannard was mentioned, but its contents were not available or known to the Committee. The accompanying graph taken from their report emphasizes the undesirability of applying acute toxicity factors to the calculation of a chronic maximum permissible dose. As pointed out in the discussion of the plutonium body tolerance, the toxicity curves for radium and polonium approach one another rapidly with extended time of observation. If one chooses to use mean survival time at 5-10 days, the ratio of toxicity of Ra/Po may be at least 1/20. At 300-400 days, the ratio may be 11 and at greater times polonium may actually be much less toxic than radium. It seems that the latter ratio would be far more applicable to chronic tolerance calculations. Chronic permissible body tolerance calculations by Rose, Hursh and Stannard in which no questionable biological toxicity factors were introduced, indicate a maximum permissible body polonium content of 0.1-0.2 uc. B. Air Tolerance Dose for Plant Personnel -- No maximum permissible polonium air tolerance for plant personnel was given in the report of the Chalk River meeting. Taking the polonium effective biological half-life value of 34 days and a body retention of 65% given by Hursh and Stannard (UR-44) and the Chalk River maximum permissible body tolerance of 0.005 uc., 12 FOR REFERENCE SEE (11bb15.gif) acceptance of unnecessary conservatism in the choice of the above tolerances will definitely affect the weapons program of the Atomic Energy Commission and specifically that of the Los Alamos Scientific Laboratory. The introduction of unnecessary safety factors will also quite probably add millions of dollars to the AEC's construction of facilities and specifically to the costs of the permanent scientific laboratories being planned at Los Alamos. A sampling of the general opinion of a number of scientific personnel, both at Los Alamos and elsewhere, seems to indicate a rather widespread feeling that the tolerance values proposed at the conference are in some instances too conservative, occasionally inconsistent, and in a few instances influenced too much by inadequate animal experimental data. 13 CONFIDENTIAL 236-39-34 FOR OFFICIAL USE ONLY COPIED/DOE LANL RC In view of these findings, it is recommended in this letter that official adoption of the Chalk River proposed values by the Atomic Energy Commission be withheld pending more careful consideration. The Chalk River conference would hardly seem to be the proper way of establishing tolerance values of such potential internal significance. It was impossible to give adequate time and consideration to any one problem and in many instances much needed information was not available. It would seem more desirable to have a committee appointed to consider each radiological hazard. After adequate time for the consideration of all available information, the recommended tolerance value should then be submitted by each chair for the approval by an international committee similar to that held at Chalk River. Despite the large amount of animal experimentation that has been done, it seems that the most firm basis for the establishment of the tolerance values for alpha emitters is to relate them to the accepted tolerance dose for radium, introducing biological factors from animal studies only when they are well-founded on carefully performed chronic experiments. As pointed out in the accompanying photostat of a letter from Dr. Robley Evans, the maximum permissible body content of radium of 0.1 ug. is well-founded on human experiences and as more and more cases are considered, it looks more as if the tolerance value has an adequate safety factor. Dr. Evans pointed out that there was a safety factor of 10 and that everyone seemed to be stuck by the fact that the osteogenic sarcomas observed a number of years ago are notably absent. This might possibly mean that the radium dosage in the earlier cases was appreciably higher than formerly surmised. He also quoted Dr. Martland as saying that the number of persons originally exposed in the luminous dial industry, etc., was probably several thousand. In view of the fact that the persons manifesting symptoms are always the ones who are called to the doctors' attention, there is little doubt that the observations of radium poisoning in humans have been made on the most susceptible individuals among the several thousand 14 CONFIDENTIAL 236-39-35 FOR OFFICIAL USE ONLY COPIED/DOE LANL RC cases. This would serve to further emphasize that the maximum permissible dose of radium is a sensible and reasonably conservative basis on which to establish tolerance values for other alpha emitters. 15