Document YDvNpmmrezBnXjqdxM4RzvrkD

March 5, 1950 \' Mr. P. L.- Magill, Stanford research Institute, Stanford University, Stanford/California. ' bear Mr. Magill: Mr. 1. E. Poberts lias told me of the questions raised 'oy you at a recent meeting, with. the .-suggestion that y o u would be interested in having certain further items of information. I am pleased to give you some additional information, and if I can supply you with more later, I should be pleased to do s o . Your question H o . 1, a? given me by Mr. Roberts, concerns the disposition of' lead in the exhaust gas of automobiles. The answer to this question is available only in general terms, and is not available in the precise terms that rotate to the newest kind of automobiles. Investigations were made a number of yeaigago, by equipping automobiles with Cottrel precipitators of high efficiency, and removing from the exhaust stream all but traces of the lead compound. Following the use of this equipment over a certain mileage, engines were torn down and as much as possible of the accumulated lead compounds gathered and analyzed. The results of these deter minations demonstrated that- somewhat variable quantities of lead compounds remained in the exhaust system, in which they condensed out and accumulated,on the sides of the tube. The proportion;varied with the newness of the car and the cleanliness of the exhaust system, tending somewhat to reach a sort of equilibrium it somewhere in the neighborhood of '5 0 $ of the total lead burned; in the fuel. -It would be -very difficult to say what is the overall picture in this regard, since the quantities deposited in the exhaust system may be as lietie as 25 or 50$, and as grt as 7$$ of the lead which is i n ;the gasoline. In any case, that which accumulates in the exhaust system is a source of little or no pollution of the atmosphere, since to the extent that it subsequently gets out of the exhaust system it is probably jarred loose and falls in chunks, so to speak, on the street or roadway. I do not have beside me all the data that are available on this subject in relation to actual road use of automo biles. A considerable number of such data are available, and they can be obtained, but actually if one were to. establish the facts in terms of present day operations^ these experiments would have to be repeated, since automobile engins and exhaust systems differ in a number of respects from those available When the observations were made. - Your question number 2 concerns the nature of the chemical compounds in the exhaust gas. This depends primarily on the quantity and character of the halogen carrier mixed with tetraethyl lead to make the antiknock compound. In automobile fuels, at present, ethylene dibromide and ethylene dichloride are used, and the lead is converted  . .. . ... , Mr. F. L. Magi 11 - (2) - March 5, 1950 , . ' .' "N \ to the corresponding halogen salts,. In approximately the proportions m in which the two occur in their mixture. In addition small quantities of the oxide, sulphate and, probably., carbonate occur, but all of these individually and collectively occur in negligible concentrations. The halogen carrier is introduced Into the fluid In quantities ; . slightly in excess of the theoretical required for the conversion of all of the lead to the .halogen'salts. The extent of the excess has varied from time to time* but there has always been' some excess- . Moreover the proportion of the bromide In the fluid, as compared to chloride, has varied from time to time over the years, largely in accordance with the ..approximate'temperature of engine operation, since the purpose of the halogen, is to convert the lead to the compound which will be volatilised almost completely out of the engine under the conditions of normal operation. . Yo u r next. question relates to particle else. F e w data are available on the actual.particle siss of. the lead compound in the exhaust g a s . Such observations as have been made from time to time have demon strated that the particles are exceedingly, small, well ^under- 1 micron,' and that they settle out very. ?lowly indeed It i^-kthtfiSW'-t$oni . observations^that it is easy to obtain lead bromide in highly finely divided i orm/n xo a very uniform extent, by the combustion .of^^fijlil.ine. Observations-have, 'been made with reference to the passage of/the particles through ordinary filtering m e d i a , -and It.is known that only the very best and most efficient filters will stop the passage of these particles. Consequently, although I do not have available adequate data giving,the distribution of particle sine, it is quite clear from the observations that have"been, made, b o t h physical and physiological, that the lead in the exhaust gas Is in such finely divided form as to behave substantially like a gas 'itself over moderate periods of time, and indeed in respiratory experiments carried out. by :fant, add his associates of the Bureau of Mines . many .years ago, in their Investigation of this problem, it was estaollshed that a large proportion of the lead inhaled in air contaminated in this fashion, is also exhaled.' Incidentally, copies of the Bureau of -Mines* report of their observations-on the study.cf this entire problem are very difficult to obtain, being, I believe, substantially out of p r i n t . I have a few copies which I have held onto, and so -far.. as- I know none other are available. I should' be willing to loan a copy to anyone who 'has reason to be interested in these experiments, but so far as I know there are none available for distribution, and I cannot provide any copies other than on the basis of a loan. ` Further question has been raised concerning, the fate of the excess halogen In the antiknock compound. So far as I know, no observations have been made that would clearly define the precise fate of the halogens. The presumption is that conversion to the halogen acid occurs, but what proportion tills i3 of the total excess, is not k n o m , so f a r as. I am able to discover. Observations have been made that Indicate that, hydrobromic acid, for example, Is present in minute concentration. Moreover, I have heard some Individuals claim that Hts- 0004317 Mr. P. L. Magill - (3) - March 3, 1950 - . they could identify the h y d r o b r o m i c a c i d . Perhaps this is true, but I hve never been able to do it. In any case, the concentration of hydrobromic acid is quite low. The nest question relates to the source of other lead compounds which occur in the atmosphere. This is an interesting question, and the answer to it is far from being complete in all respects. There are, however, a number of significant sources. One source that is important, and..is.probably the greatest single factor,is that of the combustion of common fuels in urban and in industrial centers* Coal contains appreciable quantities of leadi wood and other fuels of natural origin contain somewhat less, but the result of the combustion of all of these is to release variable quantities of lead into the atmosphere. Soil contains variable but appreciable quantities of lead, beingwherever it occurs,the result of the disintegration of stones in which appreciable quantities of lead are always found. Tne soil is more or less pulverised on the surface of the earth, and when it is dry it i3 picked up by air currents and distributed into the atmosphere. Unquestionably there are other sources of lead compounds in the atmosphere, including:, of course, the activities that go on in industrial areas. The distribution of lead in the City of Cincinnati is least in the open country abound, and greatest in the industrial areas. The lead concentration along highly traveled highways may show some incr*ese abve that in other parts of the city, but the quantities here are always, in our* experience, less than those found in certain characteristic industrial areas. Actually we have had considerable difficulty in our observations of the .occurrence of lead in the atmosphere to find that increment which should be attributed to the contamination of the atmosphere with the exhaust gases of automobiles-. That there is such an increment goes without question, but it rather tends to get lost in the other sources. We have thought we might be 'able- 'to 'determine- its quantitative significanee, by measuring the proportion of lead which occurs in the form of lead bromide. Our efforts along this line have been rather scanty up to the present time, but we anticipate following out this lead for our own purposes. In connection with the overall sources of lead in the atmosphere, it will interest you to know that some considerable improvement in the atmosphere of Cincinnati Iras been obtained in the past year or two, through efforts to control smoke and soot and fly ash. Coincident with this improvement we have noted a significant drop in the lead concentx-ation in the general atmosphere of the community. This is the biggest change that;has occurred in the picture over a period of several years,insofar as the lead concentration in the atmosphere generally is concerned, and it is fairly apparent to us that this is a very significant fact. The present overall concentr-ations of lead in areas other than Industrial areas in Cincinnati at present average along .0 3 mg. of lead per; 10 cubic liters of air. Dur results of some years ago averaged well above this level, being nearly twice this figure. In connection with this entire problem, It will. Interest you to know that we have planned a rather elaborate study of the total lead Mr. p. L. Magi11 - (4) - March 3, 1950 mtabolisa of human subjects maintained for approximately 7 hours per day on 5 days a week in a carefully measured concentration of a specific lead compound in a known and fairly uniform state of subdivision in the atmosphere. We know of no way in which the problem of industrial lead exposure can be put on a 'sound basis other than by this type of study. By a systematic study of this" type we hope to add that information*on the inhalation side, that we were able to make available on the ingestion aspects of lead absorption. I have been told that some very considerable Interest has arisen in certain circles in Los Angeles over the problem of the lead content of the atmosphere* and presumably that fraction derived from the exhaust gas of automobiles. Recently I heard some comments to the . effect that lead bromide might be a lacrimator* and .that -it mightbe- responsible for some of the eye irritation that lias been complained of. Moreover* I have been told that some representations have been made, in relation to the potential hazards of lead in the atmosphere, based on certain rather naive calculations of the totals amounts of lead available in gasoline consumed in the: Los Angeles area, and tlarefore being distributed into the atmosphere. These questions were all raised a good many years ago, in somewhat the same naive m a n n e r .. A ?ery considerable amount of -work has been done -toanswer some of the questions, and all of these data could be gathered together for the purpose of demonstrating the approximate significance of the problem. If it. became necessary to do this, I should be very glad to render the assistance, that I; can . I trust * however-, that the problem at issue can be considered on a somewhat aior-e realistic b a s i s . We have been working around toward this problem for a number of years, and I believe that v,o are now so situated that the questions at issue can be answered in: a wholly .satisfactory manner- While it is a costly u n d e r t a k i n g i t is not too difficult to ascertain the facts concerning the actual degree of the contamination of the atmosppere of representat cities in this country and elsewhere, and I feel certain that will be possible to establish where the limits of safety lie in this regard. e shall then be able to establish the. extent of the safety factor that exists at any time in relation to the existing conditions. As you nay he aware, we have been following the lead excretion o f . rather sizable numbers of people over a period-'of -some years. I have .no hesitation whatever in saying-'that- the safety factor in community lead absorption, s the results of the contamination of the atmosphere with lead, is satisfactorily larg#. There may be specific exceptions to this 'rule, in that persons who live in the immediate vicinity of an industrial plant in which'lead compounds are used extensively, may find deposits of lead compounds in the household, as well as lead concentrations in the atmosphere that moves about them, to be above wholly satisfactory levels. Finally, lei, me say that if t h i s 'problem should become one of consi derable importance in the Los Angeles area, I should consider* it a privilege to have an opportunity to come out and to talk with the people who would be concerned in the problem and in the means of Hr. P . L . Magill - (5) - March'5, 1950 " attaek upon i t . 1 trust that.what I have aaid above v i l l .answer some of your questions,, and it seems -likely that others may arise. In any case, If you have: any further-' questions, I shall do my best to answer them. , . .' Cordially yours, lobert A. Kehoe, M. D. FAS of ?.. S-.- .1 am sending a few reprints under separate cover which may interest you in connection with; tills problem at issue. There is not much in them that will actually answer your questions, but they will at least demonstrate something of 'the- manner in'- which we .have . approached the problem of lead absorption and -excretion previously, and will give you a clue to the methods which. We expect to use in the study of inhalation as well as further study of lead .ingestion. observations made on experimental subjects will' have -to include nil tf the sources'- of lead absorption that are now known to exist, and the subjects, vill'have to be followed carefully with respect . co the intake of lead in their ordinary diet, during the period of experimentation. ' Seprints tinder separate cover. .ucoosurg co Lead ' ike Concentrations -of Certain Trace Metals in Drinking Water n-perinental Studies on the Ingestion of Lead Compounds _rad Poisoning -Symposium - .- ' -. '?.- . s Some inquiry on this same subject lias come to me indirecti .from a Mr. Paul Crimes of the L. A. County Smog Control,Commission. You may or may not have the means, of talking to Mr. Grimes, but if you should, the information you might give him might be- helpful to him and to m e . R -A.K.