Document gbXme57XKJ50X5Zr8E1XM8R8a

<%?if i' - ' July-25,.. 1 9 5 6 ; '" ,. Dr* Francis M. Pobtenger, Jr* o ' 0 C9 'Torth Canyon Boulevard Vonrovia, California : '; .. ' -, . . .-,:<, Dear Pottengor: .... - , /^Thanks for the return of the letter sent tb':you by mistake, and also f 03?!yi>ur additional comments on the air pollution problem as it relates to 1 1 hope very much that you do come to see me in September when you are in this oart the country, for it would be much easier to show you some of the information on this subject as we have accumulated it, than it-is to document it by published articles, or m e r e l y t o btate the facts. One haafujd obtain a quantitative grasp of the entire situation,.v/ith respect to ib'pj occurrence of lead in nature and also its distribvition in the :;'oc1(|r|ri world, in order to have a balanced view of the problem* I hope ycujiilkjt me know when to expect you, so that I shall not be olsexyhere, for I v;OSid like to plan so as not to miss you. . should prefer to leave the entire matter to our future discussion, a idj jTjlvould do so but for the indication in the second paragraph of "our^iotter that you have considered the exposure to exhausted lead in the*[atmosphere of Los Angelos to be capable of giving rise to overt cliiiical sly,ns of lead absorption. I hesitate to let this pass without comment, for it is so far rifleId from the true situation as to demonstrate that you are not thinking in the right terms quantitatively. Thcvfoqst that one could hope to do, in undertaking to obtain some eviciehee of the absorption of lead from this specific source, would be to f:\hd a statistically significant difference- in the analytical findings - bleo^/or u r i n e .or both - in-a group subjected to-the most severe and -on11 prolonged exposure of this type, as; compared with a group or groups essentially free of such exposure or nearly so. It is this type of., investigation that we have engaged in previously and are repeating now. It appears,from both direct- and indirect evidence, that the lead in the ..onoral atmosphere of our cities contributes only something of the order of ton -or fifteen raicrograms (0,010 - 0.015 mg.) of load per day to that which is absorbed daily from other sources, there being approximately f-ree hundred to three hundred and fifty micrograms (0*30 - 0.35 mg*) . '? load per day in our ordinary food (and beverages), ..of which something less than twenty per cent (20%) is a b s o r b e d u n d e r the most favorable . conditions. At least half of the lead that is found in the American. - - 0004251 N6919 Dr* Francis M. Pottenger - (2) - July 2 $, 19^6 dietary is of natural origin, and a significant proportion, which is difficult to estimate for the lack of entirely valid control data .of that which is in the atmosphere, is also of essentially normal origin* in tho senso of being derived from sources that are almost as old as the earth itself. Suffice it to say that the collection and anal?rses of samples of the particulate material in the atmosphere in widely separated areas of tho North American continent have yielded lead in quantities of the same general (small) order of magnitude. This then is a part of the background, and the situation that exists at present, with respect to the general exposure of our people to lead, differs only a little from that which has existed for a very long time, id the contribution made by .leaded gasoline, which must certainly he has been difficult to separate out from the other factors. Only by`means of a large number of analyses a t strategic points, and after the application of statistical methods-' of differentiation of the results obtained'.`at various carefully selected locations, have we been able to fihd fairly convincing evidence of the independent significance of this factor, ;O This loaves but one other point to be mentioned; to substant iate ;ny earlier statement that clinical signs of load absorption from this source are;not to be expected. V/e have been .Observing, the clinical and. . physiological evidences of lead absorption experimentally and clinically fdr^uany yoars, as you know, The physiological responses of workmen and experimental subjects- to- the absorption- of load from the alimentary tract aneyfrem the respiratory apparatus have., been :.'-cast:red by precise methods lh a' comprohonsivo manner. It y,ill interest you to -mow that when tho concentration of respirable and absorbable (particulate) load in t h o ... tenoschore has boon increased to ten times the peales of load con centration which w*o have found in Los Angeles and. Pasadena during periods o f .severe inversion, so that the air in a respiratory chamber contabas O-.lf? ig. per cubic :otor, oho concentration of lead in the blood of experimental subjects, after 15 to 2J. months of exposure for 7u h o w s per.yday on r days por week, increases-to only O.ckh ug. per 100 grams, T1-\V/urinary load concentrt ion increases somewhat more proportionately. IJnVfer those circumstances no increase in -stippling is seen, and no load line of the gums develops, , V/ith these facts in mind, one may not expect tho absorption cf load which results from the ingestion of -load..'in food and drink and from the atmosphere of our cities to show more than a minute effect of a physiological type, if any. The occurrence of physical signs of lead absorption 'under these circumstances''-.is really out of the question, A lead-line in the grass can occur rarely (I have seen it once) when the blood level is around 0,0f> ng. per 100 grams, but it is associated generally with much higher blood levels. Stippling, I need not remind you, I am sure, occurs normally in blood, is augmented by a great variety of stimuli to the bone marrow, and even when it occurs as a response to load absorption, it exhibits no quantitative correlation with' the -extent of the absorption. K E 00C4252 Francis L. Pottenger - (3) - July 25 1956 I do not resort here to criticism, for it is necessary to loolc with haizmte care for anything one can find* Actually, in the course of our work, we have applied every clinical and physiological tool that is known and sone t3:at were invented for the purpose Indeed, it is for that reason that I know what to orpoct in relation to various levels of lead absorption, . .. , . . I did not intend to write oo long a letter when I started*. for-'.I, nave ; any things knocking at my door to 'oe done. However, having, started I was drawn into the long and wide stream of evidence, some of which I hope to have the weans' of showing you before long. S incere ly your s ,