Document 93n9VYeZOZY1jgO3JyXo7LQ85

December 22, 1969 Professor James E. McDonald Institute of Atmospheric Physics The University of Arizona Tucson, Arizona 85721 Dear Professor McDonald: I hope you will have obtained some of the information which you desired from the reprints which my secretary sent to you in response to your letter of September 23. Having now returned home, and having looked after some of my more immediately demanding affairs, I can now respond to some of my neglected correspondence. I assume, from your reference to the solubility of Pb203, in relation to that of the halides, that you are interested in the whole problem of lead in the air, and it occurs to me to call your attention to two points with which you may be familiar without my comments. (1) First, it is dubious that the solubility (in water) of very finely divided solids is the most important factor in their absorption in the lungs, and in their effects upon the pulmonary tissues. It is certainly not the sole factor. (2) Second, the lead halides which occur in the discharges from the tail-pipe of the automobile in relatively high concentration appear to be coated with something (oil, likely, and other debris) which alters their solubility in water appreciably; or perhaps they are altered in other ways. I don't know the cause of their relatively poor solubility, nor do I know whether this fact is of great importance, practically. (3) Third, I do know, from our experiments that the very finely divided sesquioxide (mean diameter of 0.05 micron) is readily absorbed (whether completely or incompletely, I cannot be sure); that considerably larger particles (mean diameter of 1 micron) are diverted, to a considerable extent into the alimentary tract (by the mechanisms of pulmonary clearance) and that the pulmonary absorption is much diminished (it is likely, from the data, that the larger particles retained in the lung are relatively poorly absorbed). The extent to which particle size is a factor in absorption (in situ) is being investigated further. Aside from the foregoing considerations, there are other factors to be taken into account. I have proposed certain physiological criteria which I believe to be valid in connection with the establishment of a tolerable level of concentration (of lead) in the ambient atmosphere. We have carried out experiments in pursuit of a number, and I believe we are very near a definitive answer. I am studying carefully the data of two recent experiments - the second of these is now being brought to termination, and all of the data will soon be available. Meanwhile, I send you two additional reprints, which I believe, will be of interest in relation to lead in the air. N13169 Sincerely yours, THE UNIVERSITY OF ARIZONA TUCSON, ARIZONA 85721 INSTITUTE OF ATMOSPHERIC PHYSICS September 23, 1969 Dr. Robert A. Kehoe Kettering LaboratoryDepartment of Preventive Medicine and Industrial Health College of Medicine University of Cincinnati Cincinnati 19, Ohio Dear Dr. Kehoe: Would it be possible to obtain from you reprints of two of your past publications on environmental lead problems? Your Harben Lectures, 1960, were published in a journal not held at our university library, and if you still have reprints of those Lectures, I would very much appreciate receiving a reference copy of them. /ty Your 1961 paper in Pure and Applied Chemistrjf^on lead inhalation, is also inaccessibile here. Might it be possible for you to send me a reprint of that paper? , / I have read your papers in the 1964 Archives of Environmental Health, concerning a number of your studies. Your use of lead sesquioxide particulates in your inhalation studies raises a question in my mind. The indicated solubility of Pb202, in chemical handbooks, is so very much lower than that or lead halides, that I am interested to see (possibly in one of the two requested reprints) what evidence there is for rapid absorption of the sesquioxide. Sincerely yours. f) 0 JEM/vlm James E. McDonald Professor N13169.01 KF 0012525