Document e7kgKOEpNNxv3OL96nXQdx54p

May 23> 195? Dr. Hugh'l . Parker, Director Industrial Hygiene Division Department of Public Health Atlanta, Georgia Dear Doctor Parkers The talk on "Experimental Inhalation of lead, etc." given at the Cincinnati Industrial Health Conference was a progress repox't on one of a series of experiments which we expect to carry out over a period of years. The experiment In point had reached a stage which justified reporting, but since It will not be completed for at least another six months, it Is not ready for publication. I expect to send this to Drinker for . publication in the "Archives" as one.of a series of papers intended to elucidate the metabolism of lead when inhaled in specific quantities and forms, i.e., specific chemical compounds, In specific else of particle, In specific dosage over prolonged periods The sign! fleant facts reported thus far are: (a) that lead oxide in a state of subdivision represented by a median size of 0.05 microns, and in the concen tration of 0.075 mg. per* cubic meter, has been breathed for 7 hours per day on 5 days per week for over a year, without symptoms or signs of lead absorption, other than those provided by chemical analyses of blood and urine; (b) the retention of lead in the lungs under these conditions | was approximately 35 per cent of that Inhaled, the ; remainder appearing in the expired air, while that retained during the inhalation can be regarded as being absorbed into the body quantitatively; (c) the metabolism of lead underwent prompt changes, In that the concentration of lead in the whole blood rose prompt ly and reached the level of almost 0.0^5 mg./lOO g., the concentration and output in the urine rose correspondingly, while no change in the fecal output could be detected; (d ) apparently an equilibrium was reached by the subject with his environment after about six months, after which no further significant increase in the levels of lead con centration In the blood or urine occurred. (This phenomenon is being tested experimentally by the contin uation of observations for mother six months or for a longer period of time if necessary.); N 6173 Dr. Hug|i L. Parker - (2) - May 23, 1952 i (e) "by* indirect means , it can be calculated that the accumulation of lead in the tissues was small but significant, amounting to not less than 9 mg. or more than 1? mg. Aside from the methodology of the work, which was derived in large part (except for some features specifically related to inhalation) from experience in the study of the metabolism of ingestea lead, these are the essential facts. They do not apply any too well to the practical problem of the safe level of lead concentration in the air of industrial establishments, for the reason that the size of the particles being breathed in i3 much smaller than that which characterizes most industrial fume and dust. Ve began at this point, however, for certain very good experimental reasons, and will proceed with larger particles of known lead compounds later. Cordially yours, RAK ef Robert A . Kehoe, M . D . 0002129