Document B5Bz8YE6v649OkR2GDY7X03Dk

M arch 7, 1956 M r. W esley C. L . H em eon _ E ngineering D irector Industrial H ygiene Foundation of A m erica , Inc. M ellon Institute 4400 Fifth Avenue Pittsburgh 13, Pennsylvania D ear W es: al I hasten to rep ly to your note of M arch 6 and to m ake som e addition/com m ents on the fig u res which I gave you h a stily when w e la s t talked togeth er. F irst; it is im portant to d ifferentiate betw een dem onstrable fa cts and p la u si ble opinions d erived from interpretation s of fa cts of various kinds. When one co n sid ers the extent to w hich the la tter enter into certain of the figu res w hich I gave you, th ere is con sid erab le doubt a s to w hether such a table as you su g g est should be published without the explanations req uired to put everyth in g in its proper lig h t. P eop le take th e se things so lite r a lly and u se th em out o f th e ir p r o p e r c o n te x t, th at I a m -w a r y in m y s ta te m e n ts o f th is ty p e. I sh a ll m ake the differentiation of the type indicated above, and then you can co n sid er further what you m ay think of the fig u r e s. The data a re adequate to substan tiate the fig u res I gave you on the intake of lead by the adult A m erican in h is food and drink. The extent of the alim en tary absorption of lead at th is le v e l of daily intake is a bit hard to d eterm in e. Our inform ation on th is point is b ased upon what happens to la r g er d o ses - i, e . higher concentrations in the alim en ta ry tra ct, w hich show that the extent of the absorption of a soluble (or r ela tiv ely soluble) compound of lead va ries d ir e c tly w ith the co n cen tra tio n , being r a r e ly m o re than 10 to 12 p er c en t. I picked the figu re of 10 p er cen t out of the a ir a s being the m axim um , in a ll p r o b a b ility . The data on the atm osphere are subject to som e juggling, dependent upon the se a so n , the lo c a lity , the a tm o sp h eric con d ition s (in v ersio n , e t c .) , but in m y judgm ent the average concentration of lead in the atm osphere breathed by an individual during an a verage 24-h our period would r a r e ly , if e v er , ex ceed 5 m icrogram s p er cubic m e te r. A ssum ing that the individual breather in 20 cubic m eters of a ir per day (probably high), 0 .1 0 m g . p a sse s through the r e sp ir a to r y apparatus p er d ay. The reten tio n of th is r e s p ir e d le a d in the lung (dependent upon p a rticle s iz e and concentration) m ay con ceivab ly be a s little a s 10 p er cen t, o r a s m uch as 50 p er cen t accord in g to our p resen t M r. W esley C . L . H em eon - (2) - M arch 7, 1956 incom plete data. Of that retained, the g rea ter portion of it is absorbed, unies* the fa ir ly recen t observations of Ted Hatch n ecessita te a rev isio n of our ideas concernin g the clea rin g of so lid p a r tic le s from the lung. If he is righ t, the p rop ortion ab sorb ed m a y be a p p recia b ly l e s s than m y e s tim a te . In any c a s e , we can only g u ess at this at p resen t b ecause of our inadequate inform ation as to the distribution of p a rticle siz e and the so lu b ility of the com pounds borne into the lu n g. In te r m s o f w hat happens in th e m e ta b o lism o f th e su b jec ts studied in our lab oratory, I have estim a ted that the quantity absorbed from the lung per day m ay be c lo s e r to 0 .0 1 m illig r a m s p er day than to any other figure I can arrive at. Ns The "level of p o ssib le con cern , " as you have set it down is in c o r re c t. What I said w as that if the lead in the food and b ev era g es w ere doubled, we would find o u r se lv e s in a situ ation in w hich for a p eriod c f y ea rs {how long one does not know; it m ight be fo r the balan ce of a lifetim e) th ere would be som e accu m ulation of lead in the body. T his would be slig h t. A cru cia l exp erim en t show ed that when w e added 1 m g. per day (every day) to that in the food and d r in k o'f a n o r m a l s u b je c t, h e a c c u m u la te d ab ou t 120 m g . in s o m e th in g o v e r 4 y e a r 3 . T h is m igh t b eco m e dangaroxis in the c o u r se of tim e . In any c a se , a co n serv a tiv e view would be ju stified to the e ffe ct that the in g estio n of 1 m g. p e r d a y , o r e v e n so m e w h a t l e s s {I s e t dow n 0 . 6 m g . a s a th r e s h o ld v a lu e ) m a y w e ll be regard ed a s e x c e s s iv e . (At th is le v e l of intake by a n orm al p erso n s th e a lim e n ta r y a b so rp tio n a p p ro x im a tes 10 p e r c e n t, varyin g w ith the tim e required for the tra ct to em pty its e lf. Thus diarrhoea d im in ish es absorption, and constipation in crea ses it.) N ow if th e a b s o r p tio n o f 10 p e r c e n t o f 1 .3 m g . {0. 3 5- 1 . 0 0 a d m in is te r e d p e r day) p er day gives r is e to a sig n ifica n t rate of lea d accu m u lation in the body (120 m g. in 4 plus y e a r s), the q u estion is ra ised , of co u rse, how much breatned into the lung, is capable of giving r ise to an equivalent rate of accum ulation. This quantity w ill vary, p resu m ab ly, 'w ith the com pound of lead inhaled, the s iz e {and shape) of the p a r tic le , and te e co n cen tra tio n . H ere w e have too m any im ponderables at p resen t, so far a s the nature of the contam ination of the a ir with lea d , to ju stify m o re than a p la u sib le g u e s s . I would h e sita te , th er e fo re , to be as con crete in m y e stim a te , fo r the reco rd , a s I have been fo r the sake of a d iscu ssio n , which at th is point related its e lf m ore to a continuing exp erim en tal program ahead of u s, than to that behind u s. I su sp e ct that the d ep o sitio n of p o ten tia lly a b so rb a b le lea d in the lung in the quantity of 0 . 01 m g. per day w ill be equivalent, on the a v era g e, to the ingestion of approxim ately 0 .1 0 per day. H ow ever, this m ak es in su fficien t allow ance fo r variation in the so lu b ility of lead in the a lim en ta ry tra ct and fo r v a ria tio n s in the behavior of th e a lim e n ta r y tr a c t in h ealth and d is e a s e . T h e re fo r e , l a m loath to m ake such an unqualified statem ent for the record . M oreover, the relationship betw een the con cen tration of lead in th e a ir and the reten tion of lead in the lung is a bit too ill-d efin ed , at p resen t, to ju stify any flat statem en t or calcu lation from the one to the o th er. Since th is is a hot su b ject at the 0010023 m om ent, and esp ec ia lly so from the a sp ect of the quotation or m isquotation of statem en ts out of context, I think it un w ise to authorize your publication of tlie table u n less you do so guardedly. I would not w ish to rela te the lead in the a ir to g a so lin e consum ption, eith er, sin c e it is not p o ssib le , at th is tim e , to d eterm in e the contribution m ade to the lead in the a ir by the exh au st of a u to m o b iles. We can find qu alitative evid en ce that som e contribution is m ade in th is m an ner, but no actu al data a r e a v a ila b le to enable us to e stim a te the quantity o r th e proportion in any in sta n ce. The so u rces are m ultiple and are subject to considerab le variation geograp h ically and on a tim e b a se . It is not w ise , th erefo re, to u se our estim a tes for the purposes of docum entation at th is tim e. I have ju st talked to Cholak about your p rop osal to him and I am sure he w ill know how to d e a l w ith it and w ith m a t te r s th at m a y c o m e out of. it l a t e r . C ordially yours, ( RAK ef Robert A . Kehoe, M. D. KE 0010024 I