Document 5qjdBnxzMDVp2LJ89p40O420

i c I n a.n I n v e s t i g a t i o n of "The F a te of Inhaled P a rtic u la te -Lead Com pounds" Supported in p a rt, (to the ap p ro x im a te extent oi one fourth of the c o s t) b y th e U. S.. .P u b lic 'H e a lth S e r v i c e , N a tio n a l I n s tit u te s of H e a lth as a P roject .identified as A. P. 00220-01-05 ' b y R o b e r t A,. K e h o e , M. D. , P r i n c i p a l I n v e s t i g a t o r , P ro fe sso r E m eritu s of Occupational Medicine . in the D epartm ent, of E n v iro n m en tal Health, College of M edicine U niversity of Cincinnati, Cincinnati, Ohio . INTRODUCTION In tl:e original- application for. a g ra n t of funds in su p p o rt of this p ro jec t, a. b r i e f d e s c r i p t i o n w a s . g i v e n of a s y s t e m a t i c , e x p e r i m e n t a l p r o g r a m w h i c h h a d h e exx in p r o g r e s s f o r s o m e y e a r s , with the objective of elucidating th e m etabolism , of lead in .man, within the lim its, ofintake (dosage) that a re su re ly -com p atib le with--the avoidance .ox'any known or dem ons t r able toxic r e - , sports e. No full .account of the r e s u l t s o b ta in ed in' the 'c o u r s e of th is e x p e r i m e n t a l p r o g r a m . , s u c h a s v.-cul.d i n c l u d e th e d e t a i l e d p r e s e n t a t i o n of a l l of t h e . h e r n a t o - logical, biochem ical, clinical'and analytical observations believed to be useful in establishing norm al baselines and certain threshold values, has been assembled, M any of.the data have m e re ly been scanned for significance, and, in th eir apparent V . r : V. ' . ... '" y .. accent ability, laid aside for la te r detailed p resen ta tio n . The p rin cip al findings-, ' ; -, , ' V . ' ; * A ; . i, e. , those rela,ted:m o s t dir ectly to the m a in objectives of the investigation, have, b e e n published, In so m ew h at le ss than extended .form, from, tim e to tim e. In I960, a s e r i e s of -t h r e e l e c t u r e s ' w e r e g i v e n , --in a n e f f o r t t o p r e s e n t t h e h i g h p o i n t s of y . -, .. ;.n ' / t h e s e ixivestigatioxis^iiT'a'mH-Thriir:?:; b u t i a i r l y w e l l i l l u s t r a t e d and. d o c u m e n t e d , . a c . c b v l l D T h o s e w e r e p u b l i s h e d u n d e r t h e t i t l e of ""'`he I f w a b c l i s m of 1 . c-ad in ' M a n i n H e a l t h a n d D i s e a s e , " a s T h e FUurben L e c t u r e s , I 9 6 0 , of- t h e R o y a l Institute- of Public H ealth and Hygiene, London, England, in the J. Roy. List. Public Health.. 24:81; 101-129; 177,. 1961. O th er'p ap ers (pr ior miblications j ^. of the K ettering Laboratory)concernedwith this s e rie s of investigations>were ". I' ' -. ' /\ ., ' the following: (a) E x p rim e n ta l Studies on the Ingestion of L ea d Compounds. I J . I n d u s t r . H y g . a n d T o x i c o l . 2 2 : 3 8 1 , 1940. .(b) E x p e r i m e n t a l S t u d i e s on 'Lead. -Absorption and E xcretion, and th eir Relation to the Diagnosis and T re a t m e n t o f L e a d P o i s o n i n g . J . I n d u s t r . H y g . l< T o x i c o l . 2 5 :7 1 , 1943. (c) E x n o s u r e to L e a d . O ccu p . Ivied. 3:156, 1947. (d) E x p e r i m e n t a l . S tu d ie s on th e I n h a l a t i o n o f L e a d b y H u m a n S u b j e c t s . P u r e A p p l . C h e m . 3; 129, 1961. T h e f i r s t of t h e s e p u b l i c a t i o n s ( T h e H a r b e n L e c t u r e s ) is s u p p l i e d h e r e w i t h 'a s a . 'k'wdj' m e a n s of s u m tn a riz in g ith e e x p e rim e n ta l b ack g ro u n d of the work'fdrhF'parsLdiwenty H 'vFyiars. - . The physiological, to-xicblogical^and clinical literatu re relative to lead fend l e a d po i so il i n g , w h i c h h a s a p p e a r e d d u r i n g t h e p a s t d e c a d e , h a s b e e n v o l u r n i - nous, and ccuildi'scarcely eyen be r e f e r r e d to, m uch le ss ab stracted and ' .s u m m a riz e d , within, a sh o rt perio d of tim e or in a re p o rt or publication of less than m onum ental p ro p o rtio n s. (The bibliography of pertinent contributions du rin g 1965 alone, a b strac ted , tra n s la te d (when n e c e ssa ry ), and a ssem b led by the staff of the K ettering .Laboratory, runs to 236 single-spaced, typewritten pag es, ) .No other prolonged ex p erim en tal o bservations of the type of "balance experim ents" on hum an subjeccs have been described, however, so that there a r e no s t r i c t l y p e r t i n e n t r e i e r e n c e s to be m a d e th a n t h o s e (a - d) given ab o v e. 0004450 THE EXPERIMENTAL METHOD or from applicants for positions in the service staff~of the Laboratory (including positions as subjects), or from graduate students in the University of Cincinnati . ' .. ' ' :. ' -' whose academic work can be fitted advantageously into the regimen of a- specific experiment yi jzfaj Each subject ;is interviewed initially by the principal investigator in an effort to ensure mutually satisfactory personal and working relationships, the probable reliability of the subject in following instructions>and his complete understanding of the purposes and procedures of the experimental program, of the theoretical hazards of his undertaking, of the background of experience and knowledge whereby he is to be maintained in complete safety and well-being, and of the necessity.of his continuing in the role of experimental subject, throughout the estimated (and actual) duration of the experimental, If the applicant Is a graduate student, the approval: of the Department of the University in which he is carrying out his academifc work,,fs-* obtained, and every effort ^irs* made 'to avoid any, comprbmlse int'the- reqirenients of th .Department and the University as to time and ' ... /-^r fi' : ' scholastic performance. All persons employed as subjects -are considered from the viewpoint of their continuation in the service of the Laboratory, following the completion of their stints as experimental Subjects, should they so desire. Involved in this consideration is the interest and capability of the -subject in\ work which wiil provide him with suitable employment throughout and after the termination, of the' experiment'.! h>4 'M U i, I ' - '/ ` , . H V lti* . \ -- Each required and apparently suitable Subject ifS" accepted tentatively by the principal investigator, on condition that he shall pass a comprehensive medical examinatlonj.augmented by. a battery of clinical.and biochemical tests in Search 4 of functional deviations of a disqualifying type. If he is found to be acceptable, he is instructed to return to the examining physician, or to the nurse, or to the appropriate technician, as the case may be, at certain intervals required by the experimental regimen, and also to report to the nurse and .physician whenever, for any reason, he feels any need for medical attention or advice. (He is also assured of access to the principal investigator as he may feel the need to do so.) From the medical viewpoint, all ailments, including dental, upper respiratory and gastroenteric problems, are to be reported promptly and dealt with appropriately, ' . .V . /w' . . at no expense to the subject except' under obviously irrelevant and agreed upon . circumstances. Each subject i-s- then advised by the principal Investigator of the requirements with respect to clothing, changing of clothing and bathing and of the financial provisions for the absorption by the Laboratory of all.expense incident to the - -v . ' V . . ' *'>'> ; W ' 4 ' ' " ' " . ' experimental regimen as specified. He is then,instructed, in detail, in tlye.._ . , , ; . ;. ' : , r- procedures involved in obtaining and delivering, suitable specimens of food, b.e.v-rdges {including water), urine and feces These^JLnstructioris. are reinforced by the advice - ... :- and supervision, of the various' persons, inltheb'staf f-of the Laboratory with whom the subject.comes: in contact in the course of the day's work. After all preparation has been made, the subject enters upon a preliminary experimental regimen which requires his careful attention to the collection and labeling of all of his urine in 12-hour specimens, all individual fecal evacuations (labeled a s ;to date and hour), and as precise duplicates as can be. obtained, by visual and ordinary household methods of measurement (i.e., pouring, spooning, ladling or forking equivalent portions into duplicate articles of tableware, as plates, bowls, cups or tumblers), of all food and beverages consumed during each meal, and at all other times. The procedure involves discarding, from the duplicates,; all. portions of all items that are not consumed, as bones, fat, . 0064452 5 cartilage and fibrous parts of animal tissues, as well as the inedible shells, hulls, peelings, cores and seeds of vegetation. Certain foods are to be avoided, such as the flesh of game animals that have been shot, while apples, for example, are to be peeled entirely, or if eaten without peeling, are to be selected in pairs and halved,, and so separated into homologous pairs for eating and sampling. ,Gum chewing and smoking are also to be avoided, excepting, as for the. latter, at such times and under such experimental conditions as may be arranged and agreed upon. The subject maintains a diary in which are listed all unusual circumstances ^ .. ' 'TJ\, S-V > in his life (such as changes in abode,,eating places,"accidents involving - : . /{ ' specimens, etc,), and all of the items eaten at each meal. This is furnished to the principal investigator for his private information and for use in cross checking if and when unusual analytical results are turned up, (From time to - time, as desired by one or another of the investigators, certain individual items of food or beverages are collected separately for analysis, especially when 'somewhat- unusual items occur, in the dietary or, when unusual analytical results are obtained. A number of investigations of this type have provided useful information.) ', 1 ' , . Clinical and Experimental Observations . , ' . During the preliminary observations, the subject reports daily to the designated technical assistant for the collection of a specimen of urine (of recorded volume, to b e ,included in that: of the specific day) for quantitative, determination of, porphyrins: and:of delta-amino levulinic acid, and for the preparation of films of blood for semi-quantitative estimation of the frequency of occurrence of reticulocytes and of erythrocytes containing basophilic granules ( stippled cells" ) . (These observations continue throughout the experiment.) Y/eekly observations are made and recorded by the responsible clinician as to weight,.temperature, pulse, blood pressure, instrumentally measured manual. . .. - . , . - KB 0. 0044&3 -6 grip bilaterally, circulatory response to "step exercise," and occuiar fundyscopic appearances. To these are added any other items of interest or concern to the clinician. Clinical urinalysis (measured volume of urine included in day 's output) is performed, and any "follow-up" test that may be indicated, thereby, is carried out. Meanwhile, the well-being of the Subject is_looked into by the clinician, without creating any pattern of inquiry through"''leading questions. . The hematological status, of the subject is investigated further, weekly, by . enumeration of the erythrocytes, leucocytes and types of leucocytes and by determination of the hemoglobin, in the peripheral blood. All results, except:;,..,, the personal part of the clinical record (which is dealt with confidentially by the clinician), including all analytical findings, are recorded by the appropriate observer and forwarded to a central record-keeper, by whom they are made available for scanning, charting and statistical handling by designated personnel. These records, after being dealt with as required, are transmitted to the principal investigator for preservation, ,. -, . ' . .. . ' . J'i'J' '' ' . ; ' - .' ' ' . The determinations of lead;in foody feces, urine and blood (or any other material desiredi-by the investigators) arc- carried out by methods of preparation and analysis which have been unchanged in their essentials since th initiation of these experiments in :1939, thus insuring valid comparisons, of contemporary with' earlier findings. Parallel results have been obtained,.during certain periods; (or regularly in dealing w i t h certain materials), through the utilizati.cn of other analytical methods based on different principles (as a spectrographic mechod '. ' .''',.,''' . ' . ' . '. developed in. the Laboratory, ;as well as a technique of atomic absorption adopted, for use more recently). The specimens of blood and urine are' analysed promptly and reported in such manner as to be used to reveal the current status of a..Subject, with respect to his absorption and excretion of lead, with but little lag in time. Other samples,. 7 excepting as there is some special need for information; are fitted into the analytical schedule according to a priority established by the head of the analytical -straff) as modified; from time to time; at the request of the principal investigator. , 4; After the preliminary (control) observations have been carried out over a period of time sufficient to disclose the general pattern of the behavior of the e ' :. - ' subject^ including his response to seasonal influences (variations in ambient temperature and, possibly; in the type and intensity of solar radiation; or in . -V-a ,i-`la^ Ur-. .1p ' ' . ,dth'er; presently speculative; environmental factors) that are to be expected; the experimental exposure to lead is initiated according to plan. /The details of. the design and operation of th.chambers have been described elsewhere (1)./ .' . ' ' ~' , A special procedure; concerned with the inhalation of air-borne particulate lead; has been that of ascertaining; at:weekly intervals; the extent of the . retention of lead in the respiratory system during the experimental exposure; by determining the lead content of a suitable volume of the expired air (2). /The content of lead in the air.of the chamber is determined once or twice (dependent upon the duration of tiie exposure) during each period of exposure./ On the basis of measurements of the. respiratory volume per minute, of the individual Subject; periodically; under a variety of conditions; approximations can be arrivedvat as to the quantities of lead made available; experimentally; for absorption. (The . precision of these observations leaves something to be desired; in view of the variability of the results obtained from Subject to Subject and from the same subject from time to time. Moreover; until recently-; the extent of the clearance (1) The Harben Lectures. Lecture II. pp. 41 and 42 of the bound reprint of the lectures. (2) Ibid. p. 43. ; : ` '. ' ^ .0004455 . s of the lead from the respiratory tree^ through mechanisms that operate after the deposition of lead h a s occurred, has been highly speculative. This matter is 1 still subject to experimental validation^ but certain theoretical considerations and observations have provided a basis for assigning numbers to both clearance and absorption (1). With these numbers at ha.nd_, one can give quantitative expression to the intake and output of lead into and out of the respiratory system., and to the absorption of lead therefrom^ in our experiments^ with a degree of confidence in their approximate accuracy.) ( 1 ) Developed by the Task Group on Lung Dynamics for Committee IIj o f the International Commission for Radi ation Protection. Health Physics (Pergamon Press). Voi. 12^ No. 2 / pp. 173-208,, 1966. 9 EXPERIM ENTAL RATIONALE As indicated in the original application for a grant from the Public H e a l t h S e r v i c e in p artial s u p p o r t of t h i s w o r k , th e e x p e r i m 2r.i' u n d e r way a t that tim e, and projected for continuation with such supplem entary support, involved 2 m e n in p ara lle l o b serv atio n s, in w hich the factor of tim e (duration of ex p o su re p e r unit of tim e overman extensive perio d of time) w as to be the sole significant variable. ' The ratio n ale of this e x p e r im e n f lay in c e rta in previously observed facts, as follow s: - When experim ental subjects had been subjected to the oral a d m in istratio n , daily, of a stan d ard dosage of lead in solution along with th eir m e a ls , over p erio d s of m onths and y e a rs , thus providing for an elevated, slightly v a ria b le but continuous rate of absorption fro m the alim en tary tract, d u r in g e v e r y s u c c e s s i v e p e r i o d of 24 h o u r s , th e r a t e of the. e x c r e t i o n of le a d . in the urine, the concentration of lead in the blood / and the .rate of accum ulation of l e a d i n ' t h e b o d y , w i t h s o m e s e a s o n a l ( an d o t h e r ) ' v a r i a b i l i t y , c o n t i n u e d a t '(. : substahti.alryfuniform y e a r l y .rates,'; "without any 'sign: of tapering- off d u rin g the entire period of the ad m in istratio n of lead, in one instance, for 4. 5 y e a rs . ( E x p e r i m e n t a l - S t u d i e s o n t h e I n g e s t i o n of L e a d C o m p o u n d s . J . I n d u s t : : . K y g. z T o x i c o l . 2,2:381, 19 4 0 . j. -When, h o w e v e r , o t h e r .e x p e r i m e n t a l s u b j e c t s w e r e confined in re sp ira to ry .chambers within which they inhaled lead dispersed,In. ?> i b a i r (u n d e r s t a n d a r d i z e d and c o n t r o l l e d c o n d i tio n s ) f o r 7. 5 h o u r s p e r d a y on 5 , ^33*' d a y s p e r -week (in s im u la tio n of the u s u a l o c c u p a tio n a l re g im e n ), i. e. i n t e r CD O - m i t t e n t l y , the; r a t e of the e x c r e tio n of le a d in the u rin e , and the c o n c e n tra tio n o f l e a d i n t h e b l o o d i n c r e a s e d s t e a d i l y t o a n e a r l y c o n s t a n t l e v e l ( in -about' 1o' . \ w eeks), (after w hich it continued essen tially unchanged for as long as the e x 10 I n h a la tio n o: L e a d by H u m a n S u b je c ts . P u r e Appl. C h em . 3; 129, 19 6 1.) It is obvious, th e re fo re, that continuous exposure to and absorption of ' '' J ' lead, above a certain m ean level (at which day-to-day variability in intake does not co u n teract the continuity of continuous absorption), resu lts in p r o g re s s iv e accu m u latio n of lead in the body. It m ay be p resu m ed , reasonably, a n d in: t h e l a c k of e v i d e n c e to th e c o n t r a r y , t h a t t h i s s t a t e of a f f a i r s p e r s i s t s du rin g the lifetim e of the individual, and that this w ill lead, at a sufficiently high r a te of intake, to the accum ulation of a dangerous "body burd en " of lead. Under the usual environm ental conditions in this country, with re sp e c t to the a b s o rp tio n of lead by p e r s o n s in the g e n e ra l population, no su ch accu m ulation, \. . . . . or only a negligible deg ree of accum ulation, seem s to occur during, a lifetim e. . This p henom enon can be accounted fo r, on tbe b a s is of the re la tiv e in significance -of the quantity of a b s o rb e d lead, th a t is r e ta in e d in the body f r o m day to day - , ,'a. q u a n t i t y t o o . s m a l l ' to b e d e t e c t e d i n o u r " b a l a n c e e x p e r i m e n t s , " o r in t h e , ' a n a ly tic a l finding^ a tjn e b r opsy, :in the face of the v a ria b ility of the t e r m in a l f in d i n g s . , B a r t h (1), T o m p s e t t (2), a n d S c h r o e d e r (3) h av e s u b m i t t e d e v i d e n c e , . w h ich , in, t h e i r ju d g m e n t, w a s to the c o n t r a r y , b u t none of th e s e in v e s t i g a t o r s lim ited the s o u rc e s of hum an sp ecim en s for analysis to those definitely identified (1) B a rth , E. U n te rs u c h u n g e n b e r d en B le ig e h a lt d er m e n s c h lic h e n Knochen. 1, V ir c h o w s A r c h . f. p ath . A n a t. 2 8 1 :1 4 6 , 1931 (2), T o m p s e t t , S, L. T he D e t e r m i n a t i o n a n d D i s t r i b u t i o n of L e a d in H u m a n T issu es and E x c re ta . .Analyst 81:330, 1956. . (3) S c h r o e d e r , H. .A. , e t a l . . A b n o r m a l T r a c e M e t a l s i n M a n : L e a d . J . C h r o n i c . . . D iseases 14:408, 1961. , ., . ' A C 0004458 11 as lacking in any influence other than the cu rren t general environm ental ex posure to lead. This point is crucial. An additional feature of the environ m en tal exposure to lead contributes fu rth er to the paucity of evidence indicative of the p r o g r e s s iv e a cc u m u la tio n of le ad in the bo d ies of p e r s o n s in the g e n e ra l population with advancing age. This factor is the variability in the rate of in take and in the consequent v ariab ility in the ra te of absorption of lead, fro m p e rs o n to p erso n , in the population, b eca u se of the variable selection and utilization of food, qualitatively and quantitatively, by individuals. Bodily size, occupation, clim ate, habits of life and of upbringing, social and econom ic s t a t u s , a n d a v a r i e t y of o t h e r f a c t o r s i n f l u e n c e t h e m a n n e r of e a t i n g a n d t h e -, quantity and .variety of food consum ed. These fa cto rs, in turn, d e te rm in e the q u a n t i t i e s of l e a d t a k e n i n t o t h e a l i m e n t a r y t r a c t . M o r e o v e r , a t d i f f e r e n t .. periods in a single lifetim e, fro m infancy through childhood and adolescence, . adulthood and old age, the quantity and v a rie ty of the food (and its content of lead) consulted by an individual undergo considerable variation, with the re - : suit, akin but not equivalent to th at of te m p o r a l in te rm itte n c y of e x p o su re, that th ere are tim es when lead is being lost from the body, and others when the re v e rs e is true. A seasonal factor (or fa c to rs ) prom otes loss of lead from the body in the sum m er months in the tem perate zone. The balance experim ents on "norm al, " healthy, young subjects have also dem onstrated once and for all tim e, if th e re has been any very serious doubt about the m atter, that the lead which finds its way into the human skeleton is actively involved in the m etabolism of the body. The o sseous m etab o lism , as lead is 12 f co m p ared to that of other tis s u e s of the"bodyj but it responds prom ptly, although, in le s s e r degree, to conditions that disturb the m etabolic equilib rium , such as in crease and d ecre ase in the rate of absorption of lead into the body, or the increased loss of lead fro m the "soft tissu es" of the body . following chelation therapy. (The m e tab o lism of lead is not influenced a p p r e c i a b l y , u n d e r tine o r d i n a r y c o n d i t i o n s of l i f e , or. within, t h e l i m i t s of cautious experim entation, so far as p re s e n t evidence is concerned, by that of ca lc iu m o r phosphorous or of any other m in e ra l elem ent, but is, ra th e r, s trik - . ingly stabile and predictable in its behavior in the body, as has been dem onstrated clearly by th ese experim en ts. M oreover, thei uniform ity in the resp o n ses of a , s e r ie s of subjects to a .v a rie ty of ex p erim en tal conditions, has been little sh o rt of rem ark ab le. ) . , B ecau se of the facts re c ite d above, it seem e d that the demonstraXion of - t h e . m a x i m u m c o n c e n t r a t i o n of a r e p r o d u c i b l e d i s p e r s i o n of a b s o r b a b l e , l e a d in. .. the air that could be Inhaled continuously, with complete safety, by norm al healthy hum an subjects, would r e q u ire d ire c t o b serv ation of the m etabolic e f f e c t s of c o n t i n u o u s e x p o s u r e a.t l e v e l s a b o v e t h o s e n o w p r e v a l e n t in th e c o m munity. Since such direct experim ental observation was not feasible, ` except, . p erhaps, through the expenditure of inordinate, sum s of m oney for the actual ' . c r e a tio n of conditions on housing, s u b sis te n c e and p rolonged m a in te n a n c e of an essen tially n o rm a l conduct of life by the ex p erim en tal skfbjects, an a lte rn a tive approach was thought to be that of establishing the gradient of the resp o n se of h u m a n s u b j e c t s to i n c r e m e n t a l i n c r e a s e s i n t h e d u r a t i o n of i n t e r n 'd ; Lent b u t . q u a n t i t a t i v e l y c o n s t a n t e x p o s u r e , f r o m w h i c h to e x t r a p o l a t e to .a n e a r 13 - X------x Average of mean values.of findings obtained by difhizone and spectrographic Preliminary Period (Control) Period of Exposure Period after termi 14' "O o 12- o m 10o O '. d o .08- 0.) CL .06.O' CL CJ> .0 4 - .02- \/ X OJ in . ^ \.i 5 / > / 48 / .dx y--XfS- ^x/+**: . / x'"' d -' X X ~T----- r 3 5 7 9 I! 13 15 7 i 2i 1-- "--~~r 4 .8 12 ; IS . 20 r i m e in Successive: Per i ods of 2 8 Days 24 14 X-- x Average of mean values of findings obtained by dithizone and 'spectogra Preliminary Period (Control) Period of Exposure ,<-r Period after terminatio .1 4 - o o .12" o CO o .10- O' - O O .0 8 - i-- O) CL ,0 6 JD a. . -- C7> .0 4 - Y / \V x 52 XC X--XsfX; / X ^x-^ sx - x/ -X" 'S,, / \ \ / v X--X -X - o ro _!_____ i y ir 1 3 5 7 9 II 13 4 8 "11r22~ IS 2200 24 28 Time in Successive Periods of 28 Days 15 approxim ation to the m etabolic effects of continuous exposure.... The use of the expression, "approxim ation" arises from the likelihood that, as the experi m ental interm ittency approaches continuity, the shortening periods of freedon fro m exposure and the lengthening perio d s of exposure will operate; against the ach iev em en t of a balance betw een the intake and output of lead, so that the curve indicative of the p r o g r e s s of events will a ssu m e a tre n d bending u p w a r d f r o m . t h e s t r a i g h t lin e i n d i c a t e d in F i g 's. 1 an d 2, to w h i c h d e t a i l e d attention will he draw n later. F r o m the stric tly p ractical point of view, this deviation should have little im p o rtan ce, especially when the concentration of lead in the re s p ire d 'a ir is low. - . .: ; E X P E R IM E N T S CARRIED OUT SINCE 1962 P relim inary Experim ent ' 'a.;: ' T h e f e a s i b i l i t y of t h e ' ' e x p e r i m e n t a l a p p r o a c h d e s c r i b e d a b o v e was- t e s t e d - in an ex p erim en t involving detailed observations (including all of the p ro ced u res ' ' d e s c r i b e d i n p r i o r 1b a l a n c e e x p b i h m e h t s ) of t w o : h u m a n s u b j e c t s o v e r t h e p e r i o d of 144 and 178 w e e k s , re s p e c tiv e ly . (The p e rio d of o b s e rv a tio n of one of the su b jects, p r io r to the initiation of e x p erim en tal ex posure to lead, w as un u s u a l l y p r o l o n g e d s o . a s t o e n a b l e t h e ' o t h e r , s e c u r e d l a t e r , to. u n d e r g o his. initial .-period of e x p e rim e n ta l ex p o su re to lead on the sam e date as the firs t, ; and so to continue parallel procedures. ) ., : Subject s ' a n d ^ ^ j ^ w ere engaged in daily p relim in ary (control) . 'o b serv atio n s, (determ inations of th eir daily intake of lead.in food and b e v era g es and; t h e i r o u t p u t of l e n d i n the. f e c e s a n d u r i n e , i n a s s o c i a t i o n w i t h the- u s u a l battery.-: of h e m a t o l o g i c a l , 'c l i n i c a l , -'m i c r o s c o p i c , and ph y sical, e x a m i n a t i o n s ) , . - 16 - o v er p e r io d s of 56 and 86 w eek s, re s p e c tiv e ly . They entered two correspondingly designed re sp ira to ry cham bers into w hich a i r containing 150 m i c r o g r a m s of lead p e r cubic m e te r , as the sesquioxide, d i s p e r s e d i n p a r t i c l e s r a n g i n g up to 0. 18 m i c r o n in d i a m e t e r , a n d h a v i n g th e m e a n d i a m e t e r of 0. 05 m i c r o n , w a s b e i n g i n t r o d u c e d and e v e n l y d i s t r i b u t e d , and fro m which it was being evacuated, strip p ed (by e le c tro s ta tic precipitation) of its lead, and d ischarged into a stack. The design of the experim ent called fo r exposure' to th e s e conditions on the follow ing sch ed u le : 16 w e e k s fo r 10. 5 h o u r s p e r w e e k ; 16 w e e k s f o r 21 h o u r s p e r w e e k ; and so on, 16 w e e k s at a t i m e , for 31. 5 and 42 h o u rs p e r week. T h i s .schedule did not r e s u lt in c a rry in g the se v e rity of the exposure beyond the level w hich has been established, by both occupational experience and physiological experimentation as being well.within1 t h e l i m i t s ,of s a f e t y . . ' - D u rin g e a c h s u c c e s s i v e p e r i o d of 16 w e e k s , as has b e e n the c a s e in every" othr C xprim ent involving in te r m itte n t ex p o su re to. lead in s im u la tio n of o ccu p a tio n a l;ex p e rien ce (i. e. u su ally 37. 5 h o u rs p e r week), the level of the u r in a r y output of lead p er day, and the co ncentration of lead in the urine of the subjects, as well as the concentration of lead in th eir blood, ro se up to a certain point.and "then continued at essen tially constant levels, so long as the c o n d i tio n s of';e x p o s u r e r e m a i n e d : u n c h a n g e d ; e a c h i n c r e m e n t a l i n c r e a s e in the . w eek ly d u ra tio n of the e x p o su re at le a s t r e s u lte d in a fu rth e r g rad u ated in c r e a s e in the levels of the lead in the urine and blood; a line connecting the points re p re s e n tin g the final levels (or the leveled out plateaux) of the eo n c e n t r a t i o n of l e a d i n the. b l o o d r e a c h e d in t h e s u c c e s s i v e . - . p e r i o d s of 16 w e e k s b ec a m e straig h t line of uniform upward, slope. The re s u lts of the extension ' - 1"7 ...... ,,wv.liv.Vi-ssWiAWJto.'ti .l.'^riid/.--mjij-j-v*.AfcOtJuaiKfaaaiJi*- rf.i-->- 18 - - 19 - - 20 -I c----- -o Mean daily output of lead in urine Preliminary Period (Control) Period of Exposure Peri termi Exp f/S mg Fb in Urine, per 2 4 boy 23 o t h i s l i n e , a t t h e s a m e s l o p e , t o a p o i n t t h a t c o r r e s p o n d e d , i n t h e c a s e of each su b ject, to continuous e x p o su re (i. e. 168 h o u rs p e r w eek) is shown in F i g u r e 1, ( S u b j e c t ), a n d i n F i g u r e 2, ( S u b j e c t Other analytical d a t a of t h i s e x p e r i m e n t h a v e b e e n g r o u p e d a n d c h a r t e d in F i g u r e s 3, `4, a n d ' . 5 ( S u b j e c t ), a n d i n F i g u r e s 6, 7 a n d 8 ( S u b j e c t The general fe a tu re s of th ese ch arts a re s im ila r to those o b serv ed in previous e x p e r i m e n ts , a n d c o m m e n t e d on e l s e w h e r e . It m a y be u s e fu l, h o w e v e r , to ca.ll attention'.to c e rta in of th eir c h a r a c te r is tic s . F i r s t and fo rem o st is the s im i- _' .. _ *' - ' ; l a r . i t y o f t h e t w o s e t s of c h a r t s . We- h a v e l e a r n e d to e x p e c t t h a t t h e b e h a v i o r of hum an subjects- will be m u c h the sa m e under the. sam e e x p e rim e n ta l con- ditionSi but it is none the less im p re ssiv e to note that two individuals have reacted so nearly identically" when, in the L aboratory, their environm ents w e re as n early idetitica.l as they could be m ade, while differing elsew here - acco rd in g to,the-c,ustom s of two different households, and the habits of life of mm,tw o i n d i v i d u a l s , o n e o f w h o m Fig. i),. a c r a f t s m a n , wa,s m a r r i e d and " s e ttle d dow n," the other, F i g . 2) w a s u n m a r r i e d ;a n i g h t - s c h o o l s t u d e n t , a n a lo o k in g to w a r d , a ' t e c h n i c a l c a r e e r . The. c o n c e n t r a t i o n of l e a d in. t h e b l o o d o f , S u b j e c t ,, a t t h e s t a r t , w a s s l i g h t l y l o w e r t h a n t h a t of S u b - .. . j f o g - the; i n i tia l, ( c o n t r o l ) p e r i o d (0. 022* v s. 0. 0 2 4 * m g . p e r 100 g r a m s ) still slightly low er by about the sam e m argin, at the end of the total period of t*. **3 C"5 e x p e r i m e n t a r exposure., and still in the- same, r e la tio n s h ip as the r e s u l t of the O . extrapolation, the slope of th e -c u rv e s ,, as plotted, being re m a rk a b ly sim ila r. U, , Iters- i n s t r u c t i v e ip c o m p a r e - t h e e n d r e s u l t s of t h e Intcv.'nict.f a: r u s - u r v m r v ' * These differences, are negligible in the practical sense, " hey are rem arked upon only because they have-resulted from calculations from data that were - 24 e x p o su re to a i r containing 150 m i c r o g r a m s of lead, with those th at e m e rg e , fro m the extrapolative p ro c e ss, as an ex p ressio n of continuous re s p ira to ry ex p o su re. Thus, the concentration of lead in the blood of the two Subjects - ' *?' - . ' w a s 0. 045 and 0.053 m illig ra m s p e r 100 g r a m s , fo r subjects and r e s p e c t i v e l y , a f t e r 16 w e e k s of e x p o s u r e fo r 42 h o u r s p e r w e e k ( c o m p a r a b l e r o u g h l y to t h e i n d u s t r i a l w e e k ), w h i l e it r e a c h e d th e d e r i v e d l e v e l s of 0, 145# and 0. 148#, re sp e c tiv e ly , at so m e point in tim e (certainly le s s than 3 y e a rs ), a fte r the subjects had been subjected, continuously, to the inhalation of a ir containing the sam e concentration of lead. / The evidence furnished by o b s e r v ation of th e effects of occupational e x p o su re to a w ell m a in tain ed lev el of lead concentration in the industrial atm osphere justifies the conclusion that the co n cen tratio n of lead in the blood.of w o rk m en in c re a s e s for a tim e, until it reach esca level vvhich undergoes little or no fu rth er in c re ase over the period pf m any years.. Under conditions in w hich the concentration in the blood of ; e v e r y w o r k m e n r e m a i n s b e lo w 0. 08 m g . per, 100 g r a m s (that; is , in v ie w of the a n a l y t i c a l d e v i a t i o n of * 0. 01, n o t in e x c e s s o f 0. 07 m g . p e r 100 g r a m s ) , no - case of lead poisoning will occur, in our experience.- The concentration of a p p r o x i m a t e l y 0. 15 m i l l i g r a m of l e a d p e r 100 g r a m s of b l o o d , o n t h e o t h e r h a n d , is unduly high, and w h ile it d o e s not. follow; th a t e v e r y in d ividual w h o s e b lo o d contains such a concentration of lead has or will have lead poisoning, som e becom e ill-p ro m p tly and o th e rs la te r , w hile so m e, unaccountably, r e m a in well__/. _ * These differenCes are negligible in the practical sense. They are rem a rk ed , : upon o n ly b e c a u s e th ey h av e r e s u l t e d f r o m c a lc u la tio n s f r o m data th a t w e r e .. l i m i t e d t o t h e s e c o n d d e c i m a l . .. .. K B' 0 0 0 4 4 7 2