Document pmqLboyq1d9XXJEXVq9Ny6y87

STOOI1657 Ca*e" of Pulmonary nee Survey*. R. Na- ANNA, P. CHANDaASBK- ), and P. Lai.. Bull. . (*NatI. Tuberculosis I. Abeles PLAINTIFF'S EXHIBIT \f\) DOW-2687 OCTOBER 1969 VOLUME 100 NUMBER 4 AMERICAN REVIEW OF RESPIRATORY DISEASE e Clinical and Laboratory Studies 0} Tuberculosis and Respiratory Disease '/ft ASBESTOS AND HEALTH IN 19691 2 HEORGE W. WRIGHT Although a group of materials referred to generically by the term "asbestos" have been known and used, to a small extent, far back in antiquity, widespread and abundant use of these fibers did not begip until the last quarter of the nineteenth century, with further augmen tation of production during the first half of the twentieth century. There are six distinct varieties of asbestiform fibrous minerals. Among some of these, there are striking differences in chemical and physical composition (1). Most commonly produced is chrysotile, a member of the serjicntine family. The amphiboles are subdivided into crocidolite (blue asbestos), amosite, anthophyllite, tremolite, and actinolite. All are silicates, crystalline in nature, and characteris tically are divisible into very small fibrils. Chrysotile and anthophyllite contain much larger amounts of magnesium than either rrocidolite or amosite, and the last two contain much more iron than the others. The crystalline -iructure and surface properties, which may be "f importance in the biologic reaction, are also strikingly different among the varieties of asbestos (1). In view of the great variation of chemical and physical properties, it is most un;|fe to predict that the biologic reactions of one 'tritty of asbestos will be mimicked by another 1,1 terms of either actual consequences or mech anisms. To interpret the biologic actions of 1 Prom the Department of Medicine, St. Luke's hisnital, Cleveland, Ohio. Presented before the Medical Session, as part "I Section SA, at the annual meeting of the Ameri ca Thoracic Societv, Miami Beach, Florida, May ?5. 1069. asbestos, it is imperative that the character of the exposure in terms of concentration, size, and types of fibers be known. This sort of data is scant or often nonexistent at present with respect to exposure of humans. Pulmonary fibrosis: In 1907, Murray (2) re ported the first cases of diffuse pulmonary fibrosis discovered among a group of persons who had experienced substantial and prolonged exposure to respirable-sized asbestiform fibers. Subsequently, the term "asbestosis" was applied to this reaction. Traditionally, asbestosis has connoted this kind of reaction and its sequelae with regard to altered pulmonary and cardio vascular function. Recently, the term has been corrupted to include such manifestations as pleural thickening, pleural plaques, and even the simple presence of ferruginous bodies. Resolution of the use of the word asbestosis must be ob tained to bring clarity to scientific reporting. Murray's report revealed the paradox of a life saving agent possessing the capacity for human harm. At first, the conditions under which this biologic reaction came about seemed to be re stricted to those created during fabrication, conditions limited to textile manufacturing at that time. In 1930, Merewether and Price (31 demonstrated that asbestosis posed a major threat to the health of workers in the asbestos textile trade. It is now known that in any of the several trades in which persons experience pro longed exposure to a high concentration of respirable-sized asbestiform fiber, it is probable that soine of them ultimately will develop pulmonary fibrosis. In response to the report of Merewether and ^vkhican Review oe ItEsriHATOiiv Disease. Volume 100. 1969 407 ST0011657 STOOI1658 46* wbiHw containing their- experience with population to redoes ptiknanary fibroin during- tbs-paal <9) will be of internet to learn how their'1 tone*. The reparttef Sayers and Drcwen (4) in 1939 fathneallMklal^ the introduetios* of molt msinlianmms-- especially in factorise of the and mBfe of Canada the fraa worfcfli - sabatantial- compare to those of the United Ki provisional-TLV expressed-in concent* respirable abed asbestos fiber* has eently in tb* United Kingdom, and a i ferect valuo ban been astabfahrd fat (8,7). Whether these are proper of iwaiam aWWHHfU^aah--tna in their tiow-havwmeeaililtiMstmdera _ of mbartbs Mid alt setfftgs to whklr poenre might occur is debatable, pational lijfiualifrieigraiii. Inadataon appheators ndenble evidence to suggest tbet^ii and MMnriadNiitat'er nail basraem fabrica penetrates to the deep long spaces tors fall intothisaatetory. and ia deared from the hmg more i The pnv--tivs efforts that were applied led to either amoeite or eroddobte (8). considerable impwwBBit in the factories, tile enures lees pulmooary fibrosis in < and raina eprironmenta and a subsequent animals then amoeite or eroeidohte (J),, ! ef theoeeumue* and severity of 5 Witb 'iejpid to the prevention of mensry/fiblMiat3Wnrtnnately, tbo reiaxei fibrosis one would cooehtde in 1969^ of^jpiuMwid--a> governing occupational hwHif ttanysettings the measurca taken i mi--im na iliir the streams of World War It adequate, aad there are populatk serioorfy ntohral with many health protection, barf fittfeor no protection at alL4 pragma, inchwhcg that for tbo raft nae ef required t<r protect all workers is ~ aabaatifonn fiber*. Aa a result, the proteetkm of at present, and its development is workers using aabeatoa in mining and raffling urgent tasks of the immediate future. ! and eapedally in factory setting* has not been aa leas, an important step has been takrfitS good aa it might othenriao have been. further defining the conditions Until quite latently, tbo threshold finrit prevention and ultimate abolition? value (TLV) for environments containing' as- pulmonary fibrosis in persona beatifonn fibers suggmted tentatively by Sayers beatoa fiber. and Drceaen (4) in 1939 has served .is a guide. Bronchogenic cancer: Although^ Data entirely adequate for the purpose were not Lynch and 8mith (10) reported available in 1999, and it baa taken year* to reeog- eaaeer In 2 patients with ai*e this inadequacy and to obtain the inform* until 1917 that the posaftHKy tion upon which to base a more meaningful TLV. biologic influence of asbestos. I Fortunately, cm* of the major naera of aabestoa raised, when Merawetber (11) in the production of textiles and textile products bronchogenic cancer m 13 per < has pursued for many year* a program of en of perron* who bad eabcstosieai vironmental and population monitoring that plqyment in the textile trade.! now ptovidea a more up-to-date experience Don (12) reported a frequency ! (5, 6). These atudiea demonstrate that pulmo of ten times the expected rate i nary fibrosis can be minimised when adequate protective measure* are instituted, and that the concentration of airborne fibers must be the focal point of attention even though the tech nology of such monitoring may be new, difficult, exposed for at leeat 20 yean, durmglhei between-1922 and 1953. This i confirmed in the textile trade by Ns Enterlioo and Kendrick (14), and El-Attar (15). More recently,1 and expensive. The U. 8. Public Health Service, which began extensive studies into the problems of asbestos and health hi 1901,* together with asbestos producer* and manufacturer* in the U5. and Canada are at this time examining co-workers (16) reported a fr chogenie cancer eight times that e group of insulation * more than 20 years who utilised a portion of their time rcmuiiug old c * Cra!lev. L. J.: IVtsottaJ comnraniratioo. imwbtion that contained * ST0011658 AKMM1W AND HRAkTH IX IW KKI t on exposure aifcj _ r,T rvjiorii* naop>te that a.J.i'ni'fiimt lil rre r pan 30 jrwn. I- j4jt* an undetermined rote in the augmented iiow thrir t,.,umr>- of brnnehugmir raneer m some cate- tiled Kmgdum. A of wotkrr*. In tunic of these i.urgorie*, it concentration <* i,,,.nt*r, has thrre been a full exposition of other s lias hem set n uManm* which roniet with ashertos in the , and a (lightly dit i .Mimofflnit and to which the worker hiw Item litthed in the U> [ ,M.*rd (5, 6, 17, IS). It h pm*ihle, therefore, |*`r<jrix rx|Kieil for JO or more years. Thia iu*iir.iim a heavy and prolong'd e,\|*iMire to n.-l>esinr for these two types of worker. Knox and *.loeiatii* (5), in a rout inuat ion ol tin* study of textile workers previously rejmrlrd by DoilOO (12), draw that the iut-idt-nre of lung eanerr tlccrrascs with progrewively smaller total ex-^ jmeurrs to asbestos fibers. Newhouse (13), also__ per for all variety n whirh human n able. There coaM that ehryxnii Hmi mrxbtinK materials ptwratiig careino:,iie |Dtrntal might lie implicated. It would be l^iaicnt to explore this possibility thoroughly' I. lure incepting asbestos per ae as the rarti- in an asbestos textile po|Nibttion, has shown_r. bat lire occurrence of jvulmouMry cancer differs markedly with total rxjioeure. Slie rejmcis noCH increase of the incidence of bronehofrwe'-O iiam kao read* M<rsk factor. cancer in a low to moderately exposed group, ; more readily that In asbestos textile mills, the exposure involves wIsims in a heavily exposed group the B*e- (S). Abo, ehrym l-rrmfirily two varieties of asbestos, ehrysotile and denee was augmented eightfold. Both groups .rneidolit'. In some factories, oil has been were from the same textile mill and were rimiar . dolite (9). i||Jird to the fibers liefore final processing. with respect to duration of exposure and the nttoo of ptUmoMi} Moreover, in the iwocera of "opening" the length of time of observation. Entrrfine aod ie in 1909 that a biers, strong possibility exists that traces Kendrick (14) demonstrated a stronger rela taken hare not ben irf metals known to have carcinogenic in tionship between lung cancer and employment' pulntiona that hart fluence* may have been added to the fibers in the asbestos textile trade than exists in the t all. The kaowledp U9-21). kB dusty manufacturing of asbestos building Icent ia not artiU* Insulation workers have hern exposed not products or building materials. In a series of tnent it one of tb ohr to ehrysotile ai.u amosite but also, espe studies, Manctwo and El-Attar (13) luggttftod tte future. Nevertbe cially in shipyards, t<. > cidolite. The nature that cancer risk is lower with lesser exposures i been taken towed if thrir work, as the; i move old insulation and to asbestos. From these olwnatioM, the m- ms neeeaaary for th* i|iph- new in various places, exposes these ferrace strongly favors u dose relationship be tolitton of signifies*' . workers to many nona*bentos substances, some tween bronchogenic cancer and whatever effect ions exposed to ar "f whirh m-'v he hydrocarbons adsorber! onto asbestos fibers may ultimately be shown to have 1\ lie asbestos fiber. The exposure history of inAlthough in 191 thtion workers k seriously beking as to specific jporled btonchogcw 'li-r.-tiU of all of the materials that they may in its causation. The question of whether the carcinogenic role of asbestos is related to the speeifle kind of jksbestosis, it was v have inhaled in addition to asbestos. fiber is more difficult to answer. For this pur bility of thia sects* <>f the numerous questions which could be pose, populations having long-term exposure to ps fiber was eerkwf l"*^d concerning the relatiooship of asbestos only one variety of fiber are needed. Virtarifc I fll) demonatrate *! bronchogenic cancer, the following three all fabricating processes use more that) Otto |>er rent of autops* ,,r of immediate practical importanew: (!) Ia variety within the same premises at any one mis arising from ew influence dose-related? (?) Is it related to time or have used more than one variety at fde. Eight years litter ` ri iv of asbestos? (5) Does the relationship various times. Populations restricted to mining ncv of hiof cane* '"'live coearcinogenesis? Some evidence bear- and milting in the production of asbestoa fiber Er in textile work** , during the peri* "* ujion these questions ia now available, but " no instance is it complete. I>.ifa concerning the question of dose rela- ks experienee has he '"w-hiiw do exist. The type of work related Be by Newhouae (O' m"*1 strongly to the development of broncho- I (14), and Manew cancer has been in the textile and the keertitlv, Selikoff ae m'"bfion applications trades; the worker, in k frequency of bn* """t instances, has been employed in either that anticipated > 'ti'le for 20 or more years. Merowetber and orkprs employed (f flr* (3), and Fclikoff and associates (21) re- utilised a suhelantr an incidence of asbestosis (pulmonary oving old or apply* *'*`*1 in there groups of SO per cent among tained asbestos. Th lend themselves best to a study of the effects of a single kind of fiber, and H is to ibas*populations that ope must look for an answer to the influence of a single variety of filler. Kivihioto aod Meurman (22) showed that exposure during the production of anthophyflife in Finland carries with it a threefold to fivefold increased risk of bronchogenic cancer for those in the age group older than 45 years w.ih more than !0 years of exposure. At this time, there art no published data with respect to the frequency of bronchogenic cancer m the STOO11659 470 cKtmor. w. wnrairr I croeidoltie or imoailc production areas of South A/nr, ilie only place in the world where ap preciable arrusmU of there type* of fih-r are produced. A verbal report* from South Africa suggest* that the frequency m somewhat hither titan anticipated in the general population of that country. Data from thcac region* will he awaited with treat intercut. In 1958, Braun and Tntan (23) reported a atody of the frequency of hint cancer in worker* of the mine* and mill* producing only ehryeotile in the eastern The considerable variation in the Im.f t-rvienlu(He cancer incidence Iwtwccn population* of yea re. fering type* employment may he csolw*. .L .,ii,sttrrrrn Tr related to dosage, hut it may also Iks tlie f<-: i .,t,< atmi ehry of dilTering eorarrinogen*. Grow and assnr**iat. I Invivtigau (26) produced a higher than anticipated ft. liave cscanum qttettey of pulmonary cancer in rata ex|meed > ir*I the lr*q chiysotile. They attributed thin variance, frv 1 i,xi* uertqin the experience of other*, to be related to r i Ih' rrsul* *- tamination of the ehryeotile fibers hv nick. I cobalt, and chromium caused by the wear . I i*>fitre i nirsuthe ^ q port of Quebec, Canada. From the data avail able to them at that time, they found no evidence of an aDemented frequency of bronchogenic cancer in this rrcmp of employee*. Although the jierind of olMcrvatton wn* only five venr* and the group was diluted by short-term exposure*, it contained more than 1,700 persona employed the metal components of the miU used in pt ; "O paring the fiber for administration to their at, auKing mab. CraHey and aaaociatea (19,20) showed txi > the (hH stantial amounts of these trace metals in tl the- 0.' asbestos fibers used commercially. Miller and a 1 mrsadi soeiates (27) have ahown that broao (a) pvm I mtImp cr* cn o plus asbestos sugments the yield of pultn.! J2), , longer than 20 yearn, aO of whom had had at ntr^ turnon produced by benso (a) pyru whceetlm least five years of exposure and 930 of whom alooe. Harington and associates (2S) raised il inrtroofmy r were older than 55 years of age. The data would poasibility that adsorbed hydrocarbons octet hmsAlm.ase have )*en more meaningful if arranged in term* ring natively or picked up in storage si f htsolation of total exposure and time from beginning of ex handling may play a role in cocareinogencs*. ucturing* fat posure. Nevertheless, if an extra* of hmg cancer As reviewed in 1909, the role of asbestos. Uotnhlp has equivalent to that seen in the settings referred augmenting the incidence of bronchogenic euf itMdsritm.Wf lo previously in this paper did actually exist ecr appears to be dose-related, may be depend; wth textile ; in this population, it seems likely it would upon the specific category' of fiber, especially nut study 0 have been found. This same jmpulalion is now relation to the degree of effect, and appears * * m Canada w leing reetudied after a much longer period of he that of a eocarcinogen. In observation and in a more adequate way. enothelioma: Subsequent to the earlier r * been rn Vigliani nnd associates (24) have found evi porta linking occupational exposure to **!*-' at rUciwitli dence of an augmented frequency of cancer of and bronchogenic cancer, there were sever t`md utrt*i tlie lung nnd pleura m a group of 288 persons, suggestion* that tumors of the peritoneal < Haee nf tec previously compensated for asbestosi* arising pleural mesothelium might be similarly link*' .'iwwttpjat from all occupation*, who died between 1943 Interest in this phenomenon remained dontm -naattbe and 1007. In a subgroup of 32 miner* exposed however, until Wagner (29), in 1959, report-i ***^^fcy *o chrysolite only, there was no augmentation 20 ennm of pleural mesothelioma tasoeiated */1 Wtflpflirtflr of the rate cf cancer of lung nnd pleura. Al the Northweat Capo region of South Africa. I I "Mtwf fef though these studio* suggest that chrysntile suggested that these were related to exposure f UnnAerwed has little or no carcinogenic influence, more ex tensive and refined epidemiologic data are needtsl liefon- reaching that conclusion. The possibility that the carcinogenic role of asbestos is solely that of a eoeareinogen is very strung. Tin- data of SelikofF nnd associates (25) arc osjieeiallv pertinent in this regard, in that not a single bronchogenic eaneer lets been found in an insulation worker who was a noncignri'tte smoker, rvrn though the exposure to experienred hy the nt.nsmnkrrs wn* the came it- that of th.*>c who smoktsl nd did' develop lung cancer. crocidolite asbestos because 14 of the |<cT" 4 were born or had spent tbeir early youth t* Kttruman, where crocidolite production b of the major industries. This nbsrrv-u I'M**: An* prompted an intensive search for all nM*1" rHatioi iiomas in South Africa. Gilson (30) plottd ' `Mean* nf numher and distribution of the South Afr- `"wmg. cases up to 1902 and demonstrated a -rnt There ji ctinrentration of cases in the Northwest <' r',?* rogar* Although almost none wa found to ** 't *he ifia- elsewhere in South Africa, the inference th*' concentration of in<ssithelk>ma* coitTceh'l r the sole source of rrocidnlitc in South A" only "e hMi*n V * Wrlwt. r. I.: Personal coinmuniratioo. would not he warranted. A substantial q*wif He* he. ST0011660 ASMKTOB AX1> HEALTH IN 1909 471 (ion in the K- ,.i ,-rucwiufite has been |Woduced for a period of populaUoa* of <1 rilIny years, hundreds of milea away in the ml may be not , ,.irra Transvaal, the ume am in which amo- ty also be the re-*. .,t- .-md chiyaotde asbestos are produced (31). Cross and --on i- Iiivcstigstofs m other parts of the world tan anticipated 1: , ,i, examined the distribution of mesotheliomas t in rata trpowl ,IM| the frequency of mesothelioma in popola- ihia variance, fiv f,.m* occupationally exposed to asbestos, with o be related to (w | ,l,,. result that a strong relationship between - ile fibeta by nirL i ..Mire to asbestos fiber and the presence of Kerf by the wear nK-Mithdioma hat been indicated. Most of the he mill need at pr outside 8ootb Africa, where mining and rtration to their a milling are implicated, have been reported in (19,20) showed ar i!ie United Kingdom and, to a lesser degree, m trace metals m t Ik- U-S. In spite of a (borough search, do It is apparent that the overwhelming number of case* lima far being related to tubeslo* are diagnosed on the basis of bio|wy alone. Further study will be needed to demonstrate whether mesothelioma is being over or under diagnosed. If one accepts that some kind of direct or indirect relationship between asbestos and mesothelioma exists, docs it involve a specific variety of fiber? The data from the U. and United Kmgdom does not lend itself to resolving this question because chrytsotile, amosite, and cTocioohte are involved m tne insutaton workers exposure, and chrysotile phis crocidolite in that of the textile manufacturing employees. If one minmw the mining and milling exposures to rehlly. Miller and * nr-ot>ieliomas have been fuund amoeiated with tbe specific variety of fiber, interesting fads hat bettxo (a) pyrr mihuphyllhe asbestos productioo in Finland emerge. Kiviluoto and Meurman (22) did Dot he yidd of pub t.'.'f, and few are reported in France (32), find a single mesothelioma in a large popula r benao (a) pyre Iktc the subject has probably not been tion of miners and mill workers cxjioaed only to infos (28) ratad: Imroughly investigated. In the United King* antbopbyllite. This group worked for three hydrocarbons otn (in, the association has been with populations months or more between the period of 1935 up b storage r insulation worker* and asbestos textile mnnu- and 1907. Although others have stressed the in roearcmogrnm* inuring factories (33). In the U.8., the rela- long period of time required for mesothelioma e role of aabestm Monship has been shown predominantly with development, one would think that if anthophyl- of bronchogenic ts n ulation workers (10) and, to a lesser degree, life by itself is implicated, at least one case ed, may be depend >nli textile manufacturing employees (15). Re- would have been found by now in a setting of fiber, especially nf tudy of the distribution of mesotheliomas known to cause asbestoaia and a somewhat aug fleet, and appear? n (Nnada will be commented upon later. mented frequency of bronchogenic cancer. In a In most of the studies to date, the question study of the distribution of mesotheliomas in nt to the earlifT ' 1 ' heen raised as to whether the population Canada, McDonald and co-workers (35) were exposure to a*b^' ' rink with respect to mesothelioma is to be unable to show exceaa frequency in the geo there were srv*' ' iiud outside as well as inside tbe factory or graphic area where ehrysotile, but no other *f the peritoneal ' ;lin> of work. There has been a plethora of variety of asbestos, is produced. t be ahaibrly linb > r-'ll:,tion by students of the problem that Tbe South African distribution of metotbe* m remained dome ' ii'ii ha* heen nccepted as fuel or interpreted aa Ikxnaa is unusually intereating. Webster (58) B), in 1959, rep'f " *' by lay writers. These dramatic speculation# reports that before the end of 1968, 179 cases Hioma associated * o of Sooth Afrir-i 'i- further compounded an already difficult of mesothelioma were agreed upon as meeting '|"t for those responsible for public protec- acceptable criteria. Of these, tbe history of ex related to exprenf ' n .is well as those responsible for the health ae 14 of the pre : '-wjiloyeea. Controversial or paradoxic iasura heir early vmiili 1 "ii inewithcliomn and nslx-nto* deserve a itc production * ' ' r-iHupletr discussion tlmn is ixewible in thia a. This nhwrv' 'l*r Among the controversial features about oh for all me-'' r,'lationship of ashestoM cxjioeure to meso- ilsnn (30) plot t<d of the South Ah nf the pleura and peritoneum arc the ' uip. non.tratrl a .tr1 i Iltf i.4 n lively controversy among patbolo- the Northwest < "Tarding die requiremem* for rsiabiish- v**i found to e - ',lr diagnosis of primary mesothelioma (3d). the inference tta' id\ k tltere a que-tion with respect to iomns coincided ' '`Inliipie criteria, but rvm more important, fite iw Sovth -V* >( rv for rsrafdishing by autopsy V substantial ,w>t the tumor h primary nr secondary. posure was known in 148 patients, and in 24 there was no asbestos exposure. Fifty-one pa tients had been exposed during the mining and milling of croeidolite in the Northwest Cape only. An additional 52 patients with mesothe lioma, not exposed occupationally, were as sociated in some way with residence in the Northwest Cajjc. STuia-Cremmer (31) has in dicated that about 20 per cent of nil croeidolite iwoductkm in South Africa actually comes from mmes located in the Transvaal, a few hundred miles from the Northwest Cape. He also indi cated that altltough the exposure insy have been somewhat less intense in these mines than m ihor nf the Northwest Cape, it nevertheless was (r) t--> o -- ^ .__ ST0011661 I 72 ucowon w. wmcurr 1. high. The wnlrr's impiirire confirm this and indicate farther that the mimi* of the Trans vaal here heew in upffslieo for as many yean v thaw m the Nerthwret Cope. The mechnnism for obtminmtr data regarding mesothelioma in ll>e Trawaaleroridolitr nrm w klentirnl 1(* ihat for the Northwest Cape. Because not a smite mk of memtbcliania hu been (liwwtwd from the eraddoBte mines nr surrounding com The question of wlictlier tliere is a ttilefel^imnJo exposure or threshold limit vnlue for nd^t^lmrh without eontrading an enhanced risk of *kir vdoping meotleloma has been raised bv i V> findingof what, on first inquiry, seemed to j 4- -- minor exposures to the fiber in nonoccupatk* . > settings as a iMtckground for some of the es-v ^ of mesothelioma reported in South Africa (- i.< __ and the United Kingdom (33). Although ores.- cn munities of theeTnnevao), although SI caees have came froas the eroeMolite mines ami 62 additional'cast*-from the neighboring commu nity in the Northwest Cape producing exactly (he same kind of fiber, the contention that rroridoJite per ar entases mesothelioma becomes nally it had been thought that there were m* a i cr sueh examples of nwaothdioms developing. *,Yl rxj aide an occupation or occupation-associated r *4 vironment, better and more complete expwraiete gl histories reduced this proportion greatly. .tLrtain present, 80 per cent or more of the meswbWy be difficult to accept. Huia-Greromer (31) pointed liotnas thus studied in the United Kingde U-h**n out this paradox in 1064. Webster (38), in his and South Africa have been shown to bars *V*reincc current report on asbestos exposures in South occupational or paraoccupational nxsoetati ' If on Africa, Kkeaisc calls attention to thia disparity. with asbestos fiber. The level of this expos ud ft It u of equal interest that only 3 eases of is substantial. Most cases occurring outse^nwlhfc mesothelionia have been reported as originat actual "on the job occupational exposure" ocwfwe ore ing from the Transvaal, tho^e being from the through an exposed worker living on the swwrupati amosite asbestos mines (3ft). No cases of premises, who brings fiber into the home-oa ksdrrabk mesothelioma have been report'd from the clothing, or through contamination of tl*** no ehryaotile mines of the Transvaal. On the basis environment surrounding an industrial ope N mm of what is known about the number of tion which has east airborne fiber into ill Ml an< persons employed, the intensity and duration of atmosphere for years and thus exposed peuwtaJwafc exposure, plus lapse time, one would expect living or working in sueh a neighborhood. Tl b adw? far more than 3 eases of mesothelioma if was especially exemplified in the Norths- wee n amosite had the same potential as the factor Cape region of South Africa where roads xvhwMtihci causing mesotheliomas in the Northwest Cape. made of asbestos-bearing waste rock, trbT The dosage and particle rise have not been women were employed in hand cobbing or f**eept sufficiently different in the Northwest Gape gleaning asbestos fiber from the waste beaj-^sal pul and Transvaal to explain the striking absence and where the mill disseminated blue fiber gr* part, or minimal occurrence of mesotheliomas in widely around its location. There is rtaasa pJFffhh the Transvaal. believe that these various types of expan'tongidm The discovery of such a striking concentra tion of mesotheliomas in the Northwest Cape suggests the need for a thorough study of the differences between this region and other areas of South Africa in terms of possible etioiogic factors. That something other than, or in ad dition to, asbestos plays a role in mesothelioma formation seems inearnpahlc. The geology and climate of the Northwest Cape differs con siderably from that of the Transvaal. Trace metals, chemicals, or oils adsorlied onto asbes tos may be factors, ff erocidoJite is impli cated, it is likely to be in the role of a eocarrinogm, some additional ngrnt providing the difference between the ex|>rrienre of the North west CVtpe nod the Transvaal. Morli more study needs to be made of this aspect. have been substantial in the population tl **** b; involved during the past 40 years. *** an With respect to neighborliood or paraoresr *'*"*'* 1 tional exposure to asbestos in the U3., H * Tl of interest that Borrow and co-workers I" '* Tlum called attention to the fart that none of th *'*cral i scries of meeothHioma, gleaned from a c* v,n*Har 1 munity medical practice, fell into this 1* '-si* > gory of exposure. la it reasonable to believe that the casw H 'be a mesothelioma in which no occupational or p1' t*',, f I' occupational asbestos exposure can Is* *-- closed, amounting to less than 20 per rent r,`t'r< tfxise reported from lire United Kingdom ^,v '* South Africa, in fact represent a reacts# f'"me the casual exposures which might be etp j**,rrh i- cncctl by the public at large? In the IVI1*** "*1' ST0011662 STOO! 1653 AMHKXTOH AND IfKALTII IN 1000 473 icr there m a ,, n^k-m. where an intensive search for m*o- rent of the imputation exhibited these bodie*. mit vahe lor alv .tanis has hren pursued actively during the enhanced risk ol . i )lMir years, fewer 0. n 100 roses thus far i.xs been rawed by ,, (sen diwomrd in jwrson* who have n>l inquiry, eemed to j known substantial rx|***Mrr t asbestos iber in nonoceupnu, ,i. If one adil to thl* a portion of the 1.12 I for acme of the n .. .ilirmt which there was no information, li in Sooth Africa (, , nonilier of persona who have not had a n (.13). Althmigh Of;* ...Mf.ihle wih-tantril rxpnmire, hut in whom t that there were m. | c ...italkinu* has developed, is lew than 200. There structures have Utii nssnniid by many to represent coated aslicsto* filsws and, Uwroforc, to indicnlc an exposure to the inhalation of asIwstus fiber, hence a higher ri*k of developing mesothelioma. Several farts militate againM this conclusion. The coated filx-rs found in the lungs of llie {sihlic have not lieen prove*I to lie asbestos fibers. When they aTe found in jer*ni* who idiom* developing t* hi. number ie such a minuscule proportion lve exjiertcnccd n heavy exjiosure to ihc in .cu patioo-oasociated die adult population from which the eaaea halation of asl>etos fiber, if is reasonable to note complete expnsi *w gleaned that it becomes difficult to en- assume that the btdk of there bodies do proportion greatly, .inn tb*- view that the asbestos fibers that represent asbestos fiber. It has been slwron, more of the mean:: ,v Is* in the air and respired in h casual however, that other materials which are the'United Kingd , hsm hy llie public at large pose a genuine been shown to hare .rrmofcnir threat. coipational amocht If one postulates that there are respirable level of that expo*: /.d filler* of asbestos in the ambient air area occurring own r<.idiorl by the grneral public, tlie strikingly rational exposure" oct tte omirrmee of mesothelioma not related to rker living on the nr mintion strongly suggests that there is a rr into the home on I i !< rable level of airborne nslwstoa fiber which contamination of i *- not pause an undue risk of development iK an industrial ojw tiH-otlielioma. The findings of Newhouse lirhome fd>er into r Id ami McDonald and ajworiatrs (35), which ad thus exposed per.-* !:> ate that a genuine occupational exposure eh a neighborhood. T vlie-to* has been tolerated without evi- fibrous in nature will produce bodies of an kk-ntieal appearance (41). Crnllev an*l arociafes (42) have listed 20 mineral materialthat are fibrous in nature and that may lie widely disseminated in the environment of the general publie. Because of the numerwts otlwr types of fibers that may, and almost cer tainly do, gain nerrsa to human lungs where they become coated with an iron-protein com plex, Cross and co-workers (43) suggested the term ferruginous bodies for these structures and suggested that they be railed aslwstos ified in the Norths nee of an inerenrd risk of developing a bmlics only when it is known with certainty, tfrica where roada ** >-"dielionia, suggest that the tolerable level or ran he presumed on the basis of known tng watte rock, why 'nlntantLal. The rvidenee strongly favora the exposure, that the central fiber of the body is . in hand cobbing or 'nopt that the casual exposure of the gen in fact asbestos. This would appear to be a far , from the waste ho; 'd public has not rxeerdrd such a level in more aenimtc designation and scientific atti tminated blue fiber q*> |cist. tude than to insist on calling all of these lion. There it reason f < rrnginou* [nxbtsto*) bodir*. In spite of the jfotis types of expoor r'suing considerations, additional develop- ,'in the population (I f "t> have caused some investigators to suggest t 40 years. J ,f epidemic of mesotheliomas will occur sborhood or paraoeni; J:;,mig the general public in the near future estoa in the US., it I ' This apprehension is based on the finding sr and co-workers I" Thomson and associates (30), confirmed by [fact that none of thr'*-fd others, that structures identified as heing w gleaned from a w*"'d-,r to asbestos bodies (commonly seen in lee, fell into this " 'r-ns known to have an intensive exposure to d-ioi fibers) are found in 25 per omt or more bodies asbestos bodies whether or not they are known to be such. The literature concerning ferruginous bodies has l)crome quite targe, and sweeping infer ences from their presence in the general pop ulation have been made (38, 44). Without attention to the necessary quantitative and qual itative factors, it has been predicted that the experience of the general puldie with respeet to racsothciioma will parallel that which has >clieVe that the ease* " ""hilt general public by direct examma- thus far been disclosed in certain very specific no occupational or "n "[ lung tissue or of the juices pressed from oerupationnl and paraoecupational settings. A i exposure can be f***ue. The frequency of occurrence of these number of facta indicate a great need for cau r than 20 per eetii f** "w in the lung* of the general public appar- tion before arriving at such a serious con be United Kingdom P''v 'Spends upon the volume of lung time clusion. To transfer the experience of a specific rrpreaaat a reacts* T'*me.l and the intensity with which the oenirationsI or pnraormpational population to which, aright be e*T * made, because Utkljian and co-workers the general public requires evidence that the it largeT In the Uiw'f * Report that in their series almost 100 per exposure of the publie does, in fact, eorre- STOO11663 474 nKOftOR^Wr wmoirr pood^lo thorn- |M|fuintimM in which ail in- ruginous IhhIics is uai>-!irv Is-fure any imau, rmnd thfc of mothriiaan w raid U> exist. ingful interpretation of llmir ini|sirt*irv i,,, This is apcailljr true mnr that it bs been demonstrated that tltcrr are some nrr)tational pnpuiaUoM-ia'whieh the exitin' 'i> asbestos fiberexceed* --nr fold that f )*r cml public and which. Be evidence of an unusual the general public can Is- made. i The finding f ferruginous imdica in a L,,r. 1 proportion of the general jstpulaliriii hn t .. | CO to the contention that the :<iigtiiciited n.-r . i --) asbestos in tlie minufarturr of pmdttets |,,, CD mi anllulii-- M *m found (13, 22, 35). Whnt greatly increased tlw degree to which the pi O is the ptutB siteslion in this regard ? rral public has l>cen exposed to this fit>i As indicatad in foregoing discussions, conebuncos with , regard to the relationship be tween mesothefimm and asbestos fiber per se, This assumption Ins lieen based upon tl. simple statistic of aslM'strw consumption.''im no attention lx:iug ]Ktid to how the filter cr cb> even m so oeewpationxl setting, are rather un used nor the degree to which its tiltmui. certain at this lane. The roles of types of fiber, fabricated form would lend itself to dawn*). j coftarciBogencris, and dosage are so far from nation of fiber among tbe public (30). .V ! being clear in these special occupational set (bough it is jtoseible that augmented comma;, tings as to give little assurance that they can be tinn of asbestos fiber led fa a greater owtj*. ' transferred m any meaningful way to the of these fibers from factories into the air mu nonocrupational related ir general public popu rounding the factory, this does not constitute,. lations. generalized public environment! f expnrat. Although a scant number of ferrugmoos Tabcrahflw (45) has pointed out that aaiwe- { bodies has been demonstrated in hmgs from is used for tbe most part in fabrication > (he general public, ihcre has been no demon materials that are unlikely to become au 'f stration that these are in fact the result of borne. It is not widely appreciated that tl, exposure to asbestos filler rather than to one bulk of the products using nsltextns sctnaP | or more of tbe many other materials known bind the fiber firmly in the product, and the to be capable of producing ferruginous bodies. is subsequently very little opportunity for r At this time, the determination of whether the lease of this fiber except by slow wear of tl fibrous core of a ferruginous body is in fact products. , aabeatos is extraordinarily difficult and quite beyond the means of other than the most sophisticated laboratories. In spite of this, the oeceamry investigation must be done before the contention that all ferruginous bodies in the Tbe estimated consumption of asbestos fib' in the U.S. has increased from 125,000 sW a tons in 1018 to 720,000 in 1965; moat of tl- I. increase occurred after 1040.* Once the filT r in tbe form of a product, is put into pbr* he genera) public are in fact asbestos fibers can it is not released except by gradual wear, *1fc+ be accepted. in most examples is minimal. During Bird* Quantitative estimates indicate that the processing, the public at large is not exposed. *.number of ferruginous bodies found in the Dtiring the use of certain products, s**rk * lungs of the general public is a small fraction of the number found in the longs of those who had been occupationally px|msrd. If one accepts the contention that ferruginous bodies reflect asbestos exposure, one must conclude that the general public has had far less ex posure than those persons in ocrnpati-ins us ing asbestos fiber. That some persons with known occupational exposure to asbestos fiber appear to Have but few ferruginous bodies insulation removal and application, filters i* released and timer in the immediate view' t. workmen and public, may be cxpoonL Tl ' 1 ratrgory of product ran be thought of- s' m liaving filters that are "loosely !>ound,* in e-e fv trast to stjeh products ns asbestos ttmctu floor tile which actually incorporate the Iff*' and bind them very tightly. The qnanti asbestos filter used for "loosely bound" pnshf ` including iuMilntion (figure 1), has inrm-' complicates an interpretation of quantitative from 30,000 onlv to .53,000 short inns bn*"' measurement of ferruginous Imdics. Tt is clear 1020 and 1005.' that much more comprehensive and reliable Tlie rnutmerrial grade of filter indica' ,w data with regard to the dynamics nod the kind of prwlucts in which it will quantitative nod qualitative aspect* of fer * Piindwirfc, I'.: Penman! communication. ST0011664 STOOI 1665 ASbKSTO* AND UF.AW11 IN WOO 475 chirr iinv inmti importance iiif 1 U. S. A. IMPORTS CHRYSOTILE ONLY Usltes in ft bir inilation has iigmented usr f,: J of products It,.! n which the frt>- i aI to this filler . Ixiscd upon tl* onsumption, wnl. l how the fiber ihich its ultnmt' itself to dissetm public (30). Al imented conmimp a grratrr output into the air sur> not constilurp mental exposure mu thftt asheslr*. in fabrication oi to liecomo sirrcriatrd that tin a.`'liestoo aetualh product, and linn pportunitv for r, .-low wear of tin Flo. 1. Amount of chrysotilc asbestos (short tons) used in the U. S. during 1930 to 1965, irrordine to the grade of fiber. Lone*-*! fibers arc grade 3 and shortest arc grade 7. "Loosely bound" prodrieis include inuUlion find other materials that may release fibers (luring use, installation, ur removal. ll of asbestos filler |T1i:if most of the augmentation of ronsump- rem 125,000 shnri 'io of rhTysotile has lieen in grades 4, 6, and lltt5: most of th (especially 7) is shown in figure 1. Grade ).* Once the fiber coos predominantly into asphalt and vinyl is put into plan. or tile which usually has a life of 20 to Tudual wear, uhirli ye-ars or mure liefore it is changed, na a al. During factor' -nit of decoration alterations rather than ; is not exposed, h'-ir. The hulk of grades 4 and C goes into i products, such n- cement products, especially asbestos ilicntion, fibers an incut pipe, in which the replacement time immediate vicinity. indefinite--system* now in use are more than Ik- exposed. Tin " years old. Air contftmin.'.tion does not occur be thought of a-.. f">*n this source. Although there may be some rlv bound,"" in con- Hr^diering of asbestos cement shingles and ftsl^stos cement w 'he rate of wear is very slow. It can lorpomte the fiber- ^dilv be seen that although there has been c. The quantity of i augmented utilisation of asfiestos fiber, th" lv ImiirKl" prodifi- 'rresi fraction of it has gone into strongly 1), has increased "<ln<l products designed to last many years. short tons between jT*n- wear from these products is also far le `'n the total product by the lime the ma- filer indrrato' the ,fbl i* discarderl. h it will lie uwd 4'hestoa forms an essential part of friction romuuiralion. h*'erinls. Concern has been expressed that the ' public is exposed to large quantities of asbestos fiber liberated by the wear of automobile brake linings. This is unwarranted. The amount of asbestos fiber used in friction material in the ILS. wns estimator] at 33,000 tons, less than 5 per rent of the total in 1965* Studies of the mnterir.l released during the use of brakes (46) demonstrated that the high hent of friction destroys the asbestos converting it to an amorphous matcrin! no longer having the char acteristics of asbestos. Of tho total materials removed from brake linings during their use, less than 5 per cent appears as actual asbestos. The amount of asliestos fiber released by normal friction material wear must bo small indeed. The fibers that might.be released from all kinds of wear cither become intimately bound with the soil nr arc captured in either rain wnter or in water used for cleansing. Ultimately the fibers are distributed predominantly where water is distributed. A study of river water has shown that asbestos fiber is almost universally present although in quite small amounts. How ST0011665 STOOI1666 47tV (.Milton \v TAIU.K 1 Auoc sr or (!imoikim-i m. T\t>- 1 ' M> InN V vntoirs PHOOUeTS IN THE Lr.S. tSlIOHT Tons in I0H71 of fibers in the general en\ iriminent as a noift of wear. It i-` tibvious from these data thv commercial tale provides a |sitent murcr ,i Told US. consunapt ion Ceramics Paint Roofing I tweet icirtra Paper Hefractoriea Ituhftrr Toilet preparation* Other 8211. UtIO 220.000 153,000 72,000 lit# ,000 45,0t)0 41,000 31,000 28,000 107,000 least equivalent in that of :t.-l>e''los for supplyine re-pinlile-sizixl fibers that could prndwr ferruginous body's. It is difficult to conceive o| a 1x4 ter way of havinjc filrora inhaled than il use of cosmetic talcum powders. In tliU re. card, it is of interest that Avril and Champm (49) found no ferruginous Itodies in 1.H autopsies in France. It is claimed that the cosmeiic talcum in France has no fibers* U* | Total U.S. rntmmnpti>n of adientiw in 1905 was extent to which other mineral or vegetable 720,000 d*ort tmw. fillers known to lie present in tire environ, ment of the general public may contribute much of ibis ntuun from wear of products and how much from learliing of soil is of course not determined. The concept that asbestos is indestructible is fallacious, and t c belief that it accumulates on the surface of streets and other places seems ill-founded. Tiie possibility that sources of fiber other than eommerrial asbestos may lead to ferrnginous bodies must be considered. Tale is a form of magnesium silicate that exists in sev eral forms, h.v> large industrial use, and com monly is contaminated bv fibrous substanres such as trctnolite and even chrysotile. It should be noted that tale production has been shown to cause pulmonary fibrosis and possibly in fluence the development of bronchogenic canrcr (47). As shown in table 1, the consumption of commercial talc in the Uf. exceeds that for asbestos. Ailention to some of the products to the prodnnion of ferruginous hndie# * a|^. yet unknown. ' Data have been reported recently by SvWhA &! and Hammond (50) showing that the frcepWoCy " of oreurrence of ferruginous IxxJies is rw4 tLally the same in lungs obtained by autopsy* p 19.14 as in 1907, a finding difficult to rocowik with the contention that the augmented use ef aslie^tos during the past .'{*> yrars ha* greatly enhanced the exposure of the general pubhr to aslicstos filn-r. It also raises the question tf whether the fibers in these ferruginous bedir* are in fact asliestos. A similar study in Grrst Hritain failed to demonstrate any femtgt* noiiH Imdies in lnnr samples obtained al ikrropsy in ]93f. or in lung samples from j males autopsied in 1940 (51). AlthoMgfctW'| may have been fewer than now, there san^r.' must have lieen jiotent sourres for the diswffiW 1J made suggests tint the opportunities for airIxinie talr dissemination may have bren aug mented to an even creator decree than Ins nation of ls>th talc and asbestos in Grra'j Hritain liefore 1939 and 1049. j Tlie previous findings provide Jittle or f> aljestos. Crnllcv and associates M8), in an evidener to suggest that an rpxlennc ' assessment of 22 cosmetic talcum powders mesothelioma among the public at large K*-* purchased in the TT.5v. found that an average lie expected. In a more positive way, the ild- | of 20 jier cent of the particles were fillers. from South Africa indicate that during tie' !*>' These fillers are fully capable of pruduring five or six years the nnmlier of new m*es . ferruginous bodies in the experimental animal. mesothelioma have been rather miistanr *' It is of interest to note that the amount of approximately 2(1 jier year, and in Cm1' i eommerrial talc that ultimately finds its way Hrifain f.Tl)` only a moderate inrrras** I- ' into toilet preparations is far in excess of the lieen shown. t amount of aslwsu s used in the manufacture of insulation rnatrrinb. Insecticide preparations ronaumc a l.ai*cr lonnacc than all of the un bound kinds of asbestos fiber put toijetlicr. Rubber, which utilizes a large ninount of rrmmrrrial tale, may contribute to the di-t barge Although the study of ferruginous l^b'i i* of interest, the ncee-sity for the nstn J core to (> identified and for i|oantuatbe >H' ! to lie obtainer! in order that more meaning* I conrhisions )w reached aliont their tmf* *A\ril. J.: Personal cnu.nniniraiton. ST0011666 ASnlCSTOfl AND HXALTU IK |W 477 i is ;i rri J ' data th I t ?ourrc 'I for nuns'.. uM prwtw conceive . | led that* it i In this . i <1 Champ!irj in l1. ; >d that il, | filters* Tbj -r vcgclnh' | lie cnvimt j rorinhni linriic* i r . hv Sefiki-' lie frrqurer f~ if foes y autopsy l to reconn)cntrd use e hn gmllrirr.al question i'' inniw holfeily in Grr-r ' ,nv femrr dned At Tie rs from frlIlf))l(th Ilf' there sure!' 1 Jlf* (Iwseni: * in Grey little ir itrpiilentie ` j large i- ' ay tltr itsi J 'illg the )n-' irw r:ii" 1 inn-tnltt 1 in Crr ' iierene !'' nous I...... I tile renn- j Illative <l>' mmninr" le-ir imp*' -iicgesls that this is an nrw\ of study with diminishing returns. A direct approach to the irmrc easily identifiable naked fibers contained in the lung would appear to bo a more fruit ful avenue of search. Stilt better would be a ilirert approach to the types and amounts of fiber present in the ambient air of the various environmental location? that are of interest epidemiologic point of view it i proper to consider these findings as evidence of asbestos exposure. Long-term implications nf pleural plaques are a matter of interest. In general, unless the thickening of the pleura is extensive, the ef fects of this patchy thickening on various as pects of pulmonary function are minimal or with respect to occupational, paraoccupational, and emend public exposure. Although this would pose the disadvantage of not giving absent.7 There is no evidence that the preaeuce of pleural plaqur> connotes anything with re spect to the ultimate development of mesothe information with regard to long-term past ex- lioma. In fact, two of the geographic areas |KHiiro, (here is equally no gtiarantee that in which the largest concentrations of pleural ferruginous bodies truly represent the complete plaques have horn reported, Finland (52) and history of past exposure. The direct approach eastern (Quebec Province,* do not have a to the study of fiber populations in the ambient demonstrated excessive frequency of me.sot be - air would have the advantage of trfling us lioma. To use the presence of pleural plaques what the conditions arc for the public at pres as a marker of previous asliestos exposure is ent. of limited value, in view cf the fact that other Pleural piaqueti Attention has been directed toward another phenomenon said to be the result of past exposure to asbestos fiber. Since the first recognition that prolonged inhalation canses lead to this condition and especially m view of the fact that the absence of plaques in no wav connotes the absence of absestos ex posure. of asbestos fibers might in some persons lead to diffuse pulmonary fibrosis, clinicians have law aware that areas of thickening of the The relationship between asbestos and health pleura occur in some such persons. At times, of humans, as review able in 1900, indicates that this thickening is localized lending to the ap serious exposures to asbestos fiber can occur pearance of plaques, some of which may be in certain occupational and immediately ad calcified. The pleura effects range all the way jacent environments. Fortunately, the con from minimal findings to extensive and bizarre, centration nf asbestos fibers in these settingup irregularly shaped, calcific masses. Pleural can be controlled. 'The environment of the in plaques with or without ealcifiration are a sulation workers is more difficult to control matter of considerable interest at the present than the more fixed and permanent environ time. Unexpectedly, these manifestations arc ment of the factoty and a.-sociated neighbor often absent in persons who have well-developed hood. An approximation of the concentration diffuse pulmonary fibrosis resulting from pro of respirabh--izod asbestos filler that can he longed exposure to asbestos fiber, and they tolerated without the risk of pulmonary fibrosis may Ik- very extensive in persons with little or has been achieved. There is ronron to belters no diffuse fibrosis. In fact, rather extensive that this concentration will al-o minimize the pleural plaques have been reported as being risk of pulmonary malignancy including meun- common in large populations not directly ex thrlinmn. Itceaue of the long time lapse at* cised oeciipation.-iJIy to aslx-sto-s, but living in soei.ited with the development of mnlignaney, <>r near the region where nsl>o*tos fiber is being longer period-; of observation are desirable for a produred or used (52). There are, of course, other ratie* for pleural plaques and calcifi cation, and, in some instances, it is unwise to I'crilio ihrsr findings to the inhalation of a.dK-sios fiber. In a geographic area where final decision on this point. There is reason to liclicvr that (lie ocnqiat tonal use of asbestos fiber can achieve the some degree of safety u (he use of explosives, radiation, and beryllium, although exun-ivo alterations may lie required a1kmios fiber is known to be present in con siderable concentration in flic ambient air, there is every reaon tn believe that from an in the control of production and manufacturing, ' Hwlihlip. M.: P<-rsonnl eommnnimlion. `Cartier. I1.: Pr rnonal communication. OO CD CD era cn t ST0011667 478 oroooRiWr mnwirr ~ the-eMMuuaMfcoIrMhnatoa-fiber so that encapee-to the oulsMffii swd the proper disposal of solid ratMtariiUi|[4hr fiber. The risk to tbe-c*90*! public poeed b>- the (13) Ncwhouan. M. L.v T!ic mortality of tdbsstas fantasy- workersr Proceedings of tho Inter national Confercnco on l*neutMaanMg|vv Departineot of Mines. Republic of Boutb' Afrien, 1969. to be published. mostly hriirmilUnt exposure to tbo low con* (H) Ktitcriine, P. E. and Kendrick, M. A.: eentntiem of mMm Bkely to be present in the smhirwt-airr.ltes been exaggerated beyond the limits imposed by known facts. Research Asbesloa dual exposures at various levels and mortality. Arch. Environ, Health, (CUcngo) 1967, IS, MI. (15) Mancuso, T. F., and El-Attar, A. E.: Car to dewlap the-.ne----y additional informatioo cinogenic risk and duration of employment upon which appropriate and realistic measures among asbestos workers, Proceedings of the for safe usO'O'f-ndbeeSss fiber ean be taken 2nd International Conference on the Bio should he the pootfcs the next few years. logical Effects of Asbestos. 1968, in prem*'.. (16) Seiikoff. I. J. Hammond, E. C,, imd-CMsfe-: (Rewind for publication July 10, 1909) J.: Mortality experience of asbestos teat*-lion nor kern, Proceedings of tfcs'.'Biltbw;;; REFERENCES national Conference on Pweumoronhisil,.Wg (1) Sped, 8, and Lcmweber. J. P.: Asbestos Department of Mines, Republic of:8nilks^ minerals in modern technology, Environ. Africa, 1909, to be published. : `.T pmf wa (17) Balser, J. L, and Cooper. W. C.: The work O) MunsprB. M.: Report of the departmental environment of insulating workers, Amer. . rnmnnltro na compensation for iadnstrial Industr. Hr*. Ann. J, 1968,99, dimn^. Rer Mijeitn S'atjooary Office, (IS) Harries. P. G.: Asbestos haurds in novel1.. London, 1907. dockyards. Ann. Occup. Hvg_ 19H^1KHS... (3) Merewetherv E. R. A,, and Price, C. W.: (19) Craliey. L. J, Keenan, R. G,, nnd'lyadfcJi ' Report on effects of asbestos dust on the IL: Exposure to metals in the manufac Inn** and. dust euppreeeion in the asbeetoo ture of asbestos textile prodnetSj,*Amec.,, industry. Her Mijistyn Stationary Office, Induatr. H.vg. Aasn. J, 1967, 93, 452. London, 1990. (20) Crallev. L. J, Kicnan, R. G.. Kupd, R. E- (4) 8aver*. R. R,, and Dreesen, W. C.: Aabestoais, Kinser, R. E, and Lyneh. J. R.: Char- Amer. J. Public Health, 1939, t9,70S. seteruatkm and solubility of metals asso (6) Knox. . F,, Holmes, S . J>oll. 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