Document wDEvwM5aGxj8qjr2J0rXDqEGD

/?s^ Lung Asbestos Content in Chrysotile Workers with Mesothelioma1'3 ANDREW CHURG, BARRY WIGGS, LISA DEPAOLI, BRIGITA KAMPE, and BONNIE STEVENS Introduction Although the association of mesothe lioma with asbestos exposure is well es tablished, there is considerable con troversy concerning the relative carcino genic effects of the different types of asbestos. It is generally agreed that com mercial forms of amphibole asbestos, amosite and crocidolite (especially crocidolite), can induce mesothelioma (1-8), but it has been suggested that, in humans (as opposed to experimental animal sys tems), chrysotile is either very weakly or not at all carcinogenic in this regard (4-8). For example, McDonald and associates (6) found only 11 cases of mesothelioma in a series of 4,547 deaths in Quebec chrysotile industry workers, compared to 9 of 56 deaths (1) in a series of workers who had assembled gas masks incor porating crocidolite asbestos. Berry and Newhouse (8) studied a series of 13,000 asbestos factory workers exposed to chrysotile and crocidolite, and conclud ed that only those exposed to crocidolite developed mesothelioma. McDonald and Fry (7) found a mesothelioma rate of 0.4/1,000 deaths in a factory processing only chrysotile, compared to 12.6/ 1,000 deaths in a factory processing chrysotile and amphiboles. Similar conclusions were reached by Acheson and coworkers (4,5) in 2 different exposure groups. How ever, many of these studies are confound ed bv uncertainties regarding the exact type of fiber to which individual work ers may have been exposed. Because more than 90<7o of the as bestos used world-wide is chrysotile, this question is of considerable importance. Mineralogic evaluation of lung tissue is one method of producing exact data re garding lung mineral burden, but to our knowledge, no series of occupationally exposed workers with mesothelioma have been shown to have only chrvsotile ore components (see definition subsequent) in iheir lungs. Wagner and associates (9) attempted such an analvsis on lungs from workers in an asbestos taeiory, and found that, in addition to chrvsotile, amosite, and especially ciocidolile, were also pres ent. thus ruling out anv definitive con- 1042 SUMM ARY The role of chrysotile asbestos in the genesis o( mesotheliomas in humans is disput ed. We analyzed the asbestos content ot the lung in 6 long term chrysotile miners and millers who had pleural mesotheliomas. In five patients, only chrysotile ore components (chrysotile and tremolite/actinolite/anthophyllite types of amphibole asbestos) were found, while the sixth patient presented both chrysotile ore components and amosite, a type of asbestos that is not derived trom the mining process. The mean number ot fibers/g dry lung for the 5 patients w ith mesothelio ma containing only chrysotile ore components was higher(chrysotile 64 x 10' and tremolite group 540 x 10`) than in a group ot long-term chrysotile miner control subjects who had no asbestos- related disease (chrysotile 23 x 10`, tremolite group 58 x 10'). but some patients w ith mesothelio ma had liber burdens near the mean of the control range. Fiber sizes and aspect ratios in the mesothelioma group were approximately the same as those in the control subjects, and analysis of fiber distribution failed to show any preferential localization in the periphery ot the lung. How ever, the concentration ratio of tremolite in the lungs of the mesothelioma cases compared to the control cases was 9.3, while the ratio ot chrysotile was only 2.8. Our findings provide strong evidence that chrysotile mine dust (chrysotile and amphibole components) can produce mesothelio mas in humans; the greater relative amounts of tremolite group amphiboles present in the patients with mesothelioma raise the possibility that these fibers may be important in the pathogenesis of the tumors. AM REV RESPIR DIS 1994; 130:1042-1045 elusions.; Langer and McCaughey (10) have suggested, based on the observation of chrysotile fibers in a tissue section of lung, that a case of mesothelioma in a brake repair worker was produced by chrysotile asbestos; although this case may indeed represent a chrysotileinduced mesothelioma, the volume of tis sue sampled is so small that amosite or crocidolite might have been missed. Chrysotile miners and millers represent a population with, theoretically, exposure only to chrysotile mine dust; in this pa per we analyze the mineral content in the lungs of 6 such workers and demonstrate that chrysotile mine dust can produce mesotheliomas. We also examine the rela tionship of fiber number, fiber type, and fiber size and shape to the development of mesothelioma. Throughout this paper, u'e shall use the term "chrysotile ore components" and "chrysotile mine dust" to signify both chrysotile asbestos and the amphiboles tremolite, actinolile, and anthophyllite, which arc integral pans of the chrysotile ore. These latter forms of asbestos are essentially contaminants of the ore, and are not purposely mined. Bv compari son. the amphibole minerals amosite and crocidolite are lomis of asbestos that arc completely unrelated to chrysotile and w hich are mined and used commerviallv. Methods The 6 cases analyzed in this study are derived from a series of approximately 90 sequential autopsies of long-term workers in the Que bec chrysotile industry; the autopsies were per formed from late 1980 through the end of 1983 at the Hopital General de la Region de I'Amiante at Thetford Mines, Quebec. Cases and exposure histories were obta ned through the courtesy of Dr. M. Poulin and Mr. C. Pratte of that institution. All tissues were fixed in formalin. The 6 patients with mesothelioma repre sent all the mesotheliomas present in the se ries of 90 cases. The diagnosis in all cases was confirmed by finding the following: a typical gross appearance of tumor encasing the lung, no evidence of another primary at autopsy, and the typical histologic and histochemical features (II) of mesothelioma. All of the iKi'a'ivcd in original form Oaoht'r 20. /'vy: am: in roust'd form May 21. IWJ) ' From llie Department ol l'.ilhologs. l imiiMti o! iinu-'h C oUinihi.i. V.iikouut. !i.( .. C ;in;ula Suppoi leJ hv ( ir.inw No XI I s'X)~ .tiu! Iiom iIk- Msjis.i I Kl-.s.ueli t uuik 11 o! ( .ui.kI.i .tini i coin: !iom :iv N.tiioiui t .m.s: In.nun, < i .m.ul.i ` Kci|us-i' Ioi icpnno -hoiiM tv .i,klis"i\l n> > [ 1\ikIu-u 1 inns. M l>. I s vm nn.iu ol I'.ii lioiosi. I nnslMIs ol ill i! i sti t iiliiinhi.i. 2CI! Ws-C'look VI.lii, V.uvomsi. Ill V n I [ W \ s .ui.iC.t -(-MV'O.IIU ANO Mf.SOrHf UOMA 1043 I. t. /' vjM-ntf [w\ ' a ihere i' LoiiMdcrdhlc mcil.ip in the I L'UHipv. 1 lie diMrihm ion ol fiber sizes in ihc Ary V / im.1i;-,'-, >( O.': nr pat tents \s till mes.'t helimna ami pares! n> 1 V, V ;r , 11 11i rX,' Mf" f'.rr'.' ' rn ii. n,; tT a ii I he control group is show n in table I he : u< *' ir 1' ' 1 966 1 U.-.J Fib*,r OdCQ1'? if' HiiM-mprharuc as|iect (length to w dili) ratios tot vari m mme ous fibers is show n in table 4. the ratios 3 60- M 36 vear5 i194~ *0 19c3t 1983 Fiber Dagqer ana sorter in mu oi' numbers of libers in central and pe 4 3 miner 67'M 43 yea--? m93T 'O 1979i 1963 Unaergrounc rrvnpf only 77 M 40 years :i933 lu 19-6- 1963 Fiber separaior min ripheral sues are listed in table 5. and the liber si/e distribution and aspect ratios 6 68- VI 47 yearsi1928 to '975- 1981 No details available lor fibers in central versus peripheral sites are shown in tables ft and 7. In all these tables, the mesothel.oma group is com tumors in this report were of pleural cavity origin. For comparison purposes, we used 9 prev iously published long-term chrysoiile in dustry workers from the same autopsy series (12); these9patients had neither mesothelio ma nor asbestos-induced parenchymal or air way fibrosis. For mineralogic analysis, we followed the same procedure as previously reported (12). This consists, in brief, of dissolving 3- to 5-g (mean SD)/g dry lung, and of the tremolite group of amphiboles, 540 840 fibers/g dry lung. These values are compared in table 2 to those found in the reference chrysotile miners (12), and a group of 25 men without occupational asbestos exposure (13). Although the pa tients with mesothelioma have higher mean levels than the control subjects, posed of patients I to 5 (those contain ing chrysotile ore components only). Be cause distributions of aspect ratios are often skewed, geometric means are in cluded in tables 4 and 7 as well. There were no differences round for fiber size distribution or fiber aspect ratios either between mesothelioma and control groups, or between central and periph eral sample sites. There was no tendency samples of formalin fixed lung in bleach, col lecting the mineral particulate sediment on a.Millipore filter, and transferring the parti cles to a coated electron microscope grid. The TABLE 2 grid is then scanned in the electron micro scope, and every fiber encountered is identi fied by a combination of morphology, elec tron diffraction, and energy dispersive X-ray spectroscopy. For the present investigation, Case NUMBERS OF FIBERS FOR ALL SITES (ALL COUNTS AS FIBERS X 10NG DRY LUNG) Chrysotile Tremolite/Actinolite/ Anthophyllite Amosite or Croctdolite a subpleural 0.5-cm deep sample and anoth er piece from 3 cm deep within the lung were obtained and processed in order to compare central and peripheral distribution of fibers. Approximately 100 fibers were examined for each case. Results were calculated using an 12 3 4 5. Mean SO* 63 6 69 10 169 64 65 - 244 44 320 62 2023 540 840 0 0 0 0 0 0 algorithm relating weight of tissue used and 6 44 54 70 (amosite) grid area, and expressed as fibers/g dry lung. Reference population of 9 chrysotile miners without mesothelioma (12): A blank control was created for each test sample. This was prepared by running the en tire preparatory procedure without tissue, and scanning approximately 50 grid squares in the electron microscope to detect contaminants Mean: - 23 58 0.02 Reference population of 25 men without occupational asbestos exposure (13): Mean: * 0.6 0.3 0.01 * Mean values tor 5 cases containing only chrysotile ore components. from solutions and air. In this study, only rare particles of very short fiber chrysotile were TABLE 3 found in the blanks, ar.d these values were subtracted from the tes: values. FIBER SIZE DISTRIBUTION FOR ALL SAMPLE SITES Percent of fibers in size range Results 0.5 to 5 p 5 to 10 m 10 + fj Demographic data and occupational de tails are shown in table 1, and results of mineralogic analysis are shown in table 2. Tremolite, actinolite, and anthophvllite are grouped into 1 category, as we have done previously (12). Five of the 6 patients with mesothelioma had only chrysotile ore components in their lungs. The sixth patient also had substantial lev els of amosite, and is excluded from the calculations of mean fiber number, size, etc., in order to deal with a mineralogicallv homogeneous population. For the 5 patients with mesothelioma, the mean number of chrysotile fibers was 64 65 Chrysotile Mesothelioma Patients 1 to 5 Mining control group (12) 89 9 2 85 8 7 Tremolitei'actinohte^anthophytlite Mesothelioma Patients 1 to 5 87 11 2 Mining control group (12} 94 6 0 TABLE 4 MEAN FIBER ASPECT RATIOS FOR ALL SAMPLE SITES' Mesothelioma Patients 1 to 5 Control Group (12) Chrysotile Tremolite/actinolite anthophyllite 92 103 (60) 14 12 (11) 96 120 (53) 13 12 (9) ' Values are mean * SO: geometric mean m paremheses 1044 CHUBG WIGGS. OEPAOU KAMPE. AND STEVENS TABLE 5 MEAN VALUES OF RATIO OF NUMBERS OF CENTRAL TO PERIPHERAL FIBERS Chrysotile Tremolite'Actmolr AnthOOhyllite Mesothelioma pat'ents Patient 1 Patient 2 Patient 3 Patient 4 Patient 5 Mean SO Control group: Mean i SD 75 1.0 04 06 3.6 26: 3 0 2.3 3 1 5.9 0.5 01 05 1.1 16 d 24 2.0 i 1 1 TABLE 6 DISTRIBUTION OF FIBER SIZES IN PERIPHERAL VERSUS CENTRAL SAMPLES OF MESOTHELIOMA PATIENTS 1 TO 5 Percent in $i2e Range 0 5 to 5 v 5-IO 10 w 10+ M Chrysotile Central Peripheral " Tremolite/Actmolite/Anthophyllite Central Peripheral 87 12 1 95 4 1 88 11 1 86 12 2 TABLE 7 ASPECT RATIOS FOR FIBERS IN CENTRAL VERSUS PERIPHERAL SITES IN MESOTHELIOMA PATIENTS 1 TO 5- Central Peripheral Chrysotile Tremoifte/Actinolite/Anthophyllite 92 10^ (57) 13 * 12 (11) 92 106 (62) 14 12 (10) Values are mean - SD: geometric mean in parentheses. for fibers to concentrate in the periph ery of the lung (table 5). The ratios of numbers of fibers of each type in mesothelioma patients 1 to 5 ver sus the reference cases are shown in table 8. The ratio of tremolite (9.3) between the groups is considerably higher than that of chrysotile (2.8). Discussion As noted in Introduction, epidemiolog ic studies suggest that chrysotile is a rel atively weak mesothelial carcinogen in man; however, it is clear that, even in mans' factories that processed largely chrysotile, amphibole was also used at one point (5,8,9), and hence, actual tis sue analysis is required to demonstrate that only chrysotile or chrysotile ore com ponents are present before a given case can be definitely ascribed to chrysotile Just inhalation. The requirement lor such analvsis is well illustrated by our Patient h. a long-term worker in the chrysotile industrv, whose lungs contained large amounts of amosiie asbestos as well as chrysotile ore dust. In this instance, il is likely that the worker was employed in one of the asbestos processing factories in Quebec that used amosite at various times (14), but we were unable to obtain enough occupational details to verify this possibility. Amosite in chrysotile miners has been demonstrated previously: Rowlands and associates (15) found it in the lungs of 2 of 47 Quebec chrysotile workers, an observation that emphasizes again the usefulness of confirming epidemiologic studies with mineralogic analysis. Nonetheless, our data from the analysis of Patients 1 to 5 provide strong evidence that chrysotile mine dust com ponents (as defined) can induce mesotheliomas. Which of the minerals in the chryso tile ore is producing the tumors is a mat ter of considerable importance. As in our prec ious study of chry sotile miners (12) and the study ol Rowlands and associ ates (15), we found more amphihole (tremolite actinolite anthophe llitei de rived from the ore body than chrysotile in these lungs, an obset canon that re Heels the failure of chrysotile, cnigmallc pics- ent in the ore in much larger quantities than amphibole, to accumulate in lung tissue. Whether this phenomenon reflects chemical leaching of the fibers (16), en hanced clearance of chrysotile compared to amphibole, or low pulmonary deposi tion of chrysotile compared to amphi bole, is not clear. Our subsequent com ments must, therefore, be interpreted in light of the fact that we cannot determine what chrysotile load may have been pres ent in these lungs, although the study of Rowlands and associates (15) suggests that estimates of fiber burden derived from mineralogic analysis correlate well with estimates of dust exposure in these workers. The types, sizes, and distribution of fibers that induce mesothelioma have been the subject of considerable discus sion based on animal experiments (17,18), measurements of mine dust size, and the oretical calculations of fiber deposition in the lung (see Harington (19) for re view). Animal studies (17,18) have shown that mesothelioma can be induced by vir tually any insoluble mineral fiber if it is sufficiently small (particularly, diameter less than 0.25 n and length greater than 8 n) and has a high aspect (length to width) ratio. In contrast to the situation in humans, chrysotile appears to be just as effective as crocidolite in inducing mesothelioma in animals (18). It has al so been postulated that, in humans who are inhaling asbestos dust, mesothelio ma is induced by dust that penetrates far into the periphery of the lung (19). Hence, it is reasonable to suppose that patients with mesothelioma might have either higher aspect ratio fibers, or greater num bers of fibers, or more fibers in the pe riphery of the lung than patients with roughly comparable exposure but no mesotheliomas. In fact, we were unable to find any con sistent differences in fiber size or fiber aspect ratio between our 5 patients with mesothelioma and 9 conrol subjects (12). There was no evidence o ' a trend for pe ripheral deposition of fibers in the pa tients with mesothelioma (table 5). One _ TABLE 8 RATIOS OF NUMBERS OF FIBERS OF DIFFERENT MINERALS IN MESOTHELIOMA PATIENTS 1 TO 5 AND CONTROL GROUPS Mint rAil RaH. M-'"m int in niu Cf'fvbMhir T ' t'dic mlf'.it t i Ikdil t- ,i(:! O; )[(.> ti ! 8 rHBTsnmE and mesothelioma 11 r - -- -**-------- --------- <r mi i 1045 iniL'hl also siispovi, a prior i. I lull hccaii'-c millmi: the ore xeparaiiw [lie lone libers, mesoihelioma should be lounJ in millers railtei ihan miners. Bui 2 ot ihe 5 pa tients r whom wchaee detailed occupa tional Histories appear to base worked only in the mines. However, we did find differences in to- ;a! fiber numbers and in the ratios of types of fibers between the groups (ta bles 2 and 8). The mean values of fiber load for the mesothelioma group were considerably higher than those for the control group, but 2 of the patients w ith mesothelioma (Patients 2 and 4) had fi ber concentrations at or below the mean ' for the reference group. Hence one can not easily ascribe the mesotheliomas only to high overall numbers of fibers. Of particular interest is the fact that the patients with mesothelioma having i only chrysotiie ore components had a 1 much higher ratio of tremolite group am- phiboies (9.3) than chrysotiie fibers (2.8) * compared to the control group (table 8), and that this was not true of Patient 6, in whom amosite was found. Stanton and ' associates (17) and Wagner and cowork . ers (20) have shewn that long, thin, high aspect ratio tremolite induces mesothelio ma in animals, whereas short thick fiber tremolite is less effective or ineffective, an observation that agrees with the the - ory of Stanton and associates (17) that tumor frequency is proportional to fiber . length and aspect ratio (aspect ratio ' greater than 32 in the study of Stanton and associates). But as Harington (19) . points out, the animal studies also show . that the requirement for high aspect ra ; tio or long length is not absolute, and j that large numbers of short lower aspect ( fibers can induce mesothelioma. Our l chrysotiie miners would presumably fall into the latter category because the mean . aspect ratio for tremolite amphiboles in ; their lungs is about 13 to 14 (table 4). t >ur ob'crvationv in chi \\onlc mine mci11hir\ woi ketw i hue raiec the poeeihilit v that the amph'bolc component ol the chi \ m>i ile ore : imponam in t he jencsi-ol mesothelioma in this group. 1 hie sit uation may be similar to that reported in mesothelioma patients exposed to mix tures of chrysotiie and the commercial amphiboles amosite and eroeidolite (21,22). where the amphibole appears to plax a major role in tumor induction. Ad ditionally, because elevated levels of tremolite and actinolite amphiboles have been found in the lungs of some secon dary chrysotiie industry workers, which we (23, and Churg A, unpublished data) and others (9) have analyzed, and in par ticular, because some of that amphibole is of relatively long length (23), the same conclusion might apply to textile work ers and others exposed to processed chrvsotile ore. References 1. McDonald AD, McDonald JC. Mesothelio ma after eroeidolite exposure during gas mask manufacture. Environ Res 1978; 17:340-6. 2. Selikoff IJ, Seidman H, Hammond ED. Mor tality effects of cigarette smoking among amosite asbestos factory workers. J Natl Cancer Inst 1980; 65*07-13. ' 3. Jpnes JSP, Smith PG. Pooley FD. The conse quences of exposure to asbestos dust in a wartime gas-mask factory. In: Biological effects of mineral fibers. Wagner JC, edl Lyon: International Agen cy for Research on Cancer, 1980, pp. 637-53. 4. Acheson ED, Gardner MJ, Pippard EC, Grime LP. Mortality of two groups of women who manufactured gas masks from chrysotiie and eroeidolite asbestos: a 40 year follow-up. Br J In dust Med 1982; 39:344-8. 5. Acheson ED, Gardner MJ, Bennett C. Winter PD. Mesothelioma in a factory using amosite and chrysotiie asbestos. Lancet 1981; 2:1403-6. 6. McDonald JC, Liddell FDK, Gibbs GW, Evssen GE. McDonald AD. Dust exposure and mor tality in chrysotiie mining, 1910-1975. Br J indust Med 1980; 37:11-24. ' 7. McDonald AD. Fry JS. Mesothelioma and fi- Hi. 1 I s I' inline, \ ! 11 .. , 11' , I ' n. I * '. i. : : i, I *rc! uiini.u \ vi'nn V.uid I XX ,, L, | r -, , i, || n ins;, s ixuppi I I si , S Her New Ihmi', XII Mm i.iiiu . II: I InJiiM XlcJ lust, 4(i I ' 9 W.iL'ncr l( . Herrs (,. I'smles I I) X Ic'i >1 Ik I n ' m.i and .mb,, to, i vpc i i jsheMns icm lie ss m kera studs ol lime conicm- Br Xlcd .1 19X2. 2 not s 10 l angci A. XlcC .tm:he\ WTl Xlesoilicln'mu in a brake repair workei. I.ancel Ws2. 2:1 H11 3 11. kannersicin XI. Xlet auuhes WTL. Churn J, Sclikol f IJ A critique c I ihe criteria lor : lie diag nosis of diffuse malignant mesoihelioma. Xli Sinai Xlcd J 1977: 44:485-94. 12. Churg A. Ashesios fibrecomem ol ihe lungs in patienis with and without ashesios airways dis ease. Am Rev Respir Dis 1983; 127:470-3. 13. Churg A. Asbestos fibers and pleural plaques in an autopsy population. Am J Paihol 1982: 109:79-96. 14. McDonald AD. Malignant mesoihelioma in Quebec. In: Wagner JC, ed. Biological effects of mineral fibres. Lyon: International Agency for Re- search on Cancer, 1980, pp. 673-81. 15. Rowlands N. Gibbs GW, McDonald AD. As bestos fibers in the lungs of chrysotiie miners and millers. Ann Occup Hyg 1982; 26:411-6. 16. Jaurand MC, Btgnon J. Sebastien P, Goni J. Leaching of chrysotiie asbestos in human lungs. Environ Res 1977; 14:245-54. 17. Stanton MF, Lavard M, Tegeris A, el at. Rela tion of particle dimension to carcinogenicity in am phibole asbestoses and other fibrous minerals. J Nat! Cancer Inst USA 1981; 67: 965-75. 18. Wagner JC, Berry G, Timbrell V. Mesotheliomata in rats after inoculation with asbestos and other minerals. Br J Cancer 1973; 28:173-85. 19. Harington JS. Fiber carcinogenesis: epidemi ologic observations and the Stanton Hypothesis. J Natl Cancer Inst USA 1981; 67:977-89. 20. Wagner JC, Chamberlain M, Brown RC, et at. Biological effects of tremolite. Br J Cancer 1982; 45:352-60. 21. McDonald AD, McDonald JC, Pooley FD. Mineral fiber content of ung in mesothelial tumours in North America. Ann Occ Hyg 1982; 26:417-22. 22. W'agner JC, Pooley FD, Berry G, el at. A pathological and mineralogical study of asbestosrelated deaths in the Un ted kingdom in 1977. Ann Occ Hyg 19S2: 26:423-31. ~ 23. Churg A, Harley RA. Long fiber asbestos in a chrysotiie textile worker. Lancet 1984; 1:845. t