Document JrdvGN3Rm20aQkMpJoZvn4j6X

Pupmcn ft?: Aaa otnup. Hp*,, Vpj. 43 N. jtp, 47i -??, **>1 200! Brifish 0ecspkw*! Hyshac Sockty Wished ttf Klc*k* Science UtL All rights rorntH Prated m (lieit Bribmt. On03-4878A?f/'S29i Asbestos Lung Fibre Concentrations in South African Chrysotile Mine Workers DAVID REESft*, JAMES I. PHILLIPS!, ESTELLE GARTONf and FRED D. POOLEY ^National CentreJbr Occupational Health, University of Wilwalemrand, JP.O. Sax 4788, Johannesburg, South Africa', %Department of Community Health, University ofthe Wittoalcrsrahd, P.O. Sox 4788, Johannesburg, South Africa; CardiffSchool ofEngineering, University of Wales, Cardiff, UK MesatbeHoma baa not been found in South African chrysotile miners and millers despite decades of producing about 100 090 tons of the mineral per year. One possible explanation for the scarcity or absence of Ac cancer may bo a relative lack of contaminating fibrous trcmolite, an amphibolo tint variably occurs with chrysotile ores. The fibre content in the longs of nine former Chrysotile mine workers was ascertained by transmission electron microscopy. Despite fairly long service in most cases (median 9S yr\ range 32-4 yr) the concentrations of chrysotile fibres were relatively low: only two cases exceeded 1.14 million fibreb/e dried lung. TremoHre fibre levels were even lower: less than 1 million fibres/g dried lung in all but one ease. Trcmolite fibre concentrations exceeded those of chrysotile la only two cases. These results support Ac contention that South African chrysotile Is not heavily contaminated by trcmolite. 2001 British Occupational Hygiene Society. Published by Elsevier Science Ltd. All rights reserved Keywords: asbestos; chrysolite; trcmolite; hjjig content; South Africa INTRODUCTION Chrysotile mining began in the eastern Transvaal region of South Africa, now Mpumalanga Province, in about 1920. African Chrysotile Asbestos (ACA), the most significant mine and mill, started in 1937 near MsaulL ACA has been by far the largest oper ation but over the decades many smaller mines pro duced Ac fibre. Today, ACA is the only active mine, but Stella and Kaapscbc Hoop extract small amounts of asbestos from tailings dumps. From 1975 to 1992 chrysotile production was near 100 000 tons per annum (Harington ik1 McGIashan, 1998), with ACA"s contribution well over 95% in later years. From 1992 ACA's output has declined quite dramati cally from 101 892 to the 20 000 tons expected in 2000. Stella and Kaapschc Hoop now contribute only a couple of tons per annum. {Personal communi cation. Hart P, Johannesburg 2000]. The number of Received 11 Febmaty 2000; In final form 30 October 2fHX). `Author to whom correspondence should be addressed. Tel,: +27-11-725-1589; Iks: +W-11-720-S008; e-mail: dnvjd@ncoh.ptvv.gvv.aa . employees on chrysolite mines was about 2600 in (he 1960s and then settled around 1500-2000 from 1975 to the mid-1990s (Rees et al., 1992). ACA's falling production in biter years led to reduced labour needs; 1811 in 1990; 1720 in 1994; 1131 in 1996; and 254 employees now. [Personal communication. Hart P, Johannesburg 2000}. South African research on asbestos induced dis eases and fibre concentrations has concentrated on the amphiboles with surprisingly little work on Sands African chrysotile; in the past few decades there has been no scientific publication on disease rates And fibre exposure in chrysotile mines. Of interest is Ibat mesothelioma has not been found in miners and mil lers of the South African fibre. For example, no cases with exclusively chrysotile exposure ware identified during a case-control study involving 123 esses of mesothelioma selected without prior knowledge of asbestos exposure (Rees et tf}., 1999). The study did enrol 24 crocidolitc, 3 amosfte and 3 mixed aruosiu: and crocidolitc mine workers, ft may be that a relative paucity oftremolite irt South African chrysotile is the explanation for the scarcity or absence of chrysotile mesotheliomas. The biopersistent arophibolc, tremo- 473 s< ui HV) i EXHIBIT Ml 474 D. Reea et al. tile, variably contaminates chrysolite ores, and may preparation procedure and instrumentation technique explain the genesis ofmesothelioma. The ease for the (Mitba and Poolcy, 1993) that is recognised by the hypothesis that the contaminating trcmolitc rather International Agency for Research on Cancer. than chrysotile is the cause of the cancer has been The instrument employed was a Philips 400T ana summarised by Chnrg (1994) and McDonald and lytical transmission electron microscope (ATEM) fit McDonald (1997), although this view Is not univer ted with sa energy dispersive X-ray analysis system. sally held (Landrigan et al., 1999). Little is known This ATEM is capable of resolving and providing about the tremolite content Of South African chtyso- analysis of all particulates detected. tile ore. The industry has not detennined the tremolite The analysis of tho tissue specimen was performed content [F Hart, Personal communication Johannes so that all fibrous particles detected were analysed burg 2000], but preliminary work by South Africa's and recorded. The definition of a fibre employed for National Centre for Occupational Health (NCOH) analytical purposes in the examination was any par suggests that it is low. Tremolite fibres were sought ticle with 3:1 axial ratio end parallel sides with no in the lungs of four individuals with service minimum length. exceeding 20 years on chrysotile mines (Rees et al^ 1992). Fibres most likely to be tremolite were not observed under optical microscopy, but scanning RESULTS electron microscopy (SBM) demonstrated tremolite in A total of 343 fibres were analysed in the nine two. These fibres were scanty, one fibre appearing in cases, and the average detection level was calculated approximately 20 fields at 1000 times magnification. as 80 090 fibres/g dry lung tissue. In 1992, the NCOH examined 20 rock samples, two The levels of tremolite found in the lungs of these bulk samples of dust from the mill and seven samples chrysotile mine workers were unremarkable, as of airborne fibres from ACA (RSJ da Tolt, NCOH, shown in Table 1, despite fairly long service in most. Johannesburg, RilT 4.13.1$ 1992). X-ray diffrnctome- ' Case 6 was a boilermaker, au occupation associated try revealed tremolite in one of the rock samples and with asbestos use, so some of the lung fibre burden possible tremolite in the bulk dust samples. No tremo may be accounted for by non-mining work. Case 9 lite was found under phase contrast microscopy of the was n despatch clerk with offices near the mills; the airborne samples, but under SKM one fibre was found absence of direct occupational exposure may explain in one sample from the mill and one fibre in a sample the non detection of fibres. taken underground (out of 100 fibres examined one There was a suggestive association between trcroo- was tremolite). lite concentrations and duration of work at ACA. Two The paucity of chrysotile mesothelioma cases and cases, 1 and 3, hod underground asbestos exposure, the preliminary data on tremolite in chrysotile ores only al ACA. Case 1 had 11 yr of exposure versus and in the lungs ofminers was the motivation for this the 4 yr of case 3, and had double the tremolite con study which aimed to characterise the fibre content of centration. Similarly, in the ACA heavy duty drivers, the lungs of South African chrysotile mine workers cases 2 and 5, the tremolite concentration was higher and examine the chrysotile:tremolite ratio. in tho driver with the longer service: 18 and 8 yr respectively. materials ants methods Tables 1 and 2 show that there wus no obvious relation between duration ofchrysotile mine work and South African miners have a statutory right to an chiysotila fibre concentrations in the lung of these autopsy examination of the audio-respiratory organs cases -- differential clearance of chrysolite from the for compensation, purposes. Alt of the autopsies are lung and their varied occupations may partly explain dona nt the National Centre for Occupational Health this. Tremolite fibres made up a thirty low proportion (NCOH), Johannesburg, and the organs are received of the total fibre concentration and were not numer with an occupational history of variable comprehen ous, under I million fibres/g of dried lung in all but siveness. This means- that deceased miners with a Case 1 (Table 2). Tremolite fibre concentrations particular exposure can be identified. For this study, exceeded those of chrysotile in only Coses 2 and 5. over a period of 18 months, deceased chrysotile mine workers Were selected, resulting in the formalin fixed lungs from nine chrysotile mine workers being avail DISCUSSION able for study. The Sungs were examined macro- The mam findings of this study are the relatively scopicslly and microscopically by a pathologist. tow fibre content in the lungs of the nine mine work Tissue samples from the upper, middle and lower ers and the low levels of both chrysotile And tremo zones ofeach lung were taken and pooled They were lite. sent to the University of Wales for fibre counting Tho laboratory that did the fibre analyses has exam sod analysts. ined lungs of control subjects without known asbestos The tissue samples were prepared for examination exposure or asbestos related diseases. Controls, taken by extracting their dust content* utilising a standard from several different areas in different countries. Ii * HWBUI0010434 Asbestos hing fibre coBcatfratsons 475 \ HWBUI0010435 476 D. Rees tt a!. Table 2. Fibre crmcentralioras (miUiont/g dried lung) by asbestos type in nine Sooth African chrysorile mine workers Case Total fibre Chrysolite Amnsits CroddoEte Tremolite Tremolitc/chrysmile I 10.4 720 ND ND 1.86 2 4.0S 0.18 0.18 0.18 0.96 3 49.! 4S.2 ND ND 0.04 4 Z1 1.14 0.06 ND 0.74 5 2.29 ND* ' 0.11 ND 0.44 6 3,2 1.01 0.25 0.1 0.9 7 239 0.07 ND ND 0.07 8 1.03 0.36 . 0.13 ND 0.1 9 0.67 0.03 n.16 ND ND Mean* 335 0:69 0.14 0.13 033 0.26 53 0 0.65 -- 0.89 1 038 0 0.48 ND=Kot defected 'Geometric mean itiehiding rural ones, have shown a crocidolito range and an amosite range from undetectable to 1 million fibres/g dried lung, and a chrysotile range from unde tectable to SO million fibres/g dried lung (Edward el a!.. 19%). One of these sets of controls was 31 women with no known histoiy of exposure to dusts, and no mesothelioma or lung cancer. The geometric mean (and range) for lromoltte -was 0.02 (0-0.8) million fibres/g of dried lung, and for chrysotile 4.4 (0-20.1) million fibres/g dried lung (Dawson ct a!., 1993). The fibre concentrations found in the longs of the South African chrysolite workers were thus rela tively low. Canadian chrysotile miners and millers usually have a much higher concentration of tremolite fibres than found in this group of South African chrysotile mine workers. Bccklakc has summarised the work of Chung and colleagues on chrysotile miners and mil lers (Becklake, 1994); six miners end millers without disease had 6 geometric mean of 2 and 9 chrysotile and ircroolite fibres/g of lung tissue respectively: and 23 with nsbestosis 30 and 140 million fibres. Patients with mesothelioma seeking compensation In Quebec have geometric mean lung concentrations oftremolite fibres well above our subjects: 12 Asbestos Township cases had tremolite concentrations of 2,2 million and 8.1 million for fibres >5 and <5 pm respectively; and 11 Thetfoid Mines cases had Concentrations of 8:4 million and 52.6 million. As in many other studies the concentrations of tremolite (hr exceeded those of chrysolite (Dufircsne el at, 1996). The preponderance of iretnolits over chrysotile fibres is usual in Canadian chrysotile miners (Clung, 1994). The difficulties in intcrlaboratpry comparisons of lung fibre levels are protean as many factors have to be considered (Gibbs and Poolcy, 1996). Neverthe less, it is striking that in this Series ofchrysotile mine workers the tremolite Concentration was well below that usually reported and the tremolitc:cluysotilc ratio exceeded one ill Only one Case. This tremolite chiysotiic relation contrasts with that found by the same lab oratory in the early studies San Canadian chrysotile miners (Pooiay, 1976): of 20-* cases of asbestotna examined eight had tremolite as the only amphibote and in five of the eight tremolite exceeded chrysolite. Id II of the 20 cases, amphibote fibres were more numerous (has chrysotile. Some of our subjects were not miners (e.g. heavy duty drivers and a despatch clerk) and most did not have asbestos related disease (thus lowering the expected fibre concentrations). It is unfortunate that we do not have data on the asbestos levels in the ACA mine and mill in the 1980s and 90s when most of our subjects were exposed, but their lung fibre contents suggest that fibre levels were relatively low. The man agement of ACA mine has stated that fibre levels were consistently below 1 fibre per ml in the 1980s and 90s, and provided average fibre levels (personal sampling) for the stupe, mill and mill surrounding for 1984-1999 (personal communication P Hart Johann esburg, 2000), The slope average ranged front 0.17 to 0.54 fibres/ml; the mill average was 0.l7r0.7; and the mill surrounding 0.1- 0.89 fibrcs/ml. Of interest is that although fibre levels were low in general, in the lungs of cases 1 and 3, with the highest chrysotile fibres counts of7.2 and 48.2 million fibres/g dry lung, the tremoliteichiysotile ratio was 0.26 and 0 respect ively. Despite the limitation ofexamining cases likely to have had moderate or low exposure, these results support the contention that South African chrysotile is not heavily contaminated with tremolite. Lung fibre concentrations in South African chryso tile miners or millers with mesothelioma, if these cases exist, would add to our understanding of the role of tremolite in the genesis of mesothelioma. As&wmtedftsm&ts*--The authors would like so thank Dr Jill Murray for access to thn VATUAUT database and the doctors of Ihe Pathology Sortiou of tho Nations! Centre for Occu pations! Health who did the port-mortem examinations. REFERENCES BeckMa; MR. Fiber burden md asbestosretared lung disease determinants ofdosercaponre relationships. Am J Resp Crit Care Mod 1994;150:1488-92. HWBUI0010436 Asbestos lung fibre concentrations 477 J\, Deposition tmd clearance of chryxotilc asbestos, Ann Occur Hyg t94J*:62S-33. Bltlrrsno A, Begin R, Charg A, Mnn S. Mineral fiber content of fungi in patients with tnraothelbisa seeking cttropen- alion In Quobee. Ara J Rop Grit One Meal 996.-153:711-8. Dawson A. Gibbs A*,Tnoloy H> Griffith* DM, Hoy 1 Malig nant mesothelioma In women- Tfaatrs* 1993;48:269-70. 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