Document bOLXGkQq9qOaEBajZJeYQ4BdZ

Ann. occup. Hyg., Vol. 46, Supplement 1, pp. 144-149, 2002 2002 British Occupational Hygiene Society Published by Oxford University Press DOI: 10.1093/annhyg/mef663 Lung-retained Fibre Content in Brazilian Chrysotile Workers BRUCE W. CASE1,2*, ANDRE DUFRESNE2, ERICSON BAGATIN3 and VERA L. CAPELOZZI4 1Department of Pathology, McGill University, 3775 University Street, Montreal, Quebec H3A 2B4, Canada; 2Combined Departments of Epidemiology, Biostatistics and Occupational Health, McGill University, Montreal, Quebec, Canada; 3University of Campinas, Campinas, Brazil; 4Department of Pathology, University of Sao Paulo, Sao Paulo, Brazil Introduction. Beginning with observations in Quebec in 1976, the study of lung-retained fibre has led to an increased understanding of exposure and disease in chrysotile mining areas. Until 2000 this was confined largely to Quebec, but recent work has outlined exposure profiles for lung content in Russian, Chinese and South African chrysotile production and factory workers. We now report the first findings from Brazilian chrysotile production and asbestos cement workers with well characterized clinical, exposure and smoking histories. Methods. Subjects working either in the chrysotile mining industry in Brazil (n = 6) or in the asbestos cement industry (n = 4) were admitted to hospital for investigation of pulmonary lesions. Six had benign infections and four lung cancer, while two also had pleural plaques (both miners) and one cement worker had asbestosis. Portions of formalin-fixed lung tissue obtained at surgery or autopsy were obtained for analysis. Asbestos bodies (AB) were quantified following bleach digestion using phase contrast optical microscopy at X312. Additional portions were examined using transmission electron microscopy at X14000. Seven hundred and four fibres (aspect ratio > 3:1) were identified and quantified by X-ray energy dispersive spectrometry in three length classes, <5, 5-20 and >20 pm, each at a theoretical detection limit of 0.1 fibres/pg dry lung. Results. AB counts confirmed occupational exposure as proportional to years of exposure (r = 0.72, P < 0.05), but were far lower than observed in workers elsewhere, possibly due in part to fibre type and to a mean duration of exposure of <10 years. Conversely, non-asbestos `fibres' were much more common than among chrysotile workers elsewhere, averaging 70% of all fibres counted. Chrysotile accounted for >90% of asbestos fibres in all length classes (median 98% of all asbestos fibres; median 4.99 fibres/pg chrysotile versus 0.11 for amphiboles; P < 0.001). As is generally the case, <5 pm fibres were most concentrated (86%). Tremolite was detected in the lung of two mining workers, but only >5 pm in one who worked in a nowabandoned mine known to contain that mineral. Keywords: amphiboles; asbestos; Brazil; chrysotile; lung fibre analysis; tremolite INTRODUCTION AND BACKGROUND Of chrysotile producing countries, Brazil is ranked fourth in the world with an estimated annual output of 170000 metric tons (Virta, 2001), half the production of Canada and ~25% of Russian production. All has come from two mines, with 10157 persons employed for at least 1 month (Bagatin, 2000). The first, the Sao Felix mine near the remote location of Pogoes in the state of Bahia, opened in 1940 and closed in *Author to whom correspondence should be addressed. Fax: +1-514-398-7446; e-mail: bruce.case@mcgill.ca 1967. At this location there were never more than ~4000 metric tons produced per year, but exposure levels were probably high as workers, often children, obtained the fibre by manual extraction. Overall, only 425 workers were employed at this location alone, with an additional 113 moving to the new location in or after 1967. Recent mineralogical characterization of this mine has demonstrated the presence of tremolite. In 1967 the larger Cana Brava mine was dis covered and developed at Minagu in the province of Goias. By 1990 production reached just under 250000 metric tons annually. 144 Lung fibre content in chrysotile workers 145 About 90% of Brazilian production has been used in the asbestos `fibre cement' industry, mostly to make roof tiles and water tanks. Imported fibre was also used in this industry, including crocidolite. From June 1997 to December 2000 a multi disciplinary team based at the State University of Campinas (UNICAMP), University of Sao Paulo and the Federal University of Sao Paulo conducted a multi-faceted clinical and epidemiological study of the workforces of the two asbestos mining areas. Results of these studies will be published elsewhere. Follow-up for workers at the old mine (Sao Felix) was limited to 35% of those known to have been employed for at least 1 month. Of these, 28% (54 of 195) had asbestos-related pathology, including 16 cases of asbestosis, one of mesothelioma, one of lung cancer and 36 with pleural plaques. Follow-up has been more complete for those working only in the larger and more recently exploited Cana Brava mine, being 74-95% for workers with at least 5 yr expos ure. To date, asbestos-related pathology has been less [1.4% of those followed, of which the majority (0.9%) had pleural plaques on X-ray alone]. Mineralogical analysis using multiple techniques at this mine site has to date not identified amphiboles of any type (M.Cruxen, Institute of Technological Research, Sao Paulo, personal communication). Although chrysotile is by far the most used form of asbestos and although attention to differential effects of fibre types was recommended by the UICC in 1964 (UICC, 1965), until very recently most studies of exposure and disease were limited to Canada (see e.g. Gibbs and Lachance, 1972; McDonald et al., 1980; Churg et al., 1993; Dufresne et al., 1996; Case et al., 2000). More recently it has been established that among Canadian miners and millers of chrysotile mesothelioma risk is concentrated among those with co-exposure to tremolite fibre (McDonald et al., 1997) and there has been interest in whether chrysotile mined in other countries showed the same pattern for non-commercial amphibole co-exposure. Studies of a group of chrysotile miners and plant workers in Russia (Tossavainen et al., 2000) and of seven chrysotile plant workers in one location in China (Tossavainen et al., 2001) have demonstrated low, although detectable, tremolite content in lung tissue from the former and very high tremolite and, espe cially, anthophyllite lung fibre content for the latter. A recent study of South African chrysotile workers reported tremolite levels as `unremarkable' , although in fact it was identified in eight of nine cases and at what we would consider substantial levels in two (Rees et al., 2001). The current study has as its principal aim a first characterization of the lung content of Brazilian chrysotile workers employed in both the mines and the asbestos cement industry. MATERIALS AND METHODS Subjects Surgically resected lung tissue samples were evaluated at the University of Sao Paulo Hospital Pathology Department for 10 workers. These were referred to McGill University in consultation for mineralogical analysis. Six had been employed in the chrysotile mines and four were asbestos cement workers. Age, exposure histories, clinical presenta tion, pathological findings and smoking habits are outlined in Table 1. Lung samples For eight of the cases, two formalin-fixed samples were available from different lobes of the same lung. For the other two a single sample was available. For each sample, lung tissue was dried and the wet: dry ratio obtained as a denominator. For subsequent analysis in the cases having two samples, each was processed separately but the arithmetic mean values for each subject were used. Asbestos body determinations A portion of each lung sample was bleach digested as described previously (Case and Sebastien, 1987) and a count of asbestos bodies (AB) obtained from the digestate. AB concentrations are expressed as AB/g dry lung, counted by light microscopy at x312 magnification. `Background' values are unknown for Brazilian subjects: generally an upper limit of 500-1000 AB/g dry lung has been found in previ ously published work using our methods in North American populations. Lung-retained fibre determination The methods have been described previously (Case and Sebastien, 1987; Case et al., 2000), consisting of bleach digestion and low temperature ashing followed by the use of a carbon replica technique. Counts were performed at x14000 on a JEOL 100CX transmission electron microscope (TEM) using X-ray energy dispersive spectrometry (EDS) and morphology to identify fibres. For each sample in the current study three separate counts were performed: one of all fibres (aspect ratio >3:1) <5 |im in length; a second for fibres between 5 and 20 |im in length; a third for fibres >20 |im. A total concentra tion was obtained by summing the three counts and, where applicable, taking the average of the two resulting values for two lung samples per subject. For each of the three length categories in each sample the theoretical detection limit was 0.1 fibres/|ig dry lung (100000 fibres/g). 146 B. W. Case et al. RESULTS Overall, subjects in the two industries did not differ in demographics or exposure history (Table 1). Results for each of the 10 cases are outlined in Table 2. Distribution of fibres by type and length category for all workers (geometric means) and for miners, millers and cement workers separately (arith metic means and medians) are shown in Table 3. Although the four cement workers had overall arith metic mean and median concentrations of chrysotile and total asbestos in their lungs exceeding those of miners and millers for every length category, none of the differences were significant. Overall, it can be seen that non-asbestos formed 70% of all fibres, but chrysotile was by far the most common asbestos fibre present in all but two cases. Tremolite was almost completely absent, as were all other non-commercial amphiboles, being identified as >5 |dm in length only in the single case who had worked at the older Sao Felix mine, known mineralogically to contain tremolite. Commercial amphibole fibres were present in rela tively low concentration in the lungs of five of the 10 workers. These included three of the six miners and millers [two were known to have worked as mechanics at the mine and two had amosite asbestos lung contents in excess of 0.5 fibres/|dg dry lung (500000 fibres/g)]. Two of the four asbestos cement workers had lung contents of crocidolite, a fibre reported by one of us (V.C.) to have been used in the asbestos cement industry in Brazil. In one of these (case 8, the only case with asbestosis) crocidolite was present at a concentration of 1.0 fibres/|dg dry lung (1000000 fibres/g); in the other (case 9) the con centration was only 0.21 fibres/|dg. However, all crocidolite fibres were >20 |dm long. Of interest is the fact that the man with the shortest duration of exposure, only 22 days in the new mine 25 yr prior to surgery, nonetheless had the highest percentage (19%) of chrysotile fibres >20 |dm long in the lung; a fact consistent with previous observations in Quebec miners and millers (Finkelstein and Dufresne, 1999) and in textile workers exposed to a mixture of fibre types in Charleston, WV (Case et al., 2000). Fibre concentrations of chrysotile and non-asbes tos were correlated (overall r for total concentrations 0.62, P = 0.05), especially for fibres of both types in the 5-20 |dm length category (r = 0.99, P < 0.0001). Within fibre types all lengths of chrysotile were highly correlated (r all > 0.93, P < 0.0001), as were commercial amphiboles in the 5-20 and >20 |dm length categories (r = 0.85, P < 0.01). No fibre type concentration was related to duration of exposure and although all chrysotile length categories were inversely correlated with years since last exposure, none of these correlations were statistically signifi cant. Concentrations of short (<5 |dm) non-asbestos fibres were also inversely related to years since last exposure, suggesting a clearance effect (r = -0.63, P = 0.05); non-asbestos fibres in the 5-20 |dm range showed similar findings (r = -0.61, P = 0.06). Asbestos body concentrations were significantly correlated with duration of exposure in years (r = 0.72, P < 0.05) and were negatively correlated with time since last exposure (r = -0.56, P = 0.09). This was true despite the relatively low level of AB concentrations (Table 3), perhaps consistent with the known poorer ability of chrysotile to form these structures. DISCUSSION In the last 2 yr the many studies of lung-retained fibre in Canadian chrysotile workers (including but not limited to Case and Sebastien, 1987; Churg et al., 1993; Dufresne et al., 1996; McDonald et al., 1997; Finkelstein and Dufresne, 1999; Case et al., 2000) have been joined by new studies in Russia (Tossavainen et al., 2000), China (Tossavainen et al., 2001), South Africa (Rees et al., 2001) and now Brazil. It is difficult to compare results from different studies, not Table 1. Demographics and disease status n Age (mean yr SD) Years worked Years since first exposure Years since end of exposure Smoking (pack-years) Mesothelioma Lung cancer Asbestosis Pleural plaques Miners/millers 6 54.8 6.7 8.8 (range 22 days-18.0 yr) 29 8.5 (range 17-39 yr) 18 (range 9-31) 40.5 57 3 2 Asbestos cement workers 4 60.5 14 8.3 (range 3 months-11.9 yr) 24 6.9 (range 14-30 yr) 16 (range 14-18) 9.5 15.7 (NS) 1 1 (grade 2) 20 (31 yr) exposure) 9.66 2.42e concentration asbestos (%) asbestos fibres concentratio asbestosc,d asbestosc (time since end ofn Total non- Asbestos in total (%) Lung fibre content in chrysotile workers <N 147 Tremolite Total 0.58 >20 pm 0.37 15.3 0 Chrysotile Chrysotile in all Per cent Maintenance worker Carcinoma lung (small cell) 2.75 (39) 57 (54 py) Years worked Age (yr since first (smoking)b exposure) =6L on a O 3 X 3 ca3 3iO>s. n32g .owo2 C63T3o33 tOcgo ? m 2axJ S8 - SSO3 2rcs2v 6 .2 CJ a <<nNN-! U X' 3 X c a >-> -- i>-, a <N oc r- g on 3 cs 'o5 3^1_3| c u3 a -s x3 ,22 C/3 X <N o 77 c 3 co -o S 2o 2& xa3 aMD CQ 0 a 'PWQ" s>. 3s c/0 S2 wO h a H r- OZ, <D Xo oo O c/o O oo O Z <C < < < a a o<N A Xa 3O 0e0 3 a w .ogS2 voc-lii ft 'vi cc o2 aO oCD S3 T33 ^* o o ns ^u 21 a ^ ,3 a e a ^ '3ooa a 2 2#o<Lo> Ox 00 s? ^ <afapDt ,-oof2t |'--1 Sc<Ds .UO0ai0 ^=oLp Xo3 'vi C ^cOs ;5s<D ' <L> +D 1 C 02 3o &6 OXh: 5^3 3oa 2ao <C w h 1(-J0-_, ^ 1 .<Sao2L->l vs3y UO Diagnosis and other lung lesions Table 2. Data for 10 chrysotile production and cement workers3 Job ID 1 148 B. W. Case et al. Table 3. Arithmetic and geometric mean fibre concentrations in lungs of Brazilian chrysotile workers for three fibre length categoriesa n Asbestos bodies Chrysotile <5^m Chrysotile 5-20 ^m Chrysotile >20 ^m Amphiboles <5 ^m Amphiboles 5-20 ^m Amphiboles >20 ^m Non-asbestos <5 ^m Non-asbestos 5-20 ^m Non-asbestos >20 ^m Chrysotile miners and millersb 6 2826 3463 (median 963) 7.0 8.5 (3.2) 1.5 2.2 (0.3) 0.3 0.2 (0.2) 0.4 0.6 (0.2) 0.2 0.4 (0) 0.1 0.3 (0) 20.3 14.6 (18.2) 1.7 2.8 ( 0.8) 0 (0) Asbestos cement workersb 4 817 603 (median 841) 17.9 26.1 (7.6) 8.0 15.7 (0.2) 1.0 1.8 (0.1) 0.2 0.4 (0) 0.1 0.3 (0) 0.1 0.1 (0) 25.3 12.6 (25.5) 7.0 13.0 ( 0.6) 0.0 0.1 (0) All workers combinedc 10 916 11.36 (71%) 4.11 (25%) 0.57 (4%) 0.32 (57%) 0.15 (27%) 0.10 (16%) 22.31 (85%) 3.82 (15%) 0.02 (-) None of the differences between groups of workers are statistically significant. "Expressed as fibres/|lg dry lung, aspect ratio >3:1, except for asbestos bodies expressed as asbestos bodies/g dry lung. bArithmetic mean SD; median concentration in parentheses. cGeometric means; percentages in parentheses represent per cent of total fibres of that type in that size category. only because of the differences in laboratory tech niques and fibre length counting ranges, but also because of inherent differences between the popula tions under study. For example, this Brazilian group had working lives in these industries averaging <10 years, with only one man developing asbestosis, whereas the single study published from China was of seven long-term factory workers, all with asbestosis, and most of the Canadian studies are of long term miners and millers. It is nonetheless of interest to compare the groups, at least in terms of the degree of lung non-commercial amphibole content. In that regard, the current series shows a low lung content of tremolite and absence of any other non-commercial amphibole fibre, when compared with any of the published data from other countries, especially Canada (Quebec) and China. Even for the Russian (Tossavainen et al., 2000) and South African studies (Rees et al., 2001), populations in which mesothe lioma is reported not to occur to date, most reported lung analyses contain tremolite at levels higher than the detection limit in the Brazilian study. In all of these areas, however, scientific work is in its infancy. Further follow-up is needed both for disease (espe cially mesothelioma) and exposure assessment. Whether the apparent absence of non-commercial amphiboles remains the case after more prolonged exposures in what is a relatively recent Brazilian mine by international standards (the Cana Brava mine at Minagu, opened in 1967) and whether the absence of mesothelioma there to date among the cohort of >10000 workers (most of whom are still living) continues will be of interest. The incidental finding not only in `chrysotile' cement workers but even in miners and millers of some degree of commercial amphibole presence reconfirms the fact that in real work environments pure exposure to chry- sotile is difficult to come by and further supports the continuing need for clinical follow-up. It is to be hoped that today's workers in Brazil are not subject to the same degree of mixed exposures, as it is well established that in addition to other factors there are important differences in cancer risk (especially for mesothelioma) as related to fibre type (Hodgson and Darnton, 2000). Acknowledgements--This work was aided by a grant to B.W.C. and A.D. by the Canadian Institutes for Health Research. REFERENCES Bagatin E. (2000) The asbestos mining project: morbidity and mortality among workers exposed to asbestos in mining activities 1940-1996. Campinas, Brazil: School of Medical Sciences, State University of Campinas. Case BW, Sebastien P. (1987) Environmental and occupational exposures to chrysotile asbestos: a comparative microanalytic study. Arch Environ Health; 42: 185-91. Case BW, Dufresne A, McDonald AD, McDonald JC, Sebastien P. (2000) Asbestos fibre type and length in lungs of chrysotile textile and production workers: fibres longer than 18 ^m. Inhal Toxicol; 12 (suppl. 3): 411-8. Churg A, Wright JL, Vedal S. (1993) Fiber burden and patterns of asbestos-related disease in chrysotile miners and millers. Am Rev Respir Dis; 148: 25-31. Dufresne A, Begin R, Masse S, Dufresne CM, Loosereewanich P, Perrault G. 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