Document Rrz0YGwkY8OYydO6kvxqgkNB

Ann. occup. Hyg., Vol. 46, Supplement 1, pp. 150-153, 2002 2002 British Occupational Hygiene Society Published by Oxford University Press DOI: 10.1093/annhyg/mef664 Malignant Mesothelioma and Occupational Exposure to Asbestos: an Analysis of 1445 Cases K. J. BUTNOR1*, A. SHARMA2, T. A. SPORN1 and V. L. ROGGLI1 1Department of Pathology, Box 3712, Duke University Medical Center, Durham, NC 27710; 2Department of Pathology, Georgetown University, Washington, DC 20007, USA Asbestos exposure is indisputably associated with the development of malignant mesothelioma (MM). However, relatively few studies have correlated the manner of exposure with asbestos fiber content and type. We report findings from 1445 MMs with known exposure histories, including fiber burden analyses performed in 268 cases. A total of 1445 histologically and immunohistochemically confirmed cases of MM were placed in 23 categories, according to the predominant manner of asbestos exposure. Asbestos body counts were determined by light microscopy. Asbestos fiber content and type were assessed using scanning electron microscopy and energy dispersive X-ray analysis. Ninety-four percent of cases fell into 19 of the 23 exposure categories. Six occupational categories, including pipefitter, boilermaker, machinist, electri cian, maintenance worker and sheetmetal worker, as well as one para-occupational (household contact) exposure category, were represented. Twelve categories reflected the kind of industry in which exposure occurred. These included insulation, shipbuilding, railroad, oil/chemical, paper mill, US Navy, molten metal, glass/ceramic, power, automotive, asbestos manufacture and construction. Elevated levels of commercial amphibole fibers were identified in all 19 categories. The highest levels were identified among insulation and asbestos manufacturing industries and pipefitters. The median value of non-commercial amphibole fibers exceeded commercial amphibole fibers in four categories (automotive industry, household contacts, building occupants and environmental exposures). Multiple exposure categories were identified in one-quarter of cases. The majority of MMs in the USA fall into a limited number of exposure categories, with overlap of categories in a substantial proportion of cases. For most exposure categories, commercial amphiboles are the predominant fiber type. Keywords: asbestos; malignant mesothelioma; occupational exposure INTRODUCTION The association between malignant mesothelioma (MM) and prior asbestos exposure is undisputed. A wide variety of occupational and environmental exposures have been implicated as the source of this exposure. Although numerous reports document MM risk associated with particular exposures, relatively few studies have examined the distribution of occu pations in a large series of MM cases. MATERIALS AND METHODS In order to investigate the types of exposures related to the development of MM, we reviewed all MMs in one of the author's (V.L.R.) consultation *Author to whom correspondence should be addressed. Tel: +1-919-970-4918; fax: +1-919-681-7377. files for which information was available regarding occupation or manner of asbestos exposure. Patients were classified as being employed in one of 12 indus tries and/or seven occupations, or into one of four non-occupational exposure groups (Tables 1-3). A substantial number of cases had exposure in more than one category. However, an attempt was made to place patients in a predominant category where the most intense exposure probably occurred. Fiber analyses were performed on formalin-fixed or paraffinembedded lung tissue using previously described methods (Roggli et al., 1992). Lung tissue was processed for digestion using the sodium hypo chlorite digestion technique and analysis was performed by light microscopy, as well as scanning electron microscopy and energy dispersive spectrometery. The results were compared with lung tissue from 19 controls who had no evidence of asbestos-related disease and no history of asbestos exposure. 150 Malignant mesothelioma and occupational exposure to asbestos 151 Table 1. Malignant mesothelioma cases by industry Single Shipbuilding 203 US Navy 91 Construction 99 Insulation 92 Oil and chemical 78 Power plant 50 Railroad 37 Automotive 24 Steel/metal 33 Asbestos manufacturing 34 Papermill 7 Ceramics/glass 6 Multiple 86 84 35 11 10 10 16 27 10 5 0 0 Total 289 175 134 103 88 60 53 51 43 39 7 6 Table 2. Malignant mesothelioma cases by occupation Pipefitter Boilermaker Maintenance Machinist Electrician Sheetmetal Other asbestos Single 159 81 75 62 59 17 23 Multiple 28 31 15 27 22 5 0 Total 187 112 90 89 81 22 23 Table 3. Malignant mesothelioma cases with non-occupational exposures Single Household contacts 86 Building occupants 17 Other 46 Environmental 5 Multiple 3 1 0 0 Total 89 18 46 5 RESULTS A total of 1445 MMs were identified. In 268 of these cases, the exposure information could be correl ated with the result of tissue fiber burden analysis. These included 1322 men and 123 women. In some occupational categories, all were men. These included insulators, railroad workers, power plant workers, steel workers, automotive workers, boilerworkers, electricians and machinists. A large percentage of women with MM were household contacts. The building occupant category included about an equal number of men and women. The median age was similar across all occupations and industrial expos ures, with the median age occurring in the seventh or eighth decade for most categories. Insulators were slightly younger, with a median age of 59.5 yr. Household contacts also had a median age of 59 yr, which reflects a mixture of individuals first exposed as adults (with median ages in the seventh or eighth decade) and those first exposed as children (mostly daughters of asbestos workers, with a median age in the fourth decade). Building occupants were also rela tively young (47 yr), since many of these involved exposures allegedly beginning during childhood while attending school. Two categories have often been considered as lowlevel exposures. These include household contacts of asbestos workers and environmental (neighborhood) exposures. There were 89 household contacts of an asbestos worker, 10 of which had additional occupa tional exposure to asbestos. Seventy-nine percent were women with an average age of 59 yr. There were four cases with environmental exposure to asbestos. All were men with an average age of 67 yr. None had any additional known exposure to asbestos. Three of these four cases were from a region of Turkey where there was intense environmental exposure to tremolite-actinolite. When these two categories, along with two fairly non-specific categories of `other asbestos' and `other' were excluded, the remaining 19 groups accounted for >94% of the 1445 MMs included in this study. Approximately 90% of our cases arose in the pleura. The other 10% arose in the peritoneum. The highest percentage of peritoneal MM occurred among insula tors and asbestos manufacturing plant workers. In each of these groups, the ratio of pleural to peritoneal tumors was about 2:1. In the remaining groups, this ratio ranged from 8.6:1 in construction workers to more than 50:1 in shipyard workers. The low ratio of 1.8:1 in building occupants indicates that peritoneal MMs in this setting are unlikely to be related to asbestos exposure. These observations also call into question the association of peritoneal MMs in women with low-dose asbestos exposure. Studies have shown that most peritoneal MMs in women are not associated with any prior history of asbestos exposure (Goldblum and Hart, 1995). When information was available regarding the pres ence or absence of plaques (PPP), a high percentage of cases had plaques. Among occupationally exposed individuals, the percentage of patients with MM and plaques ranged from 50% in glass and ceramic workers to as high as 100% of papermill workers. Lower percentages were seen for non-occupational exposures, although PPP were present in nearly 60% of household contacts of asbestos workers. When information was available regarding the presence or absence of asbestosis, a relatively low percentage of cases had histologically confirmed asbestosis. Among occupationally exposed individ uals, the percentage of cases with asbestosis ranged from 0% of glass and ceramic workers and friction product workers to as high as 67% of asbestos 152 K. J. Butnor et al. manufacturing plant workers. Asbestosis was rarely observed among patients with MM and non-occupational exposure. None of the environmental expos ures or building occupants had asbestosis, but asbestosis was confirmed histologically in 8.3% of household contacts of asbestos workers. The median asbestos body count in each of the 23 exposure categories exceeded our normal range of 0-20 AB/g, except for two categories: automotive workers and building occupants. The industry with the highest median asbestos body count was the insulation industry, while the occupation with the highest count was boilermaker. Commercial amphiboles (mostly amosite with some crocidolite) were the predominant fiber type identified in each of the categories, except for four categories: automotive workers, household contacts, building occupants and environmental (neighborhood) exposures. In these instances, non-commercial amphiboles (mostly tremolite with some actinolite and anthophyllite) predom inated over commercial amphibole fibers. Chrysotile fibers were detected less frequently, and were not detected in seven categories. Non-asbestos mineral fibers were present in all categories in roughly similar amounts. Further analyses were performed on the 12 exposure categories for which there were 10 or more analyses within the category. Commercial amphibole fibers were present in concentrations that exceeded the background level in all 12 categories, ranging from 57% (other) to 100% (insulators) of the individuals in any one category. Non-commercial amphibole fibers were also present in excess concentrations in all 12 categories, ranging from 13% (maintenance workers) to 68% (shipyard workers) of individuals in any particular category. However, the percentage of indi viduals in a category with elevated levels of non commercial amphiboles exceeded 50% in only two categories: shipyard workers and electricians. Chrysotile was present in excess concentrations in nine of the 12 categories (excluding in pipefitters, construc tion workers, or other), ranging from 5 to 23% of the individuals in any one category. In none of the categories was chrysotile found in elevated concen trations in more than half of the individuals in that category. contacts have tissue asbestos burdens that are, on average, equivalent to a mild to moderate occupa tional exposure (Gibbs et al., 1990; Roggli et al., 1998). Wives tended to have higher lung asbestos burdens than daughters or sons. In contrast, the median asbestos body count for automotive brake repair workers was within our normal range. In many of these cases, the tissue asbestos content was within the limits of background. In those cases with elevated tissue asbestos content, excess commercial amphibole fibers (mostly amosite) were invariably detected. These observations confirm our prior impression that friction product exposure, such as that encountered by automotive mechanics, is unlikely to contribute to the development of MM (Roggli et al., 1992; Woitowitz and Rodelsperger, 1994). It could be argued that these cases are not repre sentative of the types of exposures occurring in MMs in the USA, since >90% are medicolegal cases. Therefore, we compared our data with that obtained by the Australian Mesothelioma Surveillance Program, which is a survey of all MMs in Australia. Such cases must be reported to the registry as proscribed by law. With the exception of MMs related to working in the Wittenoom mine in Australia, the major categories of exposure are remarkably similar to those noted in our series of cases. CONCLUSIONS This study shows that the vast majority of MMs occurring in the USA today can be placed into a limited number of exposure categories, which include 12 industries and six occupations with known asbestos exposure. Household contacts of asbestos workers accounted for most of the remainder of the cases, with neighborhood exposures rarely contrib uting to MM. Overlap of categories was common, with individual workers often having exposures in more than one category. Commercial amphiboles were found in excess amounts in all 19 categories. Non-commercial amphiboles were found in excess amounts in a smaller percentage of cases, while cases in which the level of chrysotile exceeded background were infrequent. DISCUSSION Two of the categories deserve comment. House hold contacts of asbestos workers had tissue asbestos burdens that were similar to the median value for some occupational groups. For example, the median asbestos body count of household contacts (130 AB/g) was of the same order of magnitude as construction workers (190 AB/g), US Navy employees (170 AB/g) and machinists (100 AB/g). Hence, household REFERENCES Gibbs AR, Griffiths DM, Pooley FD, Jones JS. 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