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FILE NAME Brakes BRK DATE 2004 DOC BRK167 DOCUMENT DESCRIPTION Journal Article - Mesothelioma Among Brake Mechanics An Expanded Analysis of a Control Study Risk Analysis Vol 24 No. 3 2004 Mesothelioma Among Brake Mechanics An Expanded Analysis of a Control Study Patrick A. Hessel M. Jane Teta Michael Goodman and Edmund Lau4 A U.S. Environmental Protection Agency has begun discussions to consider its assessment The mineral form and fiber size Brake workers are typically exposed of asbestos toxicity related to brake workers considering to short chrysotile fibers To explore the mesothelioma risk among to asbestos data from a study that was published previously were other occupational exposures The National Cancer Institute provided data from obtained and the analysis was extended of brake work control study of mesothelioma Because many participants with a history in other asbestos occupations mesothelioma cases and controls also had employment of brake work controlling for employment in eight occupations were compared for a history stratified analysis was also performed excluding those with potential asbestos exposure between brake work and other occu- with any of the eighrteolactceudpattoiroinsks oPfosmseisboltehienltieroamcatiwoenrse also examined The odds ratio OR pational exposures in brake installation or repair was 0.71 95 CI 0.30 1.6w0hen controlled for employment When a history of employment in any of the eight occupations for insulation or shipbuilding controlled the OR was 0.82 95 CI 0.36 1.8O0RS wdiitdhnpootteinntciraelasaesbweistthosinecxrpeoassiunrge dwuarsation of brake work Exclusion of those with any of the resulted in an OR of 0.62 95 CI 0.01-4.71 for occupational brake work eight exposures of interaction between brake work and other occupational expo- There was no evidence an cases The results are sures These latter analyses were based on small numbers of expdooseesdnot increase the risk of consistent with the existing literature indicating that brake work mesothelioma and adds to the evidence that fiber type and size are important determinants of mesothelioma risk KEY WORDS Asbestos auto mechanics friction brake products mesothelioma 1. INTRODUCTION In February 2003 the U.S. Environmental Pro- tection Agency EPA announced plans to evaluate an asbestos cancer risk assessment methodology that 1 Exponent Wood Dale IL USA 2 Health Practice New York NY USA Exponent School of Public Health 3 Department of Epidemiology Rollins Emory University Atlanta GA USA 4 Exponent Health Practice Menlo Park CA USA ** Address correspondence to Patrick A. Hessel Ph.D. nent 185 Hansen Ct Ste 100 Wood Dale IL 60191 ExpoUSA phessel@exponent.com would distinguish carcinogenic potency by fiber type and size As noted in the announcement the ex- isting assessment has not changed since 1986 despite substantial improvements in asbestos measurement techniques and better understanding of how asbestos exposure contributes to disease A large number of epidemiologic studies have been examined to address the comparative poten- fibers cies of chrysotile and the amphibole asbestos Animal studies have proved disappointing either be- cause the routes of exposure used in these studies i.e. or intratracheal instillation bypass clear- peritoneal low sensitivity of ance mechanisms or because of the 547 0100-0547 '2004 Society for Risk Analysis 548 Hessel et al the inhalation test model Consideration of fiber length and diameter however has typically relied on experimental evidence toxicology and lung bur- den studies Given the Agency's renewed interest in mineralogy and fiber size studies of those exposed primarily to short chrysotile fibers are espe- cially relevant Automotive brakes have historically been made from friction materials containing only the chrysotile form of asbestos Motor vehicle mechanics who in- stalled and repaired brakes were exposed primarily to short chrysotile fibers with low weighted average exposures and intermittent higher short expo- sures during certain parts of the process Studies by the National Institute of Occupational Safety and Health in the late 1970s and early 1980s found timeweighted average exposures for mechanics to fibers greater than 5 ...min length and with at least a 1 aspect ratio during brake jobs ranging from 0.01 to 0.28 6.7 Fiber size distribution analyses of these samples indicated a geometric mean length of 1.70 ...mrange 0.24-10.0 and diameter of 0.15 ...mfor airborne chrysotile asbestos fibers A number of studies have examined the associ- ation between motor vehicle repair in general or brake work in particular and mesothelioma None of these have demonstrated a positive associ- ation A recent analysis found that the relative risk of mesothelioma among auto mechanics was 0.90 95 confidence interval CI 0.66 1.203.66 1.23 Addressing mesothelioma risk among brake workers is complicated by their frequent involvement in other occupations with potential asbestos exposure This was noted in a control study by Spirtas et al Thirty of the 208 cases 15.9 and 72 of the 533 controls 13.5 had worked on brakes A risk estimate was not calculated because many brake workers had also worked in shipbuilding or insulation The purpose of the present analysis was to explore the relationship between brake installation and mesothelioma in the data set originally described by Spirtas et al after adjustment for employment in occupations with known increased risk of mesothelioma and to determine whether these results sup- port the proposed new methodology for asbestos risk assessment 2. METHODS 2.1 Previous Study The study of Spirtas et 16 included cases di- agnosed from 1975 to 1980 and registered by the Los Angeles County Cancer Surveillance Program the New York State Cancer Registry excluding New York City and 39 large Veterans Administration VA hospitals Of 720 eligible cases next of kin of 536 74 were successfully interviewed Pathological material was available to confirm the diagnosis for 426 79 Of these 208 49 were accepted as definite or probable mesotheliomas Controls for cases in New York State and Los Angeles County were selected from death certificates Controls for cases from VA hospitals were se- lected from those who had died and received med- ical and financial benefits from the VA Controls were initially matched by date of birth race sex year of death and county of residence for those in New York State and Los Angeles County or hos- pital for those from the Veterans Administration to the larger group of cases Of the 687 eligible controls interviews were completed with next of kin of 533 79 Because the number of controls who responded was much greater than the number of cases accepted as having definite or probable mesothelioma all controls with completed interviews were included and the analysis was unmatched The same analytical approach was used for the present analysis The interviews requested information about asbestos exposure in general and specifically about involvement in nine activities with potential asbestos exposure These included brake lining installation or repair furnace or boiler installation or repair building demolition plumbing or heating repair insulation shipbuilding demolition work elevator installation or repair production of textiles and production of paper products For the first five activities data were available on whether the activ- ity was job related nonjob related or both job and nonjob related All interviews were conducted with next of kin and the interviewers assessed subjectively the qual- ity of the occupational histories Eighty percent of the interviews for cases and 90 for controls were rated as highly or generally reliable The authors recognized the possible failure of next of kin to recall all opportunities for asbestos exposure especially in the distant past Of the brake workers 32 did this as part of their job 57 did it on their own time and 10 did both For the present analysis those who did brake work as part of their job and those who did both were considered occupationally exposed Cases and controls were similarly distributed for occupational and nonoccupa- tional brake work Mesothelioma Among Brake Mechanics 549 2.2 Present Analysis The electronic data and documentation were ob- tained from the National Cancer Institute To en- sure that the data had been correctly converted the first three tables in the original paper were recreated For the most part these tables could be reconstructed exactly Where changes were noted these resulted from the apparent clarification of missing data i.e. there were fewer missing values for age at death in the present data set compared to the previous report The questionnaires of five cases and 12 controls had missing values for brake work The occupational histories of four of the five cases were coded as questionable quality and one as unreliable For the controls six were questionable three were gener- ally reliable and three were highly reliable Those with missing responses were excluded from the analyses This reduced the number of subjects classified as nonexposed relative to the original report in which those with missing information were classified as nonexposed There were no female brake workers only two nonwhite females in the study group both controls and 16 nonwhite males three cases and 13 controls After examining the distributions of race and sex and considering the ratings of the quality of the occupational histories and the types of brake work occupational and nonoccupational it was decided a priori that the most relevant analyses would come from 1. white males 2. with highly or generally reliable work histo- ries 3. with a nonmissing response for brake work and 4. whose brake work was occupational Of the 28 cases and 63 controls meeting the first three criteria 12 cases and 28 controls did occupational brake work Table ) The remainder did it on their own time The data were analyzed using unconditional lo- gistic regression controlling for age For the initial analysis of all relevant variables and for the analyses of shipbuilding and insulation age was entered as a continuous variable and large sample methods were used For the analyses of subsets of brake work 40 age was categorized in year age groups 40 4445 48 9 5+ and exact methods were used Categorization of age facilitated convergence of the Table I. Numbers of Cases and Controls by Exposure Subset Subset Cases Controls All Those meeting selection criteria" Brake work Noneb Nonoccupational Occupational 10 years 10 years No shipbuilding or insulation None of eight listed activitiesd 203 147 119 16 12 5 6 2 1 521 358 295 35 28 10 16 15 9 aWhite males with highly or generally reliable work histories and nonmissing response for brake work bOf these 33 cases and 171 controls were not exposed to any of the eight listed activities Length of occupational brake work was missing for one case and two controls The eight activities included furnace or boiler installation or repair building demolition plumbing or heating repair insulation shipbuilding demolition work elevator installation or repair production of textiles and production of paper products model Because smoking is not related to mesothe- lioma this was not controlled in the analysis unlike the original report Decisions regarding inclusions exclusions and analytical strategies were made be- fore risk estimates were calculated To examine the effect of exposure to brake work three approaches for controlling the effects of other asbestos exposures were used The first analysis included all relevant terms in a single model In this model age was entered as a continuous variable and 0/1 variables were entered for absence or presence respectively of occupational brake work nonoccupational brake work shipbuilding insulation and any of the remaining six activities In this analysis those with nonoccupational brake work and those with no brake work were coded as 0 i.e. not exposed for occu- pational brake work Those with occupational brake work and those with no brake work were coded as 0 for nonoccupational brake work To more clearly distinguish occupational and nonoccupational brake work a second set of analyses compared brake workers with nonbrake workers in separate analyses For the analyses of any brake work those with no history of brake work occupational or nonoccupational were considered nonexposed For the analysis of nonoccupational brake work those with no history of brake work were considered nonexposed and those with occupational brake work were excluded For the analyses of oc- cupational brake work those with nonoccupational 550 Hessel et al Table II Regression Coefficients B Standard Errors SE Odds Ratios OR and 95 Confidence Intervals for Brake Work Controlling for Age and Activities Potentially Entailing Asbestos Exposure Variable Age Occupational brake work Nonoccupational brake work Shipbuilding Insulation Other activitiesa 0.011 -0.307 -0.184 1.798 1.216 0.028 SE 0.009 0.378 0.332 0.244 0.218 0.199 Odds Ratio 1.01 0.74 0.83 6.04 3.38 1.03 95 Confidence Interval 0.99-1.03 0.35-1.54 0.43-1.59 3.74-9.75 2.20-5.17 0.70-1.52 aThe other activities included furnace or boiler installation or repair building demolition plumbing or heating repair elevator installation or repair production of textiles and production of paper products brake work were excluded and those with no his- tory of brake work were considered nonexposed This analysis was repeated including a single variable for presence of shipbuilding or insulation -1 or absence of both exposures = These were the two potentially confounding occupational exposures noted by Spirtas et al Then the analysis was repeated controlling for work in any of the eight activities considered in the original report A single variable for presence of any of these exposures = or absence of all of these exposures = was entereTdo evaluate the relationship with length of occupational exposure in these analyses subjects were classified as having no occupational brake work less than 10 years or at least 10 years The last approach dealt with the potential effects of asbestos exposures through exclusion Cases and controls were compared for a history of occupational brake work excluding those with any of the eight activities To assess the potential joint effects of brake work and other exposures interaction terms were entered into the multivariate models In addition odds ratios ORs were compared for workers in insulation and shipbuilding who either did or did not also have a history of brake work 3. RESULTS The results of the full model demonstrated positive associations between mesothelioma and both shipbuilding and insulation Table II There was no association between mesothelioma and either occu- pational or nonoccupational brake work nor was there an association with the other six activities with potential asbestos exposure Similarly the analyses that separated occupa- tional and nonoccupational brake work found no associations Table III The analysis by duration of employment showed no suggestion of increasing risk of mesothelioma with increasing length of time employed in brake work When the interactions between brake work and activities involving potential asbestos exposure were examined there were no patterns suggesting that brake work enhanced the risk associated with other asbestos exposures data not presented When participants with any of the eight activities were deleted from the analysis the OR for occupational Table III Odds Ratios OR and 95 Confidence Intervals 95 CI for Association Between Brake Work and Mesothelioma Controlling for Age and Activities Potentially Entailing Asbestos Exposure Occupational Controlled for Any Brake Work OR 95 CI Nonoccupational OR 95 CI OR Any 95 CI 10 years OR 95 CI OR 1y0ears 95 CI No activities Shipbuilding All eight activitiesa 1.03 0.74 0.82 0.59-1.75 0.42-1.30 0.46-1.41 0.99 0.74 0.79 0.48-1.96 0.34-1.53 0.37-1.61 1.04 0.71 0.82 0.46-2.22 0.30-1.60 0.36-1.80 1.32 0.99 1.03 0.39-3.97 0.27-3.22 0.30-3.22 0.86 0.53 0.68 0.26-2.41 0.15-1.60 0.21-1.98 included furnace or boiler installation or repair building demolition plumbing or heating repair insulation aThe eight activities of textiles and production of paper products shipbuilding demolition work elevator installation or repair production Note Odds ratios and % confidence intervals based on exact methods Mesothelioma Among Brake Mechanics 551 Table IV Adjusted Odds Ratios OR and 95 Confidence Intervals CI for Insulation Workers and Shipbuilders by History of Brake Work Exposure Group No History of Brake Work OR CI History of Brake Work OR CI Insulators Shipbuilders 4.14 5.16 2.55-6.77 2.94-9.23 1.74 4.36 0.69-4.46 1.36-14.8 Note Brake work included both occupational and nonoccupational brake work brake work was 0.62 95 CI 0.01-4.71 based on one exposed case and nine exposed controls The adjusted OR for insulation workers who had no history of brake work was 4.14 95 CI 2.556.77 and for insulators who were also brake workers the OR was 1.74 95 CI 0.69-4.46 Table IV For shipbuilders with no employment as brake workers the OR was 5.16 95 CI 2.94-9.23 and for shipbuilders with employment as brake workers the OR was 4.36 95 CI 1.36 14.8 4. DISCUSSION The present analysis focused on the question of the potential risk of mesothelioma associated with brake work while considering other activities involving potential asbestos exposures The results were consistent with the available literature that demonstrates no apparent risk The present analy- sis used occupational histories evaluated as reliable by the interviewers The results changed little and no conclusions differed when all respondents were in- cluded regardless of the quality of the work history Similarly including nonwhites had no discernable effect The study was limited by the relatively small numbers of brake workers especially in the analyses that excluded those with other potential asbestos exposures The confidence intervals were reasonably narrow for the overall analyses but those for the inter- action terms were quite broad In the stratified analysis only one case and nine controls with occupational brake work did not hold one of the other jobs involv- ing asbestos exposure The original study excluded from the control group those who died from can- cer and respiratory disease because the researchers felt that they might be related to asbestos exposure If these diseases were positively associated with asbestos exposure in this population the risk estimates for occupations with asbestos exposure may have been overestimated The results indicated no excess risk of mesothe- lioma among brake workers when the analyses were controlled for exposures in occupations with known risk of mesothelioma Further there was no evidence of an exposure relationship between brake work and mesothelioma This was evident in the analysis by duration of occupational brake work and the fact that the ORs for occupational brake work were indistinguishable from those for nonoccupational brake work It is assumed that on average those with occupational brake work would have had higher exposures than those with nonoccupational brake work These findings are consistent with no increase in risk of mesothelioma associated with short chrysotile fibres < ...min length There is increasing evidence that such fibres may not be carcinogenic Expla- nations for the observed results may include the fol- lowing 1 weighted average exposures are low in this occupational group 2 most of the fibers are short 3 chrysotile asbestos is used almost exclusively 4 the fibers are embedded in resin 5 much of the asbestos is transformed to forsterite a nonfibrous substance during the braking process and 6 only a small percent of brake dust is as- bestos The findings for brake mechanics reinforce the caution that direct inferences from one occupa- tional setting to another without consideration of the key determinants of risk are to be avoided ACKNOWLEDGMENTS The authors thank Dr. Aaron Blair from the Na- tional Cancer Institute for providing the data They also thank Dr. Robert Spirtas for helpful comments The project was funded by Daimler Chrysler Ford Motor Company and General Motors Corporation Drs Hessel Teta and Goodman have provided scientific consulting services to these companies in the area of friction brakes REFERENCES 1. 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