Document o01r13eQLM4xGX6ynm5r7EGr

FILE NAME: Conwed (CON) DATE: 2010 Jan DOC#: CONOOl DOCUMENT DESCRIPTION: NIOSH Current Intelligence Bulletin Conwed This information is distributed solely for the purpose ofpre-dissemination peer review under applicable information quality guidelines. It has not been form ally disseminated by the National Institute fo r Occupational Safety and Health. It does not _____________ represent and should not be construed to represent any agency determination or policy.______________ 1 on the rest of the state (146 cases, rate ratio (RR)=2.1, 95%CI=1.8-2.5), while the rate in 2 females was less than expected (RR=0.72, 95%CI=0.38-1.2). The fact that the excess of 3 mesothelioma was only observed among males strongly suggests an occupational 4 etiology. In addition to the taconite industry, a plant producing asbestos ceiling tiles 5 (Conwed Corporation) was located in the northeastern Minnesota region. From 1958-- 6 1965 amosite was used at Conwed, and from 1966-1974 chrysotile was used [Mandel 7 2008], The MDH has initiated epidemiological studies o f mesothelioma incidence 8 among workers at the Conwed Corporation and at the iron mines in northeastern 9 Minnesota. The records from a cohort o f approximately 72,000 iron miners and from 10 5,700 Conwed workers have been linked with a mesothelioma data registry. Between 11 1988 and 2007, a total of 58 mesothelioma cases have been identified among the miners 12 and 25 cases have been identified among the Conwed workers. Because only 3 of the 58 13 mesothelioma cases identified in the miner cohort had also been employed at Conwed, it 14 is unlikely that the mesothelioma excess in miners could be explained by asbestos 15 exposures during employment at the Conwed ceiling tile facility [MDH 2007]. 16 17 Brunner et al. [2008] have recently reported findings from an MDH study of 18 mesothelioma cases occurring among iron miners between 1988 and 1996. The job 19 histories of the cases were reviewed for evidence o f exposure to commercial asbestos. 20 Mining jobs were identified from company personnel files. Non-mining employment 21 information was obtained from worker application files, worker compensation records, 22 and obituaries. Potential asbestos exposures for jobs held in the mining industry were 23 identified by conducting interviews o f 350 workers representing 122 occupations and 7 24 different mining companies. To estimate the probability and intensity o f potential 25 exposure to commercial asbestos in each o f the jobs, an expert panel rated the potential 26 for asbestos exposure based on these interviews, available job descriptions from the 27 relevant time period, and their knowledge of the mining environment. Fifteen of 17 iron 28 miners known to have developed mesothelioma were judged to have sufficiently good 29 work histories for the study. Eleven o f the cases were reported to have had probable 30 exposure, and 3 were reported to have possible exposure to commercial asbestos. The 31 asbestos exposures were from non-mining jobs (4 cases), mining jobs (4 cases), or both 32 (6 cases). The findings from this study suggest that the excess of mesothelioma observed 33 among taconite miners might be explained by exposure to commercial asbestos rather 34 than from the nonasbestiform amphibole EMPs generated during iron ore processing. 35 However, this being a case series, it was not possible to determine whether commercial 36 asbestos exposure was different in the cases than in the cohort as a whole or in a control 37 group. This study also did not include the 41 additional mesothelioma cases that have 38 been reported by the MDH since 1996 [MDH 2007]. 39 40 In summary, the results from cohort mortality studies o f taconite miners and millers in 41 Minnesota have not provided any evidence of an increased risk o f respiratory cancer or 42 mesothelioma. This appears to be somewhat in conflict with reports from the MDH that 43 mesothelioma incidence is significantly elevated among males (but not females) in 44 northeastern Minnesota and that a large number of these cases were workers in the Draft NIOSH CURRENT INTELLIGENCE BULLETIN January 2010 Asbestos and Other Elongate Mineral Particles: State o f the Science and Roadmap for Research (V4) Page 30 o f 163 This information is distributed solely for the purpose o f pre-dissemination peer review under applicable information quality guidelines. It has not been form ally disseminated by the National Institute for Occupational Safety and Health. It does not ______________represent and should not be construed to represent any agency determination or policy.______________ 1 Minnesota taconite industry. There is some evidence that these cases could, at least in 2 part, be related to exposures to commercial asbestos that occurred in or outside of the 3 taconite mining industry, but fiirther research on this question is needed. The MDH is 4 currently working with researchers at the University of Minnesota, School of Public 5 Health on a mesothelioma case-control study, a respiratory morbidity study, and a 6 mortality study o f the iron miners of northeastern Minnesota [MDH 2007]. 7 8 Summary o f Epidemiological Studies o f Cohorts Exposed to Nonasbestiform EMPs 9 The results from studies o f populations reportedly exposed to nonasbestiform EMPs do 10 not provide clear answers regarding the toxicity of these EMPs. There are a number of 11 features o f these studies that limit their usefulness for answering these questions. First, 12 the populations in these studies were exposed to a complex mixture of particles. 13 Nonasbestiform EMPs generally represented only a small component of airborne 14 exposures, which included other minerals such as silica that are known to cause lung 15 diseases. Thus, although an excess o f pneumoconiosis has been observed in the studies 16 o f Homestake gold miners and New York talc workers, the extent to which these findings 17 are attributable to their exposures to nonasbestiform EMPs cannot be determined. A 18 potential limitation of the New York talc studies is that if the EMPs do include 19 asbestiform minerals as reported in the NIOSH [1980] study, it is difficult to determine 20 whether the observed health effects are from asbestiform or other EMPs. 21 22 Another major limitation o f these studies is that they lack adequate information on past 23 exposure to EMPs. An excess of respiratory cancer was observed in the occupational 24 studies of New York talc workers and a small excess was observed in the most recent 25 study of Homestake gold miners. In both studies, the excess of respiratory cancer was 26 not found to increase with cumulative exposure to dust. Relationships between health 27 outcomes and exposure to an agent o f interest can be attenuated when a nonspecific 28 exposure indicator is used as a surrogate for exposure to that agent [Blair et al. 2007; 29 Friesen et al. 2007]. Thus, when the exposure index used to assess the effect o f EMPs is 30 based on a surrogate measure, such as respirable dust, rather than on specific 31 measurement o f EMP concentrations, the lack o f an exposure-response relationship 32 between the exposure index and the health outcome must be considered suspect, 33 particularly where the composition o f a mixed exposure varies by work area. 34 Interpretation o f findings from the New York talc studies has been further complicated by 35 the employment o f the workers elsewhere, including employment at other talc mines in 36 the area. Lack o f positive findings from exposure-response analyses in the New York 37 talc studies of RTV miners and millers could also have resulted from exposure 38 misclassification--possible under-ascertainment o f exposure to talc and other mineral 39 particles caused by not considering exposures at neighboring talc mines. 40 41 The reliability o f death certificate information is another major limitation, particularly for 42 the diagnosis of mesothelioma. Mesothelioma did not have a discrete ICD code until the 43 10th revision o f the ICD, used for U.S. death certificate data only since 1999. This likely 44 explains the discordance between the apparent recent lack of excess mesothelioma deaths Draft NIOSH CURRENT INTELLIGENCE BULLETIN January 2010 Asbestos and Other Elongate Mineral Particles: State o f the Science and Roadmap for Research (V4) Page 31 o f 163