Risk Anal. 2004 Jun;24(3):547-52. Related Articles, Links
Mesothelioma among brake mechanics: an expanded analysis of a case-
Hessel PA, Teta MJ, Goodman M, Lau E.
Exponent, Wood Dale, IL 60191, USA. firstname.lastname@example.org
The U.S. Environmental Protection Agency has begun discussions to consider its
assessment of asbestos toxicity related to mineral form and fiber size. Brake workers are
typically exposed to short chrysotile fibers. To explore the mesothelioma risk among brake
workers, considering other occupational exposures to asbestos, data from a study that was
published previously were obtained and the analysis was extended. The National Cancer
Institute provided data from a case-control study of mesothelioma. Because many
participants with a history of brake work also had employment in other asbestos-related
occupations, mesothelioma cases and controls were compared for a history of brake work,
controlling for employment in eight occupations with potential asbestos exposure. A
stratified analysis was also performed excluding those with any of the eight occupations.
Possible interactions between brake work and other occupational exposures related to risk
of mesothelioma were also examined. The odds ratio (OR) for employment in brake
installation or repair was 0.71 (95% CI: 0.30-1.60) when controlled for insulation or
shipbuilding. When a history of employment in any of the eight occupations with potential
asbestos exposure was controlled, the OR was 0.82 (95% CI: 0.36-1.80). ORs did not
increase with increasing duration of brake work. Exclusion of those with any of the eight
exposures resulted in an OR of 0.62 (95% CI: 0.01-4.71) for occupational brake work.
There was no evidence of an interaction between brake work and other occupational
exposures. These latter analyses were based on small numbers of exposed cases. The results
are consistent with the existing literature indicating that brake work does not increase the
risk of mesothelioma and adds to the evidence that fiber type and size are important
determinants of mesothelioma risk.
1: Occup Environ Med. 2004 Apr;61(4):363-6. Related Articles, Links
Mortality in a cohort of vermiculite miners exposed to fibrous amphibole in
McDonald JC, Harris J, Armstrong B.
Imperial College School of Medicine, London, UK. email@example.com
BACKGROUND: Fibrous tremolite is a widespread amphibole asbestiform mineral,
airborne fibres of which constitute an environmental hazard in Libby, Montana, northern
California, and elsewhere. AIMS: To determine excess risk from lung cancer,
mesothelioma, and all-cause mortality in a cohort of men exposed to tremolite, but no other
form of asbestos. METHODS: Mortality by certified cause and various measures of
exposure to tremolite and related amphibole fibres was assessed in a cohort of 406
vermiculite mineworkers in Libby, Montana, employed before 1963 and followed until
1999. RESULTS: Total deaths were: lung cancer 44 (SMR 2.40), non-malignant
respiratory disease (NMRD) 51 (SMR 3.09), all causes 285 (SMR 1.27); included among
the total were 12 deaths ascribed to mesothelioma (4.21% of all deaths). Adjusted linear
increments in relative risks (per 100 f/ml.y), estimated by Poisson regression, were: lung
cancer (0.36, 95% CI 0.03 to 1.20), NMRD (0.38, 95% CI 0.12 to 0.96), and all deaths
(0.14, 95% CI 0.05 to 0.26). CONCLUSIONS: The all-cause linear model would imply a
14% increase in mortality for mine workers exposed occupationally to 100 f/ml.y or about
3.2% for a general population exposed for 50 years to an ambient concentration of 0.1 f/ml.
Amphibole fibres, tremolite in particular, are likely to be disproportionately responsible for
cancer mortality in persons exposed to commercial chrysotile, but to what extent cannot be
PMID: 15031396 [PubMed - indexed for MEDLINE]
Ann Occup Hyg. 2003 Jun;47(4):325-30. Related Articles, Links
Exposure to brake dust and malignant mesothelioma: a study of 10 cases
with mineral fiber analyses.
Butnor KJ, Sporn TA, Roggli VL.
University of Vermont Medical Center, Department of Pathology, Burlington, VT 05405,
OBJECTIVES: A large number of workers in the USA are exposed to chrysotile asbestos
through brake repair, yet only a few cases of malignant mesothelioma (MM) have been
described in this population. Epidemiologic and industrial hygiene studies have failed to
demonstrate an increased risk of MM in brake workers. We present our experience of MM
in individuals whose only known asbestos exposure was to brake dust and correlate these
findings with lung asbestos fiber burdens. METHODS: Consultation files of one of the
authors were reviewed for cases of MM in which brake dust was the only known asbestos
exposure. Lung fiber analyses were performed using scanning electron microscopy (SEM)
in all cases for which formalin-fixed or paraffin-embedded lung tissue was available.
RESULTS: Ten cases of MM in brake dust-exposed individuals were males aged 51-73 yr.
Nine cases arose in the pleura and one in the peritoneum. Although the median lung
asbestos body count (19 AB/g) is at our upper limit of normal (range 0-20 AB/g), half of
the cases had levels within our normal range. In every case with elevated asbestos fiber
levels by SEM, excess commercial amphibole fibers were also detected. Elevated levels of
chrysotile and non-commercial amphibole fibers were detected only in cases that also had
increased commercial amphibole fibers. CONCLUSIONS: Brake dust contains exceedingly
low levels of respirable chrysotile, much of which consists of short fibers subject to rapid
pulmonary clearance. Elevated lung levels of commercial amphiboles in some brake
workers suggest that unrecognized exposure to these fibers plays a critical role in the
development of MM.
PMID: 12765873 [PubMed - indexed for MEDLINE]
1: Ann Occup Hyg. 2002 Jul;46(5):447-53. Related Articles, Links
Tremolite and mesothelioma.
Roggli VL, Vollmer RT, Butnor KJ, Sporn TA.
Department of Pathology, Duke University and Durham VA Medical Centers, NC 27710,
BACKGROUND: Exposure to chrysotile dust has been associated with the development of
mesothelioma and recent studies have implicated contaminating tremolite fibers as the
likely etiological factor. Tremolite also contaminates talc, the most common non-asbestos
mineral fiber in our control cases. METHODS: We examined 312 cases of mesothelioma
for which fiber burden analyses of lung parenchyma had been performed by means of
scanning electron microscopy to determine the content of tremolite, non-commercial
amphiboles, talc and chrysotile. The vast majority of these patients were exposed to dust
from products containing asbestos. RESULTS: Tremolite was identified in 166 of 312
cases (53%) and was increased above background levels in 81 cases (26%). Fibrous talc
was identified in 193 cases (62%) and correlated strongly with the tremolite content (P <
0.0001). Chrysotile was identified in only 32 cases (10%), but still correlated strongly with
the tremolite content (P < 0.0001). Talc levels explained less of the tremolite deviance for
cases with an increased tremolite level than for cases with a normal range tremolite level
(22 versus 42%). In 14 cases (4.5%) non-commercial amphibole fibers (tremolite, actinolite
and/or anthophyllite) were the only fiber types found above background. CONCLUSIONS:
We conclude that tremolite in lung tissue samples from mesothelioma victims derives from
both talc and chrysotile and that tremolite accounts for a considerable fraction of the excess
fiber burden in end-users of asbestos products.
PMID: 12176759 [PubMed - indexed for MEDLINE]
Ultrastruct Pathol. 2002 Mar-Apr;26(2):55-65. Related Articles, Links
Malignant mesothelioma and occupational exposure to asbestos: a
clinicopathological correlation of 1445 cases.
Roggli VL, Sharma A, Butnor KJ, Sporn T, Vollmer RT.
Department of Pathology, Durham Veterans Administration and Duke University Medical
Center, North Carolina 27710, USA.
Asbestos exposure is indisputably associated with development of mesothelioma. However,
relatively few studies have evaluated the type of occupational exposure in correlation with
asbestos fiber content and type. This study reports findings in 1445 cases of mesothelioma
with known exposure history; 268 of these also had fiber burden analysis. The 1445 cases
of mesothelioma were subclassified into 23 predominant occupational or exposure
categories. Asbestos body counts per gram of wet lung tissue were determined by light
microscopy. Asbestos fiber content and type were determined by scanning electron
microscopy and energy dispersive x-ray analysis. Results were compared with a control
group of 19 lung tissue samples. Ninety-four percent of the cases occurred among 19
exposure categories. Median asbestos body counts and levels of commercial and
noncommercial amphibole fibers showed elevated levels for each of these 19 categories.
Chrysotile fibers were detectable in 36 of 268 cases. All but 2 of these also had above-
background levels of commercial amphiboles. When compared to commercial amphiboles,
the median values for noncommercial amphibole fibers were higher in 4 of the 19 exposure
groups. Most mesotheliomas in the United States fall into a limited number of exposure
categories. Although a predominant occupation was ascertained for each of these cases,
there was a substantial overlap in exposure types. All but 1 of the occupational categories
analyzed had above-background levels of commercial amphiboles. Commercial amphiboles
are responsible for most of the mesothelioma cases observed in the United States.
PMID: 12036093 [PubMed - indexed for MEDLINE]
: Ann Occup Hyg. 2001 Oct;45(7):513-8. Related Articles, Links
Case-referent survey of young adults with mesothelioma: I. Lung fibre
McDonald JC, Armstrong BG, Edwards CW, Gibbs AR, Lloyd HM, Pooley FD, Ross
DJ, Rudd RM.
National Heart and Lung Institute, Imperial College School of Medicine, London, UK.
OBJECTIVES: Our study aimed to determine the lung tissue concentration of asbestos and
other mineral fibres by type and length in persons with mesothelioma aged 50 yr or less at
time of diagnosis, compared to controls of similar age and geographical region. In this age
group it was thought that most, but not all, work-related exposures would have been since
1970, when the importation of crocidolite, but not amosite, was virtually eliminated.
METHODS: Eligible cases were sought from recent reports by chest physicians to the
SWORD occupational disease surveillance scheme. Lung tissue samples were obtained at
autopsy from 69 male and four female cases, and mineral fibres identified, sized and
counted by electron microscopy. Fibre concentrations per microg dry tissue were compared
with similar estimates from a control series of autopsies of sudden or accidental deaths.
Unadjusted, and adjusted odds ratios calculated by logistic regression, assessed relative risk
in relation to fibre type, length and concentration. RESULTS: Unadjusted and adjusted
odds ratios increased steadily with concentration of crocidolite, amosite, tremolite and all
amphiboles combined. There was also some increase with chrysotile, but well short of
statistical significance. Incremental risk examined in a linear model was as highly
significant for all amphiboles together as individually. Short, medium and long amphibole
fibres were all associated with increased risk in relation to length. Mullite and iron fibres
were significant predictors of mesothelioma when considered without adjustment for
confounding by amphiboles, but, after adjustment, were weak and far from statistically
significant. CONCLUSIONS: In this young age group, amosite and crocidolite fibres could
account for about 80% of cases of mesothelioma, and tremolite for some 7%. The
contribution of chrysotile, because of low biopersistence, cannot be reliably assessed at
autopsy, but to the extent that tremolite is a valid marker, our results suggest that it was
small. The steep linear trend in odds ratio shown by amphiboles combined indicates that
their effects may be additive, with increased risk from the lowest detectable fibre level.
Non-asbestos mineral fibres probably made no contribution to this disease. Contrary to
expectation, however, some 90% of cases were in men who had started work before 1970;
this was so whether or not amosite or crocidolite was found in lung tissue.
PMID: 11583653 [PubMed - indexed for MEDLINE]
1: Schweiz Med Wochenschr. 1995 Mar 11;125(10):453-7. Related Articles, Links
[Asbestos: past, present and future]
[Article in German]
Department of Environmental and Occupational Medicine, University of Aberdeen,
Owing to its particular properties asbestos has been widely used for the production
of insulating material, for fire proofing, and for strengthening to other materials
such as cements and plastics, and thus the story of this mineral was one of
progressive commercial success until the middle of this century. However, serious
health hazards were realized early: around the turn of the century a progressive form
of diffuse fibrosis (asbestosis) in asbestos workers was observed and in 1950 an
excess risk of lung cancer, while in 1960 the causal relationship between asbestos
and mesothelioma were confirmed. In view of the known potential risks of asbestos
and its widespread use in the building industry, more recently asbestos has caused
considerable public concern and anxiety. Based on numerous experimental and
epidemiological observations, present knowledge of the pathogenic effects of
asbestos is sufficient for a number of broad conclusions to be drawn. (1) The
amphibole types of asbestos are too dangerous for use as industrial material, and
should be banned. (2) Chrysotile can probably be used safely if there is strict control
of the workers' dust exposure. (3) It is very unlikely that the general public is at any
measurable risk from asbestos in buildings. Exceptions are people working
regularly on maintenance tasks involving removing or cutting of asbestos in
buildings; such people are properly classified as asbestos workers and should be
protected accordingly.(ABSTRACT TRUNCATED AT 250 WORDS)
PMID: 7892557 [PubMed - indexed for MEDLINE]