2002 Denver Annual Meeting (October 27-30, 2002)

Paper No. 3
Presentation Time: 8:55 AM


CASE, Bruce W., Departments of Pathology, Epidemiology, Occupational Health and School of Environment, McGill Univ, 3775 University Street, Montreal, QC H3A2B4, Canada, bruce.case@mcgill.ca

Over 10,000 papers have been published on the subject of “asbestos” and disease. Usage of the term is confusing. As IARC states in their 1996 monograph, there remains taxonomic confusion and lack of standardized operating definitions for fibres. Asbestos is often inappropriately used as a generic, homogeneous rubric, and even when an asbestos fibre type is specified, its source is rarely stated. The result has been a cacophony of voices on the subject of asbestos exposure, dose, and diseases. In this paper, we illustrate the problem using three examples of “tremolite” exposure. (1) The Davis et al. (Ann NY Acad Sci 1991; 643:473-504) animal injection study of “tremolite”. Although the results of this paper – which demonstrate differential effects of tremolite fibre nature for six samples for mesothelioma incidence after intraperitoneal injection – were used by OSHA for deregulation of nonasbestiform tremolite (Federal Register, 1992), their finding of a 100% mesothelioma rate for an asbestiform tremolite fibre to which humans are currently exposed in California has been systematically misunderstood with the possible result of a future epidemic of mesothelioma in that area. (2)The McDonald et al. study of lung disease as a result of exposure to a complex amphibole asbestos (tremolite-actinolite, winchite, and richterite). This study shows this asbestos exposure in Libby Montana to be one of the most carcinogenic yet encountered. Yet the results were largely ignored until 1999. Further, they led not to a specific addressing of the problems caused by the complex amphibole at issue but to proposals in the United States Senate for regulation of “all durable fibres" having aspect ratio of greater than 3:1, regardless of fibre length or type. (3) Although the first two examples demonstrate failures of public health scientists and regulators to appreciate mineralogical/ geological aspects of exposure and dose for “asbestos”; the converse has also been true. Demonstration of serious health consequences (including mesothelioma, lung cancer, and asbestosis) of tremolite “fibers” in the Province of Quebec and in nearby upstate New York due to exposures to tremolite have been hampered by mineralogical assessments of the exposures as “nonasbestiform” – a meaningless finding given the strong epidemiological evidence of harm strongly linked to the exposure.