Asbestos exposure and incidence of disease among a group of former chrysotile asbestos miners and millers from Baie Verte, NL, Canada

Giles Murphy, Tina Linda (2015) Asbestos exposure and incidence of disease among a group of former chrysotile asbestos miners and millers from Baie Verte, NL, Canada. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Asbestos is one of the most well-known and extensively studied occupational hazards. Over the past century, the health effects of asbestos exposure have been studied in thousands of books, journal articles, and media publications, from all over the world. Despite the vast amount of knowledge that exists about asbestos there continues to be controversy about the relative health risks associated with its different types, that is, serpentine (chrysotile) and amphibole asbestos fibres. The continued production and use of chrysotile asbestos in many countries around the world, as well as the ongoing exposure of millions of workers globally to asbestos, has kept it a subject of ongoing debate and concern. Although asbestos is a well-established cause of both malignant and non-malignant disease, a number of recent meta-analyses have sought to estimate the relative risk of diseases related to exposure to each of the different fibre types. The lack of epidemiological studies with good quality exposure assessments, particularly in the mining/milling industry, as well as the lack of retrospective exposure assessments for most cohorts, has led to an over-reliance on studies of a single population of chrysotile-only exposed cohorts: the Québec chrysotile miners/millers cohort. These studies, however, have been criticized as being heavily influenced by the asbestos industry. This thesis, which consists of an introductory chapter, three interrelated studies, and a concluding chapter, presents data on an under-studied cohort of chrysotile miners/millers from Baie Verte, Newfoundland and Labrador (NL), Canada. The first study will describe the development of a job exposure matrix (JEM) that was used to perform a retrospective exposure assessment for former workers of the mine/mill. The second study is an epidemiological assessment of a sub-group of the overall cohort of former employees who voluntarily joined the Baie Verte Miners Registry, an exposure/disease registry that was established to aid in the compensation process for former workers who have, or will, develop asbestos-related diseases. The third study outlines the process of enumerating the remainder of the cohort from historical union records (i.e., those who did not join the Baie Verte Miners Registry) and the epidemiological analysis of this group and of the two groups combined. Taken as a whole, this thesis demonstrates the good quality of the retrospective exposure assessment that has been conducted on this group of former asbestos workers and it supports the position that chrysotile asbestos is a cause of malignant mesothelioma. It also confirms the increased risk of asbestosis, as well as cancer of the lung, larynx, esophageal, and colorectum, in workers who were exposed to chrysotile asbestos. This cohort of chrysotile miners/millers is, therefore, a useful addition to the literature for estimating the relative potency of the different asbestos fibre types.

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