MORTALITY IN CANADIAN MINERS AND MILLERS EXPOSED TO CHRYSOTILE *

Attention drawn in 1964’ to the serious threats to health posed by airborne asbestos dust led immediately to recommendations* that epidemiologic inquiries were urgently needed in populations exposed to single fiber types. At the invitation of the Canadian government, and with encouragement from the government of Quebec, our group a t McGill University embarked in 1966 on a comprehensive multidisciplinary program of research, which is still continuing. Our primary concern was a longitudinal study of mortality in the chrysotile mines and mills located in or near the towns of Asbestos and Thetford Mines, about 100 miles east of Montreal, concentrating always on exposure-response relationships. Because malignant mesothelioma was so rare, our studies were soon extended to the ascertainment and investigation of mesothelial tumors throughout Canada and, more recently, the United States3 We have also conducted cross-sectional and longitudinal studies of morbidity in the Quebec mines and mills. Our knowledge of the mortality experienced by chrysotile workers is derived from observations on a cohort of more than 1 1,000 men and women followed from first employment, often many years ago, of whom 4547 were known to have died by the end of 1975. In this paper, we shall describe the evolution of mortality in the cohort, compare findings stage by stage, and discuss some of the implications.