THE 1891-1920 BIRTH COHORT OF QUEBEC CHRYSOTILE MINERS AND MILLERS - DEVELOPMENT FROM 1904 AND MORTALITY TO 1992

This paper draws together the mortality experience for a cohort of som e 11 000 male Quebec Chrysotile miners and millers, reported at interv als since 1971 and now again updated. Of the 10 918 men in the complet e cohort, 1138 were lost to view, almost all never traced after employ ment of only a month or two before 1935; the other 9780 men were trace d into 1992. Of these, 8009 (82%) are known to have died: 657 from lun g cancer, 38 from mesotheliona, 1205 from other malignant disease, 108 from pneumoconiosis and 561 from other non-malignant respiratory dise ases (excluding tuberculosis). After early fluctuations, SMRs (all cau ses) against Quebec rates have been reasonably steady since about 1945 . For men first employed in Asbestos, mine or factory, they were very much what might have been expected for a blue collar population withou t any hazardous exposure. SMRs in the Thetford Mines area were almost 8% higher, but in line with anecdotal evidence concerning socio-econom ic status. At exposures below 300 (million particles per cubic foot) x years, (mpcf.y), equivalent to roughly 1000 (fibres/ml)x years-or, sa y, 10 years in the 1940s at 80 (fibres/ml)-findings were as follows. T here were no discernible associations of degree of exposure and SMRs, whether for all causes of death or for all the specific cancer sites e xamined. The average SMRs were 1.07 (all causes), and 1.16, 0.93, 1.03 and 1.21, respectively, for gastric, other abdominal, laryngeal and l ung cancer. Men whose exposures were less then 300 mpcf.y suffered alm ost one-half of the 146 deaths from pneumoconiosis or mesothelioma; th e elimination of these two causes would have reduced these men's SMR ( all causes) from 1.07 to approximately 1.06. Thus it is concluded from the viewpoint of mortality that exposure in this industry to less tha n 300 mpcf.y has been essentially innocuous, although there was a smal l risk or pneumoconiosis or mesothelioma. Higher exposures have, howev er, led to excesses, increasing with degree of exposure, of mortality from all causes, and from lung cancer and stomach cancer, but such exp osures, of at least 300 mpcf.y, are several orders of magnitude more s evere than any that have been seen for many years. The effects of ciga rette smoking were much more deleterious than those of dust exposure, not only for lung cancer (the SMR for smokers of 20+ cigarettes a day being 4.6 times higher than that for non-smokers), but also for stomac h cancer (2.0 times higher), laryngeal cancer (2.9 times higher), and- most importantly-for all causes (1.6 times higher). (C) 1997 British O ccupational Hygiene Society.