Radiological changes over 20 years in relation to chrysotile exposure in Quebec.

Radiological changes in 267 male Quebec chrysotile mine and mill workers, each with five chest films spanning an average of 20 years, were related to age, smoking habit, mining area, duration of employment and average dust concentration before and between films. (1) Abnormality in the earliest film was related mainly to the time since first employment. (2) In 45 (30%) of the 150 men completely normal at earliest film, some radiological abnormality developed during the period of observation: incidence was weakly related to age; in Asbestos, the risk of developing small opacities was lower in smokers than in non-smokers. (3) There was an irregular pattern of correlation, more evident in Thetford Mines than in Asbestos, between radiological progression and various stimulus variables. That associations between radiological responses and measures of asbestos exposure were, as always, weak, despite powerful methodology, indicates that effects are obscured by other factors (including susceptibility) uncorrelated with exposure.