Radiographic changes in a group of chrysotile miners and millers exposed to low asbestos dust concentrations

Radiographic changes in 342 Quebec asbestos miners exposed to low levels of asbestos dust for an average period of 20 years were studied. Their estimated cumulative exposure ranged from 7 fibres per cubic centimeter X years (f-y/cc) to 300 f-y/cc. Of these workers, 2.1% showed a small opacity score of 1/0 or more and 2.7% showed pleural changes. No linear relationship could be established between small opacity score and any index of exposure to asbestos. Pleural changes were related to age. A referent group of office workers within the same mining industry showed a prevalence of 2.1% (1/48) for small irregular opacities 1/0 or more, and for pleural changes.