Etiology of pleural calcification: a study of Quebec chrysotile asbestos miners and millers.

A review of 15,689 chest radiographs of Quebec chrysotile miners and millers, representing the latest film prior to November 1, 1966, for all such persons ever x-rayed, identified 206 men with pleural calcification. Of these, 198 had worked in the Thetford Mines area, 6 at Asbestos, and 2 at St. Remi de Tingwick; 2.5%, 0.08%, and 1% of the films from these areas, respectively. A series of case-control studies revealed that pleural calcification was concentrated in men employed at a small group of mines in Thetford Mines and occurred more often among miners and maintenance personnel than among millers. Calcification was not related to past history of illness or injury, place of residence, or employment in other industries. The distribution of pleural calcification in this Quebec industry suggests that it is related to some characteristic of airborne dust or mineral closely associated with the chrysotile that is encountered during mining in Thetford Mines but not in other mining areas. Possible minerals include mica, talc, and breunnerite.