The morbidity and mortality of vermiculite miners and millers exposed to tremolite‐actinolite: Part I. Exposure estimates

Abstract

The vermiculite ore and concentrate of a mine and mill near Libby, Montana, [USA] was found to be contaminated with fibrous tremolite-actinolite. Of 599 fibers (length greater than 5 .mu.m and width greater than 0.45 .mu.m) counted in eight airborne membrane filter samples, 96% had an aspect ratio greater than 10 and 16% had an aspect ratio greater than 50. Additionally, 73% of the fibers were longer than 10 .mu.m, 36% were longer than 20 .mu.m, and 10% were longer than 40 .mu.m. Estimates of exposure before 1964 in the dry mill were 168 fibres/cc for working area, 182 fibres/cc for sweepers, 88 fibers/cc for skipping, and 13 fibers/cc for quality control laboratory. In 1964-1971, exposure estimates for these areas were 3, 36, 17, and 3 fibers/cc respectively. Estimates of exposures in the mine before 1971 ranged from 1971 ranged from 9-23 fibers/cc for drillers and were less than 2 fibres/cc for nondrilling jobs. All 8-hr TWA job exposure estimates decreased from 1972-1976, and from 1977-1982 were less than 1 fiber/cc.