title: 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, was found to be contaminated with fibrous tremolite-actinolite. Of 599 fibers (length greater than 5 microns and width greater than 0.45 micron) 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 microns, 36% were longer than 20 microns, and 10% were longer than 40 microns. Estimates of exposure before 1964 in the dry mill were 168 fibers/cc for working areas, 182 fibers/cc for sweepers, 88 fibers/cc for skipping, and 13 fibers/cc for the quality control laboratory. In 1964-1971, exposure estimates for these areas were 33, 36, 17, and 3 fibers/cc, respectively. Estimates of exposures in the mine before 1971 ranged from 9-23 fibers/cc for drillers and were less than 2 fibers/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.
mesh_terms: D000395:Air Pollutants, Occupational / Q000032:analysis*; D000538:Aluminum Silicates; D017636:Asbestos, Amphibole; D004781:Environmental Exposure; D006801:Humans; D008903:Minerals / Q000032:analysis*; D008906:Mining; D009009:Montana; D010316:Particle Size; D012822:Silicon Dioxide / Q000032:analysis*; D013997:Time Factors
chemical_list: D000395:Air Pollutants, Occupational; D000538:Aluminum Silicates; D017636:Asbestos, Amphibole; D008903:Minerals; C036431:ferroactinolite; C003760:vermiculite; C005846:tremolite; D012822:Silicon Dioxide