Carborundum pneumoconiosis. Fibers in the mineral activate macrophages to produce fibroblast growth factors and sustain the chronic inflammatory disease.

Carborundum is a synthetic abrasive manufactured through fusion of high grade silica sand and finely ground carbon in an electric furnace at 2,400 degrees C. It had been considered an inert dust until recently. Two recent epidemiologic studies in Quebec have documented an excess of interstitial lung disease in plant workers and some 30 workers have received workman compensation. Histopathologic lesions have been described in four of the workers. To further investigate the carborundum pneumoconiosis, nine groups of eight sheep were exposed once in the tracheal lobe to either 100 ml saline, 100 mg latex beads in 100 ml saline, 100 mg graphite in 100 ml saline, 100 mg carborundum particles in 100 ml saline, 100 mg ashed carborundum particles in 100 ml saline, 100 mg of quartz (Minusil-5) in 100 ml saline, 100 mg crocidolite fibers in 100 ml saline, 100 mg carborundum fibers in 100 ml saline, and 100 mg ashed carborundum fibers in 100 ml saline solutions. The animals had BAL at two-month intervals and autopsy at month 8. The BAL analyses of cellularity, cytotoxicity and fibrogenicity, in association to necropsy histopathology, documented that all particles except for quartz were inert. The two-carborundum fiber samples produced a similar sustained nodular fibrosing alveolitis and crocidolite asbestos fibers produced a peribronchiolar fibrosing alveolitis of comparable severity. Thus, the major bioactive dusts in the carborundum manufacturing process are quartz particles and the carborundum fibers generated in the process. The latter have fibrogenic activities comparable to asbestos fibers of similar size and are likely to contribute to the pathogenesis of the interstitial lung disease of carborundum workers.