Introduction: INSERM-IARC-CNRS workshop on biopersistence of respirable synthetic fibers and minerals.

Parameters of respirable mineral dust responsible for respiratory toxicity in humans have been investigated extensively. When the coal industry was flourishing, the major concern was with silicosis resulting from exposure to silica and silicate dusts. Epidemiological studies on asbestos workers in the 1960s brought to light the fibrogenic and carcinogenic properties of fibrous particles. Then in the 1970s, Stanton showed that fiber length and diameter had a critical influence on carcinogenicity. He inoculated different natural and synthetic fibers into the pleural cavity and found that fibers longer than 8 pm with a diameter <0.25 pm had the highest probability of inducing pleural carcinomas (1). The influence of this fiber size was confirmed by Pott, who administered fibers to rats by the intraperitoneal route (2) and by Hesterberg and Barrett who studied the effect of fibers on Syrian hamster epithelial cells in vitro (3). It now appears that the dimensional parameters of length >5 pm and diameter <1 pm are the most critical discriminants of risk for both fibrogenesis and carcinogenesis. However, it was shown that parameters other than size were involved, since acidleached chrysotile was found to be less carcinogenic for the rat pleura than native chrysotile (4,5). Lung retention of inhaled mineral dusts has been known for a long time to pulmonary pathologists, who observed that a high percentage of inhaled dusts remained