Man-made mineral fibers and health. Answered and unanswered questions.

An overall assessment of the epidemiologic evidence from 23 published studies on workers' health in the industry producing man made mineral fibers (MMMF) (21 studies) and in the user industry (2 studies) is presented. Three major studies recently published, one cross-sectional and two of the historical cohort type, conducted in the producer industry, have been singled out for closer examination and discussion. The combined evidence from the epidemiologic studies indicates that causal associations between MMMF occupational exposure, as it occurred in past decades, and lung cancer and chronic respiratory diseases cannot be excluded, neither does it offer clear support for such associations. Experimental data indicate clearly that a fibrogenic effect can be obtained by the intratracheal administration of MMMF and a carcinogenic effect by the intratracheal, intrapleural, and intraperitoneal administration of MMMF, while no appreciably fibrogenic nor carcinogenic effects have been detected in inhalation experiments. While it can be stated that no long-term pathological effects have been observed in MMMF workers in the first 20 years or so after first employment, the key scientific issue of whether MMMF are fibrogenic and/or carcinogenic in man when inhaled remains still open.