Mechanisms of mesothelioma induction with asbestos and fibrous glass

Abstract

SUMMARY-Three types of asbestos in 7 forms, 6 types of ~brous glass, 2 types of silica, and 2 types of metal particles were applied on a fibrous glass vehicle to the pleura of rats. In 2 years, amosite, chrysotile, and 4 different specimens of crocidolite yielded equally high incidences of pleural mesotheliomas in the range of 58-75%. Hand-milled crocidolite fibers not exposed to extraneous oils or metallic milling yielded dose-related tumor responses comparable to those of a standard reference milled crocidolite. Standard crocidolite, inducing a high incidence of mesotheliomas, caused fewer mesotheliomas (20-32%) when reduced to submicroscopi ¢ fibrils by excessive milling. Pulverized fragments of the steel mill and nickel metal at doses exceeding potential contaminating levels did not induce tumors. Microspheres of noncrystalline silica resulted in a single mesotheli-oma among 48 rats. The intact ~brous glass vehicle did not yield tumors, nor did its absence alter the incidence of crocidolite-induced tumors. How-ever, when the fibrous glass vehicle and 2 other types of fibrous glass