Results of recent experimental research on the carcinogenicity of natural and modified asbestos.

Long-term experimental bioassays were carried out on natural asbestos of different types and origin (crocidolite, chrysotile, amosite, antophyllite), on asbestos cement, and on industrially modified chrysotiles. The materials were tested on Sprague-Dawley rats by intraperitoneal and intrapleural injection. The experiments were carried out with highly standardized procedures on all materials to enable comparative evaluation of the results. The data presented confirm that asbestos of different types produces peritoneal and pleural mesotheliomas, show that asbestos cement is also mesotheliomatogenic, and demonstrate that the peritoneum is more responsive than the pleura. Furthermore, evidence is provided that the mesotheliomatogenic effects of different types of asbestos vary with the types and origin of the minerals, and that physical and chemical modifications of the natural chrysotile can lower its carcinogenic effect.