Mesothelioma induced by intrapleural injection of different types of fibres in rats; synergistic effect of other carcinogens.
Intrapleural injections of 20 mg of various mineral fibres were made to rats. Three types of fibres (chrysotile, crocidolite and glass fibres) were untreated; other chrysotile fibres were leached to different degrees. The results show that chrysotile is the most toxic of the three: animals died sooner and presented mesotheliomas earlier. With increased leaching, toxicity and carcinogenic effect decreased. Crocidolite is less toxic than untreated chrysotile but later produces as many mesotheliomas; with glass fibres, some mesotheliomas are observed. Small groups of animals were exposed to two types of irradiation before intrapleural injection of 2 mg of chrysotile. Whole-body irradiation was delivered to a third group of animals which were given asbestos-contaminated food. The paper analyses the synergistic action of these two insults.