THE EFFECTS OF INTRAPLEURAL INJECTIONS OF ALUMINA AND ALUMINOSILICATE(CERAMIC) FIBERS

Groups of rats, 24 male and 24 female, approximately 8 weeks old, were dosed by a single intrapleural injection with a saline suspension of refractory alumina fibres (Saffil fibres ICI plc) either as manufactur ed or after extensive thermal ageing: or one of two aluminosilicate (' ceramic') fibres with different diameter distributions. Similar groups were dosed with a suspension of UICC chrysotile A asbestos or saline solution to serve as positive and negative controls respectively. Rats were maintained to 85% mortality and all decedents and terminal sacri fices were closely examined for the presence of mesothelioma. Malignan t mesothelioma was diagnosed in ten rats, seven dosed with asbestos an d three dosed with aluminosilicate fibre B. No mesothelioma was detect ed in any rat dosed with Saffil fibres or aluminosilicate fibre A or i n negative controls. The results support the predicted inert nature of Saffil alumina fibres and provide further evidence for the importance of fibre dimension in the induction of mesothelioma. The implication of the results for inhalation exposures is discussed.