Coalinga fibre - A short, amphibole-free chrysotile - Part 2: Evidence for lack of tumourigenic activity

Controversy continues to surround the biological activity of short fibre chrysotile largely due to a Lack of 'pure exposure' situations available for study: most human exposures are confounded by concomitant long fibre and/or amphibole exposure. This report presents the morphological and morphometric findings of a lifetime inhalation study of F344 rats exposed to three types of chrysotile, Fibres from the first sample: from Coalinga, Calif., are almost all less than 5 mu m in length and do not contain amphibole types of asbestos. The other two, from Quebec, Canada, are a sample from the Jeffrey mine and the UICC/B standard. These are both long fibre preparations with a minor degree of amphibole contamination. Animals exposed to these fibres displayed no tumours above control levels following exposure to Coalinga chrysotile but gave significant tumourigenic responses with both types of Canadian fibres.