Coalinga fibre - A short, amphibole-free chrysotile .1. Evidence for a lack of fibrogenic activity

Controversy continues to surround the biological activity of short fibre chrysotile. This is largely due to a lack of studies in which there has been 'pure exposure' to this material. Most of the exposures studied, whether in humans or animals, have been confounded by the additional presence of long fibre chrysotile and/or amphibole. This report presents the morphological and morphometric findings of a lifetime inhalation study of F344 rats exposed to three types of chrysotile. The first, from Coalinga, Calif., is comprised of fibres that are almost all less than 5 mu m in length and is not contaminated with amphibole. The other two, the Jeffrey fibre and the UICC/B standard, are both Canadian long fibre preparations with a minor degree of amphibole contamination. Exposed animals displayed no fibrosis following exposure to Coalinga chrysotile but showed fibrogenic responses with both Canadian fibres.