A REAPPRAISAL OF THE CARCINOGENICITY OF SURFACE-MODIFIED ASBESTOS FIBERS

A previous study using intrapleural administration of surface-modified amosite asbestos showed a difference in the number of pleural mesothe liomas induced with C18-hydrocarbon derivatised fibres compared to nat ive amosite asbestos. The study has been repeated with larger groups o f animals (30) under specific pathogen free conditions, resulting in a n increase in the mean animal survival time for both fibre-treated gro ups. Under these conditions there was no significant difference betwee n the numbers of pleural mesotheliomas induced by C18 hydrocarbon-modi fied amosite asbestos and native amosite asbestos. The major differenc e between the two studies was the mean time to death from tumour of ra ts exposed to fibres. The C18 amosite treated rats in the first study may not have had a mean survival time long enough to allow mesotheliom as to develop.