EVALUATION OF MODIFIED BACTERIAL MUTAGENICITY ASSAYS FOR THE GENOTOXICITY TESTING OF MINERAL-OILS

A modified bacterial mutagenicity assay based on the Ames Salmonella/m ammalian microsome test has been developed for application in the geno toxicity testing of mineral oils, The assay uses washed microsomes fro m rat liver in place of S9 fraction in order to increase the sensitivi ty of detection of genotoxicity, The modified assay was used to test a series of oils for which skin carcinogenicity bioassay data in mice w ere available, Oils were tested as emulsions in water using Tween 80 a s a dispersant. A mutagenicity index for each oil was obtained using n on-linear regression analysis of data from the dose-response curve, Th e results showed an empirical correlation between increasing mutagenic ity index, carcinogenicity and the polycyclic aromatic hydrocarbon con tent of the oils, The washed-microsome assay was also compared with mo dified Ames assays developed by Blackburn et al, (Cell Biol, Toxicol,, 1, 40, 1984; Cell Biol, Toxicol,, 2, 63, 1986) which employed increas ed levels of S9 (rat and hamster liver) to test dimethyl sulphoxide ex tracts of oils, The washed-microsome assay can be used for the testing of whole oils rather than extracts which are necessary for the modifi ed Ames assay, It is recognised that the determinants of carcinogenic activity in vivo include promoting activity which such assays are unab le to detect, Nevertheless, such modified bacterial assays may be a us eful prescreen since genotoxicity is recognised as a key initial step in carcinogenesis.