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Conditions that affect the sensitivity of the Ames assay of complex hydrocarbon mixtures derived from shale oil were studied. Two fractions, one enriched in polynuclear aromatic compounds (PNA fraction), and a second fraction enriched in aromatic and heterocyclic amines (basic fraction), were selected for most of this work because of their comparatively high mutagenicity (i.e., compared with raw shale oil). The crude shale oil, as well as the basic, PNA, and tar fractions were mutagenic against the Salmonella typhimurium test strains, TA98 and TA100. Mutation was dependent on metabolic activation by microsomal (S9) enzymes. Both test strains responded equally well to the crude product and to the basic fraction; however, strain TA100 was more effective than TA198 in demonstrating the mutagenicity of the PNA fraction. The mutagenicity of the tar fraction could be most easily detected after metabolic activation in a liquid medium, as opposed to S9 activation in the top agar of the standard Ames assay. The mutagenicity of the basic fraction or 2-aminoanthracene was also demonstrated by metabolic activation in a liquid medium. In other set of experiments, the effect of chemical composition on the expression of mutagenicity in the standard Ames assay was estimated. Premutagens requiring metabolic activation were added to the basic and PNA fractions, and the numbers of revertants obtained in the presence of the fractions were compared with mutation induced by the compounds alone. The basic fraction did not interfere with the mutagenicity of 2-aminoanthracene and 7,9 dimethylbenz[c]acridine. Moreover, in certain experiments, the mutagenicity of the complex fraction plus the added compound was higher than expected on the basis of assays performed on these materials separately. Conversely, the PNA fraction prevented or strongly inhibited mutation by several polynuclear aroumatic compounds, and an acridine. However, the PNA fraction did not inhibit mutation induced by 2-aminoanthracene. The effect of the basic fraction on stability of the S9 enzymes in the standard Ames test was also determined.

Use of Ames test in evaluation of shale oil fractions.