Evaluation of Mutagenicity Testing of Extracts from Processed Oil Shale

The Ames/Salmonella mutagenicity assay was used to screen processed oil shale extracts for potentially carcinogenic chemicals. Positive mutagenic activity was detected in organic solvent extracts of all four spent shales tested. This result combined with the fact that most carcinogens (90 percent) have been detected as mutagens in the Ames test, indicates that these extracts contain carcinogens. Aqueous extracts of spent shale exhibited marginal or no mutagenic response, presumably because the techniques for extracting and concentrating trace quantities of these nearly water-insoluble compounds are inadequate. Several problems which might limit application of the Ames assay for environmental screening were also explored. The results of assays of one-to-one mixtures of two mutagens which exhibited different dose response curves when assayed separately indicated the response to the mixture was non-additive. F~rthermore, the response to the mixture was determined to be statistically indistinguishable (chi square analysis) from the dose response curve of one of the mutagens in the majority of cases. This masking effect was found to persist for one strong mutagen (benzo(a)pyrene) even when it composed only 10 percent of the mixture. The effect of various non-toxic solvents on the mutagenic response of certain mutagens was also determined. The present study showed that the choice of solvent (ethanol, methanol, dimethylsulfoxide. p-dioxane) can significantly alter the magnitude of the mutagenic response. Certain solvents may also confer a toxicity to compounds which are not otherwise toxic when assayed at the same concentration in another solvent.