Detection of photomutagens in natural and synthetic fuels

The contribution of non-ionizing radiation to synfuel-related skin carcinogenesis is largely unknown. We have employed a modification of the Salmonella histidine reversion test system to detect photomutation by various fuel substances. For photomutation testing we washed and resuspended cells in buffer, irradiated with 'visible' light in the presence of test substance, and removed aliquots after various light exposures for assay by the plate incorporation method. We have assayed photomutagenicity and microsome-mediated mutagenicity of a crude petroleum, a shale oil, and coal hydrogenation process intermediates. Photomutagenicity was studied using one concentration of each oil; peak revertants per plate for most oils tested were relatively similar to revertants per plate with microsomal activation of the same oil at the corresponding concentration. The shale oil was an exception to this pattern: with light activation, peak revertant numbers per plate were approximately 10 times the value observed with microsomal activation. The samples tested are not assumed to be representative of all petroleums, shale oils or coal oils. Our results do suggest that environmental radiation may be a significant factor in synfuel-related skin carcinogenesis and that photomutagens may be different from enzyme-activatable promutagens.