Assessment of the utility of the micronucleus test for petroleum-derived materials

The micronucleus test is a commonly used in vivo assay for chromosomal damage and is an integral part of many mutagenicity testing strategies. The present report describes an assessment of the micronucleus test for the detection of mutagenic potential of petroleum-derived materials. To this end, studies were conducted with catalytically cracked clarified oil (CCCO). This material contains high levels of polycyclic aromatic constituents (PAC) and is a very potent inducer of mouse skin tumors. CCCO is also active in the Salmonella assay and other in vitro tests. As CCCO is the most potent of the various petroleum-derived materials in other assays, it was assumed to be the most easily detectable in the micronucleus test. CCCO was tested in standard mouse micronucleus tests utilizing oral and intraperitoneal injection for test material administration. All of these studies were negative, although DMBA, tested at roughly equivalent levels based on potency in the Salmonella assay, produced statistically significant increases in micronucleus frequency. In a second series of studies, aromatic fractions of CCCO were prepared and tested at up to acutely toxic levels. Results of these studies were also negative. Finally, another petroleum-derived material which is carcinogenic and contained PAC was tested in the micronucleus assay. It also produced negative results. Thus, it was concluded that petroleum-derived materials do not produce clastogenic effects in vivo in the mouse micronucleus test, despite the fact that some pure polycyclic aromatic hydrocarbons are quite active in this assay.