AN INVESTIGATION OF THE MAIN MUTAGENIC COMPONENTS OF A CARCINOGENIC OIL BY FRACTIONATION AND TESTING IN THE MODIFIED AMES ASSAY

A low-viscosity carcinogenic oil was extracted with dimethylsulphoxide (DMSO) and the extract fractionated into 1-3 ring aromatic components , 4-6 ring polycyclic aromatic compounds (PCAs) and polar materials. E ach of these fractions was tested in the Mobil modified Ames assay at the same concentration as in the DMSO extract, alongside unfractionate d DMSO extracts from the same oil and two reference oils. In addition the fractions were combined in various ways to examine inhibitory or a dditive effects. Clear positive findings were obtained with the DMSO e xtract of the main test oil, with some reduction in activity in a samp le (the starting material for fractionation) that was back-extracted t o remove DMSO. Of the three fractions tested on their own and assessed in terms of mutagenicity index, the 1-3 ring aromatic fraction had th e greatest mutagenic activity, showing similar activity to the startin g material, whereas the 4-6 ring PCA fraction had much lower activity and the polar fraction showed the lowest activity with an absence of d oubling in one of the tests. The polar fraction showed signs of an inh ibitory effect on the response to the 1-3 ring aromatic fraction and t o a questionable extent on that of the 4-6 ring PCA fraction. Although a low level of the 4-6 ring PCA fraction showed some inhibitory effec t on the response to the 1-3 ring aromatic fraction, a low level of th e 1-3 ring aromatic fraction added to the 4-6 ring PCA fraction enhanc ed the response. It was concluded that 4-6 ring PCAs were not the main mutagenic components of the oil examined and that therefore the mutag enic components may be different from the carcinogenic components. It was recognized, however, that there is a need for further data on the carcinogenicity of oil fractions, particularly relating to 1-3 ring ar omatic compounds.