A non-solvent-refined oil, previously shown to produce tumours in a long-term skin painting assay and a positive result in the mouse skin nuclear enlargement test, was separated using silica gel elution techniques into eight fractions. Fraction 1, which contained saturated and 1-2 ring aromatic hydrocarbons, was used to dilute the other fractions to produce solutions equivalent to and twice their original concentration in the intact oil. Fraction 1, diluted fractions 2-8, the reconstituted oil, the original oil and a negative control oil were examined for their ability to produce nuclear enlargement.
The degree of nuclear enlargement observed with fraction 1 was considered to indicate marginal or no carcinogenic activity. With the fraction that contained 2-3 ring aromatic compounds, weak carcinogenic activity could not be ruled out but it is unlikely that these components played a major role in the carcinogenicity of the oil. The greatest activity was identified in the fraction containing the total 3 / 4 4 ring polycyclic aromatic hydrocarbons (PAHs) and further fractionation of this suggested that the parent 4-6 ring PAHs were responsible for more than half the activity of the intact oil, despite being present at only 0.06%. The fraction that contained polar compounds showed no activity. The reconstituted oil showed slightly less activity than the original oil. Other fractions, which contained alkylated PAHs, did not seem to have much activity. These findings, which are in close agreement with published evidence on tumour induction by fractions of oils and coal liquids, suggest that the components responsible for inducing nuclear enlargement are the same as those responsible for skin tumour induction. The results also suggest that estimates of carcinogenic activity made from analytical findings, such as the weight of DMSO extractable material, or even from the total 3-6 ring PAHs may be misleading as the main active components form such a small proportion of the material measured.