The dermal carcinogenic potential of unrefined and hydrotreated lubricating oils

Unrefined lubricating oils contain relatively high levels of polycyclic aromatic hydrocarbons (PAH) and have been shown to induce tumors in mouse skin. Exxon has developed a new method of refining these materials, a severe hydrotreatment process that is optimized for PAH removal. The specific objectives of the current study were to assess PAH reduction and then to evaluate directly the dermal carcinogenic potential of the materials that spanned the range of products produced by this method. The test samples included unrefined light and heavy vacuum distillates from a naphthenic crude oil, as well as the corresponding severely hydrotreated products. Two sets of samples were prepared to assess the effects of various operating parameters in the reactor. Additionally, positive (benzo[a]pyrene), negative (white mineral oil) and vehicle (toluene) control groups were included to assess the sensitivity and specificity of the bioassay. Each sample was applied in twice-weekly aliquots to the backs of 40 male C3H mice. In the analytical studies, significant reductions in the levels of several specific PAH were demonstrated. In the dermal carcinogenesis studies, the unrefined oils and the positive control induced tumors and also significantly reduced survival. None of the mice treated with severely hydrotreated oils or with the negative or vehicle controls developed skin tumors, and survival of these mice was not significantly different from the control. Thus, the data demonstrated that this new, severe hydrotreatment process was an effective means of converting carcinogenic feedstocks to non-carcinogenic products.