The dermal carcinogenic potential of unrefined and hydrotreated lubricating oils

Abstract

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.

Mineral oil in food, cosmetic products, and in products regulated by other legislations

“…For mineral oils, products with a high concentration of polycyclic aromatic compounds (PAC) with 3-7 rings (parent PAHs, short-alkylated MOAH, compounds containing heteroatoms), such as unrefined and poorly refined base oils, were carcinogenic in mouse skin painting assays (Roy et al 1988;McKee, Daughtrey, et al 1989;Blackburn et al 1996;Mackerer et al 2003). The aromatics concentration was determined by target analytics for specific parent PAHs (McKee, Daughtrey, et al 1989;Concawe 1994) and by solvent extraction with dimethyl sulfoxide (DMSO) followed by GC separation according to the ring number using two to seven ring unsubstituted PAHs as internal standards (Roy et al 1988;Mackerer et al 2003;Gray et al 2013). The latter technique is used by the Mobil PAC Method for predicting dermal carcinogenicity (see below).…”

“…Test materials were applied undiluted in a defined volume to the shaved backs of the animals 1-3 times per week (Doak et al 1983;Blackburn et al 1984;Doak et al 1985;Blackburn et al 1986;Roy et al 1988;McKee, Daughtrey, et al 1989;McKee, Nicolich, et al 1990;Chasey and McKee 1993;Concawe 1994). In some cases, test materials were diluted in highly refined mineral oil or toluene for reasons of high toxicity or high viscosity (Blackburn et al 1986;McKee, Daughtrey, et al 1989;McKee, Nicolich, et al 1990). Only some studies reported the size of the dermal treatment area (McKee, Daughtrey, et al 1989;Chasey and McKee 1993).…”

“…In some cases, test materials were diluted in highly refined mineral oil or toluene for reasons of high toxicity or high viscosity (Blackburn et al 1986;McKee, Daughtrey, et al 1989;McKee, Nicolich, et al 1990). Only some studies reported the size of the dermal treatment area (McKee, Daughtrey, et al 1989;Chasey and McKee 1993). White mineral oil and toluene were reported to be used as negative/ vehicle controls, and B[a]P (in toluene or acetone) and catalytically cracked clarified oil as positive controls (Doak et al 1985;Blackburn et al 1986;McKee, Daughtrey, et al 1989;McKee, Nicolich, et al 1990;).…”

“…Only some studies reported the size of the dermal treatment area (McKee, Daughtrey, et al 1989;Chasey and McKee 1993). White mineral oil and toluene were reported to be used as negative/ vehicle controls, and B[a]P (in toluene or acetone) and catalytically cracked clarified oil as positive controls (Doak et al 1985;Blackburn et al 1986;McKee, Daughtrey, et al 1989;McKee, Nicolich, et al 1990;). Shaved but untreated animals were reported to be used as additional negative controls (Doak et al 1985;Blackburn et al 1986;.…”

Acute, Subchronic, and Developmental Toxicological Properties of Lubricating Oil Base Stocks

“…Lower carcinogenic activity from biologically active PACs in residual oils compared to distillate oils has been observed in skin-painting assays. 62,63 In addition, residual LOBs can have much lower carcinogenicity than would be expected on the basis of the amount of material extracted by DMSO with the IP346 method 6 , leading CONCAWE (Conservation of Clean Air and Water in Europe) to conclude that the IP346 method is not suitable for substances, such as some residual oils, that contain large PACs (asphaltenes) and/or resins. 7 Analytical studies of these de-asphalted vacuum residua indicate that the aromatics they contain are predominantly 1-3 ring compounds that are highly alkylated (paraffinic and naphthenic).…”