Predicting carcinogenicity of petroleum distillation fractions using a modified Salmonella mutagenicity assay

Abstract

The Ames Salmonella/microsomal activation mutagenesis assay has been modified to improve sensitivity and reproducibility to complex mixtures derived from the refining and processing of petroleum. Oil samples were dissolved in cyclohexane and subsequently extracted with dimethyl sulfoxide to produce aqueous compatible solutions which readily interact with tester bacteria. Also, the liver homogenate (S-9) and NADP cofactor concentrations were increased and hamster rather than rat liver S-9 was used. The initial slope of the dose response curve relating mutagenicity (revertants per plate) to the dose of extract added was used as an index of mutagenic activity; this slope was obtained through a computerized curve fitting procedure. The modified assay was used to rank 18 oil samples for mutagenic activity; this ranking correlates highly (r = 0.92) with potency rankings of the same samples previously determined from dermal carcinogenicity bioassays. Sensitivity and reproducibility of the assay are sufficient to permit routine use for detecting potential carcinogenic activity of individual refinery streams and blends which contain components boiling above 500 degrees F.

Scientific Opinion on Mineral Oil Hydrocarbons in Food

“…Although the Salmonella typhimurium assay is not considered to give quantitative results, in this test the mutagenic index (MI), a semi-quantitative measure of mutagenic potency, was calculated. The MI represents the slope of a plot of dose versus number of revertants and samples giving a double number of revertants above background are considered positive (Blackburn et al 1986;Reddy et al, 1997;Brandt et al, 1999). Later, Brooks and co-workers (1995) found that testing a range of whole mineral oils with a method using washed rat liver microsomes correlated well with the results obtained with the modified extraction method by co-workers (1984, 1986).…”

“…Most studies on the genotoxicity of mineral oil and mineral oil fractions have been performed in the Salmonella typhimurium mutagenicity assay (Blackburn et al, 1984(Blackburn et al, , 1986IARC, 1984IARC, /1987Roy et al, 1988;Granella and Clonfero, 1991;Brooks et al, 1995;Mackerer et al, 2003). With the exception of highly purified oil varieties consisting of alkanes and naphthenes, all mineral oils are mutagenic in the Salmonella typhimurium assay ( IARC, 1984;Roy et al, 1988;Mackerer et al, 2003).…”

“…Since the mineral hydrocarbons are not soluble in water, procedures involving emulsification of oils have also been used (Brooks et al, 1995). A modified Salmonella typhimurium assay for testing was developed by Blackburn et al (1984Blackburn et al ( , 1986 using DMSO extracts of mineral oils in a test system with increased concentration of rat or hamster liver S-9 activating system as well as co-factors. Although the Salmonella typhimurium assay is not considered to give quantitative results, in this test the mutagenic index (MI), a semi-quantitative measure of mutagenic potency, was calculated.…”

“…A possible increase in microsomal enzyme activity in this assay could be in line with the use of increased amounts of S-9 by Blackburn and co-workers. The modified Ames assay developed by Blackburn et al (1986) has later been recognised by the American Standardization for Testing and Materials (ASTM) International (ASTM, E 1687-95).…”

Characterization of the toxicological hazards of hydrocarbon solvents

“…Kerosene is not mutagenic when tested under in vitro and in vivo conditions (American Petroleum Institute 1984a, 1984b, Blackburn et al 1986, McKee et al 1994, Vijayalaxmi et al 2006, and similarly, jet fuels were reported as inactive as shown in summarized information published by Sterner (2011) andMcKee et al (1994).…”