Comparison of PAC and MOAH for understanding the carcinogenic and developmental toxicity potential of mineral oils

The carcinogenicity and developmental toxicity of unrefined mineral oil is related to its 3–7 ring polycyclic aromatic compounds (PAC) content. Therefore, refining operations focus on the targeted removal PAC from mineral oil that may contain aromatics of low toxicological concern. There are thus, two types of aromatic substances in mineral oil: hazardous and non-hazardous. The first type consists of 3–7 ring PAC which may be naked (unsubstituted) or lowly alkylated. The second type or non-hazardous consists of 1–7 ring aromatics with high degree of alkylation or lack of bay or fjord regions.

Although these are toxicologically different, they may both elute in the same fraction when using chromatography. To understand how these two aromatic types are related we have assessed the entire mineral oil refinement process by measuring total mineral oil aromatic hydrocarbons (MOAH) content by chromatography next to regulatory hazard tests which focus on 3–7 ring PAC. MOAH content is positively correlated to its molecular weight resulting in aromatic content bias for high viscosity substances. Hazard to 3–7 ring PAC is best controlled by the validated IP346 or modified Ames test. We explain the concept of high vs low alkylation by shortly reviewing new data on alkylated PAC.