Petroleum Mineral Oil Refining and Evaluation of Cancer Hazard

American Petroleum Institute, Mineral Oil Mist Work Group

Carl Mackerer*, PhD, Principal Toxicologist, C&C, Consulting in Toxicology; Larry C. Griffis, PhD, DABT, Senior Toxicologist, ChevronTexaco; John S. Grabowski, Jr., MS, CIH, QEP, Manager, Product Safety and Toxicology, CITGO Petroleum Corporation; Fred A. Reitman, PhD, DABT, Senior Toxicologist, Equiva Services (*denotes speaker)

 

Petroleum mineral oils (MOs) are manufactured from crude oils by vacuum distillation and additional refining.  Aromatic compounds including polycyclics (PACs) are undesirable constituents in MOs from both a lubricant performance and health hazard standpoint.  The use of MOs with low aromatics increased as modern lubricants evolved and the concentration of PACs decreased in parallel.  In modern MO refining, aromatics are removed using solvent extraction, catalytic hydrotreating or both. At elevated concentrations, 3 to 7 ring PACs in a MO have caused tumors in a mouse skin-painting assay. In addition, high-PAC oils have been associated with skin cancer in chronically-exposed workers.  The carcinogenic activity of poorly-refined MOs is primarily due to alkylated PACs, not the “naked ring” polycyclics listed as EPA carcinogens.  To avoid the cost and time of skin-painting and to study the mechanism of MO toxicity, assays were developed in the 1980s, which measure the concentration or biological (mutagenic) activity of carcinogenic PACs in MOs.  The IP346 and Modified Ames tests are effective predictors of carcinogenicity and are now commonly used to characterize the carcinogenic potential of MOs.  The IP346 assay is a regulatory criterion in the EU and the Mod. Ames is an ASTM test.  Many industrial users require this analytical data for the MOs in the lubricants that they purchase.  Data showing how these assays are used to characterize MO cancer hazard will be presented.  Also, recent IP346 and modified Ames test data will be presented to illustrate the absence of a cancer hazard for the vast majority of MOs now used.