The mutagenic activity and polycyclic aromatic hydrocarbon content of mineral oils

Naphthenic distillates (raw or acid-treated) and motor and emulsifiable aluminium rolling oils were tested for mutagenicity in the Salmonella/microsome assay using the TA98 and TA100 strains. The polycyclic aromatic hydrocarbon (PAH) content of oil samples was also determined in parallel. In the presence of metabolic activation, both untreated and acid-treated naphthenic distillates were found to be mutagenic on a modified Ames test. One untreated sample showed the highest value of mutagenic potency (50 net revertants/mg oil for strain TA98). The PAH content of naphthenic distillates was about 10% (w/w) and was slightly reduced by sulfuric acid/earth treatment (1%). Non-mutagenic paraffin- and solvent-extracted crankcase oils became active, both with and without enzyme activation, after long use as gasoline engine lubricants, whereby their PAH content doubled (from 1.5% to 3%, w/w). A refined emulsifiable mineral oil also became directly mutagenic in both Salmonella strains after prolonged use in an aluminium hot-rolling mill. As the PAH levels found in used rolling oils was very low, we cannot explain their mutagenic activity. Mutagenicity was greatly reduced following careful cleaning of the oil bath and of the entire rolling machine. The present data reveal both the potential risk of occupational exposure to unrefined or mildly treated oils and the formation of mutagens in highly refined oils if the latter are used at high temperatures. The formation of mutagens in oils used in the metal-working industry can be prevented by careful industrial hygiene measures.