Mutagenicity and contents of polycyclic aromatic hydrocarbons in used and recycled motor oils

Thirteen samples of used motor oil and 33 recycled fractions, obtained in the laboratory by means of a recovery process similar to that currently used in Italy (vacuum distillation followed by thermal clay treatment) were examined. The Ames test (standard and modified version according to Blackburn) was used to determine the mutagenicity of the extracts and their contents of polyaromatic fraction (PAF) (IP346/80 method) and polycyclic aromatic hydrocarbons (PAH) (Grimmer's method). Used motor oils are mutagenic, both directly and indirectly. The highest values have been found in used oils from motor vehicles using leaded petrol (up to 118.8 revertants/mg). Samples from vehicles using unleaded petrol or diesel fuel are less mutagenic (up to 31.1 and 16.4 rev/mg, respectively). The enrichment in mutagens due to the use of oil in the three types of engine ranges from mean values of 6.2, 1.1 and 0.4 rev/mg per 1000 km, respectively. Recycled oils are almost completely devoid of direct mutagenic activity (33 samples: mean ± SD = 1.6 ± 1.5 rev/mg). Most recycled distillates show considerable mutagenic activity in the presence of microsomial enzymes (up to 85.5 rev/mg), although this is reduced with respect to the original oils (recycled, mean ± SD = 13.8 ± 15.5 rev/mg; original oils, mean ± SD = 30.7 ± 35.2, Mann-Whitney U-test, z = 1.793, p < 0.05). Both PAF and PAH contents are high in used oils from the types of petrol engine but not in those from diesel engines. Recycling reduces PAF contents only is used oils from petrol engines, from a mean value of 13.91 ± 7.32 to 4.23 ± 2.90% (comparison with original used oils, Mann-Whitney U-test, U = 8, p < 0.01). The light distilled fractions have a greater concentrations of indirect mutagens, PAF and PAH than the others. The increase in PAH in light recycled products with respect to the original used oils is significant (Wilcoxon's t-test, z = 2.0306, p <0.05). Benzo[a]pyrene (BaP) is found in appreciable quantities (> 10 ppm) in all used oils from petrol engines and in most of their recycled products. Recycling generally recovers 50% of mutagens and PAF and about 80% of PAH. Considered together, recycled products have in any case contents of mutagens and PAF which are significantly lower thant those in the parent oils, but not of PAH (Wilcoxon's t-test: mutagens, z = 2.935, p < 0.01; PAF, z = 3.145, p < 0.01; PAH, z = 1.397, not significant). Lastly, many recycled oils have PAH concentrations which are equal to or higher than those of the original used oils. The health risks linked to professional exposure to these types of oils and the inadequate recycling process currently used (redistillation and thermal clay treatment) in reducing mutagenic and carcenogenic substances from used motor oils are stressed.