Interaction between polycyclic aromatic hydrocarbons, crude oil and oil dispersants in the Salmonella mutagenesis assay.

Mutagenicity assays were carried out in the Salmonella/microsome test, using five S. typhimurium his(-) strains (TA1535, TA1537, TA1538, TA98 and TA100), both in the presence and absence of post-mitochondrial preparations from Aroclor-induced rat livers and suitable co-factors. Seven oil dispersants showed a wide range of toxicity towards the bacterial strains, without eliciting any mutagenic response at sub-lethal concentrations. One sample of crude oil and its dimethylsulphoxide (DMSO) extract were also negative, and no mutagenic effect could be detected by checking mixtures of crude oil with each of the seven dispersants tested. Two polycyclic aromatic hydrocarbons, benzo(a)pyrene (BP) and benz(a) anthracene (BA), which are generally considered to be the most documented carcinogenic components of crude oil, were mutagenic with a frameshift mechanism, requiring metabolic activation. BP mutagenicity was not affected by oil dispersants nor by seawater. Conversely, the mutagenicity of BP DMSO-solutions was abolished in the presence either of whole crude oil, of its DMSO extract, or of crude oil/dispersant mixtures. These losses of mutagenicity could be mainly ascribed to a mechanical trapping of BP by oil components.