Assessing the influence of methanol-containing additive on biological characteristics of diesel exhaust emissions using microtox and mutatox assays

Here we investigate the effect of the methanol-containing additive (MCA) on the biological characteristics of diesel exhaust emissions. Microtox and Mutatox assays, respectively, were used to evaluate the acute toxicity and genotoxicity of crude extracts from diesel engine exhaust. The engine was tested on a series of diesel fuels blended with five additive levels (0, 5, 8, 10 and 15% of MCA by volume). Emission tests were performed over the hot start portion of the transient Heavy-Duty-Federal Test Procedure (HD-FTP) and two selected steady-state modes. Microtox results show that MCA additive moderately lowers the toxicity levels of particle-associated (SOF) samples, but generally increase the vapor-phase (XOC) associated toxicity. A strong correlation was found between XOC-associated toxicity and total hydrocarbon (THC) concentrations, while only a slight link was found between SOF-associated toxicity and particulate matter (PM) concentrations. For Mutatox test results, when either 5 or 8% MCA used, XOC and SOF-associated genotoxicity in both steady-state and hot-start transient cycle tests were relatively lower compared to those of the base diesel. The genotoxic potential of XOC samples was significantly increased after treatment with an exogenous metabolic activation system (S9). On the contrary, the genotoxic potential of SOF samples without S9 metabolic activation was generally higher than those with S9. It is noteworthy that the total particle-associated (SOF) PAHs emissions showed trends quite similar to that of the genotoxic potential. As expected, the total particle-associated (SOF) PAHs correlated moderately with direct mutagenicity, and fairly well with indirect mutagenicity. Finally, the genotoxicity data did not parallel the Microtox results in this study, indicating that potentially long-term genotoxic agents may not be revealed by short-term toxicity assays.