Mutagenicity of diesel exhaust particles from two fossil and two plant oil fuels

Abstract

Particulate matter of diesel engine exhaust from four different fuels was studied for content of polynuclear aromatic compounds and mutagenic effects. Two so-called biodiesel fuels, rapeseed oil methylesters (RME) and soybean oil methylesters (SME), were compared directly with two fossil diesel fuels with the normal (DF) and a low sulfur content (LS-DF). Diesel exhaust particles were sampled on filters from the diluted and cooled exhaust of a test engine at five different speeds and loads. Filters were weighed for total particulate matter, Soxhlet extracted with dichloromethane and the content of insoluble material determined. The soluble organic fraction was analysed for polynuclear aromatic compounds. Mutagenicity was determined using the Salmonella typhimurium/mammalian microsome assay with strains TA98 and TA100. Compared with DF, the exhaust particles of LS-DF, RME and SME contained less insoluble material, which consisted mainly of the carbon cores of diesel exhaust particles. The concentrations of individual polynuclear aromatic compounds varied widely among the different exhaust extracts, but total concentrations of the compounds were approximately double for DF and SME compared with LS-DF and RME. In TA98 significant increases in mutation rates were obtained for the soluble organic fractions of all fuels for engines running at full speed (load modes A and D), but for DF revertants were 2- to 10-fold more frequent as compared with LS-DF, RME and SME. Revertant frequencies for DF and partly for LS-DF were also elevated in TA100, while RME and SME gave no significant increase in mutations. The results indicate that diesel exhaust particles from RME, SME and LS-DF contain less black carbon and total polynuclear aromatic compounds and are significantly less mutagenic in comparison with DF. A high sulfur content of the fuel and high engine speeds (rated power) and loads are associated with an increase in mutagenicity of diesel exhaust particles.