Biodiesel exhaust particle airway toxicity and the role of polycyclic aromatic hydrocarbons.

Renewable alternatives to fossil diesel (FD) including fatty acid methyl ester (FAME) biodiesel have become more prevalent. However, toxicity of exhaust material from their combustion, relative to the fuels they are displacing has not been fully characterised. This study was carried out to examine particle toxicity within the lung epithelium and the role for polycyclic aromatic hydrocarbons (PAHs). Exhaust particles from a 20% (v/v) blend of FAME biodiesel had little impact on primary airway epithelial toxicity compared to FD derived particles but did result in an altered profile of PAHs, including an increase in particle bound carcinogenic B[a]P. Higher blends of biodiesel had significantly increased levels of more carcinogenic PAHs, which was associated with a higher level of stress response gene expression including CYP1A1, NQO1 and IL1B. Removal of semi-volatile material from particulates abolished effects on airway cells. Particle size difference and toxic metals were discounted as causative for biological effects. Finally, combustion of a single component fuel (Methyl decanoate) containing the methyl ester molecular structure found in FAME mixtures, also produced more carcinogenic PAHs at the higher fuel blend levels. These results indicate the use of FAME biodiesel at higher blends may be associated with an increased particle associated carcinogenic and toxicity risk.

In-Cylinder Polycyclic Aromatic Hydrocarbons Sampled during Diesel Engine Combustion.

Polycyclic aromatic hydrocarbons (PAHs) are potentially carcinogenic pollutants emitted by diesel engines, both in the gas phase and adsorbed onto the surface of particulate matter (PM). There remains limited understanding of the complex and dynamic competing mechanisms of PAH formation, growth and oxidation in the gas phase, and their adsorption onto soot and how these processes impact on the abundance and composition of exhaust PAH. Therefore, this paper presents analysis of gas and particulate samples taken from the cylinder and exhaust of a diesel engine during combustion of fossil diesel with the 16 US-EPA priority PAH species identified and quantified. In-cylinder results showed that gas-phase PAHs were more abundant than soot-bound PAHs in the engine cylinder. The in-cylinder PAHs included 2- to 6-ring PAHs; however, 6-ring PAHs were not observed in the soot samples collected from the engine exhaust. Levels of both PM and the total in-cylinder PAHs decreased following a peak at 10 CAD ATDC but subsequently increased significantly during the late combustion phase. The B[a]P equivalence of PM in the engine cylinder increased during the period of early diffusion to late combustion phase, following an initial decrease during the period of premixed to early diffusion combustion.