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

Investigation of toxic pollutants formation with renewable fuels in a diesel engine using in-cylinder sampling

Intensifying awareness regarding the negative impact on public health of combustion-derived pollutants has led to increasingly stringent legislation limiting gaseous emissions, and levels of both particulate mass and number from road transport. Polycyclic aromatic hydrocarbons (PAH) are potentially carcinogenic pollutants emitted by diesel engines, both in the gas-phase and adsorbed onto particulate matter (PM) surface. While displacement of fossil fuels by renewable oxygen-bearing fuels has been observed to impact on the mass of PM emitted, there is limited understanding as to how fuel blend composition impacts PM mass concentration levels, PAH formation, and PM toxicity during combustion. To investigate fuel blends composition effects, PM and gaseous emissions present in the combustion cylinder gas and exhaust gas extracted during engine tests were collected. All compounds adsorbed on the samples were recovered, with the 16 US-EPA priority PAH species were identified and quantified. Despite not containing any fuel PAH, results showed that partially displacing diesel with 20% wt/wt oxygenate fuels (biodiesel or methyl decanoate) increased PM and the total PAH (gaseous and PM-bound) levels in the combustion cylinder. Furthermore, the presence of methyl decanoate, in the test fuel also increased toxic 5- and 6-ring PAH species during combustion to levels which exceeded that present during 100% diesel combustion, in contrast to the effect of biodiesel, likely due to a shorter alkyl chain, single-component nature and more saturation relative to biodiesel. However, in the exhaust, both oxygenate fuel blends emitted lower PM and PAH levels relative to 100% diesel, but favoured the persistence of benzo[a]pyrene, a highly toxic typically PM-bound PAH. Furthermore, diesel displacement with higher proportions of the oxygenate fuels influenced PAH formation and composition by favouring the persistence of dibenz[ah]anthracene, another highly toxic PAH species, in exhaust PM. Consequently, diesel displacement with oxygen-bearing fuels increased PM toxicity, with that of pure biodiesel being the most toxic, and was confirmed by in-vitro toxicological analysis

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