Several previous studies have suggested that various fuels emit carcinogenic polycyclic aromatic hydrocarbons (PAHs). Ballesteros et al. (2009) examined the relationship between the amount of oil, the type of oil, and the carcinogenic potential of three biofuels and a conventional fuel. The researchers conducted a chemical speciation of the sixteen most hazardous PAHs associated with fuel combustion using a newly developed method combining processes of thermal extraction, solid-phase micro-extraction (SPME), and GC/MS analysis. The researchers found that using biofuels rather than conventional fuels reduced total PAH emissions as well as the risks to human health from these emissions. Furthermore, they determined that PAH emissions depend on the oil used for the transesterfication process. —Christina Mainero
Ballesteros, R., Hernandez, J.J., Lyons, L.L., 2009. An experimental study of the influence of biofuel origin on particle-associated PAH emissions. Atmospheric Environment 44, 930–938.
Ballesteros et al. inspected the mutagenicity of the sixteen PAHs considered to be hazardous to human health. To determine the impact on human health of the type and origin of vegetable oil used for transesterfication compared with a reference fuel, the researchers conducted a chemical speciation on these compounds. Additionally, they collected data on the gaseous non-methane hydrocarbons emissions, the diesel particulate matter emissions, volatile organic matter emissions, mean particle diameter, and particle opacity for the biofuels and the reference fuel. In order to properly compare the emissions for these different fuels, the researchers made sure that the exhaust gas recirculation ratio remained constant. Moreover, they examined all of the fuels in two different operating modes: extraurban and urban. The three biofuels used in this study were rapeseed methyl ester (RSM), waste cooking oil methyl ester (WCOM), and waste cooking oil ethyl ester (WCOE), which were then compared to the conventional reference fuel.
To accurately gauge the health risks associated with the different fuels, Ballesteros et al. used a conversion factor, called the toxicity equivalent factor (TEF). This conversion factor provided them with a carcinogenic equivalence sum (KE) that represented the inherent carcinogenicity of each of these PAHs. All three biofuels showed a reduction in KE, indicating that biofuel emissions are less hazardous to human health than conventional fuels. For the RSM WCOM, and WCOE, there was a notable reduction in the emissions of the PAHs with higher molecular weights, which tend to have more carcinogenic potential. Unlike the RSM, the biofuels originating from cooking waste oils emitted significantly higher levels of lighter PAHs than the conventional fuels. However, the health risk to humans was still lower than that associated with the use of conventional fuels because PAHs with lower molecular weights tend to be far less carcinogenic than those with high molecular weights. The researchers concluded that using biofuels not only reduces the overall amount of PAH emissions, but also diminishes negative health impacts when compared with conventional fuels. Moreover, they determined that the type of oil used for the process of transesterfication significantly influences the emission of heavy or light PAHs, which, in turn, dictates their effects on human health. Thus, this study suggested that certain biofuels may be less toxic to human health than conventional biofuels, advancing the case for biofuels as plausible alternatives to conventional fuel sources.