A Comparison on the Emission of Polycyclic Aromatic Hydrocarbons and Their Corresponding Carcinogenic Potencies from a Vehicle Engine Using Leaded and Lead-Free Gasoline

Abstract

The premium leaded gasoline (PLG) and two kinds of lead-free gasoline [including 92 leadfree gasoline (92-LFG) and 95 lead-free gasoline (95-LFG) so called for their octane levels] are the three major fuels currently used in Taiwan area for spark-ignition engine vehicles. Recently worldwide efforts to reduce the use of PLG are intended to lower lead emission into the atmosphere and eventually to reduce the lead level in human blood. In Taiwan, the annual PLG consumption rates decreased significantly from 2,599 × 10 6 L/year in 1994 to 944 × 10 6 L/year in 1999. On the other hand, the annual consumption rates of 92-LFG and 95-LFG increased significantly from 1,321 × 10 6 L/year and 3,485 × 10 6 L/year in 1994, to 2,136 × 10 6 L/year and 6,118 × 10 6 L/year in 1999, respectively (Table 1). As a result, one-ring aromatic hydrocarbon in LFG fuels were added to maintain the knock resistance of vehicle engine (1). An important question, therefore, is whether the use of LFG in replacing PLG will increase emissions of some toxic substances, such as polycyclic aromatic hydrocarbons (PAHs), from gasoline-fueled engines.PAHs and their derivatives are associated with the incomplete combustion of organic material, arising partly from natural combustion, such as forest fires and volcanic eruptions; but most emissions arise from anthropogenic activities, such as the burning of gasoline in motor vehicles (2-4). For gasoline-powered engines, the emission of PAHs occurs through many factors, including the chemical compositions of the fuels, the types of lubricant and fuel additives, and the engine's operating conditions (1,5-7). However, the emission of PAHs in the above studies was assessed on the basis of total PAH concentration, without taking the carcinogenic potency of each individual PAH compound into account. To date, the International Agency for Research on Cancer (IARC) has classified several PAH compounds into probable (2A) or possible (2B) human carcinogens (8). In principle, the carcinogenic potency of a given PAH compound can be assessed based on its benzo[a]pyrene equivalent concentration (BaP eq ). Calculation of BaP eq concentration for a given PAH compound requires the use of its toxic equivalent factor (TEF)-which represents the relative carcinogenic potency of the given PAH compound by reference to the specific compound BaP-to adjust its original concentration. To date, only a few proposals for TEFs are available (9-11). Among them, the list of TEFs completed by Nisbet and LaGoy in 1992 (11) ( Table 2) reflects well the actual state of knowledge on the toxic potency of each individual PAH compound (12). On the basis of this TEFs list, the carcinogenic potency of total PAHs can be assessed by the sum of the BaP eq concentrations estimated for each PAH compound in total PAHs.In this study we aimed first to assess the effect on PAH emissions when different types of LFG replaced PLG in a test gasoline-powered engine. Assuming that PAH compositions in the engine exhaust might be affected by the types of gasoline fue...

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