Generation and characterization of radiolabeled diesel exhaust

To evaluate the potential health risks associated with increased use of diesel engines, information is needed on the biological fate of inhaled diesel exhaust components. Appropriately radiolabeled exhaust produced by burning radiolabeled fuel could be used to gain this information. The purpose of this study was to characterize different radiolabeled diesel exhausts with respect to their potential use in studies of the biological fate of exhaust carbon particles and particle-associated organic compounds (particle extracts). A single-cylinder diesel engine was used to burn diesel fuel containing trace amounts of 14C-labeled hexadecane, dotriacontane, benzene, phenanthrene or benzo(a)pyrene. Greater than 98% of the 14C in all additives was converted to volatile materials upon combustion. The remainder was distributed in varying amounts between the carbon particles and particle extracts. Aromatic additives labeled carbon particles more efficiently than aliphatic additives. Column chromatography of the particle extracts showed that, in most cases, the majority of the radioactivity eluted in fractions identical to the specific fuel additive employed, suggesting that a large amount of the particle-associated organic compounds consisted of uncombusted fuel constituents. Applying an electrical load to the engine-electrical generator increased carbon particle radioactivity, but had variable effects on the amount of radioactivity in the particle extracts. 67Ga-tetramethylheptanedione was also studied as a fuel additive to label carbon particles. 67Ga was incorporated into the exhaust particles and lung deposition of particles in rats was found to be approximately 10%. However, the 67Ga-radiolabel was found to separate from the particles in vivo, making it an unsuitable radiolabel for studying the long-term lung retention of diesel exhaust carbonaceous particles.