Abstract
Diesel engine exhausts contain high levels of toxic gases and soot. Lowering thesulfur content in fuel is expected to reduce SO2 concentration and particle acidity in exhaust. We conducted in vitro and in vivo tests to examine the health effects of lowsulfur light oil (LSLO) on rats. Marked reductions of SO2, SO42- and particle mass concentrations in LSLO exhausts were confirmed. The amounts of polycyclic aromatic hydrocarbons (PAH) and nitro-PAH in diesel exhaust particles (DEP) were variable. Mutagenicity and 8-OH-deoxyguanosine formation were slightly lower with LSLO than high-sulfur light oil (HSLO) particles. However, inhalation experiments on rats exposed to the same mass concentration of particles demonstrated a significantly higher frequency of lung tumors and higher lung burden in LSLO compared to HSLO exhaust. Intratracheal instillation using three doses of DEP also showed higher dose-related tumorigenesis with LSLO, correlating with the degree of particle retention in the lung. Distribution of particle sizes showed a higher proportion of nanoparticles in LSLO than in HSLO DEP. Lowering sulfur content in diesel fuel, thus, can significantly decrease the mass concentration and acidity of soot, but enhance tumorigenicity for its same mass concentration. Further efforts to eliminate particles from diesel exhaust are thought to be necessary.
