Chronic inhalation exposure of Wistar rats and two different strains of mice to diesel engine exhaust, carbon black, and titanium dioxide

Wistar rats were exposed for 2 yr to diesel engine exhaust, carbon black, and ultrafine TiO2 and were subsequently kept in clean air for 6 mo. Particle exposure concentration was increased during the course of the experiment for carbon black and TiO2 to reach particle lung loads similar to those found in the diesel soot-exposed rats. The average particle exposure concentrations for diesel soot, carbon black, and TiO2 were 7, 11.6, and 10 mg/m3, respectively. Lung tumor rates in these rats increased with increasing cumulative particle exposure (mg/m3 x h) independent of the type of particle employed. (...) With this study, it could be demonstrated that the carbon core of diesel soot is mainly responsible for the occurence of diesel engine exhaust-related lung tumors; the role of diesel soot-attached polycyclic aromatic hydrocarbons (PAH) and NO2-PAH is probably of minor importance in the rat lung. (Abstract truncated)