Long-term inhalation exposure of rats and mice to diesel exhaust (DE), carbon black (CB), and titanium dioxide (TiO2)

Some major results: Lung tumors occured in rats after exposure to DE, CB and TiO2 and the tumor rate increased with increasing normalized exposure concentrations independent of the kind of particle inhaled. No lung tumors were found after exposure to 0.8 mg/m3 diesel soot but, one lung tumor-bearing rat occured in controls. Alveolar lung clearance was significantly impaired already after 3 months of exposure to 0.8 mg/m3 diesel soot; at this time the lung contained 0.6 mg diesel soot. This amount increased to 6 mg after 24 months whereas the exposure to 7.5 mg/m3 diesel soot led to a lung particle load of 60 mg. Despite higher exposure concentrations of CB and TiO2 compared to diesel soot, CB and TiO2-exposed lung contained about 20 mg less particles than the DE exposed lungs after an experimental time of 24 months. None of the various groups of exposed mice showed a significantly increased lung tumor rate. (Abstract truncated)