Carcinogenic effects of solid particles

The co-carcinogenic effect of intratracheally (i.tr.) administered nuisance particulates like titanium dioxide, carbon, ferric oxide or aluminum oxide was already demonstrated in hamsters almost 20 years ago. Particle-related lung tumors in rats were reported for the first time after inhalation exposure to 200 mg/m3 coal dust. A similar tumor response occured after inhalation of 250 mg/m3 TiO2 and after i.tr. instillation of 10 mg of activated carbon. Since the unexpected high incidence of lung tumors found in rats exposed to diesel engine exhaust could not be explained solely by the low content of carcinogenic polycyclic aromatic hydrocarbons of diesel soot, the hypothesis was generated that the carbonaceous core of diesel soot might be responsible for the diesel exhaust-related tumor response. This hypothesis proved to be right when rats exposed to 6 mg/m3 carbon black particles, almost completely devoid or organic material for 10 months, also developed lung tumors.