Pathologic effects of inhaled particles in rat lungs - Associations between inflammatory and neoplastic processes

Ultrafine carbon black, diesel exhaust soot, and titanium dioxide are carcinogenic at sufficient exposure levels in rat lungs. A 30-month study is required to test properly the carcinogenicity of these and other particulates in rat inhalation studies. Carcinogenicity of the three particulate materials reviewed was shown by development of both bronchio-alveolar and squameous cell tumors. Tar/pitch condensation aerosol containing 50 ug/m3 BaP and other polycyclic hydrocarbons was shown to be carcinogenic only on the basis of development of squamous cell tumors. Particle induced tumors arose out of a background of hyperplasia and metaplasia associated with persistent inflammation in the rat lung. The association between inflammaton-related and neoplastic events indicates a high probability of a threshold effect for particle-induced carcinogenesis in the rat lung.