Relative significance of different hydrocarbons for the carcinogenic potency of emissions from various incomplete combustion processes.

Animal experiments have shown that the carcinogenic activity of organic extracts of exhaust condensates is caused predominantly by PAHs containing 4-6 rings. The carcinogenic potency not only of PAH-containing extracts but also of the whole exhausts has often been estimated from their benzo[a]pyrene (BP) content. However, this simplified yardstick should not be applied for comparison of the carcinogenic potency of different types of PAH-containing exhausts. Epidemiological and experimental studies indicate that, for the induction of a certain tumour incidence, inhaled cigarette smoke contains about 100 times less BP and inhaled diesel exhaust contains about 1000 times less BP than the exhausts from coke ovens or heated tar pitch which yield the same results. This means that diesel exhaust and cigarette smoke contain--apart from PAHs--highly potent carcinogenic substances and/or they induce tumorigenic reactions which are very effective.