Relevance of polycyclic aromatic hydrocarbons as environmental carcinogens

Summary

All emissions from incomplete combustion contain polycyclic aromatic hydrocarbons (PAH) which are a well-known class of carcinogens. The question whether additional carcinogenic compounds do exist in these emissions can be answered by separating the emission condensate into a PAH-containing and a PAH-free part. These parts have been tested in an animal experiment by means of a carcinogen-specific test system such as topical application onto the skin of mice or injection into the lung of rats. The investigation on the contribution of PAH-fractions and of benzo(a)pyrene to the carcinogenic potential of emission condensate from gasoline driven engines, Diesel engines, coal combustion in domestic furnaces and sidestream smoke of cigarettes shows that the carcinogenic effect of the particle phase of these pyrolytic condensates is predominantly caused by polycyclic aromatic compounds such as PAH. In all cases investigated the PAH-fraction containing 4 and more rings accounted for more than 75% of the total carcinogenic effect resulting from the implantation into the lung of rats or from the topical application onto mouse skin. The contribution of benzo(a)pyrene to the carcinogenic potency of various condensates, however, is minor in all cases investigated and accounts for only 0.17% to 4% of the total carcinogenicity as evaluated from implantation into the lung of rats (Table 1).