The significance of polycyclic aromatic hydrocarbons as environmental carcinogens

In vivo and in vitro experiments have shown that various polycyclic aromatic hydrocarbons are potent mutagens and/or carcinogens. Occupational and epidemiological studies suggest that they also have to be considered as hazards for humans. Due to their formation during all kind of incomplete combustions they are widespread to the environment. Balancing the carcinogenic effect of environmentally polluted matrices, after separation into PAH-free and PAH-containing fractions, by animal test systems (skin painting, lung implantation) evidence has been obtained that PAH containing more than 3 rings are by far the most relevant carcinogenic constituents in these matrices. The relative potencies of PAH in comparison to benzo[a]pyrene allow their ranking and result in efficiency equivalents generally applicable for risk assessment. Since PAH require biochemical activation prior to exhibiting carcinogenic effects the balance of various enzymes plays a key role in biological endpoints in vivo. Complex patterns of metabolites are formed in the mammalian organism the composition of which were found to be species-dependent. Hence, extrapolations from one species to another are limited and evaluations on experimental rodent data have to be reconsidered for their validity.