Polycyclic Aromatic Hydrocarbons: Metabolism, Activation and Tumour Initiation

Polycyclic aromatic hydrocarbons (PAH) are formed as products of the incomplete pyrolysis of organic materials and are present in considerable quantities in fossil fuel from which they are released by a variety of combustion processes (see Guerin 1978). Sources of environmental PAH therefore include, in the wider sense, power plants, domestic heating systems, petrol and diesel engines, refuse burning and various industrial activities, whilst tobacco smoke provides a more localized source of supply. Each of these sources of PAH produces a mixture containing between 100 and 300 different individual hydrocarbons, and the estimated total annual emission in the USA of just one of them, benzo[a]pyrene (BaP), is some 1200 tons (Grimmer 1983). Since only micrograms of this hydrocarbon are required to initiate tumours on mouse skin, it would be surprising if the human population was not placed at increased risk of developing cancer as a result of pollution of the environment on this scale by PAH.