Polycyclic aromatic compounds in nature

A great variety of polycyclic aromatic hydrocarbons (PAHs), including both known and suspected carcinogens, are widespread throughout soils, sea-bottom sediments and petroleum deposits. They are formed whenever organic substances are exposed to high temperatures. The great uniformity of composition and the nature of alkyl substituents suggest that most of the PAHs in the soil and in the sea-bed have been derived over eons from the fall-out of soot from forest and prairie fires. Conversely, the aromatic hydrocarbons of crude oil have been formed over millions of years from organic matter in sediments at 100 to 150 C. This has resulted in a much richer composition of alkylated PAH species than in soil or sea-bed. Oil spills therefore result in a changed local spectrum of PAHs, which may be detected for at least 6 yr after such an event. There is controversy about whether living organisms are able to synthesize PAHs. The ubiquity of PAHs in nature makes a direct experimental approach to this problem very difficult, but there is evidence that certain less volatile categories of PAHs are not present in plants grown in an environment free of such PAH species. This suggests that living organisms do not make PAHs.more » Natural fires and reactions in sediments produced PAHs long before the advent of man. They may be ranked with other natural mutagens such as uv radiation and natural radioactivity.« less