The term Polycyclic Aromatic Hydrocarbons (PAH's) refer to a large group of organic compounds widely distributed in the atmosphere, whose molecular structure contains two or more aromatic rings fused together. They are mainly formed during the incomplete burning of coal, oil and gas, garbage and tobacco. Because of their low vapour pressure, some PAH's are present both in the form of gases as well as associated with particles. The lighter PAH's such as phenanthrene, are found exclusively in the gas phase, the heavier PAH's such as Benzo (a ) pyrene are almost totally absorbed into particles. PAH's are relatively insoluble in water but dissolve in fats and oils.

Health Effects of PAH

Humans are always exposed to environmental mixture of PAH's. Population exposed to high concentrations of PAH mixture depict an increased incidence of tumours. Lung cancer is obviously linked to PAH's through inhaled air. Irrespective of their physical properties and initial routes of exposure, the tumor inducing effects of carcinogenic PAH's depend upon their conversion in the body into compounds which, unlike parent substances are capable of reacting with and damaging the genetic material (DNA) in the nuclei of cells, thus defined as gen-otoxic carcinogens.