Polyaromatic Hydrocarbons (PAHs): Structures, Synthesis and their Biological Profile

Polycyclic aromatic hydrocarbons (PAHs) are aromatic compounds with two or more fused benzene rings in their structural configurations. PAHs do not contain heteroatoms and substituents on the ring system. PAHs containing up to four rings are called light PAHs while those that contain more than four rings are considered as heavy PAHs. Heavy PAHs are more stable and more toxic than the light PAHs. Generally, the increase in the size and angularity of a PAH molecule results in an increase in hydrophobicity and electrochemical stability. Ring linkage patterns in PAHs may occur in such a way that the tertiary carbon atoms are centers of two or three interlinked rings. The examples of PAHs are naphthalene, anthracene, phenanthrene, acenaphthylene, acenaphthene, fluorene, fluoranthene, pyrene, benz[a]anthracene, chrysene, benzo[b]fluoranthene, etc. PAHs can be produced either naturally or anthropogenically and have toxic properties. Due to the health risk posed by their exposure, there is a need to control the release of PAHs through air quality management. Refinery industries are required to monitor and regulate their discharges. There is an urgent need for the considerable efforts to be applied in the field of research to degrade and monitor potentially hazardous substances to control, predict and avoid negative effects of PAHs pollution.