Structure of PAHs

The polynuclear aromatic hydrocarbons are composed of two or more aromatic (benzene) rings which are fused together in a linear, angular or cluster arrangement when a pair of carbon atoms is shared between them (Dhote et al. 2010). PAHs toxicity is quite structurally dependent, with isomers (PAHs with the same formula and number of rings) varying from non-toxic to extremely toxic. Thus, highly carcinogenic PAHs may be small or large. The PAH compound, benzo[a]pyrene (BAP), was notable as the first discovered chemical carcinogen (Johnsen et al. 2005). The US Environmental Protection Agency (EPA), has classified seven PAHs as probable human carcinogens: benzo[a]anthracene, BAP, benzo[b]fluo-ranthene, benzo[j]fluoranthene, chrysene, dibenzo(a,g)anthracene and inde-no(1,2,3)pyrene. PAHs known for their carcinogenic, mutagenic and teratogenic properties, are benzo[a]anthracene and chrysene (Ci8H12), benzo[b]fluoranthene,

Fig. 15.1 Schematic diagrams of different PAHs

benzo[j]fluoranthene (C20H12), benzo[a]pyrene (C20H12), coronene (C24H12), dibenz(a,g)anthracene (C20H14), and ovalene (C32H14) (Luch 2005; Xue and Warshawsky 2005). High prenatal exposure to PAH is associated with lower IQ of the progeny. Generally, PAH solubility and hydrophobicity are inversely proportional to an increase in number of fused benzene rings, whereas volatility decreases with an increasing number of fused rings (Kanaly et al. 2000b). The fused aromatic rings of different PAHs are well illustrated in Fig. 15.1.

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