DNA Damage Caused by Polycyclic Aromatic Hydrocarbons: Mechanisms and Markers

Polycyclic Aromatic Hydrocarbons (PAHs) are a group of chemicals that occur naturally in coal, crude oil and gasoline. Incomplete combustion of organic material results in emission of PAHs (ATSDR, 1996). These molecules consist of two or more aromatic rings fused in linear, angular or cluster arrangements (Fig. 1) and by definition are composed of hydrogen and carbon. PAHs containing up to six fused aromatic rings are often known as "small" PAHs while those containing more than six aromatic rings are called "large" PAHs. As pure chemicals, these compounds are colorless, white or pale yellow solids. Their physicochemical properties, vapor pressure and solubility vary according to their molecular weight. PAHs possess a highly characteristic UV absorbance spectra although some may be fluorescent (Fetzer & Biggs, 1994). PAHs are ubiquitous and persistent as a consequence of natural (forest fires and volcanic eruptions) and human activities (Jongeneelen, 2001). PAHs may distribute in water, soil and the atmosphere according to different weather and geographical factors. Although industrial activity such as coke manufacturing or asphalt production are major contributors to PAH emissions, incineration, power generation and several mobile sources also emit a considerable amount of PAHs. Significant sources of PAHs in surface waters include deposition of airborne PAHs, municipal wastewater discharge, urban storm-water runoff, and industrial waste. Food groups that tend to have the highest levels of PAHs include charcoal broiled or smoked meats, leafy vegetables, grains, and vegetable fats and oils (Yu, 2005). Therefore, workers of these industries and the general population are continually exposed to different concentrations of PAH mixtures. The Agency for Toxic Substances and Disease Registry (ATSDR) has grouped 17 PAHs according to their health effects (ATSDR, 1996). The United States Environmental Protection Agency (EPA) has designated 28 PAH compounds as priority pollutants (EPA, 2009) (Table 1). The International Agency for Research on Cancer (IARC) has classified some these compounds as carcinogenic (group 1) or likely carcinogenic (group 2A) to humans, for example benzo[a]pyrene and dibenz[a,h]anthracene, respectively (IARC, 2010). Finally, the National Institute of Standards and Technology has created a classification of PAHs according to their symbols, molecular formulas, class and notation among other properties (NIST, 2010). The most common mechanism of carcinogenesis induced by PAHs is DNA damage through the formation of adducts. Alternatively, in the presence of reactive oxidative species, DNA