**2. Metabolism of PAHs**

Once PAHs enter the body they are metabolized in a number of organs (including liver, kidney, lungs), excreted in bile, urine or breast milk and stored to a limited degree in adipose tissue. The principal routes of exposure are: inhalation, ingestion, and dermal contact. The lipophilicity of PAHs enables them to readily penetrate cellular membranes (Yu, 2005). Subsequent metabolism renders them more water-soluble making them easier for the body to remove. However, PAHs can also be converted to more toxic or carcinogenic metabolites.

Fig. 1. Structures of some polycyclic aromatic hydrocarbons.


Table 1. US EPA priority polycyclic aromatic hydrocarbons.

After exposure, these molecules induce expression of phase I and II metabolizing enzymes (Shimada, 2006) including aldo-ketone reductases, cytochrome P-450s, catechol-Omethyltransferase, epoxide hydrolase, peroxidases, glutathione S-transferases, Nacetyltransferases, sulfotransferases, and other enzymes catalyzing conjugation reactions (Williams & Phillips, 2000).
