**2. Xenobiotic metabolism**

The foreign environmental chemicals are known as xenobiotics (Gk. *xenos*— "stranger") and include drugs, drug metabolites and environmental pollutants (such as synthetic pesticides, herbicides and industrial pollutants). Xenobiotics may cause damages in the innate state (alkyl iodides, acyl halides and nitrogen mustards) or after activation in the metabolizing process.

Xenobiotic metabolism is performed in three stages (**Figure 1**):

