Biotransformation of organic xenobiotics normally proceed in a first step of oxidation (phase I) that introduces a reactive group in the xenobiotic, and a second step of conjugation (phase II) with a nontoxic endogenous metabolite that yields an excretable product.
Toxicant can be absorbed into an organism via different routes and it is distributed to various parts of the body, including the excretory organs, and is thus available for excretion. Many chemicals are known to undergo biotransformation (metabolic transformation), which occurs in the organs and tissues.