ABSTRACT
Once a toxicant is absorbed into an organism through various routes, such as the mouth, blood, lung, skin, eye, or nasal mucosa, it is distributed to various parts of the body, including the excretory organs. Many chemicals are known to undergo biotransformation (metabolic transformation or metabolism), which is catalyzed by enzymes present in the blood and tissues. Although the most important site of such reactions is the liver, other organs also contribute in some extent. Examples are the lungs, stomach, intestine, skin, and kidneys. During the process of biotransformation, “xenobiotics” (foreign substances to an organism or toxic substances) can be either activated to toxic form(s) or inactivated to nontoxic form(s) to become reactive or nonreactive with biomolecules such as DNA, RNA, proteins, and lipids.
