A xenobiotic is a foreign chemical substance found within an organism that is not normally naturally produced by or expected to be present within that organism.
The organism removes xenobiotics by xenobiotic metabolism, consisting of deactivation/activation and excretion of xenobiotics, which happen mostly in the liver. Hepatic enzymes are responsible for the metabolism of xenobiotics by first deactivating/activating them (oxidation, reduction, hydrolysis and/or hydration of the xenobiotic), and then conjugating thesecondary metabolites with glucuronic acid, sulphuric acid, or glutathione, followed by excretion in bile or urine.
http://www.creative-proteomics.com/services/xenobiotic-metabolites-analysis.htm
