Xenobiotic
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A xenobiotic is a chemical which is found in an organism but which is not normally produced or expected to be present in it. It can also cover substances which are present in much higher concentrations than are usual.
For example, drugs such as antibiotics are human xenobiotics because the human body does not produce them itself nor would they be expected to be present as part of a normal diet. However, the term is usually used in the context of pollutants such as dioxins and polychlorinated biphenyls and their effect on the biota.
The term xenobiotic is also used to refer to organs transplanted from one species to another. For example, some researchers hope that hearts and other organs could be transplanted from pigs to humans. May people die every year whose lives could have been saved if a critical organ had been available for transplant. Kidneys are currently the most commonly transplanted organ. Xenobiotic organs would need to be developed in such a way that they would not be rejected by the immune system. With the development of vitrification transplantable organs could be stored in organ banks for long periods.