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. Specifically, drugs such as antibiotics are xenobiotics in humans 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 also used in the context of pollutants such as dioxins and polychlorinated biphenyls and their effect on the biota. Natural compounds can also become xenobiotics if they are taken up by another organism (e.g., uptake of natural human hormones by fish found downstream of sewage treatment plant outfalls) (adj.) Foreign to the body or to living organisms. Used of chemical compounds (noun) A xenobiotic chemical, such as a pesticide The scientific term for toxic substances, meaning literally "foreign to life " A compound foreign to biological systems Often refers to human-made compounds that are resistant or recalcitrant to biodegradation and/or decomposition Relating to a substance foreign to the body or ecological system A chemical which is not a natural component of the living organism exposed to it - foreign substance taken into the body; often used to describe a man-made rather than natural substance; biochemical defense mechanisms have not developed to respond to these Any biological substance, displaced from its normal habitat; a chemical foreign to a biological system Yield The rate of production of cake from a dewatering device Zero discharge water When the only water that enters a sewage system is normal household sanitary water, because all the industrial and agricultural water is recycled into the process plant A xenobiotic is a chemical which is not a natural component of the organism exposed to it Synonyms: drug, foreign substance or compound, exogenous substance or compound A synthetic chemical that affects living systems A completely synthetic chemical compound that does not naturally occur on earth "A chemical or other stressor that does not occur naturally in the environment Xenobiotics occur as a result of anthropogenic activities such as the application of pesticides and the discharge of industrial chemicals to air, land, or water" (RAF 1992, 38)