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Toxic Effects
Toxicity is complex with many influencing factors; dosage is the most important. Xenobiotics cause many types of toxicity by a variety of mechanisms. Some chemicals are themselves toxic. Others must be metabolized (chemically changed within the body) before they cause toxicity.
Many xenobiotics distribute in the body and often affect only specific target organs. Others, however, can damage any cell or tissue that they contact. The target organs that are affected may vary depending on dosage and route of exposure. For example, the target for a chemical after acute exposure may be the nervous system, but after chronic exposure the liver.
Toxicity can result from adverse cellular, biochemical, or macromolecular changes. Examples are:
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|  | cell replacement, such as fibrosis
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| | damage to an enzyme system
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| | disruption of protein synthesis
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| | production of reactive chemicals in cells
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| | DNA damage
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Some xenobiotics may also act indirectly by:
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| | modification of an essential biochemical function
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| | interference with nutrition
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| | alteration of a physiological mechanism
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