Toxicity is a measure of the degree to which something is toxic or poisonous. The study of poisons is known as toxicology. Toxicity can refer to the effect on a whole organism, such as a human or a bacterium or a plant, or to a substructure, such as a cell (cytotoxicity) or an organ (organotoxicity such as the liver (hepatotoxicity). In the science of toxicology, the impact of an external substance or condition and its deleterious effects on living things: organisms, organ systems, individual organs, tissues, cells, subcellular units is the subject of study. A central concept of toxicology is that effects are dose-dependent; even water — generally not considered to be toxic — can lead to water intoxication when taken in large enough doses, whereas for even a very toxic substance such as snake venom there is a dose below which there is no dectectable toxic effect. (source: Wikipedia.org)
