The ubiquitous element arsenic (As) is a nonmetal or metalloid in group V on the periodic chart. It is often referred to as arsenic metal and for toxicologic purposes is classified as a metal. It exists in several forms and has a long history of various uses, including insecticides for animals, wood preservatives, herbicides, and even some medicinal uses. It is responsible for many poisonings in people and animals.
Arsenic poisoning is caused by several different forms of the element; the form may determine the toxicity. Arsenic is found as inorganic and organic forms with valences of +3 and +5. Arsenite (As+3) is more toxic than arsenate (As+5). Toxicity varies with factors such as oxidation state of the arsenic, solubility, species of animal involved, and duration of exposure. Therefore, the toxic effects produced by phenylarsonic feed additives and other inorganic and organic compounds must be distinguished. (See also Herbicide Poisoning.)