The chemical element arsenic (symbol As, atomic number 33) is a nonmetal or metalloid in group V on the periodic chart. It is often referred to as arsenic metal, and for toxicological purposes it is classified as a metal. It exists in several forms and has a long history of various uses, including insecticides for animals, wood preservatives (used in some aspects of the lumber industry), herbicides Herbicide Poisoning (pre-emergent weed killers), and even some medicinal uses. It is responsible for many poisonings in humans and animals.
Arsenic is found as inorganic and organic forms, with valences of +3 and +5. Arsenite (As+3) is 4–10 times as toxic as 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.