Large scale applications include its use as a precursor to forestry products, in colorless glass production, and in electronics.Being the main compound of arsenic, the trioxide is the precursor to elemental arsenic, arsenic alloys, and arsenide semiconductors. Organoarsenic compounds, e.g. feed additives (Roxarsone) and pharmaceuticals (Neosalvarsan), are derived from arsenic trioxide. Bulk arsenic-based compounds sodium arsenite and sodium cacodylate are derived from the trioxide.
A variety of applications exploit arsenic's toxicity, including the use of the oxide as a wood preservative. Copper arsenates, which are derived from arsenic trioxide, are used on a large scale as a wood preservative in the US and Malaysia, but such materials are banned in many parts of the world. This practice remains controversial. In combination with copper(II) acetate arsenic trioxide gives the vibrant pigment known as Paris green used in paints and as a rodenticide. This application has been discontinued.