[7] This initial treatment may include combination therapy of arsenic trioxide with all-trans retinoic acid (ATRA).

[15] It works by encouraging the proteosome breakdown of retinoic acid receptor alpha, by moving the protein on to the nuclear matrix and increasing ubiquitination.

[citation needed] 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 U.S. and Malaysia, but such materials are banned in many parts of the world.

[11] In combination with copper(II) acetate, arsenic trioxide gives the vibrant pigment known as Paris green used in paints and as a rodenticide.

This disorder affects workers in smelters, in populations whose drinking water contains high levels of arsenic (0.3–0.4 ppm), and in patients treated for long periods with arsenic-based pharmaceuticals.

Long-term ingestion of arsenic trioxide either in drinking water or as a medical treatment can lead to skin cancer.

Reproductive problems (high incidences of miscarriage, low birth weight, congenital deformations) have also been indicated in one study of women exposed to arsenic trioxide dust as employees or neighbours of a copper foundry.

In the U.S., the OSHA 1910.1018 occupational permissible exposure limit for inorganic arsenic compounds in breathing zone air is 0.010 mg/m3.

For example, arsenopyrite, a common impurity in gold- and copper-containing ores, liberates arsenic trioxide upon heating in air.

[11] In the laboratory, it is prepared by hydrolysis of arsenic trichloride:[23] As2O3 occurs naturally as two minerals, arsenolite (cubic) and claudetite (monoclinic).

[24] With anhydrous HF and HCl, it gives AsF3 and the trichloride:[23] Only with strong oxidizing agents such as ozone, hydrogen peroxide, and nitric acid does it yield arsenic pentoxide, As2O5 or its corresponding acid:[23] In terms of its resistance to oxidation, arsenic trioxide differs from phosphorus trioxide, which readily combusts to phosphorus pentoxide.