Arsenic-treated wood is wood that has been pressure-treated with a pesticide containing inorganic arsenic (i.e., the arsenic compound does not contain carbon) to protect it from dry rot, fungi, molds, termites, and other pests. The arsenic can be a part of a CCA (chromated copper arsenate) chemical mixture consisting of three pesticidal compounds, copper, chromate, and arsenic; the most commonly used type of CCA contains 34% arsenic as arsenic pentoxide. Less commonly used wood preservatives containing arsenic include the pesticide ACA (ammoniacal copper arsenate), which contains ammonium, copper, and arsenic, and the pesticide ACZA (ammoniacal copper zinc arsenate), which contains ammonia, copper, zinc, and arsenic. In 1996, the United States wood product industry used 30 million pounds of arsenic, or half of all the arsenic produced worldwide.

Inorganic arsenic in CCA has been used since the 1940s. CAA is injected into wood through a process that uses high...