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Wood preservative containing compounds of chromium, copper, and arsenic
Chromated copper arsenate (CCA) is a wood preservative containing compounds of chromium, copper, and arsenic, in various proportions. It is used to impregnate timber and other wood products, especially those intended for outdoor use, in order to protect them from attack by microbes and insects. Like other copper based wood preservatives, it imparts a greenish tint to treated timber. CCA was invented in 1933 by Indian chemist Sonti Kamesam, and patented in Britain in 1934. It has been used for timber treatment since the mid 1930s, and is marketed under many trade names. In 2003, the United States Environmental Protection Agency and the lumber industry agreed to discontinue the use of CCA treated wood in most residential construction. This agreement was intended to protect the health of humans and the environment by reducing exposure to the arsenic in CCA treated wood. As a result of this decision, CCA treated wood can no longer be used to construct residential structures such as playground equipment, decks, picnic tables, landscaping features, fences, patios, and walkways. Acute intoxication due to mishandling of treated products, e. g. by burning, is also a serious concern. Nevertheless, CCA remains a popular and economical option to make perishable timbers, such as plantation grown pine, viable for applications like poles, piling, retaining structures, etc.

The composition of CCA products is usually described in terms of the mass percentages of chromium trioxide or "chromic acid" |CrO3, arsenic pentoxide |As2O5, and copper(II) oxide |CuO. Arsenic is found naturally in the soil, food and water, and is still used to treat some medical conditions. Later studies however found that, while concentrations of arsenic in the soil and hand rinses were considerably higher among children who played on CCA treated playground toys than in the control group, there was no significant difference in the arsenic concentrations in urine and saliva samples.

Machining (sawing, sanding, drilling) CCA treated wood also exposes construction workers and amateur carpenters to chronic and acute health risks via inhalation. Use of CCA treated wood for beehive construction has been associated with increased levels of arsenic in the honey and winter loss of bee colonies.

Another concern is the leaching of chromium and arsenic from CCA treated timber and their release to the environment. The amount and rate of arsenic leaching varies considerably depending on numerous factors, such as local climate, acidity of rain and soil, age of the wood product, and how much CCA was applied. A study has found that soil contamination due to the presence of CCA treated wood after 45 years was minimal. Many studies in less aggressive soil types show leaching to be as low as 0.5 ppm (red pine poles in service,) or up to 14 ppm (treated pine in garden beds). Should any chemicals leach from the wood they are likely to bind to soil particles, especially in soils with clay or soils that are more alkaline than neutral. Sawdust and other residues left over by construction may be a much more significant source of arsenic pollution to soil and environment than leaching from the final timber structure.

Acute and chronic arsenicism have been reported to result from inhalation of smoke from burning of CCA treated wood, such as in the use of scrap timber as fuel for industrial or domestic fires. Regulatory agencies in the European Union and Australia also prohibited CCA treated timber in residential uses, while considering that timber already in place need not be replaced.

The EPA recommends wearing gloves when handling CCA treated wood, wearing goggles and masks when sawing or sanding it, and never burning it. CCA treated wood should not be used where it may come in contact with food, such as in kitchen tops, cutting boards, or beehives. It should not be exposed to chemicals such as bleaches, acids, soda, etc. Timber should be inspected for residues of CCA on the surface that could easily be dislodged. Sealants or other coatings will reduce the risk of environmental contamination. Disposal of scrap and waste CCA treated timber should be done only in approved incinerators or controlled landfill sites, which are designed to handle potentially toxic wastes such as paints, insecticides, batteries, etc.