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What Is Chromated Copper Arsenate?

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  • Written By: Mary McMahon
  • Edited By: O. Wallace
  • Last Modified Date: 15 August 2014
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Chromated copper arsenate (CCA) is a chemical compound which has been used as a wood preservative since the 1930s. This compound was widely used through the early 21st century, at which point several nations started enacting restrictions and bans on chromated copper arsenate in response to concerns about the environmental and health effects of exposure to this compound. While woods treated with this product are generally recognized as safe by many governments, government agencies acknowledge that they can pose a health threat over an extended period of exposure.

This chemical compound has antimicrobial and insecticidal properties which make it appealing as a wood preservative. Wood treated with chromated copper arsenate will endure longer, resist damage, and hold paint better than untreated wood. Classically, the wood has a distinctive greenish tinge from the copper when it is new, although it may weather to a gray or neutral tone over time of it is left unpainted and is used in outdoor settings.

Wood is treated with chromated copper arsenate through a pressure treatment process, in which the wood is submerged in a bath of the chemical compound and then subjected to high pressure. The pressure forces the compound into the wood, ensuring that the wood is permeated evenly in the mixture of chromium, copper, and arsenic. Once the treatment is over, the wood can be allowed to dry before being sold. When sold, the wood is clearly labeled as pressure treated, so that people know which settings are appropriate for its use.

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Primarily, wood treated with chromated copper arsenate is intended for outdoor use, as in the construction of patios, decks, fencing, signage, utility poles, and so forth. Several nations have specifically banned the use of this product in residential construction, due to concern that people could get sick from prolonged exposure to leached chemicals. The wood is also banned in playgrounds in may nations.

Health concerns about this chemical compound revolve around the fact that the chemicals leach out over time. For people in a position to receive prolonged exposure, such as children using a playground every day, levels of the chemicals could build up in the body, causing sickness. Wood treated with chromated copper arsenate can also leach chemicals into the natural environment, where they may enter the water table or cause sickness and disease in plants. This wood also cannot safely be burned, which is a concern in areas where people may burn scrap wood for heating and cooking.

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