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How can copper keep termites at bay?

Wood Preparations Treated With Copper
Copper mesh screens can foil a termite's attempt to come into your house.
Copper mesh screens can foil a termite's attempt to come into your house.

A successful approach to making a house an unappealing food source for termites is by treating the wood used in its construction with a combination of chromium as a binder, copper and arsenic. This lethal cocktail, called chromated copper arsenate (CCA), has been in use since at least the 1940s for outdoor applications, especially where wood comes in contact with the soil. It also has the advantage of being resistant to deterioration due to sun and water exposure, and inhibits the growth of microbial agents like fungus that accelerate wood's decay.

This isn't a perfect solution, though. Termites can still go around treated wood to other edible surfaces, like the wood in your furniture and even your carpeting, or find pockets in CCA-treated wood that don't have high concentrations of the pesticide. CCA is applied using a liquid solution under pressure, and the pesticide isn't always distributed evenly in all woods. There's also a problem with CCA breaking down over time and leaching into the environment. High levels of arsenic and chromium can be dangerous, and even copper in high concentrations can be lethal, particularly in aquatic systems, like ponds and lakes [source: EPA].

As a result, in the United States, CCA has been eliminated as a wood treatment for residential applications and for use in lumber that will come in direct contact with the skin, like playground structures.

As an alternative, lumber for residential use is sometimes treated with Copper Azole (ACQ), a combination of copper and azole as tebuconazole, with other co-biocides. The recipe has changed a couple of times, but the goal is to create a safer and more environmentally friendly wood treatment.

One disadvantage of both CCA- and ACQ-treated wood is that the copper reacts with other metals through electrochemical action, accelerating the oxidizing process in metal fasteners. Because ACQ contains a larger percentage of copper than CCA and doesn't have the anti-corrosive properties of chromium, wood treated with ACQ preparations may be more challenging and expensive to work with.

This isn't the only way copper helps to keep termites away. On the next page, we'll take a look at copper barriers and other interesting blockades that can keep you safe from termites.