Are Wood Preservatives Safe?

One of the more frequent questions from the public regarding wood preservatives is safety. The public is interested in two-fold safety: The first, Is this product safe for myself and my children? and the second, Is this product safe for the environment?  The EPA has always been concerned with wood preservative safety and all preservatives must carry an EPA label.  The labeling process is lengthy, expensive and includes a wide array of testing to determine if the preservative is toxic to vertebrates, marine organisms, and the environment.

The initial concern was focused on chromated copper arsenate (CCA)-treated wood.  In 1998, the Florida Center for Solid & Hazardous Waste Management (FCSHWM) sponsored CCA research at the University of Florida and the University of Miami.  The following year, arsenic was discovered in the soil at a Gainesville, Florida-area elementary school playground.  This discovery led to several newspaper articles throughout Florida and eventually in USA Today.

In 2001, the treated wood industry agreed to new voluntary warning labels on CCA-treated wood.  The environmental group Beyond Pesticides, Communication Workers of America, and others joined together to sue the EPA to ban all forms of toxic treated wood, including creosote, pentachlorophenol and CCA treated wood in 2002. Their efforts were unsuccessful. The controversy came to a head when the EPA announced the finalization of the voluntary ban on residential uses of CCA to take effect on Dec. 31, 2003. It should be noted that the EPA did not require or suggest that any existing structures, including children’s playground equipment, should be removed from service. CCA continues to be used for non-residential uses such as poles, pilings, and posts.

My experience has shown me that CCA is cost-effective with excellent efficacy against most organisms with the exception of mold fungi – which do not impact the structural integrity of a wood member. The metals in CCA-treated wood are highly resistant to leaching when the wood is placed in service. The leach-resistance of CCA is a result of the chemical “fixation” reactions that occur to render the toxic ingredients insoluble in water. The fixation of CCA is a complex process, but the essence of CCA fixation is the reduction of chromium from the hexavalent to the trivalent state, and the subsequent precipitation or adsorption of chromium, copper and arsenic complexes in the wood substrate. Some of the these reactions, such as the adsorption of copper and chromium onto wood components, occur within minutes or hours while others are completed during the ensuing days or weeks.

The length of time needed for fixation is greatly dependent on temperature, and the reactions may proceed slowly when the treated wood is stored out-doors in cool weather. So, yes,  CCA is safe for people and the environment and is a much better environmental choice than steel or concrete.