May 20, 2005  
 

 

Chemically Treated Wood Less Toxic Than Feared

By Heather Rock Woods

The chemically treated wood used for playgrounds, fences and decks appears to be less toxic than once feared. Chromated copper arsenate (CCA) protects commercial outdoor grade lumber from weathering, but in recent years the public and the government realized the chemicals could be potentially risky to the many people exposed to the ubiquitous wood.

Play structures like this are often manufactured using wood that has been chemically treated with arsenic and chromate. A study done at SSRL found the lumber is less harmful than feared.
(Image courtesy of Microsoft Clip Art)

Recent analysis done at SSRL showed that the arsenic and chromium in CCA is in a relatively stable chemical state and is bound to the wood fibers. Contrary to previous estimates of arsenic exposure, research by Peter Nico of California State University, Stanislaus, and his colleagues found that arsenic appears to be relatively stable against leaching and subsequent absorption into the skin of a toddler on a climbing structure or a do-it-yourselfer building a fence.

The Environmental Protection Agency is preparing a human health risk assessment. They had initially estimated that the major routes of CCA-related arsenic exposure to younger children would be half from dermal absorption (through the skin), nearly half from ingestion and four percent from exposure to arsenic-containing soils. In January 2004, a voluntary ban on CCA for residential use took effect but an estimated 300,000 metric tons of arsenic in the last 30 years had been used in the cocktail—and is still present on wood in yards across America.

The SSRL research resolved for the first time the chemical and structural states of the chemicals contained in the treated wood, to better determine the actual risks of coming in contact with CCA-treated lumber. An x-ray technique called XANES yielded crucial information on the oxidation states of arsenic and chromium, showing the two chemicals to be in their less toxic forms. Their molecular structures, obtained through extended x-ray absorption spectroscopy (EXAFS), show the chemicals are in a fairly stable state and they remain tightly bound to the wood despite weathering. They are therefore less likely to release to the air or soil or upon human contact.

“Dermal absorption of arsenic from CCA treated materials could perhaps be eliminated from consideration as a significant exposure pathway,” Nico said.

Nico’s colleagues include Scott Fendorf (Stanford), Mike Ruby and Yvette Lowney from Exponent, an engineering and scientific consulting firm, and Stewart Holm of Georgia-Pacific Corporation, which manufactures lumber, paper and tissue products. 

 

The Stanford Linear Accelerator Center is managed by Stanford University for the US Department of Energy

Last update Tuesday May 24, 2005 by Topher White