SSRL | Highlights Archive | Headlines | Publications | User Resources | SLAC | Stanford University


Overall structure of the ESCRT-II complex (click on image for larger view)

Science Highlight


Friday, 29 April 2005

  Chemical Structure of Arsenic and Chromium in Chromated Copper Arsenate (CCA) Treated Wood

summary written by Heather Woods, SLAC Communication Office

Peter S. Nico1, Scott E. Fendorf2, Yvette W. Lowney3, Stewart E. Holm4, and Michael V. Ruby3

1Chemistry Department, Cal State University, Stanislaus, Turlock, CA
2Geological and Environmental Sciences, Stanford University, Stanford, CA
3Exponent, Boulder, CO
4Georgia-Pacific Corporation, Atlanta, Georgia


The chemically treated wood used for playgrounds, fences and decks appears to be less toxic than feared. The chromated copper arsenate (CCA) mix 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. Recent analyses done at SSRL show that the arsenic and chromium is in a relatively stable chemical state and is bound to the wood fibers. Contrary to previous estimates of arsenic exposure, the research by Peter Nico of California State University, Stanislaus, and his colleagues supports the conclusion found that arsenic appears to be more stable than previously believed against leaching and subsequent absorption into the skin of those who come in contact with CCA-treated lumber.

The Environmental Protection Agency is preparing a human health risk assessment. The agency 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 4% from exposure to arsenic-containing soils. The SSRL research resolved for the first time the chemical and structural states of the chemicals coating the 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 fine structure (EXAFS) spectroscopy, show that the chemicals are in a fairly stable state and that they remain tightly bound to the wood despite weathering.

Eviron. Sci. Technol.. 2004 Sep; 38(19):5253-5260 [10.1021/es0351342]