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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.
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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. |
