Newswise — It's a success story so far " but the end has yet to be written.
Research supported by the University of Florida helped prompt the treated wood industry to abandon a once common but potentially harmful wood preservative from lumber in residential construction. New statistics show that since this change in 2004, imports of arsenic, a toxic metal used in the wood-treating chemical chromated copper arsenate, have plunged.
Now, the challenge is to figure out what to do with millions of board feet of CCA lumber still in service nationwide. Some structures pose a potential hazard now, while others will face demolition as they age, with all CCA-treated wood waste requiring special care, said John Schert, director of the Bill Hinkley Center for Solid and Hazardous Waste Management at the UF College of Engineering.
"Over 35,000 metric tons of arsenic has been imported into Florida from places like China, Chile and Mexico to be used as an ingredient in pressure treating CCA-treated wood since it first became available in the 1970s," Schert said. "Our focus now is figuring out how to deal with all that wood as it comes out of service in the form of old decks, docks, fences and homes."
Statistics appearing next year in a book by a University of British Columbia scholar show U.S. imports of arsenic used in treated lumber have dropped from 19,200 metric tons in 2003 to 4,450 in 2004 and 5,760 in 2005. The statistics were obtained from the U.S. Geological Survey, said Bill Cullen, a UBC professor emeritus of chemistry and the book's author.
The decline coincides with the wood industry's decision to swap the CCA preservative with a "greener," arsenic-free preservative in 2004 for all residential construction. That decision occurred after nearly a decade of research supported by the Hinkley Center that showed the propensity for CCA-treated lumber to shed its arsenic into underlying soils -- where the arsenic could accumulate in concentrations that might be hazardous to people.
Much of that research was funded with about $600,000 obtained through a National Science Foundation Partnerships For Innovation grant. Among other efforts, the NSF grants helped fund several CCA-related projects by UF and University of Miami environmental engineering researchers Tim Townsend and Helena Solo-Gabriel.
Townsend and Solo-Gabriele discovered that aging decks made of CCA-treated wood are capable of shedding enough arsenic into surrounding soil for it to be classified as a contaminated, among other findings. Subsequent investigations by Hinkley Center researchers and news organizations linked CCA wood in playgrounds to arsenic contamination in soils, a particular concern because of children unintentionally ingesting the dirt.
While the amount of arsenic flowing into the U.S. has slowed since the change, the disposal of CCA-treated lumber remains a tough problem to solve, Schert said. There are about 35,000 acres of decks in Florida alone, most built with CCA-treated lumber, and more than 1,000 playgrounds nationwide built with CCA, he said.
Solo-Gabriele said some CCA wood can be coated or painted to prevent it from shedding its arsenic, particularly when touched. But that is only a short-term solution because the paint will eventually wear away. With public structures, officials need to prioritize which ones should be replaced and which can be coated or left in place, she said.
"Playgrounds and picnic tables " these are the ones we really need to be concerned with," she said. "Decks, I would place next on the priority list."
Also needed, she said, are better methods for identifying CCA-treated lumber, which is often indistinguishable from regular lumber when aged. Today, CCA-treated wood often winds up in landfills. Concerned about contaminating the water supply, the Florida Department of Environmental Protection is considering a ban on CCA-treated wood in unlined landfills.
CCA-treated lumber also may go to plants that burn discarded vegetation and wood to generate electricity. Because burning CCA-treated lumber can release arsenic into the air or create arsenic-tainted ash, Solo-Gabriele and Townsend have developed new ways to identify and remove CCA-treated wood from the waste stream. It also may be possible to install scrubbers that cleanse the air emissions of arsenic. "If we can burn both the treated and the untreated wood that comes from the demolition industry here in Florida without having to separate the two, it could be a big green energy source," Schert said.