UF: Pressure-washing decks, fences stirs arsenic

Pressure-washing your old deck or fence could be hazardous to your health. That’s the somewhat surprising warning from the University of Florida.

"It's very straightforward science," said Dr. Julia Gress, Ph.D.

Gress, a soil scientist at the UF, recently completed a study in which she observed troubling arsenic levels when wood that was produced before 2004 becomes wet. Specifically, Gress examined wood that was pressure-treated with a chemical called CCA, chromated copper arsenate.

Manufacturers stopped using CCA in late 2003. But that type of wood remains in as many as 20 million backyards, Gress said.

"We've known that it's been there a long time. But, nobody has really looked at the effect of water on the residue,” she explained. “I found with my research is that three times as much arsenic is present on the wood when it's wet."

Pressure-washing pushed arsenic above allowable levels, Gress said.

"There's a danger,” she said. And consumers “are completely unaware of it."

Arsenic occurs naturally. It resides on the Periodic Table of Elements at position 33, right between germanium and selenium. However, the Consumer Product Safety Commission, the Environmental Protection Agency, and the Food and the National Institutes of Health all classify arsenic as a carcinogen.

Gress said adding bleach to the mix exacerbated the situation. When mixed with water and exposed to CCA-treated wood, a harmful chemical called chromium was created.

“You should not use bleach,” she said.

Gress’s recommendation for consumers who have old decks, fences, and playgrounds is blunt.

"Tear it out," she said. "Replace it when you can. That's my overall advice here. Replace it as soon as you can."

But Dr. Joette Giovinco, M.D., disagrees.

"I think ripping it out is excessive,” she said. “Number one, it's a cost factor. Number two, you might be replacing it with something that is structurally less sound."

Instead, Giovino recommends coating an old deck or fence.

"There have been several studies looking at this, where they can reduce or even eliminate that leeching depending on what [coating] you choose."

Giovinco said consumers should visit a hardware store to determine the best sealant.

"Ask questions, read the labels, do your own research,” she said. “And honestly, don't panic."

Gress acknowledged that not all families will have the resources to buy a new deck. And she agreed with Giovinco that sealing CCA-treated wood is, at the very least, a good first step.

"Definitely seal it every year," she advised.