Pressure washing that old wood deck in your backyard might make it look better, but you could create a carcinogenic hazard that puts your family and pets at risk.

Wood decks manufactured before 2004 are made of CCA-treated wood, which contains arsenic and chromium—both carcinogens. Wet wood releases arsenic at three times the rate of dry wood, a new study shows.


Adding bleach makes things even worse. It causes the wood also to release chromate, another carcinogen.

The discovery could be relevant to millions of Americans: In 2007, housing industry researchers estimated that 20 million single-family homes had a deck made from CCA-treated wood. Because the wood can last up to 40 years, most of those decks are still in use, posing a continual risk of arsenic exposure.

Polluted soil

“The levels of arsenic and chromate on the surface of the boards after cleaning with bleach and in the rinse water show the potential for soil and water contamination and public health impacts,” says Julia Gress, a postdoctoral scientist in the soil and water sciences department at the University of Florida.

For the study, published in the journal Environment International, researchers used standard wipe methods to collect arsenic from the surface of wood from a 25-year-old deck from South Florida. Although the CCA-wood came from only one deck, it is representative of wood decks constructed before 2004, Gress says.

The researchers put water on the wood, then wiped it to see how much arsenic was present. They then cleaned different pieces of the decking with either tap water or a bleach-water solution, followed by pressure washing.

Water alone caused three times more arsenic to form on the surface of wet wood than dry wood, similar to the effects from morning dew or light rainfall, and the use of bleach caused formation of chromate. These chemicals were also found in levels much higher than regulatory limits in the rinse water, which can pollute the soil around decks and present an exposure risk.

Protective steps

Wood treated with CCA was used on many residential decks built before 2004 because it is highly resistant to termites. But in 2003, the US Environmental Protection Agency pressured the industry to stop using CCA to treat wood intended for use around homes, including outdoor decks, after discovering that arsenic leaches out of it.

The results highlight the importance of avoiding skin contact with wet decking, particularly right after cleaning with bleach, Gress says.

CCA wood continually leaches arsenic into the environment from normal rainfall and contaminates the soil around decks, says Lena Maa, professor of soil and water science.

Have concerns about your deck or porch? These tips can offer protection:

  • Don’t grow vegetables on soils near the CCA-treated deck.
  • Keep children and pets off of CCA-treated lumber when it’s wet.
  • After children play outside on or near a CCA-treated deck, wash their hands.
  • Don’t give children food, such as finger foods, to eat while they’re playing outside and in
    contact with the deck.
  • Remove CCA-treated materials and replace them with non-CCA lumber. If you do remove it, don’t cut it into pieces. Researchers say the sawdust is high in arsenic and will dissolve easily into the soil. They also say not to burn it. The arsenic in the smoke and ash can harm humans and animals.

This text is published here under a Creative Commons License.
Author: Brad Buck-University of Florida
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