CORVALLIS, Ore. - Wooden decks, trellises and play structures can be important elements in your garden, both beautiful and useful. You’d probably also like to know they’re safe.
In climates with wet winters, and even sometimes wet summers, wood tends to rot. Unprotected wooden structures eventually fall apart, making them safety hazards even before the problem is noticeable to the eye. So for generations, wood for outdoor use has been treated with chemicals in a pressure process to discourage insects, mold and rot.
Until recently, the chemical most commonly used to preserve wood used outdoors was chromated copper arsenate, also known as CCA, according to the National Pesticide Information Center (NPIC), a cooperative effort between Oregon State University Extension Service and the U.S. Environmental Protection Agency. This wood is also called “pressure treated wood.”
In 2004 the US Environmental Protection Agency banned the use of CCA to preserve wood for residential use. An exception is that it can still be used for permanent wood foundations. And CCA-treated lumber is still available for industrial uses. New EPA-approved chemicals without arsenic have replaced CCA for home and garden use.
Arsenate is a form of arsenic, a substance that is present naturally at low levels in soils and at even lower, trace levels in water, food and air. Over a period of time, rain can leach arsenic from CCA-treated wood and potentially result in arsenic levels in the underlying soils, which might not be safe.
Arsenic was cheap. Most of new chemicals rely on copper, which isn’t cheap. So to keep the cost reasonable, lumber now is treated according to its intended use, with the copper content in the preserving chemicals varying from around 20 to 95 percent. The price also varies accordingly.
So, before you start buying lumber, be sure you know what it is to be used for. Tags listing appropriate end-use categories are stapled to the ends of the boards. For instance, wood labeled “Decking” is treated to a lower (and consequently less expensive) level of protection than wood labeled simply “For Above Ground Use.” The type of preservative is also listed on the tag.
Meanwhile, what should you do about your deck and play structures that were built 10 years ago, presumably with CCA-treated wood?
First, explains NPIC, it’s actual ingestion of arsenic that poses a risk. Breathing the air from around CCA-treated wood won’t poison you. As for absorbing it through the skin, while not impossible, it’s not likely during amounts of contact that are realistic.
So give some thought about how your structures are being used.
Do you have small children, say under 6 years old, playing on them frequently? NPIC explains that children in this age group generally have a lot more “hand to mouth activity” than the rest of us.
Of course, older children, while they may put their hands in their mouths less often, may also be playing on CCA-treated structures at playgrounds, at school and at friends’ houses. They also play more vigorously and might be more likely to dislodge minute bits of the wood.
Pay attention to ground surface under the play structure or deck, where particles of wood may have settled. Is the area under the deck accessible? Or even an attractive place for children to play?
Many people wonder about the safety of using pressure treated wood raised garden beds to grow vegetables or fruits. A study conducted by University of Minnesota found that vegetable crops grown in CCA-framed garden beds can accumulate arsenic from treated wood, but based on U.S. Public Health Standards, these vegetables would be safe for human consumption. To be on the safe side, you can line garden beds made of CCA-treated wood with plastic sheeting on the base and sides of the bed to separate the wood from the soil. For more information, see: http://www.extension.umn.edu/yardandgarden/YGLNews/YGLN-June0101.html#as and http://www.toronto.ca/health/factsheet_ptw.htm
Here are some simple measures you can take to reduce any potential risk from CCA in your garden:
- To minimize leaching, apply a sealant to CCA-treated wood regularly, as recommended by the wood manufacturer. Sealants also reduce the amount of arsenic that repeated or prolonged contact with the wood can leave on the skin.
- If possible, don’t encourage children to play under decks.
- Put a heavy layer of sand in areas where children play under CCA-treated wood. Arsenic doesn’t bind to sand. Any arsenic leached from above in rainwater washes through the sand and binds to the soil underneath.
- Wash children’s hands when they’re through playing. Be sure small children don’t habitually put their mouths on the wood or eat the soil.
- Wash your hands after working with CCA-treated wood.
- Don’t burn CCA-treated wood.
- Don’t use CCA-treated wood for bark or mulch.
- Take precautions when sanding or sawing CCA-treated wood. See the EPA Consumer Safety Information Sheet on using CCA-treated wood.
While the new generation of chemicals won’t bring arsenic into your garden, they may pose other problems. The higher copper content makes them more corrosive to some metals. So do some homework before you build. Some preservative treatments rely on borate rather than copper.
For more information, you can contact NPIC at 1-800-858-7378, or email.