What is pressure-treated wood?
Pressure-treated lumber is typically a green-coloured wood that is commonly used in the construction of residential housing, decks, fences, play structures, picnic tables, patios and other outdoor structures.
It is called "pressure-treated" because it has been injected with a chemical preservative that makes the wood resistant to decay and insect damage. Such treatment can make some types of wood last up to 10 times longer than they would normally.
Currently, most pressure-treated lumber contains the pesticide chromated copper arsenate (CCA). The copper in CCA serves as a fungicide, the arsenic kills insects and marine pests, and the chromium helps bind these chemicals in the wood.
Since pesticides are toxic, it is important to handle pressure-treated lumber in a way that will reduce human exposure to these chemicals, and minimize their release into the environment.
What is the concern?
Timber awaiting fixation process completion.
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Waterborne preservatives like CCA are bonded tightly to the wood during a chemical process called fixation–so leaching is minimal under normal usage conditions. However, very small quantities of arsenic, copper and chromium can migrate out of CCA-treated wood over time.
As a result, these chemicals can be released into the ground and groundwater, and can rub off onto the skin of animals and humans that come in contact with the wood. The burning of pressure-treated wood releases hazardous chemicals into the air, and concentrates them in burned ash.
Arsenic and chromium are chemical elements that occur naturally in the environment, and that do not break down. They are also the most toxic components of CCA-treated wood. Long-term exposure to arsenic can cause cancer, while signs of acute arsenic toxicity include stomach upset, weakened blood vessels and nerve damage.
Children may be at a higher risk of exposure, because they are more likely to have skin contact with treated wood and are more likely to ingest residue on their hands that has been picked up from wood surfaces or the ground. They are also more vulnerable to the toxic effects of most chemicals.
The amount of arsenic released from CCA-treated lumber is very low, and has not been deemed an unreasonable risk to the public or the environment by either Health Canada's Pest Management Regulatory Agency (PMRA) or the United States Environmental Protection Agency (EPA). Neither Agency recommends removing existing structures made from CCA-treated wood.
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Fast Facts
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The Commission of European Communities is currently considering similar restrictions to those recently announced in Canada and the United States. Switzerland, Vietnam and Indonesia have banned CCA-treated wood, while Japan, Denmark, Germany, Australia and New Zealand have limited its use or proposed restrictions.
Some wood species, like cedar and redwood, are naturally decay resistant, while spruce and pine deteriorate more rapidly. Chemical wood preservatives enhance wood durability, and can increase the life expectancy of wood by five to 10 times.
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Related Sites
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Health Canada - Pest Management Regulatory Agency
CCA Fact sheet
(June 2003 - .pdf format, 92KB)
PMRA Points (April 2002 - .pdf format, 41KB)
Consumer Safety Information Sheet on CCA-Preserved Wood
Environment Canada Wood Preservation Web site
Canadian Cancer Society: Pressure-treated lumber and cancer risk
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In the News
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Playgrounds test high for arsenic: study (CBC, Jan 15, 2003)
Arsenic Lingers in Treated Wood (Washington Post, Aug 29, 2002)
Panel Finds No Danger From Playground Wood (ENS, Aug 8, 2002)
Attention : patios à l'arsenic
(Le Point, July 11, 2002, French only)
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EnviroZine Articles
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What can be used to seal or paint a pressure-treated wooden play structure to make it safe?
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What is being done
Warning Label for CCA-treated wood.
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Since arsenic is a known carcinogen, any reduction in the levels of potential exposure to this toxic chemical is desirable. As such, steps are being taken to phase out the use of CCA-treated wood in Canada and the United States.
Canadian manufacturers of pressure-treated lumber voluntarily agreed to stop using chromated copper arsenate as a preservative in wood for consumer use by December 31, 2003. In the meantime, warning labels will be affixed to all CCA-treated lumber in order to inform consumers of proper handling methods. A similar agreement has been made by American manufacturers and the EPA.
The PMRA and U.S. EPA are currently conducting a joint CCA risk assessment, and will present the final results for public comment later this year. The PMRA is also reviewing alternative wood preservatives on a priority basis. Four of these are now available in Canada: copper azole, copper citrate, and both amine and ammoniacal forms of alkaline copper quaternary.
Safe handling and use
The safe handling and use of CCA-treated wood—or any other material that contains hazardous chemicals—is simple. Health Canada and Environment Canada offer the following tips:
- Never burn treated wood.
- Wear gloves and long sleeves when handling treated wood. If your project includes cutting or sanding, wear eye protection and a dust mask, and work outdoors.
- Wash hands after working with the wood and before eating or drinking.
- Do not use treated wood where it will come into direct contact with food (e.g., cutting boards).
- Do not use treated wood or wood scraps where they could enter the food chain (e.g., feed storage, silos, water troughs, compost, mulch, wood chips).
- Avoid using deck bleaches and cleaners on CCA-treated structures, as these may affect the release of wood-preservative chemicals.
- Some studies suggest that applying penetrating coatings (e.g. oil-based, semi-transparent stains) every year or two may reduce the migration of preservative chemicals from CCA-treated wood.
- Contact your local or provincial government for information on how to properly dispose of this material in your community.
For further information, consult the Consumer Information Sheet on CCA-Preserved Wood at www.ccasafetyinfo.ca, or contact Health Canada's Pest Management Regulatory Agency at 1-800-267-6315.
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