Question: I am planning on building a deck and a children's play structure this summer. Do you advise using pressure-treated wood for these projects?
Do You Really Want to Use
Pressure Treated Wood
by Andrea Johnson
UPdate June 2000
Andrea Johnson responds: No, I do not. Chromated copper arsenate treated wood, known as pressurized or Wolmanized wood, is used extensively in outdoor construction: for play equipment and picnic tables, for planters and garden furniture, for fences, decks, porches and walkways, and for docks and wharves. This greenish coloured wood is popular because it resists rot and can last up to thirty years.
Its longevity results from the chromated copper arsenate (CCA), a pesticide registered with Health Canada's Pest Management Regulatory Agency (PMRA). Chromium is toxic to certain fungi and helps fix the preservative to the wood fibre. Copper is toxic to a wider range of fungi, and arsenic is toxic to wood-destroying insects. But chromium in that form and arsenic are also toxic to humans. Above trace concentrations chromium is carcinogenic (causes cancer) and mutagenic (alters genetic material) and arsenic is carcinogenic, mutagenic and teratogenic (produces birth defects).
The CCA wood industry, represented in Canada by the Canadian Institute for Treated Wood, claims that the process of pressure treating "fixes" or seals in the pesticides, thereby eliminating risk to humans. However, there is considerable debate over this claim. Production of safe CCA treated wood involves complex chemical reactions that can be compromised in commercial production, resulting in less than complete chemical "fixing" and increased leaching.
A study performed in 1991 for Health and Welfare Canada found that the soil under playground equipment made from treated wood had arsenic concentrations up to 24 times higher than areas just 10 metres away. Using a cloth, they wiped 10 of the structures and got measurable amounts of arsenic each time. Chromium and copper showed up, too.
David E. Stilwell, an analytic chemist at the Connecticut Agricultural Experiment Station of New Haven, measured copper, chromium and arsenic concentrations in soils collected under seven decks built with CCA treated wood. The decks ranged in age from four months to fifteen years. In all cases, the samples collected beneath the decks had significantly higher concentrations than soil collected 5 metres away from the decks. Stilwell is now working on a playground exposure study. Thus far it indicates that the use of CCA treated wood should be avoided wherever possible in the playground, especially on surfaces children touch regularly.
Staining or painting CCA treated wood may reduce leaching in the short term but not over the long term. Part of the commercial process involves incising the wood to saturate it with pesticides. These incisions make sealing the wood impossible.
How much exposure to CCA is safe? It is hard to determine. There are several shortcomings in the testing procedures that PMRA employs for CCA and other pesticides. First, industry, not independent researchers supplies the scientific studies and trials. Second, tests for pesticides are performed on animals, not humans. Third, human tolerance levels for pesticides are set for adult males, not women and children. Children are especially vulnerable to pesticides due to their small size and less mature detoxifying systems. Finally, tests look at only short term, single pesticide exposure, not long term, cumulative or multiple exposure. But people use their decks and play structures daily, year in and year out. Families sit, lie, and eat on decks; children touch deck and play structures, then put their fingers in their mouths; toddlers chew on the railings and eat the dirt that is under and around these structures.
The Canadian Mortgage and Housing Corporation, in their publication Building Materials for the Environmentally Hypersensitive, advises that "some of the chemicals may not be fixed and can leach out. A white surface residue indicates that CCA precipitated out of the solution. The environmentally hypersensitive should not use this material."
What can be safely used instead of CCA treated wood ? For decks, cedar, a naturally rot-resistant species is an option. Tamarack is a low-priced softwood that is plentiful in Nova Scotia. It is harder and more durable than spruce. Hemlock is also a viable substitute but tends to splinter. Spruce, tamarack or hemlock deck posts can be protected against rot and insects with boron rods, which are inserted into holes drilled at an angle and sealed with wood or plastic plugs. These rods are less toxic than CCA, but children will still try to eat them if they pry them out. I do not recommend them for play structure posts. Untreated wood decks can be finished with an environmentally friendly sealant, such as Weather Bos, a vegetable resin-based product. Play structures can be built with non-splintering softwoods or recycled plastic lumber. Longevity is not the major concern for play structures' safety is. I recommend no finish for play structures, but if one is desired, use a non-toxic interior oil and reapply each year.
Andrea Johnson is an artist and writer living in Halifax, NS. In 1996, she was diagnosed with chromium and arsenic poisoning caused by contact with a porch newly constructed from CCA treated wood. Since then she has researched and written about the safety of CCA treated wood. The above is an excerpt from "Do You Really Want To Use Treated Wood?" published in Between the Issues, Winter 1999.