Q: My husband and I installed a pressure-treated deck about 15 years ago. We did not know then what we know now about the chemicals and carcinogens that were used in the manufacturing process. We installed a second redwood deck on a back portion of the house about eight years ago. We’re now interested in tearing out the pressure-treated deck and replacing it with redwood for one consistent look and maintenance plan. Our questions are:

1. Is there any risk involved to people removing a pressure-treated deck? Should workers wear protective gloves or masks?

2. Because pressure-treated lumber is toxic and non-biodegradable, where is an appropriate place to dump the deck pieces once they are removed?

3. Have you heard any studies or read any anecdotes about anyone (pets included) getting sick from living with a pressure-treated deck? I ask because our dogs often chew and lick toys and bones on that deck.

A: More than 70 years ago, Karl Wolman invented a system to infuse wood with preservatives. Wood is placed in a large cylindrical tank, and the tank is depressurized to remove the air. Then chemical preservatives are pumped into the tank under high pressure, forcing the liquid preservative deep into the wood. Incisions are often cut in the wood to allow the preservative to penetrate deeper.

The result is a wood product that will not rot or decay for more than 20 years, even under the most extreme conditions.

The most common preservative used to treat wood was chromated copper arsenate, or CCA. The arsenate part of the formula refers to arsenic, an extremely toxic chemical. Concerns over safety have led to the voluntary discontinuation of the manufacture of CCA-treated wood for residential use by the industry, although CCA will continue to be used in some industrial applications.

In 2004 the use of CCA for residential use began to be stopped. Two alternative preservatives will take the place of CCA over the next several years. They are amine copper quat (ACQ) and copper azole (CA).

As with CCA, copper is the dominant ingredient in these preservatives. According to the Forest Products Laboratory of the Department of Agriculture, there is little practical difference between CCA and these alternatives.

However, ACQ and CA are more expensive, so the amount of preservative infused into wood will differ between “in-ground” and “above-ground” applications. Lumber will be marked for each application. Use it according to these guidelines.

For additional information visit the Forest Service’s Forest Products Web site, www.fpl.fs.fed.us.

Here are our answers to your questions, but before we begin, let us calm what might be a concern. Existing decks made of pressure-treated lumber pose no danger. Like asbestos, if you leave them alone, no problem.

To be doubly safe, though, be advised that CCA contained in the surface residue of treated boards is water soluble. Some of the preservative can leach from the wood when it gets wet. Application of a penetrating oil stain or sealer can encapsulate the residue and alleviate this problem.

Now to your questions. Workers who remove your deck should wear gloves, long-sleeved shirts and long pants. Wear a dust mask to avoid inhalation of any of the preservative-laden particulates. Wear safety glasses or goggles. Finally, wash work clothes separately from other laundry to avoid cross contamination.

As to disposal, do not burn the wood or mulch it. Also, try to capture any sawdust and debris resulting from the demolition and dispose of that also.

In 2004 the California Legislature passed Assembly Bill 1343 governing disposal of treated wood waste. Under this law, pressure-treated lumber may be disposed of in a hazardous-material landfill or in a composite-lined portion of a municipal landfill that meets specific requirements. Contact your local landfill to determine whether there are any restrictions to dumping your deck there.

Finally, we haven’t heard of any toxic effects on pets from playing on pressure-treated decks. However, CCA residue on the surface of treated boards is water soluble, so excessive licking of the wood itself could transfer the toxins to your pet.

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