Q. Dear Umbra,

We are tearing down an old children’s play set and we are wondering what to do with the treated lumber. We will reuse what we can in other projects, but we are wondering if it’s safe to burn?

Andrea S.
Elgin, Ill.

A. Dearest Andrea,

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Pardon my alarm. It’s just that burning treated wood, no matter what the treatment was, is never a good idea. So please, put down the lighter and let’s chat about your lumber liquidation problem.

Every source I consulted — from university extension services to state environmental agencies to the good old EPA — strongly advises against burning planks like the ones in your old play set because doing so releases toxic chemicals. You see, the point of treating lumber in the first place is to keep wood-destroying bugs, molds, and fungi at bay, so the treatments we use are actually pesticides and fungicides, toxic by nature. True, some wood treatments are safer than others, but none are safe enough to unleash in the smoke of a backyard bonfire.

What sort of chemicals are we talking here?, you might be thinking right about now. Well, Andrea, the answer depends on how old this old play set is. If it was built before 2004, it’s likely the wood was treated with chromated copper arsenate (CCA), a real baddie in the chemical world. Its building blocks, as you might guess by the name, are copper, chromium, and arsenic; the latter two are highly poisonous, cancer-causing substances. There’s evidence that arsenic from CCA leaches into the surrounding soil and even that you can be exposed by touching treated wood — so you definitely don’t want to burn it. Kind of mind-boggling that we used to use the stuff on children’s playground equipment, isn’t it?

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Fortunately, CCA was phased out more than a decade ago and replaced with several safer alternatives. The most common treatment now is alkaline copper quaternary (ACQ), which leaves the worst parts of CCA behind. It’s water-based and considered less toxic than the treatments of the bad old days, but the copper in it is still dangerous for aquatic critters, so you don’t want to use it anywhere near waterways. And again, don’t burn it.

What, then, should you do with all this lumber? Despite the dangers I’ve just been spouting, it might still be okay for you to reuse your boards in other projects. In cases such as this, the benefits of reuse (keeping new trees out of the lumber market, diverting the old wood from the waste stream) must be carefully weighed against the risks. If you do decide to tap it for another home use, just be careful about where you put it: Federal guidelines have it that treated lumber should be kept clear of drinking water and human or animal food (so no garden boxes or cutting boards, please). I’d add that it’s probably a good idea to keep it away from anything young’uns might routinely touch, what with their hand-to-mouth habits. And make sure to take care of yourself during any construction, Andrea: Wear goggles and a dust mask if you’re sawing any wood, and wash your hands well after dealing with it.

Beyond that, unfortunately, your next best option for disposal is the landfill. Untreated lumber can often be recycled into mulch or wood chips, but that’s not a good idea with chemical-soaked planks, for obvious reasons. Some cities will haul away small amounts with your garbage, and others might require dropping it off with construction and demolition debris; give your neighborhood waste management company a call and find out what’s best in your neck of the woods.

I hope I haven’t been too much of a downer. Because I’m excited for you to enjoy your new patch of backyard! Do you have plans for it yet? If not, may I suggest a lovely raised-bed veggie garden (constructed with non-treated wood, that is)? Or how about a compost pile? Staging area for interpretive dance about the climate crisis? Oh, the possibilities.