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Pressure-treated Wood - Arsenic and Old Decks

By HHI Staff

Pressure-treated wood impregnated with chromated copper arsenate (CCA) - often with a greenish tint - was widely used for decks and porches prior to its being discontinued for residential use in 2003-2004. Since treated wood has a long lifespan, there is still plenty of CCA pressure-treated wood surrounding residences, prompting caution due to its arsenic content.


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Avoid breathing sawdust from treated wood, wash exposed hands thoroughly before eating, and wash exposed garments separately from other clothing. Dangers to small children crawling around on a CCA-treated wood deck or playground equipment seem likely; so either seal the wood or keep children away from these surfaces. 


Arsenic Tracked in from Chromated Copper Arsenate-Treated Decks



Arsenic is a known carcinogen. It is also known to be readily dislodgeable from chromated copper arsenate (CCA)-treated lumber. The floors of in-service homes were tested for inorganic arsenic using a wipe method similar to the U.S. Housing and Urban Development (HUD) method for lead dust clearance sampling. Additionally, a hand-sampling method was used that involved direct dermal contact with the indoor floor surface. Amount of dislodgeable arsenic on the decks was highly correlated with arsenic concentrations on the indoor floors. Indoor arsenic concentrations were highest directly adjacent to the door. Concentrations in samples taken from the middle of rooms were less than half the concentrations of door samples, while concentrations in samples taken from untrodden floor space in the corners were mostly below the method detection limit. At a home without a CCA-treated deck, no measurable arsenic was found.


Source: Jan/Feb 2010 Journal of Environmental Health


Copper, chromium, and arsenic have all been found in the soil under CCA-treated wood decks; evidence that the chemicals leached out of the wood and/or from sawdust when the decks were originally built. Researchers have measured the concentration of arsenic in the soil under these decks at over seven times the level allowed by the EPA for land application of sewage sludge.


How is Wood Pressure-Treated?

Wood boards are soaked in a large pressurized cylindrical tank of treatment chemicals that penetrate deep into the wood.


CCA-treated wood is resistant to most mold and decay organisms, and to termites. Treated wood was also sometimes used to construct basement walls. In such houses, traces of arsenic dust have been found in the basements.  


ACQ treatment is less toxic than products containing arsenic or chromium. ACQ contains ammonia, copper and “quat” (quaternary ammonia, a disinfecting agent, to preserve the wood). While it is not as innocuous as boron-based compounds (see below), it creates far less toxic waste than arsenic- or chromium-containing products. Because it will not leech out of the wood in damp environments, ACQ-treated wood can be used in contact with the soil and where it will be exposed to the weather—something that is not possible with the boron-based treatments.


Copper azone (CA) is another treatment that is considered less toxic than CCA. Micronized copper and azole are also being used to pressure treat wood products. One treatment system (Osmose, Inc.) forces tiny copper particles into the wood, and has been certified by Scientific Certification Systems (SCS) as environmentally preferable.

Water-soluble boron compounds

Boron compounds (e.g. borax and boric acid) have been widely used as less-toxic insecticides over the years. Tim-Bor (Nisus Corp.) is a boron-based wood treatment, consisting of a disodium-octaborate-tetrahydrate powder that, when mixed with water, can be applied to wood (by spraying, dipping, or soaking) as a permanent treatment. It works well at deterring termites, carpenter ants, mold, and decay organisms. More than a surface coating, this preservative will actually migrate toward the heart of the wood. It is probably no more toxic to humans than borax and, while it shouldn’t be ingested, it doesn’t outgas.


NiBor-D is a similar product, manufactured by Nisus Corp. It is made of the same disodium-octaborate-tetrahydrate powder as Tim-Bor, but it has slightly different labeling. This company also makes a Bora-Care product which is NiBor-D (disodium-octaborate-tetrahydrate powder) in a glycol solution. Because of the glycol, it has a mild odor when wet that can bother some sensitive individuals. In addition, they have a concentrated version of Bora-Care called Jecta that is packaged in a 30 cc syringe and can be injected into small holes drilled into wood. Jecta is particularly useful for wood that has a water-resistant coating.


These boron-based products require a certain amount of moisture to be able to penetrate into wood effectively. Therefore, Tim-Bor and NiBor-D (which are mixed with water) will penetrate damp wood more easily and effectively than dry wood. On the other hand, Bora-Care (which is in a glycol solution) will readily penetrate dry wood. The manufacturer recommends Bora-Care for treating an active termite infestation because it be will more likely to penetrate all the way through the wood.


NiBor-D and Tim-Bor are often well-tolerated by sensitive people—even when wet. In the past, Tim-Bor was classified as a registered pesticide, and it had to be applied by a certified applicator but that is no longer the case, and it can now be applied by contractors and homeowners. Termite-Prufe (Copper Brite, Inc.) is the same disodium-octaborate-tetrahydrate powder, and it is typically sold in one-pound cans in hardware stores.


A disadvantage to these boron compounds is the fact that they will remain water soluble—so they can’t be used on wood that will be in contact with the soil, or outdoors where the wood will be exposed to the weather. In new house construction, they are typically applied to all the framing lumber once a house has been protected from the weather with roofing and siding. In existing construction, it’s easy to spray exposed wood in attics and crawl spaces, but wood inside the walls is difficult—sometimes impossible—to access.


(Parts of this article are from the archives of the original Healthy House Institute, and the information was believed accurate at the time of writing.)
(Note: The views expressed in this article are those of the author, and do not necessarily represent those of The Healthy House Institute, LLC.)



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Pressure-treated Wood - Arsenic and Old Decks:  Created on April 27th, 2009.  Last Modified on February 28th, 2011


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