Blog Post

The Toxic Chemicals that Lurk in Unfinished Wood Floors

One might think that an unfinished wood floor is devoid of synthetic chemicals. It sure looks that way--but toxic preservatives may lie in plain sight.

Moist lumber is susceptible to fungal staining. This staining does not cause physical decay, but it looks bad. Commonly called "blue stain," the offending fungi may be yellow, orange, purple, gray, or red in addition to shades of blue. The stain penetrates into the sapwood and cannot be removed by resurfacing.

Lumber mills can prevent these blemishes without chemical treatment through standard air-drying practices or, especially in moist climates, kiln drying. 

However, a lot of lumber is treated with biocides called anti-sapstain treatments. While preventing visible blemishes, these can disfigure the toxicological profile of an otherwise benign product.

What is this stuff?

Anti-sapstain formulations have been used for millennia. Egyptians used powdered subcarbonate of soda to prevent the staining of papyrus, according to independent wood scientist Mike Freeman. During the Shang Dynasty in China, wood ash dissolved in water was used to prevent mildew growth on chopsticks.

These treatments grew more potent, and toxic, over the centuries. A couple hundred years ago, mercury was introduced. Then formulators found that blending compounds of mercury with chlorophenates (such as pentachlorophenol) was phenomenally effective.


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Today's treatments aren't as bad as their predecessors

Fortunately, today's anti-sapstains used to treat lumber for wood flooring are not quite as poisonous as their mercury-based predecessors--but these biocides still introduce unnecessary, toxic chemicals into outdoor and indoor environments.

In my role as senior researcher for the Pharos Project, I stumbled upon these treatments while we prepared our opening set of wood flooring evaluations. I was looking for examples of unfinished solid wood flooring. We hoped that this would be a pretty straightforward category to evaluate: the main differences between products, we assumed, would be species and harvesting practices, such as whether or not the wood was sourced from an FSC-certified forest. But one company's website complicated matters.

Middle Tennessee Lumber sells unfinished hardwood flooring, and its website includes a helpful slideshow of its production process. The first slide shows the lumber in a chemical bath, with the caption: "We treat our green lumber with a special non-toxic solution that protects our boards from fungal infestation during the drying process."

Well, dang, I thought. There goes our hope for a clean review. I dug around for more information. I asked wood flooring companies for details on these chemical baths, how prevalent they are in the industry, and how "non-toxic" these solutions are. Believe me, there was no one-stop shop for this kind of information.

Some companies were more helpful than others. One wood flooring association executive told me by email, "I have talked to some unfinished hardwood flooring

manufacturers and they have no knowledge of this anti-sapstain treatment." Maybe he was telling the truth, maybe not--but one company was forthcoming, and even emailed labels of the typical products used in the industry. From there, I developed a profile of the ingredients of these treatments.   [see for the details]

Common active ingredients include 3-iodo-2-propynyl-butylcarbamate (IPBC), propiconazole, isothiazilines, and ammonium chlorides. These mixtures may also contain solvents and chlorothalonil. Many wood companies--particularly those in British Columbia--use borate mixtures such as borax and sodium carbonate.

How we can be exposed

These chemicals are biocides, which means they attack living organisms. It should not be surprising, then, that conventional anti-sapstain treatments are toxic to aquatic organisms and mammals, including humans.

The chemical application process introduces the first potential emission pathway for these toxicants. A German Federal Environment Agency study published just last month states that these surface treatments "may result in significant emissions. . . . Wood preservatives may be released to soil or water if the treated wood is dripping, either during or shortly after application."

An emissions scenario report from the Organization for Economic Co-operation and Development notes that emissions may also come from evaporations from the open baths, wind dispersal of dried salts, and discharges from the dipping tank.

Additional exposures may occur during the storage of treated lumber, where, the German agency states, "wood preservatives may be washed out of treated wood by precipitation, resulting in contamination of soil, groundwater and/or surface water."

The problems continue after installation

Potential exposures continue after treated flooring is installed indoors. Interior air is the "primary receiving environmental compartment" for treated floors, according to the German study. Biocidal treatments are long-lasting, and exposures may continue through the service life of treated floors.

There is currently very limited literature available on indoor exposures to the preservatives used on interior wood products. However, we can look at studies of historical treatments, especially pentachlorophenol (PCP), to inform our understanding of potential human health exposures. 

One study from a Polish environmental institute found that "PCP concentrations in indoor air can be expected to reach 30  µg/m3 during the first month after treatment. Considerably higher levels, up to 160  µg/m3, have been reported in houses with concomitant poor indoor ventilation. . . . (Residues in) uncovered floors may present a relatively important exposure route for infants and toddlers."

This indicates that modern wood preservatives can introduce reproductive toxicants (like sodium tetraborate pentahydrate), developmental toxicants (like propiconazole), and carcinogens (such as sodium o-phenylphenate) into the air in homes and workplaces.

Albino fungi to the rescue

But are these chemicals really necessary?  If kiln drying is not enough to prevent lumber from staining, then there may be a benign biological solution.  It may be possible to fight fungi with fungi.

Korean scientists are studying developed a strain of colorless fungal products--using natural mating techniques, not mutation or genetic engineering--that could supplant these chemical treatments.

The albino Ophiostoma piliferum fungus is a commercially available product, marketed under the trade name Cartapip. In 2003, scientists from the University of Minnesota and the University of Waikato (New Zealand) reported that by "applying a colorless strain of Ophiostoma to freshly cut logs, the fungus can preferentially colonize the sapwood, thereby capturing nutrient resources and inhibiting subsequent colonization by dark staining fungi."

The team noted that "sapstain has traditionally been controlled with anti-sapstain chemicals; however, toxicity concerns and the environmental effects of many chemicals used have prompted the search for alternative methods of control. Biological control using albino strains of sapstaining fungi is a new method that can be used."

Market pressure

Whether or not this all-natural method of preventing sapstain in freshly cut lumber takes off and replaces known hazardous chemicals depends largely on marketplace demand.

That's why we are raising this previously obscure issue, both in the Pharos Project, where we evaluate all new wood flooring in the system as containing these unhealthy chemicals barring any manufacturer evidence to the contrary, and in GreenSpec Insights.

I hope this information helps to kick-start a consumer/manufacturer dialogue resulting in a marketplace transformation that removes the toxics from unfinished wood flooring.

Published April 18, 2012

(2012, April 18). The Toxic Chemicals that Lurk in Unfinished Wood Floors. Retrieved from

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May 8, 2012 - 4:05 pm

As a chemically sensitive person, hoping to build and green and HEALTHY house one day (if I get the money), I am more scared of wood than I was previously.  How is the average consumer supposed to know what is or isn't in the lumber they're comtemplating using as a building material?  This is why I am seriously thinking of avoiding wood as much as possible in my future healthy house.

April 19, 2012 - 5:28 am

Thanks for the heads up. This is yet one more reason to deal with small, local sawmills rather than unknown chain of custody wood industry products.

In New England, old-time sawyers know to stop milling white pine when the weather gets too warm and humid to avoid blue stain, and to shift to spruce and hemlock. Today, we tend to substitute chemical "solutions" for common sense.