April 16th, 2012
Econintersect: Chemical treatment of lumber to preserve it in hostile outdoor environments, such as exposure to dampness or actual direct water exposure, is generally believed to be safe. But the chemicals used to preserve wood from decay can leach out, where they can be toxic to bugs and other creatures that are in the vicinity. When these chemicals leach into surrounding soil they can persist there for long periods of time. Michigan Technical University has developed a process that uses nanotech particles of wood preservatives to reduce the leaching of those chemical by 90%. The value of this new development is difficult to evaluate because, even after decades of use, the dangers associated with the use of wood preservatives are simply not well understood. There are many suspicions but few proven facts. (Note: The caption photo presents an image perspective reversal dilemma. Click on photo to see larger image which makes the dilemma resolution easier.)
Follow up:Here is an excerpt from a story on the nanoparticle wood treatment process at GizMag:
[The process] encapsulated tiny droplets of the fungicide tebuconazole within spherical nanoparticles. The spheres were chemically modified to work with the fungicide, and were made from either gelatin or chitosan – the latter material is derived from chitin, the main component of the exoskeleton of crustaceans, and has been used in everything from self-healing paint to a flu virus filter to a biocompatible transistor.
Just how dangerous the chemicals are that are (and have been) used to pressure treat lumber is very much an open question. Here is what The Natural Handyman has to say:
Your local home store or lumberyard is now selling lumber treated with less toxic alternatives... amine copper quat (ACQ) and copper azole(CA)... though you may find other chemical combinations in specific areas. The reason these new copper-based alternatives are considered safer than arsenic-based preservatives is based on the human body's inability to absorb these poisons. Inorganic arsenic is readily absorbable by the body.
Whether these new chemicals will turn out to be less hazardous in the long term is anyone's guess, but all indications are that they will be. Fingers crossed!
The newer preservative chemicals are much more expensive than the older most common compound used before 2004, so manufacturers try to use less of it. That leads to at least 12 different grades of treated wood product today and makes choosing the correct wood for each application a process that requires greater care.
The most common preservative in use until 2003-4 was chromated copper arsenate (CCA) Here is a summary from HESIS ( California Health Evaluation System and Information Service) as of the date of the latest documentation (2008) on the risks and associated with and the precautions recommended for CCA:
Health Hazard Summary: Wood preservatives that contain arsenic or chromates can cause effects similar to those caused by exposure to pure inorganic arsenic or chromate compounds. Overexposure to inorganic arsenic or chromate compounds can irritate the eyes, nose, throat, lungs, and skin, and can cause lung cancer. Inorganic arsenic can damage the nervous system and can cause skin cancer.
Also from HESIS the following is the history of the personal protection information history for CCA (emphasis added by Econintersect). Note: The date of the document is 2008, 24 years after the reference date of 1984.
In July 1984, the US Environmental Protection Agency (EPA), which regulates the use of pesticides (including wood preservatives) proposed new regulations on the use of preserved wood products. These regulations have not yet gone into effect. The following recommendations are based upon the EPA proposal.
Skin: To prevent skin contamination when handling and sawing wood, it is a good work practice to wear gloves made of a material, such as rubber, which is resistant to inorganic arsenicals and chromates, although the EPA has concluded that arsenic from treated wood is not absorbed through the skin.
After using treated wood products, wash thoroughly before eating, drinking, or smoking. If oily wood preservatives or sawdust accumulate on clothes, launder before re-use. Wash work clothes separately from other clothing.
Eyes: When power sawing or sanding, wear goggles to protect your eyes from flying particles.
Respiratory: Dust masks, well sealed around the face, should be worn when sawing or sanding treated wood. In order to avoid indoor accumulation of sawdust from treated wood, sawing and sanding should be performed outside, if possible.
Substitution: One way to control hazardous exposures is to use safer chemicals in place of more toxic ones. However, the health and safety hazards of substitutes must also be carefully considered, to ensure that they are actually safer.
Wood preservatives are necessary in moist climates where wood rarely dries out or in areas where wood contacts soil.
Water repellants may be an adequate substitute in above-ground applications where there is less risk of rot.
In addition to water repellants, there are some products (polyurethane or epoxy sealers) that soak into the wood and slow down the process that allows the wood preservative to free itself from the wood and accumulate on the surfaces.
Copper-8-quinolinate and copper naphthenate are less toxic wood preservatives than the arsenic-containing products; however, their toxicity has not been well studied.
It is difficult to determine just how the nanotech process will impact the wood treatment industry. The determination of what will be the best business model is complicated by the fact that the dangers associated with and the regulations needed for the use of the previous technologies have never been settled. Another question that has not been discussed in what Econintersect has found published as of this date are the costs involved:
- How expensive is the nanotech process?
- Does the reduced leaching mean that much less of the expensive treatment chemicals can be used?
- Can nanotech processing mean that more toxic chemicals that have been phased out (or never before used) are now safe options?
Editorial Note: If the original concerns about CCA are still not settled after 28 years can there be much hope that there will be definitive information about the new nanotechnology soon?
- Keeping Wood Preservatives Where they Belong: In the Wood (Marcia Goodrich, Michigan Tech News, 6 April 2012)
- Nanotech greatly reduces leaching in pressure-treated lumber (Ben Coxworth, Gizmag, 12 April 2012)
- Pressure-Treated Wood - Its Uses, Limitations and Safety Considerations (The Natural Handyman, October 2010)
- HESIS Fact Sheet (California Health Evaluation System and Information Service, 6 May 2008)
- Chromated Copper Arsenate (CCA) (Wikipedia)