Arsenic and Old Wood (A Second Look, Part Two)
- Oily preservatives (creosote)
- Solvent-soluble organic chemicals (penta)
This month, we'll take a hard look at the third class: water-soluble salts. Due to the EPA restrictions on the use of creosote and penta as preservative treatments for wood, water-soluble salt treatments have become dominate. There are several types but the most common are:
- Ammonial copper arsenate
- Chromated copper arsenate
Not dead yetThough CCA ceased production for residential and some commercial use, as of December 2003, existing inventories of CCA treated lumber were sold through December 2004. In effect, this made the year past, the transition/test period for the adaptation of alternative preservative treatments. CCA treated wood will not cease to be produced entirely, it will still be available for industrial, highway and agricultural applications.
Common to both ACA and CCA are arsenic compounds. Particularly troubling is the white powder that often covers the surface of CCA treated wood-this is arsenic in powder form. Information sheets distributed with the sale of CCA lumber warn against breathing the sawdust while cutting it, food contamination, splinters, washing exposed skin thoroughly and work clothes separately. Moisture in the form of wet wood or perspiration helps the skin absorb the arsenic powder if present on the surface of the treated wood.
This problem is particularly acute if the lumber was treated in cold weather-especially in freezing temperatures. At 70 degrees F, CCA sets in wood in three to four days. If applied when the temperature is below 50 degrees F, the setting process can take several weeks. No setting of CCA in wood will occur if applied in sub-freezing temperatures.
The ban on CCA came as a result of voluntary action on the part of the treated wood chemical suppliers in cooperation with the EPA. Studies revealed that CCA leaches from treated wood as the result of rainwater. Such leaching can/does leave a residue of arsenic on the wood's surface as described above and will contaminate soil in close proximity. Research has revealed that all three compounds of CCA (chromium, copper and arsenic) are found in soil below CCA treated decks at seven times the EPA's allowable level. Though some of these elevated levels may be due to sawdust and/or shavings containing CCA contaminated soil below the deck during the construction process, more likely as the evidence reveals, it is due to leaching aggravated by acid rain.
Hidden dangerWater-soluble salt treatments, such as CCA, are resistant to termites, most mold species and decay organisms-that is why it was preservative treatment of choice of the construction industry for many decades. With a life cycle of plus or minus 30 years, it found a use for the construction of foundation/basement walls. When used in this way, traces of arsenic dust can be found on the surface of basement walls and in the surrounding soil as the result of leaching.
Playground equipment, wood decks, picnic tables, etc., when given "swipe tests," often reveal the presence of arsenic residue if treated with CCA. Splinters from such surfaces are especially dangerous, therefore avoid touching or walking barefoot on CCA treated wood. One worker who cut CCA treated wood daily as part of his job sued the manufacturers of the chemicals used in conjunction with CCA and was awarded $667,000. Now on 100-percent disability, he suffered terribly from a host of symptoms including:
- Vomiting blood
- Hair loss
Troubling also is the fact that an estimated 2.5 million board feet of CCA treated lumber is disposed of annually in landfills. As it does in subsurface applications, such as basement walls and deck posts, it has the potential to leach arsenic into the surrounding soil.
Silver bullet?CCA was never a silver bullet for protecting wood from rot, decay and insect infestation. Some hardy fungi can live and thrive in water-soluble salt treated lumber by consuming the arsenic itself as its food source. Arsinc, an arsenical gas with a garlic-like odor, is released when such fungi take root in salt treated wood. As well, the CCA treatment does not extend to the center or "heart of the wood." Termite species, such as the formosan subterranean termite, are voracious foragers and will test chemical barriers.
Typically, they will enter and bore through the untreated cut ends of CCA treated wood and devour all untreated wood in their path. Another problem is the type of lumber now most commonly used for framing southern yellow pine. Since yellow pine is subject to cracking, cupping, warping and splitting, it typically requires a water-resistant coating. Such a coating will prevent CCA from properly penetrating the wood's surface. Cracks and splits also provide a pathway for carpenter ants and termites.
Unlike the new breed of copper-based water-soluble salt treatments, CCA was never associated with the kind of corrosive effects these newcomers have demonstrated. Testing for corrosion has shown that ammonium copper quaternary and copper azole corrode even-galvanized metal-at a much higher rate than CCA. ACQ, like CCA, contains chromium and copper but not arsenic, thus it is less toxic.
The "carrier" or disinfecting agent providing the preservative in ACQ and substituting for arsenic is "quat" or quaternary ammonia (ethanolamine is also used). Distributed by Chemical Specialties Inc., it has a green label from the Scientific Certification Systems and is acceptable for outdoor use where it will not leach-out when in contact with soil or exposure to the elements. Some brand names for ACQ are Preserve/Preserve Plus, NatureWood and AC2.
Because of the demonstrated corrosive effects of CCA's replacements, such as ACQ, many structural connector manufacturers have upgraded their hot-dipped galvanizing coating weights from the standard G-60 (0.60 ounces of zinc per square foot) to G-90 which is used for especially corrosive environments like ocean-fronts.
Like G-60, this HDG process is an "after-fabrication" application for corrosion protection of items, such as connectors, anchors, plates, fasteners and framing components, etc. G-60 has been known to work well in non-corrosive environments but this is a subjective term. Corrosion is dependent on many variables, most of which are directly related to the environment (acid rain, animal waste, agricultural chemicals and fertilizers, ocean air/salt-spray, preservative, fire wood chemical treatments, swimming pool chemicals, alternating wet/dry conditions).
Like unto likeSome connector/fastener manufacturers, such as Simpson Strong-Tie, have issued warnings concerning the corrosive effects of some of the alternative wood preservative treatments, such as ACQ. One manufacturer, USP Connector, advocates and recommends that a G-185 (1.85 ounces of zinc per square foot) triple zinc coating (per ASTM A653) be applied for outdoor applications. Approximately three times the amount of zinc as standard grade G-60 (two times G-90) is used in this "pre-fabrication process," whereby the corrosion protection aspects of zinc are made integral with the base metal rather than simply coating the surface as with G-60 and G-90.
Most structural connector/fastener manufacturers exercise caution in this environment of risk and recommend that fasteners, such as screws, nails, bolts, etc., be made of the same material it is connecting, anchoring, etc., to the treated wood. Though it is more expensive than TZ (G-185), many manufacturers suggest using stainless steel as the best option for corrosion protection. Even so, stainless steel will corrode due to galvanic action if in direct contact with a dissimilar metal. Where metal-to-metal contact occurs, the rule of thumb is "like unto like."
Next month, we'll discuss the fourth class of chemical treatment for wood, water-soluble boron compounds.