Just the mention of chemicals can make some homeowners uneasy. They are a fact of life, however, when building with pressure-treated lumber.
To make Southern pine (a readily available and relatively inexpensive wood used in making decks, planters, and garden structures) rot- and insect-resistant, the wood fibers are impregnated with chromated copper arsenate, or CCA. This chemical contains arsenic, a naturally occurring element in the environment.
"CCA was invented in 1933 and has been widely used since the mid-1970s," says Huck DeVenzio, manager of marketing communications for Arch Wood Protection Inc., which manufactures Wolmanized wood, a leading brand of pressure-treated wood.
Currently the Environmental Protection Agency is in the early stages of a scheduled reassessment of CCA. "This is just a normal part of how the EPA looks at all these chemicals," says EPA spokesman Dave Deegan about the pesticide-reregistration process he expects to conclude late next year. "This is not done based on any new concern that has come to light. And in all our previous assessments it's been determined that the public can use pressure-treated wood safely."
The EPA is also looking at creating a new standard to reduce the allowable arsenic level in groundwater. The main impact would be to municipal water utilities, but the American Wood Preservers Institute (AWPI) and other groups filed a court action to overturn the preliminary change because of concerns about unpredictable impacts a strict ruling might ultimately have on industry manufacturing sites.
The Clinton administration directed the EPA to reduce arsenic levels in drinking water from 50 parts per billion to 10 parts per billion, effective in 2006. Though in general agreement with a reduction, the new administration says it is reviewing the decision to determine an arsenic level supported by the best-available science. The ripple effects might eventually be felt by wood preservers.
The use of safe levels of chemicals, Mr. DeVenzio says, must be considered in the context of environmental benefits that accrue from making a renewable resource like wood last longer. In Georgia, where summer heat and humidity can be intense, he adds, an untreated pine board stuck into the ground would probably show signs of decay and termites within a year and be unuseable within three to five years.
Pressure-treated wood, on the other hand, may last five to 10 times longer. "Treated boards put in the ground in the late 1940s are still doing well," DeVenzio says. With the preservatives in pressure-treated wood, termites don't recognize the wood as food.
Wood that meets industry standards carries a tag or stamp of the AWPI, the pressure-treated trade association, which sets the preservative-retention levels that guide consumers. Retention is a measure of the pounds of preservative per cubic foot of wood. A .25 retention level (a quarter-pound per cubic foot) is the norm for above-ground boards, but, for the sake of simplicity, many dealers stock only the more versatile ground-contact boards, which have a retention level of .40.
Liquid preservative is applied in a pressurized cylinder. The degree of chemical absorption varies. Generally speaking, more preservative is found near the wood's surface.
"Southern pine absorbs preservative quite well and gets good penetration," DeVenzio says. "Most Western species have to go through an incising machine, which puts all these shallow little knife cuts into the wood to help the preservative get deeper."
The EPA has been working with manufacturers and wood retailers to make sure information about pressure-treated lumber is available to consumers. This may help in making an "informed choice," Deegan says.
Basically, the normal precautions for working with wood apply to pressure-treated wood. And just as with plywood or any wood product that has been coated or glued with a chemical solution, it shouldn't be burned.
For consumers concerned with the toxicity of CCA, some manufacturers offer an alternative chemical preservative, either ACQ (alkaline copper quat) or copper azole.
"It takes some extra shopping to find these products, much like it did to find organic foods 30 years ago," says Mel Pine of the AWPI.
This may mean searching for a lumberyard that stocks arsenic-free, treated-wood products or will order them. Demand is limited for these alternatives, which usually cost 15 to 25 percent more than CCA-treated lumber. "Because they haven't been around as long as CCA, we don't know if they are as long-lasting," Mr. Pine says.
(c) Copyright 2001. The Christian Science Monitor