There are some important benefits of treating wood, the most significant of which is increasing the life of wood that is used in locations where degradation might occur. Older preservatives, such as pentachlorophenal and creosote, pose considerable health risks to users of the wood, but new waterborne preservatives are safer. They are safer in part because the toxins are fixed in the wood, which leads to a different problem: disposing of treated wood at the end of its useful life has
become a solid-waste headache that just won’t go away.
Roughly 17% of all softwood lumber is pressure-treated today—about 40% of all softwood from the Southeast. The majority is treated using chromated copper arsenate (CCA), an inorganic, waterborne preservative. In 1995, according to the American Wood Preservers Institute, 138 million pounds (63 million kg) of CCA were used in the United States to treat roughly 5.1 billion board feet (12 million m3) of lumber, timbers, and other wood products. Another 8.7 million pounds (3.9 million kg) of other waterborne preservatives were used in 1995. Since 1985, approximately 48 billion board feet (113 million m3) of wood products have been treated with CCA.
What happens to all of this wood when it comes out of service? That question is becoming an ever-more-difficult thorn in the side of the industry. Based on a 30-year service-life, researchers at the Forest Products Laboratory (FPL) in Madison, Wisconsin estimate that 2.5 billion board feet per year (6 million m3/year) of treated-wood products (all types of preservative treatments) are currently entering the solid- waste stream, and that level will increase to 8 billion board feet per year (19 million m3/yr) by the year 2020. Some of this waste is wood that has warped, twisted, or splintered, even though it has not begun to rot. There is also a substantial amount of waste from new construction, in the form of off-cuts and scraps. This article will examine the various options available for disposal of this treated wood.
Background on Treated Wood
There are three broad categories of preservative treatments for wood currently in use: creosote, oilborne chemicals, and waterborne chemicals. Creosote is a highly complex mixture of chemicals distilled from coal tar, which is a by-product of producing coke from bituminous coal in coking ovens. It has been in use in the United States since 1889 and is still the treatment of choice for the railroad industry. Since 1986, creosote has been a restricted-use pesticide and is available to certified applicators only.
The most common oilborne preservative is pentachlorophenol, generally known as penta. It is typically used in a 5% solution of light petroleum solvents. Penta was widely used both for pressure-treating and for surface treatments until the 1970s, when the price of petroleum rose and the product lost market share to CCA. Penta has also been shown to cause birth defects and fetal damage, among other health problems. Like creosote, penta has been a restricted-use pesticide since 1986. It is used primarily for treating utility poles and bridge timbers, and is also used in some glue-laminated timbers in buildings. The other fairly common oilborne preservative is copper naphthenate.
Waterborne preservatives today account for the vast majority of chemicals used in building applications. These waterborne chemicals are used in pressure-treating only and include chromated copper arsenate (CCA), ammoniacal copper zinc arsenate (ACZA), ammoniacal copper quaternary compound (ACQ), and several others. CCA accounted for 94% of the waterborne chemicals used in 1995. While the primary chemicals in CCA are, by themselves, highly toxic and are regulated as pesticides by the EPA, they are bonded quite tightly to the wood during fixing, so leaching from the wood is minimal under normal usage conditions (see
The three major producers of CCA have recently developed copper-based alternatives to CCA that eliminate its most toxic components: arsenic and chromium. Chemical Specialties, Inc. (CSI) is selling its ACQ Preserve® product nationally, and it is widely used in certain regions. Osmose also has an ammonia and copper product—Copper Citrate—but is not marketing it widely. At present, the only wood preserver using it is Thunderbolt Wood Treating Co. of Riverbank, California.
Hickson Corporation has developed Copper Azole but has not put it on the market. “We just have it ready and approved, in case something should happen to CCA,” says Huck DeVenzio, Hickson’s Director of Marketing. DeVenzio explains that Copper Azole costs more and may not work as well as CCA.
Toxicity of Treated-Wood Waste
To prevent hazardous materials from getting into the environment, the federal government has various regulations that control disposal. The EPA has developed the Toxic Characteristic Leaching Procedure (TCLP) to set threshold levels for toxicity of 39 different chemicals, including chromium and arsenic. If measured leaching from a waste product exceeds the TCLP limits, it is considered a “hazardous waste” and regulated accordingly. Federal hazardous waste regulations generally apply only to generators of significant quantities of a given waste.
Of the treated-wood products currently in use, creosote-treated wood and penta-treated wood consistently pass the TCLP rule, and the wood products are not defined as hazardous waste. CCA-treated wood, on the other hand, doesn’t have to pass the TCLP rule, because arsenic-treated wood and wood products have a special exemption from the regulation in 40 C.F.R. §261.4(b)(9)—likely the result of strong lobbying pressure. Because the point is legally moot, actual data is hard to come by, but results of one test obtained by
EBN show that CCA-treated wood actually fails the test for arsenic and only barely passes it for chromium. The ash from treated wood that has been burned certainly fails the TCLP rule and is not exempt.
How to dispose of treated wood is a vexing concern. The chemicals used for treating wood are designed to kill or repel biological organisms, so it is a reasonable assumption that their disposal could pose environmental and health risks. Let’s look at the options for disposal.
Salvage and reuse
Keeping treated wood out of the waste stream by salvaging and reusing it in another application for which treated wood is appropriate makes a great deal of sense and should be the first priority. If the wood does not enter the waste stream, it will not even be considered waste, let alone considered potentially hazardous waste. To this end, the Southern Forest Products Association has published a booklet for consumers on ways to reuse leftover scraps from new projects and usable pieces from old ones.
No type of treated wood should ever be burned in open fires or in small wood stoves or fireplaces. Creosote-treated wood can be burned safely in high-temperature municipal or industrial incinerators or waste-to-energy plants with virtually no problems, since the creosote is a coal-derived hydrocarbon—in fact, the creosote provides additional energy content.
Whether or not penta can safely be burned is a more difficult question. Many experts say yes, under controlled, high-temperature conditions. The pentachlorophenol is readily burned and most, if not all, of the combustion products are relatively safe. The possible exception, however, is significant: organochlorine compounds, which some believe may pose a serious threat as endocrine disrupters.
CCA-treated wood should not be burned, even in state-of-the-art incinerators. The heavy metals in CCA are not destroyed; the chromium and copper become concentrated in the ash, while the arsenic becomes a vapor that either escapes into the air or is trapped in pollution control equipment. In many states the issue of whether or not ash from municipal incinerators must be handled as hazardous waste is being hotly debated, with incinerator operators arguing that they cannot operate economically if they must pay for hazardous waste disposal. Adding significant quantities of CCA-treated wood to the mix will greatly increase the concentration of hazardous chemicals.
CCA-treated wood is definitely unwelcome at wood-fired power plants, some of which utilize their ash as a soil amendment in agricultural fields. “I refer to CCA-treated wood as the bad actor,” said Jeff Fehrs, P.E., research director at C. T. Donovan Associates, Inc., a consulting firm specializing in C&D waste. Fehrs managed a study in which a test burn, with CCA-treated wood making up 10.7% of the wood fuel, resulted in ash that exceeded the TCLP limits for arsenic by a factor of at least 26. Such results indicate that even modest contamination of otherwise clean wood fuel with CCA-treated wood would result in hazardous ash. Fehrs told
EBN that air emissions from burning CCA-treated wood under these conditions are also “pretty bad,” noting that the metals are “very volatile, so they tend to want to be picked up by the flue gas and carried out into the atmosphere.”
That burning CCA-treated wood can be hazardous to health and the environment is borne out by two unfortunate case studies. Agricultural extension engineer John Gird at the University of Maryland described in a fact sheet a 1982 Wisconsin case in which a father of six burned scraps of CCA-treated wood obtained from his employer:
“The family suffered arsenic poisoning by inhaling poisoned dust, by skin contact with the wood ash, and by ingesting the ash,” and they suffered blackouts, seizures, hair loss, nosebleeds, skin rashes, and extreme fatigue. The youngest children, who played on the floor, had the most severe problems. Plants and fish in the house died from copper toxicity. The problems continued long after the wood was no longer burned, and the yard was contaminated where ashes had been spread.
In another more recent incident in Minnesota, 22 cows were killed when a farmer spread fireplace ashes from CCA-treated wood in the field where they were grazing, according to Cathy Latham of the Minnesota Pollution Control Agency.
Landfilling of CCA-treated wood is the only environmentally acceptable disposal option today. The problem is that landfills are filling up, and tremendous quantities of CCA-treated wood will be coming out of service over the coming decades. As expensive, lined municipal landfills near their capacities, there is increasing pressure to keep bulky C&D waste out, sending it instead to less expensive, unlined C&D landfills. These unlined landfills may not adequately protect area groundwater from contaminants in CCA-treated wood.
A number of researchers, including Dr. Robert Smith, an assistant professor in the Department of Wood Sciences at Virginia Tech in Blacks-burg, have sought to chemically remove CCA from wood using various types of acid, but they have had only moderate success. In a recent paper, Smith and co-author Marshall Shiau reported that their research “confirms the research of others that not all the treating chemicals can be removed, and the chemicals remain a serious barrier to recycling spent CCA products.”
Another approach is to use biological organisms to remove toxins from the wood fibers. Even though treated wood protects against damage from most organisms, certain micro-organisms can not only survive around the stuff, but actually thrive on it. Researchers have been quite successful in finding fungi and bacteria that will break down creosote and penta; finding microbes that want to feast on CCA has proven more difficult. Carol Clausen, a research microbiologist at FPL, has been working with bacteria to biodegrade CCA-treated wood. After grinding up CCA-treated wood, she has achieved up to 92% removal of copper and 42% removal of arsenic, but the chromium is bonded very tightly to the wood lignins, and she has so far been unsuccessful in removing it.
The goal of Clausen’s research, as well as related research being done by Smith, is to get clean wood fiber that could then be recycled into manufactured wood products. A secondary goal of this work might be to actually harvest the metals extracted from the wood by the bacteria, as is being done in some research on remediation of contaminated soil. Unfortunately, even if researchers succeed in removing CCA from wood fiber, a survey of wood fiber users conducted by Smith found that they would be unlikely to use fiber from which CCA had been removed. “Although composite manufacturers believe that raw materials will become more difficult to obtain in the near future, they were reluctant to consider spent CCA fiber as a possible resource,” Smith reported at the Madison conference.
Recycling treated wood into other products
While Clausen’s work at FPL and Smith’s work at Virginia Tech is primarily focused on removal of CCA so that the clean wood fiber can be reused, other research is being done on recycling treated wood directly into other products without having to remove the treatment chemicals. Colin Felton, a chemical engineer with Global Resource Technologies in Madison, Wisconsin, and Rodney De Groot, a research plant pathologist at FPL, are experimenting with manufacture of fiberboard made from recycled CCA-treated wood. They are using somewhat higher quantities of phenol-formaldehyde binder than is required with untreated wood. Felton told
EBN that he thinks there could be significant demand for such a product in the South, where “they’d like to make everything out of treated wood if they could.” They have so far found their fiberboard from recycled CCA-treated wood to hold up well in stake tests in Wisconsin.
Perhaps even more promising is the idea of using treated-wood fiber in fiber-cement products, which are quickly gaining in popularity. An article by Felton and De Groot in the July-August 1996 issue of the
Forest Products Journal reported that using CCA-treated wood fiber in wood-Portland cement composites resulted in improved performance, compared with using untreated wood. The cement may help to lock up the treatment chemicals and reduce leachability, though it is not clear what effect the chemicals might have on future disposal of the projects. The authors did not think creosote- and penta-treated wood would work in fiber-cement composites, because the chemicals could interfere with cement curing, as well as inhibit wetting and ultimate bonding with the wood surface.
Safe, environmentally responsible disposal is an important—and long-ignored—priority for all treated wood products, but it is most challenging with CCA-treated wood, in part because of the huge volume in use. The bottom line with CCA-treated wood is that, other than reuse, there are currently no acceptable alternatives to landfilling. Incineration is clearly unacceptable from an environmental standpoint, and in areas that rely on incineration of municipal waste, there is no easy way to keep CCA-treated wood out of incinerators. Fiberizing treated wood and using it in recycled-wood products—with or without first removing the treatment chemicals—offers a possible use for waste CCA-treated wood, but it is probably some years down the road at the earliest, and there are health concerns for mill workers if such fiber is reused in manufacturing. This leaves only landfilling as an option, and the tremendous increase of CCA-treated wood waste entering the waste stream makes this option increasingly unattractive.
Given these disposal-related concerns, the only viable solution may be to phase out the use of CCA-treated wood in favor of preservative treatments that offer better disposal options. CCA-treated wood is already outlawed in several European countries, and the U.S. is braced for further regulatory limitations. In fact, Tom Bailey, marketing manager at CSI, one of the big-three manufacturers of CCA, told
EBN that he is surprised CCA has not been further regulated: “I would have said four years ago that…something like ACQ would displace CCA. However, the regulatory changes that I think all of us thought were going to happen haven’t really happened. In fact, it’s gotten easier probably for people to use CCA over the years.” Bailey’s company is the only one actively marketing an alternative to CCA, so he feels mixed about the lack of substantive changes: “For the CCA side of the business, it’s a good thing, but as far as introducing new products and really, I guess, making the world a better place, it’s probably not the way I’d like to see it go.”