Arsenic and Old Wood

Operators of construction and demolition (C&D) debris recycling facilities routinely address concerns associated with the quality and environmental safety of the materials they process and the products they produce for recycling and reuse.

If materials such as asbestos and lead-based paint occur in sufficient amounts, they must be separated from the rest of the C&D debris stream prior to processing. This is necessary to meet regulatory requirements, to ensure worker safety, and to produce a high-quality product that may be safely recycled.

In most cases these materials are removed prior to entering the C&D debris processing facility. The facility operator must, however, continually screen the incoming waste stream to minimize the amount of hazardous materials being processed. While the true environmental impact these contaminants pose in a recycled product can be debated, the C&D recycling industry must stay informed of such issues so that current regulations are met and to keep abreast of what possible concerns may be raised in the future.

This article presents an overview of an issue along these lines, one that has received much attention in recent years in Florida: CCA-treated wood. CCA-treated wood contains arsenic, chromium, and copper, and the presence of these metals impacts the quality of recovered C&D debris wood when present. While the debate surrounding the use of CCA-treated wood has been a subject of concern from time to time during the past decade, the potential impact on the C&D debris industry has recently surfaced.

The issue of CCA-treated wood’s effect on C&D debris wood recycling has raised some serious questions in Florida, a state with a large number of C&D debris processing and recovery facilities. Several research projects have been conducted or are underway to examine the potential magnitude of the problem and to explore solutions.

Treated Wood Basics

Wood treatment (or preservation) protects wood from environmental deterioration when the wood is used in a susceptible environment, such as contact with ground or water.

Wood treatment involves the addition of chemicals—either as a surface application or internally to the wood’s pore-space—to increase the resistance of wood to decay by fungi, insects and marine borers. While other wood treatment processes and chemicals exist, including creosote and pentachlorophenol, chromated copper arsenate (CCA) is the major wood preservative used today, representing about 80% of the wood preservation market. Copper serves as a fungicide, arsenic serves as an insecticide, and chromium is used to “fix” the copper and arsenic into the wood.

The wood treatment industry specifies CCA-treated wood by retention level, the weight of CCA retained in the wood (pounds of chemical per cubic foot of wood). When purchased new, the retention level is indicated on a tag attached to the wood product. (The chart on this page presents standard retention levels of CCA-treated wood commonly encountered and their typical applications.)

Typical CCA-treated wood applications include telephone poles, fence posts, decks, and components of home construction. At low retention values, CCA-treated wood maintains a natural look and it may be painted easily. CCA also produces no smell or vapor.

CCA-Treated Wood in C&D Debris

While the treatment of wood greatly extends the useable life of the material, at some point it is taken out of service and disposed of. Wood is removed from service because of loss of structural properties as well as loss of aseptic qualities (the fading and warping of a deck).

The primary disposal sectors for discarded CCA-treated wood in Florida are construction and demolition (C&D) debris landfills and C&D debris recycling facilities. At C&D debris landfills, CCA-treated wood is disposed of along with other components of C&D debris (e.g. untreated wood, concrete, drywall, etc) by burial in excavated pits or compaction in large above ground piles. As long as it is disposed of after being used for its intended purpose, CCA-treated wood is exempt from being a hazardous waste under U.S. federal regulations (regardless of testing results).

At C&D debris recycling facilities, some CCA-treated wood may be separated out and recovered for reuse or sent to a landfill for disposal, but much of the treated wood is indistinguishable from the untreated wood and is thus managed as part of the facility’s overall recovered wood stream.

In 1997, CCA-treated wood was documented to compose approximately 6% of the recovered wood stream at C&D recycling facilities in Florida (Tolaymat et al. 2000).

Research conducted in 1999 at three Florida C&D debris recycling facilities found CCA-treated wood to make up between 9% and 30% of the recovered wood (Solo-Gabriele et al. 2000). The amount of CCA-treated wood being disposed of is predicted to increase dramatically in the coming decades. It was not until the 1980s that CCA-treated wood dominated the wood preservation market, and given that CCA-treated wood generally maintains its structural integrity for 20 to 40 years, the majority of CCA-treated wood sold remains in service and has yet to be disposed of (Solo-Gabriele and Townsend 1999).

Impact on Wood Recycling Markets

Viable markets for materials recovered from solid waste are crucial for the successful implementation of any recycling program, and this is true for wood recovered from C&D debris recycling operations. Most C&D recycling facility operators recycle their mixed wood stream via one of two primary markets: boiler fuel or wood mulch. Research has shown that the presence of CCA-treated wood can have a major impact on both of these markets:

Wood for Boiler Fuel

Processed wood from C&D debris recycling operations has long been utilized as fuel for industrial boilers. Concerns regarding wood fuel quality typically deal with excess moisture or the presence of non-combustible material (e.g. soil), but the occurrence of toxic contaminants must also be addressed. Since arsenic can volatilize (be emitted as a gas), combustion units that burn C&D debris wood containing CCA-treated wood must have the necessary air pollution controls in place. Ash from the combustion of wood is often applied to land as a liming agent and to return minerals to the soil.

Research was performed to determine what impact CCA-treated wood had on the quality of wood ash (Solo-Gabriele et al. 1999). Several synthetic mixes of untreated wood (95%) and treated wood (5%) were combusted in an industrial furnace. Processed wood from actual C&D debris recycling facilities in Florida was also combusted. The ash was collected and analyzed.

The results showed that the presence of 5% CCA-treated wood in the processed wood caused the ash to fail the toxicity characteristic leaching procedure (TCLP) for arsenic and on occasion chromium. The TCLP is the U.S. regulatory test for determining when a solid waste is a toxicity characteristic hazardous waste.

The C&D debris wood ash samples also failed TCLP and were characterized as hazardous waste. Characterization as hazardous waste not only prohibits the practice of land applications but also requires very elaborate and expensive regulatory procedures for management and disposal. While C&D debris wood is still being burned in Florida, the combustors are becoming increasingly selective about which loads they accept and only combust the C&D wood as part of a mix with other wood wastes (e.g. green wood from land clearing and clean pallets).

Wood Mulch

Decorative mulch represents a second major market that has recently come into major use in Florida for processed C&D debris wood. Because of its grayish color, discarded C&D debris wood is often less desirable than cypress or pine bark as a source of mulch, but the advent of coloring agents designed to dye wood to more aesthetically pleasing colors has opened this market.

Recently completed research by the authors examined the impact of CCA-treated wood on this market. While the chemicals in treated wood are considered “fixed” from a wood treatment standpoint, they are known to “leach” from the wood over time. The amount that leaches may not be enough to affect the wood from a preservation standpoint, but it may be enough to exceed certain regulatory risk-based concentrations established by various regulatory agencies.

While one may argue that if CCA-treated wood does not pose an unreasonable risk to human health and the environment when used for its intended purpose (e.g. a fence post in the environment, a deck), then its presence in landscaping mulch should represent no more of a risk. But since wood is size-reduced to produce mulch, the amount that leaches increases beyond intact wood. In addition, the placement of mulch represents the final disposition of the wood. The wood contained in the mulch will, under most circumstances, remain on the ground and ultimately become integrated into the underlying soil.

Several test results show that the leaching of heavy metals from mulch, especially arsenic, do represent a concern. Tests on new CCA-treated wood using the TCLP showed that arsenic leached in sufficient amounts that nearly half the time exceeded the toxicity characteristic limit of 5 mg/l.

If the regulatory exemption were not in place, CCA-treated wood would frequently require management as a hazardous waste. CCA-treated wood is not mulched by itself, but as a mixture with untreated wood. Tests were performed on processed C&D debris wood samples from 12 facilities around Florida using a rainwater leaching test, known as the synthetic precipitation leaching procedure (SPLP).

Environmental regulators frequently use the SPLP to assess the risk presented by a contaminated soil or land applied waste. If the concentration of a chemical in the SPLP leachate exceeds a groundwater standard, it has a high potential of exceeding acceptable risk.

Nearly all of the C&D debris processed wood samples evaluated exceeded the groundwater standard for arsenic (50 parts per billion). Results such as these indicate the mulch containing as little as 1% CCA-treated wood should not be land applied, according to some regulatory standards.

Possible Solutions

A number of major conclusions have been drawn to date. C&D debris facilities (landfills and recycling facilities) represent the major disposal sector for CCA-treated wood being discarded in Florida. CCA-treated is currently present in C&D debris processed wood in amounts that may impact reuse, and this amount is predicted to grow significantly in the future.

Again, it is important to recognize that the majority of CCA-treated wood that has been sold is still in service. CCA-treated wood at current levels in Florida C&D debris wood causes the ash from the combustion of this wood to be a hazardous waste. CCA-treated wood at current levels in Florida C&D debris wood causes arsenic to leach in amounts that in most cases restricts its land application. The authors believe these facts warrant a discussion in the C&D debris recycling industry.

Several questions are raised. To what extent should C&D recycling facility operators be concerned and try to remove the material? How and when should the materials be removed? The results reported here are for a state that uses large amounts of treated wood and that has a large C&D debris recycling industry. Results may be different for other areas of the country.

If similar results are observed as in Florida, the response needed will be largely dictated by the markets (e.g. the industrial combustion facilities) and by state and local regulators. The combustion facilities will be responsible for controlling air emissions and managing ash per applicable regulatory requirements. They will require action from the fuel producers if costs associated with meeting these regulatory requirements increase (i.e. if ash has to be managed as a hazardous waste).

Research results show that regulators would be justified in taking action to minimize the amount of CCA-treated wood entering the environment as decorative mulch. What actions are taken would depend on the perceived level of risk as well as the enforceability and practicality of such actions.

This issue would not be so complicated if CCA-treated wood were easily removed from the rest of the wood stream. It is difficult, however, to distinguish CCA-treated wood from untreated wood by sight. When wood is painted, weathered, or dirty, identification of CCA treated wood from other wood becomes even more difficult. Work has been conducted with stains that can identify treated wood from non-treated wood, but the use of stains becomes limited if large amounts of wood are present. Research is currently underway at a C&D recycling facility in Florida to construct a pilot CCA-treated wood sorting system. The facility will utilize a laser-based detection system that identifies CCA-treated wood from non-treated wood. Treated wood will be identified as it travels along a conveyor belt and it will be manually removed. The authors expect to test this system in the summer of 2001.

Finally, a question often raised when discussing this issue is “what about switching to other types of treated wood that do not represent the same environment risk?” This topic has been debated heavily, for reasons beyond the issue of impact on C&D debris management. Several alternative wood treatment chemicals do exist that do not contain arsenic or chromium. These treatment chemicals are somewhat more expensive and performance testing and standardization is not available for all uses. While a complete discussion of this issue is beyond the scope of this paper, the future use of CCA-treated wood for many applications and the potential for using alternative chemicals is a subject of discussion throughout the country.

Conclusions

Research underway in Florida shows that CCA-treated wood does have a potential serious impact of the major markets for C&D debris wood reuse. The degree to which a C&D debris recycling facility should be concerned depends on how much CCA-treated wood is used for construction or other activities in their area. Treated wood use is certainly a function of location.

But where this material is used, C&D debris recyclers should pay attention to the amount entering their facility and to potential regulatory requirements in their states. Readily identifiable CCA-treated wood should be separated from the rest of the wood and disposed of properly (in a lined landfill). While the future may hold a change from treated wood products containing arsenic and chromium, the majority of CCA-treated wood sold is still in use, and it is likely that most of this material will end up at a C&D debris processing facility one day.

Tim Townsend is an assistant professor in the Department of Environmental Engineering Sciences at the University of Florida and a member of the CMRA. Helena Solo-Gabriele is an assistant professor in the Department of Civil, Architectural, and Environmental Engineering at the University of Miami. The research on CCA-treated wood is funded by the Florida Center for Solid and Hazardous Waste Management. Contact information for the authors and more information on the research (including copies of the reports referenced) can be found at www.ccaresearch.org.