Arsenic-treated wood is wood that has been pressure-treated with a pesticide containing inorganic arsenic (i.e., the arsenic compound does not contain carbon ) to protect it from dry rot, fungi , molds, termites, and other pests. The arsenic can be a part of a CCA (chromated copper arsenate) chemical mixture consisting of three pesticidal compounds, copper, chromate, and arsenic; the most commonly used type of CCA contains 34% arsenic as arsenic pentoxide. Less commonly used wood preservatives containing arsenic include the pesticide ACA (ammoniacal copper arsenate), which contains ammonium, copper, and arsenic, and the pesticide ACZA (ammoniacal copper zinc arsenate), which contains ammonia, copper, zinc, and arsenic. In 1996, the United States wood product industry used 30 million pounds of arsenic, or half of all the arsenic produced worldwide.
Inorganic arsenic in CCA has been used since the 1940s. CAA is injected into wood through a process that uses high pressure to saturate wood products with the chemicals . Preserved wood products, such as utility poles, highway noise barriers, sign posts, retaining walls, boat bulkheads, dock pilings, and wood decking, are used in the construction, railroad, and utilities industries. Historically CCA has been the principal chemical used to treat wood for outdoor uses around a home. Residential uses of arsenic-treated woods include play structures, decks, picnic tables, gazebos, landscaping timbers, residential fencing, patios, and walkways/boardwalks. After wood is pressure-treated with arsenic compounds, residues of the preservatives can remain on the surface. The initial residues wash off, but as the wood weathers, new layers of treated wood and pesticides are exposed. Arsenic is also present in paints that are used to cover the cut ends of treated wood. Freshly arsenic-treated wood, if not coated, has a greenish tint, which fades over time.
Arsenic is acutely toxic. Contact with arsenic may cause irritation of the stomach, intestines, eyes, nose, and skin, blood vessel damage, and reduced nerve function. In addition, according to the National Academy of Sciences and the National Research Council , exposure to arsenic increases the risk of human lung, bladder, and skin cancer over a lifetime and is suspected as a cause of kidney, prostate, and nasal passage cancer. The National Academy of Sciences and the Science Advisory Board of the United States Environmental Protection Agency has also reported that arsenic may cause high blood pressure, cardiovascular disease, and diabetes.
Arsenic may enter the body through the skin, by ingestion, or by inhalation. Ingestion occurs most frequently when contaminated hands are put in the mouth, or when contaminated hands are used for eating food. Repeated exposure will increase risks of adverse health effects. Splinters of wood piercing the skin may also be a means of entry of arsenic into the body, but the importance of this route has not been well-studied.
The use of most pesticides containing arsenic had been banned by the United States Environmental Protection Agency, but in 1985 CCA was designated as a restricteduse pesticide. However, CCA-treated wood products were not regulated like the pesticides the wood products contained because it was assumed that the pesticides would stay in the wood. Unfortunately adequate information was not available on whether arsenic is fixed in the wood permanently and whether the wood product is safe. It is known that fixation of the chemicals in the wood matrix is enhanced if the treated wood is wrapped in tarps and stored for a sufficient length of time, which varies with the temperature. For example, to achieve fixation, the wood must be stored for 36 days in 50° F (21° C) weather and for 12 days in 70° F (10° C) weather. At 32° F., no fixation occurs.
However, research by the Florida Center for Solid and Hazardous Waste Management and the Connecticut Agricultural Experiment Station suggests that leaching of arsenic into the soils or into surface water under CCA-treated structures occurs at greater than safe levels. Florida studies showed that arsenic was found in soils underneath the eight pressure treated decks that were investigated. Of 73 samples taken, 61 samples had levels of arsenic higher than the Florida clean up levels for industrial sites. One sample had arsenic levels 300 times higher than the state's mandated clean up level.
Based on the potential for adverse health effects, the United States Protection Agency announced in February 2002 that the use of consumer products made with CCA, including play structures, decks, picnic tables, landscaping timbers, patios, walkways, and board walks, will be phased out voluntarily by the wood treating industry by December 31, 2003. Wood treated prior to December 31, 2003, can still be used, and already-built structures using CCA-treated wood and the soil surrounding the structures will not have to be replaced or removed. As of August 2001, Switzerland, Vietnam, and Indonesia had already banned the use of CCA-treated wood, while Germany, Sweden, Denmark, Japan, Australia , and New Zealand restricted its use.
The United States Environmental Protection Agency has issued cautionary recommendations to reduce consumer exposure to arsenic-contaminated wood. Treated wood should not be used where the preservative can become a component of water, food or animal feed. Treated wood should not be used where it may come into direct or indirect contact with drinking water, except for uses where there is incidental contact, such as docks and bridges. Treated wood should not be used for cutting boards or counter tops, and food should not be placed directly on treated wood. Children and others should wash their hands after playing or working outdoors, as arsenic may be swallowed from hand-to-mouth activity. Children and pets should be kept out from under-deck areas. Edible plants should not be grown near treated decks or other structures contructed of treated wood. A plastic liner should be placed on the inside of arsenic-treated boards used to frame garden beds. Sawdust from treated wood should not be used as animal bedding, and treated boards should not be used to construct structures for storage of animal feed or human food. Treated wood should not be used in the construction of the parts of beehives that may come into contact with honey.
Only wood that is visibly clean and free of surface residues (e.g., wood that does not show signs of crystallization or resin on its surface) should be used for patios, decks, and walkways. Consumers working with arsenic-treated wood should reduce their exposure by only sawing, sanding, and machining treated wood outdoors and by wearing a dust mask, goggles, and gloves when performing these types of activities. They should also wash all exposed areas of their bodies thoroughly with soap and water before eating, toileting, drinking, or using tobacco products. Work clothes should be washed separately from other household clothing before being worn again. Sawdust, scraps, and other construction debris from arsenic-treated wood should not be composted or used as mulch , but caught on tarps for disposal off-site. Pressure-treated wood has an exemption from hazardous waste regulations and can be disposed of in municipal landfills without a permit. Pressure-treated wood should not be burned in open fires or in stoves, fireplaces, or residential boilers, as both the smoke and the ash may contain toxic chemicals. Treated wood from commercial or industrial uses, such as from construction sites, may only be burned in commercial or industrial incinerators or boilers in accordance with state and federal regulations.
The United States Consumer Product Safety Commission has recommended that playground equipment be painted or sealed with a double coat of a penetrating, non-toxic and non-slippery sealant (e.g., oil-based or semi-transparent stains) every one or two years, depending upon wear and weathering . However, available data are limited on whether sealants will reduce the migration of wood preservative chemicals from CCA-treated wood. Other potential treatments include the use of polyurethane or other hard lacquer, spar varnish, or pain. However, the use of film-forming or non-penetrating stains are not recommended, as subsequent flaking and peeling may later increase exposure to preservatives in the wood. Structures constructed of arsenic-treated wood should be inspected regularly for wood decay and/or structural weakness. If the treated wood cracks and exposes the interior of the wood is still structurally sound, the affected area should be covered with a double coat of a sealant.
Alternatives to the use of arsenic-treated lumber include the use of painted metal, stones or brick, recycled plastic lumber, which may be all plastic or a composite of plastic and wood fiber, lumber that has been treated with an alternative pesticide ACQ (alkaline copper quaternary), which does not contain arsenic, or untreated rot-resistant wood such as cedar and redwood.
Arsenic compounds are referred to as arsenicals.
[Judith L. Sims ]
Frankenberger, William T., Jr.Environmental Chemistry of Arsenic. ???: Marcel Dekker, 2001.
Chromated Copper Arsenate (CCA) and Its Use as a Wood Preservative. Office of Pesticide Programs, U.S. Environmental Protection Agency, Washington, DC, June 20, 2002. [cited June 25, 2002]. <http://www.epa.gov/pesticides/citizens/1file.htm>.
Chromated Copper Arsenate (CCA) Wood: WMRC Library Reference Guide. Waste Management & Research Center, Illinois Department of Natural Resources, Champaign, IL, May 29, 2002. [cited June 25, 2002]. <http://www.wmrc.uiuc.edu/library/libraryinfo/refguides/ccawood.htm>.