Wood preservation with copper chromium arsenate

Metals are major pollutants only at wood preserving plants that treat with water-borne salts of copper, chromium, arsenic, and zinc. 

Wood preserved with Chromated Copper Arsenate (CCA), a chemical mixture consisting of three pesticidal compounds (arsenic, chromium and copper)... 

Copper chromium arsenate as a wood preservative Calcium and sodium arsenate herbicides Lead arsenate formerly used on fruit crops Formerly in cotton defoliants Sodium arsenite in cattle and sheep dips Alloys with copper and lead for bearings With aluminum, gallium, and indium in semiconductors... 

Early insecticides were often inorganic arsenic, copper, lead, and sulfur compounds.6 An example is Bordeaux mixture, which contains copper sulfate and calcium hydroxide. Copper chromium arsenate is used today as a wood preservative. Organic natural products, such as pyrethrin and rotenone (11.1) have also been used. Rotenone is used today for killing undesirable fish, such as carp, before restocking ponds with game fish. Many synthetic pyrethrins are used today because of their relative safety to humans. However, both rotenone and pyrethrin7... 

It is possible that this or a similar compound could be used to replace the copper-chromium arsenate treatment now used on wood. Carvacrol is fairly volatile, bp 237°C. It would be interesting to see how fast it would be released from wood treated with it under pressure. If it is released too fast for purposes of preservation, the wood could be im-... 

A copper chromium arsenic preservative is used in industrial pretreatment of timber. This process creates the potential for operator exposure (Garrod etal. 1999) as well as the need to remediate soil contaminated with the preservative (Balasoiu etal. 2001). Potentially, further remediation is needed when the wood might be recycled for wood chips (Velizarova et al. 2002). 

Wood poles typically require treatment with preservatives [e.g., creosote, copper chromium arsenate (CCA), penta-chloro-phenol (Penta)] to resist rot, decay, etc., in order to yield a service life of about 30-35 years. Due to preservation treatments of wood poles [22] which are hazardous to humans, the US-EPA regulations have led to evaluating the viability of alternatives to treated wood poles, i.e., steel, concrete, and FRP composite. Recently, through a strong push from the American Composites Manufacturers Association (ACMA), FRP composite poles have been receiving greater attention from electrical utility and telecommunication companies due to their inherent advantages over poles made of conventional materials. 

Zinc in contact with wood Zinc is not generally affected by contact with seasoned wood, but oak and, more particularly, western red cedar can prove corrosive, and waters from these timbers should not drain onto zinc surfaces. Exudations from knots in unseasoned soft woods can also affect zinc while the timber is drying out. Care should be exercised when using zinc or galvanised steel in contact with preservative or fire-retardant-treated timber. Solvent-based preservatives are normally not corrosive to zinc but water-based preservatives, such as salt formulated copper-chrome-arsenic (CCA), can accelerate the rate of corrosion of zinc under moist conditions. Such preservatives are formulated from copper sulphate and sodium dichromate and when the copper chromium and arsenic are absorbed into the timber sodium sulphate remains free and under moist conditions provides an electrolyte for corrosion of the zinc. Flame retardants are frequently based on halogens which are hygroscopic and can be aggressive to zinc (see also Section 18.10). 

At the Coast Wood Preserving, Inc., Superfund site (Ukiah, California), the technology was used to remove metal contamination to comply with both state and federal cleanup standards [50 parts per billion (ppb) arsenic, 50 ppb chromium, and 1 ppm copper]. The estimated total cost for the source control component of the remedy was 1,000,000, and the estimated total operational and maintenance costs was estimated to be 19,500 for a 20-year period (D16888B, p. 3, Report Documentation p. 2). 

CCA, developed in the 1930s, was onee by far the most commonly used of all wood preservatives and until very reeently represented over 90% of the sales of waterborne wood preservatives in the United States - as the preservative of ehoiee for most ground and marine applieations. There were numerous formulations with varying ratios of copper, ehromium and arsenic. One of the most common formulations is 47.5% chromium trioxide, 18.5% eopper oxide, and 34.0% arsenie pentoxide dissolved in water (CCA Type C). Typieal retentions of active elements are several kilograms per eubie metre of wood, with yearly production of around 20 million cubic metres in the mid-1990s (Clausen and Smith, 1998). 

At older production facilities or places where wastes have been disposed off-site, the creosote materials are often mixed with other chemicals. For instance, pentachlorophenol (PCP) is commonly encountered at NPL sites involved with wood-preserving operations along with such metals as copper, chromium, and arsenic (Davis et al. 1993 Kuehl et al. 1990 Mueller et al. 1989, 1991). At many of these sites, PAHs from combustion sources other than coal tar may have been introduced. The wastes from old town-gas sites may contain benzene, toluene, ethylenebenzene, or xylenes, and sometimes cyanides (Arvin and Flyvbjerg 1992 EPA 1987b Flyvbjcrg etal. 1993). 

Since the 1940s, lumber producers and manufacturers have been using a chemical compound mixture that contains inorganic arsenic, copper, and chromium, called chromated copper arsenate (CCA) as a wood preservative. CCA is usually injected into wood by a high pressure process to saturate wood products with the chemicals, to produce pressure-treated lumber (between 75 and 90% of the arsenic used in the US is estimated to be used for wood preservation). 

The voluntary withdrawal of chromated copper arsenate (CCA) as a wood preservative for domestic applications was driven by public concerns over its health and environmental profile. In its place have risen two competing systems, the amine copper quat (ACQ) system and the copper azole system. Both systems avoid using heavy metals such as chromium and arsenic and rely on the co-biocidal effects of copper and organic biocides. The elimination of CCA has created many opportunities for oleochemicals as preservative companies try to develop formulations that are not only environmentally friendly but can also match the preservative performance of CCA [66]. The ACQ system is based on didecyldimethyl ammonium bicarbonate and has produced a significant demand for ClO-based amine and quat. The azole systems use biocides such as tebuconazole and propiconazole in combination with copper ethanolamine complexes. Ethoxylated amines [67] and amine oxides [68] have been described as providing improved performance in azole-based systems. Other copper systems have employed ethoxylated diamines [69] and amine oxides [70] to enhance performance. 

Imagine that a friend has asked you to review the title and abstract of a paper that is being written with other researchers on chromated copper arsenate (CCA), a compound used to preserve wood. The research team examined the chemical structure of arsenic (As) and chromium (Cr) in CCA to determine if the oxidation state of As and Cr changed over time due to weathering. 

Pentachlorophenol is no longer used to preserve wood. The chromium copper arsenate that is used on wood is not entirely free of problems. A study of decks in Connecticut found that soil beneath the decks contained levels of arsenic that exceeded regulatory limits.73 The amount of chromium approached levels of concern, but were within regulatory limits. Wood has also been preserved by chemical reaction with carboxylic acid anhydrides, isocyanates,... 

---