Chromium-containing preservatives

Chromium-containing wood preservatives and their chemical compositions are Hsted ia Table 13 (199). Chromium compounds have a triple function ia wood preservation (200). Most importantiy, after impregnation of the wood the Cr(VI) compounds used ia the formulations react with the wood extractives and the other preservative salts to produce relatively insoluble complexes from which preservative leaches only very slowly. This mechanism has been studied in the laboratory (201—206) and the field (207). Finally, although most of the chromium is reduced to chromium (ITT), there is probably some slight contribution of the chromium (VT) to the preservative value (208). 

Preparations containing chromium compounds are becoming increasingly important in the preservation of wood.34,36 Damage to wood occurs principally through attack by microorganisms,... 

British Standard 5666, Methods of Analysis of Wood Preservatives and Treated Timber, Part 3, Quantitative Analysis of Preservatives and Treated Timber Containing Copper, Chromium, Arsenic Formulations, British Standards Institution, 2 Park Street, London W1A 2BS, 1979. 

Preservative formulations that contain copper and chromium salts reportedly promote afterglow in treated wood subjected to fire. Once the treated wood starts to burn or glow, the wood may continue to glow until the entire member is consumed, even when no flame is present (38, 39). This characteristic can cause serious problems in utility poles, fenceposts, and highway signs, structures that might be... 

CCB and CCP are similar in many respeets to CCA except for the fact that the arsenic is replaced by boron in CCB and by phosphate in CCP. Most commonly used in Europe, both formulations were developed in part to address concerns about the toxicity of the arsenic in CCA. CCB and CCP are less efficacious than CCA and in the absence of arsenic the fixation processes are compromised. The systems still contain significant levels of chromium, which faces significant regulatory pressure from the Biocidal Products Directive in Europe. In the longer term the future for preservative formulations containing chromium is questionable. 

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,... 

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... 

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). 

Industrial nations in Europe and North America must rely on a supply of chromium ore from abroad, the US consuming 14% of world output. Because chromium is such a vital metal to the economy, government stockpiles in the US are considered an important strategy to ensure supplies during periods of military activity. Chromium ore is converted to chromium ferroalloys (for stainless steel and other alloys), chromite-containing refractory materials and chromium-based chemicals. The most important commercial applications of the latter are for pigments, leather tanning and wood preservation. 

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