Creosote chemical composition

The characterization of PIC (products of incomplete combustion) from the combustion of wood treated with pentachlorophenol (penta) is more widely documented in the open literature than creosote alone. However, both products are similar in chemical composition and likely result in comparable forms and concentrations of PIC. Literature reported studies on the combustion of these chemicals and wood treated by them, and the PIC generated are based upon optimal conditions. Optimal conditions are defined as those in which the fuel burns at the designed heat release rate with nominally 160% excess air and a low level (< 100 ppm) of carbon monoxide (CO) emissions in combustion (flue) gases. 

Creosote. The major portion of creosote is derived from coal and is a complex mixture of aromatic hydrocarbons with condensed ring systems. The remaining components are tar acids, which are phenolic derivatives of these compounds, and tar bases, which are heterocyclic compounds containing nitrogen plus some neutral oxygenated compounds. At least 200 chemical compounds have been identified in coal-tar creosote, but many of these are present in small amounts. The chemical composition is variable, but some idea of a typical creosote is given in Table I (2). 

Off-specification creosote (does not meet desired chemical composition). 

Nylund L, Heikkila P, Hameila M. et al. 1992. Genotoxic effects and chemical compositions of four creosotes. Mutat Res 265(2) 223-236. 

Coal tar creosote is a brownish-black/yellowish-dark green oily liquid with a characteristic sharp odor, obtained by the fractional distillation of crude coal tars. The approximate distillation range is 200°C-400°C (390°F-750°F). The chemical composition of creosotes is influenced by the origin of the coal and also by the nature of the distilling process as a result, the creosote components are rarely consistent in their type and concentration. 

This profile addresses the toxicological and toxicokinetics database for several substances, wood creosote, coal tar creosote, coal tar, coal tar pitch, and coal tar pitch volatiles, whose production stems from the incomplete combustion or pyrolysis of carbon-containing materials. Creosotes, coal tar, coal tar pitch, and coal tar pitch volatiles are composed of many individual compounds of varying physical and chemical characteristics. In addition, the composition of each, although referred to by specific name (e.g., wood creosote or coal tar creosote) is not consistent. For instance, the components and properties of the mixture depend on the temperature of the destructive distillation (carbonization) and on the nature of the carbon-containing material used as a feedstock for combustion. 

The pharmacokinetics of wood creosote, coal tar creosote, coal tar, coal tar pitch, and coal tar pitch volatiles have not been defined because of their chemical complexity. Creosotes vary tremendously in composition and hence, mechanisms of action most likely differ among individual samples of creosotes. Information on individual components is not adequate to define the properties of the whole mixture and for this reason no PBPK models have been proposed for creosote. 

Animal-to-human extrapolations of the toxicity of creosote are complicated by the inherent chemical variety of these substances. Creosotes are complex mixtures of variable composition and the individual components are likely to show interspecies variation in toxicity. Only one study was located that treated more than one species of animal with the same sample of creosote (Miyazato et al. 1981), and although this study suggested that mice were more susceptible to the acute effects of beechwood creosote than rats, the differential susceptibility observed with this particular sample cannot be applied to creosotes of different composition. In general, the adverse effects observed in animals are similar to those reported for humans with cancer being the most serious, but it is not possible at present to assess whether the doses required to produce adverse effects in animal systems are similar to those required to produce similar effects in humans. 

The chemical synonyms and identification numbers for wood creosote, coal tar creosote, and coal tar are listed in Tables 4-1 through 4-3. Coal tar pitch is similar in composition to coal tar creosote and is not presented separately. Coal tar pitch volatiles are compounds given off from coal tar pitch when it is heated. The volatile component is not shown separately because it varies with the composition of the pitch. Creosotes and coal tars are complex mixtures of variable composition containing primarily condensed aromatic ring compounds (coal-derived substances) or phenols (wood creosote). Therefore, it is not possible to represent these materials with a single chemical formula and structure. The sources, chemical properties, and composition of coal tar creosote, coal tar pitch, and coal tar justify treating these materials as a whole. Wood creosote is discussed separately because it is different in nature, use, and risk. 

Physical and Chemical Properties. Limited physical property data, such as boiling point and density (see Table 4-2), are available for the coal tar creosote mixture. Additional physical and chemical property data, such as water solubility, vapor pressure, Koc, and Henry s law constant values would be useful in order to predict the partitioning and transformation of coal tar creosote components in air, water, and soil. These values are currently not available because their determination is complicated by the fact that creosote is a mixture of variable composition. However, data on vapor pressure, water solubility, etc., are available for individual components of creosote, and these can be used to estimate the behavior of creosote. 

The creosote fraction of coal tar has a variable composition (Table 13.11) and may contain specific chemical compounds that can be isolated for commercial use. For example, when creosote oil is cooled, a solid referred to as anthracene cake may separate and consists primarily of anthracene, carbazole, and phenanthrene (Table 13.12). 

Anti-stripping agents are chemical substances that have a similar composition to emulsifiers and are divided into (a) anionic type, such as organic acids (creosote) and fatty acids (oleic acid, stearic acid, pine pitch, etc.), and (b) cationic type, such as amines (simple amines, diamines, tertiary amines, polyamines and imidazolines) and salts of quaternary ammonium. 

Creosote and chromated copper arsenate (CCA) have been widely used as preservatives for antibacterial treatment of wood. In spite of their excellence in this property, they have some drawbacks in toxicity. Therefore, less toxic and environmentally-benign chemicals are expected to be used. Quaternary alkylammonium salts are, thus, one of the candidates for the anti-microbial treatment of wood. In this study of wood-inorganic composites, trimethoxysilylpropyldimethyloctadecyl ammonium chloride (TMSAC), shown below, was used as a property enhancer to add an anti-bacterial property to wood (Tanno, 1997). 

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