Creosote

Did You Know?

• Creosote deposits in chimneys can become several inches thick over a season, reducing draft and increasing the likelihood of incomplete combustion.
• Marine pilings treated with creosote can be broken or washed away during hurricanes, settling on the water bottom and slowly leaching chemicals over a long period.

Creosote oils

The term creosote has a broad range of definitions depending on the origin of the coal tar oil and the intended use. All creosote-treated wood products—such as foundation and marine pilings, lumber, posts, railroad ties, timbers, and utility poles—are manufactured using this type of preservative, and the process can only be a pressure process supervised by a licensed applicator certified by State Departments of Agriculture. Brush-on, spray, or non-pressure uses are not allowed under the EPA-approved label. The AWPA Standards do not permit mixing with other creosote-type materials like lignite-tar creosote, oil-tar creosote, peat-tar creosote, water-gas-tar creosote, or wood-tar creosote, though blending with a high-boiling petroleum oil meeting AWPA Standard P4 is allowed. The other types of creosote materials are no longer manufactured and have been replaced by more economical, efficacious, or safer products. Historically, coal-tar creosote and wood-tar creosote were thought to be equivalent but were later found to be chemically different; coal-tar creosote relies on naphthalenes and anthracenes for its effects, while wood-tar creosote relies on methyl ethers of phenol.

Health effects

Eating food or drinking water contaminated with high levels of coal-tar creosote may cause burning in the mouth and throat, and stomach pains. Brief direct contact with large amounts can result in rash, severe skin irritation, chemical burns of the eyes, convulsions, mental confusion, kidney or liver problems, unconsciousness, and death. Longer skin contact with low levels or their vapors can increase light sensitivity, damage the cornea, and cause skin damage, while extended exposure to vapors can irritate the respiratory tract. The International Agency for Research on Cancer has determined that coal-tar creosote is probably carcinogenic to humans, based on adequate animal evidence and limited human evidence; animal testing involved continuous application to shaved rodent skin, leading to cancerous skin lesions and lung lesions. The United States Environmental Protection Agency considers coal-tar creosote a probable human carcinogen. Children exposed to creosote likely experience the same health effects as adults, and it is unknown whether they differ in susceptibility.

Chemical reactions with sediment and organisms

When soluble compounds from creosote preservative leach into water, they react with the environment or are consumed by organisms. Alkylation occurs when a molecule replaces a hydrogen atom with an alkyl group, often from organometallic compounds or methanol found naturally in the environment. In c-alkylation, such as between m-cresol and methanol, the methyl group replaces a hydrogen on a carbon in the benzene ring, producing isomers of dimethylphenol (DMP), which is listed as an aquatic hazard with toxic long-lasting effects. In o-alkylation, as between phenol and methanol, the methyl group replaces the hydrogen on the -OH group, forming methoxybenzene (anisole), which is listed as an acute hazard to aquatic life with long-term effects. These reactions can occur in either para- or ortho- orientations.

Environmental hazards

In aquatic sediments, chemicals released by creosote preservatives can transform into more dangerous compounds. Cresol (m-, p-, and o-), phenol, guaiacol, and xylenol (1,3,4- and 1,3,5-) are acute aquatic hazards before any reactions. Alkylation adds R-groups to produce compounds such as 3,4-dimethylphenol, 2,3-dimethylphenol, and 2,5-dimethylphenol, all listed as acute environmental hazards. Biodegradation controls the rate at which sediment holds chemicals and the number of reactions, and oxidation-reduction reactions can break compounds into more toxic molecules, such as p-benzoquinone from phenol oxidation. The byproducts of these reactions are also environmentally hazardous. Organisms in contaminated sediment are exposed to these chemicals and are then ingested by fish and other aquatic animals, leading to bioaccumulation. Mollusks and smaller crustaceans attached directly to creosote-treated pilings are at higher risk, taking on high concentrations that transfer through the ecosystem's food chain.