Creosote

Creosote is the name used for a variety of products including wood creosote and coal tar creosote. Wood creosote is created by high temperature treatment of beech and other woods, or from the resin of the Creosote bush.

The term creosote, however, is most commonly used to refer to coal tar creosote. Coal tar creosote is is an EPA-registered wood preservative. It is distilled from crude coke oven tar, and is mainly composed of polycyclic aromatic hydrocarbons (PAHs), but also contains phenols and cresols.

The term is also used to refer to the buildup of carbon materials in chimneys from wood-burning fires.

Wood creosote
Wood creosote is a colorless to yellowish greasy liquid with a smoky odor and burned taste.

Wood creosote has been used as a disinfectant, a laxative, and a cough treatment, but these have mostly been replaced by newer medicines.

The popular Japanese anti-diarrheic Seirogan has 133 mg creosote (from beech, maple or oak wood) per adult dose as its primary ingredient. 

Coal tar creosote
When most people use the term creosote, they are referring to coal tar creosote. Coal tar creosote is the most widely used wood preservative in the United States. It is a thick, oily liquid typically amber to black in color. The American Wood Preservers' association states that creosote "shall be a distillate derived entirely from tars produced from the carbonization of bituminous coal." Coal tar used for certain applications may be a mixture of coal tar distillate and coal tar. See, AWPA Standards

The prevailing use of creosote in the United States is to preserve wooden utilities/telephone poles, railroad cross ties, switch ties and bridge timbers from decay. It is registered with USEPA for this purpose. Coal tar products are also used in medicines to treat diseases such as psoriasis, and as animal and bird repellents, insecticides, animal dips, and fungicides. Some over the counter anti-dandruff shampoos contain coal tar solutions.

Chimney creosote and chimney fires
The type of creosote that builds up in the chimney of a wood burning fireplace is distinct from wood creosote and coal tar creosote. Fireplace creosote is actually condensed flue gas, consisting of steam and vaporized but unburned carbon materials present in the wood. Flue gas has fairly high ignition temperature, and most wood stoves utilizing natural air convection do not have a high enough combustion temperature to ignite the vapors. Consequently, flue gas floats up the exhaust pipe, and then condenses onto the cool interior lining of the chimney forming what is often referred to as creosote. Burning a large hot fire helps prevent creosote buildup that could lead to a chimney fire because the continued heat output from the fire eventually warms up the lining of the chimney sufficiently to revaporize the deposited creosote. Chimney fires can be volcanic and have been known to spread to roofs, destroying homes. It is important to remove chimney creosote as it builds up.

Health effects of coal tar creosote
According to the Agency for Toxic Substances and Disease Registry (ATSDR), eating food or drinking water contaminated with high levels of coal tar creosote may cause a burning in the mouth and throat, and stomach pains.

ATDSR also states that brief direct contact with large amounts of coal tar creosote may result in a rash or severe irritation of the skin, chemical burns of the surfaces of the eyes, convulsions and mental confusion, kidney or liver problems, unconsciousness, and even death. Longer direct skin contact with low levels of creosote mixtures or their vapors can result in increased light sensitivity, damage to the cornea, and skin damage. Longer exposure to creosote vapors can cause irritation of the respiratory tract.

The International Agency for Research on Cancer (IARC) has determined that coal tar creosote is probably carcinogenic to humans, based on adequate animal evidence and limited human evidence. It is instructive to note that the animal testing relied upon by IARC involved the continuous application of creosote to the shaved skin of rodents. After weeks of creosote application, the animals developed cancerous skin lesions and in one test, lesions of the lung. The United States Environmental Protection Agency has stated that coal tar creosote is a possible human carcinogen.

There is no unique exposure pathway of children to creosote. Children exposed to creosote will probably experience the same health effects seen in adults exposed to creosote. It is unknown whether children differ from adults in their susceptibility to health effects from creosote.

A 2005 mortality study of creosote workers found no evidence supporting an increased risk of cancer death as a result of exposure to creosote. Based on the findings of the largest mortality study to date of workers employed in creosote wood treating plants, there is no evidence that employment at creosote wood-treating plants or exposure to creosote-based preservatives was associated with any significant mortality increase from either site-specific cancers or non-malignant diseases. The study consisted of 2,179 employees at eleven plants in the United States where wood was treated with creosote preservatives. Some workers began work in the 1940s to 1950s. The observation period of the study covered 1979- 2001. The average length of employment was 12.5 years. One third of the study subjects was employed for over 15 years.