Dense Nonaqueous Phase Liquids (DNAPLs)

Multi-Component Waste

Coal Tars

Human Health Toxicity

Coal tars are complex mixtures that vary with the type of coal and the method of production used to produce them. However, there are general classes of compounds common to all coal tars, and these include polycyclic aromatic hydrocarbons (PAHs), phenols, and heterocyclic compounds that incorporate oxygen, sulfur, or nitrogen into their ring structure. To a large extent, the toxicity of coal tar is due to the toxicity of its major components, such as the PAHs, cresols, and phenols, but since tars are a mixture, they may behave in unexpected ways. Individual compounds or groups of compounds may potentiate or antagonize each other's effects.

The general population may be exposed to coal tars through soaps, shampoos, and ointments used to treat skin conditions, such as eczema and psoriasis. Coal tar may be ingested from contaminated water or from fish and shellfish that have taken up components of the coal tar mixture from a contaminated environment. Occupational exposure to coal tar may occur in many industries, including coal gasification, aluminum smelting, steel, and coke production. Industrial workers are exposed to coal tar through dermal contact or through inhalation of coal tar fumes.

Coal tar can be absorbed through the skin, gastrointestinal tract, and lungs, but there is little information on the rate of uptake or the amount absorbed per exposure. Metabolism of the majority of coal tar probably takes place in the liver. Components of the coal tar mixture are excreted through urine and feces. Coal tar components have been shown to bioaccumulate and may be present in body fat and also in breast milk.

Animal studies of coal tar have shown both cancer and non-cancer effects. Adverse non-cancer effects when coal tar was inhaled as an aerosol include lesions of the olfactory epithelium, increases in lung weight, alterations in the microscopic structure of lung tissue, changes in the microscopic structure of the gut, and inflammation of the caecum. Rats and guinea pigs exposed to coal tar vapors show respiratory symptoms, such as chronic fibrosing inflammation of the lung tissue and the development of adenomas around the air passages. Rats and mice show kidney changes in response to the inhalation of coal tar vapor.

Minimal information exists on the reproductive effects of coal tar in humans. While one human study found no effects (spontaneous abortions) from the use of coal tar preparations to control psoriasis during pregnancy, animal studies (by all routes of exposure) have indicated that coal tar may be a reproductive toxicant. Animal exposure to coal tar increased resorptions, decreased ovary weights, and increased testis weights. Coal tar exerts developmental toxicity in rats and mice by all routes of exposure. These effects are severe and include a rise in the incidence of cleft palate and prenatal mortality and decreases in fetal weight, ossification, crown-rump length, and placental weights.

Based on the numerous studies of occupational exposure to coal tars, it can be concluded that coal tars are human carcinogens. Occupational exposure to coal tar is associated with cancers of the skin and scrotum. In addition, cancers of the lung, bladder, kidney, and digestive tract are also associated with coal tar exposure in the workplace. An increased risk of leukemia has been reported. Animal studies support the conclusion that coal tar is carcinogenic. Dermal exposure to coal tar caused skin tumors in mice and rabbits and lung cancers in rats. Lung tumors were found in mice and rats after inhalation of coal tar. Coal tar feeding studies in mice showed a concentration-related increase in the number of neoplasms in the liver, lung, and fore-stomach, and also sarcomas.

Evidence provided by a study of lymphocytes from workers exposed to coal tar suggests that it is genotoxic. Patients treated with dermal applications of coal tar for skin conditions also show blood changes that indicate genotoxicity. In vitro studies (Ames test using S. typhimurium) have demonstrated the genotoxicity of coal tar.

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Adapted from:

Toxicological Profile for Wood Creosote, Coal Tar Creosote, Coal Tar, Coal Tar Pitch, and Coal Tar Pitch Volatiles
Agency for Toxic Substances and Disease Registry (ATSDR)
Department of Health and Human Services, Atlanta, GA, 2002

Report on Carcinogens, Eleventh Edition
National Toxicology Program (NTP), 2002
U.S. Department of Health and Human Services

Ecological Risk

No studies or reports were available regarding the toxicity of coal tar to species other than laboratory animals. However, ecological studies are available for individual compounds or classes of compounds in coal tar mixtures. As previously noted, a coal tar mixture may not exert the same effects as its components. Since coal tar components are found in fat, the potential for bioaccumulation exists.

Human Health References

Report on Carcinogens, Eleventh Edition
National Toxicology Program (NTP), 2002
U.S. Department of Health and Human Services

This two-page summary provides data on the carcinogenicity of coal tar, its uses, properties, production and exposure.

A Review of Human Carcinogens: Coal-Tar Pitch
IARC Working Group on the Evaluation of Carcinogenic Risks to Humans.
World Health Organization, International Agency for Research on Cancer (IARC) Monographs, Vol 100F, p 161-166, 2012

Toxicological Profile for Wood Creosote, Coal Tar Creosote, Coal Tar, Coal Tar Pitch, and Coal Tar Pitch Volatiles
Agency for Toxic Substances and Disease Registry (ATSDR)
Department of Health and Human Services, Atlanta, GA, 2002

This profile covers human health effects, chemical and physical properties, manufacturing volume data, potential for human exposure (environmental fate and transport), and analytical methods for coal tars among other similar mixtures.

Toxicology of polycyclic aromatic hydrocarbon mixtures
Flowers, L.
NCACSOT Spring Symposium, May 24, 2005

This PowerPoint™ presentation provides information on the occurrence and toxicology of polycyclic aromatic hydrocarbon mixtures.

Ecological References

Environmental Contaminants Encyclopedia
Irwin, R.J. et al.
National Park Service, Water Resources Division, Fort Collins, CO, 1998

This web page provides information on human health effects, fate and transport, production, and uses of many chemicals including a coal tar section.

Toxicological Profile for Wood Creosote, Coal Tar Creosote, Coal Tar, Coal Tar Pitch, and Coal Tar Pitch Volatiles
Agency for Toxic Substances and Disease Registry (ATSDR)
Department of Health and Human Services, Atlanta, GA, 2002

This profile covers human health effects, chemical and physical properties, manufacturing volume data, potential for human exposure (environmental fate and transport), and analytical methods for coal tars among other similar mixtures.