Creosote is a term that refers to two entirely different substances: a highly effective industrial chemical used for preservation and a botanical compound derived from a common desert shrub. This shared name frequently causes confusion, as the chemical and the plant have no biological or functional connection. The chemical creosote is a manufactured product, while the plant creosote is a naturally occurring organism adapted to arid climates.
Creosote as an Industrial Chemical
The chemical form of creosote, known as coal-tar creosote, is an oily mixture derived from the high-temperature distillation of coal tar. It is typically dark amber to black and possesses a characteristic smoky odor. This complex mixture is mainly composed of polycyclic aromatic hydrocarbons (PAHs), which often constitute 75% or more of the substance.
For over a century, its primary function has been as a heavy-duty wood preservative. The mixture is forced deep into wood products using high-pressure equipment at specialized treatment facilities. This process creates a barrier highly resistant to water, rot, fungi, and insect pests.
Creosote-treated lumber is commonly used for infrastructure projects requiring long-term exposure resistance. These materials include railroad ties, utility poles, and marine pilings.
Creosote as a Desert Plant
The botanical source of the name is the creosote bush (Larrea tridentata), an evergreen shrub prominent in the Mojave, Sonoran, and Chihuahuan Deserts of North America. It thrives in arid regions, growing up to 4 meters tall and displaying small, dark green leaves.
The leaves are coated in a sticky, oily resin, which is a unique adaptation for conserving water. This resin contains compounds that give the plant its strong, distinct fragrance, often compared to the smell of the industrial creosote chemical. The scent intensifies dramatically after a desert rain.
The creosote bush produces small, yellow flowers and fuzzy, spherical fruit capsules. Indigenous North American tribes widely used the shrub for medicinal purposes. Traditional applications included using leaf decoctions to treat intestinal complaints and toothache, and applying poultices as a topical antiseptic.
Navigating Health and Environmental Risks
The health consequences and environmental management strategies for the industrial chemical and the plant differ significantly. Industrial coal-tar creosote is classified by regulatory bodies as a probable human carcinogen. This classification is primarily due to the high concentration of polycyclic aromatic hydrocarbons (PAHs) in the mixture.
Long-term occupational exposure, especially through skin contact, has been linked to an increased risk of skin and respiratory cancers in workers. Consequently, the U.S. Environmental Protection Agency (EPA) strictly regulates the use of creosote, limiting its application to certified professionals in specialized facilities.
Environmental concerns arise because creosote components can persist in the environment. This persistence often leads to soil and groundwater contamination at former wood treatment sites.
For the creosote bush, the main health concerns relate to internal consumption of concentrated extracts. The plant contains an active compound called nordihydroguaiaretic acid (NDGA), a potent antioxidant.
While traditional uses involved mild teas, modern herbal supplements in capsule or highly concentrated extract form have been associated with cases of acute liver injury. Health authorities, including the U.S. Food and Drug Administration (FDA), have issued warnings regarding the internal use of concentrated chaparral—the herbal name for the creosote bush—due to the risk of liver and kidney damage.
The mechanism of liver damage is complex, but it may involve high concentrations of NDGA interfering with metabolic pathways. Modern practitioners advise caution and generally discourage the ingestion of highly concentrated supplements or teas because of the potential for adverse effects.