Polycyclic Aromatic Hydrocarbons

Also known as polyaromatic hydrocarbon or polynuclear aromatic hydrocarbon, polycyclic aromatic hydrocarbon (PAH) is a chemical compound composed of only carbon and hydrogen with multiple aromatic rings.  This group contains several hundred chemically related and environmentally persistent organic compounds of various structures and varied toxicity. 

Polycyclic aromatic hydrocarbons are found naturally in petroleum products such as coal, crude oil, and gasoline as well as products made from fossil fuels, such as coal-tar pitch, creosote, and asphalt. They can be released from the process of burning coal, oil, gasoline, wood, garbage, tobacco, and meat.  Any PAHs generated from this burning can bind to or form small particles in the air.  Naturally, both wildfires and volcanos produce PAHs.  The less efficient the burning process, the more PAHs are given off.

PAHs can persist in the environment for months or years and can be found in the air, water, and soil.  While many hundreds of PAHs exist, 16 PAHs are considered “priority pollutants” by the U.S. Environmental Protection Agency (USEPA) 1977 Clean Water Act because of their toxicity and status as known or possible human carcinogens. Structurally, the simplest of these chemicals and most abundant is naphthalene which contains two aromatic rings. 

Effects of PAHs on human health depends on the exposure interval, concentration or exposure, the toxicity of the PAHs, and mechanism of exposure (inhalation, ingestion, dermal). Low level exposure to PAHs has unknown effects on humans.  Exposure to higher concentrations to PAHs such as naphthalene in the air can irritate both the skin and eyes.  Exposures to larger quantities on the skin and from breathing concentrated naphthalene vapor have resulted the development of blood and liver abnormalities in humans. 

Industrial workers face exposure risk in facilities where petroleum, petroleum products, or coal are used or where wood, cellulose, corn, or oil is burned.  These may include coal/tar production or processing facilities, smoke houses, aluminum production plants, and municipal trash incinerators.  Workers also may be exposed by inhaling engine exhaust or when using products containing PAHs as part of their job in industries such as mining, oil refining, metalworking, chemical production, and transportation.

Several other PAHs and mixtures of PAHs are considered cancer-causing chemicals.  Examples of PAHs include Naphthalene, Biphenyl, Fluorene, Anthracene, Phenanthrene, Phenalene, Tetracene, Chrysene, Triphenylene, Pyrene, Pentacene, Perylene, Benzo[a]pyrene, Corannulene, Benzo[ghi]perylene, Coronene, Ovalene, and Benzo[c]fluorene.

The USEPA has established maximum contaminant levels (MCLs) for public water supplies to reduce the chances of drinking contaminated water. MCLs are enforceable limits that these water supplies must meet. These standards are lower than levels at which health effects have been observed. Furthermore, the USEPA has not established MCLs for individual PAHs, but has set an MCL for total PAHs of 0.2 parts per billion.  USEPA requires the reporting of any releases of PAHs into the environment that exceed one pound. There are currently no regulations for the PAH content of foods.