Research Scientist

PAH's Polycyclic Aromatic Hydrocarbons

Background Information

The U.S. Environmental Protection Agency defines PAHs as: 7-PAH (Polycyclic Aromatic Hydrocarbons). The 7-PAH group includes 7 chemical species:


    The 7-PAH are a subset of 16-PAH (16-PAH is referred to as Polycyclic Organic matter or "POM" in the presentation of results for the assessment). The 7 species that make up 7-PAH are probable human carcinogens.

What are PAHs?

    PAHs are a group of chemicals that are formed during the incomplete burning of coal, oil, gas, wood, garbage, or other organic substances, such as tobacco and charbroiled meat. There are more than 100 different PAHs. PAHs generally occur as complex mixtures (for example, as part of combustion products such as soot, not as single compounds. PAHs usually occur naturally, but they can be manufactured as individual compounds for research purposes; however, not as the mixtures found in combustion products.

    As pure chemicals, PAHs generally exist as colorless, white, or pale yellow-green solids. They can have a faint, pleasant odor. A few PAHs are used in medicines and to make dyes, plastics, and pesticides. Others are contained in asphalt used in road construction. They can also be found in substances such as crude oil, coal, coal tar pitch, creosote, and roofing tar. They are found throughout the environment in the air, water, and soil. They can occur in the air, either attached to dust particles or as solids in soil or sediment.

    In the environment, you are most likely to be exposed to PAH vapors or PAHs that are attached to dust and other particles in the air. Sources include cigarette smoke, vehicle exhausts, asphalt roads, coal, coal tar, wildfires, agricultural burning, residential wood burning, municipal and industrial waste incineration, and hazardous waste sites. Background levels of some representative PAHs in the air are reported to be 0.02–1.2 nanograms per cubic meter (ng/m³; a nanogram is one-millionth of a milligram) in rural areas and 0.15–19.3 ng/m³ in urban areas.

    You may be exposed to PAHs in soil near areas where coal, wood, gasoline, or other products have been burned. You may be exposed to PAHs in the soil at or near hazardous waste sites, such as former manufactured-gas factory sites and wood-preserving facilities. PAHs have been found in some drinking water supplies in the United States. Background levels of PAHs in drinking water range from 4 to 24 nanograms per liter (ng/L; a liter is slightly more than a quart).

    In the home, PAHs are present in tobacco smoke, smoke from wood fires, creosote-treated wood products, cereals, grains, flour, bread, vegetables, fruits, meat, processed or pickled foods, and contaminated cow's milk or human breast milk. Food grown in contaminated soil or air may also contain PAHs. Cooking meat or other food at high temperatures, which happens during grilling or charring, increases the amount of PAHs in the food. The level of PAHs in the typical U.S. diet is less than 2 parts of total PAHs per billion parts of food (ppb), or less than 2 micrograms per kilogram of food (µg/kg; a microgram is one-thousandth of a milligram).

    The Department of Health and Human Services (DHHS) has determined that some PAHs may reasonably be expected to be carcinogens.

    Some people who have breathed or touched mixtures of PAHs and other chemicals for long periods of time have developed cancer. Some PAHs have caused cancer in laboratory animals when they breathed air containing them (lung cancer), ingested them in food (stomach cancer), or had them applied to their skin (skin cancer).


Links to News & Articles:

    Hazardous Chemicals in Synthetic Turf: Rachel's Democracy & Health News #871, September 7, 2006

    Hazardous Chemicals in Synthetic Turf: Follow-Up Analyses Rachel's Democracy & Health News #992, Apr. 12, 2007.

    Environmental Health Perspectives – List of Studies on PAHs

Last updated 6-8-2016


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