PAHs


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What are PAHs?

PAH stands for polyaromatic hydrocarbon. There are more than one hundred different PAHs. Most are colorless or lightly tinted solids; some have faint odors. All have at least two benzene rings joined together (that is, sharing at least one side) in various configurations. For example, chrysene, shown below, has four benzene rings fused together. Other names for PAHs include polycyclic aromatic hydrocarbons (PAHs) and polynuclear aromatics (PNAs). PAHs known to be carcinogenic are sometimes referred to as cPAHs.

Chrysene structural diagram: National Institutes of Health


PAHs do not typically occur in isolation. Where there is one PAH, there are usually others. Most environmental investigations focus on a small subset of PAHs:

Acenaphthene

Acenaphthylene

Anthracene

Benzo(a)anthracene

Benzo(a)pyrene

Benzo(e)pyrene

Benzo(b)fluoranthene

Benzo(ghi)perylene

Benzo(j)fluoranthene

Benzo(k)fluoranthene

Chrysene

Dibenzo(a,h)anthracene

Fluoranthene

Fluorene

Indeno(1,2,3-cd)pyrene

1-Methylnaphthalene

2-Methylnaphthalene

Naphthalene

Phenanthrene

Pyrene

Sources of PAHs

PAHs occur in fossil fuels and fossil fuel derivatives like asphalt and coal tar. They also arise as byproducts of incomplete combustion of organic matter. For example, tobacco smoke and chargrilled meats contain PAHs. It is also possible to manufacture PAHs.

Uses of PAHs

Some PAHs are used to manufacture pesticides, dyes, and plastics. However, most PAHs occur as a small component of products like coal, oil, tar, and creosote and are not used individually.

Exposure to PAHs

Sources of PAH exposure include cigarette smoke, exhaust from vehicles, asphalt, coal tar, fires, including wood burning stoves, chargrilled foods, incinerators, and hazardous waste sites.

The most common exposures are from tobacco smoke, wood smoke, and foods. Worker exposure can occur in many different industries, including during production of coal tar, coke, asphalt, coal gas, smoked meats, aluminum, and at incinerators.

Health Effects of PAHs

There are many different PAHs. The health effects of exposure to PAHs, where known, differ from chemical to chemical. See the individual chemical pages (linked above, where available) for more information on health effects of individual PAHs.

References

Agency for Toxic Substances and Disease Registry. 1995. Toxicologial Profile for Polycyclic Aromatic Hydrocarbons.

National Institutes of Health