Polycyclic Aromatic Hydrocarbons (PAHs, polynuclear hydrocarbons)

Polycyclic Aromatic Hydrocarbons

(PAHs, polynuclear hydrocarbons)

Since the PAHs are rarely found individually in the environment and the

effects on the environment and human health are not well defined for discrete

PAHs, the reader is asked to refer to this toxicity profile for general information

on the PAHs and to use the individual toxicity profiles for specific compounds.

Potential sources and exposure

The PAHs are a group of compounds that are formed during the incomplete

combustion of coal, oil, gas, wood, and other organic compounds. Natural

sources of PAHs include forest fires and volcanic eruptions. PAHs are

ubiquitous in soil and are rarely found as individual compounds. The greatest

exposure sources of PAHs to humans are active or passive inhalation of the

compounds in tobacco smoke, wood smoke, and contaminated air. Exposure may

also occur through ingestion of grilled or smoked foods, contaminated water or

foods and through skin contact with soot, tars, or contaminated sediments.

Physical and chemical properties

The PAHs have been categorized by the number of aromatic rings in their

chemical structure as well as by their carcinogenicity in laboratory animals.

Although naphthalene is a two-ringed structure, it is frequently categorized as a

PAH. The other compounds are listed below and are three-, four-, or five-ringed

structures. PAHs commonly found in the environment are solids at room

temperature and are virtually insoluble in water.

3-Ringed PAHs

4-Ringed PAHs

> 4-Ringed PAHs

2-Ringed PAH

Naphthalene

Acenaphthene

Benzo(a)anthracene

Benzo(b)fluoranthene

Acenaphthylene

Benzo(a)pyrene

Benzo(k)fluoranthene

Anthracene

Chrysene

Benzo(ghi)perylene

Fluorene

Fluoranthene

Dibenz(a,h)anthracene

Phenanthrene

Pyrene

Indeno(1,2,3-cd)pyrene

Toxicity

Within the large class of PAHs, there have been many structure-activity

relationship studies to relate chemical structure to carcinogenic activity. Each of

the environmentally relevant PAHs have been tested for their carcinogenicity in

animal studies and the compounds are categorized by carcinogenicity in the

following tabulation.

D65

Appendix D Toxicological Profiles