Agency for Toxic Substances and Disease Registry 
Case Studies in Environmental Medicine (CSEM) 
Toxicity of Polycyclic Aromatic Hydrocarbons (PAHs)
Where Are PAHs Found?

Learning Objectives

Upon completion of this section, you will be able to

• identify where PAHs are found.

Introduction

PAHs are ubiquitous in the environment and are common byproducts of combustion processes. PAHs are a natural component of most fossil fuels.

Although produced naturally by forest fires and volcanoes, most PAHs in ambient air are the result of man-made processes. Such processes include

• burning fuels such as coal, wood, petroleum, petroleum products, or oil,
• burning refuse, used tires, polypropylene, or polystyrene,
• coke production, and
• motor vehicle exhaust [Cherng et al. 1996; Lewitas 1997].

There are approximately 100 different known PAHs in air, soil, foodstuffs, and water [Zedeck 1980]. Diesel exhaust contains significant amounts of PAHs.

Benzo(a)pyrene, a potent carcinogen, is commonly used as an environmental indicator for PAHs.

Industrial Use

PAHs are found in industries that produce or use coal tar, coke, or bitumen (asphalt). Coal tar pitch and creosote, which are complex mixtures of liquid and solid aromatic hydrocarbons produced in coke ovens, contain significant amounts of benzo(a)pyrene and other PAHs. PAHs are produced in

• coal gasification plants,
• municipal incinerators,
• smokehouses, and
• some aluminum production facilities.

Environmental Fate

Once emitted to the atmosphere, weight influences the fate of the gaseous PAH mixtures. Heavier PAHs (more than four rings) tend to adsorb to particulate matter, while lighter PAHs (less than four rings) tend to remain gaseous until removed via precipitation [Skupinska et al. 2004]. PAH concentrations in water tend to be low (around 100 ng/L) due to their weak solubility. The weak solubility leads to accumulation in sediments and aquatic organisms. PAHs can be absorbed by plants and can accumulate in soil.

Cigarettes

Cigarette smoke contains many PAHs; therefore, cigarette smoking and environmental tobacco smoke are additional sources of PAHs.

Environmental Indicator for PAHs

Benzo(a)pyrene, a potent carcinogen, is generally used as an environmental indicator for PAHs.

Key Points

• PAHs are ubiquitous in the environment.
• Most PAHs in ambient air are the result of man-made processes.
• PAHs are found in industries that produce or use coal tar, coke, or bitumen (asphalt). They are emitted by coal gasification plants, smokehouses, municipal incinerators, and some aluminum production facilities.
• PAHs mostly accumulate in soils.
• Benzo(a)pyrene is commonly used as an environmental indicator for PAHs.

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