Agency for Toxic Substances and Disease Registry 
Case Studies in Environmental Medicine (CSEM) 
Toxicity of Polycyclic Aromatic Hydrocarbons (PAHs)
Who Is at Risk of Exposure to PAHs?

Learning Objectives

Upon completion of this section, you will be able to

• identify the populations at high risk for exposure to PAHs.

Introduction

Persons working with coal and coal products have a greater likelihood of exposure to PAHs. Awareness of historical occupational and environmental exposures can aid the clinician in not only assessing potential sources of exposure but also in recognizing those populations who may be at higher risk of exposure.

Historical Occupational Exposures

Percival Pott, an English surgeon, was the first to report a connection between occupational exposure and cancer. In 1775, he described an unusually high incidence of scrotal cancer among London chimney sweeps and suggested this was due to their exposure to soot and ash. Since then, other coal tar-related cancers have been induced in laboratory animals and found in humans [Kennaway 1995; Kjaerheim 1999]. For example, the PAH benzo(a)pyrene, which was isolated from coal tar in the 1930s, was determined to be carcinogenic when applied to the skin of test animals. In 1947, the relationship between lung cancer and working conditions of gas industry workers and those working with coal tar was established [Kenneway 1995]. An increased incidence of cancers, particularly of the lung, was shown in epidemiologic studies of gas workers [Doll et al. 1965, 1972]. Several epidemiologic studies have shown increased cancer mortality in workers exposed to PAH mixtures. Exposure to other potentially carcinogenic substances often occurred in these studies [Lloyd 1971; Mazumdar et al. 1975; Redmond et al. 1972; Redmond and Strobino 1976; Hammond et al. 1976].

Current Occupational Exposures

Workers in industries or trades using or producing coal or coal products are at highest risk for PAH exposure. Those workers include, but are not limited to

• aluminum workers,
• asphalt workers,
• carbon black workers,
• chimney sweeps,
• coal-gas workers,
• coke oven workers,
• fishermen (coal tar on nets),
• graphite electrode workers,
• machinists,
• mechanics (auto and diesel engine),
• printers,
• road (pavement) workers,
• roofers,
• steel foundry workers,
• tire and rubber manufacturing workers, and
• workers exposed to creosote, such as
  • carpenters,
  • farmers,
  • railroad workers,
  • tunnel construction workers, and
  • utility workers.

A small increased risk of cancer in workers exposed to diesel exhaust has been suggested by some epidemiologic studies [Bhatia et al. 1998; Boffetta et al. 1988, 1990, 1997; Garshick et al. 1987, 1988; Steenland et al. 1990, 1992]. Exposure is almost always to mixtures that pose a challenge in developing conclusions [Samet 1995].

Historical Environmental Exposures

Historically, in locations where gas for lighting and heating was manufactured from coal or oil, large amounts of PAHs existed and may still exist as waste deposits. Before World War II, more than 1,000 coal gasification plants are estimated to have existed throughout the midwestern and eastern United States [Environmental Research and Technology 1984]. These plants began to phase out in the early 1950s when the use of interstate natural gas pipelines became more prominent.

Susceptible Populations

Fetuses may be at risk for PAH exposure. PAH and its metabolites have been shown to cross the placenta in various animal studies [ATSDR 1995].

Because PAHs are excreted in breast milk, nursing infants of exposed mothers can be secondarily exposed.

Key Points

• PAH and metabolites cross the placenta and are excreted in breast milk.
• Occupations that entail exposure to PAH include workers exposed to coal and coal products.

Progress Check