CHEMISTRY AND STRUCTURES

The term polycyclic aromatic hydrocarbons (PAHs) generally refers to a group of chemical compounds consisting of carbon and hydrogen atoms arranged as planar compounds whose principal structural feature is fused rings. Their nomenclature has evolved over many decades and is complex. A comprehensive listing, including traditional synonyms and chemical struc-tures, is given by Sander and Wise (1). PAHs are produced during the incomplete combustion of organic material and are among the most ubiquitous environmental pollutants. The combustion processes that release PAHs invariably produce a variety of compounds, and in fact, it is difficult or impossible to ascribe health effects in humans to particular members of the PAH family. Hence, PAHs are usually treated as a group for the purpose of risk assessment. However, the relative amounts of individual PAHs released vary from one source to another. The PAH “fingerprint ” of diesel exhaust, for example, is markedly different from that of mainstream tobacco smoke (2). Thus, environmental concentrations of PAHs reported in the literature often consist of lists with varying numbers of compounds. Polycyclic organic matter is defined as a group of 16 individual PAH species (acenaphthene, acenaphthylene, anthracene, benzo(a)anthracene, benzo(a)pyrene, benzo(b)fluo-ranthene, benzo(ghi)perylene, benzo(k)fluoranthene, chrysene, dibenz(a,h)anthracene, fluoranthene, fluo-rene, indeno(1,2,3-cd)pyrene, naphthalene, phenan-threne, pyrene) that includes a group of seven PAHs (in bold) that are probable human carcinogens. Figure 81.1 illustrates structures of key PAHs. The best-known PAH is benzo(a)pyrene (BaP), due to its early identification in coal tar and later use as a model compound for investigat-ing the carcinogenic properties of tobacco smoke