Polynuclear aromatic hydrocarbons (PNAH) are ubiquitous and are found in waters, soil, and bottom sediments throughout the world, although the concentrations are higher in industrialized locations. Interest in these compounds is generated by their carcinogenic and mutagenic properties. Although biosynthesis and petroleum spillages may be sources for PNAH's in localized areas, the major source of these compounds is pyrolytic. They tend to degrade by photo and biological oxidation. Like other hydrocarbons, they accumulate in most seafood, especially in bivalves.