A complex group of aromatic hydrocarbons containing 2 to 6 benzene rings that may have aliphatic and/or alicyclic hydrocarbon substituents. The parent compounds range from naphthalene to anthanthrene. They are found in many foods as environmental contaminants at low concentrations, including fish and shellfish, for which selected total 3 to 5 ring compounds in the edible parts are generally within the range from 0. 1 to 50 mg/kg from nonindustrialised areas. Lipid rich tissues may have concentrations up to 10 times that in lean muscle. PAHs are also found in fisheries by-products such as fish meal, fish oil and supplements derived from fish oils. In fish and shellfish exposed to environmental sources of PAHs such as industrially polluted sediments or spilled petroleum and petroleum products, the concentrations may be enhanced considerably by up to 1000 fold, particularly if exposure is acute. Once the source is removed the contaminants are slowly lost by the living animal. PAHs are invariably found in smoked fish products at concentrations up to about 10 times or more of those in unsmoked products depending on the degree of exposure to smoke.