Benzo(a)pyrene

Benzo[a]pyrene is a polycyclic aromatic hydrocarbon found in coal tar with the formula C20H12. Its metabolites are mutagenic and highly carcinogenic, and it is listed as a Group 1 carcinogen by the IARC. The compound is one of the benzopyrenes, formed by a benzene ring fused to pyrene, and is the result of incomplete combustion at temperatures between 300 °C (572 °F) and 600 °C (1,112 °F).

Chimney sweeps suffered from scrotal cancers in the 18th century, and frequent skin cancers were noted among fuel industry workers in the 19th century. In 1933, benzo[a]pyrene was determined to be the compound responsible for these cases, and its toxicity was demonstrated when skin tumors occurred in laboratory animals repeatedly painted with coal tar. When the body attempts to metabolise benzo[a]pyrene, the resulting diol epoxide reacts and binds to DNA, resulting in mutations and eventually cancer.

Benzo[a]pyrene is found in coal tar, in automobile exhaust fumes (especially from diesel engines), in all smoke resulting from the combustion of organic material (including cigarette smoke), and in charbroiled food. Cooked meat products, regular consumption of which has been epidemiologically associated with increased levels of colon cancer (although this in itself does not prove carcinogenicity), have been shown to contain up to 4 ng/g of benzo[a]pyrene, and up to 5.5 ng/g in fried chicken and 62.6 ng/g in overcooked charcoal barbecued beef.