Benzo[a]pyrene is a polycyclic aromatic hydrocarbon found in coal tar with the formula C 20 H 12. 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).roperly speaking, benzo[ a ]pyrene is a procarcinogen, meaning that the mechanism of carcinogenesis of benzo[ a ]pyrene depends on enzymatic metabolism of benzo[ a ]pyrene to the ultimate mutagen, benzo[ a ]pyrene diol epoxide, pictured above at right.