Benzo[a]pyrene causes cancer in a simple, direct way. Nearly all living things have in common a group of cellular enzymes responsible for detoxifying and metabolizing possibly harmful chemical invaders. When this enzyme group encounters benzo[a]pyrene, it inserts oxygen into the foreign molecule, the first step toward breaking it down. However, in a strange twist of fate, this addition activates benzo[a]pyrene rather than detoxifies it. The altered molecule now has the ability to bond tightly to a strand of DNA — that is, to one of the cell’s chromosomes along which lie the organism’s genes. A chemical invader so attached is called a DNA adduct, and it has the power to alter the structure of the DNA strand and cause a genetic mutation. If uncorrected, this type of damage can become a crucial step leading to the formation of cancer. Page 136
Benzo(a)pyrene (a polycyclic aromatic hydrocarbon reproductive [see below], formed when oil or gasoline burns) – Irritation to eyes and skin, cancer, possible effects.
– Taken from the Training Marine Oil Spill Response Workers under OSHA’s Hazardous Waste Operations and Emergency Response Standard
Coal tar itself is classified as a known carcinogen, but because humans are almost always exposed to its constituent ingredients in mixtures, the data from human studies are inadequate to so classify benzo[a]pyrene individually.