benzo(a)pyrene
Meaning of benzo(a)pyrene: Five fused rings made whenever organic matter burns badly, and among the first pure chemicals isolated from coal tar and shown to cause tumors.
Definition of benzo(a)pyrene
Benzo(a)pyrene is a five-ring hydrocarbon formed when organic material burns incompletely, and one of the most closely studied chemical causes of cancer. It occurs in tobacco smoke, soot, coal tar, vehicle exhaust, wood smoke and charred or grilled meat, and it lingers in soil and water. The molecule is inert as it arrives; the body converts it into the reactive form that damages DNA.
Why does the body make it dangerous?
The molecule is flat, greasy and chemically dull, so the liver and lung treat it as waste to be made water-soluble and thrown out. Enzymes add oxygen to it in stages. One of the intermediates along that route is highly reactive and latches onto DNA, wedging itself against a base and distorting the strand. When the cell next copies its DNA past the damage it inserts the wrong letter. The mutations left behind fall in a recognizable pattern and turn up in the gene that normally halts damaged cells from dividing. The detoxification pathway is the activation pathway, and without it the compound would pass straight through unchanged.
Where is exposure highest?
| Source | Notes |
|---|---|
| Tobacco smoke | The dominant avoidable source for smokers and for those nearby |
| Occupational soot and tar | Coke ovens, roofing, aluminum smelting, chimney sweeping |
| Grilled and smoked food | Formed as fat drips onto flame and smoke coats the surface |
| Solid fuel burned indoors | Wood, coal and dung used for cooking and heating |
| Traffic and industrial air | Carried deep into the lung on fine particles |
What is it a marker for?
It never appears alone. Combustion produces hundreds of related compounds together, so a measurement of benzo(a)pyrene is generally used to stand for the entire mixture of polycyclic aromatic hydrocarbon present in air, food or a workplace. It has been classified as carcinogenic to humans, one of the few single chemicals for which the evidence is treated as settled, and much of that evidence came from trades where soot and tar coated the skin daily. Those historic exposures produced skin cancer and rough warty growths as well as lung disease, which is why older descriptions attach skin changes to the compound. Regulation now targets the mixture rather than the single molecule, and environmental tobacco smoke remains a major indoor contributor.
Also known as
Used in a sentence
Air sampling at the site measured benzo(a)pyrene as an indicator of combustion products.
Good to know
Benzo(a)pyrene is inert until enzymes convert it, in the course of trying to excrete it, into a reactive form that binds DNA, and measurements of it usually stand in for a whole mixture of combustion products rather than one isolated exposure.
Word origin
Where “benzo(a)pyrene” comes from
Pyrene takes its name from the Greek pyr, meaning fire, since the compound was first obtained from the tar left by burning. The rest of the name records where an extra benzene ring is attached.