polycyclic aromatic hydrocarbon
Meaning of polycyclic aromatic hydrocarbon: The soot chemicals made whenever something organic burns badly, and among the first substances ever shown to cause cancer.
Definition of polycyclic aromatic hydrocarbon
Polycyclic aromatic hydrocarbons are a large family of chemicals built from carbon and hydrogen arranged in two or more fused rings. They form whenever organic material burns incompletely, so they occur in soot, smoke, vehicle exhaust, grilled meat and coal tar. Several members become capable of damaging DNA once the body has chemically altered them.
Where do they come from?
Anything that burns without enough oxygen makes them. That includes wood fires, coal, engines, industrial furnaces and cigarettes, and it includes cooking, because fat dripping onto a flame produces smoke that carries the compounds back onto the food. Grilling, smoking and charring meat all raise the amount present. They are also manufactured deliberately, turning up in coal tar, creosote wood preservative, roofing pitch, dyes and a few skin preparations. Because the molecules are chemically stable, they persist in soil and settle on growing plants, so some exposure arrives through food even without smoke.
How do they cause harm?
On their own these molecules are fairly inert. The body treats them as waste and tries to make them water-soluble enough to excrete. The enzymes doing that work convert some of them into highly reactive intermediates, and those intermediates attach directly to DNA. The result is a bulky addition that distorts the strand. If a cell copies its DNA before the damage is repaired, a permanent mutation is locked in. Benzo[a]pyrene, the most studied member, produces a characteristic mutation pattern in a gene that normally restrains cell growth, and the same pattern appears in lung tumors from smokers. It is one of the clearest chains of evidence linking an environmental hydrocarbon to human cancer.
How does exposure reach people?
| Source | Main route |
|---|---|
| Tobacco smoke | Inhaled |
| Vehicle exhaust and industrial emissions | Inhaled |
| Grilled, smoked and charred food | Swallowed |
| Coal tar products at work | Absorbed through skin |
Skin contact matters historically. Cancer of the scrotum among chimney sweeps was the first occupational cancer ever described, and soot was the cause. Tobacco smoke remains the largest avoidable source for most people.
Can exposure be measured?
It can. Breakdown products appear in urine, and one of them is measured routinely as an index of recent exposure. Workplaces also monitor the air. Neither measurement predicts what will happen to any one person, since the outcome depends on dose accumulated over years, on other exposures alongside it, and on inherited differences in the enzymes that activate and clear these compounds.
Also known as
Used in a sentence
The occupational history noted long-term exposure to polycyclic aromatic hydrocarbons in coal tar products.
Good to know
These compounds are harmless until the body's own detoxifying enzymes convert them into reactive forms that bind DNA, so the damage is a byproduct of trying to clear them.
Word origin
Where “polycyclic aromatic hydrocarbon” comes from
Poly- and cyclic come from the Greek polys, many, and kyklos, a circle; aromatic comes from aroma, meaning fragrance, because the earliest known members had a distinct smell.