Polycyclic Aromatic Hydrocarbons (PAHs)

Sarah Jones
Environmental Chemist
Friday, 21st June 2019
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Polycyclic Aromatic Hydrocarbons (PAHs) in Drinking Water Information:


Polycyclic aromatic hydrocarbons (PAHs) are a wide range of molecules made of carbon and hydrogen that have a characteristic ring structure featuring two or more fused rings.1 Examples of PAHs include naphthalene, anthracene, fluoranthene, phenanthrene, and pyrene. As PAHs increase in size, they become less likely to dissolve in drinking water. PAHs are generally considered carcinogenic and can pose significant risks to human health. One particularly dangerous aromatic hydrocarbon is benzo(a)pyrene, a compound with a chemical formula of C20H12.


PAHs are present in crude oil, coal, processed fossil fuels, tar, and various foods that have been smoked or charred. These compounds are also formed during the incomplete combustion of fossil fuels or other carbon-containing fuels like wood, coal, diesel, tobacco, etc.2 Industrial and anthropogenic activity such as urban runoff are the primary sources of PAHs in drinking water. PAHs can also enter drinking water if materials like coal tar are used to coat water pipes (a technique that was popular in the past).1


The limit of PAHs is 0.1 micrograms per litre (µg/L) in drinking water. The concentration of PAHs is considered the sum of the concentrations of the four PAHs most pertinent to drinking water; benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(ghi)perylene, and indeno(1,2,3-cd)pyrene.2

Health/Environmental Concerns:

Some PAHs are well-known carcinogens; benzo(a)pyrene, for example, has been shown to cause malignant skin tumours and other forms of cancer. In addition, some of these compounds are toxic.


While contamination of drinking water by PAHs is uncommon, you should contact your Water Services Authority you suspect your water source has been compromised. If drinking water makes you ill, contact a doctor right away.


1 Guidelines for Drinking Water Quality. Polycyclic Aromatic Hydrocarbons in Drinking Water; Vol. 2; World Health Organisation: Switzerland, 1996.

2 Guide to the Parameters in the European Communities. What’s in your water?;  S. I. No. 278 of 2007; National Federation of Group Water Schemes: Ireland.


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