What are Polycyclic Aromatic Hydrocarbons?

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  • Written By: Victoria Blackburn
  • Edited By: Bronwyn Harris
  • Last Modified Date: 20 September 2019
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Polycyclic aromatic hydrocarbons, also known as PAHs, are chemical compounds that occur in various types of fuel, and make up one component of pollution. There are several forms of PAHs, which differ in their specific chemical structure, but all contain a series of six-carbon rings, which are called aromatic rings. The aromatic rings are harmful because they are difficult to neutralize and destroy, leading to an accumulation of toxic PAHs in the environment and in the tissues of the body.

Polycyclic aromatic hydrocarbons are known to be harmful and toxic to the body. Their toxicity depends on the specific PAH present, and toxicity ranges from only mildly toxic to extremely toxic. There are currently seven PAHs that are known to be highly carcinogenic, and specific PAHs have been linked to a range of cancers, including breast and lung cancers. Polycyclic aromatic hydrocarbons are present in cigarette smoke, and are thought to be one of the main carcinogens in cigarettes.

PAHs are carcinogenic because they cause mutations in DNA, which is a key step in cancer development. The chemical structure of PAHs is similar to the chemical structure of parts of DNA molecules. As a result, the presence of PAHs within the cells interrupts the normal process of DNA replication. By interfering with DNA replication, PAHs can increase the number of mistakes in the DNA molecule that is formed. These mutations in turn can lead to cancer.


In addition to their toxic effects on the body, polycyclic aromatic hydrocarbons are also toxic to the environment. PAHs dissolve in oils naturally present in the soil, and within the atmosphere, contributing to soil and air pollution. They are a natural component of fuels such as oil, tar and coal, so when these materials are burned in industrial factories, the PAHS are released into the air. Some PAHs remain in the atmosphere, suspended in airborne particles, while others settle into the soil. Once deposited, the chemicals are difficult to neutralize, and cannot be washed away with water.

Recent advances in science have discovered methods that show promise in their ability to reduce the levels of polycyclic aromatic hydrocarbons within the soil. One study used soil spiked with several PAHs to see if treatment with clean soil and components of white rot fungus could decrease PAH levels. The study found that the dual treatment of clean soil and fungus almost completely destroyed PAH levels within the soil. Therefore, this method may be used to help clean the soil, and may help reverse and prevent environmental damage due to burning coal, tar and oil.


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