What are PAHs and where do they come from?

Polycyclic aromatic hydrocarbons (PAHs) are a group of hundreds of different chemicals. Most simply, PAHs are formed by burning organic material. For example, coal, oil, gas, garbage, wood, and food will all release PAHs when burned. These chemicals can be created by human activity, such as automobile exhaust or as a product of industrial facilities, and they can be naturally occurring such as from wildfires. PAHs are found in the air, water, soil, and food. PAHs are often found in the environment as a gas or attached to small particles.  

For more information, please reference the ATSDR Polycyclic Aromatic Hydrocarbons Tox FAQs (September 1996) .

 

How are people exposed to PAHs? 

PAHs are commonly found in the environment (1). However, the main way people are exposed to PAHs is from smoking (2; 3) or through the food they eat.

Smoking

People that smoke cigarettes receive the majority of their PAH exposures from smoking (3). PAHs are found in cigarettes, cigars and vape products, and well as all other smokable blends.

Through the diet

People are exposed to PAHs through eating foods that are grilled, roasted, smoked, or barbecued (4). Additionally, foods that are roasted or toasted like cereals, grains, nuts and coffee contain PAHs (3; 6). Any method that can char or burn food will produce PAHs. When cooking meat, PAHs are formed when the meat itself burns or chars, and when fat from the meat drips down and burns in the flames (4; 5). This is commonly seen with chargrilled and barbecued meats including fish (4). Additionally, foods that are commercially roasted, liked roasted cereals and coffee, can contain PAHs (3; 6) . Smoked foods may also contain PAHs as a result of the smoking process.

Drinking water can also become contaminated with PAHs, often due to hazardous waste. Drinking contaminated water can result in exposure. However, drinking water is regulated by the U.S. Environmental Protection Agency. There are drinking water standards for several PAHs. Learn more here: (Table 1).  

Through breathing contaminated air 

PAHs can be released into the air from industrial emissions, automobile exhaust, and numerous other sources (2). A commonly detected PAH is naphthalene, which used to be found in mothballs. This chemical is one of the major components of creosote (7) which is used as a preservative for railroad ties and telephone poles. 

Air containing cigarette smoke, wood smoke, vehicle exhaust, or off-gassing from asphalt roads can contain PAHs. Burn piles to dispose of garbage or yard waste also create PAHs. Indoors, certain air fresheners, smoke from cooking or from lit candles contribute PAHs to the air.

In the workplace, people may be exposed to PAHs. The Occupational Safety and Health Administration (OSHA) has specific standards and regulations for PAHs. Learn more here.

Through skin contact with contaminated water or soil

Some PAHs can be absorbed through the skin (2). This requires direct skin contact, such as touching creosote-treated logs. Additionally, swimming or wading in PAH-contaminated water may result in exposure.

Contact with contaminated soil or sediment can lead to exposure (2). Soil contaminated with PAHs can be found at some Superfund sites.

 

How can I reduce my exposure to PAHs? 

If you are concerned about exposure to PAHs, there are many things you can do. 

Reduce PAHs in your diet 

  • Reduce or stop use of cigarettes, cigars, or vape devices
  • Limit consumption of roasted or toasted foods (cereals, grains, etc.)
  • Limit grilled and smoked foods
  • Choose leaner cuts of meat to reduce the amount of fat dripping and burning
  • Raise the grill grate higher over the flames to reduce the amount of charring
  • Remove blackened portions from meat and fish

 

You can learn more about PAHs in the diet from the following references: 

 

Reduce PAHs from air

Inside the home, PAHs can come from cooking, burning candles or incense, smoking, and even some plug-in air fresheners.

  • When cooking, use the stove vent hood or open a nearby window
  • Learn about ways to reduce PAHs when using candles
  • Reducing use of plug-in air fresheners (or check the label to see if they are free of naphthalene)
  • Use cedar balls instead of traditional mothballs
  • Routinely ventilate your home by opening windows
  • If the air quality index exceeds 101, keep your windows closed to reduce PAH exposure
  • If the air quality index exceeds 151, consider cancelling outdoor public events and staying inside with windows closed
  • If you use a wood burning stove for heat, look into options for cleaner burning stoves

 

Reduce PAHs from water

Some PAHs are regulated in drinking water, as shown in Table 1 of the ATSDR Standards and Regulations website (8). PAH contamination of drinking water is relatively rare, especially once water has gone through water treatment plants which contain activated carbon filters to remove organic contaminants such as PAHs.

 

Reduce PAHs from soil

PAH-contaminated soil has been found around hazardous waste sites and Superfund sites (2). If PAH levels exceed standards set by the US Environmental Protection Agency, the agency will develop a clean-up plan.

 

How can PAHs affect my health?

More research is needed to better understand which PAHs cause health problems, what those health problems are, and how strong the effect is with a given exposure. Given how many PAHs exist, it is not surprising that there are many different health outcomes attributed to them. For example, some PAHs are known to contribute to cancer. Others are associated with respiratory diseases like asthma, or damage to the immune and reproductive systems. The goal of our center is to take this research and understand which PAHs are in our environment, and in what amounts. From there, we can determine if humans and animals are being exposed to these PAHs, and what sort of risk they pose to health.

To better understand the toxicity of PAHs, the OSU Superfund Research Program is dedicated to understanding what real people are exposed to in their daily environment. The OSU SRP is studying mixtures of these chemicals, mimicking PAHs that are found in contaminated air or water. Our researchers are using passive samplers to figure out which PAHs, and how much of them, are in the soil, air, and water. Learn more here.

We can test these chemicals in animal models and human lung models to better understand if these PAHs may pose a risk to human health. Learn about our zebrafish animal model here, and our human lung model here. Since we know that people can be exposed to PAHs, our researchers are examining how these chemicals break down in our bodies. We also have researchers studying how to remove these chemicals from our environment.  

 

How likely are PAHs to cause cancer?

There are hundreds of different types of cancer. Different chemicals can cause different types of cancer. Unfortunately, some PAHs are known to increase the possibility that a person gets cancer. In occupational settings, workers exposed to PAHs have reported increased levels of lung, skin, and bladder cancer (1).

 

Are there regulations about PAHs to protect human health?

PAHs are commonly found in the environment. However, exposure to PAHs does not necessarily mean a person will experience poor health outcomes. While there are limited regulations for some PAHs, they do not apply to the public or to outdoor air. To learn more about federal recommendations, please see this information from the Centers for Disease Control and Prevention.

 

 

References

1. Registry, Agency for Toxic Substances and Disease. Polycyclic Aromatic Hydrocarbons. Environmental Health and Medicine Education. [Online] December 10, 2013. [Cited: July 27, 2021.] https://www.atsdr.cdc.gov/csem/polycyclic-aromatic-hydrocarbons/cover-page.html.

2. —. Polycyclic Aromatic Hydrocarbons - ToxFAQs. ToxFAQs. [Online] September 1996. https://www.atsdr.cdc.gov/toxfaqs/tfacts69.pdf.

3. Polycyclic aromatic hydrocarbons: physicochemical properties, environmental appearance and impact on living organisms. Skupinska, K., Misiewicz, I. and Kasprzycka-Guttman, T. 3, 2004, Acta Pol Pharm, Vol. 61, pp. 233-240.

4. Formation and mitigation of PAHs in barbecued meat-a review. Duedahl-Olesen, L. and Ionas, A.C. 2020, Critical Reviews in Food Science and Nutrition, pp. 1-16.

5. Polycyclic aromatic hydrocarbons in grilled food. . Larsson, B.K., Sahlberg, G.P., Eriksson, A.T. and Busk, L.A. 4, 1983, Journal of agricultural and food chemistry, Vol. 31, pp. 867-873.

6. Excretion profiles an dhalf-lives of ten urinary polycyclic aromatic hydrocarbon metabolites after dietary exposure. Li, Z., Romanoff, L., Bartell, S., Pittman, E.N., Trinidad, D.A., McClean, M., Webster, T.F. and Siodin, A. 7, 2012, Chemical research in toxicology., Vol. 25, pp. 1452-1461.

7. Registry, Agency for Toxic Substances and Disease. Toxicological Profile for Wood Creosote, Coal Tar Creosote, Coal Tar, Coal Tar Pitch, and Coal Tar Pitch Volatiles. [Online] September 2002. [Cited: July 27, 2021.] https://www.atsdr.cdc.gov/toxprofiles/tp85.pdf. 

8. —. What are the Standards and Regulations for PAHs Exposure? [Online] December 10, 2013. [Cited: July 27, 2021.] https://www.atsdr.cdc.gov/csem/polycyclic-aromatic-hydrocarbons/standards_and_regulations_for_exposure.html.