That comforting fire that graces your living room is really a chemical reactor. Most of the substances produced however, (such as water and carbon dioxide) are generally harmless although the burning of fuel can produce a variety of chemicals harmful to the environment. PAH's are one of the most prominent groups of chemicals contained in smoke, soot and exhaust resulting from the incomplete combustion of carbon compounds.  Over 100 different compounds have been identified and PAH's are considered one of the most significant groups of carcinogens/mutagens found in indoor air.

Common Sources

Smoke has a lot of PAHs. Indoor household sources of PAH's include: cigarette/tobacco smoke, smoldering fireplaces, wood stoves, unvented gas burning appliances, kerosene space  heaters, and the charring or burning of food (tell the wife). Outdoor sources include internal combustion engines, coal burning, and some  wood burning appliances. The increased use of wood as a residential fuel has also led to greater releases of PAHs into the home.  

Contaminated groundwater by gasoline or diesel fuel is another source for PAH's. PAHs in petroleum fuels are of particular concern because many are carcinogenic and degrade poorly.  Soil and groundwater contaminated with petroleum products must be remediated.

PAHs can also find their way into the aquatic environment through discharges from human activities such as industrial or domestic sewage effluents; runoff from paved roads and parking lots, offshore drilling and leaching/disposal of refinery effluents.  All major industries using fossil fuels generate PAHs with higher concentrations of PAHs found near heavy industry. 

The wood preservation industry is also a significant source of PAH contamination.  Creosote can leach from treated lumber in utility poles, railway ties, wharves or pilings into marine and freshwater systems as well as ground water. 

Household Sources

• furnaces
• automobile and other exhausts
• fireplaces and woodstoves
• cigarette/tobacco smoke
• unvented gas and space heaters
• contaminated ground/well water

   Industrial Emissions

• coal and oil-fired power plants
• waste incinerators
• coke/asphalt/petroleum production
• aluminum/iron smelting
• wood preservation/creosote operations

   Natural Emissions

• forest/brush fires
• volcanic eruptions
• decaying organic matter

Health Effects

Limited exposure to most household forms of PAH's has not been shown to cause significant short term health problems although research is limited in this area.  Certain PAH's are however classified as as probable human carcinogens (such as Benzo(a)Pyrene and contaminated groundwater or air from petroleum products)  meaning that long term exposure could increase the risk of cancer.  PAHs are present in low concentrations virtually everywhere usually the result of prolonged industrial activities that involve burning. 

Benzo(a)pyrene and other PAHs are present in petroleum.  PAHs are formed by the incomplete combustion of organic matter.   Aromatic hydrocarbons are the cause for most of the toxic effects of petroleum and petroleum products. They are what give petroleum products a smell. Vaseline is a petroleum product but it is not smelly or poisonous because it has no aromatic hydrocarbons. On the other hand, mothballs are mostly aromatic hydrocarbons and therefore very poisonous and strong smelling.

Testing 

PAHs are a group of more than a hundred organic compounds composed of products derived from benzene. Benzene is the simplest of the aromatic hydrocarbons.  PAH compounds can actually grow in molecular weight and toxicity.  As this occurs, their solubility in water decreases, their solubility in fat tissues increases, and their melting and boiling points increase. The overall properties and effects of PAHs vary according to the combination of compounds involved. Testing requires laboratory analysis.

Control/Remediation

Five specific PAHs have been judged to be toxic to human health based on long term studies of exposure to PAHs in laboratory animals. The pervasive nature of PAHs and their sources of release present a significant challenge for controlling these compounds. In industry, PAHs are controlled under various laws, regulations and agreements set up to protect the environment and human health.  

The sources of PAHs in the home can usually be eliminated or at least controlled to a large degree. Effective methods for keeping the home relatively free of these pollutants are:

• Retrofit any open fireplace with an airtight seal.
• Operate wood burning stoves using small, hot fires.
• Ensure wood burning stoves are properly vented and have their own supply of combustion air. 
• Install/use a good quality stove top exhaust system.
• Eliminate cigarette smoking indoors.
• Use a balanced ventilation system to exhaust contaminated air outdoors and replace with fresh air. Recommended ventilation rate is for one-third of the air in the home to be exchanged every hour.
• Ensure that chimneys are properly maintained

Exposure Guidelines

PAHs are classified as potential human carcinogens therefore,  indoor levels should be reduced as low as possible.