Polyaromatic hydrocarbons (PAHs) are formed during the incomplete burning of organic substances. They are also found in coal, coal tar, and in the creosote oils and pitches formed from the distillation of coal tars. A few are synthetically produced as research chemicals and several have been used in the field of wood protection as fungicidal agents. PAHs are found throughout the environment, rarely alone but rather as mixtures of two or more PAHs. They can occur in the air either attached to dust particles, or in soil or sediment as solids. Most PAHs do not dissolve easily in water, but some PAHs readily evaporate into the air. PAHs generally do not burn easily and they last in the environment for months to years. Several are suspected or known carcinogens and toxins.
PAHs enter the body quickly and easily by all routes of exposure: through the lungs while breathing, ingestion or skin contact with contaminated oils. They enter tissues with fat and tend to be stored mostly in the kidneys, liver, and fat, with smaller amounts in your spleen, adrenal glands, and ovaries. PAHs do not tend to be stored in the body for a long time; most leave within a few days, primarily in the faeces and urine.
There are more than 100 different PAH compounds, the principal compounds of concern being: acenaphthene; acenaphthylene; anthracene; benz(a)anthracene; benzo(a)pyrene; benzo(e)pyrene; benzo(b)fluoranthene; benzo(ghi)perylene; benzo(k)fluoranthene; chrysene; dibenz(a,h)anthracene; benzo[b]fluoranthene; benzo[k]fluoranthene; fluoranthene; fluorene; indeno(1,2,3-cd)pyrene; phenanthrene; pyrene.
Exposure may occur at home, while outside, or most commonly, at the workplace. In the air are PAH vapours or PAHs that are attached to dust and other particles. Other sources include vehicle exhausts, asphalt roads, coal, coal tar, wildfires, agricultural burning, garbage incineration and hazardous waste sites. PAHs are likely to be in soil near areas where coal, wood, gasoline, or other products have been burned, or near hazardous waste sites, such as former manufactured-gas sites and wood-preserving facilities. PAHs have been found in some drinking water supplies in the United States. In the home, PAHs are present in tobacco smoke, smoke from home heating of wood, creosote-treated wood products. Food grown in contaminated soil or air may also contain PAHs. Cooking meat or other food at high temperatures, which happens during grilling or charring, increases the amount of PAHs in the food.
For many people, the greatest exposure to PAHs occurs in the workplace. PAHs have been found in coal-tar production plants, coking plants, bitumen and asphalt production plants, coal-gasification sites, smoke houses, aluminum production plants, coal-tarring activities, and municipal trash incinerators. PAHs have also been found in other facilities where petroleum, petroleum products, or coal are used or where wood, cellulose, corn, or oil are burned.
The US National Institute for Occupational Safety and Health (NIOSH) concludes that occupational exposure to coal products can increase the risk of lung and skin cancer in workers and recommended an occupational exposure limit for coal tar products of 0.1 milligram of PAHs per cubic meter of air (0.1 mg/m3) for a 10-hour workday, 40-hour workweek. The Occupational Safety and Health Administration (OSHA) has established a legally enforceable limit of 0.2 milligram of all PAHs per cubic meter of air (0.2 mg/m3).