Polycyclic aromatic hydrocarbons are formed by the incomplete combustion of coal, oil, petrol, wood, tobacco, charbroiled meats, garbage, or other organic materials. Most of them have no known use. A few are used in medicines, and to make dyes, plastics, and pesticides. Naphthalene, also known as mothballs, is used in making dyes, explosives, plastics, lubricants, and moth repellent. Anthracene is used in dyes, insecticides and wood preservatives.
Substance name: Polycyclic aromatic hydrocarbons
CASR number: Not applicable
Molecular formula: Not applicable - more than 100 compounds
Synonyms: PAH is the usual acronym for polycyclic aromatic hydrocarbons. Polycyclic aromatic hydrocarbons are a group of over 100 chemicals. Some of the most commonly occurring polycyclic aromatic hydrocarbons are acenaphthene, acenaphthylene, anthracene, benz(a)anthracene, benzo(a)pyrene, benzo(b)fluoranthene, benzo(ghi)perylene, benzo(k)fluoranthene, chrysene, dibenz(a,h)anthracene, fluoranthene, fluorene, indeno(1,2,3-cd)pyrene, naphthalene, phenanthrene, pyrene
Polycyclic aromatic hydrocarbons are colourless, white or pale yellow-green solids. They often attach to particulate matter (e.g. soot).
Melting Point: Depends on the particular compound, generally above room temperature
Boiling Point: Depends on the particular compound, generally above 100°C
Polycyclic aromatic hydrocarbons are organic compounds (carbon based) which include only carbon and hydrogen with a structure of fused rings. They contain at least two fused benzene (six sided) rings. They may contain other rings of carbon that are not six sided. Most do not dissolve easily into water, but some readily evaporate into the air. Most do not burn easily.
The National Pollutant Inventory (NPI) holds data for all sources of Polycyclic aromatic hydrocarbons in Australia.
Exposure can irritate the eyes, nose, throat and bronchial tubes. Skin contact can cause irritation or a skin allergy. Very high levels may cause headaches, nausea, damage the red blood cells, damage the liver and kidneys, and may even cause death. The International Agency for Research on Cancer has cited a number of polycyclic aromatic hydrocarbons as 'probably carcinogenic to humans', a number of others are cited as being 'possibly carcinogenic to humans'.
Entering the body
Polycyclic aromatic hydrocarbons will enter the body if we breathe in contaminated air, or consume food or water that has been contaminated. Skin contact with heavy oils or other products (creosote, roofing tar, other tars, oils) containing polycyclic aromatic hydrocarbons will result in uptake.
In the home, polycyclic aromatic hydrocarbons are present in tobacco smoke, smoke from home heating (buning wood or oil), char-grilled food and cresote treated wood products. Some workplaces can give exposures to polycyclic aromatic hydrocarbons. High concentrations of polycyclic aromatic hydrocarbons have been found in coal-tar production plants, coking plants, bitumen and asphalt production plants, smoke houses, aluminium production plants, and trash incinerators. They are found in facilities that manufacture or use petroleum, petroleum products or coal, or where wood, or other plant materials are burned. People may also be exposed to polycyclic aromatic hydrocarbons in the soil where coal, wood, petrol or other products have ben burned. Food produced from these soils may also contain polycyclic aromatic hydrocarbons.
Workplace exposure standards
Safe Work Australia sets the workplace exposure standard for naphthalene through the workplace exposure standards for airborne contaminants:
- Maximum eight hour time weighted average (TWA): 10 parts per million (52 mg/m3)
- Maximum short term exposure limit (STEL): 15 parts per million (79 mg/m3)
These standards are only appropriate for use in workplaces and are not limited to any specific industry or operation. Make sure you understand how to interpret the standards before you use them.
Drinking water guidelines
The Australian Drinking Water Guidelines include the following guidelines for acceptable water quality:
- Maximum of 0.00001 milligrams per litre of water for health purposes
Data are inadequate to set guidelines for other PAHs, however comparative carcinogenic potency can be used to determine an approximate risk when complex mixtures of PAHs are present in drinking water.
Polycyclic aromatic hydrocarbons have moderate to high acute (short-term) toxicity to aquatic life and birds. Some cause damage and death to agricultural and ornamental crops. They have moderate to high chronic (long-term) toxicity to aquatic life. Insufficient data are available on the acute or chronic toxicity to land animals. Polycyclic aromatic hydrocarbons are moderately persistent in the environment, and can bioaccumulate. The concentrations of polycyclic aromatic hydrocarbons found in fish and shellfish is expected to be much higher than the environment from which it was taken.
Entering the environment
Polycyclic aromatic hydrocarbons travel through the atmosphere as a gas or attached to dust particles. They are carried by air currents and deposited by dry or wet (rain, dew, etc) deposition. When deposited in water they sink to the bottom of lakes and rivers. Some will move though the soil to contaminate ground water.
Where it ends up
Polycyclic aromatic hydrocarbons usually enter the air when released to the environment. Some evaporate into the air when released to soil or water.
They then often attach to dust particles. Polycyclic aromatic hydrocarbons can break down by reacting with sunlight and other chemicals in the air, over a period of days to weeks. Polycyclic aromatic hydrocarbons do not dissolve easily in water. They stick to dust or dirt particles and settle to the bottom of lakes and rivers. Microorganisms will break them down in soil or water over a period of weeks to months. Mixed microbial populations in sediment/water systems may degrade some polycyclic aromatic hydrocarbons, with degradation progressively decreasing with increasing molecular weight.
Australian Water Quality Guidelines for Fresh and Marine Waters (ANZECC, 1992):
Maximum of 3.0 micrograms per Litre (i.e. 0.000003 g/L) in fresh or marine waters.
Industrial emissions of polycyclic aromatic hydrocarbons are mainly from petroleum refineries, fossil fuel power plants (coal, oil,), coal-tar production plants, coking plants, bitumen and asphalt production plants, paper mills, wood products manufacturers, aluminium production plants and industrial machinery manufacturers. These emissions are usually to air.
Diffuse sources, and industry sources included in diffuse emissions data
The main sources of polycyclic aromatic hydrocarbons are related to combustion processes (domestic solid fuel burning, motor vehicles, etc) and the use of solvents and aerosols.
Polycyclic aromatic hydrocarbons can be formed from any naturally occurring fire, such as bush or forest fires. They occur in crude oil, shale oil, and coal tars. They are emitted from active volcanoes.
Polycyclic aromatic hydrocarbons are found in motor vehicle exhaust.
Some polycyclic aromatic hydrocarbons are found in medicines, dyes, plastics, pesticides and wood preservatives. Naphthalene is also known as mothballs. Since most polycyclic aromatic hydrocarbons come from the incomplete combustion of organic material, polycyclic aromatic hydrocarbons will be created in wood-burning stoves, fireplaces, indoor or outdoor grills and smoking tobacco products.
Sources used in preparing this information
- Agency for Toxic Substances and Disease Registry (1990), Public Health Statement Benz[a]anthracene (accessed, May, 1999)
- Agency for Toxic Substances and Disease Registry (1990), Public Health Statement Benzo[a]pyrene (accessed, May, 1999)
- Agency for Toxic Substances and Disease Registry (1990), Public Health Statement Benzo[b]fluoranthene (accessed, May, 1999)
- Agency for Toxic Substances and Disease Registry (1990), Public Health Statement Creosote (accessed, May, 1999)
- Agency for Toxic Substances and Disease Registry (1997), ToxFAQS Polycyclic Aromatic Hydrocarbons (PAHs) (accessed, May, 1999)
- Agency for Toxic Substances and Disease Registry (December 1990), Public Health Statement Polycyclic Aromatic Hydrocarbons (PAHs) (accessed, May, 1999)
- Australian and New Zealand Environment and Conservation Council (ANZECC) (1992), Australian Water Quality Guidelines for Fresh and Marine Waters.
- CalEPA Air Resources Board Toxic Air Contaminant Summary Polycyclic Aromatic Matter (accessed, May, 1999)
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- Environmental Health Center, a division of the National Safety Council, Environment Writer – Chemical Backgrounders Naphthalene (C10H8) (accessed, May, 1999)
- National Environment Protection Council (1998a), National Environment Protection Measure for the National Pollutant Inventory (accessed, May, 1999)
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- NTP Chemical Repository, Radian Corporation, Anthracene (AUGUST 29, 1991) (accessed, May, 1999)
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- Technical Advisory Panel (1999), Final Report to the National Environment Protection Council.
- US Environmental Protection Agency and the Office of Air Quality Planning and Standards (May, 1998), Unified Air Toxics Website, Polycyclic Organic Matter (accessed, May, 1999)
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- Safe Work Australia, Workplace exposure standards for airborne contaminants, accessed February 2019.
- National Health and Medical Research Council (NHMRC), Australian Drinking Water Guidelines (2011) - Updated October 2017, accessed May 2018.