Substance fact sheet
The background information page contains information and concepts that will be useful in understanding some of the issues surrounding the NPI. It is strongly recommended that you read this before reading the information presented below.
For an explanation of some of the terms used in this page, see the Glossary
| 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 |
Physical and chemical properties Physical properties: Polycyclic aromatic hydrocarbons are colourless, white or pale yellow-green solids. They often attach to particulate matter (e.g. soot). Melting Point (°C) Depends on the particular compound, generally above room temperature; Boiling Point (°C) Depends on the particular compound, generally above 100 Chemical properties: |
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Common uses 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. |
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Sources of emissions Point sources The primary sources of emissions of reportable size are 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 point sources included in aggregated emissions data Other emitters of polycyclic aromatic hydrocarbons are asphalt roads, road and road tar, coal, coal tar, fires of all types (bush, forest, agricultural, home heating, cooking, etc), the manufacture and use of preserved wood (creosote). Natural sources 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. Mobile sources Polycyclic aromatic hydrocarbons are found in motor vehicle exhaust. Consumer products which may contain Polycyclic aromatic hydrocarbons 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. |
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Health effects How might I be exposed to Polycyclic aromatic hydrocarbons? 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. By what pathways might Polycyclic aromatic hydrocarbons enter my 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. Relative health hazard On a health hazard spectrum of 0 - 3 Polycyclic aromatic hydrocarbons registers 1.3. A score of 3 represents a very high hazard to health, 2 represents a medium hazard and 1 is harmful to health. Factors that are taken into account to obtain this ranking include the extent of the material's toxic or poisonous nature and/or its lack of toxicity, and the evaluation of its tendency to cause, or not cause cancer and/or birth defects. It does not take into account exposure to the substance. Human exposure is reflected in the NPI rank given to this substance (see comparative data below). A substance that scores highly as a health hazard is arsenic at 2.3 and one of the lowest scores is ammonia at 1.0.  Health guidelines Worksafe Australia: For naphthalene, the eight hour time weighted average (TWA) exposure limit is 10 parts per million, with the short term exposure limit (STEL) concentration not to exceed 15 parts per million. Australian Drinking Water Quality Guidelines (NHMRC and ARMCANZ, 1996): Benzo-(a)-pyrene: Maximum of 0.00001 mg/L (i.e. 0.00000001 g/L). See the Additional Information page for current health information. The Australian NOHSC National Exposure Standards Database link is probably the most useful source of information. Note that the emissions data in the NPI database is not directly comparable with these guidelines. What effect might Polycyclic aromatic hydrocarbons have on my health? 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'. |
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Environmental effects Environmental Fate 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. Environmental Transport 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. Relative hazard to the environment On an environmental spectrum of 0 - 3 Polycyclic aromatic hydrocarbons registers 1.5. A score of 3 represents a very high hazard to the environment and 0 a negligible hazard. Factors that are taken into account to obtain this ranking include the extent of the material's toxic or poisonous nature and/or its lack of toxicity, and the measure of its ability to remain active in the environment and whether it accumulates in living organisms. It does not take into exposure to the substance. Environmental exposure is reflected in the NPI rank for this substance (see comparative data below). A substance that scores highly as an environmental hazard is oxides of nitrogen at 3.0 and one of the lower scores is carbon monoxide at 0.8.  Environmental guidelines 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. See the Additional Information page for current environmental guidelines. Note that the emissions data in the NPI database is not directly comparable with these guidelines. What effect might Polycyclic aromatic hydrocarbons have on the environment? 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. |
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Comparative data NPI Rank Approximately 400 substances were considered for inclusion on the NPI reporting list. A risk ranking was given based on health and environmental hazard identification and human and environmental exposure to the substance. Some substances were grouped together at the same rank with 208 ranks in total. Polycyclic aromatic hydrocarbons was ranked as 18 out of the 208 ranks. Total hazard score (human health + environmental criteria) = 2.8.  |
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Sources of information used in preparing this article
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