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Part C: Factsheets (continued)

Polycyclic aromatic hydrocarbons (PAHs)

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 hydrocarbon. Polycyclic aromatic hydrocarbons are a group of over 100 chemicals. Some of the most commonly occurring polycyclic aromatic hydrocarbons are acenaphthene, acenaphthylene, anthracene, benzo[a]anthracene, benzo[a]pyrene, benzo[b]fluoranthene, benzo[g,h,i]perylene, benzo[k]fluoranthene, chrysene, dibenz[a,h]anthracene, fluoranthene, fluorene, indeno[1,2,3-c,d]pyrene, naphthalene, phenanthrene, pyrene

Physical and chemical properties

PAHs are colourless, white or pale yellow-green solids. They often attach to particulate matter (eg soot).

The melting point depends on the particular compound, but is generally above room temperature. The boiling point depends on the particular compound, generally above 100°C.

PAHs 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 in water, but some readily evaporate into the air. Most do not burn easily.

Common uses

PAHs 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 is used in making dyes, explosives, plastics, lubricants, and moth repellent (moth balls). Anthracene is used in dyes, insecticides and wood preservatives.

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 PAHs are asphalt roads, road and road tar, coal, coal tar, fires of all types (bush, forest, agricultural, home heating, cooking, etc), and the manufacture and use of preserved wood (creosote).

Natural sources

PAHs can be formed from any naturally occurring fire, such as bushfires or forest fires. They occur in crude oil, shale oil, and coal tars. They are emitted from active volcanoes.

Mobile sources

PAHs are found in motor vehicle exhaust.

Consumer products that may contain PAHs

Some PAHs are found in medicines, dyes, plastics, pesticides and wood preservatives. Naphthalene is also known as mothballs. Since most PAHs come from the incomplete combustion of organic material, PAHs will be created in wood-burning stoves, fireplaces and indoor or outdoor grills and in smoking tobacco products.

Health effects

How might I be exposed to PAHs?

In the home, PAHs are present in tobacco smoke, smoke from home heating (burning wood or oil), chargrilled food and creosote-treated wood products. People are exposed to PAHs in some workplaces. High concentrations of PAHs have been found in coal-tar production plants, coking plants, bitumen and asphalt production plants, smokehouses, aluminium production plants, and trash incinerators. PAHs 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 PAHs in soil where coal, wood, petrol or other products have been burned. Food produced from these soils may also contain PAHs.

By what pathways might PAHs enter my body?

PAHs 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 PAHs will result in uptake.

Health guidelines

National Occupational Health and Safety Commission (NOHSC):

• TWA (eight-hour time weighted average) exposure limit for naphthalene in the workplace: 10 ppm (52 mg/m³)
• STEL (short-term exposure limit) (15 minutes): 15 ppm (79 mg/m³).

It is recommended that exposure to benzo[a]pyrene is kept to the lowest possible level.

Australian Drinking Water Guidelines (NHMRC and ARMCANZ 1996):

• Benzo[a]pyrene: maximum 0.00001 mg/L (ie 0.00000001 g/L).

What effect might PAHs 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 and nausea, damage the red blood cells, liver and kidneys, and even cause death. The International Agency for Research on Cancer (IARC) has cited a number of PAHs as 'probably carcinogenic to humans'; a number of others are cited as being 'possibly carcinogenic to humans'.

Environmental effects

Environmental fate

PAHs usually enter the air when released to the environment. Some evaporate into the air when released to soil or water.

PAHs then often attach to dust particles. They can break down by reacting with sunlight and other chemicals in the air, over a period of days to weeks. They 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 PAHs, with degradation progressively decreasing with increasing molecular weight.

Environmental transport

PAHs 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 groundwater.

Environmental guidelines

Australian Water Quality Guidelines for Fresh and Marine Waters (ANZECC, 1992):

• Maximum of 3.0 µg/L (ie 0.000003 g/L) in fresh or marine waters.

What effect might polycyclic aromatic hydrocarbons have on the environment?

PAHs 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 and chronic toxicity to land animals. PAHs are moderately persistent in the environment, and can bioaccumulate. The concentrations of PAHs found in fish and shellfish are expected to be much higher than in the environment from which they were taken.

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