Atmosphere

Air toxics and indoor air quality in Australia

State of knowledge report
Environment Australia, 2001
ISBN 0 6425 4739 4

Part C: Factsheets (continued)

Acetaldehyde

Substance name:Acetaldehyde
CASR number: 75-07-0
Molecular formula: C2H4O
Synonyms: Ethanal; ethyl aldehyde; acetic aldehyde; aldehyde; acetaldehyde; aldehyde acetic aldehyde, NCI-C56326, RCRA waste number U001, UN 1089.

Physical and chemical properties

Acetaldehyde is a clear colourless fuming liquid with a pungent, fruity odour. Vapours are heavier than air and can travel considerable distances and cause flashback from combustion sources. When heated to decomposition acetaldehyde emits acrid smoke and toxic fumes of carbon monoxide and carbon dioxide.

Melting point: -123.5°C
Boiling point: 21°C
Specific gravity: 0.778 @ 20 °C
Vapour pressure: 400 mm Hg @ 4.9°C; 760 mm Hg @ 20.2°C
Flashpoint: -40°C
Volatility: 100% volatile by volume

This chemical is dangerous when exposed to heat or flame. It is sensitive to air and may undergo autopolymerisation. It is also sensitive to moisture. Upon prolonged storage, it may form unstable peroxides. It can react vigorously with acid anhydrides, alcohols, ketones, phenols, ammonia, hydrogen cyanide, hydrogen sulfide, halogens, amines, phosphorus, isocyanates, strong alkalis and strong acids and is incompatible with oxidising and reducing agents. It also reacts with nitric acid, peroxides, caustic soda and soda ash. Reactions with cobalt chloride, mercury(II)chlorate or mercury(II)perchlorate form sensitive and explosive products. Polymerisation may occur with acetic acid. Autoignition of vapour may occur on contact with corroded metals. Exothermic polymerisation can occur with trace metals. It is miscible with gasoline, naphtha, xylene, turpentine, ether, benzene and alcohol. Rubber products decompose on contact with acetaldehyde, but acetaldehyde is not corrosive to most metals.

Common uses

Acetaldehyde is primarily used as an intermediate in the manufacture of a range of chemicals, perfumes, aniline dyes, plastics and synthetic rubber and in some fuel compounds. Acetaldehyde is also used in the manufacture of disinfectants, drugs, perfumes, explosives, lacquers and varnishes, photographic chemicals, phenolic and urea resins, rubber accelerators and antioxidants, and room air deodorisers. It is also used as a synthetic flavouring substance, food preservative and fragrance.

Sources of emissions

Point sources

Acetaldehyde is used widely in industry, and it may be released into waste water or the air during production, use, transportation and storage. Sources of acetaldehyde include fuel combustion emissions from stationary internal combustion engines and power plants that burn fossil fuels, wood or trash, oil and gas extraction, refineries, cement kilns, lumber and wood mills, and paper mills.

Diffuse sources, and point sources included in aggregated emissions data Production by photochemical oxidation of other compounds in the air is the largest source of acetaldehyde concentrations in the ambient air. Acetaldehyde is emitted from residential fireplaces and wood stoves, bushfires, and agricultural burning.

Natural sources

Acetaldehyde has a widespread natural occurrence. Acetaldehyde occurs in nature as an intermediate product in the respiration of higher plants and can be found in ripening fruit such as apples. It is also an intermediate product of fermentation of alcohol and in metabolism of sugars in the body. It may form in wine and other alcoholic beverages after exposure to air. Natural sources include forest fires, volcanoes, animal wastes, and insects. Acetaldehyde is a volatile component of cotton leaves and blossoms. Acetaldehyde occurs in oak and tobacco leaves and is a natural component of apples, broccoli, coffee, grapefruit, grapes, lemons, mushrooms, onions, oranges, peaches, pears, pineapples, raspberries, and strawberries. It has been detected in the essential oils of alfalfa, rosemary, balm, clary sage, daffodil, bitter orange, camphor, angelica, fennel, mustard, and peppermint.

Mobile sources

Acetaldehyde is present in automobile and diesel exhaust.

Consumer products that may contain acetaldehyde

Consumers may be exposed to acetaldehyde in cheese, heated milk, cooked beef, cooked chicken, and rum. It is an important component of food flavourings (in low concentrations, which are generally recognised as safe) and is added to milk products, baked goods, fruit juices, sweets, desserts, and soft drinks. It is especially useful for imparting orange, apple, and butter flavours. It is used in the manufacture of vinegar and yeast and as a fruit and fish preservative. Consumers may have been exposed to acetaldehyde in room air deodorisers. Exposure in the home environment may occur from the products of burning wood in stoves or fireplaces.

Health effects

How might I be exposed to acetaldehyde?

People are exposed mainly by inhaling ambient air from urban areas or near sources of combustion. Workers in the organic chemicals industry are most likely to be exposed; there may be exposure for those working with fabricated rubber products and biological products. There is a potential for exposure for people involved in the manufacturing or use of industrial organic chemicals, dyes, fabricated rubber, plastics, urea-formaldehyde foam insulation, fuels, drugs, explosives, lacquers and varnishes; photographic chemicals, pesticides, food additives, leather goods, and mirrors; and for automobile and diesel mechanics, petrol station attendants, and agricultural and food industry personnel, and people in coffee-roasting operations, lithographic coating, automobile spray operations, and fat-rendering plants. Concentrations are usually higher indoors than outdoors, due, in part, to the abundance of combustion sources such as cigarettes and fireplaces indoors. Acetaldehyde can be emitted by cooking hamburgers, from some building materials such as rigid polyurethane foams, and from some consumer products such as adhesives, coatings, lubricants, inks, and nail polish remover. Other potential sources of indoor acetaldehyde concentrations are the infiltration of vehicle exhaust and the evaporation of acetaldehyde from certain foods.

By what pathways might acetaldehyde enter my body?

Exposure to acetaldehyde is primarily through breathing, though skin absorption and ingestion are also possible.

Health guidelines

National Occupational Health and Safety Commission (NOHSC)

Acetaldehyde is listed by the NOHSC as a substance under review for sensory irritation.

What effect might acetaldehyde have on my health?

At medium concentrations (about 50–200 ppm in air) acetaldehyde is an irritant of the skin, eyes, mucous membranes, throat and respiratory tract. Symptoms of short-term exposure to higher levels (of the order of 1000 ppm) of this compound include nausea, vomiting, headache, dermatitis and pulmonary oedema (fluid in the lungs). These effects may be delayed. Acetaldehyde has a general narcotic action and may cause drowsiness, delirium, hallucinations and loss of intelligence. Exposure for longer periods may also cause slow mental response, severe damage to the mouth, throat and stomach, accumulation of fluid in the lungs, chronic respiratory disease, kidney and liver damage, throat irritation, dizziness, reddening and swelling of the skin and sensitisation. It may cause photophobia. Liquid splashed in the eyes may cause a burning sensation, lacrimation and blurred vision. It may also cause transient conjunctivitis. Large doses (of around 10 000 ppm for a short period) may cause death by respiratory paralysis.

Acetaldehyde is classified by the NOHSC as a Category 3 carcinogen (substance which causes concern for humans owing to possible carcinogenic effects but in respect of which the available information is not adequate for making a satisfactory assessment).

Environmental effects

Environmental fate

Acetaldehyde will rapidly evaporate from water or land. In the atmosphere, it will degrade in a matter of hours by photochemical oxidation and reaction with hydroxyl radicals. It can leach into the ground. It degrades readily in soil, sewage, and natural waters.

Environmental transport

Since acetaldehyde rapidly evaporates, it is most likely to be transported in air, though it degrades rapidly and is, therefore, unlikely to travel far.

Environmental guidelines

There are no national guidelines.

What effect might acetaldehyde have on the environment?

In sufficient concentrations, acetaldehyde's effect on animals is similar to that on humans.

Key

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