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)

Mercury and compounds

Substance name: Mercury and compounds
CASR number: 7439-97-6
Molecular formula: Mercury (Hg): 7439-97-6
Mercury bichloride (HgCl2): 7487-94-7
Methyl mercury (CH3Hg+): 22967-92-6
Synonyms: Mercury: quick silver, liquid silver, hydragyrum
Mercury bichloride: mercuric bichloride, mercuric chloride, bichloride of mercury, corrosive sublimate, mercury perchloride, mercury (II) chloride, mercury chloride, perchloride of mercury, sublimate

Physical and chemical properties

Physical properties

Mercury, a naturally occurring element, is an odourless, very heavy, silver white, liquid metal. Mercuric chloride is an odourless, white powder or crystal. Both mercury and mercuric chloride are slightly volatile at ordinary temperatures.

Mercury

Melting point: -39°C
Boiling point: 357°C
Specific gravity: 13.6
Vapour Pressure: 0.0012mm Hg@21°C

Mercuric chloride

Melting point: 277°C
Boiling point: 320°C
Specific gravity: 5.4
Vapour Pressure: 1.3mm Hg@21°C

Chemical properties

Pure mercury is stable and does not tarnish at ordinary temperatures. It will form alloys with most metals. It is not soluble in water or most other liquids, but will dissolve in lipids (fats and oils). It is an excellent conductor of electricity. Mercuric chloride and methyl mercury are both soluble in most organic solvents. Mercuric chloride is soluble in water; methyl mercury is not.

Common uses

Mercury is used in its pure form in thermometers and barometers. Mercury is also used in many batteries; in floodlights, streetlights, and other outdoor or powerful lights; as a catalyst in the chemical manufacturing industry; to conduct electricity (ie thermostats); and in dental amalgams. It is used in the mining industry to extract gold and silver ores and as an agricultural chemical in Australia. Mercuric chloride is used in the manufacture of disinfectants and other chemicals, as a catalyst, and in photography and embalming. Bacteria in water and soil primarily produce methyl mercury.

Sources of emissions

Point sources

Fossil fuel power plants, metal smelters and cement-production facilities may emit to air. Precious metal mining operations may emit to water or land. Municipal landfills, sewage, metal refining, and chemical manufacturing are also significant potential emitters of mercury to land and water.

Diffuse sources, and point sources included in aggregated emissions data

Burning of fossil fuels (home heating oil, petrol) emits mercury to air; disposal of batteries, thermometers and other mercury containing products may emit to land; and photographic processing facilities may emit mercury to water.

Natural sources

Mercury is a naturally occurring element that is found in rocks and ores. It is released into the atmosphere by evaporation from soils, from volcanic activity, and from the burning of fossil fuels (coal, oil, petrol, asphalt, etc).

Mobile sources

The combustion of petrol releases small amounts of mercury to air.

Consumer products that may contain mercury and compounds

Batteries, thermometers, barometers, thermostats and mercury lights are some of the consumer products that contain mercury. Photographic toners contain mercuric chloride.

Health effects

How might I be exposed to mercury and compounds?

Mercury can be absorbed through the skin. Workers in the industries that use or produce mercury and its compounds (mercury mines and refineries, chemical manufacturing, dental/health fields, metal smelters) are at risk of exposure. Workers in fossil fuel power plants and in cement manufacturing may be exposed to mercury compounds if they are exposed to gaseous process emissions. Consumers can be exposed to mercury and its compounds by exposure to air from production and processing facilities using mercury and its compounds, and by eating fish or shellfish contaminated with methyl mercury. People can also be exposed to mercury from dental work and medical treatments.

By what pathways might mercury and compounds enter my body?

Mercury and mercury-containing products will enter the body if we breathe in contaminated air, drink contaminated water or eat contaminated food. Mercury may also be absorbed through the skin. Mercury released into the environment is converted into methyl mercury by bacteria. The methyl mercury accumulates in the tissues of fish and shellfish. Humans and other animals can be poisoned by eating these fish and shellfish.

Health guidelines

National Occupational Health and Safety Commission (NOHSC):

The NOHSC lists mercury, aryl and inorganic mercury as substances under review for effects on the central nervous system.

Australian Drinking Water Guidelines (NHMRC and ARMCANZ 1996):

What effect might mercury and compounds have on my health?

The nervous system is very sensitive to all forms of mercury. Methyl mercury and mercury metal vapours are especially harmful, because more mercury reaches the brain. Exposure to high levels of any types of mercury can permanently damage the brain, kidneys, and developing foetus. Effects on brain functions may result in irritability, shyness, tremors, and changes in vision or hearing and memory problems. High exposures of mercury vapour may cause chest pain, shortness of breath, and a build-up of fluids in the lungs (pulmonary oedema). This can cause death. Long-term exposures may cloud the eyes. Contact with mercuric chloride can cause burns to the skin and permanent damage to the eyes. Mercury accumulates in the body.

Environmental effects

Environmental fate

When mercury enters the environment from emissions in the air, water or soil, it oxidises into other compounds of mercury. These other forms of mercury form methyl mercury, through either chemical or biological (bacterial) processes. Methyl mercury builds up in the tissues of fish and shellfish. In areas of mercury contamination, larger and older fish tend to have higher levels of mercury. Mercury will remain in the environment for years.

Environmental transport

Mercury chloride will act as a particle, following wind patterns and being deposited by rain. Elemental mercury may be a gas in the atmosphere. Emissions of mercury and/or mercury compounds can produce elevated, but still low-level, concentrations in the atmosphere around the source. Elemental mercury can evaporate from both soil and water into the atmosphere.

Environmental guidelines

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

What effect might mercury and compounds have on the environment?

Both mercury and its compounds have high toxicity to aquatic life in the short and long terms. Eating fish contaminated with mercury has caused poisoning in humans; birds and land animals that eat contaminated mercury could also be poisoned. There are not sufficient data to determine the acute toxicity of mercury and its compounds on plants, birds or land animals. Mercury and its compounds are highly persistent in water and the environment. Mercury and its compounds will bioaccumulate or concentrate in the tissues of fish. These concentrations will be considerably higher than in the water from which the fish are taken.

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