As a fruit preserving agent and as a food preservative or additive.
In the fermentation stage of wine making.
For bleaching textile fibres.
In the manufacture of paper.
As a disinfectant in breweries and food factories.
As a fumigant for grains, grapes and citrus fruits.
Substance name: Sulfur dioxide
CASR number: 7446-09-5
Molecular formula: SO2
Synonyms: sulfurous oxide, sulfur oxide, sulfurous anhydride, sulphur dioxide
Colourless gas. Strong, suffocating odour.
Melting Point: -75.51°C
Boiling Point: -10.06°C
Specific Gravity: 0.00293
Vapour Density: 2.26
Non-flammable gas. Sulfur dioxide may oxidise to sulfur trioxide which then dissolves in water to produce sulfuric acid.
The National Pollutant Inventory (NPI) holds data for all sources of Sulfur dioxide in Australia.
Exposure to concentrations of 10 to 50 parts per million for 5 to 15 minutes causes irritation of the eyes, nose and throat, choking and coughing.
Exposure of the eyes to liquid sulfur dioxide, (from, for example an industrial accident) can cause severe burns, resulting in the loss of vision. On the skin it produces burns. Other health effects include headache, general discomfort and anxiety. Those with impaired heart or lung function and asthmatics are at increased risk. Repeated or prolonged exposure to moderate concentrations may cause inflammation of the respiratory tract, wheezing and lung damage. It has also proved to be harmful to the reproductive systems of experimental animals and caused developmental changes in their newborn.
Entering the body
Sulfur dioxide will enter the body if we breathe in contaminated air. Upon entry, nose, throat and lungs may be affected. Sulfur dioxide can also enter our bodies when we eat or drink food or beverages (wine) which contain sulfur dioxide as a preservative. Sulfur dioxide can enter the body through skin contact.
Sulfur dioxide is a common pollutant to which we are exposed at very low levels every day by breathing air in cities and some industrial environments. Higher exposure levels are more likely to be found in the workplace where it is produced as a by-product, such as in smelting and the combustion of coal or oil. Exposure can also happen from the manufacture of fumigants, food preservatives, bleaches and wine making. It can be ingested by eating preserved foods and breathed in causing a risk to asthmatics and other individuals sensitive to its effects.
Workplace exposure standards
Safe Work Australia sets the workplace exposure standard for sulfur dioxide through the workplace exposure standards for airborne contaminants:
- Maximum eight hour time weighted average (TWA): 2 parts per million (5.2 mg/m3)
- Maximum short term exposure limit (STEL): 5 parts per million (13 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
There is no guideline for sulfur dioxide in the Australian Drinking Water Guidelines.
Even low concentrations of sulfur dioxide can harm plants and trees and reduce crop productivity. Higher levels, and especially the acidic deposits from acid rain, will adversely affect both land and water ecosystems.
Entering the environment
Industrial emissions of sulfur dioxide can produce elevated, but still low level concentrations in the atmosphere around the source. Volcanic eruptions, while sporadic, are significant contributors to sulfur dioxide in their local area, and contribute to global background levels of sulfur dioxide.
Where it ends up
Sulfur dioxide in the atmosphere is absorbed by soils and plants. It is also captured within and below clouds and in certain circumstances may raise the acidity of the resultant rain. This is known as acid rain, which occurs in Europe and North America, but acid rain, from sulfur dioxide, has not been documented in Australia.
Sources of emissions
Fossil fuel combustion sites particularly coal burning power plants; industrial processes such as wood pulping, paper manufacture, petroleum and metal refining and metal smelting, particularly from sulfide containing ores, e.g. lead, silver and zinc ores all emit sulfur dioxide to air.
Diffuse sources, and industry sources included in diffuse emissions data
Small textile bleaching and food preserving facilities and wineries, fumigation activities all emit sulfur dioxide to air.
Geothermal activity, including hot springs and volcanic activity; sulfur dioxide is produced from the natural decay of vegetation on land, in wetlands and in oceans all emit sulfur dioxide to air.
Some solvents, dechlorination agents, bleaches and fumigation products.
Sources used in preparing this information
- Australian and New Zealand Environment and Conservation Council (ANZECC) (1992), Australian Water Quality Guidelines for Fresh and Marine Waters.
- ChemFinder WebServer Project (1995) (accessed, December, 1998)
- Meagher, D (1991), The Macmillan Dictionary of The Australian Environment, Macmillan Education Australia Pty Ltd.
- Messer MG Industries (1997), Material Safety Data Sheets (MSDS) (accessed, December, 1998)
- Micromedex (1995), Knowledge Bases for Healthcare, Safety and the Environment (accessed, December, 1998)
- National Academy of Sciences (1995), Laboratory Safety: Sulfur Dioxide (accessed, December, 1998)
- National Environment Protection Council (1998), National Environment Protection Measure for the National Pollutant Inventory. (accessed, December, 1998)
- National Environment Protection Council (1998b), National Environment Protection Measure for Ambient Air Quality.
- National Library of Medicine (1997), Specialized Information Services (accessed, December, 1998)
- Richardson, M (1992), Dictionary of Substances and their Effects, Royal Society of Chemistry, Clays Ltd, England.
- Sittig, M (1991), Handbook of Toxic and Hazardous Chemicals and Carcinogens, 3rd edition, Noyes Publications, USA.
- Technical Advisory Panel (1999), Final Report to the National Environment Protection Council.
- US Department of Health and Human Services (1990), NIOSH Pocket Guide to Chemical Hazards, Publication No. 90-117.
- Worksafe Australia (1996), Hazardous Substance Sulphur dioxide (accessed, March, 1999)
- 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.