Chlorine dioxide


The major use of chlorine dioxide is as a bleach in a number of industries: in cleaning and de-tanning of leather, and as a bleaching agent for wood pulp, fats and oils, cellulose, flour, textiles, and beeswax.

Chlorine dioxide is registered as a bactericide, fungicide and algaecide. It is used to disinfect human drinking water systems, commercial water cooling tower systems, and metal cutting fluids. It may also be used to disinfect dairy farm animals and milking equipment, in eating establishments and food processing/handling areas and around the house. It is used extensively in Europe for disinfecting drinking water, and its use there is increasing as well as in North America and Australia, as an alternative to chlorine due to lesser problems with disinfection by-products.

Approved food additive in Australia (No. 926).

Substance details

Substance name: Chlorine dioxide

CASR number: 10049-04-4

Molecular formula: ClO2

Synonyms: chlorine peroxide; chloroperoxyl; doxcide 50; chlorine oxide; chlorine(IV) oxide

Physical properties

Chlorine dioxide is a strongly oxidising, yellow to reddish-yellow gas or liquid with a pungent, sharp odour. The odour is similar to that of chlorine and nitric acid. Soluble in water, alkaline, and sulfuric acid solutions. It is normally supplied as a less than 10% solution in cold water.

Melting Point: -59°C

Boiling Point: 11°C

Specific Gravity: 3.09

Vapour Density: 2.3

1 ppm = 2.8 mg/m3
Formula mass 67.452

Chemical properties

Chlorine dioxide gas is flammable, and is violently explosive in air at concentrations over 10%. It can be ignited by almost any form of energy, including sunlight, heat, or sparks. Chlorine dioxide is strongly oxidising, and reacts violently with organic chemicals and can be detonated by sunlight, heat, or contact with mercury or carbon monoxide.

Further information

The National Pollutant Inventory (NPI) holds data for all sources of chlorine dioxide emissions in Australia.


Acute health effects: The following acute (short-term) health effects may occur immediately or shortly after exposure to chlorine dioxide: irritate the nose and throat, causing coughing and chest pain; eye irritation with watery eyes and seeing halos around lights; breathing chlorine dioxide can irritate the lungs causing coughing and/or shortness of breath. Higher exposures can cause a build-up of fluid in the lungs (pulmonary oedema), a medical emergency but which might not occur for 24 hours, with severe shortness of breath and possibly death.

Chronic health effects: The following chronic (long-term) health effects can occur at some time after exposure to chlorine dioxide and can last for months or years: irritate the lungs; repeated exposure may cause bronchitis to develop with cough, phlegm, and/or shortness of breath. Permanent lung damage may occur, especially with repeated exposure to the vapours. There is limited evidence that chlorine dioxide may damage the developing foetus.

Entering the body

The substance can be absorbed into the body by inhalation, ingestion of food that has been treated with chlorine dioxide, or skin contact.


People living near industries that produce or use chlorine dioxide. From using disinfectants or bleaches that contain chlorine dioxide. From foods and drinking water that have been treated with chlorine dioxide.

Health guidelines

Australian Drinking Water Guidelines (NHMRC and ARMCANZ, 1996):
Maximum of 1 mg/L (i.e. 0.001 g/L)

Worksafe Australia:
Maximum time weighted exposure (TWA) level: 0.1 ppm 0.28 mg/m3
Maximum short term exposure level (STEL): 0.3 ppm 0.83 mg/m3


Chlorine dioxide is well established to be harmful to all forms of life. Ranked in the USA as one of the most hazardous compounds (worst 10%) to ecosystems.

Entering the environment

Most releases will be as the gas to the atmosphere or in wastewater streams from plants that make or use chlorine dioxide. Because of its high reactivity chlorine dioxide will not persist long in the air, water, or soil environments - up to minutes in air and up to hours in the others.

Where it ends up

In the atmosphere it will photolyze rapidly, with a tropospheric half-life of a few seconds. Because of its high reactivity, chlorine dioxide will breakdown rapidly in natural waters (that is, waters that contain moderate amounts of organic matter). Nevertheless, this substance is considered hazardous to the environment with special attention required for water organisms.

The breakdown products are chloride ion and oxidised products of organic matter.

Environmental guidelines

No national guidelines.

Industry sources

Paper and allied products industries; textile mills; chemical industries: food processing industries; drinking water treatment plants; and commercial water-cooling tower systems.

Diffuse sources, and industry sources included in diffuse emissions data

Residues from food and drinking water that have been treated with chlorine dioxide.

Natural sources

No specific information. Because of the nature of its high chemical reactivity, it is unlikely to occur naturally.

Transport sources

None known.

Consumer products

Possibly in some disinfectants and bleaches. Foods and drinking water that have been treated with chlorine dioxide.

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.
  • CalEPA Air Resources Board Toxic Air Contaminant Summary (accessed, June, 1999)
  • ChemFinder WebServer Project (1995) (accessed, June, 1999)
  • Environmental Defense Fund - Summary, Uses, Consumer Products, Rank (industrial, by quantity) (accessed, June, 1999)
  • IPCS International Chemical Safety Card (accessed, June, 1999)
  • Meagher, D (1991), The Macmillan Dictionary of The Australian Environment, Macmillan Education Australia Pty Ltd.
  • National Environment Protection Council (1998), National Environment Protection Measure for the National Pollutant Inventory. (accessed, March, 1999)
  • National Health and Medical Research Council (NHMRC) and Agriculture and Resource Management Council of Australia and New Zealand (ARMCANZ) (1996), Australian Drinking Water Guidelines.
  • New Jersey Health and Safety (accessed, June, 1999)
  • Richardson, M (1992), Dictionary of Substances and their Effects, Royal Society of Chemistry, Clays Ltd, England.
  • Sax, N.I. Dangerous Properties of Industrial Materials. 6th Ed. Van Nostrand Reinhold. New York. 1984. pp. 1505-1506.
  • 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.
  • USEPA Integrated Risk Information System Report (accessed, June, 1999)
  • USEPA Toxic Release Inventory Fact Sheet (accessed, June, 1999)
  • Worksafe Australia (accessed, June, 1999)