Chlorine dioxide (ClO₂) is a synthetic, yellow-green gas with a chlorine-like, irritating odour. Unlike elemental chlorine, it has distinct chemical properties and behaviour. It is a volatile, reactive molecule that readily dissociates into chlorine gas, oxygen, and heat. Highly soluble in cold water—around 10 times more than chlorine—it remains a dissolved gas rather than hydrolyzing, making it useful in a range of industrial and disinfection processes.
What is Chlorine Dioxide used for?
Chlorine dioxide is primarily used as a bleaching agent in industries such as:
Paper and textiles: bleaching wood pulp, cellulose, flour, textiles, fats, and oils.
Leather: cleaning and de-tanning.
Food and beverages: disinfecting dairy equipment, food-processing areas, and eating establishments.
Public health: disinfecting drinking water, cooling towers, and metal cutting fluids.
It is approved as a food additive in Australia (No. 926) and widely adopted in Europe, North America, and Australia as an alternative to chlorine due to fewer harmful by-products.
Chlorine dioxide is primarily used as an industrial bleaching agent. In the leather industry, it plays a key role in cleaning and de-tanning processes.
In the Environment
Chlorine dioxide is highly reactive and does not persist in the environment.
Air: breaks down quickly under sunlight into chlorine and oxygen.
Water: converts to chlorite, which can migrate into groundwater but usually reacts with soil and sediments.
Bioaccumulation: neither chlorine dioxide nor chlorite builds up in the food chain.
Sources of Emission & Routes of Exposure
Sources of Emission
Industrial: pulp and paper mills, textile factories, chemical and food processing industries, water treatment plants, and cooling towers.
Diffuse: residues in treated food and water.
Consumer products: some disinfectants and bleaches.
Natural sources: unlikely, due to its high reactivity.
Routes of Exposure
Inhalation: workers in industries using chlorine dioxide may inhale the gas.
Ingestion: most people are exposed through treated drinking water or food.
Skin contact: possible when handling chlorine dioxide directly.
Occupational exposure is most common in pulp and paper mills, municipal water treatment facilities, and food processing industries.
Health Effects
Acute Effects
Short-term exposure to chlorine dioxide or chlorine (from its decomposition) can cause:
Skin: irritation and burns; absorption through skin can damage tissue and blood cells.
Eyes: irritation, watering, and blurred vision.
Inhalation: coughing, sore throat, severe headaches, bronchial spasm, and lung edoema (fluid in the lungs). Symptoms may appear after a delay and persist for some time.
Chronic Effects
Prolonged exposure to chlorine dioxide has been linked to bronchitis and ongoing respiratory issues.
Development and Reproduction
There is limited evidence suggesting chlorine dioxide may affect reproduction and development. Current research is inconclusive, and further studies are required.
Mutagenicity
Tests such as the Ames test indicate chlorine dioxide in concentrations of 5–15 mg/L may increase water mutagenicity. However, proving this effect is difficult because chlorine dioxide and its by-products are biocides that can kill test organisms.
Carcinogenicity
Currently, there is no evidence of chlorine dioxide causing cancer in humans. Both the IARC and EPA classify it as “not classifiable as to human carcinogenicity.
Safety
First Aid Measures
Inhalation: Move the person to fresh air, keep them warm and at rest. Provide oxygen if breathing is difficult. If not breathing, apply artificial respiration and seek urgent medical help.
Skin contact: Rinse thoroughly with running water, remove contaminated clothing, and wash skin/hair with soap and water until medical advice is obtained.
Eye contact: Rinse eyes with running water for at least 15 minutes while keeping eyelids open. Continue flushing until medical attention is available.
Ingestion: Rinse mouth with water, do not induce vomiting, and give a glass of water. Seek immediate medical assistance.
Exposure Controls and Personal Protection
Engineering Controls
Use process enclosures, local exhaust ventilation, or other engineering controls to maintain airborne concentrations below recommended limits.
If operations generate dust, fumes, or mist, ensure adequate ventilation to keep exposure within safe limits.
Personal Protective Equipment
Chemical-resistant overalls
Chemical goggles and face shield
Elbow-length impervious gloves
Splash apron or equivalent protective garment
Rubber boots
Air-supplied respirator (if risk of inhalation exists)
Always wash hands before eating, drinking, or smoking, and clean contaminated clothing and equipment before reuse.
Regulation
United States
OSHA: OSHA Permissible Exposure Limit (PEL):
General Industry: 0.1 ppm, 0.3 mg/m³
Construction Industry: 0.1 ppm, 0.3 mg/m³ TWA
ACGIH: American Conference of Governmental Industrial Hygienists Threshold Limit Value (TLV): 0.1 ppm, 0.28 mg/m³ TWA; 0.3 ppm, 0.83 mg/m³ STEL
NIOSH: National Institute for Occupational Safety and Health: Recommended Exposure Limit (REL): 0.1 ppm TWA; 0.3 ppm STEL
Australia
Australian Drinking Water Guidelines (NHMRC and ARMCANZ, 1996): Maximum of 1 mg/L (i.e., 0.001 g/L)
Safe Work Australia: Maximum time weighted exposure (TWA) level: 0.1 ppm (0.28 mg/m³) and Maximum short term exposure level (STEL): 0.3 ppm (0.83 mg/m³)
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