ToxFAQs™ for Chlorine Dioxide and Chlorite

Spanish: Dióxido de Cloro y Clorito

CAS#: 10049-04-4 (Chlorine Dioxide); 7758-19-2 (Chlorite)

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This fact sheet answers the most frequently asked health questions about chlorine dioxide and chlorite. For more information, you may call the ATSDR Information Center at 1-888-422-8737. This fact sheet is one in a series of summaries about hazardous substances and their health effects. This information is important because this substance may harm you. The effects of exposure to any hazardous substance depend on the dose, the duration, how you are exposed, personal traits and habits, and whether other chemicals are present.


Chlorine dioxide is a gas that does not occur naturally in the environment. It is used to disinfect drinking water and make it safe to drink. Chlorite is formed when chlorine dioxide reacts with water. High levels of chlorine dioxide can be irritating to the nose, eyes, throat, and lungs. Chlorine dioxide and chlorite have not been found in any of the 1,647 National Priorities List sites identified by the Environmental Protection Agency (EPA).

What are chlorine dioxide and chlorite?

Chlorine dioxide is a yellow to reddish-yellow manufactured gas. It does not occur naturally in the environment. When added to water, chlorine dioxide forms chlorite ion, which is also a very reactive chemical.

Chlorine dioxide is used as a bleaching agent at paper manufacturing plants, and in public water treatment facilities to make water safe to drink. In 2001, chlorine dioxide and chlorite were used to decontaminate a number of public buildings following the release of anthrax spores in the United States.

What happens to chlorine dioxide and chlorite when they enter the environment?

  • Chlorine dioxide is a very reactive compound and breaks down quickly in the environment.
  • In air, sunlight rapidly breaks down chlorine dioxide into chlorine gas and oxygen.
  • In water, chlorine dioxide quickly forms chlorite.
  • Chlorite in water may move into groundwater, although reactions with soil and sediments may reduce the amount of chlorite reaching groundwater.
  • Neither chlorine dioxide or chlorite build up in the food chain.

How might I be exposed to chlorine dioxide and chlorite?

Chlorine dioxide is added to drinking water to protect people from harmful bacteria and other microorganisms.

Most people are exposed to small amounts of chlorine dioxide and chlorite by drinking treated water.

Individuals who are employed at pulp and paper mills, municipal water treatment facilities, and other facilities that use chlorine dioxide and chlorite as a disinfectant may have high exposures to chlorine dioxide and chlorite (ions or salts).

How can chlorine dioxide and chlorite affect my health?

Both chlorine dioxide and chlorite react quickly in water or moist body tissues. Breathing air containing chlorine dioxide gas may cause nose, throat, and lung irritation. Eating or drinking large amounts of chlorite salts may cause irritation in the mouth, esophagus, or stomach. There is no evidence that chlorine dioxide or chlorite affect reproduction in humans.

Studies in animals exposed to high amounts of chlorine dioxide or chlorite have shown effects similar to those seen in exposed people.

How likely are chlorine dioxide and chlorite to cause cancer?

There are no studies on cancer in humans exposed to chlorine dioxide or chlorite. Based on inadequate information in humans and in animals, the International Agency for Research on Cancer (IARC) and the EPA have determined that chlorine dioxide and sodium chlorite are not classifiable as to human carcinogenicity.

How can chlorine dioxide and chlorite affect children?

Children exposed to large amounts of chlorine dioxide and chlorite would be expected to be affected in the same manner as adults.

Studies in rats have shown that exposure of pregnant animals to chlorine dioxide or exposure of pups shortly after birth may cause delays in the development of the brain. However, the exposure levels in these studies were much higher than what humans are usually exposed to these compounds in the drinking water. There are no reliable studies of effects of chlorine dioxide or chlorite in developing humans.

How can families reduce the risk of exposure to chlorine dioxide and chlorite?

Families that drink water treated with chlorine dioxide may reduce their exposure by drinking bottled water that has not been treated with these chemicals.

Is there a medical test to show whether I've been exposed to chlorine dioxide and chlorite?

There are no routine medical tests available to measure chlorine dioxide or chlorite in the body. There is a special test to measure chlorite in tissues, blood, urine, and feces, but the test cannot tell the extent of the exposure or whether harmful effects will occur.

Has the federal government made recommendations to protect human health?

The EPA has set a maximum contaminant level of 1 milligram of chlorite per liter (1 mg/L) and 0.8 mg/L for chlorine dioxide in drinking water. However, the concentration of both of these chemicals may be higher or lower in your drinking water.

The Occupational Safety and Health Administration (OSHA) has set a limit of 0.1 parts of chlorine dioxide or chlorite per million parts of air (0.1 ppm) in the workplace during an 8-hour shift, 40-hour workweek.


Agency for Toxic Substances and Disease Registry (ATSDR). 2004. Toxicological Profile for Chlorine Dioxide and Chlorite. Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service.

Where can I get more information?

If you have questions or concerns, please contact your community or state health or environmental quality department or:

For more information, contact:
Agency for Toxic Substances and Disease Registry
Office of Innovation and Analytics, Toxicology Section
4770 Buford Highway
Chamblee, GA 30341-3717
Phone: 1-800-CDC-INFO 888-232-6348 (TTY)
Email: Contact CDC-INFO

ATSDR can also tell you the location of occupational and environmental health clinics. These clinics specialize in recognizing, evaluating, and treating illnesses resulting from exposure to hazardous substances.

Page last reviewed: November 29, 2011