Sodium and calcium hypochlorite are disinfectants used in bleach and bleach products, purifying drinking water, swimming pools, ponds and wastewater. Sodium and calcium hypochlorite also are used in soil treatment of fruits and vegetables. Hypochlorites control bacteria, fungi and slime-forming algae that causes disease in people and animals. In the presence of oxygen, the hypochlorites convert readily into sodium chloride (table salt) and calcium chloride (road salt).
History and Benefits
In 1896, hypochlorites were used in typhoid epidemics in Austria-Hungary on the Adriatic Sea. Chlorination was introduced in England during 1905 to eliminate typhoid fever from the water supply. One of the most significant advances in public health, chlorination and filtration in the United States eliminated typhoid, cholera, dysentery and hepatitis A.
Pesticides
In 1957, sodium and calcium hypochlorite, known as bleach, were registered as pesticides. Pesticides used in the U.S. must meet Environmental Protective Agency (EPA) standards. Pesticides have to be re-registered with the EPA if they contain 5.25 to 12.5 percent sodium hypochlorite, or 65 to 70 percent calcium hypochlorite, with no other ingredients other than water.
Drinking Water
The EPA's Office of Drinking Water has tested sodium and calcium hypochlorite thoroughly for water and wastewater systems to make sure they do not create carcinogens. The EPA set a maximum contaminant level of 100 parts per billion in drinking water.
Food Processing
Sodium hypochlorite may be used in washing and peeling of fruits and vegetables or as a final sanitizer on food processing equipment.
Comparison
Calcium hypochlorite (Ca(OCl)2) contains 65 percent available chlorine by weight and requires special handling because it will ignite in contact with organic material. Sodium hypochlorite (NaOCl) is a transparent, light-yellow solution with water contains 9 to 15 percent chlorine. Sodium hypochlorite to disinfect drinking water is double the concentration of bleach.
Sodium hypochlorite is less expensive than calcium hypochlorite.
Warning
Both hypochlorites are labeled Toxicity Category I, the highest level of toxicity. Sodium and calcium hypochlorite are extremely corrosive and can damage the eyes and skin badly. Protective clothes, safety glasses, goggles and chemical-resistant gloves are required when using sodium or calcium hypochlorite products, which are labeled with precautions.
Hypobromite is formed by hypochlorite products used in seawater. The National Pollutant Discharge Elimination System (NPDES) specifies that sodium and calcium hypochlorite are almost non-toxic to avian wildlife but highly toxic to fish and invertebrates.