Chlorate is a disinfection by-product resulting from the use of chlorine dioxide as a disinfectant and for odor & taste control in water. The term “chlorate” most commonly refers only to chlorine in the +5 oxidation state. Chlorate ion is a known byproduct of the drinking water disinfection process, forming when sodium hypochlorite or chlorine dioxide are used in the disinfection process.
Chlorine dioxide is also used as a bleaching agent for cellulose, paper pulp, flour and oils and for cleaning and detanning leather. Sodium chlorate is used in the preparation of chlorine dioxide; in the manufacture of dyes, matches and explosives; for tanning and finishing leather; and in herbicides and defoliants
There is not a federal drinking water standard for chlorate ion at this time, but the EPA has set a daily reference dose of 0.03 milligrams per kilogram of body weight (0.03 mg/kg/day). EPA defines a reference dose as “an estimate of a daily oral exposure to the human population that is likely to be without an appreciable risk of deleterious effects during a lifetime.”
Exposure to chlorine dioxide and chlorite in excess of EPA-regulated maximum levels can have effects on the nervous system in infants, small children, and unborn fetuses. Chlorite and chlorate have been shown to effect red blood cells in animal studies, but similar results did not appear in the highest doses tested on humans (36 micrograms per kilogram of body weight).
According to the EPA, long term exposure to large amounts may lead to anemia. There is currently no evidence of human carcinogenicity.
According to a Canadian expert committee on drinking water, “some residential-scale treatment devices using a granular activated carbon filter may remove chlorite,” although they have not yet certified any filters for that use. There is no recommended treatment for chlorate.