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The compound chlorine dioxide (ClO2), now commercially important, is not in fact a recent discovery. The gas was first produced by Humphrey Davy in 1811 when reacting hydrochloric acid with potassium chlorate. This yielded “euchlorine”, as it was then termed. Watt and Burgess, who invented alkaline pulp bleaching in 1834, mentioned euchlorine as a bleaching agent in their first patent. Chlorine dioxide then became well known as a bleach and later a disinfectant. Since the beginning of the twentieth century, when it was first used at a Spa in Ostend, Belgium, ClO2 has been known as a powerful disinfectant of water. The production of ClO2 from the chlorate is complicated however, and the gas is explosive, so that it could not be easily utilized practically until the production of sodium chlorite by Olin Corporation in 1940. Chlorine dioxide could now be released when necessary from the chlorite salt. In municipal water supplies this is usually done by adding chlorine to the chlorite solution, and in the laboratory by adding an acid to the chlorite solution. Alliger showed in 1978, that ClO2 could be applied topically by the individual user.
Although ClO2 is a strong oxidizing agent and a particularly fast disinfectant, there are no reports in the scientific literature of toxicity by skin contact or ingestion, or moreover of mutagenicity. It would seem that effective application of this compound as a topical medication for skin diseases, as a disinfectant on food, as well as a cold sterilant on instruments and glassware, is long overdue.
ClO2 in some respects is chemically similar to chlorine or hypochlorite, the familiar household bleach. However, ClO2 reactions with other organic molecules are relatively limited as compared to chlorine. When ClO2 is added to a system – whether a wound or a water supply – more of the biocide is available for disinfection and not consumed by other materials. Until 1963 hypochlorite was a standard product of the British Pharmacopoeia (for skin medications), and burn patients even now are bathed in hypochlorite solution at some U.S. burn centers. However, for many reasons ClO2 makes a likely substitute for the better known hypochlorite since it is far less toxic and irritating when applied to the human body. ClO2 for example, does not hydrolyze to form HCl as does chlorine, but remains a true gas dissolved in solution. ClO2, unlike chlorine or hypochlorite, does not form chlorinated hydrocarbons when in contact with organic matter, or readily add to double bonds. This is a prime concern since many chlorinated hydrocarbons are known to be carcinogenic. Of the amino acids, the building blocks of proteins, only aromatic amino acids and those containing sulfur react with ClO2. When hypochlorite is applied to the skin, nitrogen trichloride is formed, a compound which appears in trace quantities but is toxic and irritating. Also, hypochlorite in swimming pool water produces chloramine, an eye irritant, and in wastewater, chloroform. Lastly, unlike hypochlorite or chlorine, ClO2 can treat water at about 10 ppm with no harmful effects to fish. The LC50 for rainbow trout at 96 hours is 290 ppm. For this reason ClO , rather than chlorine, is favored in commercial aquarium water, especially in mammal tanks.
Residuals of available chlorine in effluents from sewage treatment plants, including the hypochlorite ion and chloramines, adversely influence aquatic life in receiving waters —the potential adverse effects both on the public health and on aquatic ecosystems due to increased exposure to chlorinated compounds suggests that the use of chlorine relative to other available techniques for the treatment of sewage and other waste-waters must be reevaluated.At the time of World War I, when Dakins Solution (0.5% hypochlorite) gained fairly wide acceptance as a wound disinfectant, ClO2 was not similarly adopted as there was, again, no easy way to produce the gas in small quantities, or to transport it. The application of ClO2 to the body is still not practiced, nor does it seem particularly obvious that it can be. The gas needs to be released or “activated”, normally done with strong acids or chlorine just before use. This process appears somewhat unattractive therefore as a disinfectant in the lab or as a home remedy for the skin. Further, once ClO2 is activated, shelf life is normally on the order of hours.
DECAY OF CHLORINE DIOXIDE
IN FRESHWATER From: Development and Evaluation of an Ion Chromatographic Method for Measuring
Chlorite and Chlorate Anions in Bleached Kraft Mill Effluent, NCASL technical bulletin #673, July 1994, p. 3
However, in dilute solutions, in a closed container and absence of light, ClO2 can remain stable for long periods. This is especially the case in chilled water.
A new compound, DIOXIDERM (formerly CITRONEX) disinfectant gel, makes novel use of ClO2 and is available as a “skin cream” in a two-part system.
The amount to be applied is mixed just before use, and the chlorine dioxide is released slowly. Because disinfection and lesion response are so rapid, the needed extra step of mixing seems unimportant, especially when treating diseases such as diabetic ulcers or pox lesions. Dual or co-dispensers simplify the application. Similarly, a dual toothpaste and mouthwash, DIOXIBRITE and DIOXIRINSE are now available which kill all bacteria and deodorize the mouth. DIOXIGUARD Liquid for instrument and hospital application as well as general topical use, is a fast acting disinfectant.
The shelf life after combining the needed quantity is one day. DIOXIGUARD kills all bacteria, viruses and fungi within one minute, including mycobacteria and amoeba..