Disinfection Mechanism of Chlorine Dioxide (CIO2) (2024)

Chlorine dioxide (ClO2) is a yellow-green gas with an odor similar to chlorine with excellent distribution, penetration, and sterilization abilities due to its gaseous nature. Although chlorine dioxide haschlorinein its name, its properties are very different, much like carbon dioxide is different from elementalcarbon. Chlorine dioxide has been recognized as a disinfectant since the early 1900s and has been approved by the US Environmental Protection Agency (EPA) and the US Food and Drug Administration (FDA) for many applications. It has been demonstrated effective as a broad spectrum, anti-inflammatory, fungicidal, bactericidal, nd virucidal agent, as well as a deodorizer, and also able to inactivate beta-lactams and destroy both pinworms and their eggs.

As can be seen in the chart above, the size of a chlorine dioxide gas molecule is 0.124 nm, much smaller than microorganisms and viruses, allowing the gas to easily penetrate into any areas where these microorganisms might be concealed.

Although chlorine dioxide has "chlorine" in its name, its chemistry is radically different from that of chlorine. When reacting with other substances, it is weaker and more selective, allowing it to be a more efficient and effective sterilizer. For example, it does not react with ammonia or most organic compounds. Chlorine dioxide oxidizes products rather than chlorinating them, so unlike chlorine, chlorine dioxide will not produce environmentally undesirable organic compounds containing chlorine. Chlorine dioxide is also a visible yellow-green gas allowing it to be measured in real-time with photometric devices.

Antimicrobial Properties / Mode of Action: Chlorine dioxide (O2) acts as an oxidizing agent and reacts with several cellular constituents, including the cell membrane of microbes. By "stealing" electrons from them (oxidation), it breaks their molecular bonds, resulting in the death of the organism by the breakup of the cell. By altering the proteins involved in the structure of microorganisms, their enzymatic function is broken and causes very rapid bacterial kills. This oxidative attack on many proteins simultaneously is behind the potency of chlorine dioxide and also prevents microorganisms from mutating to a resistant form. Because of the selective reactivity of chlorine dioxide, its antimicrobial action is retained longer in the presence of organic matter than most other decontaminating agents.

Inactivation of Spores vs. Bacteria: The difference between spore and bacterial inactivation is the same as the difference between sterilization and disinfection. For a chemical agent to be classified as a sterilant, it must be demonstrated to be effective at inactivating spores. Spores are among the hardest organisms to kill and for this reasonsterilizingagents are considered the most rigorous decontaminating agents and offer complete kill of all antimicrobial life. Disinfection, on the other hand, does not require the complete inactivation of spores or all microbial life and is normally validated against a few vegetative bacteria species. For this reason,disinfectingagents are less rigorous decontaminating agents and are not as effective as sterilizing agents.

"Bacterial endospores are one of the most persistent forms of microbial life and typically require aggressive inactivation procedures. Vegetative bacteria are generally much more easily inactivated than are bacterial endospores. This is primarily because the sensitive areas of bacteria are easily contacted by chemosterilizing agents. The spore, however, has a more complex structure than the vegetative bacterial cell. Its sensitive material is contained within a core and that core is surrounded by a cortex and spore coats. These coats tend to act as a permeability barrier to the entry of chlorine dioxide and other compounds" (Knapp, 2000).

Chlorine dioxide's special properties make it an ideal choice to meet the challenges of today's environmentally concerned world and is an environmentally preferred alternative to elemental chlorine. When chlorine reacts with organic matter, undesirable pollutants such as dioxins and bio-accumulative toxic substances are produced. Thus, the EPA supports the replacement of chlorine with chlorine dioxide because it eliminates the production of these pollutants. It is a perfect replacement for chlorine, providing all of chlorine's benefits without any of its weaknesses and detriments. Most importantly, chlorine dioxide does not chlorinate organic material, eliminating the formation of trihalomethanes (THMs), haloacetic acids (HAAs) and other chlorinated organic compounds. This is particularly important in the primary use for chlorine dioxide, which is water disinfection. Other properties of chlorine dioxide make it more effective than chlorine, requiring a lower dose and resulting in a lower environmental impact.

Chlorine dioxide is widely used as an antimicrobial and as an oxidizing agent in drinking water, poultry process water, swimming pools, and mouthwash preparations. It is used to sanitize fruit and vegetables and also equipment for food and beverage processing and widely used in life science research laboratories. It is also employed in the health care industry to decontaminate rooms, passthroughs, isolators and also as a sterilant for product and component sterilization. It is also extensively used to bleach, deodorize, and detoxify a wide variety of materials, including cellulose, paper-pulp, flour, leather, fats and oils, and textiles. Approximately 4 to 5 million pounds are used daily.

The US EPA defines asterilizeras able"to destroy or eliminate all forms of microbial life including fungi, viruses, and all forms of bacteria and their spores,"meaning chlorine dioxide gas will inactivate any form of antimicrobial life including spores.

Mechanisms of gaseous chlorine dioxide against microorganisms: destabilization of cell membranes reaction with amino acids, interruption of protein synthesis and oxidation of DNA/RNA/proteins.

Material Compatibility: Chlorine dioxide gas is one of the most gentle decontaminating agents available. Its process generates a pure chlorine dioxide gas which is used every day to decontaminate sensitive materials ranging from laboratory scales, microscopes and computers, to complex machinery and entire assembly lines. Indeed, chlorine dioxide is not corrosive. Many people are familiar with liquid chlorine dioxide solutions and their corrosive nature. However, these corrosive properties are due to the manner in which these solutions are generated and not the actual chlorine dioxide itself. Many liquid solutions are generated from a typical reaction as follows:

For most chlorine dioxide liquid solutions, it is these two acidic byproducts, acidified sodium chlorite and chlorous acid that give the solution its low pH (typically around 3) and corrosive properties. However, pure chlorine dioxide gas has a non-corrosive neutral pH of 7 when dissolved in water and is gentle on materials. The table below shows common decontaminating agents and their oxidation (corrosion) potential. A higher oxidation potential means that the agent is a stronger oxidizer and thus more corrosive. As can be seen, chlorine dioxide is less corrosive than most of the common decontaminating agents.

As shown in the table above, chlorine dioxide has a relatively low oxidation (corrosion) potential, 1.9 times lower than hydrogen peroxide. Yet, due to the prevalent use of liquid chlorine dioxide and its corrosive properties, a stigma exists in which chlorine dioxide gas is also considered corrosive. Liquid chlorine dioxide’s corrosive properties stem from its generation chemistry in which multiple acidic components are involved. It is these acids that give the liquid its corrosive qualities, not the chlorine dioxide itself. Pure chlorine dioxide gas is gentle on materials and should not be considered in the same was as liquid chlorine dioxide products.

References

1-World Health Organization (WHO)

2- European Chemical Agency (ECHA)

3- Food and Drug Administration (FDA)

4- Food and Agriculture Organization (FAO)

5- The Environmental Protection Agency (EPA)

6- ProMinent

7- Grundfos

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