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Chlorine dioxide (ClO₂) is a broad-spectrum biocide with proven efficacy against a range of microbial organisms such as bacteria, viruses, protozoa, yeasts, mycobacteria and bacterial spores. Originally used in water treatment and food industries, chlorine dioxide has now been adopted as the go-to high-level disinfectant in medical, pharmaceutical, veterinary and laboratory settings.

The mechanism through which ClO₂ achieves its potent biocidal effect is oxidation¹. Oxidation involves the oxidising agent sequestering electrons from the microorganism, which causes a molecular imbalance that inevitably leads to the microorganism’s death. The main advantage of using oxidising biocides over non-oxidising biocides (alcohols, quaternary ammonium compounds) is the inability for microorganisms to develop resistance², as well as the broad range of efficacy¹.

The comparison of ClO₂ with other oxidisers, such as hydrogen peroxide is of interest. Whilst hydrogen peroxide and other oxidisers work through the same mechanisms as chlorine dioxide, they have been shown to be less effective against microbes³. This is attributed to ClO₂’s unique ability to penetrate the microorganism’s 3D protein structure³ and, thus, better oxidise the molecules. Additionally, ClO₂ forms no hazardous by-products⁴ and is less harmful to people and equipment than other common biocides such as hydrogen peroxide and chlorine².

Chlorine dioxide generated from sodium chlorite is supported for the active substance registration under the GB and the EU Biocidal Product Regulations for Product Types 2, 3, 4, 5, and is an active substance in various pesticides registered with the United States Environmental Protection Agency (EPA).

References
1. Block, S., Knapp, J. and Battisti, D. (2001). Disinfection, sterilization, and preservation. Philadelphia: Lippincott Williams & Wilkins, pp.215-227.
2. Noszticzius, Z., Wittmann, M., Kály-Kullai, K., Beregvári, Z., Kiss, I., Rosivall, L. and Szegedi, J. (2013). Chlorine Dioxide Is a Size-Selective Antimicrobial Agent. PLoS ONE, 8(11), p.e79157.
3.  Finnegan, M., Linley, E., Denyer, S.P., McDonnell, G., Simons, C., Maillard, J.Y. (2010) Mode of action of hydrogen peroxide and other oxidizing agents: differences between liquid and gas forms, Journal of Antimicrobial Chemotherapy, 65(10), pp. 2108–2115.
4. Al-Otoum, F., Al-Ghouti, M., Ahmed, T., Abu-Dieyeh, M. and Ali, M. (2016). Disinfection by-products of chlorine dioxide (chlorite, chlorate, and trihalomethanes): Occurrence in drinking water in Qatar. Chemosphere, 164, pp.649-656.