Chlorine Dioxide - an overview (2024)

Chlorine Dioxide

Chlorine dioxide (ClO₂), a potent biocide, has been used for many years to disinfect municipal water and in numerous other large-scale applications. Until recently, the benefits of chlorine dioxide have been limited to large-scale applications, because it is formulated as a volatile gas that must be produced on-site with sophisticated chemical-generation equipment. Newer methods enable cost-effective and portable ClO₂ generation and distribution for use in an ever-widening array of small-scale applications (Box 88-11).

Chlorine dioxide is not as unstable as ozone but does not produce a lasting residual. It does not form chlorinated compounds in the presence of organics and is efficacious over a wide pH range. Byproducts of chlorine dioxide are chlorite (ClO₂⁻) and chlorate (ClO₃⁻).

Chlorine dioxide has no taste or odor in water. It is capable of inactivating most waterborne pathogens, includingC. parvum oocysts, at practical doses but at extended contact times of 2 to 4 hours.^{64,168,219,237} It is as least as effective a bactericide as chlorine and far superior as a virucide.^201,336

There are several commercial point-of-use applications using chlorine dioxide in liquid or tablet form (see appendices at the end of this chapter).

Toxico*kinetics

Chlorine dioxide can be rapidly absorbed through the gastrointestinal tract. Peak blood concentration levels can be reached within 1h after a single dose administered orally. It can also be slowly absorbed through shaved skin with a half absorption time of 22h. It seems unlikely that intact chlorine dioxide is absorbed by inhalation giving its highly reactive nature; it is more likely that its derivatives can be absorbed. Chlorine dioxide is metabolized to chlorite, chlorate, and mostly chloride. Most administered chlorine dioxide and its metabolites remain in plasma followed by kidneys, lungs, stomach, intestine, liver, and spleen. About 43% of orally administered chlorine dioxide is eliminated in the urine and feces within 72h. It is not excreted via the lungs.

Chlorine Dioxide (Table 45.7)

Abstract

Chlorine dioxide is a highly effective oxidant with good germicidal properties that also provides excellent residual disinfection action and biofilm control. The chemistry of chlorine dioxide is explained, as is chemical dosing and available process technology. The advantage of chlorine dioxide over chlorine and chloramines is based on the reduction of taste and order problems and the prevention of trihalomethanes and other chlorinated disinfection by-product (DBP) formation. Unlike chlorine, it is easy to generate on site although sodium chlorite in its dry form it is highly unstable and dangerous. It does produce two DBPs of its own, chlorite and chlorate. Also, where free chlorine is released during chlorine dioxide generation, there is a risk that halogen-substitute DBPs may be formed. The WHO has set a guideline value for chlorite in drinking water of 0.2 mg L⁻¹. In the UK a limit for combined residual concentrations of chlorine dioxide, chlorite and chlorate has been set at 0.5 mg L⁻¹ as ClO₂ in treated water, with a corresponding maximum contaminant level (MCL) of 1.0 mg L⁻¹ set by the USEPA. In practice, these limit values restrict chlorine dioxide doses to 0.75 and 1.5 mg L⁻¹ in the UK and USA, respectively. Such limits mean that the use of chlorine dioxide as a main disinfectant for drinking water is no longer possible. However, it is still widely used prior to treatment for pre-disinfection or as a pre-oxidant for the removal of taste, odour, colour, phenol, iron and manganese. A pre-oxidant dose should rarely exceed 1.5 mg L⁻¹, as 0.2–0.4 mg ClO₃ L⁻¹ produced at a chlorine dioxide dose of 1.0 mg L⁻¹.

Gaseous chlorine dioxide as an alternative for bedbug control

Gibbs SG, Lowe JJ, Smith PW, Hewlett AL. Infect Control Hosp Epidemiol 2012; 33: 495–9.

At all concentrations tested (362, 724, and 1086 ppm), chlorine dioxide resulted in 100% mortality of bedbugs 18 hours after the exposure. These concentrations can be safely achieved in a hospital room.

In conjunction with chemical treatment of the home, the following strategies can be used to prevent further infestation: a sealed, plastic cover for the mattress; moving the mattress away from the wall; keeping blankets off the floor; petrolatum applied to the legs of the bed; plastic cups with or without water under the legs of the beds; white sheets to make the bed bugs or blood more visible; removing lose wallpaper; and filling in cracks of floorboards, furniture, walls, and windowsills. To prevent infection while traveling, travelers should examine the bed and area around the bed, avoid using hotel drawers, keep suitcases zipped, and launder clothes with heated drying upon return.

Chlorine Dioxide

Chlorine dioxide (ClO₂) is in general a very powerful disinfectant. Chlorine dioxide is a broad oxidant and sanitizing agent; it functions by disrupting cell membranes and protein synthesis. It can be used as a gas or in an aqueous form. Chlorine dioxide has been widely studied as a sanitizer and typical aqueous concentrations range from 50 to 200ppm. As a gas, chlorine dioxide has been shown to be sporocidal (to kill bacterial spores) at concentrations ranging from 10 to 40mgl⁻¹ and with contact times of at least 30min on surfaces such as metals, plastics, and glass (but less efficiently when applied to wood). Concentrations of chlorine dioxide gas as low as 2mgl⁻¹ have been shown to inactivate more than 5logCFUcm⁻² of Listeria monocytogenes biofilm cells on a meat slicer, demonstrating the potential of this sanitizer. However, the main problem with chlorine dioxide is that it can be corrosive to steel surfaces, especially under acidic conditions. It also needs to be produced on site.

Chlorine Dioxide

Chlorine dioxide (ClO₂), a potent biocide, has been used for many years to disinfect municipal water and in numerous other large-scale applications. Until recently, chlorine dioxide could be used only in large-scale water treatment applications, but several new chemical methods for generating chlorine dioxide on-site can now be applied in the field for small quantity water treatment, allowing this technique to gain wider use for disinfection of both community and point-of-use drinking water supplies in developed countries. Chlorine dioxide is capable of inactivating most water-borne pathogens, including Cryptosporidium parvum oocysts, at practical doses and contact times. It is at least as effective a bactericide as chlorine and in many cases superior. It is far superior as a virucide. Chlorine dioxide is not stable in solution and does not produce a lasting residual (Table 7.10).

Chlorine Dioxide (ClO₂)

Chlorine dioxide is an extremely effective disinfectant, which rapidly kills bacteria, viruses, and Giardia, and is also effective against Cryptosporidium. ClO₂ also improves taste and odor, destroys sulfides, cyanides, and phenols, controls algae, and neutralizes iron and manganese ions. It is an effective biocide at concentrations as low as 0.1 ppm (parts per million) and over a wide pH range. It is ten times more soluble in water than chlorine, even in cold water. Unlike iodine, chlorine dioxide has no adverse effects on thyroid function. Chlorine dioxide is widely used by municipal water treatment facilities.

The term “chlorine dioxide” is misleading because chlorine is not the active element. Chlorine dioxide is an oxidizing, not a chlorinating agent. ClO₂ penetrates the cell wall and reacts with amino acids in the cytoplasm within the cell, killing the microorganism. The by-product of this reaction is chlorite, which is harmless to humans. Chlorine dioxide is available in both tablet (Micropur MP 1) and liquid (Pristine) preparations.

Chlorine Dioxide

Chlorine dioxide in liquid form is now the most commonly used sterilant in gnotobiotics. It is effective against bacterial spores and other microorganisms, and chlorine dioxide gas diffused out of solutions is also effective (Chatuev and Peterson, 2010; Ezzell, 1986; Orcutt etal., 1981; Pell-Walpole and Waller, 1984; Perez etal., 2005; Thorn etal., 2013). Liquid chlorine dioxide sterilants include Exspor (Ecolab Inc.) and Clidox-S (Pharmacal Research Laboratories). These are composed of two parts, a base solution of sodium chlorite and an acidic activator, which are combined and mixed with water immediately before application to form a solution of chlorous acid and chlorine dioxide. A contact time of at least 30min is recommended. Such products can corrode stainless steel. MB-10 (Quip Laboratories) is another chlorine dioxide product, but we are not aware of reports of its use in gnotobiotics.

Chlorine Dioxide

Chlorine dioxide is commonly used as a method of water system disinfection and has been used for biofilms and Legionella control over a wide pH range.^{117,130–132} It is a powerful oxidant that disrupts protein synthesis, making it an efficient antimicrobial. However, penetration of biofilms can be challenging and chlorine dioxide can take months to achieve microbial control, can corrode pipework and readily decomposes, particularly in hot water, though higher concentrations can be used in the hot water supply.^130,133,134

Concentrations of 0.5mg/l are effective against planktonic and sessile Legionella in hot water systems. However, The Drinking Water Inspectorate advises a maximum of 0.5mg/l chlorine dioxide in drinking water and concentrations need to be closely monitored.¹⁰⁰