Chlorine dioxide has been commercially used since 1944, when it was applied to river water to remove the phenolic taste of tainted river water.  Over the next 60+ years, the role as a powerful antimicrobial has grown tremendously as scientific data digs deeper into the chlorine dioxide molecule.

Today’s largest use of chlorine dioxide is in paper pulp bleaching, where it replaced chlorine bleaching which had been polluting the waters with dioxin. It is also widely used in municipal water treatment worldwide, as both a primary and secondary water disinfectant. ClO2 has the advantage over chlorine dosing because it will not form chlorinated organic compounds, such as trihalomethanes, a toxic byproduct of chlorination.

Odor scrubbing and industrial processes are roughly in third place, with food processing applications rounding out the top four. ClO2 is on the FDA food additives list, listed as an approved terminal sanitizing rinse, and is used in virtually all types of food rinse waters from poultry to lettuce to prevent cross contamination. Chlorine dioxide (ClO2) is a yellow/green gas in its natural state, although it is extremely soluble in water, 10 times more soluble than chlorine gas. For this reason, almost all of the use applications of chlorine dioxide prior to 2001 were aqueous, that is, where the gas was dissolved in water and used as a liquid. While it is composed of one atom of chlorine and two atoms of oxygen, its chemistry is very different from that of chlorination based compounds, such as bleach. ClO2 is a pure oxidizer, that is, it does not produce toxic chlorinated byproducts as chlorine does. As such, it is considered a “green” chemistry. Its ultimate breakdown product is chloride, a component of simple salt, and universally recognized as non-toxic. For these reasons, ClO2 is on the FDA food additives list and is used as a sanitizing rinse in all types of foods, and as a sanitizer and disinfectant on food contact surfaces and non porous surfaces found in food plants. It is also one of the main compounds used to sanitize drinking water around the world. It has been only in the last ten years or so, that “gas phase” has been studied and utilized in commercial applications.

Early on, chlorine dioxide had a reputation as a dangerous compound, since extremely high concentrations (>10-12%) can be explosive in air. These levels equate in parts per million (PPM) to be 100,000 to 120,000 which is several orders of magnitude greater than what is normally used in day to day operations, that being from 5 PPM up to 200PPM. In fact, new use applications indicate a level as low as 0.03 PPM is effective against many viruses.

It is important to understand that chlorine dioxide is a very special molecule, which uses a selective oxidation to interact with the biochemistry of microorganisms. The chlorine dioxide molecule is an oxidizing free radical that reacts with several amino acids that make up proteins. ClO2 bends and breaks these proteins and causes them to be non-functional. The most important proteins that are denatured are enzymatic proteins that catalyze biochemical reactions within the bacteria, virus or fungi. This causes the microbe to shut down and die very rapidly. The literature is full of studies from leading Universities and institutions indicating very rapid and significant kill rates using chlorine dioxide. This is the reason chlorine dioxide was chosen as the compound of choice to kill the Anthrax Spores that were released into government buildings in 2001. This selective oxidation not only attacks enzymatic proteins to kill microbes, but reacts with other proteins as well including those that make up outer cellular components such as antigens. The scientific literature actually describes in detail how ClO2 attacks and destroys allergens, thereby literally clearing the air. People who suffer from workplace allergies can greatly benefit from this technology.

While it has been demonstrated both in practice and in studies that ClO2 has the ability to neutralize mold and pollen allergens, the jury is still out concerning its ability to neutralize toxins associated with fungal metabolism, known as metabolites or mycotoxins. There are approximately 25 mycotoxins that have been widely studied, but estimates of up to 300 to 400 difference mycotoxins have been made. There are several mycotoxins that have been neutralized with chlorine dioxide, but the conditions and concentrations are questionable. A review of the chemical structure of 25 mycotoxins suggests that many are oxidizable and therefore could be potentially neutralized under the right conditions with ClO2. To actually prove this hypothesis would be a very long and costly exercise, and every mycotoxin would not likely be neutralized. For this reason, DeepReach Oxidation identifies materials that have evidence of metabolizing mold growth and removes them as per EPA “Guidelines”.A common misconception about chlorine dioxide is that it is highly explosive and posses a great danger when in use. Liquid use solutions (2 PPM – 2000 PPM) have none of these characteristics.  It is true that  dry gas can spontaneously detonate in very high concentrations of 10% to 12% (120,000 PPM) in a confined space such as a pipe end.  The DeepReach process is controlled and for applications of mold, odor and allergen ellimination does not go over 250 PPM.   For this reason, the process is completely safe.

Synergism of EPA Guidelines / ClO2 gas fumigation / Industrial Hygenists
The role of the industrial hygenist working with facility managers is a most important one.  Since our application technology and label came into commercial use AFTER the IH association’s 2005 white paper on fumigation, there has been some confusion on the applicatability of gas fumigation in mold remediation.  DRO is in the process of working with leading IH consultants in bringing forth a new white paper recognizing the superior mold remediation achieved when incorporating fumigation.  In the meantime, we are eager to discuss the techincal aspects with any industrial hygenist seeking to help their clients achieve superior and cost effective results. 

To clear any confusion, it is clearly and specifically noted on the DRO 5000 label multiple EPA approved uses for fumigation applications. In Section 1.0, the process is used ” to retard or inhibit growth of bacteria and fungi including mold and mildew on floors, walls, contents and other interior building surfaces until such time as the cause of such growth can be identified and corrected”. It is also used to control odors within spaces, and  DRO5000 can also be used as a component in a comprehensive mold and/or water damage restoration program. This section also indicates an extremely wide range of surfaces and materials in which DRO5000 can be utilized. Section 2.1 focuses on pre-cleaning techniques used on various materials. It is perfectly clear that pre-cleaning and mold identification and removal is an integral part of the DRO5000 process. The DRO5000 label is the most comprehensive and detailed registration currently on the books. with USEPA. It is generally regarded as the Standard for fumigation applications within a structure for antimicrobial use.  

The addition of a fumigation step to mold abatement generates a number of significant advantages. The costs of mold remediation are high, primarily due to the expense associated with the man-hours required for the demolition and reconstruction of the interior of these contaminated structures, the replacement of the HVAC systems, and the extensive down times involved in the completion of the projects. By employing  a selected demolition strategy in conjunction with pre-cleaning and fumigation, man-hours are significantly reduced, time to completion is dramatically cut and project costs are minimized.