A: Chlorine dioxide is a biocide that can be used as a gas or as a liquid. In the past, it was created by mixing either sodium chlorite or stabilized chlorine dioxide with another "reactive" chemical, generally an acid such as citric or lactic acid. According to one source, chlorine dioxide is generated for smaller applications by the reaction of sodium chlorite with chlorine, either through gaseous chlorination or the reaction of sodium hypochlorite with hydrochloric acid. The result is chlorine dioxide in a liquid or gas that smells like chlorine bleach.
The Environmental Protection Agency first registered chlorine dioxide gas as an antimicrobial pesticide in the 1980s. Chlorine dioxide gas is registered for sterilizing manufacturing and laboratory equipment, environmental surfaces, tools, and clean rooms. The types of antimicrobial products that are available have traditionally included sanitizers, disinfectants, and sterilants.
A sanitizer is a substance that significantly reduces the bacterial population in the inanimate environment, but does not destroy or eliminate all bacteria or other microorganisms.
A disinfectant is a substance that destroys or eliminates a specific species of infectious or other public health microorganism, but not necessarily bacterial spores, in the inanimate environment.
A sterilant is a substance that destroys or eliminates all forms of microbial life in the inanimate environment, including all forms of vegetative bacteria, bacterial spores, fungi, and fungal spores.
Since chlorine dioxide is registered as a pesticide, it needs to be used consistent with its label and any other restrictions that may be applicable. It has a permissible exposure limit (PEL) of 0.1 ppm and a short-term exposure limit (STEL) of 0.3 ppm. When it was used for the emergency treatment of Anthrax, its use required an emergency exemption from the EPA.
The following is from the EPA website:
FIFRA Section 18 Emergency Exemptions and Anthrax
Under Section 18 of FIFRA, EPA "may exempt any federal or state agency from any provision of this Act if the Administrator determines that emergency conditions exist which require such exemption." Normally, a federal or state agency submits an application for a FIFRA exemption to EPA for review and approval. If EPA approves the request, it issues either a specific or a public health exemption, as appropriate. However, if the emergency is of such urgency that the federal or state agency does not have enough time to submit an application for exemption and wait for EPA's approval, then the federal or state agency may issue a crisis exemption, which is effective for 15 days. In order for the crisis exemption to be extended beyond 15 days, the federal or state agency must submit an application for exemption to EPA.
To handle all anthrax contamination cases as quickly as possible, the Agency has decided to issue all crisis exemptions itself. To obtain a crisis exemption from EPA for the unregistered use of a pesticide against anthrax, a state or federal agency must submit a written request describing the antimicrobial product(s) to be used; how, when and where they will be used; the data demonstrating efficacy of the product for the intended purpose; and how human health and safety will be protected. Prior to issuing the exemption, EPA will perform a multi-disciplinary risk assessment of the requested use, relying on data that they have supplied for the pesticide.
If, during this review, EPA notes any adverse human health or environmental concerns, EPA may deny the exemption request. If, however, EPA believes that the proposed use of an antimicrobial product will be effective and will protect human health and the environment, EPA will issue a crisis exemption. Moreover, if EPA determines that use of the product is needed beyond the 15-day use period, EPA will complete an application for a public health exemption on behalf of the requesting entity, which allows the crisis exemption to continue in effect until it is either withdrawn or EPA issues a public health exemption.
Determination of Safety and Efficacy for Crisis Exemptions for Chlorine Dioxide
EPA has reviewed data related to safety and effectiveness before allowing an emergency exemption for liquid and gaseous chlorine dioxide to be used specifically for anthrax decontamination. Available published data suggest that liquid and gaseous chlorine dioxide will reduce bacterial spore populations under specific conditions including concentration, pH, and contact time.
Based on this review, EPA issued crisis exemptions for the limited sale, distribution, and use of liquid and gaseous chlorine dioxide against anthrax.
Typically chlorine dioxide gas, as a fumigant, is generated on site and is released into a sealed treatment area where it remains for several hours before being removed. After the treatment is completed, the chlorine dioxide gas is neutralized with sodium bisulfite. The treatment may leave a fine powdery residue, but it is not considered toxic.
As you can see, the use of chlorine dioxide is not as simple and uncomplicated as the application of a liquid biocide. There are worker exposure and cleanup issues. The Institute of Inspection, Cleaning and Restoration Certification (IICRC) S520 Standard and Reference Guide for Professional Mold Remediation does not address the use of chlorine dioxide specifically. However, S520 does make the following statement under the "Not Recommended" and "Antimicrobial Pesticide Products" subheadings:
Limitations of Use
The use of antimicrobial pesticides has a number of limitations. One limitation can be a lack of clear, detailed label application directions and adequate information on hazards and risks. If used, such products must be used with full knowledge of their limitations and capabilities, in strict accordance with manufacturer's directions and all regulatory requirements, and only with client informed consent. Specifically, the use of antimicrobial pesticide products requires that a mold remediator:
The S520 makes the following statement in the "Remediation Work Procedures" section of the Reference Guide:
Physically removing mold growth and spores is the guiding principle for mold remediation. Biocide application is discouraged and is not considered effective for mold remediation.... Misapplication of biocides is a federal violation under the U.S. Federal Insecticide, Fungicide, Rodenticide Act (FIFRA). Killing microorganisms usually does not destroy their antigenic or toxigenic properties.
The American Conference of Governmental Industrial Hygienists (ACGIH) in their publication Bioaerosols: Assessment and Control makes the following comments:
16.2 Biocide use should not be considered if careful and controlled removal of contaminated material is sufficient to address a problem.
16.2.3 Effective remediation of water-damaged or microbially contaminated buildings involves (a) the use of appropriate techniques to promote rapid drying, and (b) complete removal of contaminated materials rather than the application of biocides ...
The use of chlorine dioxide in concentrations that are necessary to be effective as a fungicide within a building requires special handling and perhaps an EPA exemption. Even if it were successful in killing molds and their spores, there is still the problem of the potential allergic and toxic reactions that remain. The S520 recommends physical removal rather than the use of biocides.