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Anthrax spore decontamination using ethylene oxide

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Current as of July 2007

Bleach, chlorine dioxide, ethylene oxide, hydrogen peroxide and peroxyacetic acid, methyl bromide, paraformaldehyde and vaporized hydrogen peroxide were pesticides used in federal decontamination responses to the bioterrorism attacks of October 2001. These attacks involved the intentional placement of Bacillus anthracis spores (the causative agent of the disease anthrax) into letters addressed to various locations on the East Coast of the United States. More information about biological threats.

This page describes the Agency’s actions with regard to the chemicals used in the anthrax spore decontamination activities. EPA temporarily approved these pesticides for sale, distribution, and use based on the remediation action plans submitted for each specific site and only in accordance with the requirements of each crisis exemption under Section 18 of FIFRA. These chemicals were not intended for use by the general public.

What is ethylene oxide?

Ethylene oxide (also known as EO, EtO, ETO, anprolene, dihydrooxirene, 1,2-epoxyethane, oxacyclopropane, oxane, oxidoethane, oxirane, and others) is an industrial chemical with a variety of uses such as an ingredient or as an intermediate in the production of other chemicals (e.g., ethylene glycol and polyester), or to produce nonionic surfactants in household and industrial detergents.

Pure ethylene oxide is a colorless gas at room temperature and a colorless liquid below 54° Fahrenheit.

Registration of pesticides containing ethylene oxide

EPA first registered (licensed) ethylene oxide as an antimicrobial pesticide in 1948. It is sold as a mixture with either carbon dioxide or fluorocarbon 12., Ethylene oxide is used to sterilize hospital items and fumigate processed spices and seasonings.

When used in the gaseous form or in nonexplosive gaseous mixtures with nitrogen or carbon dioxide, ethylene oxide can be used as a disinfectant, fumigant, sterilant or insecticide.

Responding to emergencies under FIFRA

Under Section 18 of FIFRA, the 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." To respond as rapidly as possible to the bioterrorism attacks, the Agency decided in 2001 to develop and issue the crisis exemptions itself.

To obtain a crisis exemption from EPA for the unregistered use of a pesticide against anthrax, anyone who needed to use an antimicrobial product to inactivate Bacillus anthracis spores at contaminated sites had to submit:

  1. a written request to the Agency listing the antimicrobial product(s) to be used and describing how, when and where they would be used;
  2. data demonstrating efficacy of the product against bacillus spores; and
  3. remediation, sampling, and monitoring plans specific to the location of use.

Before issuing an exemption, EPA reviewed the request and the supporting information and then determined whether the product could be used safely and effectively (i.e., cause “no unreasonable adverse effects”).

If during this review data were found to be deficient or missing, or adverse human health or environmental concerns were identified, EPA could deny the exemption request.

If a crisis exemption was issued and EPA determined that use of the product would be needed beyond the 15 day use period, EPA completed an application for a public health exemption. This allowed the crisis exemption to continue in effect until the application was either withdrawn or EPA issued a public health exemption.

Crisis exemptions for ethylene oxide

EPA reviewed data related to the safety and effectiveness of using ethylene oxide for inactivation of Bacillus anthracis spores. Available data indicated that ethylene oxide would reduce bacterial spore populations under specific conditions including concentration, pH, and contact time. EPA issued several crisis exemptions after considering available data and including requirements that protected human health and the environment:

Under the crisis exemption, ethylene oxide could only be used according to the specific guidelines and procedures of the EPA-approved decontamination plans.

Use of ethylene oxide for decontamination

All antimicrobial ethylene oxide products had already been registered as sterilants by passing EPA's standard AOAC Sporicidal Activity Test (PDF). (36 pp, 682K About PDF)

Based on the Agency's review of efficacy and safety data, EPA determined ethylene oxide would be effective for the inactivation of Bacillus anthracis spores. EPA issued crisis exemptions for its use in a decontamination program that included pre-sampling, treatment, and post-treatment sampling.

With strict adherence to the label's application instructions and applicable worker monitoring and safety requirements, the Agency believed that no unreasonable adverse health effects would occur from use of this chemical. Nevertheless, EPA noted that ethylene oxide gas might adversely affect certain items such as biological samples, diagnostic kits, film, drugs and medicines, eyeglasses and contact lenses, and some garments, and that those items would have to be discarded.

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