Anthrax spore decontamination using bleach (sodium hypochlorite)

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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 bleach?

The term "bleach" originated in the late 1700’s from the discovery that chlorine gas in water "bleached" or "whitened" textiles. Bleach, as it is known today, is a liquid that contains sodium hypochlorite, not chlorine gas, as the active ingredient.

Registration of pesticides containing sodium hypochlorite

In 1957,under the authority of the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), sodium hypochlorite (bleach) was registered for use as an antimicrobial pesticide. As a sanitizer or disinfectant to kill bacteria, fungi, and viruses, sodium hypochlorite is approved for use in households, food processing plants, agricultural settings, animal facilities, hospitals, and human drinking water supplies.

Bleach containing products not claiming to sanitize or disinfect, are not a registered pesticide. These bleach containing products are often sold as a laundry additive or as an all-purpose cleaner.

Bleach containing products are often sold as a laundry additive or as an all-purpose cleaner. Products containing bleach that claim to sanitize or disinfect are considered pesticides and must be registered pesticide products.

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 spores, anyone who needed to use an antimicrobial product to inactivate Bacillus anthracis spores at contaminated sites had to submit:

a written request to the Agency listing the antimicrobial product(s) to be used and describing how, when and where they would be used;
data demonstrating efficacy of the product against bacillus spores; and
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 bleach

EPA reviewed data related to the safety and effectiveness of using diluted bleach for inactivation of Bacillus anthracis spores. Published scientific data demonstrated that bleach reduced bacterial spore populations under specific conditions including concentration, pH, and contact time.

The Agency also evaluated the efficacy of bleach as a sporicide using the Association of Official Analytical Chemists (AOAC) Sporicidal Activity Test (modified) in its own laboratory. EPA determined that the product could be used safely and effectively, and that no unreasonable adverse effects would occur from the requested uses.

Subsequently, EPA issued several crisis exemptions at different times permitting the limited sale, distribution, and use of EPA registered bleach products for use against Bacillus anthracis spores at a number of contaminated facilities such as:

Capitol Hill,
USPS Processing and Distribution Centers at Brentwood (Washington, D.C.) and Hamilton (Trenton, NJ),
Department of State, General Services Administration, and
Broken Sound Boulevard, Boca Raton, FL.

Under these crisis exemptions, registered bleach products could only be sold or distributed to employees of federal, state, or local government agencies, and the U.S. Postal Service.

In March, 2006, the New York Department of Environment and Conservation (NYDEC), in coordination with EPA, issued a crisis exemption for use of bleach to decontaminate two private residences and three storage areas in New York City. These locations had been contaminated with Bacillus anthracis spores in connection with imported animal hides that were made into drum covers. This incident was determined not be connected to bioterrorism; therefore, the NYDEC issued the crisis exemption rather than EPA.

Use of bleach for decontamination

The application of bleach under crisis exemptions was limited to specific buildings or treatment sites and was conducted in accordance with a site-specific Remediation Action Plan that contained the following basic steps:

Pre-sampling to determine the extent of spore contamination at specific locations;
Spot remediation of highly contaminated surfaces through HEPA filter vacuuming;
Gross surface decontamination with registered bleach products;
Post-treatment sampling to determine that the anthrax decontamination was effective; and
Re-treatment with registered bleach products if viable spores were detected

The following specific conditions also applied:

Only hard, non-porous surfaces could be treated;
A bleach solution close to but not above pH 7 (neutral), as tested with a paper test strip, and at a concentration of 5,000 to 6,000 parts per million (ppm) was prepared by mixing:

one part bleach (with a 5.25 percent - 6.00 percent sodium hypochlorite concentration)
one part white vinegar, and
eight parts water.

Treated surfaces had to remain in contact with the bleach solution for 60 minutes. Repeated applications were necessary to keep the surfaces wet.

These conditions did not necessarily apply to personal protective equipment and other debris that were further treated offsite or intended for disposal.

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