Research Highlights

Medical Waste Incineration of Microbiological Organisms

Many interior building materials will require disposal after a terrorist attack with a biological weapon such as anthrax (B. anthracis). Although contaminated materials are usually decontaminated before removal, officials may decide to remove the materials without first fumigating them. In either scenario, some of the building materials may retain viable agent spores. Incineration may be the best option to destroy all potentially remaining bio-contaminants.

In September 2001, B. anthracis spores were sent through the US Postal Service to various locations in Florida, New Jersey, New York, and Washington, D.C. In the Washington D.C. area, officials decided to decontaminate the building interiors with chlorine dioxide fumigation and other techniques. Although the interior materials likely were completely decontaminated, trace amounts of B. anthracis spores may have remained viable.

Most of the decontamination waste (debris, solid waste, and personal protective equipment) from the Capitol area was disposed of in medical waste incinerators (MWIs) at Fort Detrick's U.S. Army Medical Research Institute of Infectious Diseases in Maryland. Officials used MWIs because B. anthracis-contaminated materials are classified as medical waste in Washington, D.C. and Maryland. Waste classification (solid waste, hazardous waste, or medical waste) determines the available disposal options, and can vary from state to state. Based on knowledge gained from the Capitol-area waste disposal operation, incineration will likely remain the preferred disposal method of at least some of the waste materials in any future bio-terrorist events.

No federal standards exist to ensure the complete destruction of microorganisms when incinerating medical waste. Similarly, minimal data and literature are available on the thermal destruction of microorganisms in an incinerator. This lack of standards and data stems from conventional thinking that all microorganisms should be destroyed in the high-temperatures of an incinerator. However, for various technical reasons, some microorganisms in the waste feed may not be destroyed and may be emitted out of the exhaust stack or remain viable in the residue.

In the early 1990s, EPA conducted microbial survivability tests at several medical waste incinerators (MWIs). Researchers recently examined these data to evaluate microbiological destruction performance. Microorganisms were spiked into the waste feed and in test pipes, and subsequently analyzed for viability in the emissions, residue, and pipes using EPA conditional test methods. The results showed at least a five-log spore reduction in most of the test runs. However, viable spores were detected in 10 out of 48 air emission test runs, and in 10 out of 27 available ash samples. The microbial survivability data from these EPA test reports have never been summarized and published. Due to the need to ensure destruction of B. anthracis spores in incinerators, these data have now been reviewed and are presented in the report.

Contact: Joe Wood

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