Grantee Research Project Results
Final Report: Whole-Structure Decontamination of Bacillus Spores by Methyl Bromide Fumigation
EPA Contract Number: 68D02080Title: Whole-Structure Decontamination of Bacillus Spores by Methyl Bromide Fumigation
Investigators: Weinberg, Mark J.
Small Business: Cobra Termite Control
EPA Contact: Richards, April
Phase: I
Project Period: September 30, 2002 through March 31, 2003
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2002) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , SBIR - Air Pollution , Small Business Innovation Research (SBIR)
Description:
Decontamination of buildings contaminated by the release of anthrax spores resulting from acts of bioterrorism in October 2001, has been plagued by technical difficulties, months-long preparation and treatment time, and high cost. The greatest efficacy challenge in these clean-up efforts has been delivering antimicrobial treatments to the target site. The second major challenge has been to identify an antimicrobial agent that does not damage sensitive materials and devices, and that is not explosive or unstable. It was clear that chemical fumigation would be the only means for remediating the widespread contamination caused by aerosolized anthrax spores. Early in the decisionmaking process, chlorine dioxide (CD) was chosen as the remediating fumigant for the contaminated federal buildings. Efforts to use CD in the Daschle Suite of the Hart Senate Building exemplified the negative properties of CD, including chemical instability and volatility, inability to penetrate porous substrata, collateral damage to non-target materials, narrow humidity range for efficacy, and inability to containerize the gas for transport. Because CD has no registration as a fumigant, toxicological data regarding human exposure under such situations are not available.
The goal of this research project was to demonstrate that methyl bromide (MB) is superior to CD as a decontaminant of bacterial spores. MB has a long registration history as a structural, soil, and food fumigant. Literature sources verify that MB also has antimicrobial properties. Additionally, MB is stable, non-volatile, can penetrate porous surfaces, has no negative effects on fumigated materials, and is packaged in transportable metal cylinders. MB has been a well-studied pesticide that shows no ill effects to humans at its threshold limit value (3-5 ppm), and is being phased out only because of its ozone-depletion potential.
This project was divided into laboratory trials followed by a field fumigation. In the laboratory, specific combinations of MB concentration, exposure time, and temperature were selected to determine sporicidal efficacy against Bacillus stearothermophilus and B. subtilis. After efficacious parameters were identified in the laboratory study, fumigation of a building was conducted to verify laboratory results, visually determine effects on non-target materials and equipment, and assess MB aeration characteristics.
Summary/Accomplishments (Outputs/Outcomes):
Laboratory studies were used to identify the concentration, exposure time, and temperature parameters needed for MB to kill the spores of B. stearothermophilus and B. subtilis, which are considered to be surrogate spores for B. anthracis. Spores loaded on standard sterilization test strips at concentrations of 105 to 108 were exposed at constant temperature and concentration in 9 L glass fumigation chambers. After each serial exposure trial, strips were incubated in tryptic broth to assess for either complete sterilization (no vegetative growth) or for an unquantified level of failure (vegetative growth).
Laboratory exposures of test strips containing 106 B. subtilis var. niger spores to MB under undisclosed conditions prevented their germination. Test strips containing 108 spores of B. subtilis var. niger did not germinate when exposed to undisclosed conditions. Spore strips with 105 of B. stearothermophilus were sporicidal at undisclosed MB exposures. Results support the use of structural fumigation techniques with MB to decontaminate whole structures from Bacillus spores.
A partially furnished 10,000-ft3 mobile home (trailer) was fumigated with MB after 86 bacterial spore strips and 10 petri dishes with spores were placed in various locations. An undisclosed amount of MB was introduced into the trailer to yield an undisclosed mean time-weighted concentration during the fumigation. Mean temperatures near spore strips during fumigation were undisclosed and relative humidity was undisclosed. Of the 46 B. stearothermophilus 106 spore strips recovered after the fumigation, none germinated. Of the 40 B. subtilis 106 spore strips placed, 20 produced vegetative cells during incubation. No B. thuringiensis spores survived in any of the 10 petri dishes that contained 2 x 107 spores. During fumigation, 0-5 ppm MB was detected 20 ft downwind from the structure. During aeration, downwind MB concentrations were 1.5 ppm at 100 ft or 150 ft. No damage was detected among the electronic, photographic, cellulosic, fabric, or other commodities fumigated. A transient organic odor was detected after the fumigation. Contrary to laboratory and previous field results in which spores of B. subtilis showed no growth, the high number of strips containing viable spores fumigated in the trailer suggested that spore clumping had occurred during the manufacture of this lot of spore strips. In a demonstration trial, a proprietary scrubbing liquor made from water, inorganic salts, and a phase-transfer catalyst removed 99.9 percent of the MB sampled from trailer airspace.
Conclusions:
Cobra Termite Control's results indicate that MB can kill bacterial spores using current whole-structure fumigation technology for rapid field decontamination without collateral damage. Triple sealing and MB scrubbing technology will minimize atmospheric release of MB in future building decontaminations.
Supplemental Keywords:
chlorine dioxide, methyl bromide, Bacillus spores, building decontamination, biological agent, fumigation, anthrax, antimicrobial, bioterrorism, SBIR., Scientific Discipline, Air, Environmental Chemistry, Analytical Chemistry, Biochemistry, Engineering, Chemistry, & Physics, decontamination, bioterrorism, Bacillus spores, fumigation, pest control, B. anthracis, Methyl bromideSBIR Phase II:
Whole-Structure Decontamination of Bacillus Spores by Methyl Bromide Fumigation | Final ReportThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.