Some Facts About Anthrax Poisoning

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September 26, 2001

Letters to the Editor

Some Facts About Anthrax Poisoning

In his Sept. 21 editorial-page piece "Retaliation Isn't Enough," Loren Thompson states that "100 kilograms of anthrax optimally dispersed in a straight line from an aircraft over a major metropolitan area has the potential to kill over a million people." I have no idea as to the source of this figure nor what he means by "optimally dispersed" or the "potential to kill."

Unfortunately, these sorts of unsubstantiated values and undefined terms are typical of the current plethora of media comments on the destructive potential of biological warfare (BW). Doubly unfortunate is that there exist (or did exist) large amounts of experimental data and modeling analyses that do define these terms and which if re-examined would provide a realistic assessment of the magnitude of the danger. These were data collected and analyses carried out by the U.S. Army Chemical Corps and the U.S. Air Force in the 1950s and perhaps more recently.

With respect to "optimally dispersed," for example, the studies showed that to be infectious via a pulmonary route, organisms like anthrax spores would have to be dispersed as aerosolized liquid droplets or dried particles of a very restricted size range. If too large, they will not enter the lungs. If too small, they will not remain in the lungs.

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Thus, to be an effective weapon of mass destruction, terrorists must not only manufacture and smuggle in 200 pounds of anthrax, they must have devices to disperse it as properly sized droplets or particles. The latter is no simple matter.

Furthermore, even if aerosols of the proper size are created, they have only a limited lifetime. They coalesce, they settle under gravity, and the water of which they are composed rapidly evaporates. The organisms within are also subject to biological decay (although less so for the resistant anthrax spore) from dehydration, and exposure to oxygen and sunlight. Their physical and biological effective lifetimes thus depend complexly on meteorological conditions such as relative humidity and wind velocity.

All this is not to argue that the danger from BW is insignificant. It is to argue that it is folly to exacerbate fears in an already jittery public or to rush pell-mell into counter-actions and policies in the absence of a rational quantitative evaluation of the true magnitude of the risk.

Peter Mazur
Research Professor
Department of Biochemistry and Cellular and Molecular Biology
University of Tennessee
Knoxville, Tenn.