Biological Toxins

Toxins are harmful substances produced by living organisms (animals, plants, microbes). They are different from chemical agents (VX, cyanide, or mustard) in that they are not man-made, they are non-volatile (no vapor hazard), usually not absorbed through the skin (mycotoxins are the exception), and they are generally much more toxic per weight than chemical agents. The bacterial toxins, such as botulinum toxins, are the most toxic substances by weight known.

Their lack of volatility is very important and makes them unlikely to produce either secondary or person-to-person exposures or a persistent environmental hazard.

A toxin's utility as an aerosol weapon is determined by its toxicity, stability, and ease of production.

Less toxic compounds, such as the mycotoxins, are thousands of times less toxic than botulinum and have limited aerosol potential.

The relationship between aerosol toxicity and the quantity of toxin required for an effective open-air exposure is demonstrated by the fact that for some agents, such as the mycotoxins and ricin, literally tons would be needed for an effective open-air attack.

Stability limits the open-air potential of some toxins. For example, botulinum and tetanus toxins are large-molecular-weight proteins and are easily diminished or eliminated by environmental factors (heat, desiccation, UV light), thus posing little downwind threat.

Toxins, such as saxitoxin, might be both stable and highly toxic but are so difficult to extract that they can only feasibly be produced in minute quantities.

As with all biological weapons, potential to cause incapacitation, as well as lethality, must be considered. Depending on the goals of an adversary incapacitating agents may be more effective than lethal agents, due to the overwhelming demand on the medical and evacuation infrastructure or the expected panic in the population. Several toxins, such as SEB, cause significant illness at doses much lower than that required for lethality. Thus they pose a significant incapacitating threat.

This section covers four toxins considered to be among the most likely to be used against civilian targets: