The FBI has not specified or ranked individual chemical or biological agents as threats, but instead ranked groups of agents according to the likelihood that a category of chemical or biological agent would be used. The FBI analysis was based on law enforcement cases where chemical or biological agents were used or their use was threatened, including hoaxes. An example of a toxin is ricin, a poisonous protein extracted from castor beans. These chemicals are not primarily manufactured for the purpose of producing human casualties. Chlorine, phosgene, and hydrogen cyanide are industrial chemicals that have also been used as chemical warfare agents.
Anthrax is an example of a bacterial pathogen.
Excluded from consideration are riot control agents and smoke and flame materials. A national-level risk assessment based in part on the threat estimates would better enable federal agencies to establish soundly defined program requirements and prioritize and focus the nation's investments to combat terrorism. For example, in March 1999 we testified that the Department of Health and Human Services is establishing a national pharmaceutical and vaccine stockpile to prepare medical responses for possible terrorist use of chemical or biological weapons. We pointed out that the Department's effort was initiated without the benefit of a sound threat and risk assessment process. We also found that some of the items the Department plans to procure do not match intelligence agencies' judgments of the more likely chemical and biological agents that terrorists might use and seem to be based on worst-case scenarios.