Blood agents, also known as cyanogen agents, are substances that are absorbed into the body through inhalation. They interfere with the transport of oxygen gas throughout the body by damaging body tissues. Blood agents have the capacity to kill by asphyxiation (suffocation) within 15 minutes. They do not actually affect the blood itself. Instead, blood agents exert their toxic effect at the cellular level by interrupting the electron transport chain in mitochondria and subsequently disrupting ATP synthesis.
A common example of a blood agent is carbon monoxide.
Arsine is a colorless, non-irritating toxic gas with a mild odor of garlic. If one can smell the odor, then the concentration of arsine is enough to cause poisoning. Arsine is formed when arsenic comes into contact with an acid. Symptoms include weakness, fatigue, headache, drowsiness, confusion, shortness of breath, nausea, muscle cramps, and red or dark urine.
Inhalation is the only likely route of exposure. Absorption through the eyes and skin has not been known to occur. Arsine was invesigated as a warfare agent during World War II, though it was never used in the battlefield. It is commonly employed today in the semiconductor and metals refining industries.
Cyanide (CN-) is a rapidly acting, potentially deadly chemical that can exist in various forms. It can be a colorless gas or a crystal. People are exposed through inhalation, ingestion, or touch. Cyanide is released froam natural substances in some foods. It is used in industry in the manufacture of peper, textiles, and plastics. Thus, a group seeking biological weapons could rapidly convert a commercial plant to a plant manufacturing cyanide-based bioweapons.
Hydrogen cyanide is a highly toxic colorless blood agent. It is highly volatile and biols at slightly above room temperature. It has a faint, almont-like odor that some people are incapable of smelling due to a genetic trait.
Cyanogen chloride is a highly toxic colorless blood agent. Cyanogen chloride is made of two components: the cyanide ion (CN-), which is highly poisonous, bonded to a chloride ion. It was first propsoed for use by the French. It is very fast-acting and causes immediate injury upon contact with eyes or respiratory organs.
Sources:
Chapter 34, 161.