Blood agents

The name blood agent, like those of other groups of agents, derives from its effect on victims. Blood agents are distributed via the blood and generally enter the body via inhalation. They inhibit the ability of blood cells to utilise and transfer oxygen. Thus, blood agents are poisons that effectively cause the body to suffocate.

Examples of blood agents include:

  • hydrogen cyanide (AC)
  • cyanogen chloride (CK)
  • and arsine (SA).

Hydrogen Cyanide

Hydrogen cyanide is usually included among the CW agents causing general poisoning. There is no confirmed information on this substance being used in chemical warfare. However, it has been reported that hydrogen cyanide was used by Iraq in the war against Iran and against the Kurds in northern Iraq during the 1980's. Hydrogen cyanide has high toxicity and in sufficient concentrations it rapidly leads to death. During the Second World War, a form of hydrogen cyanide (Zyklon B) was used in the Nazi gas chambers.

At room temperature, hydrogen cyanide is a colourless liquid which boils at 26 oC. The most important route of poisoning is through inhalation. Both gaseous and liquid hydrogen cyanide, as well as cyanide salts in solution, can also be taken up through the skin. Its high volatility probably makes hydrogen cyanide difficult to use in warfare since there are problems in achieving sufficiently high concentrations outdoors. On the other hand, the concentration of hydrogen cyanide may rapidly reach lethal levels if it is released in confined spaces.

The most important toxic effect of hydrogen cyanide is by inhibiting the metal-containing enzymes. One such enzyme is cytochromoxidase, containing iron. This enzyme system is responsible for the energy-providing processes in the cell where oxygen is utilized, i.e., cell respiration. When cell respiration ceases, it is no longer possible to maintain normal cell functions, which may lead to cell mortality.

Symptoms of cyanide poisoning vary and depend on, for example, route of poisoning, total dose and the exposure time. If hydrogen cyanide has been inhaled, the initial symptoms are restlessness and increased respiratory rate. Other early symptoms are giddiness, headache, palpitations and respiratory difficulty. These are later followed by vomiting, convulsions, respiratory failure and unconsciousness. If the poisoning occurs rapidly, e.g., as a result of extremely high concentrations in the air, there is no time for symptoms to develop and exposed persons may then suddenly collapse and die.

The treatment against cyanide poisoning given to civilians is based on encouraging and speeding-up the body's own ability to excrete cyanide and to bind cyanide in the blood. The enzyme rhodanese is present in the body, mainly in the liver, and together with sulphur transforms cyanide into thiocyanate, which is passed out in the urine. By supplying sulphur in the form of sodium thiosulphate (Na2S2O3) the detoxification can be speeded up. The cyanide ion has high affinity to trivalent iron (Fe3+). The divalent iron in blood haemoglobin can be oxidized to trivalent, which leads to the formation of methaemoglobin which binds cyanide ions. The formation of methaemoglobin can be achieved by supplying sodium nitrite (NaNO2) or dimethylaminophenol (DMAP).

Cyanide can also be bound by metallic ions supplied to the blood in suitable form. Among others, cobalt can be supplied in the form of a cobalt complex or as hydroxycobalamin (vitamin B12).

In cases of poisoning with hydrogen cyanide it is of the utmost importance that countermeasures are immediately introduced. For this reason, a medical antidote (PAPP, para-aminopropiophenone) for use as a pretreatment is being developed in the United Kingdom.

Relationship between concentration and effects when inhaling hydrogen cyanide

Concentration (mg/m3)  Effect 
300  Immediately lethal 
200  Lethal after 10 minutes 
150  Lethal after 30 minutes 
120-150  Highly dangerous (fatal) after 30-60 min. 
50-60  Endurable for 20 min. - 1 h without effect 
20-40  Light symptoms after several hours 


Some arsenic compounds which are potential chemical weapons

Among the arsenal of chemical weapons can be found mustard agent mixed with lewisite which is an aliphatic arsenic compound, 2-chlorovinyldichloroarsine. Pure lewisite is a colourless liquid. Solubility in water is approximately the same as for mustard agent but the volatility is much higher. Hydrolysis in water is faster than for mustard agent. Injuries caused by lewisite are similar to those caused by mustard agent.

However, the mechanism of action for lewisite is different. From the diagnostic viewpoint, an important difference is that symptoms in lewisite poisoning are not delayed and the irritating effect occurs immediately. Skin damage is treated in the same way as after exposure to mustard agent. A specific antidote (BAL, British Anti Lewisite, dimercaptopropanol) gives good protection against local injuries to skin and mucous membrane. BAL also has effect against systemic poisoning.

Other arsenic-containing substances have also been of interest as CW agents. One example is adamsite, 10-chloro-5,10-dihydrophenarsazine, which is a nasal and throat-irritating powder.

Source: A FOA Briefing Book on Chemical Weapons

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