Hydrogen Cyanide
Hydrogen Cyanide
Source: A FOA Briefing Book on Chemical Weapons
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 colorless
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.
Today, there is no medical antidote against cyanide
poisoning within the Swedish Armed Forces. The treatment 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 sulfur transforms cyanide into
thiocyanate, which is passed out in the urine. By supplying sulfur 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 hemoglobin can be oxidized to
trivalent, which leads to the formation of methemoglobin which binds cyanide
ions. The formation of methemoglobin 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.
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 |
