Chemical Weapons: Hydrogen Cyanide
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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 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.
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 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
nitrate (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<br>
200 Lethal after 10 minutes<br>
150 Lethal after 30 minutes<br>
120-150 Highly dangerous (fatal) after 30-60 min.<br>
50-60 Endurable for 20 min. - 1 h without effect<br>
20-40 Light symptoms after several hours
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