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{{Short description|Type of toxic chemical agent}}
{{Chemical agents sidebar |blood}}

A '''blood agent''' is a [[toxic]] [[chemical agent]] that affects the body by being absorbed into the [[blood]].<ref name="Walsh 150">{{cite book |last=Walsh |first=C. J. |title=Forensic Science |chapter=Blood agents |editor=Ayn Embar-seddon |editor2=Allan D. Pass |publisher=Salem Press |date=2008 |page=150 |isbn=978-1-58765-423-7}}</ref> Blood agents are fast-acting, potentially lethal poisons that typically manifest at room temperature as volatile colorless gases with a faint odor.<ref name="Walsh 150" /> They are either [[cyanide]]- or [[arsenic]]-based.<ref name="Walsh 150" />

== Exposure ==

Blood agents work through [[inhalation]] or [[ingestion]].<ref name="Walsh 151" /> As [[chemical weapon]]s, blood agents are typically disseminated as [[aerosol]]s and take effect through inhalation. Due to their [[Volatility (chemistry)|volatility]], they are more toxic in confined areas than in open areas.<ref name="Walsh 150" />

[[Cyanide]] compounds occur in small amounts in the natural environment and in [[cigarette smoke]]. They are also used in several industrial processes and as pesticides. Cyanides are released when [[synthetic fabric]]s or [[polyurethane]] burn, and may thus contribute to fire-related deaths.<ref name="Walsh 151">Walsh, 151.</ref> [[Arsine]] gas, formed when [[arsenic]] encounters an acid, is used as a pesticide and in the semiconductor industry; most exposures to it occur accidentally in the workplace.<ref name="Walsh 151" />

== Symptoms ==

The symptoms of blood agent poisoning depend on concentration and duration.

Cyanide-based blood agents irritate the eyes and the [[respiratory tract]], while arsine is nonirritating.<ref name="Walsh 151" /> [[Hydrogen cyanide]] has a faint, bitter, almond odor that only about half of all people can smell. Arsine has a very faint garlic odor detectable only at greater than fatal concentrations.<ref name="Walsh 150" />

Exposure to small amounts of cyanide has no effect.<ref name="Walsh 151" /> Higher concentrations cause dizziness, weakness and nausea, which cease with the exposure, but long-time exposure can cause mild symptoms followed by permanent brain damage and muscle paralysis.<ref name="Walsh 151" /> Moderate exposure causes stronger and longer-lasting symptoms, including headache, that can be followed by convulsions and coma. Stronger or longer exposure will also lead to convulsions and coma. Very strong exposure causes severe toxic effects within seconds, and rapid death.<ref name="Walsh 151" />

The blood of people killed by blood agents is bright red, because the agents inhibit the use of the oxygen in it by the body's cells.<ref name="Walsh 151" /> Cyanide poisoning can be detected by the presence of [[thiocyanate]] or cyanide in the blood, a smell of [[bitter almond]]s, or respiratory tract inflammations and congestions in the case of [[cyanogen chloride]] poisoning.<ref name="Walsh 151" /> There is no specific test for arsine poisoning, but it may leave a garlic smell on the victim's breath.<ref name="Walsh 151" />

== Effects ==
{{main|Cyanide poisoning}}

At sufficient concentrations, blood agents can quickly saturate the blood and cause death in a matter of minutes or seconds.<ref name="Walsh 151" /> They cause powerful gasping for breath, violent convulsions and a painful death that can take several minutes.<ref name="Walsh 151" /> The immediate [[cause of death]] is usually [[respiratory failure]].<ref name="Walsh 151" />

Blood agents work at the [[cell (biology)|cellular level]] by preventing the exchange of [[oxygen]] and [[carbon dioxide]] between the blood and the body's cells. This causes the cells to suffocate from lack of oxygen.<ref name="Walsh 151" /> Cyanide-based agents do so by interrupting the [[electron transport chain]] in the inner membranes of [[mitochondria]]. Arsine damages the [[red blood cell]]s which deliver oxygen throughout the body.<ref name="Walsh 151" />

== Detection and countermeasures ==

Chemical detection methods, in the form of kits or testing strips, exist for hydrogen cyanide. Ordinary clothing provides some protection, but proper protective clothing and masks are recommended. Mask filters containing only charcoal are ineffective, and effective filters are quickly saturated.<ref name="Ledgard 72" />

Due to their high volatility, cyanide agents generally need no decontamination. In enclosed areas, fire extinguishers spraying [[sodium carbonate]] can decontaminate hydrogen cyanide, but the resulting metal salts remain poisonous on contact.<ref name="Ledgard 72" /> Liquid hydrogen cyanide can be flushed with water.<ref name="Ledgard 73">Ledgard, [https://books.google.com/books?id=atU4GuKE8x0C&pg=PA73 73].</ref>

Cyanide poisoning can be [[Cyanide poisoning#Antidote|treated with antidotes]].

== List of blood agents ==

The information in the following table, which lists blood agents of military significance,<ref name="Ledgard 72">Ledgard, [https://books.google.com/books?id=atU4GuKE8x0C&pg=PA72 72].</ref> is taken from Ledgard.<ref>{{cite book|last=Ledgard|first=Jared|title=A Laboratory History of Chemical Warfare Agents|publisher=Lulu|date=2006|pages=79 et seq|isbn=978-1-4116-9432-3|url=https://books.google.com/books?id=atU4GuKE8x0C&pg=PA79}}</ref> The values given are on a scale from 1 to 10.
{| class="wikitable sortable"
|-
! Agent
! Description
! Melting / boiling point
! Effectiveness as blood agent
! Persistence, open area
! Persistence, enclosed area
! Field stability
! Storage stability
! Toxicity as blood agent
|-
| [[Hydrogen cyanide]]
| Colorless gas or liquid, almond odor, burns with a bluish flame.
| −13 / 26&nbsp;°C
| 10
| 2
| 9
| 10
| 8
| 10
|-
| [[Cyanogen]]
| Colorless gas, almond odor, burns with a pinkish flame having a blue border.
| −28 / −21&nbsp;°C
| 9
| 2
| 9
| 8
| 7
| 9
|-
| [[Cyanogen chloride]]
| Colorless gas or liquid, pungent and biting odor, soluble in water and alcohol.
| −6 / 14&nbsp;°C
| 8
| 3
| 9
| 9
| 9
| 8
|-
| [[Cyanogen bromide]]
| Colorless needle-shaped or cubic crystals, tending to volatilize on standing, hence of limited usefulness as a weapon.
| 52 / 62&nbsp;°C
| 9
| 5
| 8
| 5
| 6
| 8
|-
| [[Arsine]]
| Colorless gas, garlic-like odor, slightly soluble in water.
| −117 / −62&nbsp;°C
| 9
| 3
| 8
| 5
| 9
| 9
|-
| [[Vinyl arsine]]
| Colorless liquid, irritating and bitter odor, slightly soluble in water, also acts as a [[blister agent]].
| 124&nbsp;°C (boiling)
| 7
| 7
| 9
| 8
| 9
| 6
|-
| [[Phosgene]]
| Colorless gas and slightly yellow liquid, moldy hay odor, slightly soluble in water and soluble in most solvents, also acts as a [[choking agent]].
| −118 / 8
| 10
| 6
| 9
| 5
| 8
| 6
|}

[[Sodium cyanide]] and [[potassium cyanide]], colorless crystalline compounds similar in appearance to sugar, also act as blood agents.<ref name="Walsh 151" /> [[Carbon monoxide]] could technically be called a blood agent because it binds with oxygen-carrying hemoglobin in the blood (see [[carbon monoxide poisoning]]), but its high volatility makes it impractical as a chemical warfare agent.<ref>{{cite book|last=Croddy|first=Eric|title=Chemical and biological warfare: a comprehensive survey for the concerned citizen|publisher=Springer|date=2002|isbn=978-0-387-95076-1|page=108|url=https://books.google.com/books?id=MQMGhInCvlgC&pg=PA108}}</ref>

One of the earliest proposed chemical weapons, [[cacodyl oxide]], or [[Cadet's fuming liquid]], also displays properties of a blood agent (as well as those of a malodorant). It was proposed as a chemical weapon in [[the British Empire]] during the [[Crimean War]], along with the significantly more potent blood agent, [[cacodyl cyanide]].<ref>{{cite book|last=Romano|first=James A.|title=Chemical Warfare Agents: Chemistry, Pharmacology, Toxicology, and Therapeutics|publisher=CRC Press|date=2007|isbn=9781420046625|page=4|url=https://books.google.com/books?id=MGcnAIu4vyIC}}</ref>

==Use==
The most significant practical application of blood agents was the use of [[hydrogen cyanide]] ([[Zyklon B]]) in [[gas chambers]] by [[Nazi Germany]] to commit the mass murder of Jews and others in the course of [[the Holocaust]].<ref>Longerich, Peter (2010). Holocaust: The Nazi Persecution and Murder of the Jews. Oxford; New York: Oxford University Press. {{ISBN|978-0-19-280436-5}}.</ref> This resulted in the largest death toll as a result of the use of chemical agents to date.<ref>[[Peter Hayes (historian)|Hayes, Peter]] (2004). ''From Cooperation to Complicity: Degussa in the Third Reich'', pp.&nbsp;2, 272. {{isbn|0-521-78227-9}}<!--needs location + publisher--></ref>

== References ==
{{reflist}}

{{Chemical warfare}}

[[Category:Blood agents| ]]