Sarin (NATO designation GB (G-series, "B"), is an extremely toxic synthetic organophosphorus compound. A colorless, odorless liquid, it is used as a chemical weapon due to its extreme potency as a nerve agent. Exposure is lethal even at very low concentrations, where death can occur within one to ten minutes after direct inhalation of a lethal dose, due to suffocation from lung muscle paralysis, unless antidotes are quickly administered. People who absorb a non-lethal dose, but do not receive immediate medical treatment, may suffer permanent neurological damage.
|Preferred IUPAC name
(RS)-O-Isopropyl methylphosphonofluoridate; IMPF;
Phosphonofluoridic acid, P-methyl-, 1-methylethyl ester
3D model (JSmol)
|Molar mass||g·mol−1 140.094|
|Appearance||Clear colorless liquid, brownish if impure|
|Odor||Odorless in pure form. Impure sarin can smell like mustard or burned rubber.|
|Density||1.0887 g/cm3 (25 °C)|
1.102 g/cm3 (20 °C)
|Melting point||−56 °C (−69 °F; 217 K)|
|Boiling point||158 °C (316 °F; 431 K)|
|Main hazards||It is a lethal cholinergic agent.|
|Safety data sheet||Lethal Nerve Agent Sarin (GB)|
|Extremely Toxic (T+)|
|Lethal dose or concentration (LD, LC):|
LD50 (median dose)
|550 μg/kg (rat, oral)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
Sarin is generally considered a weapon of mass destruction. Production and stockpiling of Sarin was outlawed as of April 1997 by the Chemical Weapons Convention of 1993, and it is classified as a Schedule 1 substance. In June 1994, the UN Special Commission on Iraqi Disarmament reported that it had destroyed Iraq's stockpiles of Sarin.
Like some other nerve agents that affect the neurotransmitter acetylcholine, Sarin attacks the nervous system by interfering with the degradation of the neurotransmitter acetylcholine at neuromuscular junctions. Death will usually occur as a result of asphyxia due to the inability to control the muscles involved in breathing.
Initial symptoms following exposure to Sarin are a runny nose, tightness in the chest and constriction of the pupils. Soon after, the person will have difficulty breathing and they will experience nausea and drooling. As they continue to lose control of bodily functions, they may vomit, defecate and urinate. This phase is followed by twitching and jerking. Ultimately, the person becomes comatose and suffocates in a series of convulsive spasms. Moreover, common mnemonics for the symptomatology of organophosphate poisoning, including Sarin gas, are the "killer B's" of bronchorrhea and bronchospasm because they are the leading cause of death, and SLUDGE – salivation, lacrimation, urination, defecation, gastrointestinal distress, and emesis (vomiting). Death may follow in 1 to 10 minutes after direct inhalation.
Sarin has a high volatility (ease with which a liquid can turn into a gas) relative to similar nerve agents, therefore inhalation can be very dangerous and even vapor concentrations may immediately penetrate the skin. A person’s clothing can release sarin for about 30 minutes after it has come in contact with sarin gas, which can lead to exposure of other people.
Treatment measures have been described. Treatment is typically with the antidotes, atropine and pralidoxime. Atropine, an antagonist to muscarinic acetylcholine receptors, is given to treat the physiological symptoms of poisoning. Since muscular response to acetylcholine is mediated through nicotinic acetylcholine receptors, atropine does not counteract the muscular symptoms. Pralidoxime can regenerate cholinesterases if administered within approximately five hours. Biperiden, a synthetic acetylcholine antagonist, has been suggested as an alternative to atropine due to its better blood–brain barrier penetration and higher efficacy.
Mechanism of actionEdit
Specifically, Sarin is a potent inhibitor of acetylcholinesterase, an enzyme that degrades the neurotransmitter acetylcholine after it is released into the synaptic cleft. In vertebrates, acetylcholine is the neurotransmitter used at the neuromuscular junction, where signals are transmitted between neurons from the central nervous systems to muscle fibres. Normally, acetylcholine is released from the neuron to stimulate the muscle, after which it is degraded by acetylcholinesterase, allowing the muscle to relax. A build-up of acetylcholine in the synaptic cleft, due to the inhibition of cholinesterase, means the neurotransmitter continues to act on the muscle fibre, so that any nerve impulses are effectively continually transmitted.
Sarin acts on cholinesterase by forming a covalent bond with the particular serine residue at the active site. Fluoride is the leaving group, and the resulting phosphoester is robust and biologically inactive.
Its mechanism of action resembles that of some commonly used insecticides, such as malathion. In terms of biological activity, it resembles carbamate insecticides, such as Sevin, and the medicines pyridostigmine, neostigmine, and physostigmine.
Controlled studies in healthy men have shown that a nontoxic 0.43 mg oral dose administered in several portions over a 3-day interval caused average maximum depressions of 22 and 30%, respectively, in plasma and erythrocyte cholinesterase levels. A single acute 0.5 mg dose caused mild symptoms of intoxication and an average reduction of 38% in both measures of cholinesterase activity. Sarin in blood is rapidly degraded either in vivo or in vitro. Its primary inactive metabolites have in vivo serum half-lives of approximately 24 hours. The serum level of unbound isopropylmethylphosphonic acid (IMPA), a Sarin hydrolysis product, ranged from 2-135 µg/L in survivors of a terrorist attack during the first 4 hours post-exposure. Sarin or its metabolites may be determined in blood or urine by gas or liquid chromatography, while cholinesterase activity is usually measured by enzymatic methods.
A newer method called "fluoride regeneration" or "fluoride reactivation" detects the presence of nerve agents for a longer period after exposure than the methods described above. Fluoride reactivation is a technique that has been explored since at least the early 2000s. This technique obviates some of the deficiencies of older procedures. Sarin not only reacts with the water in the blood plasma through hydrolysis (forming so-called ‘free metabolites’), but also reacts with various proteins to form ‘protein adducts’. These protein adducts are not so easily removed from the body, and remain for a longer period of time than the free metabolites. One clear advantage of this process is that the period, post-exposure, for determination of Sarin exposure is much longer, possibly 5 to 8 weeks according to at least one study.
Sarin is highly toxic, whether by contact with the skin or breathed in. The toxicity of Sarin in humans is largely based on calculations from studies with animals. The lethal concentration of Sarin in air is approximately 35 mg per cubic meter per minute for a two-minute exposure time by a healthy adult breathing normally (exchanging 15 liters of air per minute). This number represents the estimated lethal concentration for 50% of exposed victims, the LCt50 value. There are many ways to make relative comparisons between toxic substances. The list below compares some current and historic chemical warfare agents with Sarin, with a direct comparison to the respiratory Lct50:
Production and structureEdit
Sarin is a chiral molecule because it has four chemically distinct substituents attached to the tetrahedral phosphorus center. The SP form (the (–) optical isomer) is the more active enantiomer due to its greater binding affinity to acetylcholinesterase. The P-F bond is easily broken by nucleophilic agents, such as water and hydroxide. At high pH, sarin decomposes rapidly to nontoxic phosphonic acid derivatives.
A number of production pathways can be used to create Sarin. The final reaction typically involves attachment of the isopropoxy group to the phosphorus with an alcoholysis with isopropyl alcohol. Two variants of this process are common. One is the reaction of methylphosphonyl difluoride with isopropyl alcohol, which produces hydrofluoric acid as a byproduct:
The second process, uses equal quantities of methylphosphonyl difluoride and methylphosphonic dichloride, a mixture "Di-Di" in this process, rather than just the difluoride. This reaction also gives Sarin, but hydrochloric acid as a byproduct instead. The Di-Di process was used by the United States for the production of its unitary sarin stockpile.
The scheme below describes an example of Di-Di process. The selection of reagents is arbitrary and reaction conditions and product yield depend on the selected reagents. Inert atmosphere and anhydrous conditions are used for synthesis of sarin and other organophosphates.
As both reactions leave considerable acid in the product, bulk sarin produced without further treatment has a very poor shelf life and would be rather destructive to containers or weapon systems. Various methods have been tried to resolve these problems. In addition to industrial refining techniques to purify the chemical itself, various additives have been tried to combat the effects of the acid, such as:
- Tributylamine was added to US sarin produced at Rocky Mountain Arsenal.
- Triethylamine was added to UK sarin, with relatively poor success. The Aum Shinrikyo cult experimented with triethylamine as well.
- N,N-Diethylaniline was used by Aum Shinrikyo for acid reduction.
- N,N′-Diisopropylcarbodimide was added to sarin produced at Rocky Mountain Arsenal to combat corrosion.
- Isopropylamine was included as part of the M687 155 mm field artillery shell, which was a binary sarin weapon system developed by the US Army.
Another byproduct of these two chemical processes is diisopropyl methylphosphonate, formed when a second isopropyl alcohol reacts with the Sarin itself. This chemical degrades into isopropyl methylphosphonic acid.
Degradation and shelf lifeEdit
The most important chemical reactions of phosphoryl halides is the hydrolysis of the bond between phosphorus and the fluoride. This P-F bond is easily broken by nucleophilic agents, such as water and hydroxide. At high pH, sarin decomposes rapidly to nontoxic phosphonic acid derivatives. The initial breakdown of sarin is into isopropyl methylphosphonic acid (IMPA), a chemical that is not commonly found in nature except as a breakdown product of sarin (this is useful for detecting the recent deployment of sarin as a weapon). IMPA then degrades into methylphosphonic acid (MPA), which can also be produced by other organophosphates.
Sarin with residual acid degrades after a period of several weeks to several months. The shelf life can be shortened by impurities in precursor materials. According to the CIA, some Iraqi sarin had a shelf life of only a few weeks, owing mostly to impure precursors.
Along with nerve agents such as tabun and VX, sarin can have a short shelf life. Therefore, it is usually stored as two separate precursors that produce sarin when combined. Sarin's shelf life can be extended by increasing the purity of the precursor and intermediates and incorporating stabilizers such as tributylamine. In some formulations, tributylamine is replaced by diisopropylcarbodiimide (DIC), allowing sarin to be stored in aluminium casings. In binary chemical weapons, the two precursors are stored separately in the same shell and mixed to form the agent immediately before or when the shell is in flight. This approach has the dual benefit of solving the stability issue and increasing the safety of Sarin munitions.
Sarin was discovered in 1938 in Wuppertal-Elberfeld in Germany by scientists at IG Farben who were attempting to create stronger pesticides; it is the most toxic of the four G-Series nerve agents made by Germany. The compound, which followed the discovery of the nerve agent Tabun, was named in honor of its discoverers: Schrader, Ambros, Gerhard Ritter, and von der Linde.
Use as a weaponEdit
In mid-1939, the formula for the agent was passed to the chemical warfare section of the German Army Weapons Office, which ordered that it be brought into mass production for wartime use. Pilot plants were built, and a high-production facility was under construction (but was not finished) by the end of World War II. Estimates for total Sarin production by Nazi Germany range from 500 kg to 10 tons. Though sarin, tabun and soman were incorporated into artillery shells, Germany did not use nerve agents against Allied targets.
- 1950s (early): NATO adopted sarin as a standard chemical weapon, and both the USSR and the United States produced sarin for military purposes.
- 1953: 20-year-old Ronald Maddison, a Royal Air Force engineer from Consett, County Durham, died in human testing of Sarin at the Porton Down chemical warfare testing facility in Wiltshire, England. Ten days after his death an inquest was held in secret which returned a verdict of misadventure. In 2004, the inquest was reopened and, after a 64-day inquest hearing, the jury ruled that Maddison had been unlawfully killed by the "application of a nerve agent in a non-therapeutic experiment".
- 1957: Regular production of Sarin chemical weapons ceased in the United States, though existing stocks of bulk Sarin were re-distilled until 1970.
- 1976: Chile's intelligence service, DINA, assigned biochemist Eugenio Berríos to develop Sarin gas within its program Proyecto Andrea, to be used as a weapon against its opponents. One of DINA's goals was to package it in spray cans for easy use, which, according to testimony by former DINA agent Michael Townley, was one of the planned procedures in the 1976 assassination of Letelier. Berríos later testified that it was used in a number of assassinations.
- March 1988: Over two days in March, the ethnic Kurd city of Halabja in northern Iraq (population 70,000) was bombarded with chemical bombs, which included Sarin, in the Halabja poison gas attack. An estimated 5,000 people died.
- April 1988: Sarin was used four times against Iranian soldiers at the end of the Iran–Iraq War, helping Iraqi forces to retake control of the al-Faw Peninsula during the Second Battle of al-Faw.
- 1993: The United Nations Chemical Weapons Convention was signed by 162 member countries, banning the production and stockpiling of many chemical weapons, including Sarin. It went into effect on April 29, 1997, and called for the complete destruction of all specified stockpiles of chemical weapons by April 2007. When the convention entered force, the parties declared worldwide stockpiles of 15,047 tonnes of Sarin. As of December 2015, 89% of the stockpiles had been destroyed.
- 1994: Matsumoto incident; the Japanese religious sect Aum Shinrikyo released an impure form of Sarin in Matsumoto, Nagano, killing eight people and harming over 200. The Australian sheep station Banjawarn was a testing ground.
- 1995: Tokyo subway sarin attack; the Aum Shinrikyo sect released an impure form of Sarin in the Tokyo Metro. Twelve people died, and over 6,200 people received injuries.
- 2002: Ibn al-Khattab may have been assassinated with Sarin by the Russian government.
- 2004: Iraqi insurgents detonated a 155 mm shell containing binary precursors for Sarin near a U.S. convoy in Iraq. The shell was designed to mix the chemicals as it spun during flight. The detonated shell released only a small amount of Sarin gas, either because the explosion failed to mix the binary agents properly or because the chemicals inside the shell had degraded with age. Two United States soldiers were treated after displaying the early symptoms of exposure to Sarin.
- 2013: Khan al-Assal chemical attack
- 2013: Ghouta chemical attack; Sarin was used in an attack in the Ghouta region of the Rif Dimashq Governorate of Syria during the Syrian civil war. Varying sources gave a death toll of 322 to 1,729.
- 2017: Khan Shaykhun chemical attack; Sarin gas was allegedly released in rebel-held Idlib Province in Syria by the Syrian Air Force during an airstrike.
- 2018: Douma chemical attack victims reported to have symptoms consistent with exposure to sarin and other agents. On 6 July 2018 the Fact-Finding Mission (FFM) of the OPCW published their interim report. The report stated that, "The results show that no organophosphorous (sarin) nerve agents or their degradation products were detected in the environmental samples or in the plasma samples taken from alleged casualties".
- "Material Safety Data Sheet -- Lethal Nerve Agent Sarin (GB)". 103d Congress, 2d Session. United States Senate. May 25, 1994. Retrieved November 6, 2004.
- "Sarin". National Institute of Standards and Technology. Retrieved March 27, 2011.
- "Institut für Arbeitsschutz der Deutschen Gesetzlichen". GESTIS Substance Database. Retrieved November 15, 2011.
- Chambers, Michael. "ChemIDplus - 107-44-8 - DYAHQFWOVKZOOW-UHFFFAOYSA-N - Sarin - Similar structures search, synonyms, formulas, resource links, and other chemical information". chem.sis.nlm.nih.gov.
- Sarin (GB). Emergency Response Safety and Health Database. National Institute for Occupational Safety and Health. Accessed April 20, 2009.
- Kenneth Anderson (September 17, 2013). A Poisonous Affair: America, Iraq, and the Gassing of Halabja review of A Poisonous Affair: America, Iraq, and the Gassing of Halabja by Joost R. Hiltermann (Cambridge UP 2007). Lawfare: Hard National Security Choices (Report). Retrieved December 30, 2015.
... death can occur within one minute of direct inhalation as the lung muscles are paralyzed.
- Michael Smith (August 26, 2002). "Saddam to be target of Britain's 'E-bomb'". The Daily Telegraph. p. A18. Retrieved December 30, 2015.
The nerve agents Sarin and VX. Colourless and tasteless, they cause death by respiratory arrest in one to 15 minutes.
- "Nearly half a million litres of chemical warfare agents destroyed in two-year operation". UN Chronicle. 31 (3). September 1, 1994. p. 36. Retrieved December 30, 2015.
The two-year operation managed to destroy ... the nerve agents Sarin and Tabun .... The UN Special Commission on Iraqi disarmament, set up under Security Council resolution 687 (1991) concerning the disposal of Iraq's weapons of mass destruction, reported that it had completed in June an important part of its mandate--the elimination of that country's declared chemical weapons stockpile.
- Gussow, Leon. Nerve Agents: Three Mechanisms, Three Antidotes. Emergency Medicine News. 27(7):12, July 2005.
- "Facts About Sarin". Centers for Disease Control and Prevention. November 18, 2015. Retrieved April 10, 2017.
- Shim, TM; McDonough JH (May 2000). "Efficacy of biperiden and atropine as anticonvulsant treatment for organophosphorus nerve agent intoxication". Archives of Toxicology. 74 (3): 165–172. doi:10.1007/s002040050670. PMID 10877003.
- Abu-Qare AW, Abou-Donia MB (October 2002). "Sarin: health effects, metabolism, and methods of analysis". Food Chem. Toxicol. 40 (10): 1327–33. doi:10.1016/S0278-6915(02)00079-0. PMID 12387297.
- Millard CB, Kryger G, Ordentlich A, et al. (June 1999). "Crystal structures of aged phosphonylated acetylcholinesterase: nerve agent reaction products at the atomic level". Biochemistry. 38 (22): 7032–9. doi:10.1021/bi982678l. PMID 10353814.. See Proteopedia 1cfj.
- Hörnberg, Andreas; Tunemalm, Anna-Karin; Ekström, Fredrik (2007). "Crystal Structures of Acetylcholinesterase in Complex with Organophosphorus Compounds Suggest that the Acyl Pocket Modulates the Aging Reaction by Precluding the Formation of the Trigonal Bipyramidal Transition State†,‡". Biochemistry. 46 (16): 4815–4825. doi:10.1021/bi0621361. PMID 17402711.
- R. Baselt, Disposition of Toxic Drugs and Chemicals in Man, 11th edition, Biomedical Publications, Seal Beach, CA, 2017, pp. 1926-1928.
- Jakubowski et. al. (July 2003). Fluoride ion regeneration of sarin (GB) from minipig tissue and fluids following whole-body gb vapor exposure (PDF) (Report). United States Army.
- Degenhardt, et. al. (July 2004). "Improvements of the Fluoride Reactivation Method for the Verification of Nerve Agent Exposure" (PDF). Journal of Analytical Toxicology. doi:10.1093/jat/28.5.364.
- "Sarin gas as chemical agent – ThinkQuest- Library". Archived from the original on August 8, 2007. Retrieved August 13, 2007.
- Inns, RH; NJ Tuckwell; JE Bright; TC Marrs (July 1990). "Histochemical Demonstration of Calcium Accumulation in Muscle Fibres after Experimental Organophosphate Poisoning". Hum Exp Toxicol. 9 (4): 245–250. doi:10.1177/096032719000900407. PMID 2390321.
- US Army Field Manual 3-11.9 Potential Military Chemical/Biological Agents and Compounds. United States Department of Defense. 2005.
- US Army Field Manual 3-9 Potential Military Chemical/Biological Agents and Compounds. United States Department of Defense. 1990. p. 71.
- D. E. C. Corbridge "Phosphorus: An Outline of its Chemistry, Biochemistry, and Technology" 5th Edition Elsevier: Amsterdam 1995. ISBN 0-444-89307-5.
- Kovarik, Zrinka; Radić, Zoran; Berman, Harvey A.; Simeon-Rudolf, Vera; Reiner, Elsa & Taylor, Palmer (March 2003). "Acetylcholinesterase active centre and gorge conformations analysed by combinatorial mutations and enantiomeric phosphonates". Biochem. J. 373 (Pt. 1): 33–40. doi:10.1042/BJ20021862. PMC 1223469. PMID 12665427.
- Benschop, H. P.; De Jong, L. P. A. (1988). "Nerve agent stereoisomers: analysis, isolation and toxicology". Acc. Chem. Res. 21 (10): 368–374. doi:10.1021/ar00154a003.
- Federation of American Scientists (1998). "Chemical Weapons Technology" (PDF).
- Kirby, Reid (January 2006). "Nerve Gas: America's Fifteen Year Struggle for Modern Chemical weapons" (PDF). Army Chemical Review.
- The Determination of Free Base in Stabilised GB (PDF). United Kingdom: UK Ministry of Supply. 1956.
- Tu, Anthony. "New Information Revealed By Aum Shinrikyo Death Row Inmate Dr. Tomomasa Nakagawa" (PDF).
- Seto, Yasuo (June 2001). "The Sarin Gas Attack in Japan and the Related Forensic Investigation". OPCW.
- Chemical agent and munition disposal summary of the U.S. army's experience (PDF). United States Army. 1987. pp. B-30.
- Michael Hedges (May 18, 2004). "Shell said to contain sarin poses questions for U.S." Houston Chronicle. p. A1. Archived from the original on 2015-10-12. Retrieved December 30, 2015.
- "Toxic Substances Portal – Diisopropyl Methylphosphonate (DIMP)". Agency for Toxic Substances and Disease Registry.
- "Nerve agents". OPCW.
- Housecroft, C. E.; Sharpe, A. G. (2000). Inorganic Chemistry (1st ed.). New York: Prentice Hall. p. 317. ISBN 978-0582310803.
- Ian Sample, The Guardian, September 17, 2013, Sarin: the deadly history of the nerve agent used in Syria
- "Stability of Iraq's Chemical Weapon Stockpile". United States Central Intelligence Agency. July 15, 1996. Retrieved August 3, 2007.
- Russell Goldmanpril (April 6, 2017). "Key Points on Sarin: The 'Most Volatile' of Nerve Agents". New York Times.
- Richard J. Evans (2008). The Third Reich at War, 1939–1945. Penguin. p. 669. ISBN 978-1-59420-206-3. Retrieved January 13, 2013.
- "A Short History of the Development of Nerve Gases". Noblis. Archived from the original on April 29, 2011.
- "Nerve gas death was 'unlawful'". BBC News Online. November 15, 2004.
- Samuel Blixen, Pinochet's Mad Scientist, Consortium News, January 13, 1999 (in English)
- Townley reveló uso de gas sarín antes de ser expulsado de Chile, El Mercurio, September 19, 2006 (in Spanish)
- "Plot to kill Letelier said to involve nerve gas". New York Times. December 13, 1981. Retrieved June 8, 2015.
- "1988: Thousands die in Halabja gas attack". BBC News. March 16, 1988. Retrieved October 31, 2011.
- "Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on their Destruction". Organisation for the Prohibition of Chemical Weapons. Retrieved March 27, 2011.
- Organisation for the Prohibition of Chemical Weapons (30 November 2016). "Annex 3". Report of the OPCW on the Implementation of the Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on Their Destruction in 2015 (Report). p. 42. Retrieved 8 March 2017.
- Amy E. Smithson and Leslie-Anne Levy (October 2000). "Chapter 3 – Rethinking the Lessons of Tokyo". Ataxia: The Chemical and Biological Terrorism Threat and the US Response (Report). Henry L. Stimson Centre. pp. 91, 95, 100. Report No. 35. Retrieved 6 January 2017.
- Martin, Alex (19 March 2018). "1995 Aum sarin attack on Tokyo subway still haunts, leaving questions unanswered". The Japan Times Online.
- "More of Kremlin's Opponents Are Ending Up Dead". The New York Times. 21 August 2016.
- Ian R Kenyon (June 2002). "The chemical weapons convention and OPCW: the challenges of the 21st century" (PDF). The CBW Conventions Bulletin. Harvard Sussex Program on CBW Armament and Arms Limitation (56): 47.
- "Bomb said to hold deadly Sarin gas explodes in Iraq". MSNBC. May 17, 2004. Retrieved August 3, 2007.
- Murphy, Joe (September 5, 2013). "Cameron: British scientists have proof deadly Sarin gas was used in chemical weapons attack". The Daily Telegraph. Archived from the original on September 5, 2013.
- "Syria: Thousands suffering neurotoxic symptoms treated in hospitals supported by MSF". Médecins Sans Frontières. August 24, 2013. Archived from the original on August 24, 2013. Retrieved August 24, 2013.
- "NGO says 322 died in Syria 'toxic gas' attacks". AFP. August 25, 2013. Retrieved August 24, 2013.
- "Bodies still being found after alleged Syria chemical attack: opposition". Dailystar.com.lb. Retrieved August 24, 2013.
- "Dozens of civilians killed in alleged "poison gas" attack". Retrieved 2017-04-04.
- "Chemical attack of 4 April 2017 (Khan Sheikhoun): Clandestine Syrian chemical weapons programme" (PDF). Retrieved 2017-04-26.
- Chulov, Martin (2017-09-06). "Syrian regime dropped sarin on rebel-held town in April, UN confirms". The Guardian. ISSN 0261-3077. Retrieved 2017-12-29.
- OPCW Issues Fact-Finding Mission Reports on Chemical Weapons Use Allegations in Douma, Syria in 2018 and in Al-Hamadaniya and Karm Al-Tarrab in 2016 (Report). Organisation for the Prohibition of Chemical Weapons. 6 July 2018. Retrieved 14 July 2018.