Wednesday, September 4, 2019

History and Methods of Chemical Warfare

History and Methods of Chemical Warfare Cori Haws In this report I intend to investigate from the perspective of a chemist the history and development of chemical weapons systems focusing primarily on their development, and the usage throughout the 20th century to present day and the means to which they act. As a starting point it is important to clarify what is meant by a chemical weapon or CW. The Organisation for the Prohibition of Chemical Weapons defines a chemical weapon as a toxic chemical compound or its precursor which can cause death, injury, temporary incapacitation or sensory irritation through its chemical reaction. Delivery devices designed for the delivery of chemical agents, filled or unfilled, are also considered as such. For the purpose of this report I will be focusing on the chemical agents themselves opposed to the systems used to deliver such agents. Chemical warfare generally involves the use of the known toxic properties of chemical substances in the intent cause damage to life. This is distinct from conventional warfare, most of which requires the ‘self-destructive’ properties of particular chemical reactions (2,4,6-trinitrotoluene with Oxygen), and different from Nuclear, Radiological and Biological weapons such as Hydrogen bombs, Atom bombs and weaponised Anthrax in the method of action. There are many classifications for Chemical Weapons and are defined by the way of which they in fact act on an organism. These sub-categories include; choking agents, impede a victims breathing; blister agents, irritate and poison tissue; blood agents, inhibit the ability to transfer and utilise oxygen; nerve agents, inhibits nervous system operation, and riot control agents, short term lasting low risk to life agents. It is important to mention that while some substances are inherently toxic not all are considered chemical weapons. For example raw materials, substances for medicine, herbicides and insecticides all are able to cause significant harm to life but under controlled and regulated conditions are not significantly dangerous to be classified as chemical weapons. Brief History of Chemical Weapons While chemicals have been used for warfare for a considerable amount of time, albeit in highly primitive and at the time for yet unexplained reasons. (I.e Poison arrows, molten tar and arsenic smoke), most of the use of chemical weapons in modern history is limited to World War I where Chlorine and phosgene gasses were released in large qualities during trench warfare. Notably the first use was 22nd April 1915 on the town of Ypres in Belgium, overseen by Fritz Haber, the chemist who developed the process for production of ammonia. This attack resulted in the death of 5,000. During the war several different types of chemical weapons were developed primarily by German scientists, probably the most well-known being mustard gas and derivatives. Throughout the course of the First World War it is estimated that over 90,000 were fatally wounded by chemical weapons for a total of over a million injuries by use of approximately 124,000 tons of chemical agent. The idea of the danger posed by c hemical weapons as demonstrated by the Great War was influential in the coming years as although most countries felt reluctant in developing them the fear of even deadlier weapons being used in future conflicts. Although Chemical weapons were not used during World War II, it is know that both axis and allied powers possessed chemical weapons for use in retaliation. During the Cold War, both the United States and the Soviet Union developed and maintained large stockpiles of chemical weapons in fear of use. Statistics show that at the time both superpowers possessed enough chemical agents to destroy most organic life on the planet. It is noted that during the Iraq conflicts that Saddam Hussein used a variety of agents namely Mustard Gas and nerve agents possibly including what is considered the most potent nerve agents ‘VX’, against the Kurds in 1988. This prompted the Geneva Convention to prohibit the production and prompt the destruction of Chemical Weapons Stockpiles. The most recent examples of Chemical Weapons use were the terrorist attacks in Matsumoto, Japan and in Tokyo involving the nerve agent known by its name of Sarin (GB). Sarin was also reportedly used in Syria on the residents of the Ghouta agricultural belt around Damascus on the 21st August 2013 resulting in an estimated 350-1500 deaths. Choking Agents As stated previously the most notable Choking agents which have been used in warfare originate from WWI. Chlorine as we know is a strong oxidant agent due to its high electronegativity. This fundamentally is the reason to which it is dangerous. Being highly reactive means it is likely to react with most other elements to form chloride compounds. The second reason being that in standard conditions it is a gas meaning that containing it is difficult. The preface of which Chlorine gas works as a chemical weapon is by the means of inhalation. The respiratory system itself is highly sensitive tissue surrounded by a mucus membrane. The mucus membrane is a high percentage water. When Chlorine has been inhaled especially in high concentrations it will react with the water of the mucus membrane to form Hydrochloric Acid, which causes serve irritations within the lungs, generally causing secretion of fluid into the lungs eventually resulting in what is called secondary drowning as a result of Pulmonary Edema. In extremely high concentrations even two or three breathes of chlorine gas can be fatal due to serve tissue damage. Though due to Chlorine gases reactivity it can easily be filtered from air using activated carbon which is a form of processed carbon which has pores to increase surface area to around 500m2 per gram. The chlorine will simply react with the carbon before doing any damage to human respiratory tissue. Phosgene, the second Choking agent developed also works by means of reacting with water to form Hydrochloric acid. The reaction was generally slower but unlike Chlorine gas, did not have a distinguishable odour and usually killed it’s victims within 24 hours of inhalation. Mustard/Blistering Agents Blistering agents were developed at around the same time as the previously stated choking agents. Mustard Gas was developed in 1916 for the Imperial German Army and could be synthesised in a variety of ways including reacting Sulphur Dichloride with Ethene (1), reacting Sulphur Monochloride with Ethene (2) or using Thiodiglycol and Chlorinating with Phosphorus Trichloride (3). The third reaction was generally used by the British when creating mustard. It was a cleaner way to produce it as the purity was approximately 96% whereas the second method was fast but was only 70-80% pure and as a result did not keep for long periods as it decomposed, increasing the pressure of the containers it was in meaning it generally leaked. SCl2+ 2 C2H4→ (Cl-CH2CH2)2S 8 S2Cl2+ 16 C2H4→ 8 (Cl-CH2CH2)2S + S8 3 (HO-CH2CH2)2S + 2 PCl3→ 3 (Cl-CH2CH2)2S + 2 P(OH)3 Mustard gas is a blistering agent as it bonds an Alkl group to guanine in DNA, damaging the DNA and preventing cellular division and results in cell death or development of cancer. Due to this method of acting upon a subject it was rare for a victim to suffer immediate symptoms as the damage would not be evident until the effected cells die and fail to regenerate. As Mustard gas is not very soluble in water but is highly soluble in fats resulting in rapid absorption through skin tissue. After 24 hours skin irritation would occur then large blisters would form anywhere the mustard agent came into contact with the skin resulting in chemical burns. At the time of WWI serve mustard burns where 50% of the body was burned were often fatal. A victims eyes would also become greatly effected becoming sore and swelling causing blindness. At high concentrations blistering of the respiratory system would result in internal bleeding leading to pulmonary edema much like choking agents. While many people during have been killed by the use of Mustard gas and its derivatives, it also had done the world a large amount of good as it was discovered from autopsies of mustard gas victims that there was reduced white blood cell count and after further research Nitrogen Mustard was eventually used as the first chemotherapy drug to treat diseases related to the white blood cells such as lymphoma and leukaemia. Cyanide and Blood Agents The most well-known blood agent is Hydrogen Cyanide (HCN). HCN is produced on an industrial scale as it is a vital precursor to many useful chemicals in pharmaceuticals as well as in polymers. Cyanide ions are responsible for the effects of poisoning due to the fact cyanide ions interact with the mitochondrial enzyme cytochrome c oxidase by binding to it and reducing its effectiveness effectively halting cellular respiration. As a result the cells of an organism become unable to use the oxygen in the blood generally leading to hypoxia.

No comments:

Post a Comment

Note: Only a member of this blog may post a comment.