Chemicals have, unfortunately, been enlisted in warfare with the design of lethal and unpleasant agents with which to attack enemies during battle. This is not a new technique. The ancient Chinese were familiar with 'arsenical smokes', and during the Peloponnesian War in 429 bc, according to Greek historians, the Spartans set fire to wood soaked with pitch and sulphur which burnt furiously and produced poisonous, choking fumes. In 1456 the Christians of Belgrade were saved from their Turkish attackers by a toxic cloud generated by burning rags dipped into a chemical prepared by an alchemist.
The large-scale use of chemicals in warfare, especially the use of gases, began in the First World War. Some of the gases used in warfare, for example chlorine and phosgene, were already known but had not been designed for the purpose. Others, like lewisite, were specifically designed for warfare. During the First World War chlorine gas was first used in Flanders, where it was released by the Germans in April i9i5, killing 5,000 Allied soldiers and injuring a further 15,000. Other poisons used were phosgene, which replaced chlorine, and later in the war mustard gas and lewisite. The use of gas masks reduced the effectiveness of gas after the first few attacks. The Geneva Conference in 1925 outlawed the use of such gases, but it has not stopped them from being used altogether. In i936 the Italians used mustard gas against the Ethiopians in Abyssinia, and more recently Saddam Hussein used it in the war against Iran in the i980s, and in the massacre of thousands of Kurds in northern Iraq in 1988.
Chlorine and phosgene are both reactive gases which destroy lung
tissue. They cause the lungs of victims to become filled with fluid, a condition known as pulmonary oedema, and the victims asphyxiate. The junctions between the lung cells and the blood vessels are damaged, allowing fluid into the air spaces in the lung. Phosgene was the most effective and lethal agent used in the First World War.
Mustard gas, which smells like garlic, causes blistering of the skin, severe burns to eyes and lungs, and damage to internal organs such as the bone marrow and gut. The symptoms are delayed for some hours. Mustard gas or sulphur mustard was the most effective incapacitating agent used in the First World War.
Lewisite, dichloro(2-dichlorovinyl)arsine is a chemical that contains arsenic, which though a liquid is sufficiently volatile to be dispersed among enemy troops. The arsenic atom in the lewisite reacts with proteins and causes terrible blisters on the skin and damage to the eyes and lungs if inhaled. Fortunately, an antidote was devised as a result of the work of the British biochemist Rudolf Peters. The antidote was appropriately named British anti-lewisite (dimercaprol), and abbreviated to BAL.
The BAL molecule contains two atoms of sulphur which are able to bind with the arsenic in the lewisite and remove it. This removes the chemical from the skin of the victim and from the body. The antidote was based on an understanding of the way in which arsenic is toxic. BAL has also been found to bind metals and, as the first metal complexing agent (chelator), has been used clinically for the treatment of metal poisoning. Although it has now largely been superseded, it has been widely used as an antidote for other forms of arsenic poisoning and for poisoning by heavy metals such as mercury, gold, and sometimes lead poisoning in children.
During the Second World War far more lethal and potent poisons were developed, the nerve gases. In 1936 Dr Gerhard Schrader, working in the German chemical company I. G. Farbenindustrie synthesized a compound based around phosphorus for possible use as an insecticide. It was one of the first organophosphorus compounds to be made and was found to be highly toxic to mammals. It was manufactured under the name tabun. Further development led to another similar chemical, sarin, which was far more toxic. A third, soman, was developed in 1944. These chemicals were highly potent, lethal nerve gases. The mode of action of the nerve gases was similar to that of the insecticides that were developed from them, but they did not have the selective toxicity only for insects (see pp. 98-101 and box below). By the end of the war the Germans had 12,000 tons of tabun. About 1 mg is lethal to a human, which means that 1.2 X 1013 lethal doses were present in the stockpile, or enough to kill 10 billion people!
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If you suffer with asthma, you will no doubt be familiar with the uncomfortable sensations as your bronchial tubes begin to narrow and your muscles around them start to tighten. A sticky mucus known as phlegm begins to produce and increase within your bronchial tubes and you begin to wheeze, cough and struggle to breathe.