toxicity. compounds typified by ea-1464 formed a large group of them are carbamates like ea-3990 and ea-4056, both of which have been claimed to be about 3 times more toxic than vx. both the usa and the soviet union developed carbamate nerve agents during the cold war. they are sometimes grouped as "fourth generation" agents along with the novichok agents due to their falling outside the definitions of controlled substances under the cwc. insecticides some insecticides, including carbamates and organophosphates such as dichlorvos, malathion and parathion, are nerve agents. the metabolism of insects is sufficiently different from mammals that these compounds have little effect on humans and other mammals at proper doses, but there is considerable concern about the effects of long-term exposure to these chemicals by farm workers and animals alike. at high enough doses, acute toxicity and death can occur through the same mechanism as other nerve agents. some insecticides such as demeton, dimefox and paraoxon are sufficiently toxic to humans that they have been withdrawn from agricultural use, and were at one stage investigated for potential military applications. paraoxon was allegedly used as an assassination weapon by the apartheid south african government as part of project coast. organophosphate pesticide poisoning is a major cause of disability in many developing countries and is often the preferred method of suicide. methods of spreading many methods exist for spreading nerve agents such as: uncontrolled aerosol munitions smoke generation explosive dissemination atomizers, humidifiers and foggers the method chosen will depend on the physical properties of the nerve agent(s) used, the nature of the target, and the achievable level of sophistication. history discovery this first class of nerve agents, the g-series, was accidentally discovered in germany on december 23, 1936, by a research team headed by gerhard schrader working for ig farben. since 1934, schrader had been working in a laboratory in leverkusen to develop new types of insecticides for ig farben. while working toward his goal of improved insecticide, schrader experimented with numerous compounds, eventually leading to the preparation of tabun. in experiments, tabun was extremely potent against insects: as little as 5 ppm of tabun killed all the leaf lice he used in his initial experiment. in january 1937, schrader observed the effects of nerve agents on human beings first-hand when a drop of tabun spilled onto a lab bench. within minutes he and his laboratory assistant began to experience miosis (constriction of the pupils of the eyes), dizziness and severe shortness of breath. it took them three weeks to recover fully. in 1935 the nazi government had passed a decree that required all inventions of possible military significance to be reported to the ministry of war, so in may 1937 schrader sent a sample of tabun to the chemical warfare (cw) section of the army weapons office in berlin-spandau. schrader was summoned to the wehrmacht chemical lab in berlin to give a demonstration, after which schrader's patent application and all related research was classified as secret. colonel rüdiger, head of the cw section, ordered the construction of new laboratories for the further investigation of tabun and other organophosphate compounds and schrader soon moved to a new laboratory at wuppertal-elberfeld in the ruhr valley to continue his research in secret throughout world war ii. the compound was initially codenamed le-100 and later trilon-83. sarin was discovered by schrader and his team in 1938 and named in honor of its discoverers: gerhard schrader, otto ambros, gerhard ritter, and hans-jürgen von der linde. it was codenamed t-144 or trilon-46. it was found to be more than ten times as potent as tabun. soman was discovered by richard kuhn in 1944 as he worked with the existing compounds; the name is derived from either the greek 'to sleep' or the latin 'to bludgeon'. it was codenamed t-300. cyclosarin was also discovered during wwii but the details were lost and it was rediscovered in 1949. the g-series naming system was created by the united states when it uncovered the german activities, labeling tabun as ga (german agent a), sarin as gb and soman as gd. ethyl sarin was tagged ge and cyclosarin as gf. during world war ii in 1939, a pilot plant for tabun production was set up at munster-lager, on lüneburg heath near the german army proving grounds at raubkammer. in january 1940, construction began on a secret plant, code named "hochwerk" (high factory), for the production of tabun at dyhernfurth an der oder (now brzeg dolny in poland), on the oder river 40 km (25 mi) from breslau (now wrocław) in silesia. the plant was large, covering an area of 2.4 by 0.8 km (1.49 by 0.50 mi) and was completely self-contained, synthesizing all intermediates as well as the final product, tabun. the factory even had an underground plant for filling munitions, which were then stored at krappitz (now krapkowice) in upper silesia. the plant was operated by anorgana gmbh, a subsidiary of ig farben, as were all other chemical weapon agent production plants in germany at the time. because of the plant's deep secrecy and the difficult nature of the production process, it took from january 1940 until june 1942 for the plant to become fully operational. many of tabun's chemical precursors were so corrosive that reaction chambers not lined with quartz or silver soon became useless. tabun itself was so hazardous that the final processes had to be performed while enclosed in double glass-lined chambers with a stream of pressurized air circulating between the walls. three thousand german nationals were employed at hochwerk, all equipped with respirators and clothing constructed of a poly-layered rubber/cloth/rubber sandwich that was destroyed after the tenth wearing. despite all precautions, there were over 300 accidents before production even began and at least ten workers died during the two and a half years of operation. some incidents cited in a higher form of killing: the secret history of chemical and biological warfare are as follows: four pipe fitters had liquid tabun drain onto them and died before their rubber suits could be removed. a worker had two liters of tabun pour down the neck of his rubber suit. he died within two minutes. seven workers were hit in the face with a stream of tabun of such force that the liquid was forced behind their respirators. only two survived despite resuscitation measures. the plant produced between 10 000 and 30 000 tons of tabun before its capture by the soviet army and moved, probably to dzerzhinsk, ussr. in 1940 the german army weapons office ordered the mass production of sarin for wartime use. a number of 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. during that time, german intelligence believed that the allies also knew of these compounds, assuming that because these compounds were not discussed in the allies' scientific journals information about them was being suppressed. though sarin, tabun and soman were incorporated into artillery shells, the german government ultimately decided not to use nerve agents against allied targets. the allies did not learn of these agents until shells filled with them were captured towards the end of the war. german forces used chemical warfare against partisans during the battle of the kerch peninsula in 1942, but did not use any nerve agent. this is detailed in joseph borkin's book the crime and punishment of ig farben: speer, who was strongly opposed to the introduction of tabun, flew otto ambros, i.g.'s authority on poison gas as well as synthetic rubber, to the meeting. hitler asked ambros, "what is the other side doing about poison gas?" ambros explained that the enemy, because of its greater access to ethylene, probably had a greater capacity to produce mustard gas than germany did. hitler interrupted to explain that he was not referring to traditional poison gases: "i understand that the countries with petroleum are in a position to make more , but germany has a special gas, tabun. in this we have a monopoly in germany." he specifically wanted to know whether the enemy had access to such a gas and what it was doing in this area. to hitler's disappointment ambros replied, "i have justified reasons to assume that tabun, too, is known abroad. i know that tabun was publicized as early as 1902, that sarin was patented and that these substances appeared in patents. " (...)ambros was informing hitler of an extraordinary fact about one of germany's most secret weapons. the essential nature of tabun and sarin had already been disclosed in the technical journals as far back as 1902 and i.g. had patented both products in 1937 and 1938. ambros then warned hitler that if germany used tabun, it must face the possibility that the allies could produce this gas in much larger quantities. upon receiving this discouraging report, hitler abruptly left the meeting. the nerve gases would not be used, for the time being at least, although they would continue to be produced and tested.— joseph borkin, the crime and punishment of ig farben post–world war ii since world war ii, iraq's use of mustard gas against iranian troops and kurds (iran–iraq war of 1980–1988) has been the only large-scale use of any chemical weapons. on the scale of the single kurdish village of halabja within its own territory, iraqi forces did expose the populace to some kind of chemical weapons, possibly mustard gas and most likely nerve agents. operatives of the aum shinrikyo religious group made and used sarin several times on other japanese, most notably the tokyo subway sarin attack. in the gulf war, no nerve agents (nor other chemical weapons) were used, but a number of u.s. and uk personnel were exposed to them when the khamisiyah chemical depot was destroyed. this and the widespread use of anticholinergic drugs as a protective treatment against any possible nerve gas attack have been proposed as a possible cause of gulf war syndrome. sarin gas was deployed in a 2013 attack on ghouta during the syrian civil war, killing several hundred people. most governments contend that forces loyal to president bashar al-assad deployed the gas; however, the syrian government has denied responsibility. on 13 february 2017, the nerve agent vx was used in the assassination of kim jong-nam, half-brother of the north korean leader kim jong-un, at kuala lumpur international airport in malaysia. on 4 march 2018, a former russian agent (who was convicted of high treason but allowed to live in the united kingdom via a spy swap agreement), sergei skripal, and his daughter, who was visiting from moscow, were both poisoned by a novichok nerve agent in the english city of salisbury. they survived, and were subsequently released from hospital. in addition, a wiltshire police officer, nick bailey, was exposed to the substance. he was one of the first to respond to the incident. twenty-one members of the public received medical treatment following exposure to the nerve agent. despite this, only bailey and the skripals remained in critical condition. on 11 march 2018, public health england issued advice for the other people believed to have been in the mill pub (the location where the attack is believed to have been carried out) or the nearby zizzi restaurant. on 12 march 2018, british prime minister theresa may stated that the substance used was a novichok nerve agent. on 30 june 2018, two british nationals, charlie rowley and dawn sturgess, were poisoned by a novichok nerve agent of the same kind that was used in the skripal poisoning, which rowley had found in a discarded perfume bottle and gifted to sturgess. whilst rowley survived, sturgess died on 8 july. metropolitan police believe that the poisoning was not a targeted attack, but a result of the way the nerve agent was disposed of after the poisoning in salisbury. ocean disposal in 1972, the united states congress banned the practice of disposing chemical weapons into the ocean. thirty-two thousand tons of nerve and mustard agents had already been dumped into the ocean waters off the united states by the u.s. army, primarily as part of operation chase. according to a 1998 report by william brankowitz,