Ethyldichloroarsine (ED)
Ethyldichloroarsine, also called "Dick" by the Germans-meaning fat or thick, was developed for weapon use by German chemists during World War I. This organic arsenical was produced in anticipation of a military offensive planned for the spring of 1918 to support German infantry operations. Despite serious efforts made to weaponize this compound, little literature exists on the effectiveness and history of its use. Fast acting-compared to mustard or phosgene—ethyldichloroarsine has multiple effects on the body sharing characteristics of both vesicant and choking agents. Ethyldichloroarsine is a colorless liquid that smells like rotting fruit. Possessing a high volatility at room temperature, ethyldichloroarsine poses a significant vapor threat to exposed personnel. Within seconds of contact with the skin, the agent fixes itself to the epidermis and dermis causing immediate pain. The agent penetrates deeper into the skin layers causing the destruction of subcutaneous tissue. Fluid-filled blisters form only after prolonged exposure; ethyldichloroarsine has one-twentieth the blistering action of Lewisite. Inhalation can cause pulmonary edema or "dry-land drowning." A lethal exposure, however, depends upon the period of exposure. A dose of 3,000 to 5,000 mg·min/m3 is generally a lethal dose. Because the body detoxifies ethyldichloroarsine at an appreciable rate, the product of concentration and time is not a constant. For instance, as time increases, concentration does not decrease proportionately. Therefore, exposure to 40 mg·min/m3 for 75 minutes might have an effect similar to that produced by exposure to 30 mg·min/m3 for 166 minutes. Alarmingly, organic arsenicals are simple to produce. Any nation or terrorist group with access to a basic pesticide production facility can produce these agents with relative ease.   

Lewisite (L)
Lewisite (ß-chlorovinyldichloroarsine) is an arsenical vesicant. U.S. Army Captain W. L. Lewis is credited with first synthesizing Lewisite in 1918 though German scientists had studied it earlier. It is similar to sulfur mustard in that it damages the skin, eyes and airways, however, it differs from mustard in its clinical effects, which appear within seconds of exposure. An antidote, British anti-Lewisite (BAL) can ameliorate the effects of Lewisite if promptly administered after exposure. Pure Lewisite is an oily, colorless liquid and impure Lewisite is amber to black in color. Lewisite has a geranium-like odor and is much more volatile and persistent in colder temperatures than mustard. Lewisite remains fluid at lower temperatures, making it an ideal agent for winter conditions, however, it hydrolyzes rapidly, and on a humid day, maintaining a biologically active concentration of vapor is difficult. Highly toxic, 1,5000mg·min/m3 will kill 50 percent of those exposed by inhalation. Vesication is caused by 14µg of liquid, and 30mg of liquid on skin will cause death in 50 percent of those exposed. Large quantities of Lewisite were manufactured by the United States for use in Europe in World War I, but the war ended while the ship was en route and the vessel was sunk. There has been no verified use of Lewisite on a battlefield, though Japan may have used Lewisite against China between 1933 and 1944. Lewisite is sometimes mixed with mustard to lower the freezing point of mustard. Russia uses this mixture.   

Mustard (HD)
Sulfur mustard (HD), called LOST (derived from the names of researchers Lommel and Steinkopf) and Yeprite, is more an oily liquid than a gas. First used in World War I, sulfur mustard is yellow-brown in color and has a garlic-like odor. Sulfur mustard is a persistent agent with low volatility at cool temperatures, but becomes a vapor hazard at high ambient temperatures. Exposure to mustard vapor, not liquid, is of primary medical concern. More than 80 percent of mustard casualties in World War I were caused by exposure to mustard vapor. Mustard vapor is three times more toxic than a similar concentration of cyanide gas, but mustard liquid is also quite toxic. Skin exposure to as little as 7 grams is lethal to 50 percent of adults. There are three forms of nitrogen mustard compound, NH1, NH2 and NH3. Nitrogen mustard (NH), a derivative of sulfur mustard, has never been used on a battlefield and is generally not considered a military agent. Similar to sulfur mustard, nitrogen mustards seem to cause more severe systemic effects, particularly in the central nervous system. Nitrogen mustard was one of the first chemotherapy agents.   

Phosgene Oxime (CX)
Not to be confused with the choking gas phosgene (CG), phosgene oxime (CX) is not a true vesicant because it does not produce blisters. Rather it causes redness of the skin (erythema), wheals and irregular hives (urticaria). Its lesions have been compared with those caused by nettle stings, which gives this agent its nickname: "nettle gas." Because it causes extensive tissue damage, it has also been characterized as a corrosive gas. Pure phosgene oxime (dichloroformoxime) is a colorless, crystalline solid. The munitions-grade compound is a yellowish-brown liquid. Phosgene oxime has a melting point of 35°C to 40°C. The solid material can produce enough vapor to cause symptoms. German scientists first synthesized phosgene oxime in 1929 and both Russia and Germany had developed it prior to World War II. It is possible that both countries may have developed weapons for this agent. The United States also studied phosgene oxime, but rejected it because of its lack of biological effects and its instability. The apparently lack of biological effects was later found to be due to the low concentrations (1% to 2%) used in pre-World War II studies. Later studies indicated that a concentration less than 8 percent had little or inconsistent effects. Though phosgene oxime is not known to have been used on the battlefield, it is of military interest for several reasons. First, it penetrates garments and rubber more quickly than many other chemical agents. Secondly, it produces a rapid onset of severe and prolonged effects. Third, when mixed with other chemical agents (e.g., VX) the rapid skin damage caused by phosgene oxime will render the skin more susceptible to the second agent. Finally, if an unmasked soldier were exposed to phosgene oxime before donning his mask, the pain caused by exposure to the agent will prompt him to unmask again.