Mustard gas

= Sulfur mustard = Sulfur mustard (Chemical formula : C4H8Cl2S), commonly known as mustard gas, is a cytotoxic and vesicant chemical warfare agent with the ability to form large blisters on exposed skin and in the lungs. Related chemical compounds with similar chemical structure and similar properties form a class of compounds known collectively as sulfur mustards or mustard agents. Pure sulfur mustards are colorless, viscous liquids at room temperature. When used in impure form, such as warfare agents, they are usually yellow-brown in color and have an odor resembling mustard plants, garlic, or horseradish, hence the name. Sulfur mustard was originally assigned the name LOST, after the scientists Wilhelm Lommel and Wilhelm Steinkopf, who developed a method of large-scale production for the Imperial German Army in 1916.

Mustard agents are regulated under the 1993 Chemical Weapons Convention (C.W.C.). Three classes of chemicals are monitored under this Convention, with sulfur and nitrogen mustard grouped in Schedule 1, as substances with no use other than in chemical warfare. Mustard agents could be deployed on the battlefield by means of artillery shells, aerial bombs, rockets, or by spraying from warplanes.

Physiological effects
Soldier with moderate mustard agent burns sustained during World War I showing characteristic bullae on neck, armpit and hands

Mustard agent has extremely powerful vesicant effects on its victims. In addition, it is strongly mutagenic and carcinogenic, due to its alkylating properties. It is also lipophilic. Because people exposed to mustard agent rarely suffer immediate symptoms, and mustard-contaminated areas may appear completely normal, victims can unknowingly receive high dosages. Within 24 hours of exposure to mustard agent, victims experience intense itching and skin irritation, which gradually turns into large blisters filled with yellow fluid wherever the mustard agent contacted the skin. These are chemical burns and are very debilitating. Mustard agent vapor easily penetrates clothing fabrics such as wool or cotton, so it is not only the exposed skin of victims that gets burned. If the victim's eyes were exposed then they become sore, starting with conjunctivitis, after which the eyelids swell, resulting in temporary blindness. In rare cases of extreme ocular exposure to sulfur mustard vapors, corneal ulceration, anterior chamber scarring, and neovascularization have occurred. In these severe and infrequent cases, corneal transplantation has been used as a treatment option. Miosis may also occur, which is probably the result from the cholinomimetic activity of mustard. At very high concentrations, if inhaled, mustard agent causes bleeding and blistering within the respiratory system, damaging mucous membranes and causing pulmonary edema. Depending on the level of contamination, mustard agent burns can vary between first and second degree burns, though they can also be every bit as severe, disfiguring and dangerous as third degree burns. Severe mustard agent burns (i.e. where more than 50% of the victim's skin has been burned) are often fatal, with death occurring after days or even weeks have passed. Mild or moderate exposure to mustard agent is unlikely to kill, though victims require lengthy periods of medical treatment and convalescence before recovery is complete.

The mutagenic and carcinogenic effects of mustard agent mean that victims who recover from mustard agent burns have an increased risk of developing cancer in later life. In a study of patients 25 years after wartime exposure to chemical weaponry, c-DNA microarray profiling indicated that a total of specific 122 genes were significantly mutated in the lungs and airways of sulfur mustard victims. Those genes all correspond to functions commonly affected by sulfur mustard exposure, including apoptosis, inflammation, and stress responses.

Typical appearance of bullae on arm caused by blister agent burns

The vesicant property of mustard agent can be neutralized by oxidation or chlorination, using household bleach (sodium hypochlorite), or by nucleophilic attack using e.g. decontamination solution "DS2" (2% NaOH, 70% diethylenetriamine, 28% ethylene glycol monomethyl ether). After initial decontamination of the victim's wounds is complete, medical treatment is similar to that required by any conventional burn. The amount of pain and discomfort suffered by the victim is comparable as well. Mustard agent burns heal slowly, and, as with other types of burn, there is a risk of sepsis caused by pathogens such as Staphylococcus aureus and Pseudomonas aeruginosa. The mechanisms behind sulfur mustard’s effect on endothelial cells are still being studied, but recent studies have shown that high levels of exposure can induce high rates of both necrosis and apoptosis. In vitro tests have shown that at low concentrations of sulfur mustard, where apoptosis is the predominant result of exposure, pretreatment with 50 mM N-acetyl-L-cystein (NAC) was able to decrease the rate of apoptosis. NAC protects actin filaments from reorganization by sulfur mustard, demonstrating that actin filaments play a large role in the severe burns observed in victims.

A British nurse treating soldiers with mustard agent burns during World War I commented:

"They cannot be bandaged or touched. We cover them with a tent of propped-up sheets. Gas burns must be              agonizing because usually the other  cases do not complain, even with the worst wounds, but gas cases are               invariably beyond endurance and they cannot help crying out."