Sulfur mustard, commonly known as mustard gas, is a chemical warfare agent classified as a vesicant. It gained notoriety during World War I due to its ability to cause severe, delayed damage to the skin, eyes, and respiratory tract. Although often called a “gas,” it is technically an oily liquid dispersed as a fine mist or vapor. It causes severe injuries, though it was lethal in only a small percentage of cases.
The Chemical Identity and Properties
The chemical formula for sulfur mustard is C4H8Cl2S. This chemical structure corresponds to the common IUPAC name Bis(2-chloroethyl) sulfide.
In its purest form, sulfur mustard is a colorless, odorless, and viscous liquid. However, the impure forms commonly used in warfare appear as a yellow-brown liquid and possess a faint, characteristic odor. This smell is often described as resembling garlic, onions, or horseradish, which is the source of its common name.
Mustard gas is a relatively stable compound that is only slightly soluble in water, but it readily dissolves in fats and organic solvents. This lipophilicity allows it to penetrate biological tissues, such as the skin, quickly and efficiently. It is also denser than air, meaning its vapors can settle and persist in low-lying areas for an extended period.
How Mustard Gas Damages Cells
Mustard gas functions as an alkylating agent, reacting quickly with biological molecules by attaching an alkyl group to them. This process begins when the molecule forms a highly reactive, cyclic sulfonium ion intermediate.
This reactive intermediate then targets and permanently modifies various cellular components, including proteins, lipids, and nucleic acids. A primary target is the DNA within the cell nucleus, where the agent attaches to nucleotides, particularly guanine bases. This alkylation can cause DNA lesions, such as cross-links between the two strands of the DNA helix.
The damage prevents the cell from dividing and replicating, which is especially destructive to rapidly dividing cells. Tissues with high cellular turnover, like the bone marrow, the lining of the respiratory tract, and the basal layer of the skin, are the most severely affected. The resulting cellular damage ultimately triggers rapid cell death and tissue necrosis.
Immediate Physical Effects of Exposure
The physical effects of mustard gas exposure are characteristically delayed, often taking several hours to a full day to manifest. The degree of harm depends on the concentration and duration of exposure, as well as the environmental conditions.
Exposure to the skin initially presents as redness and itching, followed by the formation of large, painful blisters. These blisters are a hallmark of the agent and can be as severe as second- or third-degree burns. Because the agent is easily absorbed through the skin, the resulting systemic damage can sometimes be fatal.
Ocular exposure causes severe irritation and a gritty sensation in the eyes, which quickly escalates to pain and swelling of the eyelids. This can result in conjunctivitis and light sensitivity, and severe exposure carries the risk of corneal damage and temporary blindness.
Inhaling the vapor causes immediate irritation to the respiratory system, leading to coughing, a sore throat, and shortness of breath. Higher exposure levels can damage the airway lining and may lead to fluid accumulation in the lungs, known as pulmonary edema.