The Syrian civil war has taken an even darker turn in recent weeks as increasingly credible reports have surfaced suggesting President Bashar al-Assad is using not just conventional but also chemical weapons against the Syrian insurgency. Suddenly the laconic, at-arm’s-length West has snapped to attention and declared that an unacceptable moral line has been crossed.
The about-face is not a surprise. For more than a century, chemical weapons have been deemed outside the boundaries of acceptable warfare, while simple slaughter from bullets and bombs has not. Exactly why such a line has been drawn is not certain, but it may have to do with unique pain and suffering caused by chemicals.
The Centers for Disease Control and Prevention and other groups maintain lists of the various chemicals used in chemical warfare. The dozens of agents usually are categorized into four main groups, based on the effects they have on the body. Of note, chemical weapons can be delivered in solid and liquid forms but are most often, both historically and in movies, dispersed as gas.
World War I saw the use of two categories of chemical-warfare agents, those that affect the lungs—phosgene (a chloride gas) and chlorine gas, a closely related substance—and blistering agents, also called vesicants, that blister away flesh. The latter group, which includes nitrogen mustard, also can cause severe irritation in the lung sufficient to cause asphyxiation and death.
The grim events that surround the early use of chlorine gas have become a staple of horrifying war stories. The Germans, including the companies that later became IG Farben, saw the damage that chlorine gas could inflict and in 1915 began using it on British soldiers, killing hundreds. Use of it as a weapon, though, was eventually limited by the uncertainties of the wind—the Germans released the gas into a breeze upwind from the enemy soldiers and hoped and assumed the wind would not change direction. In addition, the rapid deployment of gas masks offered an effective prevention strategy.
Chlorine gas also became less commonly used because a more lethal and easy-to-control agent, and one not fully neutralized by gas masks, was weaponized at about the same time. The story of nitrogen mustard gas, so called not because of a connection to mustard but because of its acrid mustardy smell, is perhaps the strangest in 20th-century science.
As a chemical weapon it was brutally effective. Used on Belgian battlefields during World War I, it maimed, crippled, and killed many whose flesh was blistered away or who died from asphyxiation. It also was used much more recently in the Iran-Iraq war and was thought to be one of the lead “weapons of mass destruction” in the hands of Saddam Hussein.
Nitrogen mustard’s strange turn, however, was its reincarnation a generation later in substantially lower doses as cancer chemotherapy. Physicians given the grim task of performing autopsies on soldiers who had died in 1915 from exposure to mustard made several seminal observations. The bone marrow of the dead soldiers was depleted dramatically, and their lymph nodes had shriveled away. These two effects in turn were applied to treatment of cancers affecting these specific organs, leukemia and lymphoma. Indeed, from the battlefields of WWI came the entire discipline of cancer chemotherapy. The agents live on now, both chemically and etymologically, in drugs such as bendamustine that are used to treat several cancers.
A third category of chemical weapon is comparably savage—the nerve-gas agents. Sarin gas, which was released in the Tokyo subway system in 1995, killing 12 and injuring thousands, is the most famous example. These chemicals often go by top secret-sounding letter designations such as the G series and the V series, adding to their mystique. They act by unhooking the nerves one from the other by chemically interfering in the nerve synapse, resulting in complete loss of neurologic control. Symptoms may range from palpitations and severe sweating to paralysis, convulsions, and death. Assad is suspected of using this type of chemical weapon, perhaps sarin itself, on the Syrian people.
The fourth group of chemical agents is the so-called blood group—cyanide products delivered various ways that enter the bloodstream and cause lethal cyanide poisoning. Zyklon B, a gas used by the Nazis in the death camps, is a haunting example of the rapid lethality of one form, hydrogen cyanide. There are no known recent uses of this group of chemicals.
Many other chemicals have been and perhaps will be used, such as tear gas. And then there are the biologics, including ricin, the highly lethal plant product sent in letters to President Obama and others this year and used to kill the Bulgarian dissident Georgi Markov in London in 1978. But these chemicals really are more like examples of biologic warfare, not chemical warfare. And, sadly for the human species, despite the similarities in dispersal and lethality (and cruelty), biologic warfare is an entire topic unto itself.