Although the destructive power of chemical and biological weapons reached new heights in the 20th century, the use of such agents in warfare has a long history. The Greeks and Romans used human and animal corpses to poison drinking water, and the practice of throwing the corpses of plague victims over the walls of besieged cities brought many a conflict to a speedy end. In their war of attrition against the native tribes of North America, the settlers reportedly distributed infected blankets from smallpox hospitals as presents to mollify disaffected chiefs. In military terms, chemical and biological warfare has been seen as a means of rendering an opponent vulnerable by incapacitating troops, by affecting crops and livestock, and by spreading panic.
Today, chemical weapons are banned under the terms of the Chemical Weapons Convention (CWC), which came into force in 1997. The possession of biological weapons was also banned by a 1972 convention, but research proceeds under a number of guises; despite these international agreements a number of countries are suspected of having active programs to develop and test such weapons. Even with these conventions in place, there are large stockpiles of old weapons to be destroyed, and tests need to be developed to aid identification and verification of chemical and biological agents.
Chemical weapons
Thousands of different compounds have been tested as agents for killing or incapacitating people and for destroying vegetation, crops, and livestock. Casualty-producing agents include poison gas, nerve gas, and psychochemicals. Poisonous gases such as chlorine, phosgene, and mustard gas were developed for use in World War I. Chlorine and phosgene affect the air passages and promote massive secretion of fluid into the lungs. Mustard gas is a vesicant, producing blisters on exposed skin, and causing lung damage. The nerve gases are organophosphorus compounds similar to those used today as insecticides. It was the search for superior insecticides in Germany that led in 1936 to the discovery of tabun, the first nerve gas. Two related compounds (Sarin and Soman) were discovered soon afterward and together formed the basis of Germany’s secret weapon during World War II (though they were never used). Work in Britain in the 1950s (at Imperial Chemical Industries) resulted in another group of nerve gases—the V agents. These are much more toxic than the poison gases and as little as onhousandth of a gram could prove fatal. While termed gases, these agents are volatile liquids that vaporize to a greater or lesser extent depending on atmospheric conditions.
Nerve gases are highly toxic because they interfere with the passage of information in parts of the nervous system, particularly with the nervous control of muscle contraction, by inhibiting irreversibly a key enzyme—acetylcholinesterase. Initial symptoms of nerve gas exposure include sweating and vomiting. As muscular control is lost, there is tightness in the chest, convulsions, and finally death from asphyxiation. Exposure to a lethal dose results in death within minutes.
Psychochemicals were developed in the 1950s after discoveries in brain research had revealed that the passage of information between cells in the nervous system involved particular chemicals. A number of compounds, both natural and synthetic, can stimulate or block specific parts of the nervous system, for example, mescaline, lysergic acid diethylamide (LSD), and quinuclidinyl benzilate (BZ). BZ produces giddiness, disorientation, and amnesia when sprayed over troops.
Incapacitants, like the tear gases, are used by governments throughout the world. CS gas (2-chlorobenzal malonitrile), a British discovery of the 1950s, is dispersed as an aerosol (for example, from an exploding cartridge) or is dusted onto the ground as a powder. It causes a burning sensation when contacting the skin, difficulty in breathing, tears, and nausea. In confined spaces, tear gas has proved fatal.
Defoliating agents are herbicides based on compounds that mimic the action of plant growth hormones and cause plants to outgrow their strength. The defoliants 2,4-D and 2,4,5-T (di- and trhlorphenoxy acetic acid) were used in various proportions as Agents Blue, Orange, and White by the U.S. Army in the Vietnam War. These preparations were found to be contaminated with dioxin, a highly toxic carcinogen that resulted in many casualties.
