Understanding Chemical Threats
Although chemical weapons receive significantly less attention than nuclear and biological threats, the historical record shows that chemical weapons are, by far, the most widely used and widely proliferated weapons of mass destruction. Chemical weapons use the toxic properties of chemicals to cause physical harm ranging from discomfort to death. Relatively small amounts of chemical weapons can inflict devastating psychological and physical effects. The military value of chemical weapons is such that the United States and the Soviet Union stockpiled tens of thousands of tons during the Cold War. Countries traditionally have acquired chemical weapons before attempting to produce biological or nuclear weapons, because they are the least technologically demanding of the three. While 188 countries have joined the Chemical Weapons Convention (CWC) and have agreed not to develop, produce, stockpile, or use chemical weapons, a handful of key countries—particularly in the Middle East—remain outside of the treaty. Additionally, interest in chemical weapons by non-state actors continues to grow. The international community must therefore continue to work to prevent chemical weapons, and the technologies to produce them, from falling into the hands of terrorists.
What is a Chemical Weapon?
Chemical weapons use several different biochemical properties to debilitate or kill people, animals, and plants. Blister agents (sulfur mustard, nitrogen mustard, and lewisite) cause skin, eye, and lung irritation. Victims eventually develop painful blisters on their bodies, but usually do not die. Choking agents cause severe and painful breathing problems, leading to suffocation. Examples include chlorine gas, chloropicrin, diphosgene, and phosgene. Blood agents such as hydrogen cyanide and cyanogen chloride stop blood from distributing needed oxygen throughout the body. Nerve agents debilitate the nervous system, causing muscle contraction, loss of control over bodily functions, and death within minutes. The World War II-era agents (tabun, sarin, soman, and VX) remain the most widely proliferated. However, the Soviet Union also discovered, developed, tested, and produced Novichok agents – a new generation of nerve agents several times more toxic than the World War II-era agents.
What Dual-Use Challenges Exist?
In 1993, the U.S. Office of Technology Assessment noted that “the technologies required for the production of mustard and nerve agents have been known for more than 40 years and are within the capabilities of any moderately advanced chemical or pharmaceutical industry.” The production of many blistering agents and nerve agents no longer requires cutting-edge technology. Furthermore, the development of new technologies that simplify or even automate key processes further reduces the difficulty for state or non-state actors of producing chemical weapons. The chemical industry has also globalized. Once concentrated in the United States, Europe, and the Soviet Union, industrial production is now shifting to Asia, Latin America, and other developing areas. Many of the chemicals and equipment used to produce chemical weapons also serve important legitimate roles in industry and research. Thus, while the CWC regularly inspects chemical facilities to prevent their use as covert chemical agent factories, the growth of the chemical industry brings increased opportunities for sabotage and theft.
How Have Chemical Weapons Been Used in Warfare?
In warfare, chemical weapons have been used against opposing battlefield forces or dispersed to deny an enemy access to strategic areas. The introduction of chemical warheads and ballistic missiles has also expanded the list of potential targets of a chemical weapons attack to include civilian populations. Combatants used 124,000 metric tons of chemical weapons (mostly phosgene and mustard), during World War I.  During World War II, Italy used tear gas and mustard gas during the invasion in Ethiopia. During the Japanese invasion of China, a Japanese covert chemical and biological weapons branch known as Unit 731 used a variety of chemical weapons, including tear gas, phosgene, mustard gas, and lewisite. During the Cold War, conflicts in Korea, Afghanistan, and Vietnam involved only non-lethal riot control agents and defoliating agents. However, Egypt used mustard gas and possibly nerve agents during the North Yemen Civil War. During the Iran-Iraq War, Iraq employed blister agents and likely also used nerve agents against Iranian forces.
A Lingering Menace: The Challenge of Abandoned Chemical Weapons
The Chemical Weapons Convention defines abandoned chemical weapons as “chemical weapons, including old chemical weapons, abandoned by a State after 1 January 1925 on the territory of another State without the consent of the latter.” The CWC requires member states to declare and finance the destruction of any chemical weapons they have left in foreign territory. The largest such program involves the hundreds of thousands of World War II-era weapons Japan left in China. After lengthy discussions between China and Japan, destruction of Japan’s abandoned chemical weapons in China began in 2010. Italy, Panama, and South Korea have also declared the presence of abandoned chemical weapons on their territories.
The Threat of Chemical Weapons Terrorism
Terrorist organizations seeking to cause death and injury, as well as mass panic and economic disruption, would find many attractive features in chemical weapons. Very lethal weapons can be made with widely understood techniques and common equipment, and can be easily concealed until they are used. In the mid-1990s, the Japanese cult Aum Shinrikyo released self-produced sarin on multiple occasions. The deadliest incident occurred when cult members released the nerve agent into the Tokyo subway on March 20, 1995. The scale of the Aum Shinrikyo chemical ambitions revealed that non-state actors are fully capable of organizing and financing chemical programs. Because many chemicals commonly used in industry are themselves very toxic, terrorist organizations may also achieve their goals through the sabotage of chemical plants and shipments.
How is the International Community Working to Reduce the Chemical Weapons Threat?
Two international treaties – the Geneva Protocol (1925) and the Chemical Weapons Convention (CWC) (1993) – ban the use of chemical weapons. The CWC also bans their development, production, and stockpiling. CWC members have committed to eliminating any CW stockpiles they possess. Since this is a lengthy and complex process, Russia, the United States, Iraq and Libya have not yet completed elimination of their CW. The U.S. Department of State notes that current information does not rule out the possibility that China and Russia maintain additional CW stockpiles and production facilities outside their declared assets.  Further, the U.S. Congressional Research Service lists Iran, Egypt, Israel, North Korea, and Syria as additional countries that frequently arise as potential sponsors of CW programs, albeit without a clear standard of evidence.  Of these countries, only Iran participates in the CWC. Overseeing the final destruction of declared stockpiles, strengthening verification practices, and expanding CWC membership would enhance the CWC’s effectiveness. The Australia Group harmonizes export controls to participating states to reduce, if not eliminate, sales to customers who would misuse CW-related materials. However, keeping pace with technological innovation represents an ongoing challenge.
 U.S. Congress Office of Technology Assessment, Technologies Underlying Weapons of Mass Destruction, OTA-BP-ISC-115 (Washington, DC: U.S. Government Printing Office, December 1993).
 Gert Harigel, Chemical and Biological Weapons: Use in Warfare, Impact on Society and Environment (Washington, DC: Carnegie Endowment for International Peace, 2001).
 Cristina Chuen, “Global CW Assistance,” NTI Issue Brief, June 2005.
 U.S. Department of State, Adherence to and Compliance with Arms Control, Nonproliferation, and Disarmament Agreements and Commitments, July 2010.
 Paul Kerr, “Nuclear, Biological, and Chemical Weapons and Missiles: Status and Trends,” CRS Report for Congress, RL30699 (Washington, D.C.: The Library of Congress, Updated 20 February 2008).