Chemical and Biological Terror

In a changing world in which we face terrorism and war, what dangers are posed by chemical and biological weapons, and how can we protect ourselves against these threats?

By Eric Croddy

On Sept. 27, 2001, a 63-year-old man in Florida developed a fever and flulike symptoms. On October 2, he was admitted to a hospital, where doctors made the surprising diagnosis of inhalational anthrax, an extremely rare disease caused by a bacterium called Bacillus anthracis. Anthrax can cause organ failure, shock, and death. On October 5, the man died. Within the next few weeks, additional cases of anthrax were reported in half a dozen states along the East Coast. By the end of November, more than 20 people had been infected with anthrax and 5 of them had died.

Investigators traced the anthrax cases to bacteria-laden envelopes that had been deliberately sent through the U.S. mail. Spores (a dormant stage of bacteria) that had been placed in these envelopes apparently came in contact with and contaminated other mail in postal facilities. These contaminated letters then carried their deadly cargo to the unsuspecting victims, who became sick after they either inhaled the spores or touched them. In the body, the spores became active, infectious germs. Inhalational anthrax caused all of the deaths. On the skin, the spores produced a less dangerous form of the disease called cutaneous anthrax.

The anthrax incidents came just weeks after Sept. 11, 2001, when terrorists hijacked four airliners in the United States and flew two of them into the World Trade Center in New York City and another into the Pentagon near Washington, D.C. The fourth plane crashed in a field in Pennsylvania. Approximately 3,000 people were killed in the attacks.

As of mid-2002, authorities had not established any connection between the shocking events of September 11 and the anthrax mailings. Still, these incidents, coming so close together, led to fears of additional terrorist attacks, particularly of attacks involving chemical or biological weapons. Never before had ordinary citizens been more concerned about what such weapons are, what kind of damage they might do, and what steps might be taken to protect against this threat.

Chemical weapons are made of chemical compounds designed to kill or injure by their poisonous effects. Biological weapons consist of microorganisms or toxins (poisons) produced by microbes, plants, or animals. Chemical and biological weapons have been called "the poor man's nukes" because they are potentially as deadly as nuclear weapons but can be developed much more easily and at much less cost. Many countries have manufactured chemical and biological weapons. These weapons may also be in the arsenals of some terrorist organizations.

Chemical and biological weapons in history

Although the threat of chemical and biological weapons was new to the United States, it was hardly new to the world. In fact, the use of such weapons began centuries ago. In one of the earliest recorded uses of chemical weapons, the armies of the ancient Greek city-state of Sparta burned sulfur and pitch to generate poisonous fumes against their enemies from Athens during the Peloponnesian War (431 to 404 B.C.). A Chinese treatise dating to about the same time told how to produce thick, irritating smoke by burning firewood, grass, and other combustible materials. The Chinese used such smoke to overcome enemies tunneling under fortifications. Other Chinese documents reveal that by A.D. 1000, arsenic, a toxic metallic element, was being used in smoke bombs.

Infectious disease has long been used as a biological weapon. The ancient Romans poisoned the wells of their enemies with dead animals. In 1346, Mongol forces laying siege to the city of Kaffa, in what is now Ukraine, hurled corpses contaminated with bubonic plague over the city's walls to spread the disease among the population. British troops in Colonial America during the French and Indian wars (1689-1763) tried to exterminate Native Americans allied with the French by giving them blankets that had been used to wrap victims of smallpox.

Types of chemical weapons

There are several types of modern chemical weapons, which are classified according to their effects on the human body. They include choking agents, blood agents, blister agents, and nerve agents.

Choking agents are gases that irritate and injure the lungs. Chlorine and phosgene are choking gases that were first used by the armies of Germany, France, the United Kingdom, and the United States during World War I (1914-1918). They were often carried to the front in a liquid form under pressure in canisters. Once released from the canisters, the agents turned into a deadly gas, which the wind blew toward enemy lines. Choking agents, like many other chemical agents, can also be carried and released by shells, bombs, or missiles. After chlorine is inhaled, it combines with water in the body to form acid compounds that damage lung tissue. Blood plasma (the liquid part of blood) leaks out of the damaged sites in the lungs. The plasma then develops into a frothy, blood-tinged fluid that can fill the lungs, causing the victim to choke to death.

There is no antidote (medicine that counteracts the harmful effects of a poison) to treat people who have been exposed to choking agents. Chlorine gas can cause death in less than an hour after being inhaled, but symptoms of phosgene exposure may not begin for 24 hours.

Blood agents block respiration (the uptake and use of oxygen) by body cells. This often causes irreversible damage to the heart and brain. Hydrogen cyanide and another cyanide compound called cyanogen chloride are blood agents. They work rapidly. Inhaling these agents can cause convulsions, respiratory failure, unconsciousness, and death within 10 minutes.

Like choking agents, blood agents cause their most damaging effects when they are inhaled as a vapor, which might be released from a canister, a shell, or a bomb. Antidotes for blood agents are drugs that can be used to detoxify (remove the poison from) the body of a person exposed to one of these poisons.

Blister agents cause severe blisters on the skin and irritation to the eyes and respiratory system. The most infamous blister agent is mustard gas, which caused tens of thousands of casualties during World War I and again in the Iran-Iraq War (1980-1988). Mustard gas, named for its mustardlike odor, is most damaging when delivered as an aerosol (a suspension of tiny droplets or particles). Tiny aerosol droplets of mustard gas cause skin blisters to form within 1 to 24 hours after exposure. If absorbed through the skin, mustard gas can poison the whole body. As little as two grams (0.07 ounce) of the compound can be fatal. If mustard gas gets in the eyes, it can cause pain, itching, and even permanent blindness. If inhaled, the gas damages the upper airways and, in the worst cases, leads to complete respiratory failure and death.

There is no antidote for mustard-gas poisoning once the chemical has been inhaled or absorbed through the skin. However, cleansing the skin soon after exposure can help remove the agent before it is absorbed or damages the tissue.

Nerve agents, such as tabun, sarin, soman, and VX, are the deadliest and quickest-acting chemical weapons. Just 0.015 gram (0.00053 ounce) of VX on the skin can be lethal to an adult. A person who touches or inhales a nerve agent will probably be dead within 1 to 15 minutes. Nerve agents were first developed in the 1930's after a German chemist, Gerhard Schrader, discovered that a phosphorus-containing insecticide he was working on was highly toxic to humans. During World War II (1939-1945), the German government put the compound, called tabun, into production, eventually stockpiling 10,900 metric tons (12,000 tons) of the nerve agent.

Nerve agents affect the transmission of nerve impulses in the body. Nerve cells release acetylcholine, a chemical that transmits nerve impulses. Acetylcholine binds to muscle and other tissue cells at sites on the cells called receptors. This prompts the muscle to move and, for example, bend an arm. Soon after the muscle is stimulated, an enzyme called acetylcholinesterase breaks down the acetylcholine molecules to stop the muscle movement. A nerve agent, however, blocks acetylcholinesterase from breaking down acetylcholine. Thus, the muscle is continually stimulated, leading to muscle cramps, convulsions, seizures, and ultimately, death. The acetylcholine also stimulates glands to secrete large amounts of saliva in the mouth and mucus in the nose and throat, which can lead to asphyxiation (suffocation).

Military forces can use gas canisters, artillery shells, missiles, or bombs to deliver nerve agents in aerosol form to an enemy. However, terrorists can use simpler methods. For example, in 1995, a Japanese political-religious group called Aum Shinrikyo carried plastic bags filled with sarin into a Tokyo subway. There, they simply poked holes in the bags with the tips of umbrellas to release the poison. The attack killed 12 people and injured about 1,000 others.

Victims of nerve agents can be saved if they are quickly injected with an antidote that helps restore normal activity to the heart, lungs, and overstimulated glands. An anticonvulsant drug can also be administered to ease twitching and convulsions.

Types of biological weapons

Biological weapons share certain characteristics with chemical weapons but differ in others. As with many chemical weapons, biological weapons cause their most harm when delivered as aerosols, and they can be dispersed with methods similar to those used with chemical weapons. However, living organisms in biological weapons may not be able to survive the explosion of the shell or missile that they were packed into. Thus, a group using biological weapons may choose other delivery methods. Biological agents could be released through such simple means as spraying from a portable canister or with techniques requiring special skills, such as the use of crop dusters, small aircraft used to spread pesticides.

Biological weapons pose other problems that chemical weapons do not. For one thing, in order to remain active after release, biological agents require favorable environmental conditions, such as moderate humidity and warmth. Biological agents also must be "weaponized," or made into a special preparation that can easily cause illness in large numbers of people.

Unlike most chemical weapons, which cause injury or death within minutes or hours, most biological weapons have a delayed effect. The first sign of a biological weapons attack might show up days or even weeks after the attack as doctors begin to diagnose cases of a disease.

There are three main categories of biological weapons agents: bacteria, viruses, and toxins.


Bacteria are single-celled organisms that replicate by division and thrive in warm, moist environments, such as the human body. Besides the anthrax microbe, other bacteria that experts believe could be used as weapons include Yersinia pestis, which causes plague; Brucella suis, the cause of brucellosis, a disorder characterized by pain in the joints and gastrointestinal distress; Francisella tularensis, which causes tularemia, an illness marked by headache, coughing, and weight loss; and Vibrio cholerae, the culprit behind cholera, a disease that results in diarrhea, dehydration, and shock.

Some kinds of bacteria survive prolonged periods in cold, dry, or otherwise harsh environmental conditions by producing round, inactive spores, which have a thick, protective wall. The spores develop again into active bacteria when conditions become favorable.

Another group of microbes that could be used as weapons are the rickettsia. These microorganisms are classified as bacteria by some biologists but placed in a separate classification by others. Nearly all rickettsia are smaller than ordinary bacteria and can survive only in living organisms. Experts believe that one type of rickettsia, called Coxiella burnetii, can be especially damaging as a biological weapon. It causes Q fever, a disorder marked by chest pain and pneumonia.

The way anthrax bacteria act in the body is typical of the way in which many bacterial agents can cause tissue damage. After the anthrax spores are inhaled, they make their way down to the lungs. The anthrax spores grow and multiply as rod-shaped bacteria in the alveoli, small air sacs in the lungs where gases are exchanged. The bacteria excrete toxins that enter body cells, leading to severe inflammation of the tissues, leaking blood vessels, and organ failure. A victim of inhalational anthrax, if untreated, usually dies within a couple days after developing such symptoms as coughing and wheezing. To have the best chance at surviving inhalational anthrax, the victim must begin taking antibiotics before symptoms begin. In addition, there is a vaccine that can prevent the disease, provided it is administered weeks before exposure or before the spores become active in the body.


Following the anthrax scares of 2001, some health authorities raised the possibility that certain viruses might also be used as biological weapons. Viruses differ from bacteria in a number of ways. Viruses are technically not cells but merely genetic material enclosed in a coat of protein. Most viruses are much smaller than bacteria. Viruses also differ from bacteria in being completely dependent upon living cells for replication (reproduction). After entering the body, viruses usually inject their genetic material into body cells, turning the cells into tiny factories that create more viruses. The viruses then spread through the body, infecting and destroying more and more cells.

Authorities have been particularly concerned about the viral disease smallpox. In years past, this extremely contagious disease afflicted vast numbers of people, causing a high fever and disfiguring sores all over the body. A worldwide vaccination program led to the eradication of smallpox by 1980, though the United States and Russia have maintained laboratory samples of the virus. Other countries may also have the smallpox virus: Many experts fear that "rogue nations" such as Iraq may possess secret stashes of smallpox that could someday be used as weapons. Because of this concern, the U.S. government began in late 2001 to build up its stockpile of smallpox vaccine, which reduces symptoms or prevents the disease if administered up to three or four days after exposure. Smallpox kills 30 to 35 percent of unvaccinated people who come down with the disease.

A number of other dangerous viruses could be used as weapons. They include the Venezuelan equine encephalitis, or VEE, virus, which causes fever, muscle pain, nausea, and vomiting. Other viruses that might be used as weapons cause hemorrhagic fevers, such as Ebola, yellow fever, and Rift Valley fever--diseases characterized by severe bleeding of the capillaries (tiny blood vessels).


While viral and bacterial agents produce a delayed effect on the body, biological toxins cause their effects quickly--usually within minutes or hours after exposure. There are several biological toxins that could be used as weapons.

One possible weapon is the botulinum toxin, produced by the bacterium Clostridium botulinum, the cause of botulism. Botulism is a form of food poisoning that disrupts nerve-signal transmissions, leading to paralysis and respiratory failure. Botulinum toxin could be used to poison food or it could be sprayed directly on human targets as an aerosol. The disease has a 65-percent mortality rate. Botulism is treatable with an antitoxin (substance that renders a biological toxin harmless) if administered early. Vaccines are also available to prevent botulism.

Other deadly or debilitating biological toxins include saxitoxin, produced by blue-green algae; ricin, derived from castor beans; and staphylococcal enterotoxin, made by Staphylococcus aureus bacteria.

Producing chemical weapons

The wide variety of chemical and biological agents means that there are many dangerous substances available for acts of war and terror. But how likely is it that small countries and terrorist groups could develop these weapons? To help answer this question, we need to know a little about what kind of materials, equipment, and techniques are required to create chemical and biological weapons.

Substances that might be used in the production of chemical weapons are commonly used in many manufacturing industries, including the paper, rubber, pharmaceutical, insecticide, and plastics industries. For a country or terrorist group to manufacture chemical weapons, it would therefore need the same raw materials used by these industries. These include a wide variety of chemicals that are mixed together to form new chemical compounds. For example, hydrochloric acid and ethylene are two precursor chemicals used to make mustard gas. Other precursor chemicals include isopropyl alcohol, solid sulfur, fluorine, and compounds in such products as cleaning solutions, pesticides, and dyes. Terrorists interested in making chemical weapons could probably get these raw materials from any chemical supply company.

To make chemical weapons from the precursor chemicals, the terrorists would also need such standard industry equipment as chemical reactor vessels, pumps, valves, and filters. The manufacture of nerve gases requires special heavy-duty equipment, such as glass-lined steel reactor vessels, because the chemicals are highly acidic and corrosive. To reduce the likelihood of accidents, the terrorists would have to make special nerve-weapon delivery systems, such as artillery shells or canisters, that keep the chemicals sealed up until the moment of explosion or release.

Producing biological weapons

To make biological weapons, a terrorist group would first need to obtain samples of the living organisms used in the weapons. Where might a group obtain these samples? Nature is one source. The anthrax bacterium, for example, is common among farm animals. The microbes can be obtained from these animals through various methods, including by removing the spores from contaminated meat by-products. Bacteria and virus samples might also be obtained from the tissues of human victims. Toxins can be extracted from certain kinds of algae, plants, and shellfish. Other sources of biological agents include germ banks, repositories for microorganisms used in research. Law enforcement authorities believe that criminals or terrorists could pose as legitimate researchers to purchase biological agents from germ banks.

Turning biological agents into weapons begins with the use of such basic laboratory equipment as Petri dishes for culturing bacteria and incubators for growing the microbes. Viruses are usually cultured inside fertilized chicken eggs in the laboratory. These techniques could be carried out in small and easily hidden facilities, such as a trailer, to produce limited quantities of biological agents. Larger-scale production of biological agents requires the use of fermenters, tanks in which microbes are grown in a chemical solution or tissue culture.

Although it may be relatively easy to obtain and grow a biological agent, the weaponization of a biological agent is more difficult and involves fairly advanced processing techniques. For example, the anthrax spores used in the mailings of 2001 had to be processed to make the clumps of spores small enough to stay suspended in the air so they could be inhaled and lodge in the lungs. A milling machine with tiny glass or ceramic ball bearings was probably used to grind the spores into a fine powder. The anthrax spores may also have been treated with certain chemicals to neutralize electric charges that would have caused the spores to stick to each other and to surfaces, preventing them from staying suspended in the air.

Thus, the manufacture of chemical and biological weapons requires a number of skills. Nevertheless, experts believe that any group or government with enough funds, organizational ability, and technological know-how would be capable of making--or at least purchasing--chemical and biological weapons and using them to carry out attacks.

In 2001, according to a report by the U.S. Department of Defense, more than 20 countries possessed, or were in the process of acquiring, chemical or biological weapons and the means to deliver them. The United States officially ended its own offensive biological weapons program in 1969 and began destroying its chemical weapons stockpile in 1990. Many international affairs experts believe that the United States and its allies have the most to fear from various rogue nations that possess chemical or biological weapons and might give or sell them to terrorist groups. Besides Iraq, such nations included Iran, Syria, Libya, Sudan, and North Korea. United States officials were not sure which terrorist groups possessed chemical or biological weapons or the systems to deliver them, though al-Qaida--the radical Islamic network responsible for the Sept. 11, 2001, attacks--was suspected to be one such group.

Guarding against the threat

The international community has taken several actions to try to slow the spread of chemical and biological weapons. In 1975, the Biological and Toxin Weapons Convention (BTWC) went into effect, banning the development, stockpiling, transfer, and use of biological weapons worldwide. In 1997, the Chemical Weapons Convention (CWC) took effect, placing similar restrictions on chemical weapons. By 2002, each of these international agreements had been ratified by more than 140 nations, including the United States. Although the CWC has an enforcement mechanism, including on-site inspections of chemical facilities, the BTWC lacks that power. Negotiators were seeking to develop a verification system for the BTWC in 2002.

The U.S. government has instituted a number of special programs to protect the public against chemical and biological threats. Among them is the National Pharmaceutical Stockpile Program, operated by the Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia. The stockpile program is a national repository of antibiotics, chemical antidotes, antitoxins, life-support medications, and other medical and surgical items available to state and local health agencies in the event of a chemical or biological emergency. In another national program, federal officials are training local police, fire, emergency response, and health-care personnel in the best ways to respond to chemical and biological attacks. In light of the anthrax mailings, the U.S. Postal Service installed irradiation machinery at some of its facilities. These machines zap the mail with high-speed electron beams that kill microorganisms.

In February 2002, President George W. Bush proposed a nationwide "early warning system" for biological attacks based on one in Pennsylvania called the Real-time Outbreak and Disease Surveillance system, operated by the University of Pittsburgh. In this system, public health authorities track the incidence of various diseases, looking for unusual clusters of cases or other signs that an outbreak might have been deliberately caused.

The anthrax episodes led people to wonder if there was anything they could do to protect themselves against chemical and biological attacks. Many people thought they should purchase gas masks, stock up on antibiotics, or get preventive vaccinations. However, experts point out that such steps carry a number of risks. For example, a protective mask is effective against only some chemical and biological threats, and if a person is not adequately trained in the use of a mask and its filters, it may not provide any protection at all. Furthermore, by the time an individual becomes aware of a chemical or biological attack, it may be too late for a mask to do any good. In addition, physicians warn that antibiotics and vaccines are powerful drugs that can cause serious side effects. According to most public health experts, the wisest thing a person can do in the event of a chemical or biological threat is tune into the media for official directions from government authorities.

Before 2001, it had never occurred to most Americans that a determined individual or group would try to kill innocent people by purposely stuffing germs into an envelope and then sending the envelope through the mail. The anthrax mailings served as a wake-up call to the public that such danger is real. The next biological or chemical attack could be even more deadly. However, continued heightened vigilance on the part of the public and government may help ensure that chemical and biological weapons do not become the nightmare that they could be.

About the author:

Eric Croddy is an analyst at the Center for Nonproliferation Studies at the Monterey Institute of International Studies in California and the author of Chemical and Biological Warfare: A Comprehensive Survey for the Concerned Citizen.

Terms and concepts

Questions for thought and discussion

More than 140 nations have signed agreements banning the production and use of chemical and biological weapons. Yet, according to the U.S. Department of Defense, several countries, including Iraq, Iran, North Korea, and Syria, may possess offensive chemical and biological weapons. Many of these states are believed to have links to terrorist organizations.

Suppose you are hired by the United Nations to come up with a plan for ensuring that the chemical and biological weapons are never used. The first thing you must do is put together an international team of advisers. What nations would you like represented on this team and why?

You will also need scientific experts on your team. What types of scientists do you think could provide useful advice? Make a list of the questions you would ask them.

For additional information:

Books and periodicals

Croddy, Eric, with Perez-Armendariz, Clarisa, and Hart, John. Chemical and Biological Warfare: A Comprehensive Survey for the Concerned Citizen. Copernicus Books, 2002.

Miller, Judith; Engelberg, Stephen; and Broad, William J. Germs: Biological Weapons and America's Secret War. Simon and Schuster, 2001.

Web sites

The Henry L. Stimson Center, Chemical and Biological Weapons Nonproliferation Project:

Monterey Institute of International Studies, Chemical and Biological Weapons Resource Page:

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