Chemical and Biological Warfare
CHEMICAL AND BIOLOGICAL WARFARE
CHEMICAL AND BIOLOGICAL WARFARE. While limited use of chemicals and disease in warfare dates from ancient times, the origins of modern chemical and biological weapons systems date from the era of the two world wars. The term chemical warfare came into use with the gas warfare of World War I, and modern biological warfare dates from the weapons systems first introduced in the 1930s.
Early Gas Warfare
Following the first successful German gas attack with chlorine in the World War I battle at Ypres in 1915, the British, French, and, in 1918, the U.S. armies responded with gases including phosgenes, mustard gas, hydrogen cyanide, and cyanogen chloride. Initially spread from portable cylinders by the opening of a valve, delivery systems were extended to mortars and guns. In 1918 the U.S. War
Department established the Chemical Warfare Service (CWS) as part of the wartime, but not the regular, army.
The specter of future gas warfare left by the war revived earlier efforts to ban chemical warfare. Gas caused 1 million of 26 million World War I casualties, including over 72,000 of 272,000 U.S. casualties. The first attempt to ban gas warfare was a separate proposition to the first Hague Peace Conference in 1899. The United States didn't sign, arguing that there was no reason to consider chemical weapons less humane than other weapons, and that since there were no stockpiles of gas weapons it was premature to address the issue. Following World War I, the United States signed but the Senate failed to ratify the 1925 Geneva Protocol prohibiting chemical weapons, again arguing that they were as humane as other weapons and that the United States needed to be prepared. This direction was anticipated when the immediate postwar debate in the United States over chemical warfare resulted in the CWS becoming a part of the regular army in 1920. In 1932, chemical warfare preparedness became U.S. military policy.
The use of gas warfare in the 1930s by Italy in Ethiopia, Japan in China, and possibly elsewhere increased concern going into World War II. But the gas war of World War I did not recur. U.S. strategists apparently considered using gas during one crisis in the Pacific, but President Franklin D. Roosevelt, who declared a retaliation-only policy on chemical warfare at the beginning of the war, with held his approval. The most significant development in chemical weapons during the war was the well-kept secret of German nerve gases.
Early Biological Warfare
Biological warfare received little attention in the United States prior to the outbreak of World War II. But with entry into the war, and growing awareness of other biological warfare programs, the United States established a large program and entered into a tripartite agreement with the programs of Canada and Great Britain.
These cooperating programs focused on antipersonnel weapons, while also doing anticrop and antianimal work. They experimented with a range of agents and delivery systems, and anthrax delivered by cluster bombs emerged as the first choice. A production order for an anthrax-filled bomb was canceled because the war ended. U.S. strategists considered using a fungus against the Japanese rice crop near the end of the war but dropped the plan for strategic reasons. Japan became the first nation to use a modern biological weapons system in war when it employed biological warfare against China.
Biological weapons introduced several new issues, including the ethical implications of the Hippocratic oath forbidding the use of medical science to kill. They also offered new military possibilities to be weighed in any debate over banning such warfare. The United States accepted the 1907 Geneva Regulations prohibiting biological weapons but subsequently joined Japan as the only nation not to ratify the ban in the 1925 Geneva Protocol. The United States again sidestepped the issue of biological weapons in the post–World War II United Nations negotiations to limit weapons of mass destruction. Meanwhile, U.S. strategic planners and their British partners advocated the tactical, strategic, and covert possibilities of biological weapons as well as their potential as weapons of mass destruction. They also emphasized the relatively low cost of such weapons and the fact that they did not destroy physical infrastructure, thus avoiding the costs of reconstruction.
The Cold War
In 1950 the U.S. government, concurrent with the growing tensions of the early Cold War, and especially the outbreak of the Korean War, secretly launched a heavily funded and far-ranging crash program in biological warfare. Gas warfare development expanded at an equal pace, especially work with nerve gas. Sarin was standardized in 1951, but emphasis shifted in 1953 to the more potent V-series nerve gases first developed by the British. VX was standardized in 1957, though a standardized delivery system was not developed. But biological warfare had a higher priority than chemical: indeed, the biological warfare crash program introduced in 1950 shared highest-level priority with atomic warfare. The primary objective for biological weapons was to acquire an early operational capability within the emergency war plan for general war against the Soviet Union and China. By the time of the Korean War, an agent and bomb were standardized both for anticrop and antipersonnel use while research and development went forward with a broad range of agents and delivery systems. In the post–Korean War period many agents and several delivery systems were standardized, one of the more interesting being the standardization in 1959 of yellow fever carried by mosquito vectors. Further, the U.S. government secretly took over the Japanese biological warfare program, acquiring records of experiments with live subjects that killed at least 10,000 prisoners of war, some probably American. In exchange, the perpetrators of the Japanese program were spared prosecution as war criminals.
Another indication of the priority of biological warfare was the adoption in early 1952 of a secret first-use strategy. U.S. military strategists and civilian policymakers took advantage of ambiguities in government policy to allow the Joint Chiefs of Staff (JCS) to put a secret offensive strategy in place. Though the United States reaffirmed World War II retaliation-only policy for gas warfare in 1950, the JCS after some debate decided that it did not by implication apply to biological warfare. They concluded there was no government policy on such weapons, and the Defense Department concurred. Consequently the JCS sent directives to the services making first-use strategy operational doctrine, subject to presidential approval. During the Korean War, the United States also created a deeply buried infrastructure for covert biological warfare in the Far East. Data from the Chinese archives for the Korean War, corroborated by evidence from the U.S. and Canadian archives, builds a strong case for the United States experimenting with biological weapons during the Korean War. The issue remains controversial in the face of U.S. government denial. In 1956 the United States brought policy into line with strategic doctrine by adopting an official first-use offensive policy for biological warfare subject to presidential approval.
Escalation and the Search for Limits
In 1969, President Richard M. Nixon began changing U.S. policy with regard to chemical and biological warfare. In the midst of growing public and congressional criticism over the testing, storage, and transportation of dangerous chemical agents, Nixon resubmitted the 1925 Geneva Protocol, which the Senate ratified in 1974. But the United States decided there was evidence the Soviets had chemical weapons in their war plans, which set off efforts to reach agreement with the Soviets on a verifiable ban while at the same time returning to a posture of retaliatory preparedness. In 1993 the United States joined Russia and other countries in signing the Chemical Weapons Convention. The Senate delayed ratification because it was dissatisfied with the lack of "transparency" in the Russian and other programs. But negotiations continued and further agreements were reached between the U.S. and Russia.
Nixon also unilaterally dropped biological warfare from the U.S. arsenal in 1969, and in 1972 the United States signed the Biological Warfare Convention banning all but defensive preparations. The Senate ratified the convention in 1974. Negotiations to extend the 1972 convention to include an adequate inspection system continued with little progress through most of the 1990s, and early in his presidency George W. Bush withdrew from these negotiations.
Attempts to limit biological weapons under international law floundered for several reasons. There was no accord on the terms of an inspection agreement. Mutual suspicions were heightened by the Russian government's admission that their Soviet predecessors had violated the 1972 convention, and by charges and counter-charges of hidden capabilities across the international landscape.
This unrest was enhanced by a generation of growing use of biological and chemical weapons. The United States had used the biological anticrop Agent Orange in the Vietnam War. Chemical weapons were used in the Iran-Iraq war and by Iraq against the Kurds. The Soviets apparently used chemical weapons in Afghanistan, and there were unconfirmed reports of the use of both chemical and biological weapons elsewhere.
Also highly controversial was the issue of whether provisions for defense against biological warfare under the 1972 convention provided an opening for research for offensive use. Concern in this respect increased with greatly expanded funding for defense against biological weapons; evidence of offensive work hiding under the rubric of defensive work; new possibilities with recombinant DNA and genetic engineering; and pressures for preparedness arising from the 11 September 2001 terrorist attack on the United States. At the beginning of the new millennium these considerations thickened the fog surrounding the question of whether biological and chemical warfare would be limited or extended.
BIBLIOGRAPHY
Brown, Frederic J. Chemical Warfare: A Study in Restraints. Princeton, N.J.: Princeton University Press, 1968. Reprint, Westport, Conn.: Greenwood Press, 1981.
Cole, Leonard. The Eleventh Plague: The Politics of Biological and Chemical Warfare. New York: Freeman, 1997.
Endicott, Stephen, and Edward Hagerman. The United States and Biological Warfare: Secrets from the Early Cold War and Korea. Bloomington: Indiana University Press, 1998.
Harris, Robert, and Jeremy Paxman. A Higher Form of Killing: The Secret History of Chemical and Biological Warfare. New York: Hill and Wang, 1982.
Harris, Sheldon H. Factories of Death: Japanese Biological Warfare, 1932–45, and the American Cover-Up. London and New York: Routledge, 1994. Rev. ed., New York: Routledge, 2002.
Miller, Judith, Stephen Engelberg, and William Broad. Germs: Biological Weapons and America's Secret War. New York: Simon and Schuster, 2001.
EdwardHagerman
See alsoBioterrorism .
Chemical Biological Incident Response Force, United States
Chemical Biological Incident Response Force, United States
█ JUDSON KNIGHT
The Chemical and Biological Incident Response Force (CBIRF) is a unit of the United States Marines devoted to countering chemical or biological threats at home and abroad. Activated in 1996, the unit served a number of protective functions. Since the terrorist bombings of September 11, 2001, however, its prominence has increased dramatically. Now part of the 4th Marine Expeditionary Brigade (MEB), it has performed homeland security functions that included the removal of suspected toxic agents from House and Senate office buildings during a rash of anthrax attacks in late 2001.
Background and Mission
Chemical agents have been a widespread threat since World War I, when first used by German forces on the Eastern Front in 1915. Soon the British developed their own chemical weapons, and the age of chemical warfare began, forever altering the battlefield equation. Use of chemical weapons by Saddam Hussein on Kurdish civilians, use by both Iran and Iraq during their prolonged war in the 1980s, and use during the 1994 and 1995 attacks by Aum Shinrikyo (a Japanese cult) that released deadly sarin gas into the Tokyo subways and killed 12 civilians, demonstrate that both military and civilian personnel are increasingly vulnerable to chemical attacks.
On June 21, 1995, partly in response to the Aum Shinrikyo attacks, as well as the Oklahoma City bombing on April 19 of that year, the administration of President William Jefferson Clinton issued Presidential Decision Directive 39, "United States Policy on Counterterrorism." The directive called for a number of specific efforts to deter terrorism on America's shores, as well as that against Americans and allies abroad. In response to the need for a response team to deal with chemical and biological threats, the United States Marine Corps established CBIRF (the first two words are sometimes rendered as "Chemical Biological" or "Chemical, Biological) on April 4, 1996.
Training exercises. Writing in the Marine Corps magazine Leatherneck, Margaret Bone described CBIRF thus in early 1999: "It's new, it's unique to the Armed Services, and right now, it's the only quick reaction force in the world equipped to help in the aftermath of a chemical, biological, or radiological (nuclear) attack." But the writer went on to note that "CBIRF is not a counterterrorist group, and it's not direct-action oriented, though there is a security element of more than 120 Marines, with the capability to increase that strength as needed." In the words of a force protection element commander for CBIRF, "We are a consequence management force. Our mission is to respond, to come in and save lives. We bring the full package: self-contained, expeditionary, and task-organized."
During the spring and early summer of 1996, CBIRF was deployed for training in a variety of environments throughout the United States. Its members closely studied the bombing that took place at Centennial Olympic Park in Atlanta on the night of July 27, and practiced coordinating a response with local fire and police. They also undertook an experiment at the Citadel, a military college in Charleston, South Carolina, where CBIRF personnel acted to control lethal agents released by a mock chemical weapons plant. Moving beyond training to real-world situations, CBIRF provided security for President Clinton's second inauguration in January 1997, and for the Summit of Eight in Denver, Colorado, that following summer.
A changing role. In the aftermath of the September 11, 2001, terrorist attacks on the United States, CBIRF's mission became incorporated into the 4th MEB, along with the Marine Security Force Battalion, the Marine Security Guard Battalion, and the new anti-terrorism battalion. (The latter had evolved from the 1st Battalion, 8th Marines, which had been hit in the 1983 terrorist bombings of United States Marine barracks in Lebanon.) In December 2001, CBIRF sent a 100-member initial response team into the Dirksen Senate Office Building alongside Environmental Protection Agency (EPA) specialists to detect and remove anthrax. A similar mission was undertaken at the Longworth House Office Building in October, during which time samples were collected from more than 200 office spaces.
█ FURTHER READING:
PERIODICALS:
Bone, Margaret. "Marines Provide Safety Net to Terrorist
Threat." Leatherneck 82, no. 2 (February 1999): 50–53.
Cabellon, Paul C. "CBIRF Takes the (Capitol) Hill." Leatherneck 85, no. 2 (February 2002): 19.
Garamone, Jim. "Marines to Stand up Anti-Terror Brigade." Pentagon Brief (October 2001): 5.
Vogel, Steve. "Cooler Name Prevails for 'Hot' New Marine Corps Club at Indian Head." Washington Post. (April 26,2001): T15.
SEE ALSO
Chemical Safety: Emergency Responses
Chemical Warfare
Chemical and Biological Detection Technologies
Chemical and Biological Detection Technologies
█ BRIAN HOYLE
The ability to detect the components of chemical and biological weapons is an important part of a national security strategy. For example, the inability to rapidly detect letters for the presence of anthrax spores provided a route for the targeting of infectious microorganisms in the United States in 2001. The portability of chemical and biological weapons has made them attractive to individuals or groups with political, religious, or other grievances. This has spurred development of more sophisticated, accurate and rapid detection technologies.
The conventional x-ray technology long used in airports has been refined. Most of the x-ray beam is reflected back immediately upon encountering an object. Some of the radiation, however, passes through the object. By analyzing the beams that actually penetrate through an object, information on the object's composition is provided. Another version sends two different x rays of different wavelengths through an object. The different beams can distinguish between organic objects, such as food and paper, and inorganic objects.
A chemical detection technology known as gas chromatography has been sped into routine use in airports since the U.S. terrorist attacks of September 11, 2001. The different chemicals present on a cloth that is swiped over an object can be separated based on their different preference for the gas mixture that is pumped through the sample chamber. A target chemical (i.e., an explosive) is detected within seconds.
Chemical detection technologies have also been adapted for use "in the field", such as by United Nations inspectors deployed in Iraq beginning in November 2002, to the presence of missiles that were supposedly destroyed by the Iraqi government in the mid-1990s.
Sound can be used to detect chemicals. For example, the acoustic wave sensor uses a quartz surface to convert incoming sound waves into electrical signals. Over a dozen different chemicals can be detected within seconds, even from biological sources. In another sound-based technique called acoustic resonance, the pattern of vibrations when sound waves are sent inside an object like a missile can reveal whether the missile is filled with a solid or a liquid, and even the type of chemical present.
Light is another means of chemical detection. The use of light is called spectroscopy. Mass spectroscopy determines the mass of proteins, which is important in determining the identity of the chemical or biological agent. Matrix-Assisted Laser Desorption/Ionization Mass Spectroscopy (MALDI-MS) can identify proteins that are unique to Bacillus anthracis (the cause of anthrax) and Yersinia pestis (the cause of plague). Raman spectroscopy measures the change in the wavelength of a light beam by the sample molecules. Optical spectroscopy measures the absorption of light by the chemical groups and the subsequent emission of light by the same groups as the identification method.
The ability to detect genetic sequences that are unique to certain bacteria (gene probing) has been exploited to develop genetically based microbial detection methods. The best example of gene probing is the polymerase chain reaction (PCR), which can enzymatically detect a target stretch of genetic material and rapidly amplify that region to detectable levels. Handheld PCR detectors (i.e., Handheld Advanced Nucleic Acid Analyzer, or HANAA) were used in the 2002–2003 inspections of Iraqi facilities by United Nations officials.
Biological detection devices can monitor the surrounding air at regular intervals. Air is automatically drawn into the device and analyzed for target genetic sequences using the PCR technology. The results can be electronically relayed to a central base for analysis.
Another biological technology utilizes antibodies that are produced in response to the presence of a specific microorganism. Tests are available that detect Bacillus anthracis, Clostridium botulinum, viruses (e.g., smallpox), and chemicals (e.g., ricin) in minutes.
Some older biological detection technologies still prove reliable. Growth of microorganisms on artificial food sources (media) produces populations called colonies. Medium can be selected that produces colonies that have a distinctive appearance and color. Gel electrophoresis separates differently sized pieces of genetic material or other microbial components (e.g., protein) into bands. The banding pattern can be used to identify the microorganism. Finally, chromatography separates compounds from one another based on their differing speed of movement through a gas or a liquid mixture.
█ FURTHER READING:
BOOKS:
Cilluffo, Frank J., Sharon L. Cardash, and Gordon Nathaniel Lederman. Combating Chemical, Biological, Radiological, and Nuclear Technologies: A Comprehensive Strategy: A Report of the Csis Homeland Defense Project. Washington, D.C.: Center for Strategic and International Studies, 2001.
Fritz, Sandy, and Jack Brown. Understanding Germ Warfare (Science Made Accessible). New York: Warner Books, 2002.
Lederberg, Joshua, and William S. Cohen. Biological Weapons: Limiting the Threat (BCSIA Studies in International Security). Boston: MIT Press, 1999.
United States Department of Defense. 21st Century Bioterrorism and Germ Weapons: U.S. Army Field Manual for the Treatment of Biological Warfare Agent Casualties (Anthrax, Smallpox, Plague, Viral Fevers, Toxins, Delivery Methods, Detection, Symptoms, Treatment, Equipment). Washington, D.C.: Progressive Management, 2001.
SEE ALSO
Air Plume and Chemical Analysis
Biocontainment Laboratories
Bomb Detection Devices
Chemical Biological Incident Response Force, United States
Chemical Biological Incident Response Force, United States
The Chemical and Biological Incident Response Force (CBIRF) is a unit of the United States Marines devoted to countering chemical or biological threats at home and abroad. Activated in 1996, the unit serves a number of protective functions. Since the terrorist bombings of September 11, 2001, its prominence has increased dramatically. Now part of the 4th Marine Expeditionary Brigade (MEB), it has performed homeland security functions that included the removal of suspected toxic agents from House and Senate office buildings during a rash of anthrax incidents that followed the September terrorist attacks in 2001. CBIRF is a precursor to investigative efforts of forensic experts.
Chemical agents have been a widespread threat since 1915, when first used by German forces on the Eastern Front in World War I. Soon the British developed their own chemical weapons, and the age of chemical warfare began, forever altering the battlefield equation. Both military and civilian personnel are increasingly vulnerable to chemical attacks, as evidenced by use of chemical weapons by Saddam Hussein on Kurdish civilians, use by both Iran and Iraq during their prolonged war in the 1980s, and use during the 1994 and 1995 attacks by Aum Shinrikyo (a Japanese cult) that released deadly sarin gas into the Tokyo subways, the latter of which killed 12 civilians.
On June 21, 1995, partly in response to the Aum Shinrikyo attacks, as well as the Oklahoma City bombing on April 19 of that year, the administration of President William Jefferson Clinton issued Presidential Decision Directive 39, United States Policy on Counterterrorism. The directive called for a number of specific efforts to deter terrorism in the United States, as well as that against Americans and allies abroad. In response to the need for a response team to deal with chemical and biological threats, the United States Marine Corps established the Chemical Biological Incident Response Force (CBIRF) on April 4, 1996.
In a 1999 article in the Marine Corps magazine Leatherneck, the CBIRF was described thus: "It's new, it's unique to the Armed Services, and right now, it's the only quick reaction force in the world equipped to help in the aftermath of a chemical, biological, or radiological (nuclear) attack." In the words of a force protection element commander for CBIRF, "We are a consequence management force. Our mission is to respond, to come in and save lives. We bring the full package: self-contained, expeditionary, and task-organized."
During the spring and early summer of 1996, CBIRF was deployed for training in a variety of environments throughout the United States. Its members closely studied the bombing that took place at Centennial Olympic Park in Atlanta on the night of July 27, and practiced coordinating a response with local fire and police. They also undertook an experiment at The Citadel, a military college in Charleston, South Carolina, where CBIRF personnel acted to control lethal agents released by a mock chemical weapons plant. Moving beyond training to real-world situations, CBIRF provided security for President Clinton's second inauguration in January 1997, and for the Summit of Eight in Denver, Colorado, that following summer.
In the aftermath of the September 11, 2001, terrorist attacks on the United States, CBIRF's mission became incorporated into the 4th MEB, along with the Marine Security Force Battalion, the Marine Security Guard Battalion, and the new anti-terrorism battalion. (The latter had evolved from the 1st Battalion, 8th Marines, that had been hit in the 1983 terrorist bombings of United States Marine barracks in Lebanon.) In December 2001, CBIRF sent a 100-member initial response team into the Dirksen Senate Office Building alongside Environmental Protection Agency (EPA) specialists to detect and remove anthrax. A similar mission was undertaken at the Longworth House Office Building in October, during which time samples were collected from more than 200 office spaces.
see also Anthrax, investigation of the 2001 murders; Chemical warfare; Oklahoma bombing (1995 bombing of Alfred P. Murrah building); Sarin gas; September 11, 2001, terrorist attacks (forensic investigations of).
Chemical and Biological Detection Technologies
Chemical and Biological Detection Technologies
A well-recognized national security issue is the detection of chemicals and either biological agents or their components (i.e., toxins ). For example, the inability to rapidly inspect mailed letters for the presence of anthrax spores provided a route for the targeting of the mail with infectious microorganisms in the United States in 2001. This demonstration has spurred development of more sophisticated, accurate, and rapid detection technologies. Aside from national security concerns, detection of chemical and biological compounds is important in a forensic investigation.
X-ray examination has long been of value in scanning luggage at airports. The same technology can be used locate objects hidden inside other objects. As well, newer x-ray technology enables the discrimination of organic from inorganic objects. Most of the x-ray beam is reflected back immediately upon encountering an object. Some of the radiation, however, passes through the object. By analyzing the beams that actually penetrate through an object, information on the object's composition is provided. Another version sends two different x rays of different wavelengths through an object. The different beams can distinguish between organic objects, such as food and paper, and inorganic objects.
A chemical detection technology known as gas chromatography has been sped into routine use in airports since the U.S. terrorist attacks of September 11, 2001. The different chemicals present on a cloth that is swiped over an object can be separated based on their different preference for the gas mixture that is pumped through the sample chamber. A target chemical (i.e., an explosive) is detected within seconds.
Chemical detection technologies have also been adapted for use "in the field," such as by United Nations inspectors deployed in Iraq beginning in November 2002, to the presence of missiles that were supposedly destroyed by the Iraqi government in the mid-1990s. These portable technologies are beginning to find their way into forensic use.
Sound can also be used to detect chemicals. For example, the acoustic wave sensor uses a quartz surface to convert incoming sound waves into electrical signals. Over a dozen different chemicals can be detected within seconds, even from biological sources. In another sound-based technique, called acoustic resonance, the pattern of vibrations when sound waves are sent inside an object can reveal whether the object is filled with a solid or a liquid, and even the type of chemical present.
Light is another means of chemical detection. The use of light is called spectroscopy . Mass spectroscopy determines the mass of proteins, which is important in determining the identity of the chemical or biological agent. Matrix-Assisted Laser Desorption/Ionization Mass Spectroscopy (MALDI-MS) can identify proteins that are unique to Bacillus anthracis (the cause of anthrax) and Yersinia pestis (the cause of plague). Raman spectroscopy measures the change in the wavelength of a light beam by the sample molecules. Optical spectroscopy measures the absorption of light by the chemical groups and the subsequent emission of light by the same groups as the identification method.
The ability to detect genetic sequences that are unique to certain bacteria (gene probing) has been exploited to develop genetically based microbial detection methods. The best example of gene probing is the polymerase chain reaction (PCR ), which can enzymatically detect a target stretch of genetic material and rapidly amplify that region to detectable levels. Hand-held PCR detectors (i.e., Handheld Advanced Nucleic Acid Analyzer , or HANAA), used in the 2002–2003 inspections of Iraqi facilities by United Nations officials, are already being exploited in law enforcement.
Biological detection devices can monitor the surrounding air at regular intervals. Air is automatically drawn into the device and analyzed for target genetic sequences using the PCR technology. The results can be electronically relayed to a central database for analysis and shared with other law enforcement agencies.
Another biological technology utilizes antibodies that are produced in response to the presence of a specific microorganism. Tests are available that detect Bacillus anthracis, Clostridium botulinum, viruses (e.g., smallpox ), and chemicals (e.g., ricin ) in minutes.
Some older biological detection technologies still prove reliable in forensic analyses. Growth of micro-organisms on artificial food sources (media) produces populations called colonies. A medium can be selected that produces colonies that have a distinctive appearance and color. Gel electrophoresis separates differently sized pieces of genetic material or other microbial components (e.g., protein) into bands. The banding pattern can be used to identify the microorganism. Finally, chromatography separates compounds from one another based on their differing speed of movement through a gas or a liquid mixture.
see also Aflatoxin; Bacterial biology; Bioterrorism; Chemical warfare.