█ BRIAN HOYLE
Decontamination refers to the efforts to safeguard property and people that have been exposed to chemical, nuclear, or biological agents. The intent of decontamination is twofold. The first objective is to make the individual free from the contaminant, or, if complete removal of the agent is impossible, to reduce the concentration of the contaminant to a level that is safe for survival. The second objective is to make property safe for habitation.
Human decontamination can involve removal of a contaminant from the skin. Usually such decontamination must be done quickly, since the contaminant may be absorbed through the skin where it can cause internal damage. In a setting such as the home, laboratory, or factory, permanent decontamination facilities can be present. For example, washrooms equipped with arm-activated water taps and antiseptic soap allow for the rapid removal of personal spills. Decontamination is also possible "in the field", courtesy of emergency response personal decontamination kits, which can be carried with workers or soldiers.
In April, 2003, military forces of the United States, Britain, and Australia faced the prospects of chemical and biological weapons attacks by forces in Iraq, as well as decontamination resulting from the deliberate destruction of oil installations and the discovery and destruction of stored biological and/or chemical weapons. For these forces, rapid response decontamination strategies are a prudent and vital precaution during the conflict.
There are a variety of decontamination methods and strategies that can be brought to bear on a chemical problem. Often, the method selected depends on the nature of the contaminant. For example, vacuuming up a spill of a powdery chemical can be a prudent step, while the same technique would be inappropriate for a liquid spill.
There are three general chemical decontamination methods. These methods involve physical, chemical, or thermal processes.
Physical methods. Liquid chemicals can be removed from inert surfaces or living surfaces (i.e., skin) by the use of sorbents. The sorbent can be a natural material, such as soil, diatomaceous earth, or activated charcoal, or can be synthetic (i.e., Amberlite XAD-2 and XAD-7 resins). In general, the natural materials absorb, or suck up, the liquid contaminants, while the synthetic materials adsorb contaminants. Adsorption involves the concentration of a substance from the liquid phase onto the surface of the adsorbent material due to the chemistry of the surface molecules.
The most recognizable solid absorbent is a clay material known as Fuller's Earth. This material is commonly found in kitty litter. When solid absorbent materials like Fuller's Earth, soil, or diatomaceous earth are used, the contaminant is usually not altered. For example, petroleum products are readily absorbed but are not changed in their character. Thus, the sorbent material becomes toxic and so must be collected and disposed of afterwards. Caution needs to be taken during the collection process, as fine dust or particles can be inhaled or stuck to exposed skin.
A different type of physical decontamination involves washing the contaminant away using another fluid like water, an alcohol, or freon. The aim here is to dilute the
contaminant in the wash fluid, which should itself be collected for proper disposal. Washing is not a complete decontamination. Residual contaminant can remain behind in cracks or other hiding places. However, the use of high-pressure sprays can be an effective and rapid means of decontaminating surfaces like walls and floors.
Chemical methods. Chemical decontamination goes further than merely removing a contaminant from the environment. Rather, in chemical decontamination the adsorbing chemical neutralizes a contaminant. One example of chemical neutralization is the adsorption of a contaminant by material that is impregnated with an alkaline chemical. Another general example is the use of chemically reactive compounds that interact with the contaminant and change its structure into a form that is non-toxic.
A popular chemical decontamination strategy relies on the use of oxidizing agents. Bleach is a well-known example of an oxidizing agent. The use of oxidizing compounds such as calcium hypochlorite or sodium hypochlorite inactivates a variety of chemical compounds as well as dangerous microorganisms such as bacteria and viruses.
Oxidizing agents can be wiped onto a spill and collected in an absorbent material. As well, some oxidizing agents can be incorporated into topical lotions, which are smeared onto the skin to help inactivate a chemical or biological spill.
A recent innovative example of an oxidizing agent is L-Gel. Developed at Lawrence Livermore National Laboratory, L-Gel uses potassium peroxymonosulfate to deactivate a variety of biological agents, including anthrax spores and Yersinia pestis (the bacterium that causes plague). The thick gel is able to cling to surfaces better than water, especially to steeply sloping surfaces like walls, which keeps the decontaminant in contact with the target longer than using a straight water-based decontaminant. It is hoped that a powdered formulation of the product will soon be available for use in ventilation ducts, where clean up of chemical and biological agents is especially difficult.
During the fall of 2001, L-Gel was successfully used to decontaminate offices of Congress and at ABC News following the receipt of letters that were laced with anthrax spores.
Strong bases, such as hydroxide forms of calcium, sodium hydroxide, and potassium are other useful chemical decontaminants. These agents disrupt chemical bonds in the contaminant and so destroy the offending compounds' noxiousness.
Water is an ideal fluid for decontamination because a variety of chemically different detergents and soaps readily dissolve in water. These compounds can loosen or bind contaminants and so remove them from a surface. The friction of scrubbing also aids in decontamination of the skin during hand washing.
The different tendencies of chemicals to dissolve in water (a property known as solubility) affects the efficiency of a decontaminant. For example, a longer period of decontamination is needed when using a compound that is not readily soluble in water. This problem can be somewhat overcome by the use of microemulsions, which are essentially very small droplets of the decontaminant. The droplet coat is a material that is less water-soluble. The effect is best seen when oil is added to water. Then, a sheen of oil appears on the water, rather than a homogeneous oil-water mixture. If a contaminant is not water soluble, it will quickly partition into the hydrophobic ("water-hating") decontaminant portion of a microemulsion. This can speed up the action of a decontaminant. Microemulsions can be applied to a contaminated surface as a spray, which can be washed off later.
Thermal methods. Thermal decontamination is the use of heat to vaporize those chemical contaminants that will readily convert from a liquid to a gas in the presence of heat. Both water- and alcohol-based chemicals can exhibit this behavior.
Water can also be heated, even to the extent of being converted to steam. Hot water or steam treatment can be an efficient means of decontamination of greasy or oily contaminants. The use of moist heat, as in the laboratory sterilization unit called an autoclave, disrupts chemical bonds in many microorganisms, killing them. Unfortunately, certain noxious bacteria that form spores (i.e., Bacillus anthracis , Clostridium species) can, under some circumstances, survive autoclaving.
Hot air is another useful decontaminant for compounds that can be volatilized. This method is useful for situations where a spill can be isolated and treated over a longer period of time. In a battlefield situation, other more urgent methods are preferable.
Nuclear decontamination in a battlefield site, to date only applicable in the Japanese cities of Hiroshima and Nagasaki in the waning days of World War II, necessitates the removal, burial, or storage of the contamination. However, in sites such as decommissioned nuclear power plants or weapons manufacturing facilities, the less concentrated amounts of radioisotopes that are encountered can be more systematically decontaminated.
Nuclear decontamination consists of the removal of the contaminating radioisotope. Removal can be accomplished by the use of water-soluble chemicals (i.e., alkaline permanganate, citric oxalic acid), fire-fighting foam, and even the electrochemical treatment of the contaminated surface.
The specter of contamination with agents, in particular biological agents, was seared into the public consciousness in the latter months of 2001. Then, U.S. citizens were subjected to terrorist attacks as letters containing Bacillus anthracis , the bacterium that is the cause of anthrax were mailed through the U.S. Postal Service.
The concern over the use of biological weapons has not abated since that time. Indeed, the possibility of biological attack, and so the need for rapid decontamination, was one of the paramount concerns of U.S. troops and their allies involved in the war in Iraq in the winter and spring of 2003.
Suspected exposure to an aerosol of a dangerous microorganism should be dealt with promptly. The exposed clothing should be taken off and safely contained so as not to contaminate bystanders or medical personnel. It may be necessary to destroy clothing depending on the suspected contaminant. For example, spores of the anthrax bacteria can cling to clothing and retain their potential for infection for decades. Exposed skin should be decontaminated. The best strategy is to use soap and water with diligent scrubbing for at least 30 seconds. The use of diluted household bleach is acceptable.
Decontamination in the case of biological exposure is typically done in an isolated facility, where the access of personnel is tightly controlled, and the outgoing air can be filtered to prevent the spread of the biological agent. Such facilities are even used in the battlefield setting.
In battlefield settings such as Iraq, the military can use a dried resin known as M291. This resin is a dry black carbon containing material that decontaminates by absorption and physical removal of the chemical agents from the victim. M291 resin is particularly useful for localized ("spot") decontamination of exposed skin.
Organization of a military treatment area. Part of military strategy in conflicts where there is a potential for the use of biological or chemical weapons, as in the Iraq conflict of 2003, is the establishment of medical treatment facilities. In the battlefield a facility is divided into two zones. One zone (the "dirty" zone) is where contaminated personnel and equipment are segregated. The other, "clean" zone is kept free from the contaminating agents. The transition area between these zones, which is called the hotline, keeps contaminated people (including casualties) and equipment out of the clean side until decontamination is completed.
Triage, emergency treatment, and decontamination are done in the dirty zone. The emergency treatment station essentially treats patients as best as possible and stabilizes them for movement to the clean zone operation theatre, or evacuation to a hospital. Any decontamination is done in the dirty zone, with more substantive medical procedures being done in the clean zone.
The National Pharmaceutical Stockpile Program in the U.S. has assembled large quantities of antibiotics, vaccines, and other medical treatment countermeasures that can be rapidly deployed. For example, in the aftermath of the anthrax attacks in the U.S. during 2001, federal and state agencies were able to quickly provide the antibiotic ciprofloxacin (Cipro) to those potentially exposed to Bacillus anthracis .
In the event of a large scale contamination, such as the "dusting" of anthrax spores over a metropolitan area, large numbers of causalities would likely result, as decontamination strategies for such masses of people are still in the planning stages.
Decontamination during the Iraq War of 2003
The past deployment of chemical and biological weapons by the government of Iraq under Saddam Hussein, and the inconclusive findings of the United Nations weapons inspectors who were present in Iraq in 2002–2003, heightened concerns for the possible use of such weapons during the 2003 war between Iraq and coalition forces of the United States and the United Kingdom.
In the 1980–88 war with Iran, Iraq deployed chemical weapons that affected an estimated 100,000 Iranians, killing about 10,000 people. Even today, some 1,000 people are considered to be moderately to severely ill because of these attacks.
Another decontamination effort will be necessary to deal with the oil wells that have been set ablaze by Iraqi soldiers in the 2003 conflict. The residue given off by the blazing wells in sufficient numbers could be an environmental disaster, and is unhealthy to breathe. Unfortunately, decontamination is virtually impossible, other than to extinguish the blazes and to clean up the terrain immediately surrounding the wells once they have been extinguished.
Contamination of the drinking water supplies of southern Iraqi towns such as Safwan and Zubayr makes the possibility of disease more immediate. Post-war decontamination efforts involved the isolation and treatment of the contaminated surface and ground waters.
█ FURTHER READING:
Boss, Martha J., Dennis W. Day, and Roger F. Jones. Biological Risk Engineering Handbook: Infection Control and Decontamination. Boca Raton: Lewis Publishers, Inc., 2002.
Mauroni, Albert J. America's Struggle with Chemical-Biological Warfare. Westport, CN: Praeger Publishers, 2000.
United States Environmental Protection Agency. "Anthrax." EPAHome. January 14, 2003. < http://www.epa.gov/epahome/hi-anthrax.htm >(04 March 2003).