Decontamination removes hazardous material from the environment, objects, or people, including biological, chemical, or radiological hazards. Methods vary depending on the contaminant and what needs to be decontaminated, including physical removal, neutralization, or rendering harmless by chemical means. Strong disinfectants are used for decontaminating rooms and buildings, while human decontamination involves removing clothing and washing exposed skin with mild disinfectants. Toxic heavy metals may require physical removal or chelating agents, while radioactive substances require physical removal and safe disposal. Phytoextraction and electrokinetic techniques are sometimes effective for contaminated soils.
Decontamination is a process by which hazardous material is removed from the environment, buildings, objects or people. The nature of the hazard can be biological, chemical or radiological. Usually the material poses a direct threat to humans, but in some cases the threat can be indirect or economic, such as insect pests or plant or animal diseases. Sometimes the decontamination process involves the physical removal of the material in question, while in others it can be neutralized or rendered harmless by chemical means.
Biological hazards include microbial pathogens such as bacteria, viruses and parasites. The decontamination procedures employed will depend on both the nature of the contaminant and what needs to be decontaminated. Small objects, such as surgical instruments, can be decontaminated by heating, for example in an autoclave. Decontaminating rooms and buildings usually involves the use of strong disinfectants: strong oxidizing agents, such as chlorine, chlorine dioxide or hydrogen peroxide, or toxic organic chemicals such as formaldehyde or phenol. Following the anthrax attacks in the United States in 2001, premises likely to harbor anthrax spores were decontaminated using chlorine dioxide gas, a highly effective biocide.
Dealing with medium containing human pathogens is more problematic. During World War II, anthrax spores were released on Gruinard Island, a small island off the northwest coast of Scotland, in an experiment to monitor the effects of a potential biological weapon. As a result, the island was closed to the public for nearly 50 years. In 1986, the island was decontaminated using huge amounts of a formaldehyde solution in seawater. The island was finally declared safe in 1990.
Due to their toxicity and corrosiveness, strong disinfectants cannot be used to decontaminate people. Human decontamination generally involves the removal and safe disposal of clothing, followed by washing exposed skin with a mild disinfectant, such as a 0.5% aqueous solution of sodium or calcium hypochlorite. If, however, the agent is infectious or contagious, it may be necessary to quarantine exposed people to prevent the spread of disease.
Where the hazard is chemical in nature, buildings can be decontaminated using chemicals which render the hazardous agent relatively harmless. As with biohazards, toxic organic chemicals can often be decomposed using strong oxidizing agents. A mild hypochlorite solution can be applied to the skin to decontaminate people exposed to these toxins; in the event of human exposure it is important that the chemical is removed as quickly as possible.
In the case of toxic heavy metals, physical removal of the substance by thorough washing and safe wastewater disposal may be more appropriate. Where heavy metals have been ingested, chelating agents may be employed. These substances bind to and trap metal ions, rendering them inactive and removing them from the system.
The decontamination of soils containing toxic metals, usually following industrial pollution, can be divided into in-situ and ex-situ methods. In situ methods may involve electrokinetic and electroacoustic methods, in which metal ions in moist soil are mobilized by an electrical potential, aided by vibration to increase porosity, so that they migrate across a hydraulic gradient and can be pumped out through a well. . Another method is phytoextraction, in which plants capable of absorbing the metal, yet remaining relatively unaffected by it, are used to remove it from the soil. Ex-situ methods involve bulk removal of the soil, chemical or scrubbing treatment, and returning the cleaned soil to the site.
Some of the above methods are also effective for radioactive substances. However, there is no practical way to render a radioactive item non-radioactive, so decontamination methods must focus on physical removal and safe disposal of the item. Radioactivity is easily detectable and where the contamination consists of relatively large particles, these can be removed individually. Differently, for contaminated soils, phytoextraction and electrokinetic techniques are sometimes effective.
Decontamination of humans re-exposed to radioactive materials typically involves the removal of clothing and thorough washing, combined with the safe disposal of clothing and wastewater. However, where radioactive materials have been ingested, chelating agents can help remove the radioactive element; this may not be an option if it is a radioactive form of an essential element. In some cases, chemical means may be used to help prevent a radioactive element from being absorbed into the system. For example, in the event of a radioactive iodine leak from a nuclear reactor, potassium iodide tablets may be distributed to nearby residents; these provide a source of nonradioactive iodine, reducing the amount of the radioactive element that is absorbed.
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