Detoxification (environmental)

DEFINITION: Reduction or elimination of the toxic properties of a substance to make it less harmful to or more compatible with the environment

Hazardous substances often enter the environment as the result of various manufacturing processes and other human activities. The detoxification of air, water, and soil that have been negatively affected by such substances can help to minimize environmental damage.

Increasing industrialization during the twentieth century led to the release of large amounts of hazardous waste and by-products into the environment. Pesticides were another source of toxins, as agriculture worked to maintain the crop yields necessary to feed the growing population of the world. Some toxins are analogues of harmful substances that occur naturally and may degrade rapidly by natural means. Others are more persistent in the environment and produce unwanted effects. “Detoxification” is the general term applied to the various processes by which toxins are removed from the environment or are rendered less harmful.

Toxic Substances

A substance is considered hazardous if it poses a threat to human health or the environment when it is spread, treated, disposed of, or transported. Toxic and hazardous substances often occur as a result of the manufacture of materials designed to protect humans and improve quality of life. Sources of hazardous waste include the manufacture of chemicals and allied products, the manufacture of petroleum and coal products, the primary metals industry, and the metals fabrication industry. Environmental releases of toxic chemicals may occur unintentionally through emissions from compressors, pump seals, valves, spills, pipelines, and storage tanks, or intentionally through discharges of wastes into air or water or through inappropriate disposal in landfills. The Environmental Protection Agency (EPA) has reported that Americans generate 1.6 million tons of household hazardous wastes each year.

The disposal of hazardous substances is not a simple matter. Many toxic substances are not suitable for disposal in regular landfills used for trash. Some hazardous substances are water-soluble and can leach through the soil into rivers, lakes, and groundwater supplies to pollute sources of potable water. Some wastes have a significant vapor pressure and can be spread over wide areas by wind and air currents. Corrosive wastes must be disposed of in containers that will not decompose.

Public concerns regarding toxic substances in the environment have elicited different approaches to solving these problems. Environmental activists have advocated the use of natural pesticides and nonpolluting agricultural chemicals. The US Congress has addressed the issue of toxic substances in the environment with regulations that specify detoxification procedures for wastewater, contaminated soil, and landfills. These regulations include the Federal Water Pollution Control Act (1974), the Safe Drinking Water Act (1974), the Federal Environmental Pesticide Control Act (1972), the Toxic Substances Control Act (1976), and the Frank R. Lautenberg Chemical Safety for the Twenty-First Century Act (2016).

Methods of Detoxification

Many natural processes cause detoxification of harmful substances in the environment. Gaseous pollutants or toxins that are exposed to sunlight are subject to photochemical decomposition, in which ultraviolet light causes bonds within the compounds to break. The resulting fragments react with oxygen (oxidation) or water (hydration) to form less toxic compounds. These may undergo repeated degradation in the same manner. Microbial degradation, in which organisms metabolize a wide variety of organic compounds to carbon dioxide and water or convert them into less harmful substances, promotes detoxification of many organic toxins. Some newer pesticides, such as organophosphates, are designed to degrade on repeated exposure to water, forming relatively harmless products. Earlier pesticides, such as polychlorinated biphenyls (PCBs), were found to degrade slowly in the environment. Toxins with slow detoxification pathways bioaccumulate in organisms, causing harmful effects on fish and wildlife. Such effects may be magnified in the food chain.

Efforts to supplement natural detoxification processes include enzymatic (biological) and other chemical methods. Many microorganisms capable of metabolizing toxins have been isolated and cultured in order to treat hazardous wastes. Such treatments are usually carried out at regional waste management centers. One type of chemical treatment involves chelation or precipitation. This is useful for eliminating metals, either in ionic or elemental form, from water and soil. In this method, an organic compound forms an insoluble precipitate with the metal. Filtration removes the precipitate, which can then be subjected to further disposal methods in concentrated form. Composting, or land farming, involves spreading waste materials over a large land area, where they decompose. Pesticides and wastes from paper mills have been detoxified this way. Land farming requires monitoring to ensure that toxins in the wastes do not leach into groundwater.

Thermal treatment is considered a safer process. An example of this type of detoxification method is incineration, during which high temperatures oxidize the solid and liquid organic wastes to carbon dioxide and water in the presence of oxygen. However, people living in communities near incinerators often fear ill effects from possible emissions or leaks. One solution to this concern is the incineration of wastes on ships. Vulcanus, a Dutch ship, was used to incinerate large quantities of Agent Orange, a hazardous herbicide contaminated with toxic dioxins.

Another method of detoxification is vitrification, in which toxic materials are converted into a stable, glass-like solid through high-temperature melting. Vitrification has been used to dispose of asbestos, considered a highly hazardous material, and research has demonstrated its effectiveness for a wide range of wastes, including industrial sludges, lead-contaminated soils, and certain medical and municipal wastes. The process is also a central technology in the long-term management of high-level radioactive waste, with large vitrification facilities operating or under construction in countries such as the United States, France, and Japan. Although vitrification produces a durable material that resists leaching and environmental degradation, it remains energy-intensive and costly, which limits its use to particularly dangerous or persistent contaminants. Twenty-first century research focused on improving the efficiency of melting technologies, including plasma-arc systems, to make vitrification more viable for large-scale environmental cleanup projects.

Bibliography

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