The cleanup of environmental pollution involves a variety of techniques, ranging from simple biological processes to advanced engineering technologies. Cleanup activities may address a wide range of contaminants, from common industrial chemicals such as petroleum products and solvents, agricultural chemicals and metals, to radionuclides. Cleanup technologies may be specific to the contaminant (or contaminant class) and to the site. This entry addresses the cleanup of contaminated soil and water. Air pollution is addressed generally at the point of release by control technologies, because the opportunities to capture and recover airborne contaminants are limited once they are released into the atmosphere.

Cleanup costs can vary dramatically depending on the contaminants, the media affected, and the size of the contaminated area. Much of the solvent substance, usually liquid, that can dissolve other substances radionuclide radioactive particle, man-made or natural, with a distinct atomic weight number; can have a long life as soil or water pollutant media specific environmentsair, water, soil—which are the subject of regulatory concern and activities

Tractor-drawn tankers are being used to clear oil beached to the west of Angle Bay, following the grounding of the tanker Sea Empress off Milford Haven in southwest Wales, U.K., 1996. (©Bryan Pickering; Eye Ubiquitous/ Corbis. Reproduced by permission.)

remediation cleanup or other methods used to remove or contain a toxic spill or hazardous materials from a Superfund site or for the Asbestos Hazard Emergency Response program remediation reduction of harmful effects; restoration of undisturbed site

Warsaw Pact nations allied with the former Soviet Union countries remediation to date has been in response to such historical chemical management practices as dumping, poor storage, and uncontrolled release or spillage. Greater effort in recent years has been directed toward pollution prevention, which is more cost-effective than remediation. Programs such as Superfund in the United States, as well as parallel state programs, represent a commitment of billions of dollars to the cleanup of contaminated sites.

Many industry-specific cleanup programs (e.g., Florida's dry cleaner program) are funded by taxes or fees levied on that industry. Several Western European countries have environmental programs that are at least as aggressive as those in the United States. Countries with emerging economies are working hard to address environmental contamination with limited resources. Many cases of environmental contamination in former Warsaw Pact, for example, are associated with former Soviet military bases. In Poland, cleanup of several of these bases is under way. In Kluczewo, northwestern Poland, a former military base is reportedly the biggest and most contaminated such site in Central Europe. A skimming technique was used to remove liquid petroleum fuel from the subsurface followed by bioremedia-tion of the remaining contaminated soil. The Polish government paid for the work with support from local sources.

Government involvement in environmental remediation includes consideration of the safety of the cleanup workers. Professionals involved in the cleanup of contaminated sites may have long-term exposure to a variety of hazardous materials and, as such, must be protected against adverse health

Two workers wearing gas masks and protective clothing loading debris contaminated by dioxin into tractor trailers. (©Bettmann/Corbis. Reproduced by permission.)

impacts. Such protection begins with the planning and implementation of characterization and clean up efforts. Minimizing contact with contaminated media is the optimal method for managing risk to site workers. When such contact is necessary, or when the nature of the contamination is unknown, as in initial characterization activities, personnel protective equipment (PPE) is used to protect site workers. The major routes of exposure for workers at contaminated sites are through dermal (skin) or inhalation pathways. PPE is categorized by the level of protection it provides to these two exposure pathways, ranging from simple dermal protection such as overalls and gloves to fully encapsulating suits with supplied air. The level of protection needed is based on the nature and extent of knowledge of site conditions—less information requires more protection.

In most cases, it is financially or physically impractical to completely remove all traces of contamination. In such cases, it is necessary to set an acceptable level of residual contamination. Evaluating experimental toxicity data and then extrapolating to potential exposure scenarios forms the basis for such decisions. The result of these evaluations is an estimate of risk for given adverse outcome (e.g., cancer or death). Risk-based target levels typically determine when cleanup is complete. As a result, evolution of cleanup technologies has yielded four general categories of remediation approaches: (1) physical removal (with or without treatment); (2) in situ conversion by physical or chemical means to less toxic or less mobile forms; (3) containment;

Two workers wearing gas masks and protective clothing loading debris contaminated by dioxin into tractor trailers. (©Bettmann/Corbis. Reproduced by permission.)

physical removal digging up and carting away conversion chemical modification to another form containment prevention of movement of material beyond the immediate area natural attenuation reduction in a pollutant through combined action of natural factors and (4) passive cleanup, or natural attenuation. Combinations of technologies may be used at some sites.

excavate dig out leachate water that collects contaminants as it trickles through wastes, pesticides, or fertilizers; leaching may occur in farming areas, feedlots, and landfills, and may result in hazardous substances entering surface water, ground water, or soil heavy metals metallic elements with high atomic weights; (e.g. mercury, chromium, cadmium, arsenic, and lead); can damage living things at low concentrations and tend to accumulate in the food chain radionuclide radioactive particle, man-made or natural, with a distinct atomic weight number; can have a long life as soil or water pollutant

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