waste: see solid waste.

toxic waste is waste material, often in chemical form, that can cause death or injury to living creatures. It usually is the product of industry or commerce, but comes also from residential use, agriculture, the military, medical facilities, radioactive sources, and light industry, such as dry cleaning establishments. The term is often used interchangeably with "hazardous waste," or discarded material that can pose a long-term risk to health or environment. Toxics can be released into air, water, or land. In 1976 the Toxic Substances Control Act required the Environmental Protection Agency to regulate potentially hazardous industrial chemicals, including halogenated fluorocarbons, dioxin, asbestos, polychlorinated biphenyls (PCBs), and vinyl chloride. Other federal legislation pertaining to hazardous wastes includes the Atomic Energy Act (1954), the Resource Conservation and Recovery Act (1976), and the Comprehensive Environmental Response, Compensation, and Liability Act, or Superfund Act (1986). Toxic waste treatment and control has proved to be expensive and time-consuming with more resources spent on court battles than on actual cleanup. The disposal of toxic wastes is also a topic of international concern. In 1989, some 50 countries signed a treaty aimed at regulating the international shipment of toxic wastes. In some cases such wastes are shipped to developing countries for cheap disposal without the informed consent of their governments. The often substandard shipping, storage, and treatment methods endanger human health and the health of the environment. See air pollution; pollution; solid waste; water pollution.

solid waste, discarded materials other than fluids. In the United States in 1996, nearly 210 million tons—about 4.3 lb. (2 kg) per person daily (up from 2.7 lb./1.2 kg in 1960)—were collected and disposed of by municipalities. In that year, municipal garbage included 12.4 million tons of glass and about 80 million tons of paper and paperboard (by far the largest constituent); in addition enormous tonnages of food residues, yard trimmings, textiles, plastics, and sludge formed in sewage treatment were produced. Although the amount of the increase has been slowed somewhat by recycling and composting programs and improvements in packaging, the amount of solid waste continues to increase annually. Moreover, the most common disposal methods pollute land, water, or air to some degree (see pollution). Management of solid waste therefore presents an increasingly acute problem.

See also environmentalism; radioactive waste.

Landfills

Approximately 62% of municipal waste is placed in landfills. If the waste is dumped untreated, it can promote the proliferation of rats, flies, and other vermin, encourage growth of disease-carrying organisms, contaminate surface and underground water, scar the land, and preempt open space. An alternative method of solid waste disposal is the sanitary landfill, first employed in Fresno, Calif., in 1937: waste is spread in thin layers, each tamped compactly and covered by a layer of earth. While more expensive than open dumping, the sanitary landfill eliminates health hazards and permits reclamation of the site for construction, recreation, or other purposes. The chief drawbacks are that feasible locations are relatively rare and costly and that sites must be insulated from water resources to avoid polluting them (see water pollution). Both open dump and sanitary landfill disposal depend on the natural degradability of wastes for an ultimate return to normal earth conditions. Decay, however, takes time; buried paper, for example, can persist as long as 60 years. Many plastics and synthetic textiles do not degrade at all.

Incineration

To reduce the bulk of solid waste burning of paper, plastic, and other components is often resorted to, either in open dumps or incinerators. Fly ash, noxious gases, and chemical contaminants can thus be released into the air (see air pollution). However, new techniques for "scrubbing" pollutants from incinerator stacks are being developed. Incineration of typical garbage reduces its weight and volume by as much as 80%. Approximately 15.9% of municipal solid waste is combusted.

Recycling

Recycling of solid wastes is an option that many municipalities have explored in recent years. It not only facilitates disposal but conserves energy, cuts pollution, and preserves natural resources. To make cans from recovered aluminum, for example, requires 10% of the energy needed to make them from virgin ore. At the same time ore is saved, and the pollution resulting from mining and processing are avoided. Making steel bars from scrap requires 74% less energy and 50% less water, while reducing air-polluting emissions by 85% and mining wastes by 95%.

Similarly, sludge from treated sewage can be used for fertilizer, but it has been less costly to dump it at sea or on open land (see sewerage). Dumped sludge has killed marine life and threatened beaches along the Eastern seaboard; elsewhere in the United States it is a growing nuisance. Between 1975 and 1985 the amount of sludge dumped in U.S. coastal waters increased by 60%; the effects of dumping and illegal dumping are still felt despite the fact that it has been illegal since the beginning of 1992. Recycling and composting take care of approximately 2.7% of municipal solid waste.

New Techniques

The federal government now provides assistance to localities in developing new means of recovering materials and energy from solid waste, and encourages private industry to seek similar goals. One technique being tried involves intensified combustion of wastes to produce heat for generating power. A second promising approach is pyrolysis, the thermal decomposition of wastes in controlled amounts of oxygen to produce valuable petrochemicals; the residue is an inert char of little bulk. Another method of reducing solid wastes is to replace polystyrene packaging with less bulky wrapping made largely of paper. Wider application of such processes is being advocated not only to diminish pollution of the environment by solid waste, but also to conserve natural resources.

radioactive waste, material containing the unusable radioactive byproducts of the scientific, military, and industrial applications of nuclear energy. Since its radioactivity presents a serious health hazard (see radiation sickness), disposing of such material is a great problem. Methods of disposal include dumping concrete-encased containers filled with radioactive waste in the ocean and burying the waste underground in old salt mines. In 1996 the United States opened a waste processing plant in Aiken, S.C. at the Savannah River nuclear-weapons complex. The waste will be converted into cylinders of radioactive glass, which will then be encased in steel containers that will be stored in an underground concrete vault. While the glass will still be radioactive, it will no longer be possible for the waste to leak into the soil, and there will be no possibility of a chemical explosion such as the one that occurred in the Soviet Union in the late 1950s. The United States has also agreed to accept about 20 tons of waste from research reactors in 41 countries. The spent nuclear fuel, supplied by the United States for medical and research purposes, includes about 5 tons of highly enriched uranium that could be extracted and used to produce nuclear weapons.

nuclear waste: see radioactive waste.

or materials salvage

Recovery and reuse of materials from consumed products. The main motives for recycling have been the increasing scarcity and cost of natural resources (including oil, gas, coal, mineral ores, and trees) and the pollution of air (see air pollution), water (see water pollution), and land by waste materials. There are two types of recycling, internal and external. Internal recycling is the reuse in a manufacturing process of materials that are a waste product of that process, and is common in the metals industry (see scrap metal). External recycling is the reclaiming of materials from a product that is worn out or no longer useful; an example is the collection of old newspapers and magazines for the manufacture of newsprint or other paper products.

Learn more about recycling with a free trial on Britannica.com.

Bodily process for disposing of undigested food waste products and nitrogenous by-products of metabolism, regulating water content, maintaining acid-base balance, and controlling osmotic pressure to promote homeostasis. It refers to both urination and defecation and to the processes that take place in the digestive and urinary systems, as the kidney and liver filter wastes, toxins, and drugs from the blood and food reaches the last stage of digestion. Ammonia from protein digestion, the primary excretory product, is converted to urea to be excreted in urine.

Learn more about excretion with a free trial on Britannica.com.