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Article Outline
Introduction; Sources of Hazardous Wastes; Effects of Hazardous Wastes; Hazardous-Waste Control; Legislative History; International Issues
Hospitals use special care in disposing of wastes contaminated with blood and tissue, separating these hazardous wastes from ordinary waste. Hospitals and doctors' offices must be especially careful with needles, scalpels, and glassware, called “sharps.” Pharmacies discard outdated and unused drugs; testing laboratories dispose of chemical wastes. Medicine also makes use of significant amounts of radioactive isotopes for diagnosis and treatment, and these substances must be tracked and disposed of carefully.
Hazardous wastes may pollute soil, air, surface water, or underground water. Pollution of soil may affect people who live on it, plants that put roots into it, and animals that move over it. In Times Beach, Missouri, in 1983, oil contaminated with dioxin was spread on roads to keep dust down; thus, residents were exposed to high levels of dioxin. Sludge from municipal sewage disposal may contain toxic elements if industrial waste is mixed with domestic sewage. If the sludge is used as a fertilizer, these elements may contaminate fields. Toxic substances that do not break down or bind tightly to the soil may be taken up by growing plants; the toxic substances may later appear in animals that eat crops grown there and possibly in people who do so. Air may become contaminated by direct emission of hazardous wastes. Evaporation of toxic solvents from paints and cleaning agents is a common problem. The air above hazardous waste may become dangerously contaminated by escaping gas, as can occur in houses built on mine tailings or old dump sites. Basements of homes built over uranium mine tailings often contain high levels of radioactive radon gas escaping from the radioactivity below. River and lake pollution, if it is toxic enough, may kill animal and plant life immediately, or it may injure slowly. For example, fluoride concentrates in teeth and bone, and too much fluoride in water may cause dental and bone problems. Compounds such as dichlorodiphenyltrichloroethane (DDT), PCBs, and dioxins are more soluble in fats than in water and therefore tend to build up in the fats within plants and animals. These substances may be present in very low concentrations in water but accumulate to higher concentrations within algae and insects, and build up to even higher levels in fish. Birds or people that feed on these fish are then exposed to very high levels of hazardous substances. In birds, these substances can interfere with egg production and bone formation. Even pollution that is not toxic can kill. Phosphates and nitrates, usually harmless, can fertilize the algae that grow in lakes or rivers. When algae grow, in the presence of sunlight, they produce oxygen. But if algae grow too much or too fast, they consume great amounts of oxygen, both when the sun is not shining and when the algae die and begin to decay. Lack of oxygen eventually suffocates other life; some living things may be poisoned by toxins contained in the algae. This process of algal overgrowth, called eutrophication, can kill life in lakes and rivers. In some cases, particular algae can also poison the drinking water of people and livestock. Underground pollutants can be carried by underground water flow. These wastes form spreading underground plumes (long, featherlike columns) of contaminants, which may reach the surface if the water emerges in a spring or is pumped by wells. Especially dangerous are solvents that may have leaked from underground storage tanks or may have been carelessly poured on the ground. Toxic metal ions may also be present in these waste plumes.
The best way to eliminate hazardous wastes is not to generate them in the first place. For example, improvements have been made in the production of integrated circuits: The toxic chlorinated hydrocarbons commonly used in the 1970s were replaced in the 1980s by less toxic glycol ethers and in the 1990s by low-toxicity esters and alcohols.
Recycling is the recovery or reuse of usable materials from waste. About 5 percent of hazardous waste in the United States is recycled as solvents; a similar amount is recovered as metals. For example, approximately 15 percent of sulfuric acid is recycled in chemical manufacturing. In the past, most sulfur used for sulfuric acid production was mined; now the amount of sulfur recovered from smelters (facilities that remove metals from ores), refineries (facilities that purify substances), and manufacturers is more than double that produced by mining. In the United States, the practice of using industrial wastes, which often contain hazardous wastes, as ingredients in commercial fertilizers is encouraged as a means of recycling hazardous wastes. The safety of this practice has recently been called into question, however, and some states are starting to regulate it.
Wastes may be made less hazardous by physical, chemical, or biological treatment. Nearly 10 percent of hazardous waste in the United States is treated with water; another 11 percent undergoes other treatment. For example, sodium hydroxide has been used to treat acid wastes at integrated-circuit plants. Some newer plants now treat hydrofluoric acid wastes with lime, producing relatively harmless calcium fluoride, the mineral fluorite. Sulfuric acid wastes, if not recycled, can be treated with ammonia wastes from the same plant, forming ammonium sulfate, a fertilizer. Incineration has been used since human beings learned to control fire. It is the preferred method of handling infectious medical wastes. However, it should not be used for wastes that contain toxic heavy metals or chlorinated hydrocarbons: When burned, old painted surfaces can release lead or arsenic into the air, whereas chlorinated hydrocarbons produce hydrochloric acid and dioxins. Solids left over from incineration may have to be disposed of as hazardous waste. About 6 percent of hazardous waste in the United States is incinerated, and another 11 percent is burned along with fuel. Solidification of wastes involves melting them and mixing them with a binder, a substance that eventually hardens the mix into an impenetrable mass. One suggested treatment of radioactive waste involves turning it into a glass through a process known as vitrification. Approximately 8 percent of hazardous waste in the United States is stabilized—kept from moving through groundwater and air. Sometimes waste can be stabilized on-site; simple remedies such as covering the waste may be sufficient. Other stabilization methods involve building a barrier around the waste. This barrier can be of plastic, steel, concrete, clay, or even glass.
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