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Before you read think over the following questions:

- Why has pollution become a threat to modern society?

- What forms does it take today?

- What should be done to reduce every kind of pollution?

Pollution is the contamination of the air, water, or earth by harmful or potentially harmful substances. The U.S. environmental movement in the 1960s emerged from concerns that air, water, and soil were being polluted by harmful chemicals and other toxic substances. During the industrial revolution of the nineteenth century, the mass production of goods created harmful wastes, much of which was dumped into rivers and streams. The twentieth century saw the popular acceptance of the automobile and the internal combustion engine, which led to the pollution of the air. Rapidly expanding urban centers began to use rivers and lakes as repositories for sewage.

Land pollution involves the depositing of solid wastes that are useless, unwanted, or hazardous. Types of solid waste include garbage, rubbish, ashes, sewage-treatment solids, industrial wastes, mining wastes, and agricultural wastes. Most solid waste is buried in sanitary landfills. A small percentage of municipalities incinerate their refuse, while composting is rarely employed.

Modern landfills attempt to minimize pollution of surface and groundwater. They are now located in areas that will not flood and that have the proper type of soil. Solid wastes are compacted in the landfill and are vented to eliminate the buildup of dangerous gases. Hazardous wastes, including toxic chemicals and flammable, radioactive, or biological substances, cannot be deposited in landfills, and the management of these wastes is subject to federal and state regulation.

Nuclear wastes are radioactive materials that may be left after a commercial or laboratory process has been carried out. There has been public debate over the safest means of storing the waste, which can remain dangerously radioactive for up to hundreds of thousands of years. Present practice calls for encasing the waste in metal, concrete, and ceramic containers, and burying the containers deep underground in geologically stable locations

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Solid waste pollution has been reduced by recycling wastes rather than burying them. This process includes burning waste to produce steam as well as recycling of glass, metal, and paper. The elimination of these kinds of materials from landfills has prevented pollution and extended the period during which landfills can receive waste.

Land pollution also involves the accumulation of chemicals in the ground. Modern agriculture, which has grown dependent on chemical fertilizers and chemicals that kill insects, has introduced substances into the soil that kill more than pests. For many years the chemical DDTwas routinely sprayed on crops to control pests. It was banned when scientists discovered that the chemical entered the food chain and was harming wildlife and possibly humans.

Air pollution is a contamination process that modifies the natural characteristics of the atmosphere. Stratospheric ozone depletion due to air pollution has long been recognized as a threat to human health as well as to the earth's ecosystems. Worldwide air pollution is responsible for large numbers of deaths and cases of respiratory disease.

Air pollutants are classified as either directly released or formed by subsequent chemical reactions. A direct release air pollutant is one that is emitted directly from a given source, such as the carbon monoxide or sulfur dioxide, all of which are byproducts of combustion; whereas, a subsequent air pollutant is formed in the atmosphere through chemical reactions involving direct release pollutants. Anthropogenic sources of air contamination are often related to burning different kinds of fuel, e.g. burning fossil fuels in power plants and gasoline used by motor vehicles. Other anthropogenic sources include oil refining, power plant operation and industrial activity in general, fumes from paint and aerosol sprays and so on.

There are many air pollution control technologies and urban planning strategies available to reduce air pollution; however, worldwide costs of addressing the issue are high.

Water pollution has existed longer than any other type of pollution. Depositing liquid and solid wastes in rivers, streams, lakes, and oceans was convenient and inexpensive for a company or municipality, but it eventually destroyed the ecosystems found in the water. Many large rivers became nothing more than sewers. Most troubling was the polluting of groundwater, creating serious health hazards for those people who drank water containing toxic substances.


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