For the purposes of regulation, the United States Environmental Protection Agency identifies two broad categories of pollution: point-source pollution và nonpoint-source pollution.
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Waste filled water is dumped into a river, polluting it for the people và animals who use it as a source for eating & drinking.
Photograph by Kaentian Street
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Almost everything humans do, from growing food to manufacturing products khổng lồ generating electricity, has the potential khổng lồ release pollution into the environment. Regulatory agencies charged with protecting the environment identify two main categories of pollution: point-source and nonpoint-source pollution.
Point-source pollution is easy to identify. As the name suggests, it comes from a single place. Nonpoint-source pollution is harder to lớn identify & harder to lớn address. It is pollution that comes from many places, all at once.
The United States Environmental Protection Agency (EPA) defines point source pollution as any contaminant that enters the environment from an easily identified và confined place. Examples include smokestacks, discharge pipes, & drainage ditches.
Factories và power plants can be a source of point-source pollution, affecting both air & water. Smokestacks may spew carbon monoxide, heavy metal, sulfur dioxide, nitrogen dioxide, or “particulate matter” (small particles) into the air. Oil refineries, paper mills, và tự động hóa plants that use water as part of their manufacturing processes can discharge effluent—wastewater containing harmful chemical pollutants—inlớn rivers, lakes, or the ocean.
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Municipal wastewater treatment plants are another common source of point-source pollution. Effluent from a treatment plant can introduce nutrients và harmful microbes into waterways. Nutrients can cause a rampant growth of algae in water.
Nonpoint-source pollution is the opposite of point-source pollution, with pollutants released in a wide area. As an example, picture a city street during a thunderstorm. As rainwater flows over asphalt, it washes away drops of oil that leaked from oto engines, particles of tire rubber, dog waste, and trash. The runoff goes inlớn a storm sewer & ends up in a nearby river. Runoff is a major cause of nonpoint-source pollution. It is a big problem in cities because of all the hard surfaces, including streets & roofs. The amount of pollutants washed from a single thành phố bloông xã might be small, but when you add up the miles & miles of pavement in a big city you get a big problem.
In rural areas, runoff can wash sediment from the roads in a logged-over forest tract. It can also carry acid from abandoned mines and flush pesticides và fertilizer from farm fields. All of this pollution is likely lớn wind up in streams, rivers, và lakes.
Airborne pollutants are major contributors khổng lồ acid rain. It forms in the atmosphere when sulfur dioxide và nitrogen oxides combine with water. Because acid rain results from the long-range movement of those pollutants from many factories & power plants, it is considered nonpoint-source pollution.
In the United States, the Clean Air Act và the Clean Water Act have sầu helped to limit both point-source and nonpoint-source pollution. Thanks khổng lồ these two legislative initiatives, in effect for some 50 years now, America’s air và water are cleaner today than they were for most of the 20th century.