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pollution, contamination of the environment as a result of human activities. The term pollution refers primarily to the fouling of air, water, and land by wastes (see air pollution; water pollution; solid waste). In recent years it has come to signify a wider range of disruptions to environmental quality. Thus litter, billboards, and auto junkyards are said to constitute visual pollution; noise excessive enough to cause psychological or physical damage is considered noise pollution; and waste heat that alters local climate or affects fish populations in rivers is designated thermal pollution.
The 20th cent. has seen pollution approach crisis proportions throughout the world. At issue is the capacity of the biosphere to disperse, degrade, and assimilate human wastes (see ecology). The biosphere is a closed ecological system with finite resources and is maintained in equilibrium by grand-scale recycling. Under natural conditions organic and certain inorganic materials in the biosphere are continually recycled by processes including photosynthesis and respiration, nitrogen fixation and denitrification (see nitrogen cycle), evaporation and precipitation, and diffusion by wind and water action. But the introduction of massive quantities of waste matter at any point in the biosystem may "overload" it, disrupting the natural recycling mechanisms.
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