Pollution is defined as the addition of any substance or form of energy (heat, sound, radioactivity) to the environment at a rate faster than the environment can accommodate it by dispersion, breakdown, recycling, or storage in some harmless form. With the rise of advanced technology and with the rapid spread of industrialization, the problem of industrial pollution has become a universal problem.
Air pollution involves the release into the atmosphere of gases, finely divided solids, or finely dispersed liquid aerosols at rates that exceed the capacity of the atmosphere to dissipate them or to dispose of them through incorporation into solid or liquid layers of the biosphere. Air pollution results from a variety of causes, not all of which are within human control. Dust storms in desert areas and smoke from forest and grass fires contribute to chemical and particulate pollution of the air. Probably the most important natural source of air pollution is volcanic activity, which at times pours great amounts of ash and toxic fumes into the atmosphere.
Water pollution involves the release into lakes, streams, rivers, and oceans of substances that become dissolved or suspended in the water or deposited upon the bottom and accumulate to the extent that they interfere with the functioning of aquatic ecosystems. Pollution may begin as water moves through the air, if the air is polluted. The use of chemical fertilizers, pesticides, or other materials on watershed lands is an additional factor contributing to water pollution. Industries located along waterways downstream contribute a number of chemical pollutants. Finally, cities and towns contribute their loads of sewage and other urban wastes. The output of industries, agriculture, and urban communities generally exceeds the biologic capacities of aquatic systems, causing waters to become choked with an excess of organic substances. When organic matter exceeds the capacity of microorganisms in water that break it down and recycle it, the excess of nutrients in such matter encourages rapid growth, or blooms, of algae. When they die, the remains of the dead algae add further to the organic wastes already in the water; eventually, the water becomes deficient in oxygen. Anaerobic organisms (those that do not require oxygen to live) then attack the organic wastes, releasing gases such as methane and hydrogen sulfide, which are harmful to the oxygen-requiring (aerobic) forms of life. The process by which a lake changes from a clean condition to an oxygen-deficient, waste-filled body is known as acceleration eutrophication.
Land pollution involves the deposition on land of solid wastes (used cars, cans, bottles, plastic containers, paper) that cannot be broken down quickly or, in some instances, cannot be broken down at all by the action of organic or inorganic forces (the term biodegradable is used to describe those materials that can be decomposed and recycled by biologic action). When such materials become concentrated within any one area, they interfere with organic life and create unsightly accumulations of trash. Methods of disposal other than recycling include ocean dumping, which creates water pollution and destroys marine habitats; landfill, which frequently involves the destruction of marshland or swamps that have high biologic value; or burning, which increases air pollution.
One form of pollution that is characteristic of industrial societies is noise pollution. The intensity of sound is measured in logarithmic units known as decibels. At a level of 80 decibels, sound is annoying; permanent loss of hearing can be caused by steady exposure to noises in excess of 90 decibels, a level that is frequently exceeded by many common urban sounds, such as jackhammers, jet planes, and excessively loud music. Many large cities have taken measures to decrease the level of urban noise. The problem has received much attention with the advent of supersonic jet airplanes. These aircraft, which travel at speeds faster than the speed of sound, create sound waves equivalent to those of major explosions and capable of damaging structures.
The ultimate control of pollution will presumably involve the decision to contain and recycle, or not to allow the escape into the environment of the substances that are harmful to life. Essentially, therefore, pollution control does not mean an abandonment of existing productive human activities but their reordering so as to guarantee that their side effects do not outweigh their advantages.