Pollution, the presence of harmful or irritating substances, called pollutants, in the environment. As the term is generally used, a pollutant is a substance introduced into the environment as a result of human activities. Pollution is especially serious in technologically advanced and heavily populated areas.

Water—in wells, lakes, rivers, and oceans—may be polluted with untreated sewage, garbage, factory wastes, laundry detergents, pesticide residues, and oil spillage. The air of most cities is laden with automobile exhaust, fumes, fuel oil smoke, and chemicals from factories. The land is contaminated with litter, junk, pesticides, and radioactive wastes.

In the last part of the 1960's the public became concerned with the need for preserving or improving the quality of the environment. People became aware that the resources of the earth—land, air, and water—that are needed to sustain life were being threatened by pollution. Scientists warned that the biosphere (the part of the earth that sustains life) can absorb only a limited quantity of pollutants before becoming unfit for living organisms.

Some experts say that to maintain a quality environment it is necessary to limit the growth of the world's population. Others blame pollution not on the growth of population principally but on the economic growth of technologically advanced nations in which the consumption of manufactured products is high.

Although the wastes created by primitive peoples can be objectionable, they do not accumulate because such wastes are reintegrated into nature by the action of microbes and by other natural processes. There is, however, no natural process that can reintegrate into nature the wastes of modern technology, such as discarded automobiles, television sets, plastic bags, and beer cans; and the chemical components of exhaust fumes and most pesticides.

World wide efforts to curb environmental pollution exist, but effective international controls are largely lacking. It is difficult to achieve cooperation for pollution controls with developing countries whose chief concern is to provide basic needs such as food, shelter, and employment for their people. Furthermore, industries in some countries fear that the costs of pollution controls might make it difficult to compete in exporting with rival nations whose pollution controls may be less costly.

Experts agree that effective pollution controls at local, national, and international levels require massive efforts by individual consumers, industry, and government. In the United States, the Environmental Protection Agency was established in 1970 to attack on the federal level the problems of air and water pollution, solid waste management, pesticides, radiation, and noise.