Pollution contamination of the environment as a result of human activities. During the 20th cent. Pollution problems have arisen in all industrialized areas as well as in various inland and coastal waters and stretches of ocean. The capacity of the biosphere to disperse, degrade, and assimilate human wastes is in question . An early sign of environmental limits was the air pollution of the industrial revolution, brought on by the burning of coal to run mills and machinery. It was not until after world war ii, however, that pollution came to be viewed by many as a threat to the health of the planet. By the 1960s, population increases, industrial expansion, and burgeoning truck and automobile use were producing wastes in such quantity that natural dispersing and recycling processes could not always keep pace. Exacerbating the problem was the appearance of synthetic substances that degrade extremely slowly or not at all: plastics, fibers, organic pesticides such as ddt, industrial chemicals such as pcbs, and the wastes from their manufacture. Thus, garbage and toxic chemicals polluted the land and infiltrated ground and surface waters. Pesticides have poisoned wildlife, and industrial waste products have contaminated drinking water and, in more severe cases, caused evacuation of homes Effects of industrial wastes have spread over larger areas as well, e.g., When toxic mercury reached high concentrations in widely distributed species of food fish in the early 1970s. Airborne industrial wastes created acid rain and, with automobile emissions, produced severe air-pollution problems, including smog, in many urban and suburban communities. The contribution of pollutants to global environmental problems, such as global warming and depletion of the earth's ozone layer, has prompted international meetings and agreements. Radioactive materials from the nuclear reactor accident at chernobyl spread through e europe and scandinavia; lack of appropriate disposal facilities has led some countries to dump radioactive wastes in the oceans.