Pollution

Pollution, contamination of the environment by man-made substances or energy that have adverse effects on living or non-living matter. This contamination of air, water, or soil materials interferes with human health, the quality of life, or the natural functioning of ecosystems. In simple terms, pollution can be seen as the wrong substance in the wrong place in the wrong quantities at the wrong time. This implies that harm is caused to the environment, and if the same substance is present at levels too low to cause harm, then it can be considered as contamination. Many substances that can be pollutants also occur naturally, in which case they are not classified as pollution. However, other pollutants result entirely from human activity, such as most toxic organic compounds and artificial forms of radioactivity, particularly from nuclear waste.

Pollution can be categorized according to the medium in which it occurs: atmospheric pollution (see Air Pollution), freshwater and sea pollution (see Water Pollution), or land pollution (see Solid Waste Disposal). However, transfers can occur in both directions between the atmosphere, water, and the land, with consequences for both the spread of pollution and its effects. For example, the emission of sulphur dioxide—caused by the combustion of fossil fuels such as gas, petroleum, and coal—into the air can result in the acidification of soils and lakes when it reaches the Earth’s surface (see Acid Rain). Pollution can also be classified on the basis of the type of pollutant, such as pesticides (see Pest Control) and other persistent toxic organic compounds, heavy metals, radioactivity, human and animal effluent, and toxic gases. The most familiar forms of pollution result from the chemical properties of the substances concerned, but the physical properties may also be important, for example ionizing radiation, noise pollution, and excessive heat.

Water pollution arises from the discharge of industrial, agricultural, and human wastes into freshwaters, estuaries, and seas. This may result in the poisoning of aquatic organisms or the depletion of oxygen owing to excessive growth of micro-organisms (anthropogenic eutrophication), which makes less of the water habitable for fish. Metal pollution and toxic organic compounds are of concern for human and environmental health as a result of discharges to water, air, and the terrestrial environment. Air pollution can result in adverse effects on health, crops, natural ecosystems, materials, and visibility. The major concerns over air pollution are acidification of soils and waters with its detrimental affects on animal and plant life, and the impact of traffic-derived pollutants on health in cities (see Traffic Pollution). On a global scale air pollution probably represents the greatest problem of all, with greenhouse gases (such as carbon dioxide) resulting in global warming and synthetic chlorine compounds (chlorofluorocarbons) depleting the stratospheric ozone layer. Nuclear waste is a further modern environmental concern, which poses a problem not just for the present generation, but for future generations as the waste remains radioactive for thousands of years.

Trends in pollution are difficult to determine accurately, particularly on a world scale. The best-documented trend is the global increase in carbon dioxide, which in the 1990s was at a rate of about 0.5 per cent per year but had risen to about 2.5 per cent by 2005. Overall, however, there is a trend for decreasing levels of pollutants in the developed world, but the opposite in many developing countries as they rapidly industrialize. For example, it has been predicted that sulphur dioxide emissions will fall by 63 per cent in Europe from 1990 to 2010, while they will rise in China by 118 per cent. The reductions in the developed world result largely from environmental legislation, which has led to the introduction of control measures and cleaner technology. Examples are the introduction of more advanced waste-water treatment processes, shifts to cleaner fuels, and the recycling of potential contaminants.

See also Conservation; Oil Pollution; and Environmentalism.