Pollution

Pollution is the contamination of the natural environment by harmful substances that are produced by human activity. Pollution of Earth's air and water have become so widespread that the problem is now global and could threaten the biosphere (a life-supporting zone extending from Earth's crust into the atmosphere). Pollution by chemicals and nuclear material may have especially severe and long-lasting effects.

The term pollution can have several different meanings. Derived from the Latin pollutus, it suggests something that is made unclean or dirty. Today, the word pollution is almost always applied to the environment and usually has one of two meanings. The wider of the two suggests that pollution includes any unpleasant or unwanted environmental change, whatever its cause. According to this meaning, a natural event like a volcano can certainly cause pollution.

TYPES OF POLLUTION

In a narrower sense, pollution can be interpreted as any harmful environmental changes caused specifically by human activity. Human-caused pollution will be discussed here, since it not only poses the bigger threat today but is really the only type that humans can prevent. Pollution caused by human activities is extensive, since people produce an enormous variety of pollutants that eventually end up contaminating the air and the water that is so important to human life.

Air Pollution. Air pollution is sometimes the most obvious since at its worst, we can literally see the pollution in the sky. Air is polluted by the release of harmful gases and particles into the atmosphere. The gases given off by running an automobile are the major causes of today's air pollution. Although the United States has drastically improved its performance on auto emissions, the fact remains that although it has only 5 percent of the world's population, it accounts for 70 percent of the carbon monoxide (an odorless, tasteless, colorless, and poisonous gas) and 45 percent of the nitrous oxides (a poisonous gas) that are pumped into the atmosphere.

Heavy industry and power plants around the world also contribute to a steady stream of sulfur dioxide (toxic gas) released into the air. All of these gases are noxious or have harmful effects. Carbon monoxide increases the demands on the heart and reduces the blood's supply of oxygen to the tissues. Nitrogen oxides dissolve in water and form nitric acid, one of the components of acid rain. Sulfur oxides also combine with water to produce sulfuric acid. All of these air pollutants work to undermine humans' health, erode buildings, and kill green plants.

More alarmingly, what we are putting into the atmosphere may be changing the climate of the entire Earth. It has been argued that the accumulation of what are called "greenhouse gases," like carbon dioxide, methane, and chlorofluorocarbons (CFCs), have the effect of trapping the Sun's heat close to Earth. This can create a greenhouse effect that will lead to global warming, the results of which may be the melting of the polar ice cap (causing widespread flooding). Also, agricultural regions may become too hot and dry to grow crops. The protective ozone layer is also becoming thinner. This upper atmospheric layer shields Earth and its inhabitants from the harmful ultraviolet radiation contained in ordinary sunlight. When CFCs are released from our refrigerators, air conditioners, and spray cans, they react with the ultraviolet radiation and release chlorine atoms. These in turn destroy the oxygen molecules that make up the protective ozone layer.

Water Pollution. As important as air pollution is, the issue of water pollution is equally so. Clean water is as essential to life on Earth as is clean air, yet human activity has routinely polluted its sources of fresh water by allowing it to be contaminated by organic and industrial waste. Organic waste is mainly sewage, and even the best sewage treatments plants in the biggest cities cannot keep drinking water supplies from being contaminated. In fact, many larger cities get their drinking water from filtered and treated sewage water. Industrial pollution of water adds many dangerous inorganic (man-made) chemicals to our water supply. These chemicals may cause cancer and interfere with reproduction.

Pesticides and Nuclear Waste. In addition to the vast problems the world faces with air and water pollution, the pollution problems relating to pesticides (chemicals that kill insects) and nuclear power are also critically important. Ever since World War II (1939–45), increasingly powerful

chemicals have been used to kill or control insects that are considered harmful to people or products. The first major success was the synthetic chemical DDT. Although able to kill any insect, DDT also was later found to infect fish and kill birds. It has since been found in the tissues of living things from the poles to the most remote forests. It sometimes can even be found in mother's milk. As a result of these harmful effects, the United States banned the use of DDT in 1972 and many other countries followed suit.

While the use of DDT has been banned in the United States and other countries, many other chemical pesticides (as well as herbicides and even fertilizers) used by commercial agriculture have been found to severely interfere with normal human and animal life processes, causing illness, mutations, and even death. However, as bad as these chemicals can be for living things, they have nowhere near the permanence found in radioactive materials. While nuclear power plants generate no air pollution, they result in the steady production of nuclear or radioactive waste. There is no known way of safely disposing of this near-permanent material which will remain radioactive for up to half a million years. The radioactive waste can result in cancers, birth defects, and death.

POLLUTION CONTROL

Beginning in the 1960s, a growing public and governmental awareness of the importance of the environment led to campaigns for laws and international agreements to curb pollution. In the United States alone, water quality has been improved (with dramatic reversals of "dead" lakes like Lake Erie), and air pollution has been reduced substantially. Recycling has also become a standard way of conserving resources. However, the world's pollution problems cannot be solved in only one country. All countries share the growing realization that the biosphere, or all the parts of Earth that make up the living world, includes everyone on Earth. For this reason, international cooperation is essential if Earth is to be restored to its natural and livable state.

[See alsoCarbon Dioxide; Carbon Monoxide; Ozone ]