Water Pollution

Shortages of drinkable water are increasingly common. The greatest demand for water is in industrialized countries that practise irrigation. The average North American, for example, uses 70 times more water than the average Ghanian. Yet personal uses of water are very low: 69 per cent of all the water consumed on the planet is used in agriculture (mainly for irrigation); 23 per cent is used by industry; and domestic uses account for only 8 per cent.

The UN Global Environment Monitoring System (GEMS), which is coordinated by UNEP, now includes 344 water-monitoring stations in 59 countries. It reports that 10 per cent of the rivers it monitors are polluted, principally by human sewage - a problem mainly confined to developing countries.

Industry and agriculture are the culprits in developed countries. Nitrate levels in the European rivers monitored by GEMS are, on average, 45 times higher than in unpolluted rivers. Phosphates and pesticides also cause widespread pollution, which is not confined to industrialized countries; pesticide levels in some Tanzanian, Colombian and Malaysian rivers are higher than those found in Europe.

The symptoms of the malaise include the spread of algal blooms, coral bleaching, oil pollution and a decline in the quantity and quality of marine food. The latter is particularly important: more than half the people of developing countries obtain more than 30 percent of their protein from marine fish.

Nutrients that people add to water, such as nitrates from agricultural fertilizers and phosphates from detergents in sewage, greatly increase the growth of algae in water. As larger amounts of algae grow, larger amounts also die. The dead algae become wastes, and, as they decay, they use up the water's oxygen supply. Sewage and agricultural nitrate, fertilizers are responsible for the blooms of algae, called red tides, now becoming more common. These deplete the water of oxygen, producing what are known as ‘dead zones’; one such zone, of 4000 km2, has been found in the Gulf of Mexico, near the mouth of the Mississippi.

The addition of heated water to a body of water also upsets cycles. Heated water can kill animals and plants that are accustomed to living at lower temperatures. It also reduces the amount of oxygen that water can hold. The addition of heated water is called thermal pollution. Most heated water comes from industries and power plants that use water for cooling.

Another major pollutant is fuel oil, which enters oceans primarily from oil tankers and offshore oil wells. Such spills ruin beaches and kill birds and marine life.

Many countries have joined together to improve the management of the 214 river basins that are shared by more than one country. These schemes are already improving water quality and management of the North American Great Lakes and of the European Rhine. Thanks to a UNEP initiative, many developing countries have joined a scheme to promote the Environmentally Sound Management of Inland Waters (EMINWA), notably those that share the Zambesi River, Lake Chad and the Nile.

Air pollution comes in many forms, but four pollutants are particularly important: the sulphur oxides, emitted mainly by power stations and industry; nitrogen oxides, emitted by power stations, industry and vehicles; carbon monoxide, emitted mainly by vehicles; and soot and dust, known technically as suspended particulate matter (SPM), found everywhere where fuels are burnt.

Toxic air pollutants are substances that cause or may cause cancer or other serious health effects, such as reproductive or birth defects, and neurological, cardiovascular, and respiratory disease. They can be found in gaseous, aerosol, or particulate forms. Some toxic air pollutants, such as mercury (Hg), are persistent bioaccumulative toxics (i.e., they are stored indefinitely in the body and increase over time). These toxics can deposit onto soils or surface waters, where they are taken up by plants and are ingested by animals, with concentrations increasing as the toxics move up through the food chain to humans. Sources of hazardous air pollutants include stationary sources such as power plants, factories, dry cleaners, and hospitals, as well as mobile sources such as cars, buses, and construction equipment.

The industrial countries have begun to clean up their air and have invested heavily in the technology to do so.

Overall, GEMS concluded, nearly 900 million urban residents are exposed to unhealthy levels of sulphur oxides and more than one billion people are exposed to excessive dust and soot.

Many countries have introduced tougher laws, cleaner fuels and installed pollution control equipment.

Soil pollution damages the thin layer of fertile soil that covers much of the earth's land and is essen-tial for growing food. Natural processes took thousands of years to form the soil that supports crops. But, through careless treatment, people can destroy soil in a few years.

In nature, cycles similar to those that keep water clean work to keep soil fertile. Plant and animal wastes, including dead organisms, accumulate in the soil. Bacte­ria and fungi decay these wastes, brea-king them down into nitrates, phosphates, and other nutrients. The nutri­ents feed growing plants, and when the plants die the cycle begins again.

People use fertilizers and pesticides to grow more and better crops. Fertilizers add extra nutrients to the soil and increase the amount of a crop that can be grown on an area of land. But the use of large amounts of fertilizer may decrease the ability of bacteria to decay wastes and produce nutrients naturally. Pesticides destroy weeds and insects that harm crops. But pesticides may also harm helpful insects, worms, and bacteria, and other helpful organisms in the soil.

Solid wastes are probably the most visible forms of pollution. People throw away billions of tons of solid material each year. Much of this waste ends up littering roadsides, floating in lakes and streams, and collecting in ugly dumps. Examples of solid wastes include aban­doned cars, tyres, refrigerators, and cookers; cans and other packaging materials; and scraps of metal, paper, and plastic. Such solid pollutants are most common in the heavily populated areas in and near cities. Slag and other wastes from mining processes pollute much land away from cities.

Solid wastes present a serious problem because most of the methods used to dispose of them result in some type of damage to the environment. When the wastes are put into open dumps, they ruin the attractiveness of the surrounding areas. Dumps also provide homes for disease-carrying animals, such as cockroaches and rats. Some solid wastes can be destroyed by burning them. But burning produces smoke that causes air pollution. When wastes are dumped in water, they contribute to various forms of water pollution.

Solid wastes include mining, industrial, and agricul­tural wastes, in addition to household wastes. Most solid wastes are buried in large, open areas called land fills. But in many places, especially near large cities, the land available for dumping is running out. In the mean­time, the production of solid wastes is increasing rap­idly. In addition, more and more wastes that are difficult to dispose of are being produced. Tin and steel cans that rust and can be absorbed by the soil have been re­placed by aluminium cans that stay in their original state for many years. Paper and cardboard packaging that can decay and burn easily is being replaced by plastics that will not decay and that give off harmful gases when they are burned.

Other kinds of pollution. Some things that pollute the environment cannot be classified as air, water, or soil pollutants, or as solid wastes. They travel through and affect various parts of the environment. These pollu­tants include noise, radiation, acid rain, pesticides, and such metals as mercury and lead.

Noise is an especially troublesome pollutant in urban areas. People in and near cities are exposed to loud noise much of the time. Noises are measured in units called decibels. The noise comes from such things as aeroplanes, buses, cars, motorcycles, trains, trucks, construction projects, and industries. The noise causes discomfort in human beings. In extreme cases, loud noise can also damage hearing or even cause deafness. In addition, some studies have linked prolonged exposure to loud noises with the development of high blood pressure and ulcers.

Radiation is an invisible pollutant that can be highly dangerous. Nuclear radiation comes from radioactive substances, including waste from nuclear weapons testing and from nuclear power plants. Small amounts of electromagnetic radiation are produced by a variety of electronic devices, including computers, lasers, microwave ovens, televisions, and X-ray machines. Scientists have not determined exactly what effects small amounts of radiation have on people. But exposure to large amounts can cause cancer and harmful changes in reproductive cells. International agreements ban most testing of nuclear weapons in the atmosphere. Such regulations have helped to eliminate the major sources of radiation. However, the amount of radioactive waste is steadily increasing. Scientists are studying ways to dispose of these wastes safely and permanently.

Pesticides affect more than the natural cycles in soil and water. Much pesticide material never reaches the insects or other pests it is intended to kill. Instead, tiny particles of the pesticide travel through the air and water, sometimes for great distances. Humans and animals that come in direct contact with the pesticide take it into their bodies, and the material collects in tissues and organs. Humans and animals also take in pesticides indirectly when they eat organisms that contain the material. For example, a large fish can take in heavy amounts of pesticide by eating smaller fish that have the material in their bodies. A human being may then eat the large fish and acquire the highly concentrated pesticide material that the fish contains. When materials are passed along from one organism to another in this way, the materials travel through an ecological system that is called a food chain.

Дата добавления: 2015-10-30