Environmental pollution is one of the most serious problems facing humanity and other life forms on our planet today. Badly polluted air can harm crops and cause life-threatening illnesses. Some air pollutants have reduced the capacity of the atmosphere to filter out the sun's harmful ultraviolet radiation. Many scientists believe that these and other air pollutants have begun to change climates around the world. Water and soil pollution threaten the ability of farmers to grow enough food to feed the world's population. Ocean pollution endangers many marine organisms.

Many people think of air, water, and soil pollution as distinct forms of pollution. However, each of the parts of an environment--air, water, and soil--depends upon the others and upon the plants and animals living within the environment. The relationships among all the living and nonliving things in an environment make up an ecological system, called an ecosystem. All the ecosystems of the earth are connected. Thus, pollution that seems to affect only one part of the environment may also affect other parts. For example, sooty smoke from a power plant might appear to harm only the atmosphere. But rain can wash some harmful chemicals in the smoke out of the sky and onto land or into waterways.

Some pollution comes from one specific point or location, such as a sewage pipe spilling dirty water into a river. Such pollution is called point source pollution. Other pollution comes from large areas. Water can run off farmland and carry pesticides and fertilizers into rivers. Rain water can wash petrol, oil, and salt from roads and car parks into the wells that supply drinking water. Pollution that comes from such large areas is called nonpoint source pollution.

Nearly everyone would like to have pollution reduced. Unfortunately, most of the pollution that now threatens the health of our planet comes from products that many people want and need. For example, cars provide the convenience of personal transportation, but they create a large percentage of the world's air pollution. Factories make products that people use and enjoy, but industrial processes can also pollute. Pesticides and fertilizers aid in growing large quantities of food, but they also poison the soil and waterways.

To end or greatly decrease pollution, people would have to reduce the use of cars and other modern conveniences, and some factories would have to close or change production methods. Because most people's jobs are dependent on industries that contribute to environmental pollution, shutting down these industries would increase unemployment. In addition, if farmers suddenly stopped using chemical fertilizers and pesticides, there would be less food to feed the people of the world.

Over time, however, pollution can be reduced in many ways without seriously disrupting people's lives. For example, governments can pass laws that encourage businesses to adopt less polluting methods of operation. Scientists and engineers can develop products and processes that are cleaner and safer for the environment. And individuals and groups of people around the world can themselves find ways to reduce environmental pollution.

Types of pollution

The chief types of environmental pollution include air pollution, water pollution, soil pollution, pollution caused by solid waste and hazardous waste, and noise pollution.

Air pollution is the contamination of the air by substances such as fuel exhaust and smoke. It can harm the health of plants and animals and damage buildings and other structures. According to the World Health Organization, about one-fifth of the world's people are exposed to hazardous levels of air pollutants.

The atmosphere normally consists of nitrogen, oxygen, and small amounts of carbon dioxide and other gases and particulates (tiny particles of liquid or solid matter). A number of natural processes work to keep the constituents of the atmosphere in balance.

For example, plants use carbon dioxide and produce oxygen. Animals, in turn, use up oxygen and produce carbon dioxide through respiration. Forest fires and volcanic eruptions shoot gases and particulates into the atmosphere, and rain and wind wash them out or scatter them.

Air pollution occurs when industries and vehicles release such large amounts of gas and particulates into the air that natural processes can no longer keep the atmosphere in balance. There are two chief types of air pollution: (1) outdoor and (2) indoor.

Outdoor air pollution. Each year, hundreds of millions of tons of gases and particulates pour into the atmosphere. Most of this pollution results from the burning of fuel to power motor vehicles and heat buildings. Some air pollution also comes from business and industrial processes. For example, many dry-cleaning plants remove dirt from clothing with a chemical called perchloroethylene, a hazardous air pollutant. The burning of rubbish may discharge smoke and heavy metals, such as lead and mercury, into the atmosphere. Most heavy metals are highly poisonous.

One of the most common types of outdoor air pollution is smog. Smog is a brown, hazy mixture of gases and particulates. It develops when certain gases released by the combustion of petrol and other petroleum products react with sunlight in the atmosphere. This reaction creates harmful chemicals that make up smog.

One of the chemicals in smog is a toxic form of oxygen called ozone. Exposure to high concentrations of ozone causes headaches, burning eyes, and irritation of the respiratory tract in many individuals. In some cases, ozone in the lower atmosphere can cause death. Ozone can also damage plant life and even kill trees.

Acid rain is a term for rain and other precipitation that is polluted mainly by sulphuric acid and nitric acid. These acids form when gases called sulphur dioxide and nitrogen oxides react with water vapour in the air. These gases come chiefly from the burning of coal, gas, and oil by cars, factories, and power plants. The acids in acid rain move through the air and water and harm the environment over large areas. Acid rain has killed entire fish populations in a number of lakes. It also damages buildings, bridges, and statues. Scientists believe high concentrations of acid rain can harm forests and soil. Regions affected by acid rain include large parts of eastern North America, Scandinavia, and central Europe.

Chemicals called chlorofluorocarbons (CFC's) are pollutants that destroy the ozone layer in the upper atmosphere. CFC's are used in refrigerators and air conditioners and to make plastic foam insulation. Ozone, the same gas that is a harmful pollutant in smog, forms a protective layer in the upper atmosphere. It shields the earth's surface from more than 95 per cent of the sun's ultraviolet radiation. As CFC's thin the ozone layer, more ultraviolet radiation reaches the surface of the earth. Overexposure to such radiation damages plants and greatly increases people's risk of skin cancer.

The greenhouse effect is the warming that results when the earth's atmosphere traps the sun's heat. It is created by carbon dioxide, methane, and other atmospheric gases, which allow sunlight to reach the earth but prevent heat from leaving the atmosphere. These heat-trapping gases are often called greenhouse gases.

Fuel burning and other human activities are increasing the amount of greenhouse gases in the atmosphere. Many scientists believe such an increase is intensifying the greenhouse effect and raising temperatures worldwide. This increase in temperature, called global warming, may cause many problems. A strong greenhouse effect could melt glaciers and polar icecaps, flooding coastal areas. It could also shift rainfall patterns, creating more droughts and severe tropical storms.

Indoor air pollution occurs when buildings with poorly designed ventilation systems trap pollutants inside. The main types of indoor pollutants are tobacco smoke, gases from stoves and furnaces, household chemicals, small fibre particles, and hazardous fumes given off by building materials, including insulation, glue, and paint. In some office buildings, high amounts of these substances cause headaches, eye irritation, and other health problems in workers. Such health problems are sometimes called sick building syndrome.

Radon, a radioactive gas given off through the decay of uranium in rocks within the earth, is another harmful indoor pollutant. It can cause lung cancer if inhaled in large quantities. People can be exposed to radon when the gas leaks into basements of homes built over radioactive soil or rock. Energy-efficient buildings, which keep in heated or cooled air, can trap radon indoors and lead to high concentrations of the gas.

In a healthy water system, a cycle of natural processes turns wastes into useful or harmless substances. The cycle begins when organisms called aerobic bacteria use the oxygen dissolved in water to digest wastes. This digestion process releases nitrates, phosphates, and other nutrients (chemical elements that living things need for growth). Algae and aquatic green plants absorb these nutrients. Microscopic animals called zooplankton eat the algae, and fish eat the zooplankton. The fish, in turn, may be eaten by larger fish, birds, or other animals. These larger animals produce body wastes and eventually die. Bacteria break down dead animals and animal wastes, and the cycle begins again.

Water pollution occurs when people put so much waste into a water system that its natural cleansing processes cannot function properly. Some waste, such as oil, industrial acids, or farm pesticides, poisons aquatic plants and animals. Other waste, such as phosphate detergents, chemical fertilizers, and animal manure, pollutes by supplying excess nutrients for aquatic life. This pollution process is called eutrophication. The process begins when large amounts of nutrients flow into a water system. These nutrients stimulate excessive growth of algae. As more algae grow, more also die. Bacteria in the water use up large amounts of oxygen digesting the excess dead algae. The oxygen level of the water then drops, causing many aquatic plants and animals to die.

Water pollution comes from businesses, farms, homes, industries, and other sources. It includes sewage, industrial chemicals, agricultural chemicals, and livestock wastes. Another form of water pollution is the clean but heated water discharged by power plants into waterways. This heated water, called thermal pollution, harms fish and aquatic plants by reducing the amount of oxygen in the water. Chemical and oil spills can also cause devastating water pollution that kills water birds, shellfish, and other wildlife.

Some water pollution occurs when there is improper separation of sewer wastewater from clean drinking water. In areas that lack modern sewage treatment plants, water carrying human waste can flow into drinking water supplies. Disease-carrying bacteria in the waste can then contaminate the drinking water and cause illnesses such as cholera and dysentery. In areas with good sanitation, most human waste flows through underground pipes to special treatment plants that kill the harmful bacteria and remove the solid waste.
(Source: World Book)