Water Pollution
What is it?
Water pollution is one of the most serious environmental problems we, as a planet, face today. It occurs when substances such as human and other animal wastes, toxic chemicals, metals, and oils contaminate water. This contamination can affect rain, rivers, lakes, oceans, and the water beneath the surface of the earth, ground water (Lanz.)
Polluted water may look clean or dirty, but it all contains bacteria, viruses, chemicals, or other materials that can cause illness or death. Impurities must be removed before such water can be used safely for drinking, cooking, washing, or laundering. Some industries must clean the water before it can be used in their manufacturing processes (Dineen.)
Water pollution has become a serious problem in most countries. As a result, governments have passed laws limiting the amounts and kinds of wastes that can be dumped into water. Nations, states and provinces, cities and towns, and various industries have spent billions of dollars on research to reduce pollution and on the construction of water treatment plants. Nevertheless, pollution continues. In many parts of the world, cities and towns release untreated sewage into rivers, lakes, and coastal waters. Also, pollution that does not come from a direct point, such as a sewerage outlet or factory drain, is largely uncontrolled. These nonpoint sources of pollution include water that runs off construction sites and farmland, carrying soil particles and nutrients into streams and lakes. They also include water from lawns and gardens that may carry fertilizer and insecticide, and water from roads and parking lots that carries salt, oil, and grease (Lanz.)
Sources
There are three chief sources of water pollution. These sources are: industrial wastes, sewage, and agricultural chemicals and wastes.
Industrial Wastes
Industrialized nations discharge pollutants that include many toxic chemicals. Industries discharge much of its chemical waste directly into natural bodies of water. In addition, the burning of coal, oil, and other fuels by power plants, factories, and motor vehicles releases sulphur and nitrogen oxides into the air. These pollutants cause acid rain, which enters streams and lakes (Lanz.)
High levels of mercury have been found in fish far from industrial areas. The main sources of the mercury appear to be emissions to the atmosphere from coal-fired boilers, municipal incinerators, and smelters (Lanz.)
Some industries pollute water in a different way. They use large quantities of water to cool certain equipment. Heat from the equipment makes the water hot. The industries then discharge the hot water into rivers and lakes, heating those bodies of water. Such heating that harms plants or animals is known as thermal pollution (Dineen.)
Sewage consists of human wastes, garbage, and water that have been used for laundering or bathing. Most of the sewage in countries like the United States and Canada, go through treatment plants that remove solids and such dissolved substances as the nutrients nitrogen and phosphorus. About 25 percent of the households of the United States use septic tank systems, which pass the sewage through tanks and filter it through leaching fields into the land. Some sewage in the United States still goes untreated directly into waterways or the ocean. However, government regulations control the amount and the quality of the discharge (Gunning.)
Agricultural Chemicals and Wastes.
Water from rain or melted snow flows from farmland into streams, carrying chemical fertilizers and pesticides that farmers have used on the land. Animal wastes also can cause water pollution, particularly from feedlots with many animals. Cattle, hogs, sheep, and poultry raised on feedlots do not distribute their wastes over widespread pastureland. Instead, much of their wastes run off into nearby streams. Salt, agricultural pesticides, and toxic chemicals on the soil surface also may pollute water used for irrigation before it flows back into the ground (Lanz.)
Effects
Human illness. Water polluted with human and animal wastes can spread typhoid fever, cholera, dysentery, and other diseases. About 80 percent of the U.S. community water supplies are disinfected with chlorine to kill disease-causing germs. However, disinfection does not remove harmful chemical compounds, such as polychlorinated biphenyls (PCB's) and chloroform, or harmful metals, such as arsenic, lead, and mercury. The careless release of such toxic wastes, primarily into waste dumps, threatens ground water supplies. PCB's, chloroform, and pesticides have been found in some municipal drinking water. Scientists are concerned that drinking even small quantities of these substances over many years may have harmful effects (Batmanghelidj.)
Reduced recreational use. Pollution prevents people from enjoying some bodies of water for recreation. For example, odours and floating debris make boating and swimming unpleasant, and the risk of disease makes polluted water unsafe. Oil spilled from ships or offshore wells may float to shore. It can kill water birds, shellfish, and other wildlife. Water pollution also affects commercial and sport fishing. Fish can be killed by oil or by a lack of oxygen in the water, or they may die because of a reduction in the quantity and quality of their food supply. Industrial wastes, particularly PCB's, also harm fish (Gunning.)
Disruption of Natural Processes.
Various natural processes that occur in water turn wastes into useful or harmless substances. These processes use oxygen that is dissolved in the water. Water pollution upsets these processes, mainly by robbing the water of oxygen (Eliav.)
Mineralization is a natural process by which aerobic (oxygen-using) bacteria break down organic wastes into simpler substances. Some of these substances, such as phosphates and nitrates, are nutrients for plants. Normal quantities of these nutrients help support normal quantities of life in the water. When there are too many nutrients, however, a body of water may suffer from a process called eutrophication. The added nutrients may come from fertilizers draining off farmland or from detergents and other substances in sewage. An excess of nutrients causes the growth of higher-than-normal numbers of plants, such as pondweeds and duckweeds, plant like organisms called algae, fish and other animals, and bacteria. As more grow, more also die and decay (Weiss.)
Because the decay process uses oxygen, the additional decay uses up more of the oxygen in the water. Thus, less oxygen becomes available to support living things in the water (Weiss.)
Some types of game fish—such as salmon, trout, and whitefish—cannot live in water with reduced oxygen. Fish that need less oxygen, such as carp and catfish, will replace them. If all the oxygen in a body of water were to be used up, most forms of life in the water would die (Weiss.)
Thermal pollution can also reduce the amount of oxygen dissolved in water. In addition, the warmer-than-normal water can kill some kinds of plants and fish (Weiss.)
Control
Sewage treatment.
The most efficient sewage treatment plants use three processes—primary, secondary, and tertiary treatment. Primary and secondary treatment can remove up to 95 percent of the waste in sewage. Tertiary treatment removes even more impurities. Many plants use primary and secondary processes, and some use tertiary processes as well. However, most treated sewage still contains nutrients and toxic chemicals because secondary processes cannot remove them all (Lanz.)
Pre-treatment of Wastes.
Industries can reduce pollution by treating wastes to remove harmful chemicals before dumping the wastes into water. Using manufacturing processes that recover and reuse polluting chemicals can also reduce industrial wastes (Lanz.)
Ocean Pollution
Pollutants (substances that cause pollution) enter the ocean through accidents, carelessness, and the deliberate dumping of wastes. The ocean can absorb some types of pollutants in certain quantities because of its great size and the natural chemical processes that occur within it. But people continue to introduce more and more pollutants into the sea. The ocean will not be able to absorb it all. The ocean provides us with many necessities—and it helps keep our environment healthful. It is therefore extremely important that we work to control ocean pollution (Dineen.)
Oil is a major source of ocean pollution. Most oil pollution enters the ocean from oil spills on land or in rivers used to transport petroleum. Oil also seeps into the ocean naturally from cracks in the sea floor. Oil tanker and oil well accidents at sea account for only a small portion of ocean oil pollution, but their effects may be disastrous. The world's largest accidental oil spill occurred in June 1979, when an oil well blew out off the east coast of Mexico and spilled about 130 million gallons (490 million litres) of oil. The world's worst tanker oil spill occurred in March 1978, when a tanker ran aground off the coast of France, spilling 68 million gallons (257 million litres). The worst oil spill in the United States occurred in March 1989, when a tanker ran aground off Alaska and leaked nearly 11 million gallons (42 million litres). The world's largest oil spill occurred when Iraq deliberately released about 465 million gallons (13/4 billion litres) of oil into the Persian Gulf during the Persian Gulf War (1991). In water, much of the oil forms tar like lumps, which litter beaches and other coastal areas. Oil also coats fish, birds, and marine mammals, killing many of them (Dickinson.)
Scientists and engineers have devised several methods to clean up oil spills. One method involves placing a ring of floating devices around the spill to prevent it from spreading. Pumps or skimming devices then collect the oil, which floats on the surface of the water. Oil may also be recovered by placing sheets or particles of floating, oil-absorbing material on the ocean surface. Burning the oil cleans a spill, but it produces air pollution. Detergents help break up spills, but they may cause additional harm to marine life (Weiss.)
Ocean dumping
The deliberate dumping of waste products into the sea is another major source of ocean pollution. Such products include industrial wastes and sewage. Industries dump chemicals, animal and plant matter, and other pollutants. Sewerage systems carry human wastes, ground-up garbage, and water used for bathing and laundering to the sea. Waste treatment plants remove some of the most poisonous wastes from sewage, but most treated sewage still contains material harmful to the ocean. By the late 1980's, the United States and Europe were dumping millions of tons of waste products into the ocean every year (Lanz.)
Plastics dumped into the ocean form an especially damaging group of pollutants because they do not break down easily. Sea birds, turtles, seals, whales, and other marine animals eat plastic nets, bags, and packing material. Animals that mistake plastic items for food die of starvation if the plastic blocks the digestive system. Tiny plastic pellets also litter the ocean. These pellets tend to float on the ocean surface, where they disrupt the environment of microscopic, surface-dwelling organisms (Eliav, Gunning.)
By the late 1980's, an estimated 16 billion pounds (6.4 billion kilograms) of plastic was being dumped into the ocean annually. The figure includes plastic trash discarded from ships and fishing vessels. In December 1988, an international treaty banning the dumping of plastics from ships and other vessels went into effect. Russia, the United Kingdom, the United States, and several other countries have ratified the treaty (Gunning.)