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Sources of water pollution in lakes, streams, rivers, oceans, and other water bodies include municipal sewage, industrial waste, agricultural runoff, and oil spills, among others. Waste may be dumped in water intentionally or accidentally. Although water pollution is usually caused by human activity, some natural phenomena-like volcanoes, storms, and earthquakes-cause changes in water chemistry. Sometimes, high saline or mineral content of water makes it unfit for certain uses, even though the water is not polluted in the traditional definition of pollution.
Many toxic synthetic chemicals cannot be broken down by natural processes and cause serious harm. These substances may be dissolved or suspended in water or deposited in sediments, but they do not go away. This results in the pollution of water-the quality of the water deteriorates affecting aquatic ecosystems. Pollutants can also seep down and affect groundwater deposits.
Water pollution has worsened since World War II with the advent of what is known as the “chemical age,” which has impacted the quality of water worldwide with industrial and agricultural chemicals. Eutrophication of water bodies (caused by nitrates and phosphates from various sources, including fertilizer runoff) has greatly affected the quality of water in large parts of the world. The effects of water pollution are devastating for living beings. Contaminated water destroys aquatic life, reduces its reproductive ability, and results in ecosystems that can no longer support full biological diversity.
Sources of Pollution
There are many sources of water pollution, such as city sewage, also known as sanitary sewage or domestic sewage, which refers to wastewater from households. This water contains a wide variety of dissolved and suspended impurities such as organic materials and plant nutrients, and human waste. It contains inorganic products such as synthetic detergents containing phosphates, which affect the health of all forms of life in water. Most cities do not have adequate facilities to treat wastewater and much of it is discharged into water bodies.
Bacterial contamination of surface water from sewage caused serious health problems in major cities in Europe and North America in the mid-19th century. Cities built sewer networks to route domestic waste downstream of drinking water intakes to prevent contamination of the drinking water. These sewage networks and waste treatment facilities expanded rapidly in the developed world. In the developing world, where governments sometimes lack financial resources to expand sewage and water infrastructure, outbreaks of waterborne diseases like cholera still occur.
Industrial waste or effluents, usually containing specific and readily identifiable chemical compounds, are another source of water pollution. Many plants (e.g., paper mills, tanneries, sugar mills, distilleries, and thermal power stations) generating these effluents do not have adequate treatment facilities because these small-scale industries cannot afford enormous investments in pollution control equipment. Major industries have treatment facilities for industrial effluents, yet enough small-scale operations pollute water to counter measures taken by major industries.
Agricultural runoff is another source of water pollution. Intensive cultivation of crops usually involves chemicals (nitrates, phosphates) and pesticides (such as DDT) and water from these fields containing fertilizers and pesticides not only drains into rivers or lakes, but also seeps into groundwater in a process known as leaching. Scientists also believe that massive and largely unregulated use of antibiotics in agriculture and aquaculture may present a great risk to the aquatic environment and human health.
Petrochemicals are also threats to water quality. One of the greatest disasters with petrochemicals was the 1989 oil spill of the Exxon Valdez, which contaminated about 1,500 miles of Alaska’s coastline. It killed birds, mammals, and fish and disrupted the ecosystem in the path of the oil. Major spills like these are few, but they pollute water and cause damage to the aquatic ecosystem. Ships and tankers also discharge water taken on in one location in other locations, causing transmission of pollutants, diseases transmission vectors, and nonnative species, which can be disastrous for certain delicate aquatic ecosystems.
Point and Nonpoint Sources
Water pollution sources can be categorized in another way: as direct, or point, sources and indirect, or nonpoint, sources of pollution. Liquid effluents from factories, refineries, and waste treatment plants, which are emitted directly into water bodies, are called point sources of pollution. It is simpler to regulate the standards for such emissions, since they are identifiable and quantifiable. Even though there are regulations governing the emissions, it does not guarantee that these emissions are pollutant-free.
Rain water flowing from improperly disposed of waste, whether domestic or industrial, can also result in water pollution. Leachate from landfill sites also results in water pollution. These are examples of nonpoint source pollution. Indirect sources also include contaminants that enter water bodies from the atmosphere via acid rain, which contains emissions from cars and factories. Both point and nonpoint pollutants and contaminants can be many different types, including organic, inorganic, radioactive, and acid or base.
Other Types of Pollution
Metals or other elements in water are also of great concern. Mercury can be released into the air by human activities such as metallurgical processing, municipal and medical waste incineration, and power generation from coal combustion. It is also released to the atmosphere by natural phenomena like volcanic eruptions, forest fires, and the weathering of geological formations. Once deposited in or discharged to water bodies, mercury can be converted by bacteria into mercury compounds, such as methyl mercury, which accumulate in the food chain. Fish consumption exposes humans to methyl mercury, as observed in Minamata Bay in Japan in the 1950s. Even though eating fish offers nutritional benefits, caution must be taken to avoid eating too much fish containing excessive levels of methyl mercury or PCBs.
Researchers are detecting trace amounts of pharmaceuticals in water, especially in the developed world, because of high consumption of medicines. Other chemical ingredients from cosmetics, toiletries, food additives, and veterinary drugs have also been found. As a group, these chemicals have been dubbed PPCPs (pharmaceuticals and personal care products). Scientists and policy makers have started worrying about the possible effect and harm to human health and environment of these chemicals, even though the amounts detected are minutetypically between 20 parts per billion and less than one part per trillion for each substance. Many drug compounds dissolve in water, but about one third dissolve only in fat.
This enables them to enter cells and move up through the food chain to become more concentrated. Deformities in the reproductive systems of fish and frogs show that these chemicals are not harmless. Recent research has shown that exposure to even very small amounts of toxic chemicals can be harmful to humans and other forms of life. A developing fetus, an infant, or an adult with a compromised immune system would be even more at risk. The Canadian government is pioneering approaches to the problem of PPCPs under a program called the Environmental Impact Initiative. The program includes research, public education, and the introduction of environmental assessment regulations.
Both developed and developing countries have to deal with water pollution. In the developed world, different types of pollution occurred sequentially, with the result that most developed countries successfully dealt with major surface water pollution. In contrast, in developing countries (such as China, India, Brazil, and Mexico) both surface and groundwater pollution not only occurred simultaneously but also at such a rapid rate that these countries hardly had financial resources, technologies, or time to cope with them.
Legislatures all over the world have passed laws and developed regulations to combat water pollution. Governments alone, however, cannot solve the problem, especially during the present era when downsizing of governments to conserve funds has resulted in losses of environmental monitoring capability and capacity. Science is also seeking practical solutions to minimize the present level at which pollutants are introduced into the environment and for remediation of past problems. Individuals and communities can help minimize water pollution by planting trees, reducing household waste, disposing of household chemicals responsibly, recycling packages made with polluting dyes, and reducing the use of fertilizers and lawn chemicals. The developed world and developing countries must collaborate to prevent further pollution. Our leaders-whether political or industrial-must think of sustainable development rather than economic expansion.
- Boczek, “Global and Regional Approaches to the Protection and Preservation of the Marine Environment,” Case Western Reserve Journal of International Law (v.39, 1984);
- J. Puckett, “Identifying the Major Sources of Nutrient Water Pollution,” Environmental Science & Technology (v.29, 1995).