Aspects of this topic are discussed in the following places at Britannica.
Among the most serious chemical pollutants are the chlorinated hydrocarbon pesticides, such as DDT, aldrin, and dieldrin; the polychlorinated biphenyls (PCBs), which are used in a variety of industrial processes and in the manufacture of many kinds of materials; and such metals as mercury, lead, cadmium, arsenic, and beryllium. All of these substances persist in the environment, being slowly,...
...such as drinking, swimming, or fishing. Although water quality is affected by natural conditions, the word pollution usually implies human activity as the source of contamination. Water pollution is caused primarily by the drainage of contaminated waters into surface water or groundwater. Water-pollution control, therefore, primarily involves the removal of impurities before...
in environmental works: Sources of pollution )Water pollutants may originate from a point source or from a dispersed source. A point-source pollutant is one that reaches water from a single pipeline or channel, such as a sewage discharge or outfall pipe. Dispersed sources are broad, unconfined areas from which pollutants enter a body of water. Surface runoff from farms, for example, is a dispersed source of pollution, carrying animal...
...technology, some process streams are recycled, and process streams that cannot be reused are subjected to advanced water treatment prior to discharge into the receiving environment. In this way, water pollution is kept to the minimum achievable by modern technology. Compare sulfite process.
Water pollution involves the release into lakes, streams, rivers, and oceans of substances that become dissolved or suspended in the water or deposited upon the bottom and accumulate to the extent that they interfere with the functioning of aquatic ecosystems. It may also include the release of energy in the form of radioactivity or heat, as in the case of thermal pollution. Any body of water...
in hydrologic sciences: Water quality )...through organic material such as roots and leaf litter, dissolves minerals from the soil and rock through which it flows, and reacts with living things from microscopic organisms to humans. Water quality also is modified by temperature, soil bacteria, evaporation, and other environmental factors.
...became a centre of commercial transportation. It subsequently became highly industrialized, and by the mid-20th century the lower reaches of the Cuyahoga River had become one of the most severely polluted rivers in the United States; national attention was focused on the Cuyahoga’s condition when, on June 22, 1969, an oil slick floating on the river surface caught fire, damaging two railroad...
...difference is caused by suspended sediment—in lakes may result in a rapid decrease of reservoir capacity. Equally significant, the industrial discharge of large amounts of polluted or heated water may generate density currents that have adverse effects on neighbouring human or animal communities.
Pollution produced by chemical preparations applied for agricultural purposes has created serious problems for the world’s freshwater fisheries; fish cultivation is increasingly restricted to man-made waters. Traditional freshwater fisheries still supply basic protein to China, Southeast Asia, and tropical Africa but have been seriously affected in the United Kingdom, continental Europe, Japan,...
...and the southern portion of Lake Michigan are now ringed with large population concentrations. The lakes have not benefited from this development, however, and have been seriously affected by pollution. Concern over the fate of the lakes reached a high pitch in the late 20th century, with both the U.S. and the Canadian governments and individuals investigating methods for reversing the...
...wells. In the southwestern region of the country, water supplies have been tapped heavily and in some areas have been exhausted with no hope of replacement. This extensive utilization of fresh waters in the United States and throughout the globe make them particularly susceptible to pollution. Leachates from fertilizers, herbicides, and pesticides are found in some freshwater bodies; toxic...
Lake water is also used extensively for cooling purposes. Although this water may not be affected chemically, its change in thermal quality may be detrimental to the environment into which it is disposed, either directly, by affecting fish health or functions, or indirectly, by causing excessive plant production and ultimate deoxygenation due to biological decay. Both fossil- and...
in lake: Heat transfer )Heat introduced to lakes in large quantities, as a waste product of cooling processes in power-generating plants and other industrial concerns, is presently viewed with some concern as a pollutant, especially in small lakes. If the heat is injected at the surface it will spread initially according to the momentum of the influent and the speed and direction of ambient surface currents. When the...
Some of the most complex relationships in biotoxicology are found in the marine environment. Certain marine biotoxins, such as ciguatera fish poison, apparently originate in marine plants, are ingested by herbivores and then passed on to carnivores and eventually to humans. The extremely complex mechanism by which this is accomplished is not clear. With the buildup of toxic industrial chemical...
A variety of pollutants, derived from municipal, industrial, and agricultural sources, have been identified in the waters and sediments of the Mississippi River. Organic compounds and trace metals occur in relatively low concentrations; in addition to those naturally present in the water, they derive from industrial and municipal wastes and runoff from agricultural and urban areas. High...
Similar changes occur in aquatic systems in response to chronic pollution. The early stages of pollution in bodies of water usually involve enrichment with nutrient elements, especially nitrogen and phosphorus, a process known as eutrophication.
...of death in captivity and, exceptionally, in the wild. Bacterial diseases take their toll and sometimes cause wholesale die-offs. Thousands of ducks have succumbed to botulism when shallow, brackish waters dry out in warm countries and the bacteria responsible multiply, producing toxins that cause a fatal paralysis if ingested. Fowl cholera (Pasteurella) sometimes...
...adverse ecological consequences. This left southern and western Kazakhstan, as before, greatly in need of additional water resources. Kazakhstan also suffers from the disastrous depletion and the contamination (by pesticides and chemical fertilizers) of the Syr Darya flow, on which the republic depends greatly for crop irrigation.
in Kazakhstan: Health and welfare )...protection a high priority. In the vicinity of the Aral Sea, and especially in Qyzylorda (Kzyl-Orda) and Aqtöbe provinces, Kazaks suffer from the pollution and salinization of the sea. Its waters are contaminated with pesticides, especially DDT, and with chemical fertilizer fed into it by various rivers; the contraction of the Aral Sea has left a toxic dust in the newly formed salt...
...operations on the Ile River. The diversion of water to fill the Qapshaghay reservoir and to provide for irrigation reduced the flow of the Ile River by two-thirds and caused a decline in the lake’s water level. The surface of Lake Balkhash dropped 7 feet (2.2 m) between 1970 and 1987. The lake has become increasingly saline and has also suffered pollution from the leakage of fuel-storage depots...
Pesticides and chemical fertilizers used on the cotton fields have damaged the environment and led to health problems in the population. The upriver irrigation systems carry these pollutants into the rivers descending from Tajikistan’s mountains and into neighbouring republics.
...beans, kenaf, sesame, grapes, vegetables, and melons, and nurtures cattle and silkworms. Serious problems, however, threaten the prosperity of this region. The disastrous decline in the Amu Darya’s outflow, the effects of extreme pollution from pesticide and chemical runoff, and soil and water salinization resulting from the desiccation and shrinkage of the Aral Sea threaten to ruin the Amu...
The diversion of the Amu Darya and the Syr Darya has resulted in intense salinization of the sea, which also has suffered tremendous pollution from insecticides and chemical fertilizers during the past several decades. This chemical pollution and the decline in water level have killed the once-flourishing fishing industry, grounded most ships that formerly worked within the Aral’s shores, and...
Shifting demographic patterns in the United States since 1950 have brought millions of new residents to the gulf region. This growing population has increased the demand for fresh water and generated large quantities of sewage and industrial waste (including heavy metals and polychlorinated biphenyls), much of which have been discharged directly into gulf waters or indirectly by rivers draining...
Until the 1960s the waters of London’s rivers were as polluted as its air. Deoxygenated and black with scum, they showed the effects of sewage pollution and uncontrolled industrial effluents. Tighter environmental standards, combined with the closure of factories, produced an improvement in water quality. Salmon, sea trout, roach, and flounder returned to the tidal Thames, together with...
Growing industrialization, shoreline populations, and tourism since the mid-20th century have resulted in severely polluted waters in many Mediterranean coastal areas. Pollution in the Mediterranean tends to remain near its source of discharge because of relatively weak tidal and current movements. Despite the absence of significant transborder effects, the countries of the region have agreed...
...as the level of the western European economy has risen. The volume of shipping to the sea’s bordering countries has grown steadily, thereby generating problems not only of navigation but also of pollution from operational discharges as well as from accidents. Land-based pollution, including the dumping of sewage and industrial wastes, is also a serious problem, particularly in the southern...
...the discharge of untreated sewage or the seepage of soluble mineral fertilizers, for example) to coastal waters results in increased phytoplankton growth, high levels of dissolved and particulate organic materials, decreased penetration of light through seawater, and alteration of the community structure of bottom-dwelling organisms. Through industrial and automotive emissions, lead...
in ocean: Waste disposal and other related actions )...in global population, have given rise to quantities and forms of waste that are now taxing the capacity of the oceans to absorb them. Extensive marginal areas of the oceans have been heavily polluted by human wastes ranging from the raw sewage of urban centres to junked appliances and automobiles. Less apparent but more insidious forms of pollution are toxic chemicals, nuclear wastes,...
Open-ocean areas of the Atlantic have remained largely free of human-generated wastes, but increases in marine pollution have been found in poorly mixed coastal waters, especially those located near population and industrial centres and river mouths. Although marine pollution is frequently associated with such activities as ocean dumping, shipping (notably crude oil), and offshore hydrocarbon...
...wastes, but the increasing pace of economic activity—particularly the transport of crude oil and other hazardous substances—has led to measurable levels of pollution in some nearshore waters, especially close to ports and large coastal cities. At the same time, the loads of pollutants in waters close to land have increased—primarily raw sewage, industrial waste products such...
Major rivers, including the Dnieper, Dniester, Inhul, and Donets, are seriously polluted with chemical fertilizers and pesticides from agricultural runoff and with poorly treated or untreated sewage. Coastal water pollution in the Sea of Azov and the Black Sea has necessitated the closing of beaches and has led to a dramatic reduction in fish catches. The freshwater flow into the Sea of Azov...
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Aspects of this topic are discussed in the following places at Britannica.
Among the most serious chemical pollutants are the chlorinated hydrocarbon pesticides, such as DDT, aldrin, and dieldrin; the polychlorinated biphenyls (PCBs), which are used in a variety of industrial processes and in the manufacture of many kinds of materials; and such metals as mercury, lead, cadmium, arsenic, and beryllium. All of these substances persist in the environment, being slowly,...
...such as drinking, swimming, or fishing. Although water quality is affected by natural conditions, the word pollution usually implies human activity as the source of contamination. Water pollution is caused primarily by the drainage of contaminated waters into surface water or groundwater. Water-pollution control, therefore, primarily involves the removal of impurities before...
in environmental works: Sources of pollution )Water pollutants may originate from a point source or from a dispersed source. A point-source pollutant is one that reaches water from a single pipeline or channel, such as a sewage discharge or outfall pipe. Dispersed sources are broad, unconfined areas from which pollutants enter a body of water. Surface runoff from farms, for example, is a dispersed source of pollution, carrying animal...
...became a centre of commercial transportation. It subsequently became highly industrialized, and by the mid-20th century the lower reaches of the Cuyahoga River had become one of the most severely polluted rivers in the United States; national attention was focused on the Cuyahoga’s condition when, on June 22, 1969, an oil slick floating on the river surface caught fire, damaging two railroad...
...difference is caused by suspended...
Aspects of this topic are discussed in the following places at Britannica.
Water pollutants may originate from a point source or from a dispersed source. A point-source pollutant is one that reaches water from a single pipeline or channel, such as a sewage discharge or outfall pipe. Dispersed sources are broad, unconfined areas from which pollutants enter a body of water. Surface runoff from farms, for example, is a dispersed source of pollution, carrying animal...
Aspects of this topic are discussed in the following places at Britannica.
...Because wastewater treatment plants cannot handle large volumes of storm water, sewage must bypass the treatment plants during wet weather and be discharged directly into the receiving water. These combined-sewer overflows, containing untreated domestic sewage, cause recurring water-pollution problems and are very troublesome sources of pollution.
Aspects of this topic are discussed in the following places at Britannica.
...efforts and pursued a policy promoting the international control of nuclear weaponry. Canada undertook efforts to reduce pollution in its coastal waters, signing with the United States in 1972 the Great Lakes Water Quality Agreement to control pollution of the lakes.
Aspects of this topic are discussed in the following places at Britannica.
...or channel, such as a sewage discharge or outfall pipe. Dispersed sources are broad, unconfined areas from which pollutants enter a body of water. Surface runoff from farms, for example, is a dispersed source of pollution, carrying animal wastes, fertilizers, pesticides, and silt into nearby streams. Urban storm water drainage is also considered a dispersed source because of the many...
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