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Water Pollution


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Introduction to water pollution:


Water pollution is a major problem in the global context. It has been suggested that it is the leading worldwide cause of deaths and diseases,[#cite_note-death-0 ]and that it accounts for the deaths of more than 14,000 people daily. In addition to the acute problems of water pollution in developing countries and industrial countries continue to struggle with pollution problems as well. In the most recent national report on water qualities in the United states 45 percent of assessed stream lines, 47 percent of assessed lake acres, and 32 percent of assessed bay and estuarine square miles were classified as polluted. Water is typically referred to as polluted when it is impaired by contaminants and either does not support a human use, like serving as drinking water, and/or undergoes a marked shift in its ability to support its constituent biotic communities, such as fish. Natural pena such as volcanoes, algae blooms, and earthquakes, and earth quakes also cause major changes in water quality and the ecological status of water. Water pollution has many causes and characteristics.

Water pollution categories

Surface water and groundwater have often been studied and managed as separate resources, although they are interrelated. Sources of surface water pollution are generally grouped into two categories based on their origin.

Groundwater pollution

Interactions between groundwater and surface water are complex. Consequently, groundwater pollution, sometimes referred to as groundwater contamination, is not as easily classified as surface water pollution.[#cite_note-circ1139-3 [4]] By its very nature, groundwater [/wiki/Aquifer aquifers] are susceptible to contamination from sources that may not directly affect surface water bodies, and the distinction of point vs. nonpoint source may be irrelevant. A spill of a chemical contaminant on soil, located away from a surface water body, may not necessarily create point source or non-point source pollution, but nonetheless may contaminate the aquifer below. Analysis of groundwater contamination may focus on [/wiki/Soil soil] characteristics and [/wiki/Hydrology hydrology], as well as the nature of the contaminant itself. Causes of water pollution== Causes of water pollution == The specific contaminants leading to pollution in water include a wide spectrum of [/wiki/Chemical chemicals], [/wiki/Pathogen pathogens], and physical or sensory changes such as elevated temperature and discoloration. While many of the chemicals and substances that are regulated may be naturally occurring ([/wiki/Calcium calcium], [/wiki/Sodium sodium], [/wiki/Iron iron], [/wiki/Manganese manganese], etc.) the [/wiki/Concentration concentration] is often the key in determining what is a natural component of water, and what is a contaminant.

[/wiki/Oxygen Oxygen]-depleting substances may be natural materials, such as [/wiki/Plant plant] matter (e.g. leaves and grass) as well as man-made chemicals. Other natural and anthropogenic substances may cause [/wiki/Turbidity turbidity] (cloudiness) which blocks light and disrupts plant growth, and clogs the [/wiki/Gill gills] of some fish species.[#cite_note-EPA-AGFact-6 [7]]

Many of the chemical substances are [/wiki/Toxic toxic]. Pathogens can produce [/wiki/Waterborne_diseases waterborne diseases] in either human or animal hosts. Alteration of water's physical chemistry include acidity (change in [/wiki/PH pH]), [/wiki/Electrical_conductivity electrical conductivity], temperature, and eutrophication. [/wiki/Eutrophication Eutrophication] is the [/wiki/Fertilization fertilization] of [/wiki/Surface_water surface water] by [/wiki/Nutrients nutrients] that were previously [/wiki/Scarce scarce].

Chemical and other contaminants

Muddy river polluted by sediment. Photo courtesy of [/wiki/United_States_Geological_Survey United States Geological Survey].

Contaminants may include [/wiki/Organic_compound organic] and [/wiki/Inorganic inorganic] substances.

Organic water pollutants include:

  • [/wiki/Detergents Detergents]
  • [/wiki/Disinfection_by-product Disinfection by-products] found in chemically [/wiki/Disinfection disinfected] [/wiki/Drinking_water drinking water], such as [/wiki/Chloroform chloroform]
  • [/wiki/Food_processing Food processing] waste, which can include oxygen-demanding substances, fats and grease
  • [/wiki/Insecticide Insecticides] and [/wiki/Herbicide herbicides], a huge range of [/wiki/Organohalide organohalides] and other [/wiki/Chemical_compounds chemical compounds]
  • [/wiki/Petroleum Petroleum] hydrocarbons, including fuels ([/wiki/Gasoline gasoline], [/wiki/Diesel_fuel diesel fuel], jet fuels, and [/wiki/Fuel_oil fuel oil]) and lubricants (motor oil), and fuel [/wiki/Combustion combustion] byproducts, from [/wiki/Stormwater stormwater] [/wiki/Surface_runoff runoff][#cite_note-Burton_.26_Pitt-11 [12]]
  • [/wiki/Tree Tree] and bush debris from [/wiki/Logging logging] operations
  • [/wiki/Volatile_organic_compounds Volatile organic compounds] (VOCs), such as industrial [/wiki/Solvent solvents], from improper storage. [/wiki/Chlorinated_solvent Chlorinated solvents], which are dense non-aqueous phase liquids ([/wiki/DNAPL DNAPLs]), may fall to the bottom of reservoirs, since they don't mix well with water and are denser.
  • Various chemical compounds found in personal [/wiki/Hygiene hygiene] and [/wiki/Cosmetic cosmetic] products

Inorganic water pollutants include:

  • [/wiki/Acidity Acidity] caused by industrial discharges (especially [/wiki/Sulfur_dioxide sulfur dioxide] from [/wiki/Power_plants power plants])
  • [/wiki/Ammonia Ammonia] from food processing waste
  • [/wiki/Chemical_waste Chemical waste] as industrial by-products
  • [/wiki/Fertilizer Fertilizers] containing nutrients--[/wiki/Nitrates nitrates] and [/wiki/Phosphate phosphates]--which are found in stormwater runoff from [/wiki/Agriculture agriculture], as well as commercial and residential use[#cite_note-Burton_.26_Pitt-11 [12]]
  • [/wiki/Heavy_metals Heavy metals] from [/wiki/Motor_vehicle motor vehicles] (via [/wiki/Urban_runoff urban stormwater runoff])[#cite_note-Burton_.26_Pitt-11 [12]][#cite_note-12 [13]] and [/wiki/Acid_mine_drainage acid mine drainage]
  • [/wiki/Silt Silt] ([/wiki/Sediment sediment]) in runoff from [/wiki/Construction construction] sites, [/wiki/Logging logging], [/wiki/Slash_and_burn slash and burn] practices or land clearing sites

Macroscopic pollution—large visible items polluting the water—may be termed "floatables" in an urban stormwater context, or [/wiki/Marine_debris marine debris] when found on the open seas, and can include such items as:

  • [/wiki/Trash_(material) Trash] (e.g. paper, plastic, or food waste) discarded by people on the ground, and that are washed by [/wiki/Rainfall rainfall] into [/wiki/Storm_drain storm drains] and eventually discharged into surface waters
  • [/wiki/Nurdle Nurdles], small ubiquitous waterborne plastic pellets
  • [/wiki/Shipwreck Shipwrecks], large derelict ships

File:180px-Unit 3 - Potrero Power Plant.jpg

[/wiki/Potrero_Generating_Station Potrero Generating Station] discharges heated water into [/wiki/San_Francisco_Bay San Francisco Bay].[#cite_note-13 [14]]

Thermal pollution

[/wiki/Thermal_pollution Thermal pollution] is the rise or fall in the temperature of a natural body of water caused by human influence. A common cause of thermal pollution is the use of water as a [/wiki/Coolant coolant] by [/wiki/Power_plants power plants] and industrial manufacturers. Elevated water temperatures decreases oxygen levels (which can kill fish) and affects [/wiki/Ecosystem ecosystem] composition, such as invasion by new [/wiki/Thermophilic thermophilic] species. Urban runoff may also elevate temperature in surface waters.

Thermal pollution can also be caused by the release of very cold water from the base of [/wiki/Reservoir reservoirs] into warmer rivers.

Transport and chemical reactions of water pollutants

Most water pollutants are eventually carried by rivers into the oceans. In some areas of the world the influence can be traced hundred miles from the mouth by studies using [/wiki/Hydrology_transport_model hydrology transport models]. Advanced [/wiki/Computer_model computer models] such as [/wiki/SWMM SWMM] or the [/wiki/DSSAM_Model DSSAM Model] have been used in many locations worldwide to examine the fate of pollutants in aquatic systems. Indicator [/wiki/Filter_feeding filter feeding] species such as [/wiki/Copepods copepods] have also been used to study pollutant fates in the [/wiki/New_York_Bight New York Bight], for example. The highest [/wiki/Toxin toxin] loads are not directly at the mouth of the [/wiki/Hudson_River Hudson River], but 100 kilometers south, since several days are required for incorporation into [/wiki/Plankton planktonic] tissue. The Hudson discharge flows south along the coast due to [/wiki/Coriolis_force coriolis force]. Further south then are areas of [/wiki/Hypoxia_(environmental) oxygen depletion], caused by chemicals using up oxygen and by [/wiki/Algae_bloom algae blooms], caused by excess [/wiki/Nutrient nutrients] from algal cell death and decomposition. Fish and [/wiki/Shellfish shellfish] kills have been reported, because toxins climb the food chain after small fish consume [/wiki/Copepods copepods], then large fish eat smaller fish, etc. Each successive step up the food chain causes a stepwise concentration of pollutants such as [/wiki/Heavy_metals heavy metals] (e.g. [/wiki/Mercury_(element) mercury]) and [/wiki/Persistent_organic_pollutants persistent organic pollutants] such as [/wiki/DDT DDT]. This is known as biomagnification, which is occasionally used interchangeably with bioaccumulation.

Large [/wiki/Gyre gyres] ([/wiki/Vortex vortexes]) in the oceans trap floating [/wiki/Plastic_debris plastic debris]. The [/wiki/North_Pacific_Gyre North Pacific Gyre] for example has collected the so-called "[/wiki/Great_Pacific_Garbage_Patch Great Pacific Garbage Patch]" that is now estimated at 100 times the size of Texas. Many of these long-lasting pieces wind up in the stomachs of marine birds and animals. This results in obstruction of digestive pathways which leads to reduced appetite or even starvation.

Many chemicals undergo reactive [/wiki/Decay decay] or chemically change especially over long periods of time in [/wiki/Groundwater groundwater] reservoirs. A noteworthy class of such chemicals is the [/wiki/Chlorinated_hydrocarbons chlorinated hydrocarbons] such as [/wiki/Trichloroethylene trichloroethylene] (used in industrial metal degreasing and electronics manufacturing) and [/wiki/Tetrachloroethylene tetrachloroethylene] used in the dry cleaning industry (note latest advances in liquid carbon dioxide in dry cleaning that avoids all use of chemicals). Both of these chemicals, which are [/wiki/Carcinogens carcinogens] themselves, undergo partial decomposition reactions, leading to new hazardous chemicals (including dichloroethylene and vinyl chloride).

Groundwater pollution is much more difficult to abate than surface pollution because groundwater can move great distances through unseen [/wiki/Aquifer aquifers]. Non-porous aquifers such as [/wiki/Clay clays] partially purify water of bacteria by simple filtration (adsorption and absorption), dilution, and, in some cases, chemical reactions and biological activity: however, in some cases, the pollutants merely transform to [/wiki/Soil_contaminant soil contaminants]. Groundwater that moves through cracks and [/wiki/Caverns caverns] is not filtered and can be transported as easily as surface water. In fact, this can be aggravated by the human tendency to use natural [/wiki/Sinkhole sinkholes] as dumps in areas of [/wiki/Karst Karst] topography.

There are a variety of secondary effects stemming not from the original pollutant, but a derivative condition. An example is [/wiki/Silt silt]-bearing [/wiki/Surface_runoff surface runoff], which can inhibit the penetration of sunlight through the water column, hampering [/wiki/Photosynthesis photosynthesis] in aquatic plants.

Measurement of water pollution

This article is missing [/wiki/Wikipedia:Citing_sources citations] or needs [/wiki/Wikipedia:Footnotes footnotes]. Please help add [/wiki/Wikipedia:Inline_citations inline citations] to guard against copyright violations and factual inaccuracies. (August 2008)

See also: [/wiki/Water_quality Water quality]

File:240px-Research- water sampling equipment.jpg

[/wiki/Environmental_science Environmental Scientists] preparing water autosamplers.

Water pollution may be analyzed through several broad categories of methods: physical, chemical and biological. Most methods involve collection of samples, followed by specialized analytical tests. Some methods may be conducted [/wiki/In_situ in situ], without sampling, such as [/wiki/Temperature temperature]. Government agencies and research organizations have published standardized, validated analytical test methods to facilitate the comparability of results from disparate testing events.[#cite_note-14 [15]]


Sampling of water for physical or chemical testing can be done by several methods, depending on the accuracy needed and the characteristics of the contaminant. Many contamination events are sharply restricted in time, most commonly in association with rain events. For this reason "grab" samples are often inadequate for fully quantifying contaminant levels. Scientists gathering this type of data often employ auto-sampler devices that pump increments of water at either time or [/wiki/Discharge_(hydrology) discharge] intervals.

Sampling for biological testing involves collection of plants and/or animals from the surface water body. Depending on the type of assessment, the organisms may be identified for [/wiki/Biosurvey biosurveys] (population counts) and returned to the water body, or they may be dissected for [/wiki/Bioassay bioassays] to determine [/wiki/Toxicity toxicity].

Physical testing

Common physical tests of water include temperature, solids concentration and turbidity.

Chemical testing

Water samples may be examined using the principles of [/wiki/Analytical_chemistry analytical chemistry]. Many published test methods are available for both organic and inorganic compounds. Frequently-used methods include [/wiki/PH pH], [/wiki/Biochemical_oxygen_demand biochemical oxygen demand] (BOD), [/wiki/Chemical_oxygen_demand chemical oxygen demand] (COD), nutrients ([/wiki/Nitrate nitrate] and [/wiki/Phosphorus phosphorus] compounds), metals (including [/wiki/Copper copper], [/wiki/Zinc zinc], [/wiki/Cadmium cadmium], [/wiki/Lead lead] and [/wiki/Mercury_(element) mercury]), oil and grease, total petroleum hydrocarbons (TPH), and [/wiki/Pesticide pesticides].

See also: [/wiki/Environmental_chemistry Environmental chemistry]

Biological testing

Main article: [/wiki/Bioindicator Bioindicator]

Biological testing involves the use of plant, animal, and/or microbial indicators to monitor the health of an [/wiki/Aquatic_ecosystem aquatic ecosystem].

For microbial testing of drinking water, see [/wiki/Bacteriological_water_analysis Bacteriological water analysis].

Control of water pollution

omestic sewage

Main article: [/wiki/Sewage_treatment Sewage treatment]

File:180px-Deer Island MA.JPG

[/wiki/Deer_Island_Waste_Water_Treatment_Plant Deer Island Waste Water Treatment Plant] serving [/wiki/Boston,_Massachusetts Boston, Massachusetts] and vicinity.

In urban areas, domestic sewage is typically treated by centralized [/wiki/Sewage_treatment sewage treatment] plants. In the U.S., most of these plants are operated by local government agencies. Municipal treatment plants are designed to control [/wiki/Conventional_pollutant conventional pollutants]: BOD and suspended solids. Well-designed and operated systems (i.e., secondary treatment or better) can remove 90 percent or more of these pollutants. Some plants have additional sub-systems to treat nutrients and pathogens. Most municipal plants are not designed to treat toxic pollutants found in industrial waste water.[#cite_note-15 [16]]

Cities with sanitary sewer overflows or combined sewer overflows employ one or more [/wiki/Environmental_engineering engineering] approaches to reduce discharges of untreated sewage, including:

  • utilizing a [/wiki/Green_infrastructure green infrastructure] approach to improve storm water management capacity throughout the system[#cite_note-16 [17]]
  • repair and replacement of leaking and malfunctioning equipment[#cite_note-EPARTC-10 [11]]
  • increasing overall [/wiki/Hydraulic hydraulic] capacity of the sewage collection system (often a very expensive option).

A household or business not served by a municipal treatment plant may have an individual [/wiki/Septic_tank septic tank], which treats the waste water on site and discharges into the soil. Alternatively, domestic wastewater may be sent to a nearby privately-owned treatment system (e.g. in a rural community).

Industrial waste water

File:180px-REDOX DAF unit 225 m3-h-1000 GPM.jpg

[/wiki/Dissolved_air_flotation Dissolved air flotation] system for treating industrial waste water.

Some industrial facilities generate ordinary domestic sewage that can be treated by municipal facilities. Industries that generate waste water with high concentrations of conventional pollutants (e.g. oil and grease), toxic pollutants (e.g. heavy metals, volatile organic compounds) or other non conventional pollutants such as ammonia, need specialized treatment systems. Some of these facilities can install a pre-treatment system to remove the toxic components, and then send the partially-treated waste water to the municipal system. Industries generating large volumes of waste water typically operate their own complete on-site treatment systems.

Some industries have been successful at redesigning their manufacturing processes to reduce or eliminate pollutants, through a process called [/wiki/Pollution_prevention pollution prevention].

Heated water generated by power plants or manufacturing plants may be controlled with:

  • [/wiki/Cooling_pond cooling ponds], man-made bodies of water designed for cooling by [/wiki/Evaporation evaporation], [/wiki/Convection convection], and [/wiki/Radiation radiation]
  • [/wiki/Cooling_tower cooling towers], which transfer waste heat to the [/wiki/Atmosphere atmosphere] through [/wiki/Evaporation evaporation] and/or [/wiki/Heat_transfer heat transfer]
  • [/wiki/Cogeneration cogeneration], a process where waste heat is recycled for domestic and/or industrial heating purposes.

Agricultural waste water

File:150px-Riparian buffer on Bear Creek in Story County, Iowa.JPG

[/wiki/Riparian_buffer Riparian buffer] lining a creek in [/wiki/Iowa Iowa]

Nonpoint source controls[/wiki/Sediment Sediment] (loose [/wiki/Soil soil]) washed off fields is the largest source of agricultural pollution in the [/wiki/United_States United States].[#cite_note-EPA-AGFact-6 [7]] Farmers may utilize [/wiki/Erosion_control erosion controls] to reduce runoff flows and retain soil on their fields. Common techniques include [/wiki/Contour_plowing contour plowing], crop [/wiki/Mulch mulching], [/wiki/Crop_rotation crop rotation], planting [/wiki/Perennial perennial] crops and installing [/wiki/Riparian_buffer riparian buffers].[#cite_note-NRCS-NCPS-17 [18]][#cite_note-EPA-agmm-18 [19]]:pp. 4-95–4-96

Nutrients ([/wiki/Nitrogen nitrogen] and [/wiki/Phosphorus phosphorus]) are typically applied to farmland as commercial [/wiki/Fertilizer fertilizer]; animal [/wiki/Manure manure]; or spraying of municipal or industrial wastewater (effluent) or sludge. Nutrients may also enter runoff from [/wiki/Crop_residue crop residues], [/wiki/Irrigation irrigation] water, [/wiki/Wildlife wildlife], and [/wiki/Deposition_(Aerosol_physics) atmospheric deposition].[#cite_note-EPA-agmm-18 [19]]:p. 2-9 Farmers can develop and implement [/wiki/Nutrient_management nutrient management] plans to reduce excess application of nutrients.[#cite_note-NRCS-NCPS-17 [18]][#cite_note-EPA-agmm-18 [19]]:pp. 4-37–4-38

To minimize pesticide impacts, farmers may use [/wiki/Integrated_Pest_Management Integrated Pest Management] (IPM) techniques (which can include [/wiki/Biological_pest_control biological pest control]) to maintain control over pests, reduce reliance on chemical pesticides, and protect water quality.[#cite_note-19 [20]]


Confined Animal Feeding Operation in the [/wiki/United_States United States]

Point source wastewater treatmentFarms with large [/wiki/Livestock livestock] and [/wiki/Poultry poultry] operations, such as [/wiki/Factory_farm factory farms], are called concentrated animal feeding operations or confined animal feeding operations in the U.S. and are being subject to increasing government [/wiki/Regulation regulation].[#cite_note-20 [21]][#cite_note-21 [22]] Animal [/wiki/Slurry slurries] are usually treated by containment in [/wiki/Manure_lagoon lagoons] before disposal by spray or trickle application to grassland. [/wiki/Constructed_wetland Constructed wetlands] are sometimes used to facilitate treatment of animal wastes, as are [/wiki/Anaerobic_lagoons anaerobic lagoons]. Some animal slurries are treated by mixing with [/wiki/Straw straw] and [/wiki/Composting composted] at high temperature to produce a bacteriologically sterile and friable manure for soil improvement.

Construction site stormwater

File:180px-Silt fence EPA.jpg

[/wiki/Silt_fence Silt fence] installed on a construction site.

Sediment from construction sites is managed by installation of:

  • [/wiki/Erosion_control erosion controls], such as [/wiki/Mulch mulching] and [/wiki/Hydroseeding hydroseeding], and
  • [/wiki/Sediment_control sediment controls], such as [/wiki/Sediment_basin sediment basins] and [/wiki/Silt_fence silt fences].[#cite_note-22 [23]]

Discharge of toxic chemicals such as motor fuels and concrete washout is prevented by use of:

  • spill prevention and control plans, and
  • specially-designed containers (e.g. for concrete washout) and structures such as overflow controls and diversion berms.[#cite_note-23 [24]]

Urban runoff (stormwater)

Main article: [/wiki/Urban_runoff Urban runoff]

File:180px-Trounce Pond.jpg

[/wiki/Retention_basin Retention basin] for controlling [/wiki/Urban_runoff urban runoff]

Effective control of urban runoff involves reducing the velocity and flow of stormwater, as well as reducing pollutant discharges. Local governments use a variety of stormwater management techniques to reduce the effects of urban runoff. These techniques, called [/wiki/Best_management_practice_for_water_pollution best management practices] (BMPs) in the U.S., may focus on water quantity control, while others focus on improving water quality, and some perform both functions.[#cite_note-EPA-PDS-24 [25]]

Pollution prevention practices include [/wiki/Low_impact_development low impact development] techniques, installation of [/wiki/Green_roof green roofs] and improved chemical handling (e.g. management of motor fuels & oil, fertilizers and pesticides).[#cite_note-25 [26]] Runoff mitigation systems include [/wiki/Infiltration_basin infiltration basins], [/wiki/Bioretention bioretention] systems, constructed wetlands, [/wiki/Retention_basin retention basins] and similar devices.[#cite_note-26 [27]][#cite_note-27 [28]]

Thermal pollution from runoff can be controlled by stormwater management facilities that absorb the runoff or direct it into [/wiki/Groundwater groundwater], such as bioretention systems and infiltration basins. Retention basins tend to be less effective at reducing temperature, as the water may be heated by the sun before being discharged to a receiving stream.[#cite_note-EPA-PDS-24 [25]]:p. 5-58

See also: [/wiki/Green_infrastructure Green infrastructure]

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