A practical definition of water pollution is: "Water pollution is the addition of substances or energy forms that directly or indirectly alter the nature of the water body in such a manner that negatively affects its legitimate uses."[1]: 6 Water is typically referred to as polluted when it is impaired byanthropogenic contaminants. Due to these contaminants, it either no longer supports a certain human use, such asdrinking water, or undergoes a marked shift in its ability to support its biotic communities, such as fish.
Hormones (fromanimal husbandry and residue from humanhormonal contraception methods) and synthetic materials such asphthalates that mimic hormones in their action. These can have adverse impacts even at very low concentrations on the natural biota and potentially on humans if the water is treated and utilized for drinking water.[7][8][9]
Pathogens likeHepatovirus A (HAV may be present in treated wastewater outflows and receiving water bodies but is largely removed during further treatment of drinking water[10])
Inadequately treated wastewater can convey nutrients, pathogens, heterogenous suspended solids and organic fecal matter.[1]: 6
Poster to teach people in South Asia about human activities leading to the pollution of water sources
Coliforms, such asE. coli, may not be pathogenic in and of themselves, but are used asan indicator of co-occurring pathogens that should take slightly less time to die or degrade[1]: 51
* Sources of these pollutants are household and industrial wastewater, urban runoff and stormwater drainage from agricultural areas[1]: 7
Pathogens
Bacteria, viruses,protozoans andparasitic worms are examples of pathogens that can be found in wastewater.[1]: 47 In practice,indicator organisms are used to investigate pathogenic pollution of water because the detection of pathogenic organisms in water sample is difficult and costly, because of their low concentrations. The indicators (bacterial indicator) of fecal contamination of water samples most commonly used are total coliforms (TC) or fecal coliforms (FC), the latter also referred to as thermotolerant coliforms, such asEscherichia coli.[1]: 52–53
Bauxite residue is anindustrial waste that is dangerously alkaline and can lead to water pollution if not managed appropriately (photo fromStade, Germany).Muddy river polluted by sediment
Theenvironmental effect of pharmaceuticals and personal care products (PPCPs) is being investigated since at least the 1990s. PPCPs include substances used by individuals for personal health orcosmetic reasons and the products used byagribusiness to boost growth or health of livestock. More than twenty million tons of PPCPs are produced every year.[23] TheEuropean Union has declaredpharmaceutical residues with the potential of contamination of water and soil to be "priority substances".[3]
In 2022, the most comprehensive study of pharmaceutical pollution of the world's rivers found thatit threatens "environmental and/or human health in more than a quarter of the studied locations". It investigated 1,052 sampling sites along 258 rivers in 104 countries, representing the river pollution of 470 million people. It found that "the most contaminated sites were in low- to middle-income countries and were associated with areas with poor wastewater and waste management infrastructure andpharmaceutical manufacturing" and lists the most frequently detected and concentrated pharmaceuticals.[29][30]
Solid waste can enter water bodies through untreated sewage, combined sewer overflows, urban runoff, people discardinggarbage into the environment, wind carrying municipal solid waste fromlandfills and so forth. This results inmacroscopic pollution– large visible items polluting the water– but alsomicroplastics pollution that is not directly visible. The termsmarine debris andmarine plastic pollution are used in the context of pollution of oceans.
Microplastics persist in the environment at high levels, particularly inaquatic andmarine ecosystems, where they cause water pollution.[33] 35% of all ocean microplastics come from textiles/clothing, primarily due to the erosion of polyester, acrylic, or nylon-based clothing, often during the washing process.[34]
Stormwater, untreated sewage and wind are the primary conduits for microplastics from land to sea. Synthetic fabrics, tyres, and city dust are the most common sources of microplastics. These three sources account for more than 80% of all microplastic contamination.[35][36]
Types of surface water pollution
Surface water pollution includes pollution of rivers, lakes and oceans. A subset of surface water pollution ismarine pollution which affects the oceans.Nutrient pollution refers to contamination by excessive inputs ofnutrients.
As of 2022,Europe andCentral Asia account for around 16% of globalmicroplastics discharge into the seas,[35][38] and although management of plastic waste andits recycling is improving globally, the absolute amount of plastic pollution continues to increase unabated due to the large amount of plastic that is being produced and disposed of.[39] Even if sea plastic pollution were to stop entirely, microplastic contamination of the surface ocean would be projected to continue to increase.[39]
Marine pollution occurs when substances used or spread by humans, such asindustrial,agricultural, andresidentialwaste;particles;noise; excesscarbon dioxide; orinvasive organisms enter theocean and cause harmful effects there. The majority of this waste (80%) comes from land-based activity, althoughmarine transportation significantly contributes as well.[40] It is a combination of chemicals and trash, most of which comes from land sources and is washed or blown into the ocean. This pollution results in damage to theenvironment, to the health of all organisms, and to economic structures worldwide.[41] Since most inputs come from land, viarivers,sewage, or theatmosphere, it means thatcontinental shelves are more vulnerable to pollution.Air pollution is also a contributing factor, as it carries iron, carbonic acid,nitrogen, silicon, sulfur,pesticides, and dust particles into the ocean.[42] The pollution often comes fromnonpoint sources such as agriculturalrunoff, wind-blowndebris, and dust. These nonpoint sources are largely due to runoff that enters the ocean through rivers, but wind-blown debris and dust can also play a role, as these pollutants can settle into waterways and oceans.[43] Pathways of pollution include direct discharge, land runoff,ship pollution,bilge pollution,dredging (which can createdredge plumes), atmospheric pollution and, potentially,deep sea mining.
Thermal pollution, sometimes called "thermal enrichment", is the degradation ofwater quality by any process that changes ambient watertemperature. Thermal pollution is the rise or drop in the temperature of a naturalbody of water caused byhuman influence. Thermal pollution, unlike chemical pollution, results in a change in the physicalproperties of water. A common cause of thermal pollution is the use of water as acoolant bypower plants and industrial manufacturers.[46]Urban runoff—stormwater discharged to surface waters from rooftops, roads, and parking lots—andreservoirs can also be a source of thermal pollution.[47] Thermal pollution can also be caused by the release of very cold water from the base of reservoirs into warmer rivers.
Elevated water temperatures decreaseoxygen levels (due to lower levels ofdissolved oxygen, as gases are less soluble in warmer liquids), which can kill fish (which may then rot) and alterfood chain composition, reduce speciesbiodiversity, and foster invasion by newthermophilic species.[48]: 179 [15]: 375
In many areas of the world, groundwater pollution poses a hazard to the wellbeing of people and ecosystems. One-quarter of the world's population depends on groundwater for drinking, yet concentrated recharging is known to carry short-lived contaminants into carbonate aquifers and jeopardize the purity of those waters.[51]
Pollution from point sources
Point source water pollution refers to contaminants that enter a waterway from a single, identifiable source, such as apipe orditch. Examples of sources in this category include discharges from a sewage treatment plant, a factory, or a citystorm drain.
The U.S.Clean Water Act (CWA) defines point source for regulatory enforcement purposes (seeUnited States regulation of point source water pollution).[52] The CWA definition of point source was amended in 1987 to include municipal storm sewer systems, as well as industrial storm water, such as from construction sites.[53]
Sewage
Sewage typically consists of 99.9% water and 0.1% solids.[54] Sewage contributes many classes of nutrients that lead toEutrophication. It is a major source of phosphate for example.[55] Sewage is often contaminated with diverse compounds found in personalhygiene,cosmetics,pharmaceutical drugs (see alsodrug pollution), and their metabolites[31][32] Water pollution due to environmental persistent pharmaceutical pollutants can have wide-ranging consequences. When sewers overflow during storm events this can lead to water pollution from untreated sewage. Such events are calledsanitary sewer overflows orcombined sewer overflows.
Industrial processes that use water also produce wastewater. This is calledindustrial wastewater. Using the US as an example, the main industrial consumers of water (using over 60% of the total consumption) are power plants, petroleum refineries, iron and steel mills, pulp and paper mills, and food processing industries.[2] Some industries discharge chemical wastes, including solvents and heavy metals (which are toxic) and other harmful pollutants.
Industrial wastewater could add the following pollutants to receiving water bodies if the wastewater is not treated and managed properly:
Organic matter and nutrients such asfood waste: Certain industries (e.g.food processing,slaughterhouse waste, paper fibers, plant material, etc.) discharge high concentrations of BOD, ammonia nitrogen and oil and grease.[57]: 180 [15]
Inorganic particles such assand, grit, metal particles, rubber residues from tires,ceramics, etc.;
Pharmaceuticals, endocrine disrupting compounds, hormones, perfluorinated compounds, siloxanes, drugs of abuse and other hazardous substances[58][59][60]
Microplastics such as polyethylene and polypropylene beads, polyester and polyamide[61]
Nonpoint source (NPS) pollution refers to diffusecontamination (orpollution) of water or air that does not originate from a single discrete source. This type of pollution is often the cumulative effect of small amounts of contaminants gathered from a large area. It is in contrast topoint source pollution which results from a single source. Nonpoint source pollution generally results fromland runoff, precipitation,atmospheric deposition,drainage,seepage, or hydrological modification (rainfall and snowmelt) where tracing pollution back to a single source is difficult.[62] Nonpoint source water pollution affects a water body from sources such as polluted runoff fromagricultural areas draining into a river, or wind-bornedebris blowing out to sea. Nonpoint sourceair pollution affects air quality, from sources such assmokestacks or cartailpipes. Although thesepollutants have originated from a point source, the long-range transport ability and multiple sources of the pollutant make it a nonpoint source of pollution; if the discharges were to occur to a body of water or into the atmosphere at a single location, the pollution would be single-point.
Agriculture
Agriculture is a major contributor to water pollution from nonpoint sources. The use of fertilizers as well assurface runoff from farm fields, pastures andfeedlots leads to nutrient pollution.[63] In addition to plant-focused agriculture, fish-farming is also a source of pollution. Additionally, agricultural runoff often contains high levels of pesticides.[2]
Atmospheric contributions (air pollution)
Air deposition is a process whereby air pollutants from industrial or natural sources settle into water bodies. The deposition may lead to polluted water near the source, or at distances up to a few thousand miles away. The most frequently observed water pollutants resulting from industrial air deposition are sulfur compounds, nitrogen compounds, mercury compounds, other heavy metals, and some pesticides and industrial by-products. Natural sources of air deposition include forest fires and microbial activity.[64]
Acid rain is caused by emissions ofsulfur dioxide andnitrogen oxide, which react with thewater molecules in theatmosphere to produce acids.[65] Some governments have made efforts since the 1970s to reduce the release of sulfur dioxide and nitrogen oxide into the atmosphere. The main source of sulfur and nitrogen compounds that result in acid rain areanthropogenic, but nitrogen oxides can also be produced naturally bylightning strikes and sulphur dioxide is produced byvolcanic eruptions.[66] Acid rain can have harmful effects on plants, aquatic ecosystems and infrastructure.[67][68]
Water pollution may be analyzed through several broad categories of methods: physical, chemical and biological. Some methods may be conductedin situ, without sampling, such as temperature. Others involve collection of samples, followed by specialized analytical tests in the laboratory. Standardized, validated analytical test methods, for water and wastewater samples have been published.[71]
The use of a biomonitor orbioindicator is described asbiological monitoring. This refers to the measurement of specific properties of an organism to obtain information on the surrounding physical and chemical environment.[73] Biological testing involves the use of plant, animal or microbial indicators to monitor the health of anaquatic ecosystem. They are any biological species or group of species whose function, population, or status can reveal what degree of ecosystem or environmental integrity is present.[74] One example of a group of bio-indicators are thecopepods and other small watercrustaceans that are present in many water bodies. Such organisms can be monitored for changes (biochemical, physiological, or behavioral) that may indicate a problem within their ecosystem.
Water pollution is a major globalenvironmental problem because it can result in the degradation of allaquatic ecosystems – fresh, coastal, and ocean waters.[75] The specific contaminants leading to pollution in water include a wide spectrum ofchemicals, pathogens, and physical changes such as elevated temperature. While many of the chemicals and substances that are regulated may be naturally occurring (calcium,sodium, iron,manganese, etc.) theconcentration usually determines what is a natural component of water and what is a contaminant. High concentrations of naturally occurring substances can have negative impacts on aquatic flora and fauna. Oxygen-depleting substances may be natural materials such as plant matter (e.g. leaves and grass) as well as human-made chemicals. Other natural and anthropogenic substances may cause turbidity (cloudiness) which blocks light and disrupts plant growth, and clogs thegills of some fish species.[76]
A study published in 2017 stated that "polluted water spreadgastrointestinal diseases andparasitic infections and killed 1.8 million people" (these are also referred to as waterborne diseases).[77] Persistent exposure to pollutants through water areenvironmental health hazards, which can increase the likelihood for one to develop cancer or other diseases.[78]
Eutrophication from nitrogen pollution
Nitrogen pollution can cause eutrophication, especially in lakes. Eutrophication is an increase in the concentration of chemical nutrients in anecosystem to an extent that increases theprimary productivity of the ecosystem. Subsequent negative environmental effects such asanoxia (oxygen depletion) and severe reductions in water quality may occur.[1]: 131 This can harm fish and other animal populations.
Eutrophication is a general term describing a process in whichnutrients accumulate in a body of water, resulting in an increased growth of organisms that may deplete theoxygen in the water; ie. the process of too many plants growing on the surface of a river, lake, etc., often because chemicals that are used to help crops grow have been carried there by rain.[79][80] Eutrophication may occur naturally or as a result of human actions. Manmade, or cultural, eutrophication occurs whensewage,industrial wastewater,fertilizer runoff, and other nutrient sources are released into the environment.[81] Suchnutrient pollution usually causesalgal blooms and bacterial growth, resulting in the depletion ofdissolved oxygen in water and causing substantialenvironmental degradation.[82] Many policies have been introduced to combat eutrophication, including the United Nations Development Program (UNDP)'s sustainability development goals.[83]
Ocean acidification
Ocean acidification is another impact of water pollution. Ocean acidification is the ongoing decrease in the pH value of the Earth's oceans, caused by the uptake ofcarbon dioxide (CO2) from the atmosphere.[69]
View of secondary treatment reactors (activated sludge process) at theBlue Plains Advanced Wastewater Treatment Plant, Washington, D.C., United States. Seen in the distance are the sludge digester building and thermal hydrolysis reactors.
Pollution control philosophy
One aspect of environmental protection is mandatory regulations, which are only part of the solution. Other important tools in pollution control include environmental education, economic instruments, market forces, and stricter enforcement. Standards can be "precise" (for a defined quantifiable minimum or maximum value for a pollutant), or "imprecise" which would require the use ofBest available technology (BAT) orBest practicable environmental option (BPEO). Market-based economic instruments for pollution control can include charges, subsidies, deposit or refund schemes, the creation of a market in pollution credits, and enforcement incentives.[85]
Moving towards a holistic approach in chemical pollution control combines the following approaches: Integrated control measures, trans-boundary considerations, complementary and supplementary control measures,life-cycle considerations, the impacts of chemical mixtures.[85]
Well-designed and operated systems (i.e., with secondary treatment stages or more advanced tertiary treatment) can remove 90 percent or more of thepollutant load in sewage.[88] Some plants have additional systems to removenutrients and pathogens. While such advanced treatment techniques will undoubtedly reduce the discharges ofmicropollutants, they can also result in large financial costs, as well as environmentally undesirable increases in energy consumption andgreenhouse gas emissions.[89]
Sewer overflows during storm events can be addressed by timely maintenance and upgrades of thesewerage system. In the US, cities with large combined systems have not pursued system-wide separation projects due to the high cost,[90] but have implemented partial separation projects andgreen infrastructure approaches.[91] In some cases municipalities have installed additional CSO storage facilities[92] or expanded sewage treatment capacity.[93]
Industrial wastewater treatment describes the processes used fortreating wastewater that is produced by industries as an undesirable by-product. After treatment, the treated industrial wastewater (or effluent) may be reused or released to asanitary sewer or to asurface water in the environment. Some industrial facilities generate wastewater that can be treated insewage treatment plants. Most industrial processes, such aspetroleum refineries, chemical andpetrochemical plants have their own specialized facilities to treat their wastewaters so that the pollutant concentrations in the treated wastewater comply with the regulations regarding disposal of wastewaters intosewers or into rivers, lakes oroceans.[94]: 1412 This applies to industries that generate wastewater with high concentrations of organic matter (e.g. oil and grease), toxic pollutants (e.g. heavy metals,volatile organic compounds) or nutrients such asammonia.[95]: 180 Some industries install a pre-treatment system to remove some pollutants (e.g., toxic compounds), and then discharge the partially treated wastewater to the municipal sewer system.[96]: 60
Sediment from construction sites can be managed by installation oferosion controls, such asmulching andhydroseeding, andsediment controls, such assediment basins andsilt fences.[98] Discharge of toxic chemicals such as motor fuels and concrete washout can be 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.[99]
Erosion caused bydeforestation and changes inhydrology (soil loss due to water runoff) also results in loss of sediment and, potentially, water pollution.[100][101]
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, calledbest management practices for water pollution (BMPs) in some countries, may focus on water quantity control, while others focus on improving water quality, and some perform both functions.[102]
Share of water bodies with goodwater quality in 2020. A water body is classified as "good" quality if at least 80% of monitoring values meet target quality levels, see alsoSDG 6, Indicator 6.3.2.
Legislation
Philippines
In the Philippines, Republic Act 9275, otherwise known as the Philippine Clean Water Act of 2004,[107] is the governing law on wastewater management. It states that it is the country's policy to protect, preserve and revive the quality of its fresh, brackish and marine waters, for which wastewater management plays a particular role.[107]
United Kingdom
In 2024, TheRoyal Academy of Engineering released a study into the effects wastewater on public health in the United Kingdom.[108] The study gained media attention, with comments from the UKs leading health professionals, including SirChris Whitty. Outlining 15 recommendations for various UK bodies to dramatically reduce public health risks by increasing the water quality in itswaterways, such as rivers and lakes.
After the release of the report,The Guardian newspaper interviewed Whitty, who stated that improving water quality and sewage treatment should be a high level of importance and a "public health priority". He compared it to eradicatingcholera in the 19th century in the country following improvements to thesewage treatment network.[109] The study also identified that low water flows in rivers saw high concentration levels ofsewage, as well as times of flooding or heavy rainfall. While heavy rainfall had always been associated with sewage overflows into streams and rivers, the British media went as far to warn parents of the dangers ofpaddling in shallow rivers during warm weather.[110]
Whitty's comments came after the study revealed that the UK was experiencing a growth in the number of people that were using coastal and inland waters recreationally. This could be connected to a growing interest in activities such asopen water swimming or otherwater sports.[111] Despite this growth in recreation, poor water quality meant some were becoming unwell during events.[112] Most notably, the2024 Paris Olympics had to delay numerous swimming-focused events like the triathlon due to high levels of sewage in theRiver Seine.[113]
TheClean Water Act is the primary federal law in the United States governing water pollution in surface waters.[114] The 1972 CWA amendments established a broad regulatory framework for improving water quality. The law defines procedures for pollution control and developing criteria and standards for pollutants in surface water.[115] The law authorizes the Environmental Protection Agency to regulate surface water pollution in the United States, in partnership with state agencies. Prior to 1972 it was legal to discharge wastewater to surface waters without testing for or removing water pollutants. The CWA was amended in 1981 and 1987 to adjust the federal proportion of construction grant funding for local governments, regulate municipal storm sewer discharges and to later establish theClean Water State Revolving Fund. The fund provides low-interest loans to improve municipal sewage treatment systems and finance other water quality improvements.[116]
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^Schueler, Thomas R. "Microbes and Urban Watersheds: Concentrations, Sources, & Pathways." Reprinted inThe Practice of Watershed Protection.Archived January 8, 2013, at theWayback Machine 2000. Center for Watershed Protection. Ellicott City, MD.
^Downs CA, Kramarsky-Winter E, Fauth JE, Segal R, Bronstein O, Jeger R, et al. (March 2014). "Toxicological effects of the sunscreen UV filter, benzophenone-2, on planulae and in vitro cells of the coral, Stylophora pistillata".Ecotoxicology.23 (2):175–91.Bibcode:2014Ecotx..23..175D.doi:10.1007/s10646-013-1161-y.PMID24352829.S2CID1505199.
^Adelana, Segun Michael (2014).Groundwater: Hydrogeochemistry, Environmental Impacts and Management Practices. Nova Science Publishers, Inc.ISBN978-1-63321-791-1.OCLC915416488.
^For example, seeEaton, Andrew D.; Greenberg, Arnold E.; Rice, Eugene W.; Clesceri, Lenore S.; Franson, Mary Ann H., eds. (2005).Standard Methods For the Examination of Water and Wastewater (21 ed.). American Public Health Association.ISBN978-0-87553-047-5. Also available on CD-ROM andonline by subscription.
^Donat-P. Häder; E. Walter Helbling; Virginia E. Villafañe (September 30, 2021).Anthropogenic Pollution of Aquatic Ecosystems. Springer Nature. p. 1.ISBN978-3-030-75602-4. RetrievedAugust 9, 2022.Pollution is a major stress factor affecting all aquatic ecosystems including fresh, coastal and open ocean waters.
^Tchobanoglous G, Burton FL, Stensel HD (2003).Metcalf & Eddy Wastewater Engineering: treatment and reuse (4th ed.). McGraw-Hill Book Company.ISBN0-07-041878-0.
^George Tchobanoglous; Franklin L. Burton; H. David Stensel (2003). "Chapter 3: Analysis and Selection of Wastewater Flowrates and Constituent Loadings".Metcalf & Eddy Wastewater engineering: treatment and reuse (4th ed.). Boston: McGraw-Hill.ISBN0-07-041878-0.OCLC48053912.
