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 by
anthropogenic contaminants. Due to these contaminants, it either no longer supports a certain human use, such as
drinking water, or undergoes a marked shift in its ability to support its biotic communities, such as fish.
Hormones (from
animal husbandry and residue from human
hormonal contraception methods) and synthetic materials such as
phthalates 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.[6][7][8]
Pathogens like Hepatovirus A (HAV may be present in treated wastewater outflows and receiving water bodies but is largely removed during further treatment of drinking water[9])
Inadequately treated wastewater can convey nutrients, pathogens, heterogenous suspended solids and organic fecal matter.[1]: 6
Coliforms, such as E. coli, may not be pathogenic in and of themselves, but are used as
an 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 and
parasitic 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 as Escherichia coli.[1]: 52–53
The
environmental 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 or
cosmetic reasons and the products used by
agribusiness to boost growth or health of livestock. More than twenty million tons of PPCPs are produced every year.[22] The
European Union has declared
pharmaceutical 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 that
it 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 and
pharmaceutical manufacturing" and lists the most frequently detected and concentrated pharmaceuticals.[28][29]
Solid waste can enter water bodies through untreated sewage, combined sewer overflows, urban runoff, people discarding
garbage into the environment, wind carrying municipal solid waste from
landfills and so forth. This results in
macroscopic pollution– large visible items polluting the water– but also
microplastics pollution that is not directly visible. The terms
marine debris and
marine plastic pollution are used in the context of pollution of oceans.
Microplastics persist in the environment at high levels, particularly in
aquatic and
marine ecosystems, where they cause water pollution.[32] 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.[33]
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.[34][35]
Types of surface water pollution
Surface water pollution includes pollution of rivers, lakes and oceans. A subset of surface water pollution is
marine pollution which affects the oceans.
Nutrient pollution refers to contamination by excessive inputs of
nutrients.
As of 2022,
Europe and
Central Asia account for around 16% of global
microplastics discharge into the seas,[34][37] and although management of plastic waste and
its 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.[38] Even if sea plastic pollution were to stop entirely, microplastic contamination of the surface ocean would be projected to continue to increase.[38]
Marine pollution occurs when substances used or spread by humans, such as
industrial,
agricultural and
residentialwaste,
particles,
noise, excess
carbon dioxide or
invasive organisms enter the
ocean and cause harmful effects there. The majority of this waste (80%) comes from land-based activity, although
marine transportation significantly contributes as well.[39] 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 the environment, to the health of all organisms, and to economic structures worldwide.[40] Since most inputs come from land, either via the
rivers,
sewage or the atmosphere, it means that
continental shelves are more vulnerable to pollution.
Air pollution is also a contributing factor by carrying off iron, carbonic acid,
nitrogen, silicon, sulfur,
pesticides or dust particles into the ocean.[41] The pollution often comes from
nonpoint sources such as agricultural
runoff, wind-blown
debris, 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.[42] Pathways of pollution include direct discharge, land runoff,
ship pollution,
bilge pollution, atmospheric pollution and, potentially,
deep sea mining.
Thermal pollution, sometimes called "thermal enrichment", is the degradation of
water quality by any process that changes ambient water
temperature. Thermal pollution is the rise or drop in the temperature of a natural
body of water caused by
human influence. Thermal pollution, unlike chemical pollution, results in a change in the physical
properties of water. A common cause of thermal pollution is the use of water as a
coolant by
power plants and industrial manufacturers.[45]Urban runoff—
stormwater discharged to surface waters from rooftops, roads, and parking lots—and
reservoirs can also be a source of thermal pollution.[46] Thermal pollution can also be caused by the release of very cold water from the base of reservoirs into warmer rivers.
Elevated water temperatures decrease
oxygen levels (due to lower levels of
dissolved oxygen, as gases are less soluble in warmer liquids), which can kill fish (which may then rot) and alter
food chain composition, reduce species
biodiversity, and foster invasion by new
thermophilic species.[47]: 179 [14]: 375
Groundwater pollution (also called groundwater contamination) occurs when
pollutants are released to the ground and make their way into
groundwater. This type of water pollution can also occur naturally due to the presence of a minor and unwanted constituent, contaminant, or impurity in the groundwater, in which case it is more likely referred to as
contamination rather than
pollution. Groundwater pollution can occur from on-site
sanitation systems,
landfill leachate, effluent from
wastewater treatment plants, leaking sewers, petrol
filling stations,
hydraulic fracturing (fracking) or from over application of
fertilizers in
agriculture. Pollution (or contamination) can also occur from naturally occurring contaminants, such as
arsenic or
fluoride.[49] Using polluted groundwater causes hazards to
public health through poisoning or the spread of disease (
water-borne diseases).
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.[50]
Pollution from point sources
Point source water pollution refers to contaminants that enter a waterway from a single, identifiable source, such as a
pipe or
ditch. Examples of sources in this category include discharges from a sewage treatment plant, a factory, or a city
storm drain.
The U.S.
Clean Water Act (CWA) defines point source for regulatory enforcement purposes (seeUnited States regulation of point source water pollution).[51] 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.[52]
Sewage
Sewage typically consists of 99.9% water and 0.1% solids.[53] Sewage contributes many classes of nutrients that lead to eutrophication. It is a major source of phosphate for example.[54] Sewage is often contaminated with diverse compounds found in personal
hygiene,
cosmetics,
pharmaceutical drugs (see also
drug pollution), and their metabolites[55][31] 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 called
sanitary sewer overflows or
combined sewer overflows.
Industrial processes that use water also produce wastewater. This is called
industrial 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 as
food 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 [14]
Inorganic particles such as
sand, 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 diffuse
contamination (or
pollution) 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 to
point source pollution which results from a single source. Nonpoint source pollution generally results from
land 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 from
agricultural areas draining into a river, or wind-borne
debris blowing out to sea. Nonpoint source
air pollution affects air quality, from sources such as
smokestacks or car
tailpipes. Although these
pollutants 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 as
surface runoff from farm fields, pastures and
feedlots 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 of
sulfur dioxide and
nitrogen oxide, which react with the
water molecules in the
atmosphere 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 are
anthropogenic, but nitrogen oxides can also be produced naturally by
lightning strikes and sulphur dioxide is produced by
volcanic 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 conducted in 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 or
bioindicator is described as
biological 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 an
aquatic 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 the
copepods and other small water
crustaceans 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.
The complexity of water quality as a subject is reflected in the many types of measurements of water quality indicators. Some measurements of water quality are most accurately made on-site, because water exists in
equilibrium with its
surroundings. Measurements commonly made on-site and in direct contact with the water source in question include
temperature,
pH,
dissolved oxygen,
conductivity,
oxygen reduction potential (ORP),
turbidity, and
Secchi disk depth.
Impacts
Ecosystems
Water pollution is a major global
environmental problem because it can result in the degradation of all
aquatic ecosystems – fresh, coastal, and ocean waters.[75] The specific contaminants leading to pollution in water include a wide spectrum of
chemicals, 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.) the
concentration 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 the
gills of some fish species.[76]
A study published in 2017 stated that "polluted water spread
gastrointestinal diseases and
parasitic infections and killed 1.8 million people" (these are also referred to as waterborne diseases).[77] Persistent exposure to pollutants through water are
environmental 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 an
ecosystem to an extent that increases the
primary productivity of the ecosystem. Subsequent negative environmental effects such as
anoxia (oxygen depletion) and severe reductions in water quality may occur.[1]: 131 This can harm fish and other animal populations.
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 of
carbon dioxide (CO2) from the atmosphere.[69]
One aspect of environmental protection are mandatory regulations but they are only part of the solution. Other important tools in pollution control include environmental education, economic instruments, market forces and stricter enforcements. Standards can be "precise" (for a defined quantifiable minimum or maximum value for a pollutant), or "imprecise" which would require the use of
Best available technology (BAT) or
Best 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.[84]
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.[84]
Well-designed and operated systems (i.e., with secondary treatment stages or more advanced tertiary treatment) can remove 90 percent or more of the
pollutant load in sewage.[87] Some plants have additional systems to remove
nutrients and pathogens. While such advanced treatment techniques will undoubtedly reduce the discharges of micropollutants, they can also result in large financial costs, as well as environmentally undesirable increases in energy consumption and
greenhouse gas emissions.[88]
Sewer overflows during storm events can be addressed by timely maintenance and upgrades of the
sewerage system. In the US, cities with large combined systems have not pursued system-wide separation projects due to the high cost,[89] but have implemented partial separation projects and
green infrastructure approaches.[90] In some cases municipalities have installed additional CSO storage facilities[91] or expanded sewage treatment capacity.[92]
Industrial wastewater treatment describes the processes used for
treating 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 a
sanitary sewer or to a
surface water in the environment. Some industrial facilities generate wastewater that can be treated in
sewage treatment plants. Most industrial processes, such as
petroleum refineries, chemical and
petrochemical 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 into
sewers or into rivers, lakes or
oceans.[93]: 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 as
ammonia.[94]: 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.[95]: 60
Sediment from construction sites can be managed by installation of
erosion controls, such as
mulching and
hydroseeding, and
sediment controls, such as
sediment basins and
silt fences.[97] 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.[98]
Erosion caused by
deforestation and changes in
hydrology (soil loss due to water runoff) also results in loss of sediment and, potentially, water pollution.[99][100]
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
best 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.[101]
In the Philippines, Republic Act 9275, otherwise known as the Philippine Clean Water Act of 2004,[106] 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.[106]
The
Clean Water Act is the primary federal law in the United States governing water pollution in surface waters.[107] 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.[108] 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 the
Clean Water State Revolving Fund. The fund provides low-interest loans to improve municipal sewage treatment systems and finance other water quality improvements.[109]
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