Definition of the word water pollution

Water pollution (or aquatic pollution) is the contamination of water bodies, usually as a result of human activities, so that it negatively affects its uses.^[1]: 6 Water bodies include lakes, rivers, oceans, aquifers, reservoirs and groundwater. Water pollution results when contaminants mix with these water bodies. Contaminants can come from one of four main sources: sewage discharges, industrial activities, agricultural activities, and urban runoff including stormwater.^[2] Water pollution is either surface water pollution or groundwater pollution. This form of pollution can lead to many problems, such as the degradation of aquatic ecosystems or spreading water-borne diseases when people use polluted water for drinking or irrigation.^[3] Another problem is that water pollution reduces the ecosystem services (such as providing drinking water) that the water resource would otherwise provide.

Sources of water pollution are either point sources or non-point sources. Point sources have one identifiable cause, such as a storm drain, a wastewater treatment plant or an oil spill. Non-point sources are more diffuse, such as agricultural runoff.^[4] Pollution is the result of the cumulative effect over time. Pollution may take the form of toxic substances (e.g., oil, metals, plastics, pesticides, persistent organic pollutants, industrial waste products), stressful conditions (e.g., changes of pH, hypoxia or anoxia, increased temperatures, excessive turbidity, changes of salinity), or the introduction of pathogenic organisms. Contaminants may include organic and inorganic substances. A common cause of thermal pollution is the use of water as a coolant by power plants and industrial manufacturers.

Control of water pollution requires appropriate infrastructure and management plans as well as legislation. Technology solutions can include improving sanitation, sewage treatment, industrial wastewater treatment, agricultural wastewater treatment, erosion control, sediment control and control of urban runoff (including stormwater management).

Definition

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.

Contaminants

Contaminants with an origin in sewage

The following compounds can all reach water bodies via raw sewage or even treated sewage discharges:

• Various chemical compounds found in personal hygiene and cosmetic products.
• Disinfection by-products found in chemically disinfected drinking water (whilst these chemicals can be a pollutant in the water distribution network, they are fairly volatile and therefore not usually found in environmental waters).^[5]
• 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]
• insecticides and herbicides, often from agricultural runoff.

If the water pollution stems from sewage (municipal wastewater), the main pollutants are: suspended solids, biodegradable organic matter, nutrients and pathogenic (disease-causing) organisms.^[1]: 6

Poster to teach people in South Asia about human activities leading to the pollution of water sources

Pollutants and their effects*

Pollutant	Main representative parameter	Possible effect of the pollutant
Suspended solids	Total suspended solids	Aesthetic problems Sludge deposits Pollutants adsorption Protection of pathogens
Biodegradable organic matter	Biological oxygen demand (BOD)	Oxygen consumption Death of fish Septic conditions
Nutrients	Nitrogen Phosphorus	Excessive algae growth Toxicity to fish (ammonia) Illnesses in new-born infants (Blue baby syndrome from nitrate) Pollution of groundwater
Pathogens	Coliforms, such as E. coli Helminth eggs[9]	Waterborne diseases
Non-biodegradable organic matter	Pesticides Some detergents Others	Toxicity (various) Foam (detergents) Reduction of oxygen transfer (detergents) Non-biodegradability Bad odors (e.g.: phenols)
Inorganic dissolved solids	Total dissolved solids Conductivity	Excessive salinity – harm to plantations (irrigation) Toxicity to plants (some ions) Problems with soil permeability (sodium)
* Sources of these pollutants are municipal and industrial wastewater, urban runoff, agricultural and pasture activities[1]: 7

Pathogens

The major groups of pathogenic organisms are: (a) bacteria, (b) viruses, (c) protozoans and (d) helminths.^[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), fecal coliforms (FC) or thermotolerant coliforms, E. coli.^[1]: 47

Pathogens can produce waterborne diseases in either human or animal hosts.^[10] Some microorganisms sometimes found in contaminated surface waters that have caused human health problems include: Burkholderia pseudomallei, Cryptosporidium parvum, Giardia lamblia, Salmonella, norovirus and other viruses, parasitic worms including the Schistosoma type.^[11]

The source of high levels of pathogens in water bodies can be from human feces (due to open defecation), sewage, blackwater, or manure that has found its way into the water body. The cause for this can be lack of sanitation procedures or poorly functioning on-site sanitation systems (septic tanks, pit latrines), sewage treatment plants without disinfection steps, sanitary sewer overflows and combined sewer overflows (CSOs)^[12] during storm events and intensive agriculture (poorly managed livestock operations).

Organic compounds

Organic substances that enter water bodies are often toxic.^[13]: 229

• Petroleum hydrocarbons, including fuels (gasoline, diesel fuel, jet fuels, and fuel oil) and lubricants (motor oil), and fuel combustion byproducts, from oil spills or storm water runoff^[14]
• Volatile organic compounds, such as improperly stored industrial solvents. Problematic species are organochlorides such as polychlorinated biphenyl (PCBs) and trichloroethylene, a common solvent.

Per- and polyfluoroalkyl substances (PFAS) are persistent organic pollutants.^[15][16]

Inorganic contaminants

Muddy river polluted by sediment

Inorganic water pollutants include for example:

• Ammonia from food processing waste
• Heavy metals from motor vehicles (via urban storm water runoff)^[14][17] and acid mine drainage
• Nitrates and phosphates, from sewage and agriculture (see nutrient pollution)
• Silt (sediment) in runoff from construction sites or sewage, logging, slash and burn practices or land clearing sites.
• Salt: Freshwater salinization is the process of salty runoff contaminating freshwater ecosystems.^[18] Human-induced salinization is termed as secondary salinization, with the use of de-icing road salts as the most common form of runoff.^[19][20]

Pharmaceutical pollutants

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.^[21] The European Union has declared pharmaceutical residues with the potential of contamination of water and soil to be «priority substances».^[3]

PPCPs have been detected in water bodies throughout the world More research is needed to evaluate the risks of toxicity, persistence, and bioaccumulation, but the current state of research shows that personal care products impact over the environment and other species, such as coral reefs^[22][23][24] and fish.^[25][26] PPCPs encompass environmental persistent pharmaceutical pollutants (EPPPs) and are one type of persistent organic pollutants. They are not removed in conventional sewage treatment plants but require a fourth treatment stage which not many plants have.^[21]

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.^[27][28]

• Environmental persistent pharmaceutical pollutants, which can include various pharmaceutical drugs and their metabolites (see also drug pollution), such as antidepressant drugs, antibiotics or the contraceptive pill.
• Metabolites of illicit drugs (see also wastewater epidemiology), for example methamphetamine and ecstasy.^[29][30]

Solid waste and plastics

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.^[31] 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.^[32]

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.^[33][34]

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.

Globally, about 4.5 billion people do not have safely managed sanitation as of 2017, according to an estimate by the Joint Monitoring Programme for Water Supply and Sanitation.^[35] Lack of access to sanitation is concerning and often leads to water pollution, e.g. via the practice of open defecation: during rain events or floods, the human feces are moved from the ground where they were deposited into surface waters. Simple pit latrines may also get flooded during rain events.

As of 2022, Europe and Central Asia account for around 16% of global microplastics discharge into the seas.^[36][33][37]

Marine pollution

Marine pollution occurs when substances used or spread by humans, such as industrial, agricultural and residential waste, 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.^[38] 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.^[39] 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.^[40] Pathways of pollution include direct discharge, land runoff, ship pollution, bilge pollution, atmospheric pollution and, potentially, deep sea mining.

Nutrient pollution

Nutrient pollution, a form of water pollution, refers to contamination by excessive inputs of nutrients. It is a primary cause of eutrophication of surface waters (lakes, rivers and coastal waters), in which excess nutrients, usually nitrogen or phosphorus, stimulate algal growth.^[41] Sources of nutrient pollution include surface runoff from farm fields and pastures, discharges from septic tanks and feedlots, and emissions from combustion. Raw sewage is a large contributor to cultural eutrophication since sewage is high in nutrients. Releasing raw sewage into a large water body is referred to as sewage dumping, and still occurs all over the world. Excess reactive nitrogen compounds in the environment are associated with many large-scale environmental concerns. These include eutrophication of surface waters, harmful algal blooms, hypoxia, acid rain, nitrogen saturation in forests, and climate change.^[42]

Thermal pollution

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 fall 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.^[43] Urban runoff—stormwater discharged to surface waters from rooftops, roads and parking lots—and reservoirs can also be a source of thermal pollution.^[44] 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.^{[45]: 179 [13]: 375}

Biological pollution

The introduction of aquatic invasive organisms is a form of water pollution as well. It causes biological pollution.^[46]

Groundwater pollution

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.^[48]

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 (see United States regulation of point source water pollution).^[49] 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.^[50]

Sewage

Sewage typically consists of 99.9% water and 0.1% solids.^[51] Sewage contributes many classes of nutrients that lead to eutrophication. It is a major source of phosphate for example.^[52] Sewage is often contaminated with diverse compounds found in personal hygiene, cosmetics, pharmaceutical drugs (see also drug pollution), and their metabolites^[53][30] 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 wastewater

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:

• Heavy metals, including mercury, lead, and chromium
• 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.^{[55]: 180 [13]}
• Inorganic particles such as sand, grit, metal particles, rubber residues from tires, ceramics, etc.;
• Toxins such as pesticides, poisons, herbicides, etc.
• Pharmaceuticals, endocrine disrupting compounds, hormones, perfluorinated compounds, siloxanes, drugs of abuse and other hazardous substances^[56][57][58]
• Microplastics such as polyethylene and polypropylene beads, polyester and polyamide^[59]
• Thermal pollution from power stations and industrial manufacturers
• Radionuclides from uranium mining, processing nuclear fuel, operating nuclear reactors, or disposal of radioactive waste.
• Some industrial discharges include persistent organic pollutants such as per- and polyfluoroalkyl substances (PFAS).^[15][16]

Oil spills

An oil spill is the release of a liquid petroleum hydrocarbon into the environment, especially the marine ecosystem, due to human activity, and is a form of pollution. The term is usually given to marine oil spills, where oil is released into the ocean or coastal waters, but spills may also occur on land. Oil spills may be due to releases of crude oil from tankers, offshore platforms, drilling rigs and wells, as well as spills of refined petroleum products (such as gasoline, diesel) and their by-products, heavier fuels used by large ships such as bunker fuel, or the spill of any oily refuse or waste oil.^{[citation needed]}

Pollution from nonpoint sources

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.^[60] 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.^[61] 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.^[62]

Acid rain is caused by emissions of sulfur dioxide and nitrogen oxide, which react with the water molecules in the atmosphere to produce acids.^[63] 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.^[64] Acid rain can have harmful effects on plants, aquatic ecosystems and infrastructure.^[65][66]

Carbon dioxide concentrations in the atmosphere have increased since the 1850s due anthropogenic influences (emissions of greenhouse gases).^[67] This leads to ocean acidification and is another form of water pollution from atmospheric contributions.^[68]

Sampling, measurements, analysis

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.^[69]

Common physical tests of water include temperature, Specific conductance or electrical conductance (EC) or conductivity, solids concentrations (e.g., total suspended solids (TSS)) and turbidity. Water samples may be examined using analytical chemistry methods. Many published test methods are available for both organic and inorganic compounds. Frequently used parameters that are quantified are pH, BOD,^[70]: 102 chemical oxygen demand (COD),^[70]: 104 dissolved oxygen (DO), total hardness, nutrients (nitrogen and phosphorus compounds, e.g. nitrate and orthophosphates), metals (including copper, zinc, cadmium, lead and mercury), oil and grease, total petroleum hydrocarbons (TPH), surfactants and pesticides.

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.^[71] 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.^[72] 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.

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.^[73] 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 man-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.^[74]

Public health and waterborne diseases

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).^[75] Persistent exposure to pollutants through water are environmental health hazards, which can increase the likelihood for one to develop cancer or other diseases.^[76]

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

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.^[67]

Prevalence

Water pollution is a problem in developing countries as well as in developed countries.

By country

For example, water pollution in India and China is wide spread. About 90 percent of the water in the cities of China is polluted.^[82]

Control and reduction

View of secondary treatment reactors (activated sludge process) at the Blue 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 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.^[83]

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.^[83]

Control of water pollution requires appropriate infrastructure and management plans. The infrastructure may include wastewater treatment plants, for example sewage treatment plants and industrial wastewater treatment plants. Agricultural wastewater treatment for farms, and erosion control at construction sites can also help prevent water pollution. Effective control of urban runoff includes reducing speed and quantity of flow.

Water pollution requires ongoing evaluation and revision of water resource policy at all levels (international down to individual aquifers and wells).

Sanitation and sewage treatment

Plastic waste on the big drainage, and air pollution in the far end of the drainage in Ghana

Municipal wastewater can be treated by centralized sewage treatment plants, decentralized wastewater systems, nature-based solutions^[84] or in onsite sewage facilities and septic tanks. For example, waste stabilization ponds are a low cost treatment option for sewage, particularly for regions with warm climates.^[1]: 182 UV light (sunlight) can be used to degrade some pollutants in waste stabilization ponds (sewage lagoons).^[85] The use of safely managed sanitation services would prevent water pollution caused by lack of access to sanitation.^[35]

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.^[86] 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.^[87]

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,^[88] but have implemented partial separation projects and green infrastructure approaches.^[89] In some cases municipalities have installed additional CSO storage facilities^[90] or expanded sewage treatment capacity.^[91]

Industrial wastewater treatment

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.^[92]: 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.^[93]: 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.^[94]: 60

Agricultural wastewater treatment

Management of erosion and sediment control

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.^[96] 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.^[97]

Erosion caused by deforestation and changes in hydrology (soil loss due to water runoff) also results in loss of sediment and, potentially, water pollution.^[98][99]

Control of urban runoff (storm water)

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.^[100]

Pollution prevention practices include low impact development (LID) or green infrastructure techniques — known as Sustainable Drainage Systems (SuDS) in the UK, and Water-Sensitive Urban Design (WSUD) in Australia and the Middle East — such as the installation of green roofs and improved chemical handling (e.g. management of motor fuels & oil, fertilizers, pesticides and roadway deicers).^[101][102] Runoff mitigation systems include infiltration basins, bioretention systems, constructed wetlands, retention basins, and similar devices.^[103][104]

Share of water bodies with good water quality in 2020. A water body is classified as «good» quality if at least 80% of monitoring values meet target quality levels, see also SDG 6, Indicator 6.3.2.

Legislation

Philippines

In the Philippines, Republic Act 9275, otherwise known as the Philippine Clean Water Act of 2004,^[105] 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.^[105]

United States

The Clean Water Act is the primary federal law in the United States governing water pollution in surface waters.^[106] 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.^[107] 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.^[108]

See also

• Aquatic toxicology
• Environmental impact of pesticides § Water
• Human impacts on the environment
• Pollution
• Trophic state index (water quality indicator for lakes)
• Water resources management
• Water security

References

External links

• Tackling global water pollution — UN Environment Programme

Over two thirds of Earth’s surface is covered by water; less than a third is taken up by land. As Earth’s population continues to grow,
people are putting ever-increasing pressure on the planet’s water
resources. In a sense, our oceans, rivers, and other inland waters are
being «squeezed» by human activities—not so they take up less room, but
so their quality is reduced. Poorer water quality means water pollution.

We know that pollution is a human problem because it is a
relatively recent development in the planet’s history: before the 19th
century Industrial Revolution, people lived more in harmony with their
immediate environment. As industrialization has spread around the
globe, so the problem of pollution has spread with it. When Earth’s
population was much smaller, no one believed pollution would ever
present a serious problem. It was once popularly believed that
the oceans were far too big to pollute. Today, with around 7 billion
people on the planet, it has become apparent that there are limits.
Pollution is one of the signs that humans have exceeded those limits.

How serious is the problem? According to the environmental campaign organization
WWF: «Pollution from toxic chemicals threatens life on this planet. Every ocean and every continent, from the tropics to the once-pristine polar regions, is contaminated.»

Photo: Stormwater pollution entering a river from a drain. Photo by Peter C Van Metre courtesy of US Geological Survey.

What is water pollution?

Water pollution can be defined in many ways. Usually, it means one
or more substances have built up in water to such an extent that they
cause problems for animals or people. Oceans, lakes, rivers, and other
inland waters can naturally clean up a certain amount of pollution by
dispersing it harmlessly. If you poured a cup of black ink into a
river, the ink would quickly disappear into the river’s much larger volume of clean water. The ink
would still be there in the river, but in such a low concentration that
you would not be able to see it. At such low levels, the chemicals in the ink probably would not present any real problem.
However, if you poured gallons of ink into a river every few seconds through a pipe,
the river would quickly turn black.
The chemicals in the ink could very quickly have an effect on the quality of the water.
This, in turn, could affect the health of all the plants, animals, and humans whose
lives depend on the river.

Photo: Pollution means adding substances to the environment that don’t belong there—like the
air pollution from this smokestack. Pollution is not always as obvious as this, however.

Thus, water pollution is all about quantities: how much of a
polluting substance is released and how big a volume of water it is
released into. A small quantity of a toxic chemical may have little
impact if it is spilled into the ocean from a ship. But the same amount
of the same chemical can have a much bigger impact pumped into a lake
or river, where there is less clean water to disperse it.

Water pollution almost always means that some damage has been done to an ocean, river, lake, or other water source.
A 1969 United Nations report defined ocean pollution as:

«The
introduction by man, directly or indirectly, of substances or energy
into the marine environment (including estuaries) resulting in such
deleterious effects as harm to living resources, hazards to human
health, hindrance to marine activities, including fishing,
impairment of quality for use of sea water and reduction of amenities.»
[1]

Fortunately, Earth is forgiving and damage from water pollution is often reversible.

What are the main types of water pollution?

When we think of Earth’s water resources, we think of huge
oceans, lakes, and rivers. Water resources like these are called surface
waters. The most obvious type of water pollution affects surface
waters. For example, a spill from an oil tanker creates an oil slick
that can affect a vast area of the ocean.

Photo: Detergent pollution entering a river—an example of surface water pollution. Photo courtesy of US Fish & Wildlife Service Photo Library.

Not all of Earth’s water sits on its surface, however. A great deal
of water is held in underground rock structures known as aquifers,
which we cannot see and seldom think about.
Water stored underground in aquifers is known as groundwater.
Aquifers feed our rivers and supply much of our drinking water. They
too can become polluted, for example, when weed killers used in
people’s gardens drain into the ground. Groundwater pollution is much
less obvious than surface-water pollution, but is no less of a problem.
In 1996, a study in Iowa in the United States found that over half the
state’s groundwater wells were contaminated with weed killers.
You might think things would have improved since then, but,
two decades on, all that’s really changed is the name of the chemicals
we’re using. Today, numerous scientific studies are still finding
weed killers in groundwater in worrying quantities:
a 2012 study discovered glyphosate
in 41 percent of 140 groundwater samples from Catalonia, Spain;
scientific opinion differs on whether this is safe or not.
[2]

Surface waters and groundwater are the two types of water resources
that pollution affects. There are also two different ways in which
pollution can occur. If pollution comes from a single location, such as
a discharge pipe attached to a factory, it is known as point-source
pollution. Other examples of point source pollution include an oil
spill from a tanker, a discharge from a smoke stack (factory chimney),
or someone pouring oil from their car down a drain. A great deal of
water pollution happens not from one single source but from many
different scattered sources. This is called nonpoint-source
pollution.

Photo: Above: Point-source pollution comes from a single, well-defined place such as this pipe.
Below: Nonpoint-source pollution comes from many sources. All the industrial plants alongside a river and the
ships that service them may be polluting the river collectively. Both photos courtesy of US Fish & Wildlife Service Photo Library.

When point-source pollution enters the environment, the place most
affected is usually the area immediately around the source. For
example, when a tanker accident occurs, the oil slick is concentrated
around the tanker itself and, in the right ocean conditions, the
pollution disperses the further away from the tanker you go. This is
less likely to happen with nonpoint source pollution which, by
definition, enters the environment from many different places at once.

Sometimes pollution that enters the environment in one place has an
effect hundreds or even thousands of miles away. This is known as transboundary
pollution. One example is the way radioactive waste travels through
the oceans from nuclear reprocessing plants in England and France to
nearby countries such as Ireland and Norway.

How do we know when water is polluted?

Some forms of water pollution are very obvious: everyone has seen TV
news footage of oil slicks filmed from helicopters flying overhead.
Water pollution is usually less obvious and much harder to detect than
this. But how can we measure water pollution when we cannot see it? How
do we even know it’s there?

There are two main ways of measuring the quality of water. One is to
take samples of the water and measure the concentrations of different
chemicals that it contains. If the chemicals are dangerous or the
concentrations are too great, we can regard the water as polluted.
Measurements like this are known as chemical indicators of
water quality. Another way to measure water quality involves examining
the fish, insects, and other invertebrates that the water will support.
If many different types of creatures can live in a river, the quality is likely to
be very good; if the river supports no fish life at all, the quality is
obviously much poorer. Measurements like this are called biological
indicators of water quality.

What are the causes of water pollution?

Most water pollution doesn’t begin in the water itself.
Take the oceans: around 80 percent of ocean pollution enters our seas from the land.
[16]
Virtually any human activity can have an effect on the quality of our
water environment. When farmers fertilize the fields, the chemicals
they use are gradually washed by rain into the groundwater or surface
waters nearby. Sometimes the causes of water pollution are quite
surprising. Chemicals released by smokestacks (chimneys) can enter the
atmosphere and then fall back to earth as rain, entering seas, rivers,
and lakes and causing water pollution. That’s called atmospheric deposition.
Water pollution has many different causes and this is one of the reasons why it is such a
difficult problem to solve.

Sewage

With billions of people on the planet, disposing of sewage waste
is a major problem. According to 2017 figures from the World Health Organization, some
2 billion people (about a quarter of the world’s population) don’t have access to
safe drinking water
or the most basic sanitation, 3.4 billion (60 people of the population) lack
«safely managed» sanitation
(unshared, with waste properly treated). Although there have been great improvements in securing access to clean water, relatively
little, genuine progress has been made on improving global sanitation in the last decade. [20]
Sewage disposal affects people’s immediate environments and leads to
water-related illnesses such as diarrhea that kills 525,000 children under five each year.
[3]
(Back in 2002, the World Health Organization
estimated that water-related diseases could kill as many as 135 million people by 2020;
in 2019, the WHO was still
estimating the annual death toll from poor water and sanitation at over 800,000 people a year.)
In developed countries, most people have flush toilets that take
sewage waste quickly and hygienically away from their homes.

Yet the problem of sewage disposal does not end there. When you
flush the toilet, the waste has to go somewhere and, even after it
leaves the sewage treatment works, there is still waste to dispose of.
Sometimes sewage waste is pumped untreated into the sea.
Until the early 1990s, around 5 million tons of sewage was dumped
by barge from New York City each year. [4]
According to 2002 figures from the UK government’s Department for
the Environment, Food, and Rural Affairs (DEFRA), the sewers of Britain collect around 11 billion liters
of waste water every day; there are still 31,000 sewage overflow pipes through which, in certain circumstances,
such as heavy storms, raw sewage is pumped untreated into the sea.
[5]
The New River that crosses the border from Mexico
into California once carried with it 20–25 million gallons (76–95 million
liters) of raw sewage each day; a new waste water plant on the US-Mexico border, completed in 2007, substantially
solved that problem.
[6] Unfortunately, even in some of the richest nations, the
practice of dumping sewage into the sea continues. In early 2012,
it was reported that the tiny island of Guernsey (between Britain and France) has decided to continue dumping 16,000 tons of raw sewage
into the sea each day.

In theory, sewage is a completely natural substance that should be
broken down harmlessly in the environment: 90 percent of sewage is water.
[7]
In practice, sewage contains all kinds of other chemicals, from the pharmaceutical drugs people take to
the paper, plastic, and other wastes they flush down their toilets.
When people are sick with viruses, the sewage they produce carries
those viruses into the environment. It is possible to catch illnesses
such as hepatitis, typhoid, and cholera from river and sea water.

Nutrients

Photo: During crop-spraying, some chemicals will drain into the soil. Eventually, they seep into
rivers and other watercourses. Photo courtesy of US Department of Agriculture Agricultural Research Service (ARS).

Suitably treated and used in moderate quantities, sewage can be a
fertilizer: it returns important nutrients to the environment, such as
nitrogen and phosphorus, which plants and animals need for growth. The
trouble is, sewage is often released in much greater quantities than
the natural environment can cope with. Chemical fertilizers used by
farmers also add nutrients to the soil, which drain into rivers and
seas and add to the fertilizing effect of the sewage. Together, sewage
and fertilizers can cause a massive increase in the growth of algae or
plankton that overwhelms huge areas of oceans, lakes, or rivers. This
is known as a harmful algal bloom (also known as an HAB or red
tide, because it can turn the water red). It is harmful because it
removes oxygen from the water that kills other forms of life, leading
to what is known as a dead zone. The Gulf of Mexico has one of
the world’s most spectacular dead zones. Each summer, according
to studies by the
NOAA, it typically grows to an area of around 5500–6500 square miles (14,000–16,800 square kilometers), which is
about the same size as the state of Connecticut. [21]

Waste water

A few statistics illustrate the scale of the problem that waste
water (chemicals washed down drains and discharged from factories) can
cause. Around half of all ocean pollution is caused by sewage and waste
water. Each year, the world generates perhaps 5–10 billion tons of industrial
waste, much of which is pumped untreated into rivers, oceans, and other
waterways.
[8] In the United States alone, around 400,000 factories take
clean water from rivers, and many pump polluted waters back in their
place. However, there have been major improvements in waste water
treatment recently. Since 1970, in the United States, the
Environmental Protection Agency (EPA) has invested about $70 billion in improving water treatment plants that, as of 2021, serve around 90 percent of the US population (compared to just 69 percent in 1972). However, another $271 billion is still needed to update and upgrade the system.
[15]

Factories are point sources of water pollution, but quite a lot of
water is polluted by ordinary people from nonpoint sources; this is how
ordinary water becomes waste water in the first place.
Virtually everyone pours chemicals of one sort or another down their
drains or toilets. Even detergents used in
washing machines and
dishwashers eventually end up in our rivers and oceans. So do the
pesticides we use on our gardens. A lot of toxic pollution also enters
waste water from highway runoff. Highways are typically covered
with a cocktail of toxic chemicals—everything from spilled fuel and
brake fluids to bits of worn tires (themselves made from chemical
additives) and exhaust emissions. When it rains, these chemicals wash
into drains and rivers. It is not unusual for heavy summer rainstorms
to wash toxic chemicals into rivers in such concentrations that they
kill large numbers of fish overnight. It has been estimated that, in
one year, the highway runoff from a single large city leaks as much oil
into our water environment as a typical tanker spill.
Some highway runoff runs away into drains; others can pollute groundwater or accumulate in the land next to a road, making it increasingly toxic as the years go by.

Chemical waste

Detergents are relatively mild substances. At the opposite end of the
spectrum are highly toxic chemicals such as polychlorinated
biphenyls (PCBs). They were once widely used to manufacture
electronic circuit boards, but their harmful effects have now been recognized and their use is highly restricted in many countries.
Nevertheless, an estimated half million tons of PCBs were discharged
into the environment during the 20th century.
[9] In a classic
example of transboundary pollution, traces of PCBs have even been found
in birds and fish in the Arctic. They were carried there through the
oceans, thousands of miles from where they originally entered the
environment. Although PCBs are widely banned, their effects will be
felt for many decades because they last a long time in the environment
without breaking down.

Another kind of toxic pollution comes from heavy metals, such as
lead, cadmium, and mercury. Lead was once commonly used in gasoline
(petrol), though its use is now restricted in some countries. Mercury
and cadmium are still used in batteries (though some brands
now use other metals instead). Until recently, a highly
toxic chemical called tributyltin (TBT) was used in paints to
protect boats from the ravaging effects of the oceans. Ironically,
however, TBT was gradually recognized as a pollutant: boats painted
with it were doing as much damage to the oceans as the oceans were
doing to the boats.

The best known example of heavy metal pollution in the oceans took
place in 1938 when a Japanese factory discharged a significant amount
of mercury metal into Minamata Bay, contaminating the fish stocks
there. It took a decade for the problem to come to light. By that time,
many local people had eaten the fish and around 2000 were poisoned.
Hundreds of people were left dead or disabled.
[10]

Radioactive waste

People view radioactive waste with great alarm—and for good reason.
At high enough concentrations it can kill; in lower concentrations it
can cause cancers and other illnesses. The biggest sources of
radioactive pollution in Europe are two factories that reprocess waste
fuel from nuclear power plants:
Sellafield on the north-west coast of Britain and Cap La Hague on the
north coast of France. Both discharge radioactive waste water into the
sea, which ocean currents then carry around the world. Countries such
as Norway, which lie downstream from Britain, receive significant
doses of radioactive pollution from Sellafield. [19]
The Norwegian government has repeatedly complained that Sellafield has
increased radiation levels along its coast by 6–10 times.
Both the Irish and Norwegian governments continue to press for
the plant’s closure.
[11]

Oil pollution

Photo: Oil-tanker spills are the most spectacular forms of pollution and the ones that catch public attention,
but only a fraction of all water pollution happens this way. Photo courtesy of US Fish & Wildlife Service Photo Library.

When we think of ocean pollution, huge black oil slicks often spring
to mind, yet these spectacular accidents represent only a tiny fraction
of all the pollution entering our oceans.
Even considering oil by
itself, tanker spills are not as significant as they might seem: only
12 percent of the oil that enters the oceans comes from tanker accidents; over
70 percent of oil pollution at sea comes from routine shipping and from the
oil people pour down drains on land.
[12] However, what makes tanker spills
so destructive is the sheer quantity of oil they release at once — in
other words, the concentration of oil they produce in one very
localized part of the marine environment. The biggest oil spill in
recent years (and the biggest ever spill in US waters)
occurred when the tanker Exxon Valdez broke up in
Prince William Sound in Alaska in 1989. Around 12 million gallons (44
million liters) of oil were released into the pristine wilderness—enough to fill your living room 800 times over!
Estimates of the marine animals killed in the spill
vary from approximately 1000 sea otters and
34,000 birds to as many as 2800 sea otters and 250,000 sea birds.
Several billion salmon and herring eggs are also believed to have been destroyed.
[13]

Plastics

If you’ve ever taken part in a community beach clean, you’ll know
that plastic is far and away the most common substance that washes up
with the waves. There are three reasons for this: plastic is one of
the most common materials, used for making virtually every kind of
manufactured object from clothing to automobile parts; plastic
is light and floats easily so it can travel enormous distances across
the oceans; most plastics are not biodegradable (they do not
break down naturally in the environment), which means that things like
plastic bottle tops can survive in the marine environment for a long time.
(A plastic bottle can survive an estimated 450 years in the ocean
and plastic fishing line can last up to 600 years.)

While plastics are not toxic in quite the same way as poisonous
chemicals, they nevertheless present a major hazard to seabirds, fish,
and other marine creatures. For example, plastic fishing lines and
other debris can strangle or choke fish. (This is sometimes
called ghost fishing.) About half of all
the world’s seabird species are known to have eaten plastic residues.
In one study of 450 shearwaters in the North Pacific,
over 80 percent of the birds were found to contain plastic residues in their stomachs.
In the early 1990s, marine scientist Tim Benton collected
debris from a 2km (1.5 mile) length of beach in the remote Pitcairn islands
in the South Pacific. His study recorded approximately a thousand
pieces of garbage including 268 pieces of plastic, 71 plastic bottles,
and two dolls heads.
[14]

Today, much media attention focuses on the
Great Pacific Garbage Patch,
a floating, oceanic graveyard of plastic junk roughly three times the size of France,
discovered by sailor Charles J. Moore in 1997.
But, as you’ll know well enough if you’ve ever taken part in a community beach
clean, persistent plastic litters every ocean on the planet: some
8 million tons of new plastic are dumped in the sea every single year.
[17]

Alien species

Most people’s idea of water pollution involves things like sewage,
toxic metals, or oil slicks, but pollution can be biological as well as
chemical. In some parts of the world, alien species are a major
problem. Alien species (sometimes known as invasive species)
are animals or plants from one region that have been introduced into a
different ecosystem where they do not belong. Outside their normal
environment, they have no natural predators, so they rapidly run wild,
crowding out the usual animals or plants that thrive there. Common
examples of alien species include zebra mussels in the Great Lakes of
the USA, which were carried there from Europe by ballast water (waste
water flushed from ships). The Mediterranean Sea has been invaded by a
kind of alien algae
called Caulerpa taxifolia. In the Black Sea, an alien jellyfish
called Mnemiopsis leidyi reduced fish stocks by 90 percent after
arriving in ballast water. In San Francisco Bay, Asian clams called Potamocorbula
amurensis, also introduced by ballast water, have dramatically
altered the ecosystem. In 1999, Cornell University’s David Pimentel estimated that alien invaders like this cost the US economy $123 billion a year;
in 2014, the European Commission put the cost to Europe at €12 billion a year and «growing
all the time.
[18]

Photo: Invasive species: Above: Water hyacinth crowding out a waterway around an old fence post. Photo by Steve Hillebrand. Below: Non-native zebra mussels clumped on a native mussel.
Both photos courtesy of US Fish & Wildlife Service Photo Library.

Other forms of pollution

These are the most common forms of pollution—but by no means the
only ones. Heat or thermal pollution from factories and power
plants also causes problems in rivers. By raising the temperature, it
reduces the amount of oxygen dissolved in the water, thus also reducing
the level of aquatic life that the river can support.

Another type of pollution involves the disruption of sediments
(fine-grained powders)
that flow from rivers into the sea. Dams built for hydroelectric power
or water reservoirs can reduce the sediment flow.
This reduces the formation of beaches, increases coastal erosion (the
natural destruction of cliffs by the sea), and reduces the flow of
nutrients from rivers into seas (potentially reducing coastal fish
stocks).
Increased sediments can also present a problem. During construction work, soil, rock, and other fine powders sometimes enters nearby rivers in large quantities, causing it to become turbid (muddy or silted). The extra sediment can block the gills of fish, effectively suffocating them.
Construction firms often now take precautions to prevent this kind of pollution from happening.

What are the effects of water pollution?

Some people believe pollution is an inescapable result of human
activity: they argue that if we want to have factories, cities, ships,
cars, oil, and coastal resorts, some degree of pollution is almost
certain to result. In other words, pollution is a necessary evil that people
must put up with if they want to make progress. Fortunately, not
everyone agrees with this view. One reason people have woken up to the
problem of pollution is that it brings costs of its own that
undermine any economic benefits that come about by polluting.

Take oil spills, for example. They can happen if tankers are too
poorly built to survive accidents at sea. But the economic benefit of
compromising on tanker quality brings an economic cost when an oil
spill occurs. The oil can wash up on nearby beaches, devastate the ecosystem,
and severely affect tourism. The main problem is that the people who
bear the cost of the spill (typically a small coastal community) are
not the people who caused the problem in the first place (the people
who operate the tanker). Yet, arguably, everyone who puts gasoline
(petrol) into their car—or uses almost any kind of petroleum-fueled
transport—contributes to the problem in some way. So oil spills are a
problem for everyone, not just people who live by the coast and tanker
operates.

Sewage is another good example of how pollution can affect us all.
Sewage discharged into coastal waters can wash up on beaches and cause
a health hazard. People who bathe or surf in the water can fall ill if
they swallow polluted water—yet sewage can have other harmful effects
too: it can poison shellfish (such as cockles and mussels) that grow
near the shore. People who eat poisoned shellfish risk suffering from
an acute—and sometimes fatal—illness called paralytic shellfish
poisoning. Shellfish is no longer caught along many shores because
it is simply too polluted with sewage or toxic chemical wastes that
have discharged from the land nearby.

Pollution matters because it harms the environment on which people
depend. The environment is not something distant and separate from our
lives. It’s not a pretty shoreline hundreds of miles from our homes or
a wilderness landscape that we see only on TV. The environment is
everything that surrounds us that gives us life and health. Destroying
the environment ultimately reduces the quality of our own lives—and
that, most selfishly, is why pollution should matter to all of us.

How can we stop water pollution?

There is no easy way to solve water pollution; if there were, it
wouldn’t be so much of a problem. Broadly speaking, there are three
different things that can help to tackle the problem—education, laws,
and economics—and they work together as a team.

Education

Making people aware of the problem is the first step to solving it.
In the early 1990s, when surfers in Britain grew tired of catching illnesses
from water polluted with sewage, they formed a group called Surfers
Against Sewage to force governments and water companies to clean up
their act. People who’ve grown tired of walking the world’s polluted
beaches often band together to organize community beach-cleaning
sessions. Anglers who no longer catch so many fish have campaigned for
tougher penalties against factories that pour pollution into our
rivers. Greater public awareness can make a positive difference.

Laws

One of the biggest problems with water pollution is its
transboundary nature. Many rivers cross countries, while seas span
whole continents. Pollution discharged by factories in one country with
poor environmental standards can cause problems in neighboring
nations, even when they have tougher laws and higher standards.
Environmental laws can make it tougher for people to pollute, but to be
really effective they have to operate across national and international
borders. This is why we have international laws governing the oceans,
such as the 1982 UN Convention on the Law of the Sea (signed by over
120 nations), the 1972
London (Dumping) Convention, the 1978
MARPOL International Convention for the Prevention of Pollution from Ships,
and the 1998 OSPAR Convention for the Protection of the Marine
Environment of the North East Atlantic. The European Union has
water-protection laws (known as directives) that apply to all of its
member states. They include the 1976 Bathing Water Directive (updated 2006), which seeks to ensure the quality of the waters that people use for
recreation. Most countries also have their own water pollution laws. In
the United States, for example, there is the 1972
Clean Water Act
and the 1974 Safe Drinking Water Act.

Economics

Most environmental experts agree that the best way to tackle
pollution is through something called the polluter pays principle.
This means that whoever causes pollution should have to pay to clean it
up, one way or another. Polluter pays can operate in all kinds of ways.
It could mean that tanker owners should have to take out insurance that
covers the cost of oil spill cleanups, for example. It could also mean
that shoppers should have to pay for their plastic grocery bags, as is
now common in Ireland, to encourage recycling and minimize waste. Or it
could mean that factories that use rivers must have their water inlet
pipes downstream of their effluent outflow pipes, so if they cause
pollution they themselves are the first people to suffer. Ultimately,
the polluter pays principle is designed to deter people from polluting
by making it less expensive for them to behave in an environmentally
responsible way.

Our clean future

Life is ultimately about choices—and so is pollution. We can live
with sewage-strewn beaches, dead rivers, and fish that are too
poisonous to eat. Or we can work together to keep the environment clean
so the plants, animals, and people who depend on it remain healthy. We
can take individual action to help reduce water pollution, for example,
by using environmentally friendly detergents, not pouring oil down
drains, reducing pesticides, and so on. We can take community action
too, by helping out on beach cleans or litter picks to keep our rivers
and seas that little bit cleaner. And we can take action as countries
and continents to pass laws that will make pollution harder and the
world less polluted. Working together, we can make pollution less of a
problem—and the world a better place.

Find out more

On this site

• Air pollution (introduction)
• Climate change and global warming
• Environmentalism (introduction)
• Fracking
• Land pollution
• Organic food and farming
• Recycling

Books

For older readers

• Understanding Environmental Pollution by Marquita K. Hill. Cambridge University Press, 2020. A clear, wide-ranging introduction that covers all types of pollution, recycling, energy use, and related issues.
• Pollution: Causes, Effects, and Control by Roy Harrison (editor). Royal Society of Chemistry, 2001. Comprehensive (579-page) introduction to all forms of pollution.
• An Introduction to Pollution Science by Roy Harrison (editor). Royal Society of Chemistry, 2006. Another good introductory text covering all types of pollution.
• Managing Environmental Pollution by Andrew Farmer. Routledge, 2002. More emphasis on «pollution solutions» in this book.
• Biology of Freshwater Pollution by Christopher Mason. Prentice Hall, 2001. This book is aimed at advanced undergraduates and water pollution professionals.

For younger readers

• Pollution (Ecographics) by Izzi Howell. Franklin Watts, 2019. An illustrated introduction to air and water pollution for ages 9–11.
• What a Waste: Rubbish, Recycling, and Protecting our Planet by Jess French. DK, 2019. A simple, colorful overview that puts pollution into a much broader context for, for younger readers aged 7–9.
• Trash Vortex: How Plastic Pollution Is Choking the World’s Oceans by Danielle Smith-Lera. Compass Point/Capstone, 2018. A 64-page introduction to the Great Pacific Garbage Patch and the issues it raises.
• Pollution: What if we do nothing? by Christiane Dorion. Britannica, 2009/2015. A 49-page guide that summarizes the problem of pollution and the current state of our planet, and concludes with an optimistic section on what young readers can do.
• Earth Matters by Lynn Dicks et al. Dorling Kindersley, 2008: A more general guide to problems Earth faces, with each major biome explored separately. In case you’re interested, I contributed the polar regions chapter. The book is mostly a simple read and probably suitable for 7–10 (and maybe 9–12).

Selected news articles

• Water Pollution: A collection of interesting recent water pollution news stories from The New York Times.
• Poor water infrastructure puts world at greater risk by Fiona Harvey, The Guardian, 22 March 2020.
  Half the world’s population still lacks adequate sanitation.
• In China, the water you drink is as dangerous as the air you breathe by Deng Tingting, The Guardian, 2 June 2017. Half the country fails to meet its water quality targets.
• Cleaning the world’s water: ‘We are now more polluted than we have ever been’ by John Vidal. The Guardian, 31 August 2016. Prof Joan Rose, winner of the Stockholm Water Prize, sees great progress in tackling water-borne diseases, but acknowledges that the world is as polluted as ever.
• Water Pollution and the Farm Economy by Justin Gillis. The New York Times, December 11, 2012. In the United States, progress in farm output carries a cost in polluted rivers and streams.
• Human impact on world’s rivers ‘threatens water security of 5 billion’ by Adam Vaughan, The Guardian, 29 September 2010. A major study finds rivers throughout the world under severe pressure from pollution.
• Water pollution expert derides UN sanitation claims by Juliette Jowit, The Guardian, 25 April 2010. One of the world’s top pollution experts, Prof. Asit Biswas, challenges a lack of progress in providing clean water to developing countries.
• World’s pollution hotspots mapped: BBC News, 18 October 2006. The Blacksmith Institute produces a list of the 10 most polluted places on the planet.

Water pollution videos

• NOAA: Humans impact the oceans: This short, 2.5-minute animation shows how various different human activities affect the oceans around our planet. Only the polar regions have relatively low impacts, so far.
• EPA Ireland: Water pollution: A longer, 7-minute introduction describing how Ireland’s Environmental Protection Agency (EPA) is trying to tackle water pollution. Although filmed in Ireland, the issues are general and apply to most other countries.
• Scripps Institution of Oceanography: Investigating Ocean Pollution: Scripps scientists research the effects of pollution on marine life in San Diego Bay, California. (6.5 minutes.)
• Water pollution: Paul Andersen gives a nice summary of most of the topics I’ve introduced here, so you could watch this for a quick review. (10 minutes.)

Websites

• Water pollution photos: From our friends at the UK Rivers Network, a collection of public-domain (copyright free) pollution photos you can use in school and college projects. You can find links to all the photos we’ve used on this page, in a much larger size, on there.

Notes and references

Wherever possible, I’ve referenced my sources with links; the following notes (indicated by bracketed numbers in the text) are mostly references to books, journals, and other «offline» reports that can’t be linked the same way.

1. ↑ The original definition appeared in UN Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection, Report of the First Session, March 1969, p.5.
   It omitted the word «energy,» which was added at the Stockholm Conference (the UN Conference on Human Development) in 1972.
2. ↑ For a summary, see «Agricultural Chemicals in Iowa’s Ground Water, 1982–95.» by Dana Koplin. US Geological Survey, 1997.
   More recent studies have found glyphosate (sold under brand names such as Roundup®) in groundwater samples in
   Spain,
   Canada,
   Sri Lanka,
   Argentina,
   Mexico, and elsewhere.
   For a review of the complex debate over glyphosate safety,
   see (for example)
   Vandenberg et al (2017),
   and Tarazona et al (2017).
3. ↑ World Health Organization (WHO): Diarrhoeal disease, Fact sheet Number 330, May 2017.
   (This is still the latest available revision in 2020.)
4. ↑ Estimates in different publications quote 4–5 million tons. See «Our World.» New York Magazine, April 16, 1990, p.28.
5. ↑ Sewage Treatment in the UK: UK Implementation of the EC Urban Waste Water Treatment Directive. Report by DEFRA, London, 2002, p.1.
   The figure of 31,000 pipes comes from Surfers Against Sewage.
6. ↑ «Wastewater Treatment Cleans Up Border Waterways» in U.S.–Mexico Border. US Environmental Protection Agency (undated).
7. ↑ In Our Backyard: A Guide to Understanding Pollution and Its Effects by Travis P. Wagner. John Wiley & Sons, 1993. p.26
8. ↑ It’s very hard to find a decent estimate for the world’s total annual production of industrial waste—partly because the term isn’t precisely defined and partly because no-one has any obligation to measure. In 2000, the AAAS Atlas of Population & Environment suggested a figure of 1.5 billion tons was being produced by the entire OECD during the mid 1990s. In 1998, James Spalding et al told the Academy of Marketing Science (AMS) annual conference that the US produced around 2.5 billion tons of industrial waste per year and estimated that to be «perhaps a third of the world’s refuse,» giving a grand worldwide total of 7.5 billion tons. From these and other similar estimates, it seems 5–10 billion tons might be a reasonable ballpark figure.
9. ↑ Around 1.5 million tons were produced worldwide according to
   12. Polychlorinated Biphenyls (PCBs): Uses and Environmental Releases by Dr Heidi Fisher (archived via the Wayback Machine).
   A 1982 estimate suggested about four percent of this total has been destroyed,
   two thirds of the remainder has been stored or is still in use,
   and a third has been discharged into the environment.
   See «Polychlorinated biphenyl (PCB) contaminated sites worldwide» by Ivan Holoubek in
   PCBs: Recent Advances in Environmental Toxicology and Health Effects by Larry W. Robertson et al (eds), University Press of Kentucky, 2015.
   Other chapters in this book cover PCB transport into remote parts of the world.
10. ↑ Bitter Sea: The Human Cost of Minamata Disease by Akio Mishima. Kosei Pub, 1982.
11. ↑ See for example «Norway fury at UK nuclear waste flood.» by Paul Brown, The Guardian, December 20, 1997.
    A recent (2017) study found that a major accident at Sellafield could pollute a significant proportion
    of Norway in as little as 12 hours.
    See Worst Case Meteorological Scenario for Norway in Case of an Accident in Sellafield Nuclear Site by Heiko Klein and Jerzy Bartnicki.
12. ↑ International Maritime Organization: Marine Environmental Awareness, 2011 Edition, IMO Press, 2011 reveals that routine shipping adds three times as much oil to the marine environment as accidental pollution (but that doesn’t factor in significant discharges coming from the land). According to Pollution Impacts on Marine Biotic Communities by Michael J. Kennish, CRC Press, 2007, about 58 percent of oil added to the oceans comes
    from land runoff, atmospheric deposition, and ocean dumping; 24 percent comes from all kinds of «marine transportation activities» (including routine shipping operations and tanker spills); 8 percent comes from oil wells and refineries; and natural inputs add 10 percent.
13. ↑ There have been many estimates of the impact of the Exxon Valdez spill. They differ wildly, largely because
    the spill was studied at different times, by different groups with different scientific, political,
    and financial agendas. My upper figures are taken from
    Exxon Valdez: Ten Years On, BBC News, March 18, 1999. One definitive academic study worth seeking out is
    Exxon Valdez Oil Spill: Fate and Effects in Alaskan Waters, ASTM International, 1995, which collected 25 papers from an ASTM symposium in April 1993.
14. ↑ The impact on seabirds of marine debris is explored in The American Bird Conservancy Guide to Bird Conservation by Daniel J. Lebbin et al. University of Chicago Press, 2010, p.340. The shearwater study is quoted in Biological Oceanography: An Introduction by Carol Lalli et al. Elsevier, 1993. p.253.
    Tim Benton’s studies of the Pitcairn Islands are thoroughly documented in
    The Pitcairn Islands: Biogeography, Ecology and Prehistory: Proceedings of an International Discussion Meeting Held at the Linnean Society by T.G. Benton et al, Linnean Society of London, 1995.
15. ↑ [PDF] Clean Watersheds Needs Survey 2012 Report to Congress, Environmental Protection Agency, January 2016.
16. ↑ The figure of 80 percent is widely quoted in books
    on pollution. For example, here’s a sample from Google Books.
17. ↑ The figure of 8 million tons comes from
    a research study by Kara Lavender Law et al. See Plastic waste inputs from land into the ocean, Science 13 Feb 2015.
    There’s a more accessible account in
    Eight Million Tons of Plastic Dumped in Ocean Every Year by Lara Parker, National Geographic, 13 February 2015.
18. ↑ David Pimentel’s report is detailed in Alien animals, plants and microbes cost U.S. $123 billion a year, Cornell ecologists report, Cornell Chronicle, January 24, 1999, archived via the Wayback Machine.
    The EU figure comes from [PDF]
    Invasive Alien Species: A European Response, European Union, 2014.
19. ↑ «Radioactive pollution from land» in Strategic Management of Marine Ecosystems: Proceedings of the NATO Advanced Study Institute on Strategic Management of Marine Ecosystems, Nice, France, 1–11 October, 2003, p.20.
20. ↑ Water pollution expert derides UN sanitation claims by Juliette Jowit, The Guardian, 25 April 2010. One of the world’s top pollution experts, Prof. Asit Biswas, challenges a lack of progress in providing clean water to developing countries.
21. ↑ For a couple of recent examples, see
    Happening Now: Dead Zone in the Gulf 2021, NOAA, 2021 and Happening Now: Dead Zone in the Gulf 2019, NOAA, 2019. The biggest dead zone ever recorded, 8776 square miles or 22700 square kilometers, happened in 2017.

We can survive for some time without food, but we cannot survive even for some minutes without air. This easy fact tells us how important fresh air is to livings. It is well known that air is a mixture of a variety of gases. By volume, about 78% of the mixture is nitrogen and about 21% is oxygen. Carbon dioxide (CO₂), argon, methane, ozone, and water vapour are also present in very small amounts. When air is contaminated by unsought substances that have a harmful result on the living and also the non-living organism, it’s remarked as air pollution.

Air Pollution

The substances which contaminate(add impurities) the air are called Air pollutants. Sometimes, these substances may come naturally like smoke and dust from forest fires or volcanic eruptions. Pollutants are mostly added to the atmosphere by human activities. The sources of air pollutants are multi factories, automobiles, power plants, and burning of firewood and waste. Vehicles produce high levels of pollutants like carbon monoxide (CO), carbon dioxide (CO₂), nitrogen oxides (NO), and smoke. Incomplete burning of fuels such as petrol and diesel produces harmful carbon monoxide gas. these are poisonous gases. such gases reduce the oxygen-carrying capacity of the blood in our body. 

Fact to grasp: If the vehicles registered in Delhi state are lined up one after the other in a row, the total length would be nearly equal to the sum of the length of the longest rivers of the world i.e. Nile and Amazon!

Many big or small industries are also responsible for causing air pollution. Petroleum refineries are a major source of gaseous pollutants like Sulphur and nitrogen dioxide. Sulphur dioxide (SO₂) is produced by the combustion of fuels like coal in power plants. It can cause respiratory problems, including permanent lung damage or asthma. Other pollutants are chlorofluorocarbons (CFCs) which are used in refrigerators, air conditioners (ACs), and aerosol sprays. Chlorofluorocarbons (CFCs) damages the ozone layer of the atmosphere.  the ozone layer protects us from harmful ultraviolet rays of the sun., these harmful gases lead to the ozone hole.

Various Measures to Reduce Air Pollution

• Remove or lessen the number of pollutants before they are released into the atmosphere. air purify must fit in the exhaust of vehicles so that it leads to less pollution.
• It is the duty of the state government and other focused agencies to monitor the quality of air. We can use this data to generate awareness about air pollution among friends and school students.
• small drives can be organized by schools and institutes to aware students of the cleaning of the air, with a small contribution on our part can make a big difference in the state of the environment.
• Instead of using personal automobiles daily to go for work one can use a bicycle or can use public transport which can improve quality of the air we can think that this is our task to do.
• Do not use plastic bags which pollute the environment and can increase the heat on earth, by burning these wastes they produce harmful gases which lead to air pollution.

 Water Pollution

When harmful substances such as sewage, kitchen waste, toxic chemicals, silt, etc., get mixed with water, contaminate the water, and become polluted, this phenomenon is known as water pollution. The substances that pollute water are called water pollutants, and the pollution is called water pollution. 

Water pollutants are bacteria, parasites, fertilizers, plastics, faecal waste, Sewage, agricultural chemicals, and industrial waste are some of the major contaminants of water.

How does Water get Polluted?

• Sewage that is untreated and effluents from cities and big industries are discharged into this river.
• Rivers are used by many people for bathing and washing their clothes, also for bathing their cattle and other animals.
• Cremation of dead bodies on the banks of the Ganges is a very old practice, and this practice leads to pollution of the river water.
• Rivers are preferred for immersing flowers, idols, and many other residues of rituals and worships.
• Many industrial towns and big cities are situated on the banks of this river, e.g. Kanpur.
• There are about 4000 industrial units in Kanpur; which include fertilizer, chemicals, tanneries, and paint industries. these factories emit unwanted chemicals into this river.
• weedicides such as Rampant, pesticides, and chemical fertilizers pollute river water and groundwater.

How to Prevent Water Pollution?

• Direct discharge of untreated sewage in water bodies should be strictly prohibited/restricted.
• Every state should have a sewage treatment plant government to initiate such projects like the government of India initiate Namami Gange to purify the Ganga river.
• Human awareness about the harms of idol and flower immersion should be increased.
• The crematorium method should be done far away from the fresh sources of water.

Potable Water

Potable water, which is fit for drinking. Potable water is water that is safe to drink or use for food preparation. 

The amount of drinking water required to maintain good health varies differently for different persons. Such conditions are age, environmental condition, level of work, etc.16 litres of water are needed for a person who worked in a hot climate, and a normal human must drink 10 to 12 glasses of water per day. 

Methods of Water Purification

• It is a major duty of the municipality to treat industrial water before supplying drinking water to households.
• One of the common methods for the purification of water is Filtration. Numerous sorts of filter area units are utilized in households.
• Boiling is another common method of water purification. It kills the germs and bacteria in water.
• The chlorination process also helps in killing the germs present in water. Chlorine tablets must distribute through the government.

Sample Problems 

Problem 1: Describe the ‘Green House Effect’ and name some greenhouse gases.

Solution: 

The greenhouse effect is a natural process that warms the Earth’s surface. When the Sun’s energy reaches the Earth’s atmosphere, some of the radiation reflects back to space, and the rest is absorbed and re-radiated by greenhouse gases. greenhouse gases are methane, carbon dioxide, ozone, nitrous oxide, etc.

Problem 2: What is the threat to the Taj Mahal?

Solution: 

Acid rain has one of the major threats to the beauty of the Taj Mahal. Taj Mahal is made up of various eye-catching marbles. When acid rains fall on the Taj Mahal or other monuments made of marble, Acid reacts with marble to form a powder-like substance that is then washed away by the rain and makes marbles decolourized. This phenomenon is known as marble cancer. Also, the particles emitted from the Mathura oil refinery established near Agra are leading to the yellowing of the marble of the Taj Mahal.

Problem 3: What are water cleansing agents that can be used in the home?

Solution: 

Baking Soda, Soap, Lemon, Borax, White Vinegar, Washing Soda or SAL Soda, Cornstarch all are effective water cleansing agents that can be used in a home.

Problem 4: What is Potable Water?

Solution: 

Potable water is that water that is safe for drinking and comes from surface and ground sources and is treated to levels that meet some standards of pure water. 

Problem 5: Define air pollutants with some examples.

Solution: 

The agents which contaminate the air of the atmosphere that agents are called air pollutants. e.g. Smoke, dust, carbon monoxide, lead, etc.

Problem 6: What are water pollutants and water pollution?

Solution: 

When some impurities are added to water and make it contaminated is known as water pollution. The substances which contaminate(add impurities) the water is called Air pollutants. e.g. bacteria, parasites, fertilizers, plastics, faecal waste, etc.

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Water Pollution

Water pollution occurs mostly, when people overload
the water environment such as streams, lakes, underground water, bays or seas
with wastes or substances harmful to living beings.

Water is necessary for life. All organisms contain it,
some drink it and some live in it. Plants and animals require water that is
moderately pure, and they cannot survive, if water contains toxic chemicals or
harmful microorganisms. Water pollution kills large quantity of fish, birds,
and other animals, in some cases killing everything in an affected area.

Pollution makes streams, lakes, and coastal waters
unpleasant to swim in or to have a rest. Fish and shellfish harvested from
polluted waters may be unsafe to eat. People who polluted water can become ill,
if they drink polluted water for a long time, it may develop cancer or hurt
their future children.

The major water pollutants are chemical, biological,
and physical materials that lessen the water quality. Pollutants can be
separated into several different classes:

The first class is petroleum products: oil, fuel,
lubrication, plastics. The petroleum products get into water by accidental
spills from ships, tanker trucks and when there are leaks from underground
storage tanks. Many petroleum products are poisonous for animals. Spilled oil
damages the feathers of birds and the fur of animals, often it causes death.

The second class is pesticides and herbicides. There
are chemicals used to kill harmful animals and plants. If they penetrate into
streams, rivers, lakes, these chemicals can be very dangerous. The chemicals
can remain dangerous for a long time. When an animal eats a plant that’s been
treated with it, the poisons are absorbed into the tissues and organs of the
animals.

When other animals feed on a contaminated animal, the
chemicals are passed up to them. As it goes up through the food chain, the
chemical becomes more harmful, so animals at the top of the food chains may
suffer cancers, reproductive problems, and death. Nitrates can cause a lethal
form of anemia in infants.

The third class are heavy metals, such as, mercury,
selenium, uranium, radium, cesium, etc. They get into the water from
industries, automobile exhausts, mines, and natural soil. Heavy metals also
become more harmful as they follow the food chain. They accumulate in living
being’s cells and when they reach high levels of concentration in the organism,
they can be extremely poisonous, or can result in long-term health problems.
They can sometimes cause liver and kidney damage.

The fourth class is fertilizers and other nutrients
used to promote plant growth on farms and in gardens.

The fifth class is infectious organisms and pathogens.
They enter water through sewage, storm drains, runoff from farms, etc.

The last one is thermal pollution. Water is often
taken from rivers, lakes or seas to be used in factories and power plants. The
water is usually returned to the source warmer than when it was taken. Even a
small temperature change in a body of water can drive away the fish and other
species that were originally there, and attract other species in place of them.
It breaks a balance and can cause serious circumstances in future.

Загрязнение воды

Загрязнение воды
происходит главным образом, когда люди перегружают водную окружающую среду,
ручьи, озера, подземные воды, заливы и моря, отходами или веществами, вредными
для живых существ.

Вода, необходима для
жизни. Все организмы содержат воду, некоторые пьют ее, некоторые живут в ней.
Растениям и животным нужна относительно чистая вода, и они не выживут, если в
воде будут токсические химикалии или вредные микроорганизмы. Загрязнение воды
убивает большое количество рыбы, птиц и других животных, а в некоторых случаях
в пострадавших районах убивает все живое.

Загрязнение превращает
ручьи, озера и прибрежные воды в места, непригодные для отдыха и купания. Рыба
и моллюски, пойманные в загрязненной воде, могут быть небезопасны для еды.
Люди, которые пьют загрязненную воду, могут заболеть, если они пьют
загрязненную воду в течение долгого времени, это может вызвать рак или
повредить их будущим детям.

Больше всего воду
загрязняют химические, биологические вещества, которые ухудшают качество воды.
Загрязняющие вещества могут быть разделены на несколько различных классов.

Первый класс — это
нефтепродукты: нефть, топливо, смазочные вещества, пластмассы. Нефтепродукты попадают в воду через случайные утечки с
судов, грузовых танкеров, когда есть утечки из подземных хранилищ и
резервуаров. Многие нефтепродукты ядовиты для животных. Пролитая нефть
повреждает перья птиц и мех животных, часто это приводит к смерти.

Второй класс — это пестициды и гербициды. Это
химические вещества, которые используются для уничтожения вредных животных и
растений. Если они попадают в ручьи, реки, озера, то могут быть очень опасны.
Химикалии могут оставаться опасными в течение долгого времени. Когда животное
съедает растение, которое было обработано этими химикатами, яд попадает в ткани
и органы животного.

Когда другие животные съедают пораженное животное,
химикалии попадают к ним. Проникая вверх по пищевой цепочке, химикаты
становятся все более и более вредоносными, так что животные на верхних ступенях
пищевой цепочки могут страдать раковыми образованиями, проблемами
воспроизводства, могут погибнуть. Нитраты могут стать причиной смертельного
исхода от анемии у младенцев.

Третий класс — это тяжелые металлы, такие как ртуть,
селен, уран, радий, цезий и т. д. Они попадают в воду с промышленных
предприятий, выхлопных труб автомобилей, шахт и обычного грунта. Тяжелые
металлы также становятся более вредными, поскольку они следуют по пищевой цепи.
Они накапливаются в клетках живых организмов. Когда они достигают высокого
уровня концентрации в организме, они могут быть чрезвычайно ядовитыми или могут
стать причиной серьезных проблем со здоровьем. Они могут иногда вызывать
повреждения печени и почек.

Четвертый класс — это удобрения и другие вещества, которые
используются для улучшения роста растений на фермах и в садах.

Пятый класс — инфекционные организмы и патогенные
микроорганизмы. Они попадают в воду через сточные воды, дренажи, каналы отвода
сточных вод с ферм и т. д.

И последний класс — тепловое загрязнение. Вода,
которая забирается из рек, озер, морей для нужд предприятий, часто возвращается
к источнику теплее, чем она забиралась. Даже малое температурное изменение воды
может отпугнуть рыбу и другие виды животных, которые изначально жили там, и привлечь
другие разновидности вместо них. Это нарушает баланс и может вызвать серьезные
последствия в будущем.

Questions:

1. When does water pollution occur?

2. Why do plants and animals require pure water?

3. What are the major water pollutants?

4. How can pollutants be separated?

5. How do petroleum products affect the animals?

6. Why can pesticides and herbicides be dangerous if
they penetrate into streams, rivers and lakes?

7. What do heavy metals result in?

8. How do fertilizers penetrate to water?

9. What damage can thermal pollution cause?

Vocabulary:

pollution — загрязнение

to occur — происходить, случаться, совершаться

mostly — главным образом» но большей части

environment — окружение, окружающая обстановка;
окружающая среда

stream — река, ручей

underground water — подземные воды

bay — залив» бухта

harmful — вредный

living beings — живые существа

to contain — содержать в себе, включать, иметь в своем
составе; вмещать

to require — требовать

moderately — умеренно, сдержанно

to survive — выдержать, пережить, перенести

quantity — количество

shellfish — моллюск, ракообразное

to harvest — проводить массовые охоты

to ingest — глотать, проглатывать

to lessen — уменыпать(ся), сокращать(ся)

petroleum products — нефтепродукты

fuel — топливо, бензин

lubrication — смазка, смазывание (машины)

accidental — случайный

to spill — проливаться), разливать(ся),
расплескивать(ся)

tanker truck — грузовой танкер

leak — течь, протечка, утечка

underground storage tank — подземные хранилища
(резервуары)

poisonous — ядовитый

to penetrate — проникать внутрь, проходить сквозь,
пронизывать

to remain — оставаться

to absorb — всасывать, впитывать; абсорбировать,
поглощать

tissue — ткань

contaminated — зараженный, загрязненный

to suffer — страдать; испытывать, претерпевать

lethal form — летальный исход

exhausts — выхлопные газы

to cause damage — причинять ущерб, вред

liver — печень

kidney — почка

nutrient — питательное вещество

sewage — сточные воды, нечистоты

storm drains — дренажи

circumstance — обстоятельство, случай; условие