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                                          TOPIC 4.4: WATER POLLUTION

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.

This unit is a minimum of 4.5 hours.

Significant Ideas:

  • Water pollution, both to groundwater and surface water, is a major global problem, the effects of which influence human and other biological systems.


Big questions:

  • What strengths and weaknesses of the systems approach and the use of models have been revealed through this topic?

  • To what extent have the solutions emerging from this topic been directed at preventing environmental impacts, limiting the extent of the environmental impacts, or restoring systems in which environmental impacts have already occurred?

  • How are the issues addressed in this topic of relevance to sustainability or sustainable development?

  • In what ways might the solutions explored in this topic alter your predictions for the state of human societies and the biosphere some decades from now?

  • To what extent can water pollution be considered as a system?

  • Are the existing solutions to pollution likely to cope with current levels of water pollution?

  • Which is the lesser evil - less food production or eutrophication? How are the linked?

  • How is water pollution likely to change in the next decades? Give reasons for your answers.


Knowledge & Understanding:

​4.4.U1 There are a variety of freshwater and marine pollution sources.
[Sources of freshwater pollution should include runoff, sewage, industrial discharge
and solid domestic waste.]
[Sources of marine pollution should include rivers, pipelines, atmosphere and
activities at sea (operational and accidental discharges)]

  • ​Identify different sources of freshwater and marine pollution.

Industrial waste:
Industries produce huge amount of waste which contains toxic chemicals and pollutants which can cause air pollution and damage to us and our environment. They contain pollutants such as lead, mercury, sulphur, asbestos, nitrates and many other harmful chemicals. Many industries do not have proper waste management system and drain the waste in the fresh water which goes into rivers, canals and later in to sea. The toxic chemicals  have the capability to change the color of water, increase the amount of minerals, also known as Eutrophication, change the temperature of water and pose serious hazard to water organisms.

Sewage and wastewater:
The sewage and waste water that is produced by each household is chemically treated and released into sea with fresh water. The sewage water carries harmful bacteria and chemicals that can cause serious health problems. Pathogens are known as a common water pollutant; The sewers of cities house several pathogens and thereby diseases. Microorganisms in water are known to be causes of some very deadly diseases and become the breeding grounds for other creatures that act like carriers. These carriers inflict these diseases via various forms of contact onto an individual. A very common example of this process would be Malaria.

Mining activities:
Mining is the process of crushing the rock and extracting coal and other minerals from underground. These elements when extracted in the raw form contains harmful chemicals and can increase the amount of toxic elements when mixed up with water which may result in health problems. Mining activities emit several metal waste and sulphides from the rocks and is harmful for the water.

Marine dumping:
The garbage produced by each household in the form of paper, aluminum, rubber, glass, plastic, food if collected and deposited into the sea in some countries. These items take from 2 weeks to 200 years to decompose. When such items enters the sea, they not only cause water pollution but also harm animals in the sea.

Accidental Oil leakage:
Oil spill pose a huge concern as large amount of oil enters into the sea and does not dissolve with water; thereby opens problem for local marine wildlife such as fish, birds and sea otters. For e.g.: a ship carrying large quantity of oil may spill oil if met with an accident and can cause varying damage to species in the ocean depending on the quantity of oil spill, size of ocean, toxicity of pollutant.

Burning of fossil fuels:
Fossil fuels like coal and oil when burnt produce substantial amount of ash in the atmosphere. The particles which contain toxic chemicals when mixed with water vapor result in acid rain. Also, carbon dioxide is released from burning of fossil fuels which result in global warming.

Chemical fertilizers and pesticides:
Chemical fertilizers and pesticides are used by farmers to protect crops from insects and bacterias. They are useful for the plants growth. However, when these chemicals are mixed up with water produce harmful for plants and animals. Also, when it rains, the chemicals mixes up with rainwater and flow down into rivers and canals which pose serious damages for aquatic animals.

Leakage from sewer lines:
A small leakage from the sewer lines can contaminate the underground water and make it unfit for the people to drink. Also, when not repaired on time, the leaking water can come on to the surface and become a breeding ground for insects and  mosquitoes.

Global warming:
An increase in earth’s temperature due to greenhouse effect results in global warming. It increases the water temperature and result in death of aquatic animals and marine species which later results in water pollution.

Radioactive waste:
​Nuclear energy is produced using nuclear fission or fusion. The element that is used in production of nuclear energy is Uranium which is highly toxic chemical. The nuclear waste that is produced by radioactive material needs to be disposed off to prevent any nuclear accident. Nuclear waste can have serious environmental hazards if not disposed off properly. Few major accidents have already taken place in Russia and Japan

4.4.2U Types of aquatic pollutants include floating debris, organic material, inorganic plant nutrients (nitrates and phosphates), toxic metals, synthetic compounds, suspended solids, hot water, oil, radioactive pollution, pathogens, light, noise and biological pollutants (invasive species).

  • Outline the effects of a variety of different aquatic pollutants.

  • Explain sources and effects of organic pollution.

  • Discuss with reference to a case study, impacts of toxic metal poisoning.

Suspended Matter
Some pollutants do not dissolve in water as their molecules are too big to mix between the water molecules. This material is called particulate matter and can often be a cause of water pollution. The suspended particles eventually settle and cause a thick silt at the bottom. This is harmful to marine life that lives on the floor of rivers or lakes. Biodegradable substances are often suspended in water and can cause problems by increasing the amount of anaerobic microorganisms present. Toxic chemicals suspended in water can be harmful to the development and survival of aquatic life.

Toxic Metals
​Toxic Metals and solvents from industrial work can pollute rivers and lakes. These are poisonous to many forms of aquatic life and may slow their development, make them infertile or even result in death.

​Pesticides are used in farming to control weeds, insects and fungi. Run-offs of these pesticides can cause water pollution and poison aquatic life. Subsequently, birds, humans and other animals may be poisoned if they eat infected fish.

Petroleum is another form of chemical pollutant that usually contaminates water through oil spills when a ship ruptures. Oil spills usually have only a localised affect on wildlife but can spread for miles. The oil can
cause the death of many fish and stick to the feathers of seabirds causing them to lose the ability to fly.2. Fertilizer
Some wastewater, fertilizers and sewage contain high levels of nutrients. If they end up in water bodies, they encourage algae and weed growth in the water. This will make the water undrinkable, and even clog filters. Too much algae will also use up all the oxygen in the water, and other water organisms in the water will die out of oxygen starvation.

Synthetic compounds
Many industries and farmers work with chemicals that end up in water. These include chemicals that are used to control weeds, insects and pests. Metals and solvents from industries can pollute water bodies. These are poisonous to many forms of aquatic life and may slow their development, make them infertile and kill them.

Microbial Pollution
Microbiological pollution is the natural form of water pollution that is caused by microorganisms in uncured water. Most of these organisms are harmless but some bacteria, viruses, and protozoa can cause serious diseases such as cholera and typhoid. This is a significant problem for people in third world countries who have no clean drinking water and/or facilities to cure the water.


4.4.U3 A wide range of parameters can be used to directly test the quality of aquatic systems, including pH, temperature, suspended solids (turbidity), metals, nitrates and phosphates.
[With respect to measuring aquatic pollution, a polluted and an unpolluted site (for example, upstream and downstream of a point source) should be compared.]

  • Evaluate different parameters used to determine water quality.

  • Distinguish between direct and indirect parameters used to determine water quality

​​Direct measurement is performed by monitoring the level of the pollutant itself, e.g. nitrates in a lake or temperature levels in a lake or stream. An indirect method would monitor the effects of the pollutants on other factors, e.g. dissolved oxygen, B.O.D., presence or absence of indicator species 

Indirect measurement involves the monitoring and measurement of organisms in the ecosystem and more specifically indicator species or index species. These are species that by virtue of their abundance or absence will indicate the level of pollution in that ecosystem. For example: leafy lichens on trees if the air is unpolluted

Marine—salinity, pH, temperature, dissolved oxygen, wave action
Freshwater—turbidity, flow velocity, pH, temperature, dissolved oxygen


4.4.U4 ​Biodegradation of organic material utilizes oxygen, which can lead to anoxic conditions and subsequent anaerobic decomposition, which in turn leads to formation of methane, hydrogen sulfide and ammonia (toxic gases).

  • Describe the effects of biodegradation of organic matter

Biodegradability is the ability of organic substances and materials to be broken down into simpler substances through the action of enzymes from microorganisms. If this process is complete, the initial organic substances are entirely converted into simple inorganic molecules such as water, carbon dioxide and methane.

Changes to the organic matter load can affect organic matter concentrations in the water. The breakdown of organic matter can result in low dissolved oxygen (e.g. hypoxia or anoxia) in the water (eutrophication). Sediment oxygen demand is higher when production is higher. Algal (both macroalgae and microalgae) blooms and increased plant growth occur in areas with increased nutrients and high light availability.

Changes to the organic matter concentrations in the water of a wetland can result in: eutrophication a loss of sensitive species. The breakdown of organic matter can result in low dissolved oxygen (e.g. hypoxia or anoxia) in the water (eutrophication). Animals that are sensitive to low dissolved oxygen and cannot move to areas with better conditions may die, often in mass mortality events.

4.4.U5 Biochemical oxygen demand (BOD) is a measure of the amount of dissolved oxygen required to break down the organic material in a given volume of water through aerobic biological activity. BOD is used to indirectly measure the amount of organic matter within a sample.

  • Define BOD

  • Describe how BOD is used to determine water quality

  • State how BOD is measured


The biochemical oxygen demand is a measure of the total demand for oxygen by living and chemical components in a water body.  The greater the amount of polluting organic matter, the more microbes are required to break it down. (So, high dissolved oxygen, high levels of pollution) 

Measuring BOD is a very useful when examining the health of water, e.g. stream, rivers and lakes. BOD is essentially the amount of dissolved oxygen required to break down organic materials in a given volume of water through aerobic activity. Essentially it is a measure of oxygen uptake in water.

How to calculate BOD

  • Determined by the number of aerobic organisms and their rate of respiration.

  • The greater the amount of organic pollutant in the water the more microbes are required to break it down. Hence, there is a positive relationships between pollutant level and BOD

How to measure BOD?

  • Take a sample of water at measure volume

  • Measure the oxygen level

  • More the sample in a dark place at 20 degree for five days

  • After five days re-measure the oxygen level

  • BOD is the difference between the two measurement

What does this mean?

  • High BOD indicates there are many organisms using oxygen for respiration

  • Low BOD indicates relatively few organisms needing oxygen for respiration

  • High BOD - low DO levels - high pollutant levels, especially nitrate & phosphate

  • Low BOD - high DO levels - low pollutant levels

4.4.U6 Some species can be indicative of polluted waters and can be used as indicator species.

  • Discuss the role of using biotic indices to determine the quality of aquatic ecosystems.


Biological indicators are aquatic plant and animal life that are susceptible to specific types and levels of pollutants. Many organisms require a specific range of physical and chemical parameters to flourish in a surface water.The level of pollution in water can be indicated by the species living there.​Typically, unpolluted water will contain a greater diversity of organisms than polluted water. Polluted water will support larger numbers of tolerant organisms and have less diversity.

4.4.U7 A biotic index indirectly measures pollution by assaying the impact on species within the community according to their tolerance, diversity and relative abundance.

  • Discuss the role of using biotic indices to determine the quality of aquatic ecosystems.


​Biotic index is a scale 1-10 that gives a measure of the quality of an ecosystem by the presence and abundance of the species living in it. The Trent Biotic Index is based on the fact that certain species tend to disappear and the species diversity decreases as the organic pollution in a water course increases. The scale corresponds to the four basic water quality (Excellent, Good, Fair or Poor). 

Using this index and indicator species is another indirect method of measuring pollution. The pollutant are not measured directly but their effect on biodiversity is measured. 

  • Aquatic macroinvertebrates are often used as an indicator species. They have some general characteristics that make them very useful to assess stream health. 

  • abundant and found in water bodies throughout the world

  • not extremely mobile.

  • carry out part or all of their life cycle within the stream or river.

The biotic index works by assigning different levels of tolerance to pollution to the different types of organisms. The types of macroinvertebrates found during sampling are grouped as:

1: Pollution intolerant: These organisms are highly sensitive to pollution. (e.g., stonefly or alderfly larva)
2: Semi-Pollution intolerant: These organisms are sensitive to pollution. (e.g.. dragonfly larva or crawfish)
3: Semi-Pollution tolerant: These organisms will be found in clean and slightly polluted waterways. (e.g., snails or black fly larva)
4: Pollution tolerant: These organisms will be found in polluted, as well as clean aquatic ecosystems (e.g., leechs,bloodworms)

4.4.U8 Eutrophication can occur when lakes, estuaries and coastal waters receive inputs of nutrients (nitrates and phosphates), which results in an excess growth of plants and phytoplankton.
[The role of positive and negative feedback in the process of eutrophication should be covered. Coastal eutrophication can lead to red tide blooms.]

  • ​Explain the process of eutrophication and its impacts.

  • Describe positive and negative feedback as applied to eutrophication.


In eutrophication, increased amounts of nitrogen and/or phosphorus are carried into streams, lakes and groundwater causing nutrient enrichment. This lead to rapid growth of algae, accumulation of dead organic matter, high rate of decomposition and lack of oxygen. The role of positive feedback should be noted in these processes.

Process(Positive Feedback):

  1. Increase in inputs of nutrients (nitrates and phosphates) which enter the lake

  2. Increase in algae productivity in the lake

  3. Massive increase in algae

  4. Increase in dead organic matter due to increase in decomposer as there are more algae for food

  5. Higher rate of decomposition as the decomposers respiration

  6. Increase in oxygen demand but decline in oxygen level

  7. Death of organisms

The consequences of marine eutrophication is very simple to explain. The quiet unseen changes of the body of water caused by algae and plants suffocates many of the organisms as we said before. Not only does eutrophication kill other species but the organisms that happen to survive in the water with few oxygen change.


Their bodies that were originally used of their surroundings evolve and adapt to the low oxygen level. They were once edible to eat, but as their body changes, so does the human reactions toward it. Many of the fishes that change, they become poisonous to our bodies causing either weakness, blurred vision, burning muscles, difficulty breathing, memory loss, organ damage, and even death.

Impact includes

  • Death of aerobic organisms

  • Increased turbidity

  • Loss of macrophytes

  • Reduction in length of food chains

  • Loss of species diversity.

​Human activities worldwide have caused the nitrogen and phosphorus content in may waters to double.

4.4.U9 Dead zones in both oceans and fresh water can occur when there is not enough oxygen to support marine life.

  • Discuss with reference to a case study, impacts of dead zones.

In coastal marine environments, “Dead Zones” are regions where oxygen concentrations are very low. This condition of oxygen deficiency, known as hypoxia, is caused by an interaction between biological, chemical and physical factors. In the absence of sufficient oxygen, animals and plants either die or leave the dead zone

4.4.U10 Water pollution management strategies include:

  1. reducing human activities that produce pollutants (for example, alternatives to current fertilizers and detergents)

  2. reducing release of pollution into the environment (for example, treatment of wastewater to remove nitrates and phosphates)

  3. ​removing pollutants from the environment and restoring ecosystems (for example, removal of mud from eutrophic lakes and reintroduction of plant and fish species).

You need to apply the model in Figure 3 in the evaluation of the strategies. 

Minimize the amount of nutrients being released into the system by:

  • limiting production/use of detergents containing phosphates

  • alternative methods of enhancing crop growth

  • create buffer zones between agricultural land and water sources

  • regulating and reducing at point of emission

  • prevent animal waste from leaching into groundwater and rivers/streams

Treat the polluted area by:

  • pumping air into the water source

  • divert or treat sewage properly

  • dredge (dig up) contaminated sediments

  • physically remove algae blooms

  • reintroduce plant and fish species

  • pumping mud from eutrophic lakes

Application & Skills

4.4.A1 Analyse water pollution data

Water quality monitoring is a crucial aspect to protecting water resources. Agencies must monitor lakes, streams, rivers and other types of water bodies to assist them in determining water quality condition. From these monitoring activities, water quality monitoring data is generated. Without this data, water resource managers cannot know where pollution problems exist, where we need to focus our pollution control energies or where we've made progress

4.4.A2 Explain the process and impacts of eutrophication.

A major problem with the use of fertilisers occurs when they're washed off the land by rainwater into rivers and lakes. The resulting increase of nitrate or phosphate in the water encourages algae growth, which forms a bloom over the water surface. This prevents sunlight reaching other water plants, which then die. Bacteria break down the dead plants and use up the oxygen in the water so the lake may be left completely lifeless

The main effects caused by eutrophication can be summarized as follows:

  1. Species diversity decreases and the dominant biota changes

  2. Plant and animal biomass increase

  3. Turbidity increases

  4. Rate of sedimentation increases, shortening the lifespan of the lake

  5. Anoxic conditions may develop

Because of the high concentration of organisms in a eutrophic system, there is often a lot of competition for resources and predator pressure. This high degree of competition and the sometimes-high chemical or physical stress make high the struggle for survival in eutrophic systems. As a result the diversity of organisms is lower

4.4.A3 Evaluate the uses of indicator species and biotic indices in measuring aquatic pollution.

​Biomonitoring involves the use of indicators, indicator species or indicator communities. Macroinvertebrates, fish, and/or algae are often used. Certain aquatic plants have also been used as indicator species for pollutants including nutrient enrichment. There are advantages and disadvantages to each. Macroinvertebrates are most frequently used. Biochemical, genetic, morphological, and physiological changes in certain organisms have been noted as being related to particular environmental stressors and can be used as indicators.

The presence or absence of the indicator or of an indicator species or indicator community reflects environmental conditions. Absence of a species is not as meaningful as it might seem as there may be reasons, other than pollution, that result in its absence (e.g., predation, competition, or geographic barriers which prevented it from ever being at the site). Absence of multiple species of different orders with similar tolerance levels that were present previously at the same site is more indicative of pollution than absence of a single species. It is clearly necessary to know which species should be found at the site or in the system.

4.4.A4 Evaluate pollution management strategies with respect to water pollution.

Changing human activities Possible measures to reduce nitrate loss (based on the northern hemisphere) include the

  • Avoid using nitrogen fertilizers between mid-September and mid-February when soils are wet and fertilizer is most likely to be washed through the soil.

  • Do not apply nitrogen just before heavy rain is forecast (assuming that forecasts are accurate).

  • Use less nitrogen if the previous year was dry because less will have been less lost. This is difficult to assess precisely.

  • Do not plough up grass as this releases nitrogen.

  • Use steep slopes for permanent pasture grass or woodland; use flat land above slopes for arable crops. This minimizes the greater risk of wash from steep land.

  • Incorporate straw – straw decay uses nitrogen, with up to 13 per cent less nitrogen lost – it also locks up phosphorus.

  • Direct drilling and minimal cultivation reduces nitrogen loss by up to a half. Less disturbance means less conversion of nitrogen to nitrate but straw has to be burnt.

Regulating and reducing the nutrient source Public campaigns in Australia have encouraged people to:

  • use zero- or low-phosphorus detergents

  • wash only full loads in washing machines

  • wash vehicles on porous surfaces away from drains or gutters

  • reduce use of fertilizers on lawns and gardens

  • compost garden and food waste

  • collect and bury pet faeces.

Clean-up strategies
Once nutrients are in an ecosystem, it is much harder and more expensive to remove them than it would have been to tackle the eutrophication at source. The main clean-up methods available are:

  • precipitation (e.g. treatment with a solution of aluminium or ferrous salt to precipitate phosphates)

  • removal of nutrient-enriched sediments, for example by mud pumping

  • removal of biomass (e.g. harvesting of common reed) and using it for thatching or fuel. 

Classroom Material
Dirty Waters
Water Pollution Guide
Procedure for Measuring BOD
Freshwater Pollution Case Study Activity
Water Pollution Case Study Activity

Case Studies
 Lake Udaisagar in India
Loch Leven in UK
Baltic Sea
Lake Washington
Ganges River
Deep Water Horizons
​Flint Water Crisis

Useful Links
Water Pollution Guide
Environmental Biotechnology - EnviroTech
Measuring Air PollutionAir Pollution Monitoring - EPA
Dissolved Oxygen and Biochemical Oxygen Demand - EPA
Biotic Index - Water Action Volunteers
Chesapeake Bay BioIndex - IAN
Bio-indicators - Knowledge Group​Animation from the Center for Ocean Sciences Education Excellence.
Sources and Impact of Eutrophication
Eutrophication: Policies, Action and Strategies to Address Nutrient Pollution
Facts and Figures about Eutrophication
Planning and Management of Lakes and Reservoirs focusing on Eutrophication (PAMOLARE)
How bad is Eutrophication at Present?
Lake Eutrophication
Planning and Management of Lakes and Reservoirs: An Integrated Approach to Eutrophication - A Student's Guide By the

United Nations Environment Programme (UNEP) International Environmental Technology Centre (IETC). © UNEP 2001.
Dead Zones - Save The Seas
Causes of Water Pollution: Nine Significant Contributors
Water Pollution Facts: For the U.S. and Throughout the World
Effects of Water Pollution: 8 Significant Issues
Radioactive Water from Japan’s Nuclear Power Plant - Does It Affect People in the United States
Solutions to Water Pollution - 5 Simple Ways You Can Make a Difference

In the News
Trying to Save World's Lakes: Controlling Nitrogen Can Actually Worsen  Problem - Science Daily July 24, 2008
Eutrophication on the Baltic Sea - The Baltic Sea Portal
150 Dead Zones Counted In Ocean - NBC News 3/29/2004
Creeping Dead Zones - NASA Science Focus
What Causes Dead Zones - Scientific America Sep 2015



  • Countries with limited access to clean water often have higher incidences of waterborne illnesses.

Theory of knowledge:

  • A wide range of parameters are used to test the quality of water and judgments are made about causes and effects of water quality—how can we effectively identify cause–effect relationships, given that we can only ever observe correlation?

Video Clips

Paul Andersen explains how water quality can be degraded by pollutants. Wastewater is the main source of water pollution and can be measure using the BOD (biochemical oxygen demand). Dead zones, cultural eutrophication, disease, and other pollutants are included. A basic description of sewage treatment, septic systems, and water purification is also included.











Pete McBride takes a photographic and scientific journey along India's sacred waterway, the Ganges, which is revered as a god but struggles with a detrimental pollution problem




















Water Pollution and Cholera





















Here, Dr.Askwar Hilonga demonstrates how his water filter works.......some sort of marketing and INSPIRATION to his community. Of course it takes time for people to believe that this is TRULY what they have been missing! Hilonga won the Africa Prize for Engineering 2015, sponsored by the Royal Academy of Engineering, UK





















Even though 80% of trash starts on land, tons of it ends up in the ocean, swirling around in a massive patch of plastic debris.

















TED talk on the Great Pacific Garbage Patch -- an endless floating waste of plastic trash.























Measuring Water Quality Turbidity































Measuring Water Quality Dissolved Oxygen





















​Learn Water Action Volunteers Stream Monitoring protocols to monitor aquatic macroinverterbates to assess water quality in stream




















What is eutrophication? Here's an overview in a one minute video. Harmful algal blooms, dead zones, and fish kills are the results of a process called eutrophication—which begins with the increased load of nutrients to estuaries and coastal waters.



















Folke Rydén is one of Sweden's leading documentary and non-fiction program producers. He was for a long time correspondent for SVT stationed in Washington and Hong Kong. His latest project is on DIRTY WATERS, algae blooms, dead sea beds -- the Baltic Sea is suffering. 



















Discovering the dirty truth about the future of the Baltic Sea. - See more at:




































Keeping farm field runoff from reaching the Mississippi River is the focus of a U.S. Department of Agriculture conservation effort in Missouri.








The Chesapeake Bay Program visited three different wastewater treatment plants in the Chesapeake Bay watershed in various stages of upgrading their management systems. Join Doug Abbott, Superintendent of Wastewater Treatment Facilities in Easton, MD and George Hawkins, General Manager of the District of Columbia Water and Sewer Authority, as they explain the importance of these upgrades and getting the message out to the public.






















Water Pollution (4.4)

Water Pollution/ Impacts

6 Types of Water Pollution
Causes and Effects of Water Pollution
Eutrophication- causes, consequences, and controls
Stages of Eutrophication
Water Borne Diseases- CDC


Management Strategies

Two management Strategies- Case Study
Water Pollution Methods
Tool for Improving Water Quality


Water Quality

Water Quality Tests
What is an indicator Species?
Examples of Indicator Species
Water Quality Parameter Definitions
Interpreting Water Analysis Data

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