Water pollution: an introduction
by Chris Woodford. Last updated: June 4, 2017.
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: Detergent pollution entering a river. Photo courtesy of US Fish & Wildlife Service Photo Library.
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. Photo courtesy of US Department of Energy/National Renewable Energy Laboratory (DOE/NREL) (image id 6312198).
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." 
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.
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. 
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. 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.
With billions of people on the planet, disposing of sewage waste is a major problem. According to 2015 and 2016 figures from the World Health Organization, some 663 million people (9 percent of the world's population) don't have access to safe drinking water, while 2.4 billion (40 percent of the world's population) don't have proper sanitation (hygienic toilet facilities); although there have been great improvements in securing access to clean water, relatively little progress has been made on improving global sanitation in the last decade. 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.  (Back in 2002, the World Health Organization estimated that water-related diseases could kill as many as 135 million people by 2020.) 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.  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, some of it still pumped untreated into the sea through long pipes.  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.  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.  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.
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 grows to an area of around 5500–6000 square miles (14,000–15,500 square kilometers), which is about the same size as the state of Connecticut.
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.  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 2015, serve around 88 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.
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.
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 electroniccircuit 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.  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. 
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. 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. 
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.  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. 
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. 
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.
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.
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.
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.
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
For older readers
For younger readers
- 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.
- Pollution: Earth in Danger by Helen Orme. Bearport/TickTock, 2008. A basic 32-page introduction for readers aged about 9-12.
- 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 and Toxic Waters: A collection of interesting recent water pollution news stories from The New York Times.
- 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.
- 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.)
- 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.
- ↑ 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.
- ↑For a summary, see "Agricultural Chemicals in Iowa's Ground Water, 1982–95." by Dana Koplin. US Geological Survey, 1997.
- ↑World Health Organization (WHO): Diarrhoeal disease, Fact sheet Number 330, May 2017.
- ↑Estimates in different publications quote 4–5 million tons. See "Our World." New York Magazine, April 16, 1990, p.28.
- ↑Sewage Treatment in the UK: UK Implementation of the EC Urban Waste Water Treatment Directive. Report by DEFRA, London, 2002, p.1.
- ↑"Wastewater Treatment Cleans Up Border Waterways" in U.S.–Mexico Border. US Environmental Protection Agency (undated).
- ↑In Our Backyard: A Guide to Understanding Pollution and Its Effects by Travis P. Wagner. John Wiley & Sons, 1993. p.26
- ↑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.
- ↑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.
- ↑Bitter Sea: The Human Cost of Minamata Disease by Akio Mishima. Kosei Pub, 1982.
- ↑See for example "Norway fury at UK nuclear waste flood." by Paul Brown, The Guardian, December 20, 1997.
- ↑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.
- ↑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.
- ↑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.
- ↑[PDF] Clean Watersheds Needs Survey 2012 Report to Congress, Environmental Protection Agency, January 2016.
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This article was originally written for the UK Rivers Network and first published on their website in April 2006. It is revised and updated every year.
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The conclusion comes at the tail-end of your research paper. It plays a crucial part in shaping the opinion of the reader. It is meant to wrap up all the ideas discussed in the body and make a statement on your position on the subject under discussion. A resounding conclusion will add great value to your paper. How do you write the best conclusion for a paper on water pollution?
The conclusion should capture what has been discussed in the body paragraphs. This means that no new information should be included. There is no room to introduce new facts since they will need to be supported for them to be valid. The conclusion thus becomes a summary of the main ideas discussed in the body paragraphs.
Since the conclusion is a summary of ideas, it should be short and precise. The points should be restated in the least number of words possible. This enables the reader to recall the discussion. Do not repeat what has been said in the body or during discussion word for word. A single sentence should be used to summarize each point. It should contain inferences and recommendations from discussions made in the body.
Extensive discussions in the body are likely to cause the reader to forget the main point in your research paper. This makes it necessary to restate the thesis statement. It helps in recalling the anchoring point of the paper and at the same time makes it easier to justify the position taken in the thesis statement. This can be accomplished in a single paragraph.
The conclusion brings your arguments to an end. As such, you are required to summarize your main points. It is during the summary that you create a connection between the questions you have been probing and the inferences made in the literature review and discussion of findings. The conclusion brings all points being discussed to a close.
Based on the points you have given in the discussion and summary, it is time to state your position. This should be done firmly since you have made your case during the discussion and literature review. The stand must be aligned to the facts revealed in the literature review and discussion.
The conclusion to your research paper should be short and precise. It must capture all the main points discussed in the body. It is the last thing to write in your paper.