This article throws light upon the twelve main causes of water pollution. The causes are: 1. Sewage 2. Domestic or Sanitary Sewage 3. Agricultural Run-Off 4. Industrial Effluents 5. Thermal Pollution 6. Ecological Pollution 7. Chemical Waste 8. Radioactive Waste 9. Oil Pollution 10. Plastics 11. Alien Species 12. Other Forms of Pollution.
Water Pollution: Cause # 1. Sewage:
With billions of people on the planet, disposing of sewage waste is major problem. In developing countries, many people still lack clean water and basic sanitation (hygienic toilet facilities). Sewage disposal affects people’s immediate environments and leads to water-related illnesses such as diarrhoea that kills 3-4 million children each year.
According to the World Health Organization, water-related diseases could kill 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.
The population of Britain produces around 300 million gallons of sewage 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 carries with it 20—25 million gallons (76—95 million litres) of raw sewage each day.
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.
Water Pollution: Cause # 2. Domestic or Sanitary Sewage:
Sewage amounts to a very small fraction of the sewage by weight, but it is large by volume and contains impurities such as organic materials and plant nutrients that tend to rot.
Today, many people dump their garbage into streams, lakes, rivers and seas, thus making water bodies the final resting place of cans, bottles, plastics and other household products. The various substances that we use for keeping our houses clean add to water as pollution as they contain harmful chemicals.
Biochemical Oxygen Demand or BOD:
BOD is the amount of oxygen required by micro-organisms to decompose the organic substances in sewage. Therefore, the more organic material there is in the sewage, the higher the BOD. In this manner BOD is a measure of organic materials in sewage. BOD levels of industrial sewage may be many times that of domestic sewage.
Dissolved oxygen is an important factor that determines the quality of water in lakes and rivers. The higher the concentration of dissolved oxygen, the better the water quality. When sewage enters a lake or stream, micro-organisms begin to decompose the organic materials. Oxygen is consumed by micro-organisms in their metabolism.
This can quickly deplete the available oxygen in the water. When the dissolved oxygen levels drop too low, many aquatic species die. In fact, if the oxygen level drops to zero, the water will become septic. When organic compounds decompose without oxygen, it gives rise to the undesirable odours usually associated with septic or putrid conditions.
Water Pollution: Cause # 3. Agricultural Run-Off:
The use of land for agriculture and the practices followed in cultivation greatly affect the quality of groundwater.
Intensive cultivation of crops causes chemicals from fertilizers (e.g., nitrate) and pesticides to seep into the groundwater, through the process of leaching. Routine applications of fertilizers and pesticides for agriculture and indiscriminate disposal of industrial and domestic wastes are increasingly being recognized as significant sources of water pollution.
Fertilizers add 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 a dead zone. The Gulf of Mexico has one of the world’s most spectacular dead zones. Each summer, it grows to an area of around 7000 square miles (18,000 square kilometers).
When fresh water is artificially supplemented with nutrients (organic waste), it results in an abnormal increase in water plants. This is known as eutrophication. The discharge of water from industries, agriculture, and urban communities into water bodies generally stretches the biological capacities of aquatic systems.
Chemical run-off from fields also adds nutrients to water. Excess nutrients cause the water body to become choked with organic substances and organisms. When organic matter exceeds the capacity of the micro-organisms in water that break down the organic matter, it encourages rapid growth of algae and results in algae bloom.
When they die, the remains of the algae also add to the organic wastes eventually, the water becomes deficient in oxygen. Anaerobic organisms (those that do not require oxygen to live) then attack the organic wastes, releasing gases such as methane and hydrogen sulphide, which are harmful to the oxygen-requiring (aerobic) forms of life.
The result is a foul-smelling, waste-filled body of water. This has already occurred in such places as Lake and is a growing problem in freshwater lakes all over India.
Eutrophication can produce problems such as bad tastes and odours as well as green scum algae. Also the growth of rooted plants increases, which decreases the amount of oxygen in the deepest waters of the lake. It also leads to the death of all forms of life in the water bodies.
The high nitrate content in ground water is mainly from irrigation run-off from agricultural fields where chemical fertilizers have been used indiscriminately.
Pesticides are responsible for water poisoning. They are specially difficult to remove from freshwater and is found in municipal or bottled water, even after conventional treatment. A study from the CSE recently drew the alarm about the concentration in pesticides such as organochlorines and organophosphaters that was exceeding the WHO standards in almost all the Indian brands of bottled water.
As for the fertilizers, they have an indirect adverse impact on the water resources. Indeed, by increasing the nutritional content of the water courses, fertilizers allow organisms to proliferate. These organisms may be disease vectors or algae. The proliferation of algae may slower the flow in the water courses, thus increasing again the proliferation of organisms and sedimentation.
Water Pollution: Cause # 4. Industrial Effluents:
The toughest choice that Indian authorities have to face is industrial Pollution by Small Scale Industries (SSIs).
The smallest facilities are the one for which adaptation to the environmental standard are less affordable. The number of SSIs is estimated to be over 0.32 million units, of which many are highly polluting. The share of the SSIs in term of wastewater generation among several of the major polluting industries was reported to be about 40%.
Waste water from manufacturing or chemical processes in industries contributes to water pollution. Industrial waste water usually contains specific and readily identifiable chemical compounds. During the last fifty years, the number of industries in India has grown rapidly.
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.
A number of large-and medium-sized industries add a number of effluents to water bodies.
Most of these defaulting industries are sugar mills, distilleries, leather processing industries and thermal power stations. Most major industries have treatment facilities for industrial effluents. But this is not the case with small-scale industries, which cannot afford enormous investments in pollution control equipment as their profit margin is very slender.
The IPPS (Industrial Pollution Projection System) has developed by the World Bank merges data from US-EPA about pollution emissions and the Longitudinal Research Database (LRD) on industrial activity, in order to calculate a pollution intensity for different industrial sectors.
The pollution intensity is defined as the level of pollution emission per unit of industrial activity, this last value being measured either by the value of production, the value added, or the employment. The pollution intensities from the World Bank have been computed for the year 1987.
Recently (2002) an attempt has been made to estimate industrial pollution in India using the IPPS. The data used were provided by the Annual Survey of Industries (ASI) from the Indian Central Statistical Organisation (CSO).
The estimated pollution load for the different states is presented in the following table:
Around half of all ocean pollution is caused by sewage and waste water. Each year, the world generates 400 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 pump polluted waters back in their place.
Water Pollution: Cause # 5. Thermal Pollution:
Thermal pollution can occur when water is used as a coolant near a power or industrial plant and then is returned to the aquatic environment at a higher temperature than it was originally. Thermal pollution can lead to a decrease in the dissolved oxygen level in the water while also increasing the biological demand of aquatic organisms for oxygen.
Water Pollution: Cause # 6. Ecological Pollution:
Ecological pollution takes place when chemical pollution, organic pollution or thermal pollution is caused by nature rather than by human activity. An example of ecological pollution would be an increased rate of salvation of a waterway after a landslide which would increase the amount of sediments in runoff water.
Another example would be when a large animal, such as a deer, drowns in a flood and a large amount of organic material is added to the water as a result. Major geological events such as a volcano eruption might also be sources of ecological pollution.
Water Pollution: Cause # 7. Chemical Waste:
Detergents are relatively mild substances but are highly toxic chemicals e.g., polychlorinated biphenyls (PCBs). They were widely used to manufacture electronic circuit boards. 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 carried these 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 commonly used in gasoline (petrol). Mercury and cadmium are still used in batteries.
A highly toxic chemical called tributyltin (TBT) was used in paints to protect boats from the ravaging effects of the oceans.
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.
Water Pollution: Cause # 8. 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 source of radioactive pollution is nuclear power plants. They discharge radioactive waste water into the sea, which with ocean currents then carry around the world.
Water Pollution: Cause # 9. Oil Pollution:
Oil tanker spills are not as significant as they might seem:
Only 12% of the oil that enters the oceans comes from tanker accidents; over 70% of oil pollution at sea comes from routine shipping and from the oil people pour down drains on land. 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 litres) of oil were released into the pristine wilderness. 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 240,000 sea birds. Several billion salmon and herring eggs are also destroyed.
Water Pollution: Cause # 10. Plastics:
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 to about 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). In 1980s it was estimated that a quarter of all seabirds contain some sort of plastic residue.
In another study about a decade later, a scientist collected debris from a 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.
Water Pollution: Cause # 11. 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.
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% after arriving in ballast water. In San Francisco Bay, Asian clams called Potamocorbula amurensis, also introduced by ballast water (waste water).
Water Pollution: Cause # 12. Other Forms of Pollution:
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 enter 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.