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Chemistry > Environmental Chemistry > Water Pollution
Environmental Chemistry

Water Pollution

What are the types of pollution? Water pollution is one of the major issues India is facing at present. Untreated sewage is one of the prominent causes of this form of pollution in India. CPCB (Central Pollution Control Board) estimates 62 billion litres of urban sewage flows into rivers per day. Almost 80 percent of Indian water bodies fall among the polluted category. Imagine what will happen in the next twenty years if proper action is not taken by each and every citizen living in the country. So, it is very important to know more about the causes of water pollution.

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Water Pollution and Its Types

types of pollution

[Source: Wikipedia]

Water is a necessary component for the sustenance of life. Even after knowing how essential water is for the sustenance of life, we still take water for granted and waste it time and again. Mostly, it is the human activities that have led to water pollution and compromised with the quality of water.

Water pollution reaches the surface or grounds via different paths. The places of pollution or source that can be easily identified easily called point source. In the case of the point source such as industrial and municipal discharge pipes, the pollutant enters via these mediums in the water source.

The identification of certain pollution sources is difficult such as agricultural run-offs, stormwater drainage, acid rain, etc. These sources of pollution are non-point sources. It is difficult to recognize them because it is possible to have many agricultural runoffs like farms, animals or crop lands from where water can enter into the water source. Below is a list of major water pollutants and the different sources from it originates to finally enter the water bodies.

types of pollution

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Causes of Water Pollution

Contamination of Water by Pathogens

Disease-causing agents or pathogens is one of the major water pollutants responsible for contamination of water and causes of water pollution. Domestic sewage and animal excreta contain different types of pathogens such as bacteria and other microorganisms. For instance, human excreta contain bacteria like Streptococcus faecalis and E. coli responsible for gastrointestinal diseases.

Water Pollution Due to Organic Wastes

Another very important pollutant is organic matter like leaves, trash, grass, dried leaves, etc. The runoff of the organic matter leads to the pollution of water. Excessive growth of phytoplankton in water can also be among the causes of water pollution. However, these wastes are biodegradable (waste that can decompose).

The large bacterial population present in the water can decompose the organic matter. These bacteria consume the oxygen present in the water. However, the amount of oxygen present in the water depends upon the holding capacity of the water.

The oxygen present in water is the concentration of dissolved oxygen (DO). The DO concentration in cold water is up to 10 parts per million or 10 ppm. This amount is very small in comparison to oxygen in the air which is around 200,000 ppm. The DO concentration in water is a very important factor in terms of aquatic life.

The inhibition of life can take place if the DO concentration is lower than 6 ppm.  Photosynthesis of aquatic plants releases oxygen or the atmospheric oxygen reaching the water is the source of oxygen in any water body. Thus, during the night there is a decrease in the concentration of oxygen in the water because photosynthesis is not possible and the aquatic plants constantly consume oxygen for the respiration process.

However, if organic matter enters the water bodies, the microorganisms present in the organic matter utilize the oxygen available in water. Therefore, this will, in turn, cause the oxygen-dependent aquatic life to slowly diminish and die due to lack of oxygen in the water. Hence, anaerobic bacteria (bacteria that do not require oxygen for their survival) will gradually start decomposing the organic waste and produce foul-smelling chemicals harmful to human health.

Biological Oxygen Demand

In most cases, aerobic bacteria (bacteria that do require oxygen for their survival) utilizes the DO to decompose the organic wastes thereby depleting the DO concentration. Therefore, a particular amount of oxygen is needed by bacteria to decompose the organic matter present in a particular volume of the water sample.

This is known as BOD or Biochemical Oxygen Demand. Therefore, the amount of BOD indicates the amount of organic matter present in a water sample. BOD indicates the amount of oxygen which can easily break down the organic material present in a water body. The BOD value of clean water is 5ppm. The BOD value of highly polluted water can reach up to 17 ppm and sometimes more.

Chemical Pollutants

All of us have read that water is an excellent solvent. Therefore it can dissolve even harmful heavy metals like mercury, cadmium, nickel, etc. These types of heavy metals fall into the category of important types of pollutants because they are very harmful to human body.

Moreover, human beings are not capable of excreting these heavy metals. It will not show its effect is present in small quantity. However, over the time the concentration of the metals will rise in the human body due to gradual decomposition and can possibly cross the tolerance limit.

Heavy metals if cross the tolerance limit can cause damage in different parts of human body including kidney, liver, central nervous systems, etc. Moreover, another type of chemical pollutants includes acids and salts. An acid such as sulphuric acid can be found in mine drainage and salts can be found in many sources such as sodium and calcium chloride to melt snow and ice in colder regions.

Another set of chemical pollutants responsible for water pollution are organic chemicals. For instance, oil spills (petroleum products) pollute the oceans. Similarly, pesticides are a class of organic substance that can one of the causes of water pollution when they drift down as run-off from lands or in the form of sprays.

Additionally, industrial chemicals such as PCBs or polychlorinated biphenyls are a class of very harmful class water pollutant. Recent studies indicate they are carcinogenic (cancer-causing). PCB is present in many regular household and industrial chemicals like cleansing solvent, detergents, and fertilizers. However, nowadays biodegradable detergents are used.

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The lack of oxygen can be responsible for destroying the aquatic life of any waterbody. Chemical pollutants like fertilizer contain phosphates in the form of additives. Therefore, phosphate addition in water can lead to rapid growth of algae. Hence, gradually the algae growth can cover entire water surface which can lead to the reduction in oxygen concentration.

Therefore, lack of oxygen can cause death and decay of aquatic animals thereby creating anaerobic conditions in the waterbody.  Hence, the water body will become bloom-infested and can inhibit the growth of other living organisms. This entire process is eutrophication.

Therefore, eutrophication refers to a process where water bodies support dense plant population due to nutrient enrichment, which can also cause animal death by depriving the animal life of oxygen thereby resulting in gradual loss of biodiversity.

International Standards of Drinking Water


It is important to regularly check and maintain the fluoride ion concentration in drinking water within the permissible limit. Lack of fluoride in drinking water can lead to tooth decay. It is important to add soluble fluoride in drinking water to make the concentration up to 1 ppm. However, the concentration should not cross 2 ppm or it can lead to brown mottling of teeth. Moreover, excessive fluoride can cause harmful effect to teeth and bones.


Lead pipes are used for water transportation and contaminate the water in the process.  The maximum permissible limit for the concentration of lead in drinking water is 50 parts per billion. High concentration of lead in drinking water can cause problems associated with liver, kidney, reproductive system, etc.

Sulfates & Nitrates

Sulfate concentration greater than 500 ppm in drinking water can cause the laxative effect. Nitrate concentration in drinking water should not exceed 50 ppm. High nitrate concentration in drinking water leads to harmful effects such as methemoglobinemia or blue baby syndrome.

Other Metals

Many other types of metals can be present in drinking water. However, the permissible limit for each metal may vary from each other. Below table represents the permissible concentration of few metals in drinking water.

types of pollution

Solved Question for You

Question: Explain the disadvantage of using biodegradable detergents?

Solution: Even though biodegradable detergents do not contain harmful chemicals like PCBs but there is a possibility the bacteria responsible for decomposing biodegradable detergent can consume it and grow rapidly. Therefore, hen these biodegradable detergents enter the water as waste bacteria will feed and rapidly start growing thereby using up all the oxygen present in the water. Hence, the aquatic life will be affected.

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