The term ‘water pollution’ is referred to the addition to water of an excess of material or energy like heat that is harmful to human beings, animals and many other aquatic forms of life.
According to Water (Prevention and Control of Pollution) Act, 1974 of India, the pollution of water means ‘such contamination of water or such alteration of physical, chemical or biological properties if water or such discharge of any sewage or trade effluent or any other liquid, gaseous or solid substance into water as may, or is likely to, create a nuisance or render such water harmful or injurious o public helath safety, or to domestic, commercial , industrial , agricultural or other legitimate uses or to life and healh of animals or plants or of aquatic organisms.’
Types of Water Pollution
Water pollution is classified as
i. Freshwater Pollution
ii. Marine water Pollution
i. Fresh water pollution
This includes both surface and ground water pollution. Surface water pollution occurs when pollutants enter water bodies such as pond, river and lakes. The causes of surface water pollution may be either natural or man-made or both. For example, silt in rivers and sedimentation on river beds by the discharge of sewage and industrial effluents, blocks the free flow of water, causing floods. Discharge of industrial effluents into rivers also causes pollution due to discharge of harmful chemicals. However, when pollutants find their way into ground water through an aquifer they pollute it too. As a result of which the quality of ground water decreases.
ii. Marine Water Pollution
Marine water is easily polluted by contaminants carried by rivers and also by oil spills and radioactive and industrial waste. Thermal pollution also occurs due to the discharge of hot water from different industries. Mining of polymetallic nodules also damages the ocean bed.
Source of Water Pollution
Water, the most abundant and wonderful natural resources, is extremely essential for survival of all living organisms. But today clean water has become a precious commodity and its quality is threatened by numerous sources of pollution which are as follows-
1. Sewage and Domestic Wastes
2. Industrial Effluents
3. Agricultural Discharges
4. Shipping or Coastal water pollution
1. Sewage and Domestic Wastes
Discharging untreated or partly treated sewage of domestic and municipal origin into nearby rivers, lakes or seas has been a common practice. Domestic or public sewage mainly contains food waste, water from domestic use and water from lavatories. More accurately, this sewage contains pollutants that originate from different human metabolism and vital activities. Various bacteria, yeast, algae, mould and eggs of helmonth viruses are detected in this water. It also contains clay, mineral salts and sand as inorganic impurities. These pollutant which are rich in carbonaceous organic material are oxidized by micro organisms to carbon dioxide and water. As a result, the Dissolved Oxygen (DO) level of water decreases, affecting aquatic life. When the amount of discharge in sewage is less, this biological degradation method helps to remove the waste from rivers. In case of strong sewage and when dissolved oxygen in water is less, the waste cannot be removed through biodegradation and ends up polluting the river. Water becomes septic when dissolved oxygen level is low.
The level of these types of pollutant in water can be measured in terms of:
i. Biological Oxygen Demand (BOD)
Biochemical oxygen demand (BOD, also called biological oxygen demand) is the amount of dissolved oxygen needed (i.e., demanded) by aerobic biological organisms to break down organic material present in a given water sample at certain temperature over a specific time period. The BOD value is most commonly expressed in milligrams of oxygen consumed per litre of sample during 5 days of incubation at 20°C and is often used as a surrogate of the degree of organic pollution of water.
BOD for very pure water is one ppm. However, water with a BOD level of up to three ppm can be considered pure.
ii. Chemical Oxygen Demand (COD)
The chemical oxygen demand (COD) is an indicative measure of the amount of oxygen that can be consumed by reactions in a measured solution. It is commonly expressed in mass of oxygen consumed over volume of solution which in SI units is milligrams per litre(mg/L). A COD test can be used to easily quantify the amount of organics in water. The most common application of COD is in quantifying the amount of oxidizable pollutants found in surface water (e.g. lakes and rivers) or wastewater. COD is more scientific than BOD.
iii. Dissolved Oxygen (DO)
Dissolved oxygen refers to the level of free, non-compound oxygen present in water or other liquids. It is an important parameter in assessing water quality because of its influence on the organisms living within a body of water. In limnology (the study of lakes), dissolved oxygen is an essential factor second only to water itself . A dissolved oxygen level that is too high or too low can harm aquatic life and affect water quality.
2. Industrial Effluents
Due to industrial activities, a wide variety of waste products are generated which are generally discharged into surface waters. Some of these wastes are toxic in nature and some are poisonous, threatening life of living organisms to varying extent. Most of India rivers and fresh water streams are polluted in varying degrees by industrial wastes and effluents which come along with waste waters or effluents of many kinds of industries such as paper and pulp mills, textiles industries, food processing units, chemical, pharmaceutical, fertilizer and metal industries, petro chemical industries and refineries. Besides these sugar industries, distilleries, steel mills, tanneries and coal washeries, synthetic material plants for the manufacturer of fibers, rubber, plastics, paints, colorants and many else items are included in the list of industries producing harmful wastes.
The industrial wastes of these industries and mills include toxicants like metals (such as copper, zinc, lead, mercury etc.), detergents, petroleum, acids, alkalies, phenols, carbonates, alcohols, cyanide, arsenic, chlorine and man other inorganic and organic matters.
A survey of major rivers in India indicates that all major rivers have turned polluted to varying degrees.
Effects of Heavy Metal Water Pollutants on Man
|Metal||Toxic effects on man|
|Cadmium||Diarrhea, growth retardation, bone deformation, kidney damage, testicular atrophy, hypertension, tumour formation hepatic injury, central nervous system injury, anemia.|
|Copper||Hypertension, sporadic fever, uremia, coma etc.|
|Zinc||Vomiting, renal damage, cramps.|
|Mercury||Abdominal pain, headache, diarrhoea haemolysis, chest pain.|
|Lead||Anaemia, brain damage, vomiting, loss of appetite convulsions, liver damage, kidney damage.|
|Arsenic||Disturbances of peripheral circulation mental disturbances, liver cirrhosis, hyper-keratitis, kidney damage, ulcers in gastrointestinal tract, lung cancer.|
|Selenium||Fever, nervousness, vomiting, dental cares, fall in blood pressure, and death. Liver kidney and spleen damage, blindness.|
|Chromium||Cancer, nephritis, gastro-intestinal ulceration, diseases in central nervous system.|
|Cobalt||Paralysis, diarrhea, low blood pressure lung irritation and bone defects lung irritation and bone defects.|