Water is essential for the survival of living organisms.On an average, a human being consumes about 2 litres of water every day. Water accounts for about 70% of the weight of a human body. About 80% of the earth’s surface (i.e. 80% of the total 50,000 million hectares in area) is covered by water. Out of the estimated 1,011 million km3 of the total water present on earth, only 33,400 km3 of water is available for drinking, agriculture, domestic and industrial consumption. The rest of the water is locked up in oceans as salt water, polar ice-caps and glaciers and underground. Owing to increasing industrialization on one hand and exploding population on the other, the demands of water supply have been increasing tremendously. Moreover, considerable part of this limited quantity of water is polluted by sewage, industrial wastes and a wide array of synthetic chemicals.
Water pollution means deterioration of quality of water as measured by physical, chemical or biological criteria. The quality of water is judged keeping in view the planned use of the water, the level of pollution or contamination and its impact on the ecology and public health. A pollutant is defined as any substance, when present in excess is harmful to living organisms. In other words, it is defined as the presence of biological agents and toxic chemicals in groundwater that exceed what is naturally found in the water and may cause a hazard to human health and/or the environment.
In simple words, Water pollution occurs when undesirable foreign substances are introduced into natural water. Water pollution is the contamination of water bodies, usually as a result of human activities. In fact, today billions of people are facing the problem of water pollution especially in the developing world. The clean drinking water is scarce which are free disease causing substances or organisms. About 20% of world’s population has no access to disease free clean drinking water. Another 20% population of the world suffers from water born diseases due to poor sanitation conditions and about two million people are killed annually. Majority of the sufferers are children under 5 years.
Chemical pollution of the water is a budding problem worldwide, affecting almost all the countries. The important chemical pollutants are toxic metals such as lead or mercury; agricultural chemicals such as pesticides, herbicides, or fertilizers and acid rain. Industrial, municipal and Agricultural processes release chemical pollutants which contaminate water bodies.
There are several classes of water pollutants which can pollute surface water or groundwater. Important classes are:
Oxygen demanding waste includes domestic and animal sewage, bio-degradable organic compounds and industrial wastes from food-processing plants, meat-packing plants, slaughter houses, paper and pulp mills, tanneries etc.., as well as agricultural run-off. All these wastes undergo degradation and decomposition by bacterial activity in presence of dissolved oxygen (D.O). This waste is decomposed by oxygen-requiring bacteria (aerobic bacteria). When huge populations of decomposing bacteria are converting these wastes it can deplete oxygen levels in the water. This causes other organisms in the water, such as fish, other marine animals, and marine plants to die. The optimum D.O. in natural waters is 4-6 ppm, which is essential for supporting aquatic life. Any decrease in this D.O value is an index of pollution.
The quantity of oxygen utilized for bacterial decomposition is the biochemical oxygen demand (BOD). It is commonly used measure in water-quality management. A high BOD measure indicates the presence of large quantity of decaying organic matter in the water. Usually natural sources such as fallen leaves as well as agricultural activities and sewage are the major sources of organic matter in streams and rivers.
Pathogenic microbes or microorganisms are main biological pollutants. These include pathogenic microorganisms which may enter the water along with sewage and other wastes and may cause tremendous damage to public health. These microbes, comprising mainly of viruses and bacteria, can cause dangerous water borne diseases such as cholera, typhoid, dysentery, polio and infectious hepatitis in humans. It is difficult to monitor pathogenic microbes directly. Usually human fecal coliform bacteria are used to monitor the biological contamination of water and as a standard measure of pollution. Fecal coliform bacteria are usually harmless and are part of the normal constituents of human intestines, and are found in all human waste. However, Escherichia coli have been responsible for human illnesses and deaths. The very young and old are most vulnerable to the ravages of the disease, which can damage the kidneys Waterborne disease epidemics have killed thousands of people in U.S. cities.
Such epidemics were controlled by separating sewage water and drinking water and by treating drinking water before consumption. Unfortunately, in poor countries, billions of people are exposed to water born diseases. For example, an epidemic of cholera broke out in October of 2010 in Haiti.
Water pollution is also caused by the nutrients released by human activity. Phosphorus and nitrogen are two important nutrients which are released from a variety of materials, including fertilizers, detergents, and the products of sewage treatment plants. The concentration of nitrogen and phosphorus in streams is related to land use. Forested land has the lowest concentrations of phosphorus and nitrogen, while the highest concentrations are found in agricultural areas, such as fertilized farm fields and feedlots. Urban areas can also add phosphorus and nitrogen to local waters, particularly where wastewater-treatment plants discharge treated waters into lakes, rivers, or other water bodies. These plants are useful in eliminating organic pollutants and pathogens, but nutrients pass through the system.
Increased concentration of nitrogen and phosphorus in water result in cultural eutrophication which is a process characterized by a rapid increase in the abundance of plant life, particularly algae. Blooms of algae form thick mats that sometimes nearly cover the surface of the water in fresh water ponds and lakes. These thick algae mats block sunlight to plants below and those plants eventually die. In addition, the algae also consume oxygen as they decompose, and results in lowering the oxygen content of the water which may result the fish and aquatic animals to die as well. In the marine environment, nutrients in
Algae-contaminated beach near shore waters may cause blooms of seaweed, referred to as marine algae, to flourish. The marine algae become a nuisance when they are torn loose and accumulate on beaches. Algae may also damage or kill coral in tropical areas.
Oil pollution may take place because of oil spills from cargo oil tankers on the seas, losses during off-shore exploration and production of oil, accidental fires in ships and oil tankers. Oil discharged into surface water (i.e., rivers, lakes, and the ocean) has caused major pollution problems. The largest oil discharges have usually involved oil-tanker accidents at sea. Oil spills leading to water pollution had very significant short-term impacts. Commercial fisheries, sport fisheries, and tourism were disrupted. In addition, many seabirds and mammals were lost.
A large oil spill in 2006 was caused by the war in Lebanon, when a coastal power plant was bombed and over 100,000 barrels of fuel oil entered the Mediterranean Sea. Over half of Lebanon’s tourist beaches were polluted, including a popular public beach visited by people from the capital city Beirut.
A variety of methods have been used to try to control the spread of oil and clean it up after it has made landfall at a beach or wetland (Figure). The methods include deploying booms, skimmers, and chemical dispersants; burning the oil in water in situ; washing the oil off beaches; and vacuuming or picking up the oil. Sometimes, equipment as simple as shovels and road equipment is used to pick up oil from sandy beaches. The particular methods used depend upon the site, how much oil is present, and the accessibility of the site to necessary equipment.
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