Water Pollution
Water covers two-thirds of the Earth’s surface, with over 97% present in the oceans and less than 1% in freshwater streams and lakes. Water is also present in the atmosphere in solid form in the polar icecaps and as groundwater in aquifers (water-bearing rocks) deep underground.
Water has many remarkable properties. It is sometimes referred to as ‘the universal solvent’, readily dissolving a wide range of chemical substances. It also acts as a fluid medium facilitating the dispersal of un-dissolved particulate matter.
Water pollution may be defined as any chemical or physical change in water detrimental to living organisms. It can occur through natural processes, for example by sediments produced by natural erosion. Water bodies are a major recipient of an extensive array of wastes produced by human activity. These may be discharged directly into watercourses by sewers or pipes from factories or be washed down from agricultural or urban areas particularly after heavy rains. Under rather exceptional circumstances, water bodies may become significantly contaminated by the atmospheric deposition of pollutants.
Sources and consequences:
Water pollution is a global problem and one that does not respect national boundaries. Sources of pollution may be domestic, agricultural or industrial. In less-developed countries, human and animal waste and sediments from unsound agricultural and forestry practices are the main pollutants. In more-developed countries; industrial pollutants, such as toxic metals, organic Chemicals and heat add to the water pollution problem. The effectiveness of treating wastes prior to their release into the environment determines the balance between potential and actual pollution.
Organic oxygen-demanding wastes
The release of large quantities of oxygen-demanding organic waste into watercourses often has disastrous effects on the indigenous flora and fauna. The primary source of organic waste released into fresh waters is sewage effluent. Other sources include run-off from urban areas and farms, and some industrial effluents. The recent intensification of livestock production, with larger herds concentrated in smaller areas, has exacerbated the problem of organic pollution from farm animal wastes.
Plant nutrients
Aquatic primary productivity is often limited by the availability of inorganic plant nutrients. In freshwater lakes and rivers, the limiting nutrient element is usually phosphorus, whilst in marine waters nitrogen is often in short supply. If small amounts of nutrients enter aquatic ecosystems where they are normally limiting, primary productivity is stimulated. The water body becomes over-enriched by excessive nutrient input and consequently polluted.
Acidification
Both acid rain and acid mine drainage contribute significantly to the acidification of natural waters. These two phenomena are dealt with in detail in this section. However, there are other causes of this particular type of water pollution. For example, the planting of extensive tracts of coniferous forests, usually in upland areas, results in the acidification of the soil and the waters which drain these plantations.
Organochlorines
Organochlorines are, as name suggests, organic compounds containing chlorine. Manufactured organochlorines include a number of pesticides, for example DDT, and polychlorinated biphenyls, or PCBs as they are known. These two groups will be considered separately, although they do share a number of important characteristics. For example, both groups are reported to have endocrine-disrupting properties.
Organochlorine pesticides: In 1940, the first organochlorine pesticide, DDT (dichloro-diphenyl-trichloro-ethane) was manufactured for the Allied Forces to be used during the Second World War. It met with unprecedented success against a number of insect-borne diseases, for example malaria in the tropics and typhus in Italy. It had many advantages; it was cheap to manufacture, persistent in the environment and could be applied from the air. After the war, DDT was used extensively not only to control insect populations responsible for the spread of disease but to control insects’ pest attacking agricultural crops. The success of DDT resulted in the development and manufacture of other organochlorine pesticides, for example lindane and dieldrin.
Oil
Drilling for oils is one of the major extractive industries. Crude oil is a complex mixture of thousands of different organic molecules, mainly hydrocarbons (aromatics, alkenes and cyclohexanes). It is refined by the process of fractional distillation to yield a number of commercially important products such as petrol, diesel oil and tar. From these different types of oil, seas and rivers are being polluted regularly. Sometime accidental spillage from oil tankers causes drastic damage to the environment through oil pollution. All types of aquatic forms of life thus face the ill-effects.
Thermal Pollutants
Water is able to absorb large quantities of heat without appreciably increasing its own temperature or changing from its liquid sate. This high heat capacity means that it is extensively used as a coolant in many industries. The principal user of water as a coolant is the electricity generating industry. They often discharge a huge quantity of hot water and thus causing thermal pollution.
Thermal pollution affects aquatic ecosystems in a variety of ways. In general, the species composition changes as species tolerant of warmer waters replace those unable to adapt. This transition is often accompanied by an overall decrease in species richness. For example, attached algae in heated effluents were reported to show an increase in biomass but a decrease in the number of species represented.
Water Pollution due to Fluoride and Arsenic Pollutants
Fluoride and Arsenic pollutants are important amongst the inorganic pollutants. Vast areas of Haryana, Rajasthan and Punjab are highly contaminated with fluoride compounds in potable water. There the amount of fluoride present in water is very high above the danger level. Flow of waste products from glass industry, hydrocarbon producing industry etc. carrying high amounts of fluoride compounds, polluted water bodies there. In Rajasthan thousands and thousands of people became disabled due to fluorosis or fluoride pollution. Fluorine is responsible for the decay and damage of calcium of Teeth and bones. This disease is termed as ‘Fluorosis?.
Water gets polluted when underground layers of Arsenic come in contact with ground water. Ground water from the tube-wells is highly contaminated with arsenic compounds in six districts of West Bengal covering a vast area. Here the amount of Arsenic compound is as much as 200 times higher than its permissible amount. Apart from West Bengal, the long and vast Gangetic basin of India including Bihar, Jharkhand and some part of Uttar Pradesh is highly contaminated with arsenic compounds. Even in Bangladesh the ground water is highly polluted with arsenic compounds. Symptoms of arsenic pollution are ‘melanosis’ where large black spots appear all over the body surface. Tumors may appear in the feet and it’s sole. Bronchitis, Cirrhosis of liver, skin cancer etc. is the other effects of Arsenic pollution.
Preventive Measures
Various preventive measures can be taken to combat water pollution:
Industries should not be allowed to discharge untreated chemicals into the water bodies. There should be a mechanism to ensure that only harmless substances are poured into rivers, lakes and oceans.
The domestic sewage system should be designed in a scientific manner.
Underground water can be saved from pollution if the land is not exposed to harmful pesticides and other industrial chemicals. The farmers should be encouraged for organic farming.
