There are number of pollutants responsible for deteriorating quality of water. Some of the pollutants responsible for water pollution are mentioned below:
a) Pathogenic pollution: – Pathogenic pollution is pollution of a system by disease causing organisms called pathogens. Marine and freshwater systems can become polluted by polluted runoff or untreated sewage released into the water. Pathogens are organisms capable of eliciting disease symptoms. They are disease causing bacteria, viruses and protozoa found in human and animal wastes. Pathogens are small in size, and once released into the environment they are easily transported by water; such as rivers, storm water drains and canals. Illnesses such as respiratory illness, fever, cryptosporidiosis, gastroenteritis and hepatitis have been associated with waterborne microorganisms. Many pathogenic viruses and bacteria are not harmful to fish and shellfish, but they accumulate in the aquatic animals. When fish and shellfish contaminated with the pathogens are ingested, the bacteria and viruses can be passed on to humans. (80% deaths in India are due to diseases cause by pathogenic pollution).
b) Organic pollution: – Organic pollution can occur when organic pollutants such as nitrogen and phosphates accumulate in aquatic ecosystems. High levels of these nutrients cause an overgrowth of plants and algae. As the plants and algae die, they become organic material in the water. The enormous decay of this plant matter, in turn, lowers the oxygen level. The process of rapid plant growth followed by increased activity by decomposers and a depletion of the oxygen level is called Eutrophication. Human generated wastes when released in water bodies they require oxygen to decompose. Due to excessive absorption of oxygen from the water bodies it disturbs the aquatic life. This waste contains pollutants generally as carbohydrates, proteins, fats, nucleic acids, nucleotides and other bimolecular wastes.
c) Nutrient pollution: – Humans add excessive amounts of plant nutrients (primarily phosphorus, nitrogen, potassium, magnesium, and carbon) to streams and lakes in various ways:
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a) Atmospheric deposition (48.7 percent nitrogen; 7.1 percent phosphorus): Atmospheric deposition arising from agriculture, industry, and urban areas contributes most of the nitrogen load to the state’s waters. Atmospheric deposition may be wet, in the form of rain or snow, or dry, in the form of gases or particles. “Nitrogen in synthetic fertilizers and manure can rise as a gas, and then come back down”. “Also, a lot of the nitrogen that rises from the combustion of fossil fuels, such as coal and oil, comes back down as wet or particulate matter.”
b) Urban storm water run off (8.4 percent nitrogen; 10.8 percent phosphorus): “When you have precipitation coming down on an urban area, it carries away nutrients and sediments from things such as food products and dead animals.
c) Septic systems (3.4 percent nitrogen; 13.1 percent phosphorus): “Even in the best septic systems, some nutrients will migrate into the surface and groundwater, although septic systems don’t appear to contribute a lot of nitrogen or phosphorus.
d) Agriculture (39.2 percent nitrogen; 68.8 percent phosphorus): Agriculture is the number one source of phosphorus pollution in the state and second highest source of nitrogen. Combined, atmospheric deposition and agriculture account for 88 percent of the nitrogen and 76 percent of the phosphorus load to surface and groundwater
D) Industrial pollution: – These are the direct sources of water pollution. Factories, refineries, waste treatment plants etc. that emit fluids of varying quality directly into urban water supplies. These are the non-biodegradable industrial wastes which are deposited directly into water bodies. The important causes that take place due to this are:
a) Bio accumulation – Concentration of toxic pollutant in water.
b) Bio magnification – Many industrial and power plants use rivers, streams and lakes to dispose of waste heat. The resulting hot water can cause thermal pollution. Thermal pollution can have a disastrous effect on life in an aquatic ecosystem as temperature increases, the amount of oxygen in the water decreases, thereby reducing the number of animals that can survive there.
E) Pollution due to pesticides: –
a) Wastewater from manufacturing industries.
b) From farms in the form of surface run off from irrigated fields.
c) Due to percolation of water in the ground water resource.